Split (1)

train · 2.1M rows

title stringlengths 1 149 ⌀	section stringlengths 1 1.9k ⌀	text stringlengths 13 73.5k
Sutimlimab	History	The effectiveness of sutimlimab was assessed in a study of 24 adults with cold agglutinin disease who had a blood transfusion within the past six months. All participants received sutimlimab for up to six months and could choose to continue therapy in a second part of the trial. Based on body weight, participants received either a 6.5g or 7.5g infusion of sutimlimab into their vein on day 0, day 7, and every 14 days through week 25.In total, 54% of participants responded to sutimlimab. The response was defined in the study as an increase in hemoglobin (an indirect measurement of the amount of red blood cells that are not destroyed) of 2 g/dL or greater (or to 12 g/dL or greater), and no red blood cell transfusions after the first five weeks of treatment; and no other therapies for cold agglutinin disease as defined in the study.The U.S. Food and Drug Administration (FDA) granted the application for sutimlimab orphan drug, breakthrough therapy, and priority review designations.
Sutimlimab	Society and culture	Legal status On 15 September 2022, the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion, recommending the granting of a marketing authorization for the medicinal product Enjaymo, intended for the treatment of hemolytic anemia in adults with cold agglutinin disease (CAD). The applicant for this medicinal product is Genzyme Europe BV. Sutimlimab was approved for medical use in the European Union in November 2022.
Sutimlimab	Society and culture	Names Sutimlimab is the International nonproprietary name (INN).
Aeronautical operational control	Aeronautical operational control	Aeronautical operational control (AOC) is a group or the entirety of applications used for communication of an aircraft with its airline or service partners on the ground. An AOC application was traditionally hosted on an ACARS MU or Communications Management Unit (CMU). AOC communication is required for the exercise of authority over the initiation, continuation, diversion or termination of flight for safety, regularity and efficiency reasons.AOC were often user-defined, because they were only exchanged between an airline and its own aircraft; controlling both ends, there was no need for standardization.However, by introducing airframe-defined ACARS messages (e.g. the Airbus A380) and because of the increasing need to connect airline handling partners such as fuel suppliers or de-icing companies, a need to standardize appeared. In 2007, ARINC 633 was created developed to standardize these AOC messages.
INK4	INK4	INK4 is a family of cyclin-dependent kinase inhibitors (CKIs). The members of this family (p16INK4a, p15INK4b, p18INK4c, p19INK4d) are inhibitors of CDK4 (hence their name INhibitors of CDK4), and of CDK6. The other family of CKIs, CIP/KIP proteins are capable of inhibiting all CDKs. Enforced expression of INK4 proteins can lead to G1 arrest by promoting redistribution of Cip/Kip proteins and blocking cyclin E-CDK2 activity. In cycling cells, there is a resassortment of Cip/Kip proteins between CDK4/5 and CDK2 as cells progress through G1. Their function, inhibiting CDK4/6, is to block progression of the cell cycle beyond the G1 restriction point. In addition, INK4 proteins play roles in cellular senescence, apoptosis and DNA repair.INK4 proteins are tumor suppressors and loss-of-function mutations lead to carcinogenesis.INK4 proteins are highly similar in terms of structure and function, with up to 85% amino acid similarity. They contain multiple ankyrin repeats.
INK4	Genes	The INK4a/ARF/INK4b locus encodes three genes (p15INK4b, ARF, and p16INK4a) in a 35-kilobase stretch of the human genome. P15INK4b has a different reading frame that is physically separated from p16INK4a and ARF. P16INK4a and ARF have different first exons that are spliced to the same second and third exon. While those second and third exons are shared by p16INK4a and ARF, the proteins are encoded in different reading frames meaning that p16INK4a and ARF are not isoforms, nor do they share any amino acid homology.
INK4	Evolution	Polymorphisms of the p15INK4b/p16INK4a homolog were found to segregate with melanoma susceptibility in the Xiphophorus indicating that INK4 proteins have been involved with tumor suppression for over 350 million years. Furthermore, the older INK4-based system has been further bolstered by the evolution of the recent addition of the ARF-based anti-cancer response.
INK4	Function	INK4 proteins are cell-cycle inhibitors. When they bind to CDK4 and CDK6, they induce an allosteric change that leads to the formation of CDK-INK4 complexes rather than CDK-cyclin complexes. This leads to an inhibition of retinoblastoma (Rb) phosphorylation downstream. Therefore, the expression of p15INK4b or p16INK4A keeps the Rb-family proteins hypophosphorylated. This allows the hypophosphorylated Rb to repress transcription of S-phase genes causing cell cycle arrest in the G1 phase.
INK4	Subsets	P16INK4a P16 is formed from four ankyrin repeat (AR) motifs that exhibit a helix-turn-helix conformation except that the first helix in the second AR consists of four residues. P16 regulation involves epigenetic control and multiple transcription factors. PRC1, PRC2, YY1, and Id1 play a role in the suppression of p16INK4A expression and transcription factors CTCF, Sp1, and ETs activate p16INK4A transcription. In knockout experiments, it was found that mice lacking just p16INK4a were more prone to spontaneous cancers. Mice lacking both p16INK4a and ARF were found to be even more tumor prone than the mice lacking just p16INK4a.
INK4	Subsets	P15INK4b P15 is also formed from four ankyrin repeat (AR) motifs. Expression of P15INK4b is induced by TGF-b indicating its role as a potential downstream effector of TGF-b mediated growth arrest.
INK4	Subsets	P18INK4c P18INK4c has been shown to play an important role in modulating TCR-mediated T cell proliferation. The loss of p18INK4c in T cells reduced the requirement of CD28 costimulation for efficient T cell proliferation. Other INK4 family members did not affect this process. Furthermore, it was shown that p18INK4c is preferentially inhibitory to CDK6, but not CDK4 activity in activated T cells that suggest p18INK4c may set an inhibitory threshold in resting T cells.
INK4	Clinical significance	Role in cancer Cells containing oncogenic mutations in-vivo often responded by activating the INK4A/ARF/INK4B locus that encodes the INK4 tumor suppressor proteins. The unusual genomic arrangement of the INK4a/ARF/INK4b locus functions as a weakness in our anti-cancer defenses. This is due to the fact that three crucial regulators of the RB and p53 (regulated by ARF) are vulnerable to one single, small deletion. This observation yields two possible opposing conclusions: Either tumor formation does not provide any evolutionary selection pressure because the overlapping INK4a/ARF/INK4b is not selected against or tumorigenesis provides such a strong pressure, that an entire group of genes has been selected for at the INK4a/ARF/INK4b locus to prevent cancer. The response of the INK4a/ARF/INK4b locus efficiently prevents cancers that could occur to the constant oncogenic mutations that occur in long-lived mammals.
INK4	Clinical significance	When the INK4a/ARF/INK4b locus was overexpressed, the mice demonstrated a 3-fold reduction in the incidence of spontaneous cancers. This evidence further indicated that the INK4a/ARF/INK4b locus in mice plays a role in tumor suppression.
INK4	Clinical significance	Role in aging The INK4 family has been implicated in the aging process. The expression of p16INK4a increases with aging in many tissues of rodents and humans. It was also shown that INK4a/ARF deficient animals increase an age-related decline in T-cell responsiveness to CD3 and CD28, which is a hallmark of aging. Furthermore, neural stem cells from Bmi-1- deficient animals demonstrate increased INK4a/ARF expression and impaired regenerative potential. The phenotype; however, can be rescued by p16INK4a deficiency implying that while p16INK4a can potentially be used as a biomarker of physiologic, rather than chronologic age, it is also an effector of aging. The mechanism by which it does this is by limiting the self-renewal capacity of disparate tissues such as lymphoid organs, bone marrow, and the brain.
INK4	Regulation of INK4 expression	Initially, it was thought that each INK4 family member was structurally redundant and equally potent. It was later found; however, that INK4 family members are differentially expressed during mouse development. The diversity in expression pattern indicates that the INK4 gene family may have cell lineage-specific or tissue-specific functions. Evidence has shown that INK4a/ARF expression increase at an early stage of tumorigenesis, but the precise stimuli relevant to cancer that induces the expression of the locus is unknown. Expression of p15INK4b does not correlate with p16INK4a in many normal rodent tissues. Induction and repression of p15INK4b; however, has been noted in response to a few signaling events such as RAS activation, that also induce INK4/ARF expression.
INK4	Regulation of INK4 expression	RAS activation might lead to increased INK4/ARF expression potentially through ERK-mediated activation of Ets1/2 to induce p16INK4. A few repressors of INK4a/ARF/INK4b expression have been identified as well. T box proteins and the polycomb group have been shown to repress p16INK4a, p15INK4b, and ARF.
Cylindrical σ-algebra	Cylindrical σ-algebra	In mathematics — specifically, in measure theory and functional analysis — the cylindrical σ-algebra or product σ-algebra is a type of σ-algebra which is often used when studying product measures or probability measures of random variables on Banach spaces. For a product space, the cylinder σ-algebra is the one that is generated by cylinder sets.
Cylindrical σ-algebra	Cylindrical σ-algebra	In the context of a Banach space X, the cylindrical σ-algebra Cyl ⁡(X) is defined to be the coarsest σ-algebra (that is, the one with the fewest measurable sets) such that every continuous linear function on X is a measurable function. In general, Cyl ⁡(X) is not the same as the Borel σ-algebra on X, which is the coarsest σ-algebra that contains all open subsets of X.
Run queue	Run queue	In modern computers many processes run at once. Active processes are placed in an array called a run queue, or runqueue. The run queue may contain priority values for each process, which will be used by the scheduler to determine which process to run next. To ensure each program has a fair share of resources, each one is run for some time period (quantum) before it is paused and placed back into the run queue. When a program is stopped to let another run, the program with the highest priority in the run queue is then allowed to execute.
Run queue	Run queue	Processes are also removed from the run queue when they ask to sleep, are waiting on a resource to become available, or have been terminated.
Run queue	Run queue	In the Linux operating system (prior to kernel 2.6.23), each CPU in the system is given a run queue, which maintains both an active and expired array of processes. Each array contains 140 (one for each priority level) pointers to doubly linked lists, which in turn reference all processes with the given priority. The scheduler selects the next process from the active array with highest priority. When a process' quantum expires, it is placed into the expired array with some priority. When the active array contains no more processes, the scheduler swaps the active and expired arrays, hence the name O(1) scheduler.
Run queue	Run queue	In UNIX or Linux, the sar command is used to check the run queue. The vmstat UNIX or Linux command can also be used to determine the number of processes that are queued to run or waiting to run. These appear in the 'r' column.
Run queue	Run queue	Example: $ vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 2 0 0 4579152 324416 4619528 0 0 402 236 3357 15 20 2 78 0 0 There are two models for Run queues: one that assigns a Run Queue to each physical processor, and the other has only one Run Queue in the system
SXBL	SXBL	sXBL (SVG's XML Binding Language) is a mechanism for defining the presentation and interactive behavior of elements described in a namespace other than SVG's (an XML language supporting vector graphics, user events and scripted behavior). sXBL is very similar to XBL, as it does for SVG documents what XBL does for XUL documents. For example, it is possible to define a generic scrollArea in sXBL and use it in SVG documents.
SXBL	History, objectives, and future	sXBL specification derived from a specification called RCC (Rendering Custom Content) that was embedded in a 2003 working draft of the SVG 1.2 specification. The RCC part of the specification has since been removed in favor of the sXBL more modular approach.
SXBL	History, objectives, and future	As stated in the sXBL working draft: sXBL is intended to be an SVG-specific first version of a more general-purpose XBL specification (e.g., "XBL 2.0"). The intent is that, in the future, a general-purpose and modularly-defined XBL specification will be developed which will replace this specification and will define additional features that are necessary to support scenarios beyond SVG, such as integration into web browsers that support CSS. Once a general-purpose XBL is defined, sXBL would just become an SVG-specific subset (i.e., a profile) of the larger XBL specification.
SXBL	History, objectives, and future	Even if sXBL has borrowed a lot from XBL, there are some differences between these two standards (for example, the name of some of the elements are different). However, there are also some subtle differences between the current state of the Mozilla XBL 2.0 working draft and the current state of the sXBL working draft. As the sXBL specification has not evolved since the last working draft in August 2005, and since the September 2006 release of the XBL 2.0 last call working draft, it seems that sXBL will be dropped in favour of the more general XBL 2.0 approach.
SXBL	Implementations	sXBL is a W3C working draft, and has not yet reached the status of a recommendation. However, the Batik SVG Toolkit, a Java library that can be used to render, generate, and manipulate SVG graphics, has a preliminary "almost full" implementation of the current state of the sXBL specification in its code base.
Dose profile	Dose profile	In external beam Radiotherapy, transverse and longitudinal dose measurements are taken by a radiation detector in order to characterise the radiation beams from medical linear accelerators. Typically, an ionisation chamber and water phantom are used to create these radiation dose profiles. Water is used due to its tissue equivalence. Transverse dose measurements are performed in the x (crossplane) or y (inplane) directions perpendicular to the radiation beam, and at a given depth (z) in the phantom. These are known as dose profiles.
Dose profile	Dose profile	Dose measurements taken along the z direction create radiation dose distribution known as a depth-dose curve.
Test tube	Test tube	A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top and closed at the bottom. Test tubes are usually placed in special-purpose racks.
Test tube	Types and usage	Chemistry Test tubes intended for general chemical work are usually made of glass, for its relative resistance to heat. Tubes made from expansion-resistant glasses, mostly borosilicate glass or fused quartz, can withstand high temperatures up to several hundred degrees Celsius. Chemistry tubes are available in a multitude of lengths and widths, typically from 10 to 20 mm wide and 50 to 200 mm long. The top often features a flared lip to aid pouring out the contents. A chemistry test tube typically has a flat bottom, a round bottom, or a conical bottom. Some test tubes are made to accept a ground glass stopper or a screw cap. They are often provided with a small ground glass or white glaze area near the top for labelling with a pencil. Test tubes are widely used by chemists to handle chemicals, especially for qualitative experiments and assays. Their spherical bottom and vertical sides reduce mass loss when pouring, make them easier to wash out, and allow convenient monitoring of the contents. The long, narrow neck of test tube slows down the spreading of gases to the environment.
Test tube	Types and usage	Test tubes are convenient containers for heating small amounts of liquids or solids with a Bunsen burner or alcohol burner. The tube is usually held by its neck with a clamp or tongs. By tilting the tube, the bottom can be heated to hundreds of degrees in the flame, while the neck remains relatively cool, possibly allowing vapours to condense on its walls. A boiling tube is a large test tube intended specifically for boiling liquids.
Test tube	Types and usage	A test tube filled with water and upturned into a water-filled beaker is often used to capture gases, e.g. in electrolysis demonstrations. A test tube with a stopper is often used for temporary storage of chemical or biological samples. Biosciences Culture tubes are test tubes used in biology and related sciences for handling and culturing all kinds of live organisms, such as molds, bacteria, seedlings, plant cuttings, etc.. Some racks for culture tubes are designed to hold the tubes in a nearly horizontal position, so as to maximize the surface of the culture medium inside.
Test tube	Types and usage	Culture tubes for biology are usually made of clear plastic (such as polystyrene or polypropylene) by injection molding and are often discarded after use. Plastic test tubes with a screwtop cap are often called "Falcon tubes" after a line manufactured by Becton Dickinson.Some sources consider that the presence of a lip is what distinguishes a test tube from a culture tube.
Test tube	Types and usage	Clinical medicine In clinical medicine, sterile test tubes with air removed, called vacutainers, are used to collect and hold samples of physiological fluids such as blood, urine, pus, and synovial fluid. These tubes are commonly sealed with a rubber stopper and often have a specific additive placed in the tube with the stopper color indicating the additive. For example, a blue-top tube is a 5 ml test tube containing sodium citrate as an anticoagulant, used to collect blood for coagulation and glucose-6-phosphate dehydrogenase testing. Small vials used in medicine may have a snap-top (also called a hinge cap) molded as part of the vial.
Test tube	Types and usage	Other uses Test tubes are sometimes put to casual uses outside of lab environments, e.g. as flower vases, glassware for certain weak shots, or containers for spices. They can also be used for raising queen ants during their first months of development.
Test tube	Variants	Boiling tube A boiling tube is a small cylindrical vessel used to strongly heat substances in the flame of a Bunsen burner. A boiling tube is essentially a scaled-up test tube, being about 50% larger.
Test tube	Variants	They are designed to be wide enough to allow substances to boil violently as opposed to a test tube, which is too narrow; a boiling liquid can explode out of the end of test tubes when they are heated, as there is no room for bubbles of gas to escape independently of the surrounding liquid. This phenomenon is called bumping.
Test tube	Variants	Ignition tube An ignition tube is used in much the same way as a boiling tube, except it is not as large and thick-walled. It is primarily used to hold small quantities of substances which are undergoing direct heating by a Bunsen burner or other heat source. This type of tube is used in the sodium fusion test. Ignition tubes are often difficult to clean due to the small bore. When used to heat substances strongly, some char may stick to the walls as well. They are usually disposable.
Universal powerline bus	Universal powerline bus	Universal Powerline Bus (UPB) is a proprietary software protocol developed by Powerline Control Systems for power-line communication between devices used for home automation. Household electrical wiring is used to send digital data between UPB devices via pulse-position modulation.Communication is peer to peer, with no central controller necessary.UPB addressing allows 250 devices per house and 250 houses per transformer, allowing over 62,500 total device addresses and can co-exist with other powerline carrier systems within the same home.As of 2018, UPB enjoys one of the broadest range of device types when compared to most protocols and has support from some major manufacturers in the home automation space. Most notably, Leviton and their Omni series of home automation products, as well as the UPB devices they market. UPB is also supported by many major home automation software manufacturers. A few of which are listed below.
Universal powerline bus	Reliability	UPB is a highly reliable protocol for home automation. It is not susceptible to RF interference, signal blockage by walls or short distance broadcast issues like some wireless protocols. UPB transmits on the building's existing wiring and has extensive noise reduction circuitry. This allows it to traverse long distances without issues, even across multiple electrical panels, making it ideal for very large homes. Appliances that have traditionally plagued X10 devices, usually do not affect UPB. In fact, UPB signals can reliably be received by the target device even with significant amounts of electrical noise on the power lines. However, in the event that an appliance in your home causes extreme interference when operating, an inexpensive wire-in noise filter can be applied at the circuit breaker panel to solve the issue.
Universal powerline bus	Interoperability	As of 2020, control of UPB devices is supported by the Home Assistant open source software (in version 0.110 and later).As of 2017, control of UPB devices is supported by the OpenHAB open source software.HomeSeer is a well known commercial home automation software package that has support for UPB. Mobile App support (IOS and Android) is available by using the PulseWorx Gateway (PGW) plug-in module. Voice recognition products such as Alexa, Automated Living's HAL and Google's Assistant are supported either directly or indirectly through a device or automation controller.
Universal powerline bus	Interoperability	UPB can coexist with other powerline technologies. It can also interoperate with other automation devices that use RF (for example) through the use of a multi protocol automation controller (See Leviton Omni, HomeSeer devices). This allows for a mixed technology automation system to achieve best in class devices from many manufacturers. However, it is interesting to note that unlike most wireless protocols, UPB does not require an automation controller or hub to operate.
Universal powerline bus	Interoperability	Since UPB is a peer to peer protocol, individual switches, scene controllers and various types of plug-in modules can be individually programmed to do multiple tasks without the need to purchase a hub or controller. Some examples of actions that can be achieved without a hub or controller would be: timed shutoff of a bathroom fan (timer plug-in module or a switch with timer feature built-in), lights turning on or off based on a photocell's sensing of sunlight (I/O plug-in module), turning on one set of lights with a single tap of the switch and turning on another set of lights or devices on a double tap of the switch (dimmer switch). Turning on/off a Hot Tub (load controller switch), multiple preset light dimming settings (scene controller switch), turn on/off a motorized device (relay switch).
Universal powerline bus	Interoperability	Scene controllers with built in Infrared (IR) sensors are available. This allows for a single programmable remote control (universal remote) like those made by Logitech to control both your lighting and your television or other media devices.
Universal powerline bus	Hardware Manufacturers	The following is a list of UPB device manufacturers. This is not a comprehensive list: Advanced Quonset Technologies Leviton HLC line Powerline Control Systems PulseWorx line Simply Automated Web Mountain WGL Designs
Ecotechnics	Ecotechnics	Ecotechnics is defined as the 'techne' of bodies. Ecotechnics thinks of the body as a technology which makes possible the inclusion of a whole new range of bodies. This gives people more agency and biopower over their own use of their bodies. This makes it usable for queer theory and disability studies. An interpretation also refers to the term as the craft of the home.In classifying the body as a technical object, Jean-Luc Nancy explained how it works by partitioning bodies into their own zones and spaces, which also allow such bodies to connect with other bodies. Hence, Nancy claims that technology determine our interactions with other beings in the world. Ecotechnics is also central in Sullivan's and Murray's collection of essays Queering the Technologisation of Bodies. It is built on Bernard Stiegler's work that sees the body and technology as a double process: the technology and the body are informed by each other. Derrida who extends on both Nancy and Stiegler's ideas argues that the 'proper body' implicates interconnections of technical additions. Ecotechnics goes against the essentialist and binary notion of the body as a technological object which positions it within post-structuralism. The body can only be understood within its environment and this environment is a technical one.
Ecotechnics	Ecotechnics	Nancy also applied the ecotechnics concept to contemporary issues such as war and globalization. He maintained, for instance, that modern conflicts are produced by the dividing lines between: North and South; rich and poor; and, integrated and excluded. He also believes that ecotechnics is undoing communities due to the elimination of the polis and the prevalence of oikos, calling for a global sovereignty that would administer the world as a single household.
Stone skipping	Stone skipping	Stone skipping and stone skimming are considered related but distinct activities: both refer to the art of throwing a flat stone across the water in such a way (usually sidearm) that it bounces off the surface. The objective of "skipping" is to see how many times a stone can bounce before it sinks into the water; the objective of "skimming" is to see how far a bouncing stone can travel across the water before it sinks into the water. In Japan, the practice is referred to as Mizu Kiri, which loosely translates to "water cutting". In Mizu Kiri contests, both skimming and skipping principles, as well as a throw's overall aesthetic quality, are taken into account to determine the winners.
Stone skipping	History	The act of skipping stones was mentioned by Marcus Minucius Felix in his dialogue Octavius, in which he described children playing a game on the beach. Greek scholar Julius Pollux also noted the game in Onomastikon. Among the first documented evidence stone skipping as a sport was in England, where it was described as "Ducks and Drakes" in 1583. An early explanation of the physics of stone-skipping was provided by Lazzaro Spallanzani in the 18th century.
Stone skipping	History	Records The world record for the number of skips, according to the Guinness Book of Records, is 88, by Kurt "Mountain Man" Steiner. The cast was achieved on September 6, 2013, at Red Bridge in the Allegheny National Forest, Pennsylvania. The previous record was 65 skips, by Max Steiner (no relation), set at Riverfront Park, Franklin, Pennsylvania. Before him, the record was 51 skips, set by Russell Byars on July 19, 2007, skipping at the same location. Kurt Steiner also held the world record between 2002 and 2007 with a throw of 40 skips, achieved in competition in Franklin, PA.
Stone skipping	History	The Guinness World Record for the furthest distance skimmed using natural stone stands at 121.8m for men, established by Dougie Isaacs (Scotland), and 52.5m for women, thrown by Nina Luginbuhl (Switzerland). These records were made on 28 May 2018 at Abernant Lake, Llanwrtyd Wells, Powys, Wales. There are several stone skimming championships held. The record for most World Championship wins also sits with Dougie Isaacs (Scotland), with 8 Men's World Stone Skimming Championship wins (2005, 2007, 2010, 2011, 2013, 2014, 2015, 2016) and the Women's World Stone Skimming Championship wins record sits with Lucy Wood (England) with 5 wins (2012, 2013, 2015, 2016, 2018).
Stone skipping	Championships	The "Big Four" American stone skipping contests include (in order of establishment and participant rankings): The Mackinac Island championship, held on July 4 in northern Michigan (entry by invite only; must win prior Mackinac Open or Pennsylvania Qualifier to enter); The Pennsylvania championship, held usually the 3rd Saturday of August in Franklin, PA, about one hour southeast of Erie (winners invited to the subsequent Michigan contest); The Vermont championship (about one month after Pennsylvania) on the shore of Lake Paran, North of Bennington; and The Great Southern championship in Arkansas (Labor Day weekend).Former world champion Coleman-McGhee founded the North American Stone Skipping Association (NASSA) in 1989 in Driftwood, Texas. NASSA-sanctioned world championships were held from 1989 through 1992 in Wimberley, Texas. The next official NASSA World Championship is expected to be held at Platja d'en Ros beach in Cadaqués, Catalonia, Spain..
Stone skipping	Championships	A stone skimming championship takes place every year in Easdale, Scotland, where relative distance counts as opposed to the number of skips, as tends to be the case outside of the US. The event was run for more than 20 years by Donald Melville, who is seen as having done more for the sport than anyone. Since 1997, competitors from all over the world have taken part in the World Stone Skimming Championships (WSSC) in a disused water-filled quarry on Easdale Island using sea-worn Easdale slate of maximum 3" diameter. Each participant gets three throws and the stone must bounce/skip at least twice to count (i.e. 3 water touches minimum).. The event featured in the 2019 BBC Scotland documentary Sink or Skim. The WSSC for 2020-2022 were cancelled due to coronavirus concerns. The next is scheduled for Sept 2023.
Stone skipping	Championships	Other domestic distance-based championships in the UK are currently the Welsh and British, but they were cancelled in 2020 and 2021 for reasons including the COVID-19 pandemic. The British is next due to be held in 2023. Japan holds competitions where both skimming and skipping principles, as well as a throw's overall aesthetic quality, are taken into account to determine the winners. At present, there is also a competition at Ermatingen in Switzerland and occasionally in the Netherlands (both skimming/distance-based).
Stone skipping	Championships	Men's World Skimming Championship winners by year 2020, 2021 and 2022 Championships cancelled due to aspects of the COVID-19 pandemic. Women's World Skimming Championship winners by year 2020, 2021 and 2022 Championships cancelled due to the COVID-19 pandemic.
Stone skipping	Underlying physics	Although stone skipping occurs at the air-water interface, surface tension has very little to do with the physics of stone-skipping. Instead, the stones are a flying wing akin to a planing boat or Frisbee, generating lift from a body angled upwards relative to a high horizontal velocity.The same physical laws apply to stones traveling in air or in water, but the effect is only comparable to gravity when immersed in water, because of the latter fluid's higher density. The result is a characteristic bouncing or skipping motion, in which a series of extremely brief collisions with the water superficially appear to support the stone.During each collision, the stone's horizontal velocity is approximately constant and its vertical motion can be approximated as a distorted pendulum. The stone is only partially immersed, and the lift applied at the back torques the stone towards tumbling. That torque is stabilized by the gyroscope effect: the stone-skipper imparts a perpendicular initial angular momentum much larger than the collisional impulse, so that the latter induces only a small precession in the axis of rotation.Stones improperly oriented at the moment of collision will not rebound: the largest observed angle of attack preceding a rebound occurred at an angle of approximately 45°. Conversely, a stone making angle 20° with the water's surface may rebound even at relatively low velocities, as well as minimizing the time and energy spent in the following collision.In principle, a stone can skip arbitrarily-long distances, given a sufficiently high initial speed and rotation. Each collision saps an approximately constant kinetic energy from the stone (a dynamical equation equivalent to Coulomb friction), as well as imparting an approximately constant angular impulse. Experiments suggest that initial angular momentum's stabilizing effect limits most stones: even "long-lived" throws still have high translational velocities when they finally sink.
Stone skipping	Names	English: "skipping stones" or "skipping rocks" (North America); "lobsta cutting" (Cape Cod, North America); "stone skimming" or "ducks and drakes" (Britain); Skliffing or "skiting" (Scotland) and "stone skiffing" (Ireland) Bengali: "frog jumps" (Bengbaji); "kingfisher" (Machhranga) Bulgarian: "frogs" (жабки) Cantonese: "skipping (little) stones" (片石(仔)) [pin3 sek6 (zai2)] Catalan: "making step-stone bridges" (fer passeres); "making furrows" (fer rigalets); "skipping stones" (llençar passanelles) Czech: "to make/throw froggies" (dělat (házet) žabky/žabičky – countrywide and generally intelligible); "to make ducks/drakes/ducklings" (dělat kačky/kačeny/kačery/kačenky/káčata/káčírky - in East Bohemia and parts of Moravia); "little fishes" (rybičky/rybky); "saucers" (mističky); "plates/dishes" (talíře); "wagtails" (podlisky/podlíšky/lyšky); "divers" (potápky); "pot-lids" (pokličky/pukličky); "flaps" (plisky/plesky); "plops" (žbluňky); "darts" (šipky); "bubbles" (bubliny); "Jews" (židy); "figures" (páni/panáky); "gammers"/"wagtails" (babky); "dolls"/"girls"/"dragonflies" (panenky); "to ferry Virgin Mary" (převážet panenku Mariu) Danish: "slipping" (smut or at smutte); "to make slips" (at slå smut) Dutch: "ketsen" (bouncing) Estonian: "throwing a burbot" (lutsu viskama) Finnish: "throwing bread/a sandwich" (heittää leipiä/voileipiä) French: "making ricochets" (faire des ricochets) German: "stone skipping" (Steinehüpfen); colloquially i.a. "flitting" (flitschen, old synonym of schwirren, "whirring"), its diminutive flitscheln, and "bouncing" (ditschen, a variant of titschen); older synonyms rarely used are i.a. "leading the bride" (die Braut führen), "throwing frogs" (Frösche werfen), "shooting/throwing maids/virgins" (Jungfern schießen/werfen), "skiffing" (schiffeln, schippern), "springing" (schnellern, from schnellen, "springing" or "darting"), and "pebbling" (steineln) Greek: "little frogs" (βατραχάκια) Hungarian: "making it to waddle", lit. "making it walk like a duck" (kacsáztatás) Italian: rimbalzello Japanese: "cutting water" (「水切り」[mizu kiri]) Korean: mulsujebi (물수제비), meaning water (Korean: 물; RR: mul) and Korean soup sujebi.
Stone skipping	Names	Latvian: "throwing (stone) froggies" (mest (akmens) vardītes) Lithuanian: "making frogs" (daryti varlytes) Macedonian: "frogs" (жабчиња) Mandarin: da shui piao (打水漂) Marathi: bhakrya kadhne Mongolian: "making the rabbit leap" (tuulai kharailgakh); "making the dog lick" (nokhoi doloolgokh) Nigerian: "the way a dragonfly skips across the water" (lami lami) Norwegian: "fish bounce" (fiskesprett) Polish: "letting the ducks out" (puszczanie kaczek) Portuguese "water shearing" ("capar a água"); "making tiny hats" ("fazer chapeletas") Russian: "pancakes" (блинчики [Blinchiki]); "frogs" (лягушки [Lyagushki]) Serbo-Croatian: "(to throw) little frogs" ([bacati] žabice) Spanish: "making white-caps" (hacer cabrillas); "making little frogs" (hacer ranitas); making ducklings (hacer patitos) Swedish: "throwing a sandwich" (kasta smörgås or kasta macka) Telugu: "frog jumps" (kappa gantulu) Turkish: "skimming stone" (taş sektirme) Ukrainian: "letting the frogs out" (zapuskaty zhabky) Farsi/Persian: "Syrian bashing" (سوری زدن) Vietnamese: "ricochet" (ném thia lia); "tossing stone" (liếc đá, lia đá)
Stone skipping	In popular culture	The lead character of the 2001 film Amélie skips stones along the Canal Saint-Martin in Paris as a plot point, and picks up good skipping stones when she spots them.
Sigma 24mm f/1.8 EX DG lens	Sigma 24mm f/1.8 EX DG lens	The Sigma 24mm f/1.8 EX DG is wide-angle lens which features a fast f/1.8 maximum aperture for use in low-light situations, and macro focusing capability to a reproduction ratio of 1:2.7. It uses aspherical lens elements. Though intended for 35mm film and full-frame digital SLRs, this lens is available for several makes of APS-C digital SLR cameras, where the angle of view is similar to a moderate wide-angle lens (in the 35mm-40mm range, depending on the size of the D-SLR sensor).
Sigma 24mm f/1.8 EX DG lens	Sigma 24mm f/1.8 EX DG lens	This lens is capable of macro photography, with minimum focusing down to 18 cm/7.1" (reproduction ratio 1:2.7). It incorporates a floating focus system in order to minimize distortion, spherical aberration and astigmatism, and provides high performance at all shooting distances. The high reproduction ratio and wide angle of view allow capturing high quality images not only of a subject but also the surrounding scenery.
Sigma 24mm f/1.8 EX DG lens	Sigma 24mm f/1.8 EX DG lens	The Lens was introduced in 2001.
Fucosyltransferase 4	Fucosyltransferase 4	Fucosyltransferase 4 is a protein that in humans is encoded by the FUT4 gene.
Fucosyltransferase 4	Function	The product of this gene transfers fucose to N-acetyllactosamine polysaccharides to generate fucosylated carbohydrate structures. It catalyzes the synthesis of the non-sialylated antigen, Lewis x (CD15). [provided by RefSeq, Jan 2009].
Helmsman	Helmsman	A helmsman or helm (sometimes driver) is a person who steers a ship, sailboat, submarine, other type of maritime vessel, or spacecraft. The rank and seniority of the helmsman may vary: on small vessels such as fishing vessels and yachts, the functions of the helmsman are combined with that of the skipper; on larger vessels, there is a separate officer of the watch who is responsible for the safe navigation of the ship and gives orders to the helmsman, who physically steers the ship in accordance with those orders.
Helmsman	Helmsman	In the merchant navy, the person at the helm is usually an able seaman, particularly during ship arrivals, departures, and while maneuvering in restricted waters or other conditions requiring precise steering. An ordinary seaman is commonly restricted to steering in open waters. Moreover, military ships may have a seaman or quartermaster at the helm.
Helmsman	Helmsman	A professional helmsman maintains a steady course, properly executes all rudder orders, and communicates to the officer on the bridge using navigational terms relating to ship's heading and steering. A helmsman relies upon visual references, a magnetic and gyrocompass, and a rudder angle indicator to steer a steady course. The mate or other officer on the bridge directs the helmsman aboard merchant or navy ships.
Helmsman	Helmsman	Clear and exact communication between the helmsman and officer on the bridge is essential to safe navigation and ship handling. Consequently, a set of standard steering commands, responses by the helmsman, and acknowledgment by the conning officer are widely recognized in the maritime industry. The helmsman repeats any verbal commands to demonstrate that the command is heard and understood. The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW) requires that a helmsman be able to understand and respond to helm orders in English.The proliferation of autopilot systems and the increased computerization of operations on a ship's bridge lessen the need for helmsmen standing watch in open waters.
Helmsman	Helm commands	Helm orders or commands fall into two categories: rudder commands and heading commands. A rudder command dictates changing the angle of the rudder, which is a single-event action, whereas steering a heading is a comparatively long event and will require ongoing or continuous rudder adjustments.
Helmsman	Helm commands	The following are helm orders used in the United States Navy and United States Coast Guard:Rudder Midships (Bring rudder angle to 0 degrees) Meet Her (Counter steer to stop the movement or swing of the ship's bow) Hard rudder (Used infrequently, such as emergencies, when maximum rudder is required) Left or right standard rudder (~20 degrees. Varies per ship) Shift your rudder (Steer the same number of degrees but opposite rudder angle)Heading Steady as she goes (Steer as needed to continue current heading) Steady on a course (Steer as needed to bring ship on desired course)
Helmsman	Acquired skills	Steering a ship effectively requires skills gained through training and experience. An expert helmsman has a keen sense of how a particular ship will respond to the helm or how different sea conditions impact steering. For instance, experience teaches a helmsman the ability to correct the rudder in advance of a ship substantially falling off course. This requires the capacity to anticipate the delay between when the helm is applied and when the ship responds to the rudder. Similarly, a skilled helmsman will avoid overcompensating for a ship's movement caused by local conditions, such as wind, swells, currents, or rough seas.
Helmsman	Acquired skills	Ship simulators Computer-based ship simulators provide a training environment for learning skills to steer a ship. Training can be programmed to replicate a variety of ship sizes and environmental conditions. Scenarios depicted in 3-D graphics range from making course corrections in open waters to maneuvering in port, rivers, or other shallow waters. Cost compared to a real vessel is low. Mariners learn responses to dangerous situations, such as steering failure, in the safety of a virtual environment.
Helmsman	Acquired skills	Land-based ship simulators may feature a full-scale replica of a steering stand with a ship's wheel. Such simulators incorporate magnetic and gyro compasses (or repeaters) for steering. Moreover, a rudder angle indicator that responds appropriately to the helm is part of the configuration.
Helmsman	Acquired skills	However technology also allows for a multitude of smaller workstations in a classroom setting. Administrators network student workstations so that the instructor can launch individual scenarios at each station. Computer models are used to accurately simulate conditions such as wind, seas, and currents. Moreover, shallow-water effects or other hydrodynamic forces, such as ships passing close to each other, can also be depicted. A computer application records training sessions, complete with voice commands issued by the instructor which are received by the students via a headset.
Helmsman	Acquired skills	On the job training On-the-job training at sea is critical to a helmsman developing ability to "sense" or anticipate how a ship will respond in different conditions. The experienced helmsman uses measured responses to sea conditions, even when encountering heavy weather that may cause a ship to pitch and roll as it pounds its way through oncoming waves. Subsequently, the helmsman learns to relax and take into account the vessel's natural rhythm in order to avoid oversteering whatever the maritime environment. Consequently, more accurate steering is attained with less rudder. Applying the minimal rudder required to steer a course reduces drag of the ship, thereby favorably impacting the ship's speed and operating costs.
Helmsman	Acquired skills	One of the helmsman's most important duties is steering a ship in a harbor or seaport when reduced speeds slow a ship's response to the rudder. For it is during ship arrivals and departures, when most ship collisions or groundings occur. Clear communication, then, between the officer of the bridge and the helmsman is essential for safe operations. The officer or harbor pilot relies upon the helmsman to flawlessly execute steering commands to avoid a variety of hazards, including man-made obstacles, land formations, grounding in shallow waters, and the threat of collision with other vessels. In addition, powerful sea tides and river currents encountered in seaports heighten navigation dangers, as a ship's ability to stop is severely limited.
Helmsman	Relieving the helm	Helmsmen of merchant and military ships that are underway stand watch at the helm for a set period of time before being relieved by another watchstander. The person being relieved will complete any course change or other critical maneuver that is in progress before handing over the helm.
Helmsman	Relieving the helm	Merchant vessels The helmsman handing over the helm will inform the relief helmsman of any rudder commands in place and pertinent conditions. "Steering 180. We have oncoming traffic two points on the starboard" for example. In addition, the current helmsman should inform the relief if there are any peculiarities affecting steerage. Similarly, the helmsman will also point out if he or she is steering on a landmark, range, or navigational light. The relief helmsman is obligated to repeat the course being steered or other rudder command in order to demonstrate an understanding of the situation at the helm.
Helmsman	Relieving the helm	On merchant ships, it is taught at the various maritime academies that the proper way to relieve the helm is for the helmsman being relieved to call out loudly the ship's course per gyro, course per standard magnetic compass, steering mode, rudder angle, and the pump the vessel is steering off of. The relief helmsman will then take the helm and repeat all the information to ensure that he/she knows what to steer while on watch. An example of this would be: Helmsman: "Helm is being relieved... steering two-four-eight per gyro, checking two-four-five per standard. Helm is in hand, rudder amidships, steering off the port pump." Relief: "Helm has been relieved... steering two-four-eight per gyro, checking two-four-five per standard. Helm is in hand, rudder amidships, steering off the port pump." The officer on watch will usually reply with "very well."
PyAOP reagent	PyAOP reagent	PyAOP ((7-Azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate) is a coupling reagent used in solid phase peptide synthesis. It is a derivative of the HOAt family of coupling reagents. It is preferred over HATU, because it does not side react at the N-terminus of the peptide. Compared to the HOBt derivates, PyAOP (and HOAt in general) are more reactive due to the additional nitrogen.
Cotton tensor	Cotton tensor	In differential geometry, the Cotton tensor on a (pseudo)-Riemannian manifold of dimension n is a third-order tensor concomitant of the metric. The vanishing of the Cotton tensor for n = 3 is necessary and sufficient condition for the manifold to be conformally flat. By contrast, in dimensions n ≥ 4, the vanishing of the Cotton tensor is necessary but not sufficient for the metric to be conformally flat; instead, the corresponding necessary and sufficient condition in these higher dimensions is the vanishing of the Weyl tensor, while the Cotton tensor just becomes a constant times the divergence of the Weyl tensor. For n < 3 the Cotton tensor is identically zero. The concept is named after Émile Cotton.
Cotton tensor	Cotton tensor	The proof of the classical result that for n = 3 the vanishing of the Cotton tensor is equivalent to the metric being conformally flat is given by Eisenhart using a standard integrability argument. This tensor density is uniquely characterized by its conformal properties coupled with the demand that it be differentiable for arbitrary metrics, as shown by (Aldersley 1979).
Cotton tensor	Cotton tensor	Recently, the study of three-dimensional spaces is becoming of great interest, because the Cotton tensor restricts the relation between the Ricci tensor and the energy–momentum tensor of matter in the Einstein equations and plays an important role in the Hamiltonian formalism of general relativity.
Cotton tensor	Definition	In coordinates, and denoting the Ricci tensor by Rij and the scalar curvature by R, the components of the Cotton tensor are Cijk=∇kRij−∇jRik+12(n−1)(∇jRgik−∇kRgij). The Cotton tensor can be regarded as a vector valued 2-form, and for n = 3 one can use the Hodge star operator to convert this into a second order trace free tensor density Cij=∇k(Rli−14Rgli)ϵklj, sometimes called the Cotton–York tensor.
Cotton tensor	Properties	Conformal rescaling Under conformal rescaling of the metric g~=e2ωg for some scalar function ω . We see that the Christoffel symbols transform as Γ~βγα=Γβγα+Sβγα where Sβγα is the tensor Sβγα=δγα∂βω+δβα∂γω−gβγ∂αω The Riemann curvature tensor transforms as R~λμαβ=Rλμαβ+∇αSβμλ−∇βSαμλ+SαρλSβμρ−SβρλSαμρ In n -dimensional manifolds, we obtain the Ricci tensor by contracting the transformed Riemann tensor to see it transform as R~βμ=Rβμ−gβμ∇α∂αω−(n−2)∇μ∂βω+(n−2)(∂μω∂βω−gβμ∂λω∂λω) Similarly the Ricci scalar transforms as R~=e−2ωR−2e−2ω(n−1)∇α∂αω−(n−2)(n−1)e−2ω∂λω∂λω Combining all these facts together permits us to conclude the Cotton-York tensor transforms as C~αβγ=Cαβγ+(n−2)∂λωWβγαλ or using coordinate independent language as grad ω⌟W, where the gradient is plugged into the symmetric part of the Weyl tensor W.
Cotton tensor	Properties	Symmetries The Cotton tensor has the following symmetries: Cijk=−Cikj and therefore 0. In addition the Bianchi formula for the Weyl tensor can be rewritten as δW=(3−n)C, where δ is the positive divergence in the first component of W.
Alkaloid	Alkaloid	Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure may also be termed alkaloids. In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen or sulfur. More rarely still, they may contain elements such as phosphorus, chlorine, and bromine.Alkaloids are produced by a large variety of organisms including bacteria, fungi, plants, and animals. They can be purified from crude extracts of these organisms by acid-base extraction, or solvent extractions followed by silica-gel column chromatography. Alkaloids have a wide range of pharmacological activities including antimalarial (e.g. quinine), antiasthma (e.g. ephedrine), anticancer (e.g. homoharringtonine), cholinomimetic (e.g. galantamine), vasodilatory (e.g. vincamine), antiarrhythmic (e.g. quinidine), analgesic (e.g. morphine), antibacterial (e.g. chelerythrine), and antihyperglycemic activities (e.g. piperine). Many have found use in traditional or modern medicine, or as starting points for drug discovery. Other alkaloids possess psychotropic (e.g. psilocin) and stimulant activities (e.g. cocaine, caffeine, nicotine, theobromine), and have been used in entheogenic rituals or as recreational drugs. Alkaloids can be toxic too (e.g. atropine, tubocurarine). Although alkaloids act on a diversity of metabolic systems in humans and other animals, they almost uniformly evoke a bitter taste.The boundary between alkaloids and other nitrogen-containing natural compounds is not clear-cut. Compounds like amino acid peptides, proteins, nucleotides, nucleic acid, amines, and antibiotics are usually not called alkaloids. Natural compounds containing nitrogen in the exocyclic position (mescaline, serotonin, dopamine, etc.) are usually classified as amines rather than as alkaloids. Some authors, however, consider alkaloids a special case of amines.
Alkaloid	Naming	The name "alkaloids" (German: Alkaloide) was introduced in 1819 by German chemist Carl Friedrich Wilhelm Meissner, and is derived from late Latin root alkali and the Greek-language suffix -οειδής -('like'). However, the term came into wide use only after the publication of a review article, by Oscar Jacobsen in the chemical dictionary of Albert Ladenburg in the 1880s.There is no unique method for naming alkaloids. Many individual names are formed by adding the suffix "ine" to the species or genus name. For example, atropine is isolated from the plant Atropa belladonna; strychnine is obtained from the seed of the Strychnine tree (Strychnos nux-vomica L.). Where several alkaloids are extracted from one plant their names are often distinguished by variations in the suffix: "idine", "anine", "aline", "inine" etc. There are also at least 86 alkaloids whose names contain the root "vin" because they are extracted from vinca plants such as Vinca rosea (Catharanthus roseus); these are called vinca alkaloids.
Alkaloid	History	Alkaloid-containing plants have been used by humans since ancient times for therapeutic and recreational purposes. For example, medicinal plants have been known in Mesopotamia from about 2000 BC. The Odyssey of Homer referred to a gift given to Helen by the Egyptian queen, a drug bringing oblivion. It is believed that the gift was an opium-containing drug. A Chinese book on houseplants written in 1st–3rd centuries BC mentioned a medical use of ephedra and opium poppies. Also, coca leaves have been used by Indigenous South Americans since ancient times.Extracts from plants containing toxic alkaloids, such as aconitine and tubocurarine, were used since antiquity for poisoning arrows.Studies of alkaloids began in the 19th century. In 1804, the German chemist Friedrich Sertürner isolated from opium a "soporific principle" (Latin: principium somniferum), which he called "morphium", referring to Morpheus, the Greek god of dreams; in German and some other Central-European languages, this is still the name of the drug. The term "morphine", used in English and French, was given by the French physicist Joseph Louis Gay-Lussac.
Alkaloid	History	A significant contribution to the chemistry of alkaloids in the early years of its development was made by the French researchers Pierre Joseph Pelletier and Joseph Bienaimé Caventou, who discovered quinine (1820) and strychnine (1818). Several other alkaloids were discovered around that time, including xanthine (1817), atropine (1819), caffeine (1820), coniine (1827), nicotine (1828), colchicine (1833), sparteine (1851), and cocaine (1860). The development of the chemistry of alkaloids was accelerated by the emergence of spectroscopic and chromatographic methods in the 20th century, so that by 2008 more than 12,000 alkaloids had been identified.The first complete synthesis of an alkaloid was achieved in 1886 by the German chemist Albert Ladenburg. He produced coniine by reacting 2-methylpyridine with acetaldehyde and reducing the resulting 2-propenyl pyridine with sodium.
Alkaloid	Classifications	Compared with most other classes of natural compounds, alkaloids are characterized by a great structural diversity. There is no uniform classification. Initially, when knowledge of chemical structures was lacking, botanical classification of the source plants was relied on. This classification is now considered obsolete.More recent classifications are based on similarity of the carbon skeleton (e.g., indole-, isoquinoline-, and pyridine-like) or biochemical precursor (ornithine, lysine, tyrosine, tryptophan, etc.). However, they require compromises in borderline cases; for example, nicotine contains a pyridine fragment from nicotinamide and a pyrrolidine part from ornithine and therefore can be assigned to both classes.Alkaloids are often divided into the following major groups: "True alkaloids" contain nitrogen in the heterocycle and originate from amino acids. Their characteristic examples are atropine, nicotine, and morphine. This group also includes some alkaloids that besides the nitrogen heterocycle contain terpene (e.g., evonine) or peptide fragments (e.g. ergotamine). The piperidine alkaloids coniine and coniceine may be regarded as true alkaloids (rather than pseudoalkaloids: see below) although they do not originate from amino acids.
Alkaloid	Classifications	"Protoalkaloids", which contain nitrogen (but not the nitrogen heterocycle) and also originate from amino acids. Examples include mescaline, adrenaline and ephedrine. Polyamine alkaloids – derivatives of putrescine, spermidine, and spermine. Peptide and cyclopeptide alkaloids.
Alkaloid	Classifications	Pseudoalkaloids – alkaloid-like compounds that do not originate from amino acids. This group includes terpene-like and steroid-like alkaloids, as well as purine-like alkaloids such as caffeine, theobromine, theacrine and theophylline. Some authors classify ephedrine and cathinone as pseudoalkaloids. Those originate from the amino acid phenylalanine, but acquire their nitrogen atom not from the amino acid but through transamination.Some alkaloids do not have the carbon skeleton characteristic of their group. So, galanthamine and homoaporphines do not contain isoquinoline fragment, but are, in general, attributed to isoquinoline alkaloids.Main classes of monomeric alkaloids are listed in the table below:
Alkaloid	Properties	Most alkaloids contain oxygen in their molecular structure; those compounds are usually colorless crystals at ambient conditions. Oxygen-free alkaloids, such as nicotine or coniine, are typically volatile, colorless, oily liquids. Some alkaloids are colored, like berberine (yellow) and sanguinarine (orange).Most alkaloids are weak bases, but some, such as theobromine and theophylline, are amphoteric. Many alkaloids dissolve poorly in water but readily dissolve in organic solvents, such as diethyl ether, chloroform or 1,2-dichloroethane. Caffeine, cocaine, codeine and nicotine are slightly soluble in water (with a solubility of ≥1g/L), whereas others, including morphine and yohimbine are very slightly water-soluble (0.1–1 g/L). Alkaloids and acids form salts of various strengths. These salts are usually freely soluble in water and ethanol and poorly soluble in most organic solvents. Exceptions include scopolamine hydrobromide, which is soluble in organic solvents, and the water-soluble quinine sulfate.Most alkaloids have a bitter taste or are poisonous when ingested. Alkaloid production in plants appeared to have evolved in response to feeding by herbivorous animals; however, some animals have evolved the ability to detoxify alkaloids. Some alkaloids can produce developmental defects in the offspring of animals that consume but cannot detoxify the alkaloids. One example is the alkaloid cyclopamine, produced in the leaves of corn lily. During the 1950s, up to 25% of lambs born by sheep that had grazed on corn lily had serious facial deformations. These ranged from deformed jaws to cyclopia (see picture). After decades of research, in the 1980s, the compound responsible for these deformities was identified as the alkaloid 11-deoxyjervine, later renamed to cyclopamine.
Alkaloid	Distribution in nature	Alkaloids are generated by various living organisms, especially by higher plants – about 10 to 25% of those contain alkaloids. Therefore, in the past the term "alkaloid" was associated with plants.The alkaloids content in plants is usually within a few percent and is inhomogeneous over the plant tissues. Depending on the type of plants, the maximum concentration is observed in the leaves (for example, black henbane), fruits or seeds (Strychnine tree), root (Rauvolfia serpentina) or bark (cinchona). Furthermore, different tissues of the same plants may contain different alkaloids.Beside plants, alkaloids are found in certain types of fungus, such as psilocybin in the fruiting bodies of the genus Psilocybe, and in animals, such as bufotenin in the skin of some toads and a number of insects, markedly ants. Many marine organisms also contain alkaloids. Some amines, such as adrenaline and serotonin, which play an important role in higher animals, are similar to alkaloids in their structure and biosynthesis and are sometimes called alkaloids.
Alkaloid	Extraction	Because of the structural diversity of alkaloids, there is no single method of their extraction from natural raw materials. Most methods exploit the property of most alkaloids to be soluble in organic solvents but not in water, and the opposite tendency of their salts.
Alkaloid	Extraction	Most plants contain several alkaloids. Their mixture is extracted first and then individual alkaloids are separated. Plants are thoroughly ground before extraction. Most alkaloids are present in the raw plants in the form of salts of organic acids. The extracted alkaloids may remain salts or change into bases. Base extraction is achieved by processing the raw material with alkaline solutions and extracting the alkaloid bases with organic solvents, such as 1,2-dichloroethane, chloroform, diethyl ether or benzene. Then, the impurities are dissolved by weak acids; this converts alkaloid bases into salts that are washed away with water. If necessary, an aqueous solution of alkaloid salts is again made alkaline and treated with an organic solvent. The process is repeated until the desired purity is achieved.
Alkaloid	Extraction	In the acidic extraction, the raw plant material is processed by a weak acidic solution (e.g., acetic acid in water, ethanol, or methanol). A base is then added to convert alkaloids to basic forms that are extracted with organic solvent (if the extraction was performed with alcohol, it is removed first, and the remainder is dissolved in water). The solution is purified as described above.Alkaloids are separated from their mixture using their different solubility in certain solvents and different reactivity with certain reagents or by distillation.A number of alkaloids are identified from insects, among which the fire ant venom alkaloids known as solenopsins have received greater attention from researchers. These insect alkaloids can be efficiently extracted by solvent immersion of live fire ants or by centrifugation of live ants followed by silica-gel chromatography purification. Tracking and dosing the extracted solenopsin ant alkaloids has been described as possible based on their absorbance peak around 232 nanometers.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.