Split (1)

train · 2.1M rows

title stringlengths 1 149 ⌀	section stringlengths 1 1.9k ⌀	text stringlengths 13 73.5k
Vermifilter	Vermifilter	Vermifiltration is a low-cost aerobic wastewater treatment option. Because energy is not required for aeration, vermifilters can be considered "passive treatment" systems (pumps may be required if gravity flow is not possible). Another advantage is the high treatment efficiency given the low space requirement.
Vermifilter	Terminology	Alternative terms used to describe the vermifiltration process include aerobic biodigester, biological filter with earthworms, or wet vermicomposting. The treatment system may be described using terms such as vermi-digester and vermi-trickling filter. When this kind of sanitation system is used to treat only the mixture of excreta and water from flush toilets or pour-flush toilets (called blackwater) then the term "toilet" is added to the name of the process, such as vermifilter toilet.
Vermifilter	Overview	Vermifiltration was first advocated by researchers at the University of Chile in 1992 as a low-cost sustainable technology suitable for decentralised sewage treatment in rural areas. Vermifilters offer treatment performance similar to conventional decentralised wastewater treatment systems, but with potentially higher hydraulic processing capacities.Vermifilters are a type of wastewater treatment biofilter or trickling filter, but with the addition of earthworms to improve treatment efficiency. Vermifilters provide an aerobic environment and wet substrate that facilitates microorganism growth as a biofilm. Microorganisms perform biochemical degradation of organic matter present in wastewater. Earthworms regulate microbial biomass and activity by directly or/and indirectly grazing on microorganisms. Biofilm and organic matter consumed by composting earthworms is then digested into biologically inert castings (humus). The vermicast is incorporated into the media substrate, slowly increasing its volume. When this builds up, it can be removed and applied to soil as an amendment to improve soil fertility and structure.
Vermifilter	Overview	Microorganisms present are heterotrophic and autotrophic. Heterotrophic microorganisms are important in oxidising carbon (decomposition), whereas autotrophic microorganisms are important in nitrification.
Vermifilter	Overview	As a result of oxidation reactions, biodegradation and microbial stimulation by enzymatic action, organic matter decomposition and pathogen destruction occurs in the vermifilter. In a study where municipal wastewater was treated in a vermifilter, removal ratios for biochemical oxygen demand (BOD5) were 90%, chemical oxygen demand (COD) 85%, total suspended solids (TSS) 98%, ammonia nitrogen 75% and fecal coliforms eliminated to a level that meets World Health Organisation guidelines for safe re-use in crops.
Vermifilter	Process types	Vermifilters can be used for primary, secondary and tertiary treatment of blackwater and greywater.
Vermifilter	Process types	Primary treatment of blackwater Vermifilters can be used for aerobic primary treatment of domestic blackwater. Untreated blackwater enters a ventilated enclosure above a bed of filter medium. Solids accumulate on the surface of the filter bed while liquid drains through the filter medium and is discharged from the reactor. The solids (feces and toilet paper) are aerobically digested by aerobic bacteria and composting earthworms into castings (humus), thereby significantly reducing the volume of organic material.
Vermifilter	Process types	Primary treatment vermifilter reactors are designed to digest solid material, such as contained in raw sewage. Twin-chamber parallel reactors offer the advantage of being able to allow one to rest, while the other is active, in order to facilitate hygienic removal of humus with reduced pathogen levels.
Vermifilter	Process types	Worms actively digest the solid organic material. Over time, an equilibrium is reached in which the volume digested by a stable population of worms is equal to the input volume of solid waste. Seasonal and environmental factors (such as temperature) and variable influent volumes can cause buildup of solid waste as a pile. Although oxygen is excluded from the centre of this "wet" compost pile, worms work from the outside in and introduce air as necessary into the pile to meet their nutritional requirements. This food resource buffer ensures primary treatment vermifilters have a level of resilience and reliability, provided space is provided for a pile to build up. There is some evidence that the wet environment facilitates digestion of solid waste by worms. The volume of vermicast humus increases only slowly and occasionally needs to be removed from the primary treatment reactor.
Vermifilter	Process types	Primary treatment of wet mixed blackwater can also include greywater containing food solids, grease and other biodegradable waste. Solid material is reduced to stable humus (worm castings), with volume reductions of up to tenfold.The process produces primary treated blackwater, with much of the solid organic material removed from the effluent. Because liquid effluent is discharged almost immediately on entering the digester, little dissolved oxygen is consumed by the wastewater through the filtration stage. However, oxygen demand is leached into the wastewater flow through the filter as worms digest the retained solids. This oxygen demand can be removed with secondary treatment vermifilter reactors. Primary treatment vermifilters provide a similar level of liquid effluent treatment to a septic tank, but in less time because digestion of solids by worms takes place rapidly in an aerobic environment.The liquid effluent is either discharged directly to a drain field or undergoes secondary treatment before being used for surface or subsurface irrigation of agricultural soil.
Vermifilter	Process types	Secondary treatment Secondary and tertiary treatment vermifilters can be underneath the primary vermifilter in a single tower, but are typically single reactors, where several reactors can be chained in series as sequential vermifilters. Drainage within the reactor is provided by filter media packed according to the hydraulic conductivity and permeability of each material that is present within the vermifilter. The filter packing retains the solid particles present in the effluent wastewater, increases the hydraulic retention time and also provides a suitable habitat for sustaining a population of composting earthworms. This population requires adequate moisture levels within the filter media, but also adequate drainage and oxygen levels.
Vermifilter	Process types	Sprinklers or drippers can be used in secondary and tertiary treatment vermifilter reactors (see image). Hydraulic factors (hydraulic retention time, hydraulic loading rate and organic loading rate) and biological factors (earthworm numbers, levels of biofilm) can influence treatment efficiency.
Vermifilter	Design	Vermifilters are enclosed reactors made from durable materials that eliminate the entry of vermin, usually plastic or concrete. Ventilation must be sufficient to ensure an aerobic environment for the worms and microorganisms, while also inhibiting entry of unwanted flies. Temperature within the reactor needs to be maintained within a range suitable for the species of compost worms used.
Vermifilter	Design	Influent entry Influent entry is from above the filter media. Full-flush toilets can have the entry point into the side of the reactor, whereas micro-flush toilets, because these do not provide sufficient water to convey solids through sewer pipes, are generally installed directly above the reactor. For primary treatment reactors, sufficient vertical space must be provided for growth of the pile. This is dependent on the volume of solids in the influent and the presence of slower decomposing materials such as toilet paper. Secondary and tertiary treatment reactors can use sprinklers or tricklers to distribute the influent wastewater evenly over the filter media to improve treatment efficiency of the filter media.
Vermifilter	Design	Filter substrate Drainage within the vermifilter reactor is provided by the filter media. The filter media has the dual purpose of retaining the solid organic material, while also providing a habitat suitable for sustaining a population of composting worms. This population requires adequate moisture levels within the media, along with good drainage and aerobic conditions.
Vermifilter	Design	Vermifilter reactors may comprise a single section packed only with organic media, or up to three filter sections comprising an organic top layer that provides habitat for the earthworms, an inorganic upper layer of sand and lower layer of gravel. The filter sits on top of a sump or drainage layer of coarse gravel, rocks or pervious plastic drainage coil where the treated effluent is discharged and/or recirculated to the top of the reactor. Alternatively the filter media may be suspended above the sump in a basket. Synthetic geotextile cloth is sometimes used to retain the filter media in place above the drainage layer. To remain aerobic, adequate ventilation must be provided, along with an outlet for the liquid effluent to drain away.
Vermifilter	Design	Common filter packing materials include sawdust, wood chips, coir, bark, peat, and straw for the organic layer. Gravel, quartz sand, round stones, pumice, mud balls, glass balls, ceramsite and charcoal are commonly used for the inorganic layer. The surface area and porosity of these filter materials influence treatment performance. Materials with low granulometry (small particles) and large surface area may improve the performance of the vermifilter but impede its drainage.
Vermifilter	Sizing	Vermifilters can be constructed as single tower systems, or separate staged reactors (either gravity or pump operated) for the treatment of wastewater according to design requirements (primary, secondary, tertiary treatment). More stages can increase the degree of treatment because multiple stage systems provide accumulating aerobic conditions suitable for nitrification of ammonium and removal of COD.
Vermifilter	Sizing	The design parameters of vermifilters include stocking density of earthworms (although over time earthworm population tends to be self-moderating), filter media composition, hydraulic loading rate, hydraulic retention time and organic loading rate. Hydraulic retention time and hydraulic loading rate both affect effluent quality. Hydraulic retention time is the actual time the wastewater is in contact with the filter media and is related to the depth of the vermifilter (which may increase over time due to the accumulation of earthworm vermicastings), reactor volume and type of material used (porosity). The hydraulic retention time determines wastewater inflow rate (hydraulic loading as influent volume per hour).
Vermifilter	Sizing	In principle, provided the environment is aerobic, the longer the wastewater remains inside the filter, the greater the BOD5 and COD removal efficiency will be, but at the expense of hydraulic loading. Wastewater requires sufficient contact time with the biofilm to allow for the adsorption, transformation, and reduction of contaminants. The hydraulic loading rate is an essential design parameter, consisting of the volume of wastewater that a vermifilter can reasonably treat in a given amount of time. For a given system, higher hydraulic loading rates will cause hydraulic retention time to decrease and therefore reduce level of treatment. Hydraulic loading rate may depend on parameters such as structure, effluent quality and bulk density of filter packing, along with method of effluent application. Common hydraulic retention time values in vermifiltration systems range from 1 to 3 hours. Hydraulic loading rates commonly vary between 0.2 m3 m−2 day−1, 3.0 m3 m−2 day−1 or 10–20 g L−1. Organic loading rate is defined as the amount of soluble and particulate organic matter (as BOD5) per unit area per unit time.Treatment efficiency is influenced by health, maturity and population abundance of the earthworms. Abundance is a fundamental parameter for efficient operation of a vermifiltration system. Different values are reported in the literature, usually in grams or number of individuals per volume of filter packing or surface area of filter packing. Common densities vary between 10 g L−1 and 40 g L−1 of filter packing material.An abundance of earthworms improves treatment efficiency, in particular BOD5, TSS and NH4+ removal. This is because earthworms release organic matter into the filter media and stimulate nitrogen mineralization. Earthworm castings may have substances which contribute to higher BOD5 removal.
Vermifilter	Operation and maintenance	A vermifilter has low mechanical and manual maintenance requirements, and, where gravity operated, requires no energy input. Recirculation, if required for improved effluent quality, would require a pump. Occasional topping up of organic materials may be required as these decompose and reduce in volume. The volume of worm castings increases only slowly and occasionally vermicompost needs to be removed from the vermifilter.
Vermifilter	Operation and maintenance	Solids accumulate on the surface of the organic filter media (or filter packing). The liquid fraction drains through the medium into the sump or equaliser and is either discharged from the reactor or recirculated to the top for further treatment. Wastewater is discharged to the surface of the filter material by direct application or by sprinklers, drippers or tricklers.
Vermifilter	Examples	Construction of primary and secondary domestic vermifilters from readily available materials A household pour-flush toilet, with combined primary vermifiltration and direct effluent infiltration into the soil below, is called the "Tiger Toilet" and has been tested by Bear Valley Ventures and Primove Infrastructure Development Consultants in rural India. Unlike a pit latrine , it was found that there was virtually no accumulation of fecal material over a one-year period. In the effluent, there was a 99% reduction in fecal coliforms . User satisfaction is high, driven mainly by a lack of odour. This system is now being marketed commercially in India, where over 2000 of these toilets and treatment systems had been sold and installed by May 2017.
Vermifilter	Examples	"Tiger worm toilets" are also being promoted by Oxfam as a sanitation solution in refugee camps, slums and peri-urban areas in Africa, for example in Liberia. Low-flush vermifilter toilet systems with direct subsoil soakage are being marketed in Ghana and other African countries by the Ghana Sustainable Aid Project (GSAP) with support by Providence College in the U.S. and the University of Ghana. Biofilcom is a company active in Ghana which is marketing the process under the name of "Biofil Digester". In Australia and New Zealand, there are numerous suppliers offering vermifilter systems for domestic greywater and/or blackwater treatment, with primary treated effluent disposal to subsurface leach fields. Examples include Wormfarm, Zenplumb, Naturalflow, SWWSNZ and Autoflow.
Paraboloid	Paraboloid	In geometry, a paraboloid is a quadric surface that has exactly one axis of symmetry and no center of symmetry. The term "paraboloid" is derived from parabola, which refers to a conic section that has a similar property of symmetry.
Paraboloid	Paraboloid	Every plane section of a paraboloid by a plane parallel to the axis of symmetry is a parabola. The paraboloid is hyperbolic if every other plane section is either a hyperbola, or two crossing lines (in the case of a section by a tangent plane). The paraboloid is elliptic if every other nonempty plane section is either an ellipse, or a single point (in the case of a section by a tangent plane). A paraboloid is either elliptic or hyperbolic.
Paraboloid	Paraboloid	Equivalently, a paraboloid may be defined as a quadric surface that is not a cylinder, and has an implicit equation whose part of degree two may be factored over the complex numbers into two different linear factors. The paraboloid is hyperbolic if the factors are real; elliptic if the factors are complex conjugate. An elliptic paraboloid is shaped like an oval cup and has a maximum or minimum point when its axis is vertical. In a suitable coordinate system with three axes x, y, and z, it can be represented by the equation z=x2a2+y2b2. where a and b are constants that dictate the level of curvature in the xz and yz planes respectively. In this position, the elliptic paraboloid opens upward. A hyperbolic paraboloid (not to be confused with a hyperboloid) is a doubly ruled surface shaped like a saddle. In a suitable coordinate system, a hyperbolic paraboloid can be represented by the equation z=y2b2−x2a2. In this position, the hyperbolic paraboloid opens downward along the x-axis and upward along the y-axis (that is, the parabola in the plane x = 0 opens upward and the parabola in the plane y = 0 opens downward). Any paraboloid (elliptic or hyperbolic) is a translation surface, as it can be generated by a moving parabola directed by a second parabola.
Paraboloid	Properties and applications	Elliptic paraboloid In a suitable Cartesian coordinate system, an elliptic paraboloid has the equation z=x2a2+y2b2. If a = b, an elliptic paraboloid is a circular paraboloid or paraboloid of revolution. It is a surface of revolution obtained by revolving a parabola around its axis. A circular paraboloid contains circles. This is also true in the general case (see Circular section). From the point of view of projective geometry, an elliptic paraboloid is an ellipsoid that is tangent to the plane at infinity. Plane sectionsThe plane sections of an elliptic paraboloid can be: a parabola, if the plane is parallel to the axis, a point, if the plane is a tangent plane. an ellipse or empty, otherwise.
Paraboloid	Properties and applications	Parabolic reflector On the axis of a circular paraboloid, there is a point called the focus (or focal point), such that, if the paraboloid is a mirror, light (or other waves) from a point source at the focus is reflected into a parallel beam, parallel to the axis of the paraboloid. This also works the other way around: a parallel beam of light that is parallel to the axis of the paraboloid is concentrated at the focal point. For a proof, see Parabola § Proof of the reflective property.
Paraboloid	Properties and applications	Therefore, the shape of a circular paraboloid is widely used in astronomy for parabolic reflectors and parabolic antennas. The surface of a rotating liquid is also a circular paraboloid. This is used in liquid-mirror telescopes and in making solid telescope mirrors (see rotating furnace). Hyperbolic paraboloid The hyperbolic paraboloid is a doubly ruled surface: it contains two families of mutually skew lines. The lines in each family are parallel to a common plane, but not to each other. Hence the hyperbolic paraboloid is a conoid. These properties characterize hyperbolic paraboloids and are used in one of the oldest definitions of hyperbolic paraboloids: a hyperbolic paraboloid is a surface that may be generated by a moving line that is parallel to a fixed plane and crosses two fixed skew lines.
Paraboloid	Properties and applications	This property makes it simple to manufacture a hyperbolic paraboloid from a variety of materials and for a variety of purposes, from concrete roofs to snack foods. In particular, Pringles fried snacks resemble a truncated hyperbolic paraboloid.A hyperbolic paraboloid is a saddle surface, as its Gauss curvature is negative at every point. Therefore, although it is a ruled surface, it is not developable.
Paraboloid	Properties and applications	From the point of view of projective geometry, a hyperbolic paraboloid is one-sheet hyperboloid that is tangent to the plane at infinity. A hyperbolic paraboloid of equation z=axy or z=a2(x2−y2) (this is the same up to a rotation of axes) may be called a rectangular hyperbolic paraboloid, by analogy with rectangular hyperbolas.
Paraboloid	Properties and applications	Plane sectionsA plane section of a hyperbolic paraboloid with equation z=x2a2−y2b2 can be a line, if the plane is parallel to the z-axis, and has an equation of the form bx±ay+b=0 a parabola, if the plane is parallel to the z-axis, and the section is not a line, a pair of intersecting lines, if the plane is a tangent plane, a hyperbola, otherwise.
Paraboloid	Properties and applications	Examples in architecture Saddle roofs are often hyperbolic paraboloids as they are easily constructed from straight sections of material. Some examples: Philips Pavilion Expo '58, Brussels (1958) IIT Delhi - Dogra Hall Roof St. Mary's Cathedral, Tokyo, Japan (1964) Cathedral of Saint Mary of the Assumption, San Francisco, California, US (1971) Saddledome in Calgary, Alberta, Canada (1983) Scandinavium in Gothenburg, Sweden (1971) L'Oceanogràfic in Valencia, Spain (2003) London Velopark, England (2011) Waterworld Leisure & Activity Centre, Wrexham, Wales (1970) Markham Moor Service Station roof, A1(southbound), Nottinghamshire, England
Paraboloid	Cylinder between pencils of elliptic and hyperbolic paraboloids	The pencil of elliptic paraboloids z=x2+y2b2,b>0, and the pencil of hyperbolic paraboloids z=x2−y2b2,b>0, approach the same surface z=x2 for b→∞ which is a parabolic cylinder (see image).
Paraboloid	Curvature	The elliptic paraboloid, parametrized simply as σ→(u,v)=(u,v,u2a2+v2b2) has Gaussian curvature K(u,v)=4a2b2(1+4u2a4+4v2b4)2 and mean curvature H(u,v)=a2+b2+4u2a2+4v2b2a2b2(1+4u2a4+4v2b4)3 which are both always positive, have their maximum at the origin, become smaller as a point on the surface moves further away from the origin, and tend asymptotically to zero as the said point moves infinitely away from the origin. The hyperbolic paraboloid, when parametrized as σ→(u,v)=(u,v,u2a2−v2b2) has Gaussian curvature K(u,v)=−4a2b2(1+4u2a4+4v2b4)2 and mean curvature H(u,v)=−a2+b2−4u2a2+4v2b2a2b2(1+4u2a4+4v2b4)3.
Paraboloid	Geometric representation of multiplication table	If the hyperbolic paraboloid z=x2a2−y2b2 is rotated by an angle of π/4 in the +z direction (according to the right hand rule), the result is the surface z=(x2+y22)(1a2−1b2)+xy(1a2+1b2) and if a = b then this simplifies to z=2xya2 .Finally, letting a = √2, we see that the hyperbolic paraboloid z=x2−y22. is congruent to the surface z=xy which can be thought of as the geometric representation (a three-dimensional nomograph, as it were) of a multiplication table. The two paraboloidal ℝ2 → ℝ functions z1(x,y)=x2−y22 and z2(x,y)=xy are harmonic conjugates, and together form the analytic function f(z)=z22=f(x+yi)=z1(x,y)+iz2(x,y) which is the analytic continuation of the ℝ → ℝ parabolic function f(x) = x2/2.
Paraboloid	Dimensions of a paraboloidal dish	The dimensions of a symmetrical paraboloidal dish are related by the equation 4FD=R2, where F is the focal length, D is the depth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim), and R is the radius of the rim. They must all be in the same unit of length. If two of these three lengths are known, this equation can be used to calculate the third.
Paraboloid	Dimensions of a paraboloidal dish	A more complex calculation is needed to find the diameter of the dish measured along its surface. This is sometimes called the "linear diameter", and equals the diameter of a flat, circular sheet of material, usually metal, which is the right size to be cut and bent to make the dish. Two intermediate results are useful in the calculation: P = 2F (or the equivalent: P = R2/2D) and Q = √P2 + R2, where F, D, and R are defined as above. The diameter of the dish, measured along the surface, is then given by ln ⁡(R+QP), where ln x means the natural logarithm of x, i.e. its logarithm to base e.
Paraboloid	Dimensions of a paraboloidal dish	The volume of the dish, the amount of liquid it could hold if the rim were horizontal and the vertex at the bottom (e.g. the capacity of a paraboloidal wok), is given by π2R2D, where the symbols are defined as above. This can be compared with the formulae for the volumes of a cylinder (πR2D), a hemisphere (2π/3R2D, where D = R), and a cone (π/3R2D). πR2 is the aperture area of the dish, the area enclosed by the rim, which is proportional to the amount of sunlight a reflector dish can intercept. The surface area of a parabolic dish can be found using the area formula for a surface of revolution which gives A=πR((R2+4D2)3−R3)6D2.
Gravity spreading	Gravity spreading	Gravity spreading is a phenomenon in which a geological body laterally extends and vertically contracts to reduce its gravitational potential energy. It has been observed on many different scales, and at numerous locations on Earth, from rhyolite lava flows to passive margins. Additionally, gravity spreading is likely to have occurred on both Mars and Venus.
Gravity spreading	Distinction from Gravity Gliding	Historically, geologists have used the terms "gravity spreading" and "gravity gliding" interchangeably, or with little distinction. This article follows the convention of "Excursus on gravity gliding and gravity spreading" by D.D. Schultz-Ela, which defines gravity spreading as a lateral extension and vertical contraction, which thus must be applied to a non-rigid body. Gravity gliding, however, is applied to a block that is not being deformed, and is therefore less common to observe. However, it can be difficult to distinguish between the two in real world scenarios, and often both occur simultaneously.
Gravity spreading	Mechanism	For gravity spreading to occur, a rock mass must be driven to deformation by gravity. As long as the center of gravity of the system descends, portions of the system may rise. Of course, a material normally resists such deformation. For gravity spreading to occur, the differential stress must be greater than that rock body's yield strength. Gravity spreading can be thought of as a mound of molasses that spreads out, and gravity gliding can be imagined as a wooden block sliding down a slope.
Gravity spreading	Examples	Earth Mountains Heart Mountain in Wyoming, United States, has been extensively studied, because Ordovician age carbonates (Madison Limestone), sit on top of a much younger (~50Ma) sedimentary formation (Willwood Formation). It is now largely accepted that this juxtaposition of old rocks on top of young is the result of gravity spreading and gliding. Field observations, such as slight internal deformations of the older formation, indicate the gravity gliding and spreading of the Madison Limestones. The specific details of the gravity spreading event are unclear, but it is thought that it was induced by the Laramide Orogeny, approximately 50 Ma. This caused the Madison Limestones to slide into the nearby Bighorn Basin, where it came to rest on top of the Willwood Formation. The cause for block motion is debated, with numerous models to explain how such a large block could have moved tens of kilometers down a slope of less than 2°. Models have ranged from lubrication by hydrothermal circulation, movement initiation from volcanogenic seismicity, to frictional heating dissociating CO2 from the carbonates, resulting in dramatically reduced friction. The last of these theories is among the most recent, and by far the most spectacular. The authors envisage initially slow sliding, likely as the result of a volcanic eruption, until frictional heating of the carbonate rocks creates a supercritical CO2 layer, decreasing the friction tremendously. From this point, the sliding would occur rapidly, perhaps as high as 150 km/h.
Gravity spreading	Examples	Passive Margins Gravity spreading in passive margins occurs when gravitational forces are strong enough to overcome the overburdens resistance to motion along its basal surface, and the internal strength. The gravitational forces are a function of the dip of the slope and the dip of the décollement layer. Lava Flows Rhyolite lava flows in northeastern New South Wales, Australia show recumbent folds that record a history of vertical shortening and lateral extension during deposition, consistent with what one would expect from gravity spreading. This is the result of lava being displaced by new lava extruding from the vent.
Gravity spreading	Examples	Mars Satellite images of Mars have shown that the Thaumasia Plateau has large amounts of thrust faults, normal faults, and ridges. This rifting has resulted in canyons, and compression at the front of the "mega-slide" has caused the ridges and thrust faults observed at low end of the region. To explain these faults and ridges, a four-stage model involving gravity spreading is used: A thick salt layer is deposited. This is possible in either wet or dry conditions.
Gravity spreading	Examples	Tharsis, a volcanic plateau, was emplaced. This increased both the heat flux of the area, as well as the topographic slope. Volcanism associated with Tharsis also deposited ash and lava flows. The layers of salt and ice beneath the volcanics provided detachment points for the initiation of gravity spreading to the southeast. Fractures from the basal detachment plane opened an aquifer, resulting in the release of water and incision of outflow channels. Venus It has been suggested that the "blocky" surface of Venus is the result of gravity spreading. This is thought because of flow-like structures correlated with topography, and as well as potential regions of thermal uplift, and has been reinforced by terrestrial analogues.
Relations (philosophy)	Relations (philosophy)	Relations are ways in which things, the relata, stand to each other. Relations are in many ways similar to properties in that both characterize the things they apply to. Properties are sometimes treated as a special case of relations involving only one relatum. In philosophy (especially metaphysics), theories of relations are typically introduced to account for repetitions of how several things stand to each other.
Relations (philosophy)	Overview	The concept of relation has a long and complicated history. One of the interests for the Greek philosophers lay in the number of ways in which a particular thing might be described, and the establishment of a relation between one thing and another was one of these. A second interest lay in the difference between these relations and the things themselves. This was to culminate in the view that the things in themselves could not be known except through their relations. Debates similar to these continue into modern philosophy and include further investigations into types of relation and whether relations exist only in the mind or the real world or both.
Relations (philosophy)	Overview	An understanding of types of relation is important to an understanding of relations between many things including those between people, communities and the wider world. Most of these are complex relations but of the simpler, analytical relations out of which they are formed there are sometimes held to be three types, although opinion on the number may differ. The three types are (1) spatial relations, which include geometry and number, (2) relations of cause and effect, and (3) the classificatory relations of similarity and difference that underlie knowledge. Similar classifications have been suggested in the sciences, mathematics, and the arts.
Relations (philosophy)	Internal and external relations	An important distinction is between internal and external relations. A relation is internal if it is fully determined by the features of its relata. For example, an apple and a tomato stand in the internal relation of similarity to each other because they are both red. Some philosophers have inferred from this that internal relations do not have a proper ontological status since they can be reduced to intrinsic properties. External relations, on the other hand, are not fixed by the features of their relata. For example, a book stands in an external relation to a table by lying on top of it. But this is not determined by the book's or the table's features like their color, their shape, etc. One problem associated with external relations is that they are difficult to locate. For example, the lying-on-top is located neither in the table nor in the apple. This has prompted some philosophers to deny that there are external relations. Properties do not face this problem since they are located in their bearer.
Relations (philosophy)	History	Ancient Greek philosophy Traditionally the history of the concept of relation begins with Aristotle and his concept of relative terms. In Metaphysics he states: "Things are called relative as the double to the half... as that which can act to that which can be acted upon... and as the knowable to knowledge". It has been argued that the content of these three types can be traced back to the Eleatic Dilemmas, a series of puzzles through which the world can be explained in totally opposite ways, for example things can be both one and many, both moving and stationary and both like and unlike one another.For Aristotle relation was one of ten distinct kinds of categories (Greek: kategoriai) which list the range of things that can be said about any particular subject: "...each signifies either substance or quantity or quality or relation or where or when or being-in-a-position or having or acting or being acted upon". Subjects and predicates were combined to form simple propositions. These were later redefined as "categorical" propositions in order to distinguish them from two other types of proposition, the disjunctive and the hypothetical, identified a little later by Chrysippus.An alternative strand of thought at the time was that relation was more than just one of ten equal categories. A fundamental opposition was developing between substance and relation. Plato in Theaetetus had noted that "some say all things are said to be relative" and Speusippus, his nephew and successor at the Academy maintained the view that "... a thing cannot be known apart from the knowledge of other things, for to know what a thing is, we must know how it differs from other things".Plotinus in third century Alexandria reduced Aristotle's categories to five: substance, relation, quantity, motion and quality.: VI.3.3, VI.3.21 He gave further emphasis to the distinction between substance and relation and stated that there were grounds for the latter three: quantity, motion and quality to be considered as relations. Moreover, these latter three categories were posterior to the Eleatic categories, namely unity/plurality; motion/stability and identity/difference concepts that Plotinus called "the hearth of reality".: V.1.4 Plotinus liked to picture relations as lines linking elements, but in a process of abstraction our minds tend to ignore the lines "and think only of their terminals".: VI.5.5 His pupil and biographer, Porphyry, developed a tree analogy picturing the relations of knowledge as a tree branching from the highest genera down through intermediate species to the individuals themselves.: V.3.10, V.6.1 Scholasticism to the Enlightenment The opposition between substance and relation was given a theological perspective in the Christian era. Basil in the Eastern church suggested that an understanding of the Trinity lay more in understanding the types of relation existing between the three members of the Godhead than in the nature of the Persons themselves. Thomas Aquinas in the Western church noted that in God "relations are real",: 52 and, echoing Aristotle, claimed that there were indeed three type of relation which give a natural order to the world. These were quantity, as in double and half; activity, as in acting and being acted upon; and understanding, through the qualitative concepts of genus and species. "Some have said that relation is not a reality but only an idea. But this is plainly seen to be false from the very fact that things themselves have a mutual natural order and relation... There are three conditions that make a relation to be real or logical ..."The end of the Scholastic period marked the beginning of a decline in the pre-eminence of the classificatory relation as a way of explaining the world. Science was now in the ascendant and with it scientific reason and the relation of cause and effect. In Britain, John Locke, influenced by Isaac Newton and the laws of motion, developed a similar mechanistic view of the human mind. Following Hobbes's notion of "trains of thought" where one idea naturally follows another in the mind, Locke developed further the concept of knowledge as the perception of relations between ideas. These relations included mathematical relations, scientific relations such as co-existence and succession, and the relations of identity and difference.
Relations (philosophy)	History	It was left to the Scottish philosopher David Hume to reduce these kinds of mental association to three: "To me there appears to be only three principles of connexion among ideas namely Resemblance, Contiguity in time or place, and Cause or Effect".The problem which troubled Hume of being able to establish the reality of relations from experience, in particular the relation of cause and effect, was solved in another way by Immanuel Kant who took the view that our knowledge is only partly derived from the external world. Part of our knowledge he argued must be due to the modifying nature of our own minds which imposes on perception not only the forms of space and time but also the categories of relation which he understood to be a priori concepts contained within the understanding. Of these he famously said: "Everything in our knowledge... contains nothing but mere relations".: 87 Kant took a more analytical view of the concept of relation and his categories of relation were three namely, community, causality and inherence.: 113 These can be compared with Hume's three kinds of association in that, firstly, community depicts elements conjoined in time and space, secondly causality compares directly with cause and effect, and thirdly inherence implies the relation of a quality to its subject and plays an essential part in any consideration of the concept of resemblance. Preceding the table of categories in the Critique of Pure Reason is the table of judgements and here, under the heading of relation, are the three types of syllogism namely the disjunctive, the hypothetical and the categorical,: 107, 113 developed as we have seen through Aristotle, Chryssipus and the logicians of the Middle Ages. Schopenhauer raised objections to the term Community and the term disjunction, as a relation, can be usefully substituted for the more complex concept of community. G.W.F. Hegel also referred to three types of proposition but in Hegel the categories of relation which for Kant were "subjective mental processes" have now become "objective ontological entities".
Relations (philosophy)	History	Late modern and contemporary philosophy Late modern American philosopher C. S. Peirce recorded that his own categories of relation grew originally out of a study of Kant. He introduced three metaphysical categories which pervaded his philosophy, and these were ordered through a consideration of the development of our mental processes: Firstness: "The first is predominant in feeling... the whole content of consciousness is made up of qualities of feeling as truly as the whole of space is made up of points or the whole of time by instants".: 149–159 Consciousness in a sense arises through the gradual disjunction of what was once whole. Elements appear to be monadic in character and are represented as points in space and time.
Relations (philosophy)	History	Secondness: The idea of secondness "is predominant in the ideas of causation" coming into being as "an action and reaction" between ourselves and some other, or between ourselves and a stimulus.: 159–163 It is essentially dyadic in character and in some versions of symbolic logic is represented by an arrow.
Relations (philosophy)	History	Thirdness: "Ideas in which thirdness predominates include the idea of a sign or representation... For example, a picture signifies by similarity". This type of relation is essentially triadic in nature and is represented in Peirce's logic as a brace or bracket.These categories of relation appeared in Peirce's logic of relatives and followed earlier work undertaken by the mathematician Augustus De Morgan at Cambridge who had introduced the notion of relation into formal logic in 1849. Among the philosophers who followed may be mentioned T. H. Green in England who took the view that all reality lies in relations and William James in America who, emphasising the concept of relation, pictured the world as a "concatenated unity" with some parts joined and other parts disjoined.Contemporary British philosopher Bertrand Russell, in 1921, reinforced James's view that "... the raw material out of which the world is built up, is not of two sorts, one matter and one mind but that it is designed in different patterns by its interrelations, and that some arrangements may be called mental, while others may be called physical". Wittgenstein, also in 1921, saw the same kinds of relation structuring both the material world and the mental world. While the real world consisted of objects and their relations which combined to form facts, the mental world consisted of similar subjects and predicates which pictured or described the real world. For Wittgenstein there were three kinds of description (enumeration, function and law) which themselves bear a notable if distant "family resemblance" to the three kinds of relation whose history we have been following.Also of note at the beginning of the twentieth century were arguments associated with G. E. Moore among others concerning the concept of internal and external relations whereby relations could be seen as either contingent or accidental parts of the definition of a thing.
Infertility	Infertility	Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state of a human child or other young offspring, because they have not undergone puberty, which is the body's start of reproductive capacity.
Infertility	Infertility	In humans, infertility is the inability to become pregnant after one year of unprotected and regular sexual intercourse involving a male and female partner. There are many causes of infertility, including some that medical intervention can treat. Estimates from 1997 suggest that worldwide about five percent of all heterosexual couples have an unresolved problem with infertility. Many more couples, however, experience involuntary childlessness for at least one year: estimates range from 12% to 28%.
Infertility	Infertility	The main cause of infertility in humans is age, and an advanced maternal age can raise the probability of suffering a spontaneous abortion during pregnancy.
Infertility	Infertility	Male infertility is responsible for 20–30% of infertility cases, while 20–35% are due to female infertility, and 25–40% are due to combined problems in both parts. In 10–20% of cases, no cause is found. The most common cause of female infertility is age, which generally manifests in sparse or absent menstrual periods. Male infertility is most commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.Women who are fertile experience a period of fertility before and during ovulation, and are infertile for the rest of the menstrual cycle. Fertility awareness methods are used to discern when these changes occur by tracking changes in cervical mucus or basal body temperature.
Infertility	Definition	"Demographers tend to define infertility as childlessness in a population of women of reproductive age," whereas the epidemiological definition refers to "trying for" or "time to" a pregnancy, generally in a population of women exposed to a probability of conception. Currently, female fertility normally peaks in young adulthood and diminishes after 35 with pregnancy occurring rarely after age 50. A female is most fertile within 24 hours of ovulation. Male fertility peaks usually in young adulthood and declines after age 40.The time needed to pass (during which the couple tries to conceive) for that couple to be diagnosed with infertility differs between different jurisdictions. Existing definitions of infertility lack uniformity, rendering comparisons in prevalence between countries or over time problematic. Therefore, data estimating the prevalence of infertility cited by various sources differ significantly. A couple that tries unsuccessfully to have a child after a certain period of time (often a short period, but definitions vary) is sometimes said to be subfertile, meaning less fertile than a typical couple. Both infertility and subfertility are defined similarly and often used interchangeably, but subfertility is the delay in conceiving within six to twelve months, whereas infertility is the inability to conceive naturally within a full year.
Infertility	Definition	World Health Organization The World Health Organization defines infertility as follows: Infertility is "a disease of the reproductive system defined by the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse (and there is no other reason, such as breastfeeding or postpartum amenorrhoea). Primary infertility is infertility in a couple who have never had a child. Secondary infertility is failure to conceive following a previous pregnancy. Infertility may be caused by infection in the man or woman, but often there is no obvious underlying cause" United States One definition of infertility that is frequently used in the United States by reproductive endocrinologists, doctors who specialize in infertility, to consider a couple eligible for treatment is: a woman under 35 has not conceived after 12 months of contraceptive-free intercourse. Twelve months is the lower reference limit for Time to Pregnancy (TTP) by the World Health Organization.
Infertility	Definition	a woman over 35 has not conceived after six months of contraceptive-free sexual intercourse.These time intervals would seem to be reversed; this is an area where public policy trumps science. The idea is that for women beyond age 35, every month counts and if made to wait another six months to prove the necessity of medical intervention, the problem could become worse. The corollary to this is that, by definition, failure to conceive in women under 35 is not regarded with the same urgency as it is in those over 35.
Infertility	Definition	United Kingdom In the UK, previous NICE guidelines defined infertility as failure to conceive after regular unprotected sexual intercourse for two years in the absence of known reproductive pathology. Updated NICE guidelines do not include a specific definition, but recommend that "A woman of reproductive age who has not conceived after 1 year of unprotected vaginal sexual intercourse, in the absence of any known cause of infertility, should be offered further clinical assessment and investigation along with her partner, with earlier referral to a specialist if the woman is over 36 years of age." Other definitions Researchers commonly base demographic studies on infertility prevalence over a five-year period. Practical measurement problems, however, exist for any definition, because it is difficult to measure continuous exposure to the risk of pregnancy over a period of years.
Infertility	Definition	Primary vs. secondary infertility Primary infertility is defined as the absence of a live birth for women who desire a child and have been in a union for at least 12 months, during which they have not used any contraceptives. The World Health Organisation also adds that 'women whose pregnancy spontaneously miscarries, or whose pregnancy results in a still born child, without ever having had a live birth would present with primarily infertility'.Secondary infertility is defined as the absence of a live birth for women who desire a child and have been in a union for at least 12 months since their last live birth, during which they did not use any contraceptives.Thus the distinguishing feature is whether or not the couple have ever had a pregnancy that led to a live birth.
Infertility	Effects	Psychological The consequences of infertility are manifold and can include societal repercussions and personal suffering. Advances in assisted reproductive technologies, such as IVF, can offer hope to many couples where treatment is available, although barriers exist in terms of medical coverage and affordability. The medicalization of infertility has unwittingly led to a disregard for the emotional responses that couples experience, which include distress, loss of control, stigmatization, and a disruption in the developmental trajectory of adulthood. One of the main challenges in assessing the distress levels in women with infertility is the accuracy of self-report measures. It is possible that women "fake good" in order to appear mentally healthier than they are. It is also possible that women feel a sense of hopefulness/increased optimism prior to initiating infertility treatment, which is when most assessments of distress are collected. Some early studies concluded that infertile women did not report any significant differences in symptoms of anxiety and depression than fertile women. The further into treatment a patient goes, the more often they display symptoms of depression and anxiety. Patients with one treatment failure had significantly higher levels of anxiety, and patients with two failures experienced more depression when compared with those without a history of treatment. However, it has also been shown that the more depressed the infertile woman, the less likely she is to start infertility treatment and the more likely she is to drop out after only one cycle. Researchers have also shown that despite a good prognosis and having the finances available to pay for treatment, discontinuation is most often due to psychological reasons. Fertility does not seem to increase when the women takes antioxidants to reduce the oxidative stress brought by the situation.Infertility may have psychological effects. Parenthood is one of the major transitions in adult life for both men and women. The stress of the non-fulfilment of a wish for a child has been associated with emotional consequences such as anger, depression, anxiety, marital problems and feelings of worthlessness.
Infertility	Effects	Partners may become more anxious to conceive, increasing sexual dysfunction. Marital discord often develops, especially when they are under pressure to make medical decisions. Women trying to conceive often have depression rates similar to women who have heart disease or cancer. Emotional stress and marital difficulties are greater in couples where the infertility lies with the man. Male and female partner respond differently to infertility problems. In general, women show higher depression levels than their male partners when dealing with infertility. A possible explanation may be that women feel more responsible and guilty than men during the process of trying to conceive. On the other hand, infertile men experience a psychosomatic distress. Social Having a child is considered to be important in most societies. Infertile couples may experience social and family pressure leading to a feeling of social isolation. Factors of gender, age, religion, and socioeconomic status are important influences. Societal pressures may affect a couple's decision to approach, avoid, or experience an infertility treatment. Moreover, the socioeconomic status influences the psychology of the infertile couples: low socioeconomic status is associated with increased chances of developing depression.
Infertility	Effects	In many cultures, inability to conceive bears a stigma. In closed social groups, a degree of rejection (or a sense of being rejected by the couple) may cause considerable anxiety and disappointment. Some respond by actively avoiding the issue altogether.In the United States some treatments for infertility, including diagnostic tests, surgery and therapy for depression, can qualify one for Family and Medical Leave Act leave. It has been suggested that infertility be classified as a form of disability.
Infertility	Causes	Male infertility is responsible for 20–30% of infertility cases, while 20–35% are due to female infertility, and 25–40% are due to combined problems in both parts. In 10–20% of cases, no cause is found. The most common cause of female infertility are ovulation problems, usually manifested by scanty or absent menstrual periods. Male infertility is most commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.
Infertility	Causes	Iodine Deficiency Iodine deficiency may lead to infertility.
Infertility	Causes	Natural infertility Before puberty, humans are naturally infertile; their gonads have not yet developed the gametes required to reproduce: boys' testicles have not developed the sperm cells required to impregnate a female; girls have not begun the process of ovulation which activates the fertility of their egg cells (ovulation is confirmed by the first menstrual cycle, known as menarche, which signals the biological possibility of pregnancy). Infertility in children is commonly referred to as prepubescence (or being prepubescent, an adjective used to also refer to humans without secondary sex characteristics).
Infertility	Causes	The absence of fertility in children is considered a natural part of human growth and child development, as the hypothalamus in their brain is still underdeveloped and cannot release the hormones required to activate the gonads' gametes. Fertility in children before the ages of eight or nine is considered a disease known as precocious puberty. This disease is usually triggered by a brain tumor or other related injury.
Infertility	Causes	Delayed puberty Delayed puberty, puberty absent past or occurring later than the average onset (between the ages of ten and fourteen), may be a cause of infertility. In the United States, girls are considered to have delayed puberty if they have not started menstruating by age 16 (alongside lacking breast development by age 13). Boys are considered to have delayed puberty if they lack enlargement of the testicles by age 14. Delayed puberty affects about 2% of adolescents.Most commonly, puberty may be delayed for several years and still occur normally, in which case it is considered constitutional delay of growth and puberty, a common variation of healthy physical development. Delay of puberty may also occur due to various causes such as malnutrition, various systemic diseases, or defects of the reproductive system (hypogonadism) or the body's responsiveness to sex hormones.
Infertility	Causes	Immune infertility Antisperm antibodies (ASA) have been considered as infertility cause in around 10–30% of infertile couples. In both men and women, ASA production are directed against surface antigens on sperm, which can interfere with sperm motility and transport through the female reproductive tract, inhibiting capacitation and acrosome reaction, impaired fertilization, influence on the implantation process, and impaired growth and development of the embryo. The antibodies are classified into different groups: There are IgA, IgG and IgM antibodies. They also differ in the location of the spermatozoon they bind on (head, mid piece, tail). Factors contributing to the formation of antisperm antibodies in women are disturbance of normal immunoregulatory mechanisms, infection, violation of the integrity of the mucous membranes, rape and unprotected oral or anal sex. Risk factors for the formation of antisperm antibodies in men include the breakdown of the blood‑testis barrier, trauma and surgery, orchitis, varicocele, infections, prostatitis, testicular cancer, failure of immunosuppression and unprotected receptive anal or oral sex with men.
Infertility	Causes	Sexually transmitted infections Infections with the following sexually transmitted pathogens have a negative effect on fertility: Chlamydia trachomatis and Neisseria gonorrhoeae. There is a consistent association of Mycoplasma genitalium infection and female reproductive tract syndromes. M. genitalium infection is associated with increased risk of infertility.
Infertility	Causes	Genetic Mutations to NR5A1 gene encoding steroidogenic factor 1 (SF-1) have been found in a small subset of men with non-obstructive male factor infertility where the cause is unknown. Results of one study investigating a cohort of 315 men revealed changes within the hinge region of SF-1 and no rare allelic variants in fertile control men. Affected individuals displayed more severe forms of infertility such as azoospermia and severe oligozoospermia.Small supernumerary marker chromosomes are abnormal extra chromosomes; they are three times more likely to occur in infertile individuals and account for 0.125% of all infertility cases. See Infertility associated with small supernumerary marker chromosomes and Genetics of infertility#Small supernumerary marker chromosomes and infertility.
Infertility	Causes	Other causes Factors that can cause male as well as female infertility are: DNA damage DNA damage reduces fertility in female ovocytes, as caused by smoking, other xenobiotic DNA damaging agents (such as radiation or chemotherapy) or accumulation of the oxidative DNA damage 8-hydroxy-deoxyguanosine DNA damage reduces fertility in male sperm, as caused by oxidative DNA damage, smoking, other xenobiotic DNA damaging agents (such as drugs or chemotherapy) or other DNA damaging agents including reactive oxygen species, fever or high testicular temperature. The damaged DNA related to infertility manifests itself by the increased susceptibility to denaturation inducible by heat or acid or by the presence of double-strand breaks that can be detected by the TUNEL assay. In this assay, the sperm's DNA will be denaturated and renatured. If DNA fragmentation occurs (double and single-strand-breaks) a halo will not appear surrounding the spermatozoas, but if the spermatozoa does not have DNA damaged, a halo surrounding the spermatozoa could be visualized under the microscope.
Infertility	Causes	General factors Diabetes mellitus, thyroid disorders, undiagnosed and untreated coeliac disease, adrenal disease Hypothalamic-pituitary factors Hyperprolactinemia Hypopituitarism The presence of anti-thyroid antibodies is associated with an increased risk of unexplained subfertility with an odds ratio of 1.5 and 95% confidence interval of 1.1–2.0.
Infertility	Causes	Environmental factors Toxins such as glues, volatile organic solvents or silicones, physical agents, flame retardants, chemical dusts, polychlorinated biphenyls, and pesticides. Tobacco smokers are 60% more likely to be infertile than non-smokers.German scientists have reported that a virus called adeno-associated virus might have a role in male infertility, though it is otherwise not harmful. Other diseases such as chlamydia, and gonorrhea can also cause infertility, due to internal scarring (fallopian tube obstruction).
Infertility	Causes	Alimentary habitsObesity: Obesity can have a significant impact on male and female fertility. BMI (body mass index) may be a significant factor in fertility, as an increase in BMI in the male by as little as three units can be associated with infertility. Several studies have demonstrated that an increase in BMI is correlated with a decrease in sperm concentration, a decrease in motility and an increase in DNA damage in sperm. A relationship also exists between obesity and erectile dysfunction (ED). ED may be the consequence of the conversion of androgens to estradiol. The enzyme aromatase is responsible for this conversion and is found primarily in adipose tissue. As the number of adipose tissue increases, there is more aromatase available to convert androgens, and serum estradiol levels increase. Other hormones including inhibin B and leptin, may also be affected by obesity. Inhibin B levels have been reported to decrease with increasing weight, which results in decreased Sertoli cells and sperm production. Leptin is a hormone associated with numerous effects including appetite control, inflammation, and decreased insulin secretion, according to many studies. Obese women have a higher rate of recurrent, early miscarriage compared to non-obese women.
Infertility	Causes	Low weight: Obesity is not the only way in which weight can impact fertility. Men who are underweight tend to have lower sperm concentrations than those who are at a normal BMI. For women, being underweight and having extremely low amounts of body fat are associated with ovarian dysfunction and infertility and they have a higher risk for preterm birth. Eating disorders such as anorexia nervosa are also associated with extremely low BMI. Although relatively uncommon, eating disorders can negatively affect menstruation, fertility, and maternal and fetal well-being.
Infertility	Causes	Females The following causes of infertility may only be found in females.
Infertility	Causes	For a woman to conceive, certain things have to happen: vaginal intercourse must take place around the time when an egg is released from her ovary; the system that produces eggs has to be working at optimum levels; and her hormones must be balanced.For women, problems with fertilization arise mainly from either structural problems in the Fallopian tube or uterus or problems releasing eggs. Infertility may be caused by blockage of the Fallopian tube due to malformations, infections such as chlamydia or scar tissue. For example, endometriosis can cause infertility with the growth of endometrial tissue in the Fallopian tubes or around the ovaries. Endometriosis is usually more common in women in their mid-twenties and older, especially when postponed childbirth has taken place.Another major cause of infertility in women may be the inability to ovulate. Ovulatory disorders make up 25% of the known causes of female infertility. Oligo-ovulation or anovulation results in infertility because no oocyte will be released monthly. In the absence of an oocyte, there is no opportunity for fertilization and pregnancy. World Health Organization subdivided ovulatory disorders into four classes: Hypogonadotropic hypogonadal anovulation: i.e., hypothalamic amenorrhea Normogonadotropic normoestrogenic anovulation: i.e., polycystic ovarian syndrome (PCOS) Hypergonadotropic hypoestrogenic anovulation: i.e., premature ovarian failure Hyperprolactinemic anovulation: i.e., pituitary adenomaMalformation of the eggs themselves may complicate conception. For example, polycystic ovarian syndrome (PCOS) is when the eggs only partially develop within the ovary and there is an excess of male hormones. Some women are infertile because their ovaries do not mature and release eggs. In this case, synthetic FSH by injection or Clomid (Clomiphene citrate) via a pill can be given to stimulate follicles to mature in the ovaries.Other factors that can affect a woman's chances of conceiving include being overweight or underweight, or her age as female fertility declines after the age of 30.Sometimes it can be a combination of factors, and sometimes a clear cause is never established.
Infertility	Causes	Common causes of infertility of females include: ovulation problems (e.g. PCOS, the leading reason why women present to fertility clinics due to anovulatory infertility) tubal blockage pelvic inflammatory disease caused by infections like tuberculosis age-related factors uterine problems previous tubal ligation endometriosis advanced maternal age immune infertility Males Male infertility is defined as the inability of a male to make a fertile female pregnant, for a minimum of at least one year of unprotected intercourse. There are multiple causes for male infertility. These include endocrine disorders (usually due to hypogonadism) at an estimated 2% to 5%, sperm transport disorders (such as vasectomy) at 5%, primary testicular defects (which includes abnormal sperm parameters without any identifiable cause) at 65% to 80% and idiopathic (where an infertile male has normal sperm and semen parameters) at 10% to 20%.The main cause of male infertility is low semen quality. In men who have the necessary reproductive organs to procreate, infertility can be caused by low sperm count due to endocrine problems, drugs, radiation, or infection. There may be testicular malformations, hormone imbalance, or blockage of the man's duct system. Although many of these can be treated through surgery or hormonal substitutions, some may be indefinite.
Infertility	Causes	Infertility associated with viable, but immotile sperm may be caused by primary ciliary dyskinesia. The sperm must provide the zygote with DNA, centrioles, and activation factor for the embryo to develop. A defect in any of these sperm structures may result in infertility that will not be detected by semen analysis. Antisperm antibodies cause immune infertility. Cystic fibrosis can lead to infertility in men.
Infertility	Causes	Combined infertility In some cases, both the man and woman may be infertile or subfertile, and the couple's infertility arises from the combination of these conditions. In other cases, the cause is suspected to be immunological or genetic; it may be that each partner is independently fertile but the couple cannot conceive together without assistance.
Infertility	Causes	Unexplained infertility In the US, up to 20% of infertile couples have unexplained infertility. In these cases, abnormalities are likely to be present but not detected by current methods. Possible problems could be that the egg is not released at the optimum time for fertilization, that it may not enter the fallopian tube, sperm may not be able to reach the egg, fertilization may fail to occur, transport of the zygote may be disturbed, or implantation fails. It is increasingly recognized that egg quality is of critical importance and women of advanced maternal age have eggs of reduced capacity for normal and successful fertilization. Also, polymorphisms in folate pathway genes could be one reason for fertility complications in some women with unexplained infertility. However, a growing body of evidence suggests that epigenetic modifications in sperm may be partially responsible.
Infertility	Diagnosis	If both partners are young and healthy and have been trying to conceive for one year without success, a visit to a physician or women's health nurse practitioner (WHNP) could help to highlight potential medical problems earlier rather than later. The doctor or WHNP may also be able to suggest lifestyle changes to increase the chances of conceiving.Women over the age of 35 should see their physician or WHNP after six months as fertility tests can take some time to complete, and age may affect the treatment options that are open in that case.A doctor or WHNP takes a medical history and gives a physical examination. They can also carry out some basic tests on both partners to see if there is an identifiable reason for not having achieved a pregnancy. If necessary, they refer patients to a fertility clinic or local hospital for more specialized tests. The results of these tests help determine the best fertility treatment.
Infertility	Treatment	Treatment depends on the cause of infertility, but may include counselling, fertility treatments, which include in vitro fertilization. According to ESHRE recommendations, couples with an estimated live birth rate of 40% or higher per year are encouraged to continue aiming for a spontaneous pregnancy. Treatment methods for infertility may be grouped as medical or complementary and alternative treatments. Some methods may be used in concert with other methods. Drugs used for both women and men include clomiphene citrate, human menopausal gonadotropin (hMG), follicle-stimulating hormone (FSH), human chorionic gonadotropin (hCG), gonadotropin-releasing hormone (GnRH) analogues, aromatase inhibitors, and metformin.
Infertility	Treatment	Medical treatments Medical treatment of infertility generally involves the use of fertility medication, medical device, surgery, or a combination of the following. If the sperm is of good quality and the mechanics of the woman's reproductive structures are good (patent fallopian tubes, no adhesions or scarring), a course of ovulation induction may be used. The physician or WHNP may also suggest using a conception cap cervical cap, which the patient uses at home by placing the sperm inside the cap and putting the conception device on the cervix, or intrauterine insemination (IUI), in which the doctor or WHNP introduces sperm into the uterus during ovulation, via a catheter. In these methods, fertilization occurs inside the body.If conservative medical treatments fail to achieve a full-term pregnancy, the physician or WHNP may suggest the patient to undergo in vitro fertilization (IVF). IVF and related techniques (ICSI, ZIFT, GIFT) are called assisted reproductive technology (ART) techniques.ART techniques generally start with stimulating the ovaries to increase egg production. After stimulation, the physician surgically extracts one or more eggs from the ovary, and unites them with sperm in a laboratory setting, with the intent of producing one or more embryos. Fertilization takes place outside the body, and the fertilized egg is reinserted into the woman's reproductive tract, in a procedure called embryo transfer.Other medical techniques are e.g. tuboplasty, assisted hatching, and preimplantation genetic diagnosis.
Infertility	Treatment	In vitro fertilization IVF is the most commonly used ART. It has been proven useful in overcoming infertility conditions, such as blocked or damaged tubes, endometriosis, repeated IUI failure, unexplained infertility, poor ovarian reserve, poor or even nil sperm count. Intracytoplasmic sperm injection ICSI technique is used in case of poor semen quality, low sperm count or failed fertilization attempts during prior IVF cycles. This technique involves an injection of a single healthy sperm directly injected into mature egg. The fertilized embryo is then transferred to womb. Tourism Fertility tourism is the practice of traveling to another country for fertility treatments. It may be regarded as a form of medical tourism. The main reasons for fertility tourism are legal regulation of the sought procedure in the home country, or lower price. In-vitro fertilization and donor insemination are major procedures involved.
Infertility	Treatment	Stem cell therapy Nowadays, there are several treatments (still in experimentation) related to stem cell therapy. It is a new opportunity, not only for partners with lack of gametes, but also for same-sex couples and single people who want to have offspring. Theoretically, with this therapy, we can get artificial gametes in vitro. There are different studies for both women and men.
Infertility	Treatment	Spermatogonial stem cells transplant: it takes places in the seminiferous tubule. With this treatment, the patient experience spermatogenesis, and therefore, it has the chance to have offspring if he wants to. It is specially oriented for cancer patients, whose sperm is destroyed due to the gonadotoxic treatment they are submitted to.
Infertility	Treatment	Ovarian stem cells: it is thought that women have a finite number of follicles from the very beginning. Nevertheless, scientists have found these stem cells, which may generate new oocytes in postnatal conditions. Apparently there are only 0.014% of them (this could be an explanation of why they were not discovered until now). There is still some controversy about their existence, but if the discoveries are true, this could be a new treatment for infertility.Stem cell therapy is really new, and everything is still under investigation. Additionally, it could be the future for the treatment of multiple diseases, including infertility. It will take time before these studies can be available for clinics and patients.
Infertility	Epidemiology	Prevalence of infertility varies depending on the definition, i.e. on the time span involved in the failure to conceive. Infertility rates have increased by 4% since the 1980s, mostly from problems with fecundity due to an increase in age. Fertility problems affect one in seven couples in the UK. Most couples (about 84%) who have regular sexual intercourse (that is, every two to three days) and who do not use contraception get pregnant within a year. About 95 out of 100 couples who are trying to get pregnant do so within two years. Women become less fertile as they get older. For women aged 35, about 94% who have regular unprotected sexual intercourse get pregnant after three years of trying. For women aged 38, however, only about 77%. The effect of age upon men's fertility is less clear. In people going forward for IVF in the UK, roughly half of fertility problems with a diagnosed cause are due to problems with the man, and about half due to problems with the woman. However, about one in five cases of infertility have no clear diagnosed cause. In Britain, male factor infertility accounts for 25% of infertile couples, while 25% remain unexplained. 50% are female causes with 25% being due to anovulation and 25% tubal problems/other. In Sweden, approximately 10% of couples wanting children are infertile. In approximately one-third of these cases the man is the factor, in one third the woman is the factor, and in the remaining third the infertility is a product of factors on both parts. In many lower-income countries, estimating infertility is difficult due to incomplete information and infertility and childlessness stigmas.
Infertility	Epidemiology	Data on income-limited individuals, male infertility, and fertility within non-traditional families may be limited due to traditional social norms. Historical data on fertility and infertility is limited as any form of study or tracking only began in the early 20th century. Per one account, "The invisibility of marginalised social groups in infertility tracking reflects broader social beliefs about who can and should reproduce. The offspring of privileged social groups are seen as a boon to society. The offspring of marginalised groups are perceived as a burden."
Infertility	Society and culture	Perhaps except for infertility in science fiction, films and other fiction depicting emotional struggles of assisted reproductive technology have had an upswing first in the latter part of the 2000s decade, although the techniques have been available for decades. Yet, the number of people that can relate to it by personal experience in one way or another is ever-growing, and the variety of trials and struggles is huge.Pixar's Up contains a depiction of infertility in an extended life montage that lasts the first few minutes of the film.Other individual examples are referred to individual sub-articles of assisted reproductive technology Ethics There are several ethical issues associated with infertility and its treatment.
Infertility	Society and culture	High-cost treatments are out of financial reach for some couples. Debate over whether health insurance companies (e.g. in the US) should be required to cover infertility treatment. Allocation of medical resources that could be used elsewhere The legal status of embryos fertilized in vitro and not transferred in vivo. (See also beginning of pregnancy controversy). Opposition to the destruction of embryos not transferred in vivo. IVF and other fertility treatments have resulted in an increase in multiple births, provoking ethical analysis because of the link between multiple pregnancies, premature birth, and a host of health problems. Religious leaders' opinions on fertility treatments; for example, the Roman Catholic Church views infertility as a calling to adopt or to use natural treatments (medication, surgery, or cycle charting) and members must reject assisted reproductive technologies. Infertility caused by DNA defects on the Y chromosome is passed on from father to son. If natural selection is the primary error correction mechanism that prevents random mutations on the Y chromosome, then fertility treatments for men with abnormal sperm (in particular ICSI) only defer the underlying problem to the next male generation. Specific procedures, such as gestational surrogacy, have led to numerous ethical issues, particularly when people living in one country contract for surrogacy in another (transnational surrogacy).Many countries have special frameworks for dealing with the ethical and social issues around fertility treatment.
Infertility	Society and culture	One of the best known is the HFEA – The UK's regulator for fertility treatment and embryo research. This was set up on 1 August 1991 following a detailed commission of enquiry led by Mary Warnock in the 1980s A similar model to the HFEA has been adopted by the rest of the countries in the European Union. Each country has its own body or bodies responsible for the inspection and licensing of fertility treatment under the EU Tissues and Cells directive Regulatory bodies are also found in Canada and in the state of Victoria in Australia
Allen Brain Atlas	Allen Brain Atlas	The Allen Mouse and Human Brain Atlases are projects within the Allen Institute for Brain Science which seek to combine genomics with neuroanatomy by creating gene expression maps for the mouse and human brain. They were initiated in September 2003 with a $100 million donation from Paul G. Allen and the first atlas went public in September 2006. As of May 2012, seven brain atlases have been published: Mouse Brain Atlas, Human Brain Atlas, Developing Mouse Brain Atlas, Developing Human Brain Atlas, Mouse Connectivity Atlas, Non-Human Primate Atlas, and Mouse Spinal Cord Atlas. There are also three related projects with data banks: Glioblastoma, Mouse Diversity, and Sleep. It is the hope of the Allen Institute that their findings will help advance various fields of science, especially those surrounding the understanding of neurobiological diseases. The atlases are free and available for public use online.

Subsets and Splits

No community queries yet

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