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Chlorpyrifos
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Regulation
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National regulations Chlorpyrifos was used to control insect infestations of homes and commercial buildings in Europe until it was banned from sale in 2008. Chlorpyrifos is restricted from termite control in Singapore as of 2009. It was banned from residential use in South Africa as of 2010. It has been banned in the United Kingdom in 2016 apart from a limited use in drenching seedlings.Chlorpyrifos has not been permitted for agricultural use in Sweden at all United States In the United States, several laws directly or indirectly regulate the use of pesticides. These laws, which are implemented by the EPA, NIOSH, USDA and FDA, include: the Clean Water Act (CWA); the Endangered Species Act (ESA); the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA); the Federal Food, Drug, and Cosmetic Act (FFDCA); the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA); and the Emergency Planning and Community Right-to-Know Act (EPCRA). As a pesticide, chlorpyrifos is not regulated under the Toxic Substances Control Act (TSCA).Chlorpyrifos is sold in restricted-use products for certified pesticide applicators to use in agriculture and other settings, such as golf courses or for mosquito control. It may also be sold in ant and roach baits with childproof packaging. In 2000, manufacturers reached an agreement with the EPA to voluntarily restrict the use of chlorpyrifos in places where children may be exposed, including homes, schools and day care centers.In 2007 Pesticide Action Network North America and Natural Resources Defense Council (collectively, PANNA) submitted an administrative petition requesting a chlorpyrifos ban. On 10 August 2015, the Ninth Circuit Court of Appeals in PANNA v. EPA ordered the EPA to respond to PANNA's petition by "revok[ing] all tolerances for the insecticide chlorpyrifos", den[ying] the Petition or [issuing] a "proposed or final tolerance revocation" no later than 31 October 2015. The EPA was "unable to conclude that the risk from aggregate exposure from the use of chlorpyrifos [met] the safety standard of section 408(b)(2) of the Federal Food, Drug, and Cosmetic Act (FFDCA)" and therefore proposed "to revoke all tolerances for chlorpyrifos."In an 30 October 2015 statement Dow AgroSciences disagreed with the EPA's proposed revocation and "remain[ed] confident that authorized uses of chlorpyrifos products, as directed, offer wide margins of protection for human health and safety." In a November 2016 press release, DOW argued that chlorpyrifos was "a critical tool for growers of more than 50 different types of crops in the United States" with limited or no viable alternatives." The Environment News Service quoted the Dow AgroSciences' statement disagreeing with the EPA findings.
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Chlorpyrifos
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Regulation
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Chlorpyrifos is one of the most widely used pest control products in the world. It is authorized for use in about 100 nations, including the U.S., Canada, the United Kingdom, Spain, France, Italy, Japan, Australia and New Zealand, where it is registered for protection of essentially every crop now under cultivation. No other pesticide has been more thoroughly tested.
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Chlorpyrifos
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Regulation
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In November 2016, the EPA reassessed its ban proposal after taking into consideration recommendations made by the agency's Science Advisory Panel which had rejected the EPA's methodology in quantifying the risk posed by chlorpyrifos. Using a different methodology as suggested by the panel, the EPA retained its decision to completely ban chlorpyrifos. The EPA concluded that, while "uncertainties" remain, a number of studies provide "sufficient evidence" that children experience neurodevelopment effects even at low levels of chlorpyrifos exposure.On 29 March 2017, EPA Administrator Scott Pruitt, appointed by the Trump administration, overturned the 2015 EPA revocation and denied the administrative petition by the Natural Resources Defense Council and the Pesticide Action Network North America to ban chlorpyrifos.The American Academy of Pediatrics responded to the administration's decision saying they are "deeply alarmed" by Pruitt's decision to allow the pesticide's continued use. "There is a wealth of science demonstrating the detrimental effects of chlorpyrifos exposure to developing fetuses, infants, children and pregnant women. The risk to infant and children's health and development is unambiguous."Asked in April whether Pruitt had met with Dow Chemical Company executives or lobbyists before his decision, an EPA spokesman replied: "We have had no meetings with Dow on this topic." In June, after several Freedom of Information Act requests, the EPA released a copy of Pruitt's March meeting schedule which showed that a meeting had been scheduled between Pruitt and Dow CEO Andrew Liveris at a hotel in Houston, Texas, on 9 March. Both men were featured speakers at an energy conference. An EPA spokesperson reported that the meeting was brief and the pesticide was not discussed.In August, it was revealed that in fact Pruitt and other EPA officials had met with industry representatives on dozens of occasions in the weeks immediately prior to the March decision, promising them that it was "a new day" and assuring them that their wish to continue using chlorpyrifos had been heard. Ryan Jackson, Pruitt's chief of staff, said in an 8 March email that he had "scared" career staff into going along with the political decision to deny the ban, adding "[T]hey know where this is headed and they are documenting it well."On 9 August 2018 the U.S. 9th Circuit court of Appeals ruled that the EPA must ban chlorpyrifos within 60 days from that date. A spokesman for Dow DuPont stated that "all appellate options" would be considered. In contrast, Marisa Ordonia, a lawyer for Earthjustice, the organization that had conducted much of the legal work on the case, hailed the decision. The ruling was almost immediately appealed by Trump administration lawyers.On August 18, 2021 the U.S. Environmental Protection Agency (EPA) announced a ban on the use of chlorpyrifos on food crops in the United States.On February 25, 2022 the EPA released a statement upholding its decision to revoke all tolerance standards on chlorpyrifos use, and sent letters to registered chlorpyrifos food producers confirming the ban to be in effect as of February 28, 2022.On 14 December, 2022 the EPA filed a Notice of Intent to Cancel (NOIC) for three chlorpyrifos pesticide products because they bear labeling for use on food, despite the ban.
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Chlorpyrifos
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Regulation
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Residue The use of chlorpyrifos in agriculture can leave chemical residue on food commodities. The FFDCA requires EPA to set limits, known as tolerances, for pesticide residue in human food and animal feed products based on risk quotients for acute and chronic exposure from food in humans. These tolerances limit the amount of chlorpyrifos that can be applied to crops. FDA enforces EPA's pesticide tolerances and determines "action levels" for the unintended drift of pesticide residues onto crops without tolerances.After years of research without a conclusion and cognizant of the court order to issue a final ruling, the EPA proposed to eliminate all tolerances for chlorpyrifos ("Because tolerances are the maximum residue of a pesticide that can be in or on food, this proposed rule revoking all chlorpyrifos tolerances means that if this approach is finalized, all agricultural uses of chlorpyrifos would cease."), and then solicited comments.The Dow Chemical Company is actively opposed to tolerance restrictions on chlorpyrifos and is currently lobbying the White House to, among other goals, pressure EPA to reverse its proposal to revoke chlorpyrifos food residue tolerances.The EPA has not updated the approximately 112 tolerances pertaining to food products and supplies since 2006. However, in a 2016 report, EPA scientists had not been able to find any level of exposure to the pesticide that was safe. The EPA 2016 report states in part "... this assessment indicates that dietary risks from food alone are of concern ..." the report also states that previous published risk assessments for "chlorpyrifos may not provide a [sufficient] ... human health risk assessment given the potential for neurodevelopmental outcomes."″The ... [food only] exposures for chlorpyrifos are of risk concern ... for all population subgroups analyzed. Children (1–2 years old) is the population subgroup with the highest risk estimate at 14,000% of the ssPADfood.″ (This acronym refers to the steady-state population-adjusted dose for food, which is considered the maximum safe oral dose.) Based on 2006 EPA rules, chlorpyrifos has a tolerance of 0.1 part per million (ppm) residue on all food items unless a different tolerance has been set for that item or chlorpyrifos is not registered for use on that crop. EPA set approximately 112 tolerances pertaining to food products and supplies. In 2006, to reduce childhood exposure, the EPA amended its chlorpyrifos tolerance on apples, grapes and tomatoes, reducing the grape and apple tolerances to 0.01 ppm and eliminating the tolerance on tomatoes. Chlorpyrifos is not allowed on crops such as spinach, squash, carrots, and tomatoes; any chlorpyrifos residue on these crops normally represents chlorpyrifos misuse or spray drift.Food handling establishments (places where food products are held, processed, prepared or served) are included in the food tolerance of 0.1 ppm for chlorpyrifos. Food handling establishments may use a 0.5% solution of chlorpyrifos solely for spot and/or crack and crevice treatments. Food items are to be removed or protected during treatment. Food handling establishment tolerances may be modified or exempted under FFDCA sec. 408.
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Chlorpyrifos
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Regulation
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Water Chlorpyrifos in waterways is regulated as a hazardous substance under section 311(b)(2)(A) of the Federal Water Pollution Control Act and falls under the CWA amendments of 1977 and 1978. The regulation is inclusive of all chlorpyrifos isomers and hydrates in any solution or mixture. EPA has not set a drinking water regulatory standard for chlorpyrifos, but has established a drinking water guideline of 2 ug/L.In 2009, to protect threatened salmon and steelhead under CWA and ESA, EPA and National Marine Fisheries Service (NMFS) recommended limits on the use of chlorpyrifos in California, Idaho, Oregon and Washington and requested that manufacturers voluntarily add buffer zones, application limits and fish toxicity to the standard labeling requirements for all chlorpyrifos-based products. Manufacturers rejected the request. In February 2013 in Dow AgroSciences vs NMFS, the Fourth Circuit Court of Appeals vacated EPA's order for these labeling requirements. In August 2014, in the settlement of a suit brought by environmental and fisheries advocacy groups against EPA in the U.S. District Court for the Western District of Washington, EPA agreed to re-instate no-spray stream buffer zones in California, Oregon and Washington, restricting aerial spraying (300 ft.) and ground-based applications (60 ft.) near salmon populations. These buffers will remain until EPA makes a permanent decision in consultation with NMFS.
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Chlorpyrifos
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Regulation
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Reporting EPCRA designates the chemicals that facilities must report to the Toxics Release Inventory (TRI), based on EPA assessments. Chlorpyrifos is not on the reporting list. It is on the list of hazardous substances under CERCLA (aka the Superfund Act). In the event of an environmental release above its reportable quantity of 1 lb or 0.454 kg, facilities are required to immediately notify the National Response Center (NRC).In 1995, Dow paid a $732,000 EPA penalty for not forwarding reports it had received on 249 chlorpyrifos poisoning incidents.
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Chlorpyrifos
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Regulation
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Occupational exposure In 1989, OSHA established a workplace permissible exposure limit (PEL) of 0.2 mg/m3 for chlorpyrifos, based on an 8-hour time weighted average (TWA) exposure. However, the rule was remanded by the U.S. Circuit Court of Appeals and no PELs are in place presently.EPA's Worker Protection Standard requires owners and operators of agricultural businesses to comply with safety protocols for agricultural workers and pesticide handlers (those who mix, load and apply pesticides). For example, in 2005, the EPA filed an administrative complaint against JSH Farms, Inc. (Wapato, Washington) with proposed penalties of $1,680 for using chlorpyrifos in 2004 without proper equipment. An adjacent property was contaminated with chlorpyrifos due to pesticide drift and the property owner suffered from eye and skin irritation.
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Chlorpyrifos
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Regulation
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State laws Additional laws and guidelines may apply for individual states. For example, Florida has a drinking water guideline for chlorpyrifos of 21 ug/L.In 2003, Dow agreed to pay $2 million to New York state, in response to a lawsuit to end Dow's advertising of Dursban as "safe".Oregon's Department of Environmental Quality added chlorpyrifos to the list of targeted reductions in the Clackamas Subbasin as part of the Columbia River National Strategic Plan, which is based on EPA'S 2006–11 National Strategic Plan.In 2017, chlorpyrifos was included California's Proposition 65.California included regulation limits for chlorpyrifos in waterways and established maximum and continuous concentration limits of 0.025 ppb and 0.015 ppb, respectively. Sale and possession of chlorpyrifos have been largely banned in California, as of 6 February – 31 December 2020, respectively. The California ban has an exception that, "a few products that apply chlorpyrifos in granular form, representing less than one percent of agricultural use of chlorpyrifos, will be allowed to remain on the market."In Hawaii, a 2018 law introduced a complete ban on products containing chlorpyrifos, which went into effect on January 1, 2023. Before that, starting in 2019, the law mandated temporary application permits and annual reporting as well as mandating a 100-foot buffer around schools during school hours.
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Chlorpyrifos
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Regulation
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Australia The Australian Pesticides and Veterinary Medicine Authority has a Chlorpyrifos Chemical Review in progress.
Denmark Chlorpyrifos was never approved for use in Denmark, except on ornamental plants grown in greenhouses. This use was banned in 2012.
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Chlorpyrifos
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Regulation
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European Union On 6 December 2019, the European Union (EU) announced that it will no longer permit sales of chlorpyrifos after 31 January 2020.The European Food Safety Authority released a statement in July 2019 which concluded that the approval criteria for chlorpyrifos which apply to human health are not met. Their literature review concluded that there is no evidence for reproductive toxicity in rats, but that chlorpyrifos is potentially genotoxic. The report stated that chlorpyrifos is clearly a potent acetylcholinesterase inhibitor, that it can be absorbed by ingestion, inhalation, and through the skin, and that epidemiological evidence supports the hypothesis that it is a human developmental neurotoxin that can cause early cognitive and behavioral deficits through prenatal exposure.
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Chlorpyrifos
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Regulation
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India The FSSAI (Food Safety and Standards Authority of India) did not set a usage limits for chlorpyrifos. In 2010, India barred Dow from commercial activity for 5 years after India's Central Bureau of Investigation found Dow guilty of bribing Indian officials in 2007 to allow the sale of chlorpyrifos. In 2020, the Indian government had published a draft bill to ban 27 pesticides including chlorpyrifos.
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Chlorpyrifos
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Regulation
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New Zealand Chlorpyrifos is currently approved in New Zealand for commercial use in crops, as a veterinary medicine, and as a timber treatment chemical.
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Chlorpyrifos
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Regulation
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Thailand Chlorpyrifos was banned under Thai law effective from 1 June 2020. Farmers were given 270 days to destroy their stock, while a 90-day deadline was also given to farmers to return the chemicals for destruction, as their possession is considered illegal by the Department of Agriculture. After deadline, any person who possesses the illegal agrochemicals will be fined one million baht, jailed for 10 years, or both.
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Chlorpyrifos
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Manufacture
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Chlorpyrifos is produced via a multistep synthesis from 3-methylpyridine, eventually reacting 3,5,6-trichloro-2-pyridinol with diethylthiophosphoryl chloride.
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Quantum beats
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Quantum beats
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In physics, quantum beats are simple examples of phenomena that cannot be described by semiclassical theory, but can be described by fully quantized calculation, especially quantum electrodynamics. In semiclassical theory (SCT), there is an interference or beat note term for both V-type and Λ -type atoms. However, in the quantum electrodynamic (QED) calculation, V-type atoms have a beat term but Λ -types do not. This is strong evidence in support of quantum electrodynamics.
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Quantum beats
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Historical overview
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The observation of quantum beats was first reported by A.T. Forrester, R.A. Gudmundsen and P.O. Johnson in 1955, in an experiment that was performed on the basis of an earlier proposal by A.T. Forrester, W.E. Parkins and E. Gerjuoy. This experiment involved the mixing of the Zeeman components of ordinary incoherent light, that is, the mixing of different components resulting from a split of the spectral line into several components in the presence of a magnetic field due to the Zeeman effect. These light components were mixed at a photoelectric surface, and the electrons emitted from that surface then excited a microwave cavity, which allowed the output signal to be measured in dependence on the magnetic field.Since the invention of the laser, quantum beats can be demonstrated by using light originating from two different laser sources. In 2017 quantum beats in single photon emission from the atomic collective excitation have been observed. Observed collective beats were not due to superposition of excitation between two different energy levels of the atoms, as in usual single-atom quantum beats in V -type atoms. Instead, single photon was stored as excitation of the same atomic energy level, but this time two groups of atoms with different velocities have been coherently excited. These collective beats originate from motion between entangled pairs of atoms, that acquire relative phase due to Doppler effect.
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Quantum beats
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V-type and
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Λ -type atoms There is a figure in Quantum Optics that describes V -type and Λ -type atoms clearly.
Simply, V-type atoms have 3 states: |a⟩ , |b⟩ , and |c⟩ . The energy levels of |a⟩ and |b⟩ are higher than that of |c⟩ . When electrons in states |a⟩ and : |b⟩ subsequently decay to state |c⟩ , two kinds of emission are radiated.
In Λ -type atoms, there are also 3 states: |a⟩ , |b⟩ , and : |c⟩ . However, in this type, |a⟩ is at the highest energy level, while |b⟩ and : |c⟩ are at lower levels. When two electrons in state |a⟩ decay to states |b⟩ and : |c⟩ , respectively, two kinds of emission are also radiated.
The derivation below follows the reference Quantum Optics.
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Quantum beats
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Calculation based on semiclassical theory
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In the semiclassical picture, the state vector of electrons is |ψ(t)⟩=caexp(−iωat)|a⟩+cbexp(−iωbt)|b⟩+ccexp(−iωct)|c⟩ .If the nonvanishing dipole matrix elements are described by Pac=e⟨a|r|c⟩,Pbc=e⟨b|r|c⟩ for V-type atoms, Pab=e⟨a|r|b⟩,Pac=e⟨a|r|c⟩ for Λ -type atoms,then each atom has two microscopic oscillating dipoles P(t)=Pac(ca∗cc)exp(iν1t)+Pbc(cb∗cc)exp(iν2t)+c.c.
for V-type, when ν1=ωa−ωc,ν2=ωb−ωc ,P(t)=Pab(ca∗cb)exp(iν1t)+Pac(ca∗cc)exp(iν2t)+c.c.
for Λ -type, when ν1=ωa−ωb,ν2=ωa−ωc .In the semiclassical picture, the field radiated will be a sum of these two terms E(+)=E1exp(−iν1t)+E2exp(−iν2t) ,so it is clear that there is an interference or beat note term in a square-law detector |E(+)|2=|E1|2+|E2|2+{E1∗E2exp[i(ν1−ν2)t]+c.c.}
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Quantum beats
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Calculation based on quantum electrodynamics
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For quantum electrodynamical calculation, we should introduce the creation and annihilation operators from second quantization of quantum mechanics.
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Quantum beats
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Calculation based on quantum electrodynamics
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Let En(+)=anexp(−iνnt) is an annihilation operator and En(−)=an†exp(iνnt) is a creation operator.Then the beat note becomes ⟨ψV(t)|E1(−)(t)E2(+)(t)|ψV(t)⟩ for V-type and ⟨ψΛ(t)|E1(−)(t)E2(+)(t)|ψΛ(t)⟩ for Λ -type,when the state vector for each type is |ψV(t)⟩=∑i=a,b,cci|i,0⟩+c1|c,1ν1⟩+c2|c,1ν2⟩ and |ψΛ(t)⟩=∑i=a,b,cci′|i,0⟩+c1′|b,1ν1⟩+c2′|c,1ν2⟩ .The beat note term becomes ⟨ψV(t)|E1(−)(t)E2(+)(t)|ψV(t)⟩=κ⟨1ν10ν2|a1†a2|0ν11ν2⟩exp[i(ν1−ν2)t]⟨c|c⟩=κexp[i(ν1−ν2)t]⟨c|c⟩ for V-type and ⟨ψΛ(t)|E1(−)(t)E2(+)(t)|ψΛ(t)⟩=κ′⟨1ν10ν2|a1†a2|0ν11ν2⟩exp[i(ν1−ν2)t]⟨b|c⟩=κ′exp[i(ν1−ν2)t]⟨b|c⟩ for Λ -type.By orthogonality of eigenstates, however ⟨c|c⟩=1 and ⟨b|c⟩=0 Therefore, there is a beat note term for V-type atoms, but not for Λ -type atoms.
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Quantum beats
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Conclusion
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As a result of calculation, V-type atoms have quantum beats but Λ -type atoms do not. This difference is caused by quantum mechanical uncertainty. A V-type atom decays to state |c⟩ via the emission with ν1 and ν2 . Since both transitions decayed to the same state, one cannot determine along which path each decayed, similar to Young's double-slit experiment. However, Λ -type atoms decay to two different states. Therefore, in this case we can recognize the path, even if it decays via two emissions as does V-type. Simply, we already know the path of the emission and decay.
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Quantum beats
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Conclusion
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The calculation by QED is correct in accordance with the most fundamental principle of quantum mechanics, the uncertainty principle. Quantum beats phenomena are good examples of such that can be described by QED but not by SCT.
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Homoaromaticity
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Homoaromaticity
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Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp3 hybridized carbon atom. Although this sp3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.
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Homoaromaticity
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Homoaromaticity
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The concept of homoaromaticity was pioneered by Saul Winstein in 1959, prompted by his studies of the “tris-homocyclopropenyl” cation. Since the publication of Winstein's paper, much research has been devoted to understanding and classifying these molecules, which represent an additional class of aromatic molecules included under the continuously broadening definition of aromaticity. To date, homoaromatic compounds are known to exist as cationic and anionic species, and some studies support the existence of neutral homoaromatic molecules, though these are less common. The 'homotropylium' cation (C8H9+) is perhaps the best studied example of a homoaromatic compound.
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Homoaromaticity
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Overview
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Naming The term "homoaromaticity" derives from the structural similarity between homoaromatic compounds and the analogous homo-conjugated alkenes previously observed in the literature. The IUPAC Gold Book requires that Bis-, Tris-, etc. prefixes be used to describe homoaromatic compounds in which two, three, etc. sp3 centers separately interrupt conjugation of the aromatic system.
History The concept of homoaromaticity has its origins in the debate over the non-classical carbonium ions that occurred in the 1950s. Saul Winstein, a famous proponent of the non-classical ion model, first described homoaromaticity while studying the 3-bicyclo[3.1.0]hexyl cation.
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Homoaromaticity
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Overview
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In a series of acetolysis experiments, Winstein et al. observed that the solvolysis reaction occurred empirically faster when the tosyl leaving group was in the equatorial position. The group ascribed this difference in reaction rates to the anchimeric assistance invoked by the "cis" isomer. This result thus supported a non-classical structure for the cation.Winstein subsequently observed that this non-classical model of the 3-bicyclo[3.1.0]hexyl cation is analogous to the previously well-studied aromatic cyclopropenyl cation. Like the cyclopropenyl cation, positive charge is delocalized over three equivalent carbons containing two π electrons. This electronic configuration thus satisfies Huckel's rule (requiring 4n+2 π electrons) for aromaticity. Indeed, Winstein noticed that the only fundamental difference between this aromatic propenyl cation and his non-classical hexyl cation was the fact that, in the latter ion, conjugation is interrupted by three -CH2- units. The group thus proposed the name "tris-homocyclopropenyl"—the tris-homo counterpart to the cyclopropenyl cation.
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Homoaromaticity
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Evidence for homoaromaticity
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Criterion for homoaromaticity The criterion for aromaticity has evolved as new developments and insights continue to contribute to our understanding of these remarkably stable organic molecules. The required characteristics of these molecules has thus remained the subject of some controversy. Classically, aromatic compounds were defined as planar molecules that possess a cyclically delocalized system of (4n+2)π electrons, satisfying Huckel's rule. Most importantly, these conjugated ring systems are known to exhibit enormous thermochemical stability relative to predictions based on localized resonance structures. Succinctly, three important features seem to characterize aromatic compounds: molecular structure (i.e. coplanarity: all contributing atoms in the same plane) molecular energetics (i.e. increased thermodynamic stability) spectroscopic and magnetic properties (i.e. magnetic field induced ring current)A number of exceptions to these conventional rules exist, however. Many molecules, including Möbius 4nπ electron species, pericyclic transition states, molecules in which delocalized electrons circulate in the ring plane or through σ (rather than π) bonds, many transition-metal sandwich molecules, and others have been deemed aromatic though they somehow deviate from the conventional parameters for aromaticity.Consequently, the criterion for homoaromatic delocalization remains similarly ambiguous and somewhat controversial. The homotropylium cation, (C8H9+), though not the first example of a homoaromatic compound ever discovered, has proven to be the most studied of the compounds classified as homoaromatic, and is therefore often considered the classic example of homoaromaticity. By the mid-1980s, there were more than 40 reported substituted derivatives of the homotropylium cation, reflecting the importance of this ion in formulating our understanding of homoaromatic compounds.
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Homoaromaticity
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Evidence for homoaromaticity
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Early evidence for homoaromaticity After initial reports of a "homoaromatic" structure for the tris-homocyclopropenyl cation were published by Winstein, many groups began to report observations of similar compounds. One of the best studied of these molecules is the homotropylium cation, the parent compound of which was first isolated as a stable salt by Pettit, et al. in 1962, when the group reacted cyclooctatraene with strong acids. Much of the early evidence for homoaromaticity comes from observations of unusual NMR properties associated with this molecule.
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Homoaromaticity
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Evidence for homoaromaticity
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NMR spectroscopy studies While characterizing the compound resulting from deprotonation of cyclooctatriene by 1H NMR spectroscopy, the group observed that the resonance corresponding to two protons bonded to the same methylene bridge carbon exhibited an astonishing degree of separation in chemical shift.
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Homoaromaticity
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Evidence for homoaromaticity
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From this observation, Pettit, et al. concluded that the classical structure of the cyclooctatrienyl cation must be incorrect. Instead, the group proposed the structure of the bicyclo[5.1.0]octadienyl compound, theorizing that the cyclopropane bond located on the interior of the eight-membered ring must be subject to considerable delocalization, thus explaining the dramatic difference in observed chemical shift. Upon further consideration, Pettit was inclined to represent the compound as the "homotropylium ion," which shows the "internal cyclopropane" bond totally replaced by electron delocalization. This structure shows how delocalization is cyclic and involves 6 π electrons, consistent with Huckel's rule for aromaticity. The magnetic field of the NMR could thus induce a ring current in the ion, responsible for the significant differences in resonance between the exo and endo protons of this methylene bridge. Pettit, et al. thus emphasized the remarkable similarity between this compound and the aromatic tropylium ion, describing a new "homo-counterpart" to an aromatic species already known, precisely as predicted by Winstein.
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Homoaromaticity
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Evidence for homoaromaticity
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Subsequent NMR studies undertaken by Winstein and others sought to evaluate the properties of metal carbonyl complexes with the homotropylium ion. Comparison between a molybdenum-complex and an iron-complex proved particularly fruitful. Molybdenum tricarbonyl was expected to coordinate to the homotropylium cation by accepting 6 π electrons, thereby preserving the homoaromatic features of the complex. By contrast, iron tricarbonyl was expected to coordinate to the cation by accepting only 4 π electrons from the homotropylium ion, creating a complex in which the electrons of the cation are localized. Studies of these complexes by 1H NMR spectroscopy showed a large difference in chemical shift values for methylene protons of the Mo-complex, consistent with a homoaromatic structure, but detected virtually no comparable difference in resonance for the same protons in the Fe-complex.
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Homoaromaticity
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Evidence for homoaromaticity
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UV spectroscopy studies An important piece of early evidence in support of the homotropylium cation structure that did not rely on the magnetic properties of the molecule involved the acquisition of its UV spectrum. Winstein et al. determined that the absorption maxima for the homotropylium cation exhibited a considerably shorter wavelength than would be precited for the classical cyclooctatrienyl cation or the bicyclo[5.1.0]octadienyl compound with the fully formed internal cyclopropane bond (and a localized electronic structure). Instead, the UV spectrum most resembled that of the aromatic tropylium ion. Further calculations allowed Winstein to determine that the bond order between the two carbon atoms adjacent to the outlying methylene bridge is comparable to that of the π-bond separating the corresponding carbon atoms in the tropylium cation. Although this experiment proved to be highly illuminating, UV spectra are generally considered to be poor indicators of aromaticity or homoaromaticity.
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Homoaromaticity
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Evidence for homoaromaticity
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More recent evidence for homoaromaticity More recently, work has been done to investigate the structure of the purportedly homoaromatic homotropylium ion by employing various other experimental techniques and theoretical calculations. One key experimental study involved analysis of a substituted homotropylium ion by X-ray crystallography. These crystallographic studies have been used to demonstrate that the internuclear distance between the atoms at the base of the cyclopropenyl structure is indeed longer than would be expected for a normal cyclopropane molecule, while the external bonds appear to be shorter, indicating involvement of the internal cyclopropane bond in charge delocalization.
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Homoaromaticity
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Molecular orbital description
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The molecular orbital explanation of the stability of homoaromaticity has been widely discussed with numerous diverse theories, mostly focused on the homotropenylium cation as a reference. R.C. Haddon initially proposed a Mobius model where the outer electrons of the sp3 hybridized methylene bridge carbon(2) back-donate to the adjacent carbons to stabilize the C1-C3 distance.
Perturbation molecular orbital theory Homoaromaticity can better be explained using Perturbation Molecular Orbital Theory (PMO) as described in a 1975 study by Robert C. Haddon. The homotropenylium cation can be considered as a perturbed version of the tropenylium cation due to the addition of a homoconjugate linkage interfering with the resonance of the original cation.
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Homoaromaticity
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Molecular orbital description
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First-order effects The most important factor in influencing homoaromatic character is the addition of a single homoconjugate linkage into the parent aromatic compound. The location of the homoconjugate bond is not important as all homoaromatic species can be derived from aromatic compounds that possess symmetry and equal bond order between all carbons. The insertion of a homoconjugate linkage perturbs the π-electron density an amount δβ, which depending on the ring size, must be greater than 0 and less than 1, where 0 represents no perturbation and 1 represents total loss of aromaticity (destabilization equivalent to the open chain form). It is believed that with increasing ring size, the resonance stabilization of homoaromaticity is offset by the strain in forming the homoconjugate bridge. In fact, the maximum ring size for homoaromaticity is fairly low as a 16-membered annulene ring favours the formation of the aromatic dication over the strained bridged homocation.
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Homoaromaticity
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Molecular orbital description
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Second-order effects Second homoconjugate linkage A significant second-order effect on the Perturbation Molecular Orbital model of homoaromaticity is the addition of a second homoconjugate linkage and its influence on stability. The effect is often a doubling of the instability brought about by the addition of a single homoconjugate linkage, although there is an additional term that depends on the proximity of the two linkages. In order to minimize δβ and thus keep the coupling term to a minimum, bishomoaromatic compounds form depending on the conformation of greatest stability by resonance and smallest steric hindrance. The synthesis of the 1,3-bishomotropenylium cation by protonating cis-bicyclo[6.1.0]nona-2,4,6-triene agrees with theoretical calculations and maximizes stability by forming the two methylene bridges at the 1st and 3rd carbons.
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Homoaromaticity
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Molecular orbital description
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Substituents The addition of a substituent to a homoaromatic compound has a large influence over the stability of the compound. Depending on the relative locations of the substituent and the homoconjugate linkage, the substituent can either have a stabilizing or destabilizing effect. This interaction is best demonstrated by looking at a substituted tropenylium cation. If an inductively electron-donating group is attached to the cation at the 1st or 3rd carbon position, it has a stabilizing effect, improving the homoaromatic character of the compound. However, if this same substituent is attached at the 2nd or 4th carbon, the interaction between the substituent at the homoconjugate bridge has a destabilizing effect. Therefore, protonation of methyl or phenyl substituted cyclooctatetraenes will result in the 1 isomer of the homotropenylium cation.
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Homoaromaticity
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Examples of homoaromatic compounds
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Following the discovery of the first homoaromatic compounds, research has gone into synthesizing new homoaromatic compounds that possess similar stability to their aromatic parent compounds. There are several classes of homoaromatic compounds, each of which have been predicted theoretically and proven experimentally.
Cationic homoaromatics The most established and well-known homoaromatic species are cationic homoaromatic compounds. As stated earlier, the homotropenylium cation is one of the most studied homoaromatic compounds. Many homoaromatic cationic compounds use as a basis a cyclopropenyl cation, a tropylium cation, or a cyclobutadiene dication as these compounds exhibit strong aromatic character.
In addition to the homotropylium cation, another well established cationic homoaromatic compound is the norbornen-7-yl cation, which has been shown to be strongly homoaromatic, proven both theoretically and experimentally.
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Homoaromaticity
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Examples of homoaromatic compounds
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An intriguing case of σ-bishomoaromaticity can be found in the dications of pagodanes. In these 4-center-2-electron systems the delocalization happens in the plane that is defined by the four carbon atoms (prototype for the phenomenon of σ-aromaticity is cyclopropane which gains about 11.3 kcal mol−1 stability from the effect). The dications are accessible either via oxidation of pagodane or via oxidation of the corresponding bis-seco-dodecahedradiene: Reduction of the corresponding six electrons dianions was not possible so far.
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Homoaromaticity
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Examples of homoaromatic compounds
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Neutral homoaromatics There are many classes of neutral homoaromatic compounds although there is much debate as to whether they truly exhibit homoaromatic character or not. One class of neutral homoaromatics are called monohomoaromatics, one of which is cycloheptatriene, and numerous complex monohomoaromatics have been synthesized. One particular example is a 60-carbon fulleroid derivative that has a single methylene bridge. UV and NMR analysis have shown that the aromatic character of this modified fulleroid is not disrupted by the addition of a homoconjugate linkage, therefore this compound is definitively homoaromatic.Substituted neutral barbaralane derivatives (homoannulenes) have been disclosed as stable ground state homoaromatic molecules in 2023. Evidence for the homoaromatic character in this class of molecules stems from bond length analysis (X-Ray structural analysis) as well as shifts in the NMR spectrum. The homoannulenes also act as photoswitches by which means a local 6π homoaromaticity can be switched to a global 10π homoaromaticity.
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Homoaromaticity
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Examples of homoaromatic compounds
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Bishomoaromatics It was long considered that the best examples of neutral homoaromatics are bishomoaromatics such as barrelene and semibullvalene. First synthesized in 1966, semibullvalene has a structure that should lend itself well to homoaromaticity although there has been much debate whether semibullvalene derivatives can provide a true delocalized, ground state neutral homoaromatic compound or not. In an effort to further stabilize the delocalized transition structure by substituting semibullvalene with electron donating and accepting groups, it has been found that the activation barrier to this rearrangement can be lowered, but not eliminated. However, with the introduction of ring strain into the molecule, aimed at destabilizing the localized ground state structure's through the strategic addition of cyclic annulations, a delocalized homoaromatic ground-state structure can indeed be achieved.
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Homoaromaticity
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Examples of homoaromatic compounds
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Of the neutral homoaromatics, the compounds best believed to exhibit neutral homoaromaticity are boron containing compounds of 1,2-diboretane and its derivatives. Substituted diboretanes are shown to have a much greater stabilization in the delocalized state over the localized one, giving strong indications of homoaromaticity. When electron-donating groups are attached to the two boron atoms, the compound favors a classical model with localized bonds. Homoaromatic character is best seen when electron-withdrawing groups are bonded to the boron atoms, causing the compound to adopt a nonclassical, delocalized structure.
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Homoaromaticity
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Examples of homoaromatic compounds
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Trishomoaromatics As the name suggests, trishomoaromatics are defined as containing one additional methylene bridge compared to bishomoaromatics, therefore containing three of these homoconjugate bridges in total. Just like semibullvalene, there is still much debate as to the extent of the homoaromatic character of trishomoaromatics. While theoretically they are homoaromatic, these compounds show a stabilization of no more than 5% of benzene due to delocalization.
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Homoaromaticity
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Examples of homoaromatic compounds
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Anionic homoaromatics Unlike neutral homoaromatic compounds, anionic homoaromatics are widely accepted to exhibit "true" homoaromaticity. These anionic compounds are often prepared from their neutral parent compounds through lithium metal reduction. 1,2-diboretanide derivatives show strong homoaromatic character through their three-atom (boron, boron, carbon), two-electron bond, which contains shorter C-B bonds than in the neutral classical analogue. These 1,2-diboretanides can be expanded to larger ring sizes with different substituents and all contain some degree of homoaromaticity.
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Homoaromaticity
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Examples of homoaromatic compounds
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Anionic homoaromaticity can also be seen in dianionic bis-diazene compounds, which contain a four-atom (four nitrogens), six-electron center. Experiment results have shown the shortening of the transannular nitrogen-nitrogen distance, therefore demonstrating that dianionic bis-diazene is a type of anionic bishomoaromatic compound. Peculiar feature of these systems is that the cyclic electron delocalization is taking place in the σ-plane defined by the four nitrogens. These bis-diazene-dianions are therefore the first examples for 4-center-6-electron σ-bishomoaromaticity. The corresponding 2 electron σ-bishomoaromatic systems were realized in the form of pagodane dications (see above).
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Homoaromaticity
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Antihomoaromaticity
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There are also reports of antihomoaromatic compounds. Just as aromatic compounds exhibit exceptional stability, antiaromatic compounds, which deviate from Huckel's rule and contain a closed loop of 4n π electrons, are relatively unstable. The bridged bicyclo[3.2.1]octa-3,6-dien-2-yl cation contains only 4 π electrons, and is therefore "bishomoantiaromatic." A series of theoretical calculations confirm that it is indeed less stable than the corresponding allyl cation.
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Homoaromaticity
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Antihomoaromaticity
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Similarly, a substituted bicyclo[3.2.1]octa-3,6-dien-2-yl cation (the 2-(4'-Fluorophenyl) bicyclo[3.2.1]oct-3,6-dien-2-yl cation) was also shown to be an antiaromate when compared to its corresponding allyl cation, corroborated by theoretical calculations as well as by NMR analysis.
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Sony Xperia Z Ultra
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Sony Xperia Z Ultra
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The Sony Xperia Z Ultra is a 2013 Android phablet designed and manufactured by Sony Mobile.
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Sony Xperia Z Ultra
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Sony Xperia Z Ultra
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Codenamed Togari and marketed as "the world's slimmest Full HD smartphone it is the first phone that allows users to take notes or draw on with a regular pen or pencil.Like the Sony Xperia Z and Z1, the phone is dust protected, low pressure water jet protected, and waterproof, allowing immersion under 1.5 metres of water for up to 30 minutes (IP55/58), as well as being shatterproof and scratch-resistant, making it the world's thinnest IP certified smartphone.
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Sony Xperia Z Ultra
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Design
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The Xperia Z Ultra uses the same "Omni-Balance" design as Xperia Z. Combining tempered glass on both the front and rear with a metallic frame, the phablet is described as an "attractive-looking gadget" which has "minimalistic" yet "stylish" appeal and "premium feel".Designed to be the same width as a passport, the device will fit normal jacket pockets. The metal frame also makes it more comfortable to hold with one hand.Sony Xperia Z Ultra is available in three colors: black, white and purple.
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Sony Xperia Z Ultra
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Hardware
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The Sony Xperia Z Ultra has a 6.44" display, is slim (175 x 92 x 6.5 mm) and lightweight (212 g); it is also dust protected, low pressure water jet protected, waterproof (IP55/IP58), shatterproof and scratch-resistant. It has a 2 megapixel front camera and 8 megapixel rear camera with an Exmor R sensor, 16x digital zoom with auto focus, 1080 p HD recording, HDR, continue burst mode, face detection.FM RADIO with stereo.On the inside, the Z Ultra is first smartphone announced with the Qualcomm Snapdragon 800 quad-core processor. It comes with a sealed 3050 mAh Lithium polymer battery, 2 GB RAM, 16 GB of flash storage, and also has a microSD card slot (up to 128 GB). For connectivity, the phone has LTE, Bluetooth 4.0, NFC, Wi-Fi and screen mirroring.Sony will also release a Smart Bluetooth Headset (SBH52) that allows answering calls without taking the phablet out, as well as reading call logs and text messages, listening to music and FM radio. The headset has NFC for single-touch pairing with Xperia Z Ultra, and it is also water-resistant.
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Sony Xperia Z Ultra
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Features
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The 6.44" Full HD (1080p) 342 ppi touchscreen display uses Sony's Triluminos™ and X-Reality for mobile technology, with an OptiContrast panel to reduce reflection and enable clearer viewing even in bright sunlight. The screen is highly responsive and compatible with stylus as well as regular pencils or metal pens.Being waterproof means that users can use the phablet in the rain, or take it to the pool or beach. Although lacking a rear LED flash, the phone's cameras are capable of taking pictures/videos at any light.The Xperia Z Ultra was originally shipped with Sony's custom version of Android 4.2.2, and as of 27 June 2014, the Xperia Z Ultra has received the Android 4.4.4 (KitKat) update. In addition to Sony's own applications like Walkman, PlayStation Mobile, battery stamina mode, several Google apps also come preloaded (Google Chrome, Google Play, Google Voice Search, Google Maps, NeoReader™ barcode scanner). On 2 November 2014, the Xperia Z Ultra Google Play Edition received an update to Android 5.0 Lollipop.On 4 December 2015, the international version of the Xperia Z Ultra received the Android 5.1.1 update from Sony.
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Sony Xperia Z Ultra
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Features
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Because of its size, the phone's on-screen keyboard and dialer can be switched to either sides for users to easily reach all keys with only the thumb.For gaming, DualShock 3 is natively supported.C6843 variant with 1seg TV tuner is sold in Brazil.
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Sony Xperia Z Ultra
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Variants
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All variants (except SOL24) support four 2G GSM bands 850/900/1800/1900 and five 3G UMTS band 850/900/1700/1900/2100.
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Sony Xperia Z Ultra
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Reception
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Sony Xperia Z Ultra is praised for its "very classy" exterior, "stunning" massive Triluminos display, stylish premium design, slim form, light weight, impressive build quality, durability (water and dustproof), interesting pencil/pen compatibility, and powerful specs.CNET's editor Aloysius Low wrote that "Sony has set a very high benchmark with the Xperia Z Ultra", challenging the leadership position in the phablet market.PhoneArena wrote that the Xperia Z Ultra is "an engineering marvel" "towering above all other phablets not only in screen size, but also in specs and design". Its performance is described as "blazing fast", claimed to be the "fastest mobile device they've tested so far" (as of 13 August 2013). According to ExpertReviews, the Xperia Z Ultra is "more than twice as fast as a Galaxy S4".
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Da Capo 4
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Da Capo 4
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Da Capo 4 (～ダ・カーポ4～, Da Kāpo 4, commonly abbreviated as D.C.4) is a Japanese visual novel developed by Circus that was released for Windows on May 31, 2019, and was released for the Nintendo Switch and PlayStation 4 on December 19, 2019. It has a spin-off, Da Capo 4 Fortunate Departures, which was released for Windows on February 26, 2021 and was released for the Nintendo Switch and PlayStation 4 on October 27, 2022. Both game has its adult version, named Da Capo 4 Plus Harmony and Da Capo 4 Sweet Harmony respectively, released for Windows on August 27, 2021 and April 28, 2022. D.C.4 is the fourth main installment in the Da Capo series, after Da Capo, Da Capo II and Da Capo III. The game was first announced on September 23, 2018, and takes place in a different setting to its predecessors: Kagami Island. The story is told from the perspective of the protagonist Ichito Tokisaka and the narrative focuses on his relationship with the seven main heroines. The gameplay is mostly reading text and dialogue between the characters and making decisions which can alter the story route that the player takes.
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Da Capo 4
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Gameplay
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Da Capo 4 is a romance visual novel in which the player assumes the role of Ichito Tokisaka. The gameplay requires little interaction from the player, as most of the duration of the game is spent simply reading the text that appears on the screen which represents either dialogue between the various characters or the inner thoughts of the protagonist. The text is accompanied by character sprites, which represent who Kanata is talking to, over background art. Throughout the game, the player encounters CG artwork at certain points in the story, which take the place of the background art and character sprites. Every so often, the player will come to a point where he or she is given the chance to choose from multiple options. Gameplay pauses at these points and depending on which choice the player makes, the plot will progress in a specific direction. To experience all of Da Capo 4's plot lines, the player will have to replay the game multiple times and make different decisions to progress the plot in an alternate direction.
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Da Capo 4
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Synopsis
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Unlike its predecessors in the Da Capo series which take place on Hatsune Island, Da Capo 4 is set on Kagami Island (香々見島, Kagami-jima) where "cherry blossoms float in the sky". However, the story takes place in winter so the cherry blossoms are replaced with snow. Ichito Tokisaka, the protagonist, has a magical power to see floating mirrors around the island that reflect smiles. He aims to become a true magician in the future. Ichito attends the high school Kagami Academy (香々見学園, Kagami Gakuen), as do his love interests.
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Da Capo 4
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Synopsis
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The Da Capo 4 love interests are Arisu Sagisawa, the main heroine and a popular and outgoing student at the high school who frequently has to turn down confessions; Nino Tokisaka, Ichito's younger sister-in-law and an honor student who loves cats despite her cat allergy and has a devilish personality; Sorane Ōmi, Ichito and Nino's childhood friend and next-door neighbour who likes to cook and acts like an older sister to them; Hiyori Shirakawa, a beautiful troublemaker in Ichito's class who assumes the role of love contractor with a high success rate; Shīna Hōjō, a quiet but sharp-tongued girl who likes games and often comes across as difficult to approach; Miu Mishima, the president of the discipline committee who has a timid disposition and always has to scold Hiyori; finally, Chiyoko Hinohara, an eccentric and happy-go-lucky girl who records herself in live broadcasts using the stagename Choco.
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Da Capo 4
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Development and release
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Da Capo 4 was announced on September 23, 2018 as Circus' 20th project and the official website opened on November 11, 2018. Similarly to Da Capo III, no adult scenes were created for Da Capo 4 so the game is rated for all-ages. The character designers for the game were Natsuki Tanihara, Yuki Takano, Mamu Mitsumoto, Yū Kisaragi and Shayuri. Tanihara designed the characters Arisu, Sorane, Chiyoko, KotoRI and Alice; Nino and Hiyori's designs were drawn by Takano; Mitsumomo drew the character design for Shīna; marking both their first work on a visual novel, Kisaragi designed Miu, while Shayuri designed Ichito and supporting characters. Six writers were appointed to the game scenario: Hasama, Nakamichi Sagara, Shingo Hifumi, Kei Hozumi, Izumi Yūnagi and Hakumai Manpukutei.A limited edition of Da Capo 4 was released for Windows PCs on May 31, 2019. A port for the Nintendo Switch and PlayStation 4 will be released on December 19, 2019.
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Da Capo 4
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Music
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The opening theme for Da Capo 4 is "D.C.4 (Atarashii Sekai)" (D.C.4 ～新しい世界～) sung by Rin'ca. The intermediate route opening theme "Koisuru Mode" (恋するMODE) is also sung by Rin'ca. Yozuca sings "Sakura Biyori" (サクラ日和), the grand theme song of Da Capo 4.
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Mapumental
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Mapumental
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Mapumental was a web-based application for displaying journeys in terms of how long they take, rather than by distance, a technique also known as isochrone or geospatial mapping. It was developed by British organisation mySociety but was withdrawn in 2020.Users input one or more postcodes and Mapumental displays a map overlaid with coloured bands, each of which represent a set increment of time. Initial work on the project was done by Chris Lightfoot, using open data from Railplanner, Transport Direct and the Transport for London Journey Planner.It was built with support from Channel 4iP, the former public service arm of British TV broadcaster Channel 4. The software the Mapumental runs on is licensed under the GNU Affero General Public License.Mapumental can be combined with other data sets, for example, property prices and ‘scenicness’ data (see ScenicorNot, below). It is now provided as a commercial service by mySociety to clients such as the Fire Protection Association.
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Slirp
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Slirp
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Slirp (sometimes capitalized SLiRP) is a software program that emulates a PPP, SLIP, or CSLIP connection to the Internet using a text-based shell account. Its original purpose became largely obsolete as dedicated dial-up PPP connections and broadband Internet access became widely available and inexpensive. It then found additional use in connecting mobile devices, such as PDAs, via their serial ports. Another significant use case is firewall piercing/port forwarding. One typical use of Slirp creates a general purpose network connection over a SSH session on which port forwarding is restricted. Another use case is to create external network connectivity for unprivileged containers.
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Slirp
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Usage
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Shell accounts normally only allow the use of command line or text-based software, but by logging into a shell account and running Slirp on the remote server, a user can transform their shell account into a general purpose SLIP/PPP network connection, allowing them to run any TCP/IP-based application—including standard GUI software such as the formerly popular Netscape Navigator—on their computer. This was especially useful in the 1990s because simple shell accounts were less expensive and/or more widely available than full SLIP/PPP accounts.In the mid-1990s, numerous universities provided dial-up shell accounts (to their faculty, staff, and students). These command line-only connections became more versatile with SLIP/PPP, enabling the use of arbitrary TCP/IP-based applications. Many guides to using university dial-up connections with Slirp were published online (e.g. [1], [2], [3], [4]). Use of TCP/IP emulations software like Slirp, and its commercial competitor TIA was banned by some shell account providers, who believed its users violated their terms of service or consumed too much bandwidth.Slirp is also useful for connecting PDAs and other mobile devices to the Internet: by connecting such a device to a computer running Slirp, via a serial cable or USB, the mobile device can connect to the Internet.
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Slirp
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Limitations
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Unlike a true SLIP/PPP connection, provided by a dedicated server, a Slirp connection does not strictly obey the principle of end-to-end connectivity envisioned by the Internet protocol suite. The remote end of the connection, running on the shell account, cannot allocate a new IP address and route traffic to it. Thus the local computer cannot accept arbitrary incoming connections, although Slirp can use port forwarding to accept incoming traffic for specific ports.
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Slirp
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Limitations
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This limitation is similar to that of network address translation. It does provide enhanced security as a side effect, effectively acting as a firewall between the local computer and the Internet.
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Slirp
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Current status
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Slirp is free software licensed under a BSD-like, modified 4-clause BSD license by its original author. After the original author stopped maintaining it, Kelly Price took over as maintainer. There were no releases from Kelly Price after 2006. Debian maintainers have taken over some maintenance tasks, such as modifying Slirp to work correctly on 64-bit computers. In 2019, a more actively maintained Slirp repository was used by slirp4netns to provides network connectivity for unprivileged, rootless containers.
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Slirp
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Influence on other projects
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Despite being largely obsolete, Slirp made a great influence on the networking stacks used in virtual machines and other virtualized environments. The established practice of connecting the virtual machines to the host's network stack was to use the various packet injection mechanisms. Raw sockets, being one of such mechanisms, were originally used for that purpose, and, due to many problems and limitations, were later replaced with the TAP device.
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Slirp
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Influence on other projects
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Packet injection is a privileged operation that may introduce a security threat, something that the introduction of TAP device solved only partially. Slirp-derived NAT implementation brought a solution to this long-standing problem. It was discovered that Slirp has the full NAPT implementation as a stand-alone user-space code, whereas other NAT engines are usually embedded into a network protocol stack and/or do not cooperate with the host OS when doing PAT (use their own port ranges and require packet injection). QEMU project have adopted the appropriate code portions of the Slirp package and got the permission from its original authors to re-license it under 3-clause BSD license.
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Slirp
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Influence on other projects
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Such license change allowed many other FOSS projects to adopt the QEMU-provided Slirp portions, which was (and still is) not possible with the original Slirp codebase because of the license compatibility problems. Some of the notable adopters are VDE and VirtualBox projects. Even though the Slirp-derived code was heavily criticized, to date there is no competing implementation available.
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Israel Institute for Biological Research
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Israel Institute for Biological Research
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Israel Institute for Biological Research (IIBR) is an Israeli research and development laboratory It is under the jurisdiction of the Prime Minister's Office that works in close cooperation with Israeli government agencies. IIBR has many public projects on which it works with international research organizations (governmental and non-governmental) and universities. It has approximately 350 employees, 150 of whom are scientists. Its research findings are often published in national and international scientific publications. It is widely believed to be involved in the manufacturing of biological and chemical weapons. The IIBR is currently developing a COVID-19 vaccine Brilife.
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Israel Institute for Biological Research
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History
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IIBR originated with Hemed Bet, the Haganah biological warfare unit, which Alexander Kenyan, then a microbiology student, established in Jaffa in February 1948, shortly before Israeli independence, at the direction of Yigael Yadin, the Haganah's chief operations officer. Ephraim Katzir was Hemed Bet's first commander.The institute in its current form was founded in 1952, after Hemed Bet relocated to an orange grove near Ness Ziona. It was founded partly in a former Palestinian mansion of Wadi Hunayn. Among the founders were Professor Ernst David Bergmann, Prime Minister David Ben-Gurion's science adviser and the head of R&D at the Ministry of Defense. Keynan was IIBR's first director.Some of the fields in which IIBR conducts research include: Medical diagnostic techniques Mechanisms of pathogenic diseases Vaccines and pharmaceuticals Protein and enzyme synthesis and engineering Process biotechnology Air pollution risk assessment Environmental detectors and biosensorsThe institute is widely suspected of being involved in developing chemical and biological weapons. It is also assumed that the Institute develops vaccines and antidotes for such weapons. While refusing to confirm it, Israel is widely suspected of having developed offensive biological and chemical weapons capabilities, and the Israeli intelligence service Mossad is known to have used biological weapons in assassination missions. Israel has not signed the Biological Weapons Convention and has signed but not ratified the Chemical Weapons Convention.Marcus Klingberg, the highest-ranking spy for the Soviet Union ever caught in Israel, served as the IIBR's Deputy Scientific Director. He had joined the IIBR in 1957 and served as Deputy Scientific Director until 1972 as well as Head of the Department of Epidemiology until 1978. He was arrested in 1983 and convicted of espionage. His arrest and sentencing was kept a secret for over a decade.El Al Flight 1862, which crashed in the Netherlands in 1992, was carrying cargo destined for the Israel Institute for Biological Research which included 190 litres of dimethyl methylphosphonate, which (among many other uses) could be used in the synthesis of Sarin nerve gas, and is now a Chemical Weapons Convention schedule 2 chemical. Israel stated that the material was non-toxic, was to have been used to test filters that protect against chemical weapons, and that it had been listed on the cargo manifest in accordance with international regulations. The Dutch foreign ministry confirmed that it had already known about the presence of chemicals on the aircraft. According to the chemical weapons site CWInfo the quantity involved was "too small for the preparation of a militarily useful quantity of Sarin, but would be consistent with making small quantities for testing detection methods and protective clothing".According to British intelligence writer Gordon Thomas, the facility is surrounded by a high concrete wall topped with sensors, and armed guards patrol its perimeter. No aircraft are allowed to overfly the facility, and it does not appear on any map or telephone directory of the area. Inside the facility, code words and visual identification control access to each area, and there are numerous bombproof sliding doors that can only be opened by swipe cards whose codes are changed every day. Corridors inside the facility are patrolled by guards. Many of the research facilities are deep underground. All employees and their families undergo intense health checks every month.
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Israel Institute for Biological Research
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Life Science Research Israel
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Life Science Research Israel (LSRI), a subsidiary of IIBR, is dedicated to the commercial exploitation of innovative technologies developed by IIBR. According to its 2000 annual report, the 2000 budget was 16.6 million NIS (about US$4 million), with revenues of 12.9 million NIS (US$3 million).
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Seafloor spreading
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Seafloor spreading
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Seafloor spreading or Seafloor spread is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
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Seafloor spreading
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History of study
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Earlier theories by Alfred Wegener and Alexander du Toit of continental drift postulated that continents in motion "plowed" through the fixed and immovable seafloor. The idea that the seafloor itself moves and also carries the continents with it as it spreads from a central rift axis was proposed by Harold Hammond Hess from Princeton University and Robert Dietz of the U.S. Naval Electronics Laboratory in San Diego in the 1960s. The phenomenon is known today as plate tectonics. In locations where two plates move apart, at mid-ocean ridges, new seafloor is continually formed during seafloor spreading.
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Seafloor spreading
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Significance
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Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. The motivating force for seafloor spreading ridges is tectonic plate slab pull at subduction zones, rather than magma pressure, although there is typically significant magma activity at spreading ridges. Plates that are not subducting are driven by gravity sliding off the elevated mid-ocean ridges a process called ridge push. At a spreading center, basaltic magma rises up the fractures and cools on the ocean floor to form new seabed. Hydrothermal vents are common at spreading centers. Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone. Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. (The rate at which new oceanic lithosphere is added to each tectonic plate on either side of a mid-ocean ridge is the spreading half-rate and is equal to half of the spreading rate). Spreading rates determine if the ridge is fast, intermediate, or slow. As a general rule, fast ridges have spreading (opening) rates of more than 90 mm/year. Intermediate ridges have a spreading rate of 40–90 mm/year while slow spreading ridges have a rate less than 40 mm/year.: 2 The highest known rate was over 200 mm/yr during the Miocene on the East Pacific Rise.In the 1960s, the past record of geomagnetic reversals of Earth's magnetic field was noticed by observing magnetic stripe "anomalies" on the ocean floor. This results in broadly evident "stripes" from which the past magnetic field polarity can be inferred from data gathered with a magnetometer towed on the sea surface or from an aircraft. The stripes on one side of the mid-ocean ridge were the mirror image of those on the other side. By identifying a reversal with a known age and measuring the distance of that reversal from the spreading center, the spreading half-rate could be computed. In some locations spreading rates have been found to be asymmetric; the half rates differ on each side of the ridge crest by about five percent. This is thought due to temperature gradients in the asthenosphere from mantle plumes near the spreading center.
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Seafloor spreading
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Spreading center
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Seafloor spreading occurs at spreading centers, distributed along the crests of mid-ocean ridges. Spreading centers end in transform faults or in overlapping spreading center offsets. A spreading center includes a seismically active plate boundary zone a few kilometers to tens of kilometers wide, a crustal accretion zone within the boundary zone where the ocean crust is youngest, and an instantaneous plate boundary - a line within the crustal accretion zone demarcating the two separating plates. Within the crustal accretion zone is a 1-2 km-wide neovolcanic zone where active volcanism occurs.
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Seafloor spreading
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Incipient spreading
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In the general case, seafloor spreading starts as a rift in a continental land mass, similar to the Red Sea-East Africa Rift System today. The process starts by heating at the base of the continental crust which causes it to become more plastic and less dense. Because less dense objects rise in relation to denser objects, the area being heated becomes a broad dome (see isostasy). As the crust bows upward, fractures occur that gradually grow into rifts. The typical rift system consists of three rift arms at approximately 120-degree angles. These areas are named triple junctions and can be found in several places across the world today. The separated margins of the continents evolve to form passive margins. Hess' theory was that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge.
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Seafloor spreading
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Incipient spreading
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If spreading continues past the incipient stage described above, two of the rift arms will open while the third arm stops opening and becomes a 'failed rift' or aulacogen. As the two active rifts continue to open, eventually the continental crust is attenuated as far as it will stretch. At this point basaltic oceanic crust and upper mantle lithosphere begins to form between the separating continental fragments. When one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea. The Red Sea is an example of a new arm of the sea. The East African rift was thought to be a failed arm that was opening more slowly than the other two arms, but in 2005 the Ethiopian Afar Geophysical Lithospheric Experiment reported that in the Afar region, September 2005, a 60 km fissure opened as wide as eight meters. During this period of initial flooding the new sea is sensitive to changes in climate and eustasy. As a result, the new sea will evaporate (partially or completely) several times before the elevation of the rift valley has been lowered to the point that the sea becomes stable. During this period of evaporation large evaporite deposits will be made in the rift valley. Later these deposits have the potential to become hydrocarbon seals and are of particular interest to petroleum geologists.
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Seafloor spreading
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Incipient spreading
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Seafloor spreading can stop during the process, but if it continues to the point that the continent is completely severed, then a new ocean basin is created. The Red Sea has not yet completely split Arabia from Africa, but a similar feature can be found on the other side of Africa that has broken completely free. South America once fit into the area of the Niger Delta. The Niger River has formed in the failed rift arm of the triple junction.
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Seafloor spreading
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Continued spreading and subduction
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As new seafloor forms and spreads apart from the mid-ocean ridge it slowly cools over time. Older seafloor is, therefore, colder than new seafloor, and older oceanic basins deeper than new oceanic basins due to isostasy. If the diameter of the earth remains relatively constant despite the production of new crust, a mechanism must exist by which crust is also destroyed. The destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust. Today, the Atlantic basin is actively spreading at the Mid-Atlantic Ridge. Only a small portion of the oceanic crust produced in the Atlantic is subducted. However, the plates making up the Pacific Ocean are experiencing subduction along many of their boundaries which causes the volcanic activity in what has been termed the Ring of Fire of the Pacific Ocean. The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 +/- 4 mm/yr between the Pacific and Nazca plates. The Mid-Atlantic Ridge is a slow-spreading center, while the East Pacific Rise is an example of fast spreading. Spreading centers at slow and intermediate rates exhibit a rift valley while at fast rates an axial high is found within the crustal accretion zone. The differences in spreading rates affect not only the geometries of the ridges but also the geochemistry of the basalts that are produced.Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world's ocean basins decreases during times of active sea floor spreading. During the opening of the Atlantic Ocean, sea level was so high that a Western Interior Seaway formed across North America from the Gulf of Mexico to the Arctic Ocean.
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Seafloor spreading
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Debate and search for mechanism
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At the Mid-Atlantic Ridge (and in other mid-ocean ridges), material from the upper mantle rises through the faults between oceanic plates to form new crust as the plates move away from each other, a phenomenon first observed as continental drift. When Alfred Wegener first presented a hypothesis of continental drift in 1912, he suggested that continents plowed through the ocean crust. This was impossible: oceanic crust is both more dense and more rigid than continental crust. Accordingly, Wegener's theory wasn't taken very seriously, especially in the United States.
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Seafloor spreading
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Debate and search for mechanism
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At first the driving force for spreading was argued to be convection currents in the mantle. Since then, it has been shown that the motion of the continents is linked to seafloor spreading by the theory of plate tectonics, which is driven by convection that includes the crust itself as well.The driver for seafloor spreading in plates with active margins is the weight of the cool, dense, subducting slabs that pull them along, or slab pull. The magmatism at the ridge is considered to be passive upwelling, which is caused by the plates being pulled apart under the weight of their own slabs. This can be thought of as analogous to a rug on a table with little friction: when part of the rug is off of the table, its weight pulls the rest of the rug down with it. However, the Mid-Atlantic ridge itself is not bordered by plates that are being pulled into subduction zones, except the minor subduction in the Lesser Antilles and Scotia Arc. In this case the plates are sliding apart over the mantle upwelling in the process of ridge push.
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Seafloor spreading
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Seafloor global topography: cooling models
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The depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is closely correlated with its age (age of the lithosphere where depth is measured). The age-depth relation can be modeled by the cooling of a lithosphere plate or mantle half-space in areas without significant subduction.
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Seafloor spreading
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Seafloor global topography: cooling models
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Cooling mantle model In the mantle half-space model, the seabed height is determined by the oceanic lithosphere and mantle temperature, due to thermal expansion. The simple result is that the ridge height or ocean depth is proportional to the square root of its age. Oceanic lithosphere is continuously formed at a constant rate at the mid-ocean ridges. The source of the lithosphere has a half-plane shape (x = 0, z < 0) and a constant temperature T1. Due to its continuous creation, the lithosphere at x > 0 is moving away from the ridge at a constant velocity v, which is assumed large compared to other typical scales in the problem. The temperature at the upper boundary of the lithosphere (z = 0) is a constant T0 = 0. Thus at x = 0 the temperature is the Heaviside step function T1⋅Θ(−z) . The system is assumed to be at a quasi-steady state, so that the temperature distribution is constant in time, i.e. T=T(x,z).
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Seafloor spreading
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Seafloor global topography: cooling models
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By calculating in the frame of reference of the moving lithosphere (velocity v), which has spatial coordinate x′=x−vt, T=T(x′,z,t).
and the heat equation is: ∂T∂t=κ∇2T=κ∂2T∂2z+κ∂2T∂2x′ where κ is the thermal diffusivity of the mantle lithosphere.
Since T depends on x' and t only through the combination x=x′+vt, :∂T∂x′=1v⋅∂T∂t Thus: ∂T∂t=κ∇2T=κ∂2T∂2z+κv2∂2T∂2t It is assumed that v is large compared to other scales in the problem; therefore the last term in the equation is neglected, giving a 1-dimensional diffusion equation: ∂T∂t=κ∂2T∂2z with the initial conditions T(t=0)=T1⋅Θ(−z).
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Seafloor spreading
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Seafloor global topography: cooling models
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The solution for z≤0 is given by the error function: erf (z2κt) .Due to the large velocity, the temperature dependence on the horizontal direction is negligible, and the height at time t (i.e. of sea floor of age t) can be calculated by integrating the thermal expansion over z: h(t)=h0+αeff∫0∞[T(z)−T1]dz=h0−2παeffT1κt where αeff is the effective volumetric thermal expansion coefficient, and h0 is the mid-ocean ridge height (compared to some reference).
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Seafloor spreading
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Seafloor global topography: cooling models
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The assumption that v is relatively large is equivalent to the assumption that the thermal diffusivity κ is small compared to L2/A , where L is the ocean width (from mid-ocean ridges to continental shelf) and A is the age of the ocean basin.
The effective thermal expansion coefficient αeff is different from the usual thermal expansion coefficient α due to isostasic effect of the change in water column height above the lithosphere as it expands or retracts. Both coefficients are related by: αeff=α⋅ρρ−ρw where 3.3 g⋅cm−3 is the rock density and ρ0=1g⋅cm−3 is the density of water.
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Seafloor spreading
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Seafloor global topography: cooling models
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By substituting the parameters by their rough estimates: 10 10 1220 for the Atlantic and Indian oceans 1120 for the eastern Pacific we have: 390 for the Atlantic and Indian oceans 350 for the eastern Pacific where the height is in meters and time is in millions of years. To get the dependence on x, one must substitute t = x/v ~ Ax/L, where L is the distance between the ridge to the continental shelf (roughly half the ocean width), and A is the ocean basin age.
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Seafloor spreading
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Seafloor global topography: cooling models
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Rather than height of the ocean floor h(t) above a base or reference level hb , the depth of the ocean d(t) is of interest. Because d(t)+h(t)=hb (with hb measured from the ocean surface) we can find that: 350 t ; for the eastern Pacific for example, where hb−h0 is the depth at the ridge crest, typically 2600 m.
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Seafloor spreading
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Seafloor global topography: cooling models
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Cooling plate model The depth predicted by the square root of seafloor age derived above is too deep for seafloor older than 80 million years. Depth is better explained by a cooling lithosphere plate model rather than the cooling mantle half-space. The plate has a constant temperature at its base and spreading edge. Analysis of depth versus age and depth versus square root of age data allowed Parsons and Sclater to estimate model parameters (for the North Pacific): ~125 km for lithosphere thickness 1350 ∘C at base and young edge of plate 3.2 10 −5∘C−1 Assuming isostatic equilibrium everywhere beneath the cooling plate yields a revised age depth relationship for older sea floor that is approximately correct for ages as young as 20 million years: 6400 3200 exp 62.8 ) metersThus older seafloor deepens more slowly than younger and in fact can be assumed almost constant at ~6400 m depth. Parsons and Sclater concluded that some style of mantle convection must apply heat to the base of the plate everywhere to prevent cooling down below 125 km and lithosphere contraction (seafloor deepening) at older ages. Their plate model also allowed an expression for conductive heat flow, q(t) from the ocean floor, which is approximately constant at 10 −6calcm−2sec−1 beyond 120 million years: 11.3 /t
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Memory bank
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Memory bank
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A memory bank is a logical unit of storage in electronics, which is hardware-dependent. In a computer, the memory bank may be determined by the memory controller along with physical organization of the hardware memory slots. In a typical synchronous dynamic random-access memory (SDRAM) or double data rate SDRAM (DDR SDRAM), a bank consists of multiple rows and columns of storage units, and is usually spread out across several chips. In a single read or write operation, only one bank is accessed, therefore the number of bits in a column or a row, per bank and per chip, equals the memory bus width in bits (single channel). The size of a bank is further determined by the number of bits in a column and a row, per chip, multiplied by the number of chips in a bank.
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Memory bank
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Memory bank
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Some computers have several identical memory banks of RAM, and use bank switching to switch between them. Harvard architecture computers have (at least) two very different banks of memory, one for program storage and other for data storage.
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Memory bank
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In caching
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A memory bank is a part of cache memory that is addressed consecutively in the total set of memory banks, i.e., when data item a(n) is stored in bank b, data item a(n + 1) is stored in bank b + 1. Cache memory is divided in banks to evade the effects of the bank cycle time (see above) [=> missing "bank cycle" definition, above]. When data is stored or retrieved consecutively each bank has enough time to recover before the next request for that bank arrives.The number of memory modules needed to have the same number of data bits as the bus. A bank can consist of one or more memory modules.
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Supplied-air respirator
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Supplied-air respirator
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A supplied-air respirator (SAR) or air-line respirator is a breathing apparatus used in places where the ambient air may not be safe to breathe. It uses an air hose to supply air from outside the danger zone. It is similar to a self-contained breathing apparatus (SCBA), except that SCBA users carry their air with them in high pressure cylinders, while SAR users get it from a remote stationary air supply connected to them by a hose.
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Supplied-air respirator
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Description
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SARs are lightweight, but tether the user. Unlike SCBAs, the worker will not run out of air when the tank they carry is empty. They can therefore be used for longer continuous work periods. The mask end of a SAR is generally lower-maintenance than an SCBA, but the air compressors or tanks at the other end of the hose require monitoring and maintenance. It is important that they deliver good air; contaminants (which may also be introduced by faulty operation of the machinery) can be dangerous.If the air-supply line is cut or pinched shut, the user will not have any air to breathe. SAR users therefore often carry a small backup air tank (called an auxiliary escape cylinder). In an emergency, they can switch to using this supply, which should last long enough for them to escape the dangerous area. This backup bottle is required in some jurisdictions. Other regulations also apply. Users of SARs must generally be given hands-on training with the specific model they are to use.SARs may be either constant-flow or pressure-demand respirators. Constant-flow respirators supply a steady stream of air, some of which escapes from the wearer end unbreathed. Pressure-demand respirators supply air only when the pressure in the wearer's mask drops (that is, when they inhale). This saves air but allows more inwards leakage. Pressure-demand respirators can only be used with a sealed elastomeric mask, not with a loose-fitting hood (like those used in powered air-purifying respirators) or helmet (used in construction). Hoods may be made of Tyvek, polyethylene, or polypropylene.
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Supplied-air respirator
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Use
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According to the NIOSH Respirator Selection Logic, SARs with an auxiliary SCBA are recommended for oxygen-deficient atmospheres, atmospheres that are immediately dangerous to life or health, and unknown atmospheres, all of which are conditions that air-purifying respirators such as N95 masks do not protect against. SARs without an auxiliary SCBA may also be used in conditions where an air-purifying respirator may be used, and have the benefit of a higher range of assigned protection factors (APF). Air-purifying respirators have APFs in the range 5–50 while SARs are in the range 25–2000, and full-facepiece pressure-demand SARs with an auxiliary pressure-demand SCBA have an APF of 10,000. For substances hazardous to the eyes, a respirator equipped with a full facepiece, helmet, or hood is recommended. SARs are not effective during firefighting, for which a SCBA is recommended instead.
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Solar power forecasting
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Solar power forecasting
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Solar power forecasting is the process of gathering and analyzing data in order to predict solar power generation on various time horizons with the goal to mitigate the impact of solar intermittency. Solar power forecasts are used for efficient management of the electric grid and for power trading.As major barriers to solar energy implementation, such as materials cost and low conversion efficiency, continue to fall, issues of intermittency and reliability have come to the fore. The intermittency issue has been successfully addressed and mitigated by solar forecasting in many cases.Information used for the solar power forecast usually includes the Sun´s path, the atmospheric conditions, the scattering of light and the characteristics of the solar energy plant. Generally, the solar forecasting techniques depend on the forecasting horizon Nowcasting (forecasting 3–4 hours ahead), Short-term forecasting (up to seven days ahead) and Long-term forecasting (weeks, months, years)Many solar resource forecasting methodologies were proposed since the 1970 and most authors agree that different forecast horizons require different methodologies. Forecast horizons below 1 hour typically require ground based sky imagery and sophisticated time series and machine learning models. Intra-day horizons, normally forecasting irradiance values up to 4 or 6 hours ahead, require satellite images and irradiance models. Forecast horizons exceeding 6 hours usually rely on outputs from numerical weather prediction (NWP) models.
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Solar power forecasting
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Nowcasting
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Solar power nowcasting refers to the prediction of solar power output over time horizons of tens to hundreds of minutes ahead of time with up to 90% predictability. Solar power nowcasting services are usually related to temporal resolutions of 5 to 15 minutes, with updates as frequent as every minute. The high resolution required for accurate nowcast techniques require high resolution data input including ground imagery, as well as fast data acquisition form irradiance sensors and fast processing speeds.
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Solar power forecasting
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Nowcasting
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The actual nowcast is than frequently enhanced by e.g. Statistical techniques. In the case of nowcasting, these techniques are usually based on time series processing of measurement data, including meteorological observations and power output measurements from a solar power facility. What then follows is the creation of a training dataset to tune the parameters of a model, before evaluation of model performance against a separate testing dataset. This class of techniques includes the use of any kind of statistical approach, such as autoregressive moving averages (ARMA, ARIMA, etc.), as well as machine learning techniques such as neural networks, support vector machines (etc.). An important element of nowcasting solar power are ground based sky observations and basically all intra-day forecasts.
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