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Fuel consumption and emissions reductions
The hybrid vehicle typically achieves greater fuel economy and lower emissions than conventional internal combustion engine vehicles (ICEVs), resulting in fewer emissions being generated. These savings are primarily achieved by three elements of a typical hybrid design:
Relyin... | Hybrid vehicle | Wikipedia | 495 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
Hybrid vehicle emissions
Hybrid vehicle emissions today are getting close to or even lower than the recommended level set by the EPA (Environmental Protection Agency). The recommended levels they suggest for a typical passenger vehicle should be equated to 5.5 metric tons of . The three most popular hybrid vehicles, Ho... | Hybrid vehicle | Wikipedia | 359 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
The toxicity levels and environmental impact of nickel metal hydride batteries—the type previously used in hybrids—are much lower than batteries like lead acid or nickel cadmium according to one source. Another source claims nickel metal hydride batteries are much more toxic than lead batteries, also that recycling the... | Hybrid vehicle | Wikipedia | 445 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
Charging
There are two different levels of charging in plug-in hybrids. Level one charging is the slower method as it uses a 120 V/15 A single-phase grounded outlet. Level two is a faster method; existing Level 2 equipment offers charging from 208 V or 240 V (at up to 80 A, 19.2 kW). It may require dedicated equipment ... | Hybrid vehicle | Wikipedia | 470 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
How hybrid-electric vehicles work
Hybrid-electric vehicles (HEVs) combine the advantage of gasoline engines and electric motors. The key areas for efficiency or performance gains are regenerative braking, dual power sources, and less idling.
Regenerative braking. The electric motor normally converts electricity into ... | Hybrid vehicle | Wikipedia | 383 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
In 2005, sales went beyond 200,000 Hybrids, but in retrospect that only reduced the global use for gasoline consumption by 200,000 gallons per day—a tiny fraction of the 360 million gallons used per day. According to Bradley Berman author of Driving Change—One Hybrid at a time, "cold economics shows that in real dollar... | Hybrid vehicle | Wikipedia | 487 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
Adoption rate
While the adoption rate for hybrids in the US is small today (2.2% of new car sales in 2011), this compares with a 17.1% share of new car sales in Japan in 2011, and it has the potential to be very large over time as more models are offered and incremental costs decline due to learning and scale benefits.... | Hybrid vehicle | Wikipedia | 421 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
Emissions target: The agreement will reduce average CO2 emissions from new cars to 95 g/km from 2020, as proposed by the commission. This is a 40% reduction from the mandatory 2015 target of 130 g/km. The target is an average for each manufacturer's new car fleet; it allows OEMs to build some vehicles that emit less th... | Hybrid vehicle | Wikipedia | 266 | 157736 | https://en.wikipedia.org/wiki/Hybrid%20vehicle | Technology | Basics_7 | null |
Permafrost () is soil or underwater sediment which continuously remains below for two years or more: the oldest permafrost had been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than . Similarly, the area of individu... | Permafrost | Wikipedia | 458 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Apart from its climate impact, permafrost thaw brings more risks. Formerly frozen ground often contains enough ice that when it thaws, hydraulic saturation is suddenly exceeded, so the ground shifts substantially and may even collapse outright. Many buildings and other infrastructure were built on permafrost when it wa... | Permafrost | Wikipedia | 427 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Around 15% of Northern Hemisphere land that is not completely covered by ice is directly underlain by permafrost; 22% is defined as part of a permafrost zone or region. This is because only slightly more than half of this area is defined as a continuous permafrost zone, where 90%–100% of the land is underlain by permaf... | Permafrost | Wikipedia | 420 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
The below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth due to the geothermal crustal gradient. Thus, if the mean annual air temperature is only slightly below , permafrost will form only in spots that are sheltered (usually w... | Permafrost | Wikipedia | 459 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Alpine permafrost
A range of elevations in both the Northern and Southern Hemisphere are cold enough to support perennially frozen ground: some of the best-known examples include the Canadian Rockies, the European Alps, Himalaya and the Tien Shan. In general, it has been found that extensive alpine permafrost requires... | Permafrost | Wikipedia | 477 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Past extent of permafrost
At the Last Glacial Maximum, continuous permafrost covered a much greater area than it does today, covering all of ice-free Europe south to about Szeged (southeastern Hungary) and the Sea of Azov (then dry land) and East Asia south to present-day Changchun and Abashiri. In North America, only... | Permafrost | Wikipedia | 481 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
When the ice content of a permafrost exceeds 250 percent (ice to dry soil by mass) it is classified as massive ice. Massive ice bodies can range in composition, in every conceivable gradation from icy mud to pure ice. Massive icy beds have a minimum thickness of at least 2 m and a short diameter of at least 10 m. First... | Permafrost | Wikipedia | 386 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Intrasedimental or constitutional ice has been widely observed and studied across Canada. It forms when subterranean waters freeze in place, and is subdivided into intrusive, injection and segregational ice. The latter is the dominant type, formed after crystallizational differentiation in wet sediments, which occurs w... | Permafrost | Wikipedia | 482 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
While permafrost soil is frozen, it is not completely inhospitable to microorganisms, though their numbers can vary widely, typically from 1 to 1000 million per gram of soil.
The permafrost carbon cycle (Arctic Carbon Cycle) deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes,... | Permafrost | Wikipedia | 430 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
There are only two large cities in the world built in areas of continuous permafrost (where the frozen soil forms an unbroken, below-zero sheet) and both are in Russia – Norilsk in Krasnoyarsk Krai and Yakutsk in the Sakha Republic. Building on permafrost is difficult because the heat of the building (or pipeline) can ... | Permafrost | Wikipedia | 511 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
In Yukon, the zone of continuous permafrost might have moved poleward since 1899, but accurate records only go back 30 years. The extent of subsea permafrost is decreasing as well; as of 2019, ~97% of permafrost under Arctic ice shelves is becoming warmer and thinner.
Based on high agreement across model projections,... | Permafrost | Wikipedia | 365 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
In the northern circumpolar region, permafrost contains organic matter equivalent to 1400–1650 billion tons of pure carbon, which was built up over thousands of years. This amount equals almost half of all organic material in all soils, and it is about twice the carbon content of the atmosphere, or around four times l... | Permafrost | Wikipedia | 464 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Another factor which complicates projections of permafrost carbon emissions is the ongoing "greening" of the Arctic. As climate change warms the air and the soil, the region becomes more hospitable to plants, including larger shrubs and trees which could not survive there before. Thus, the Arctic is losing more and mor... | Permafrost | Wikipedia | 419 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Fewer studies have attempted to describe the impact directly in terms of warming. A 2018 paper estimated that if global warming was limited to , gradual permafrost thaw would add around to global temperatures by 2100, while a 2022 review concluded that every of global warming would cause and from abrupt thaw by the... | Permafrost | Wikipedia | 420 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Permafrost thaw can also result in the formation of frozen debris lobes (FDLs), which are defined as "slow-moving landslides composed of soil, rocks, trees, and ice". This is a notable issue in the Alaska's southern Brooks Range, where some FDLs measured over in width, in height, and in length by 2012. As of Decembe... | Permafrost | Wikipedia | 309 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
In Alaska alone, damages to infrastructure by the end of the century would amount to $4.6 billion (at 2015 dollar value) if RCP8.5, the high-emission climate change scenario, were realized. Over half stems from the damage to buildings ($2.8 billion), but there's also damage to roads ($700 million), railroads ($620 mill... | Permafrost | Wikipedia | 499 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
By 2022, up to 80% of buildings in some Northern Russia cities had already experienced damage. By 2050, the damage to residential infrastructure may reach $15 billion, while total public infrastructure damages could amount to 132 billion. This includes oil and gas extraction facilities, of which 45% are believed to be ... | Permafrost | Wikipedia | 507 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
About a fifth of both the industrial and the polluted sites (1000 and 2200–4800) are expected to start thawing in the future even if the warming does not increase from its 2020 levels. Only about 3% more sites would start thawing between now and 2050 under the climate change scenario consistent with the Paris Agreement... | Permafrost | Wikipedia | 342 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Another issue associated with permafrost thaw is the release of natural mercury deposits. An estimated 800,000 tons of mercury are frozen in the permafrost soil. According to observations, around 70% of it is simply taken up by vegetation after the thaw. However, if the warming continues under RCP8.5, then permafrost e... | Permafrost | Wikipedia | 424 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Plants
In 2012, Russian researchers proved that permafrost can serve as a natural repository for ancient life forms by reviving a sample of Silene stenophylla from 30,000-year-old tissue found in an Ice Age squirrel burrow in the Siberian permafrost. This is the oldest plant tissue ever revived. The resultant plant wa... | Permafrost | Wikipedia | 422 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
Beginning in 1942, Siemon William Muller delved into the relevant Russian literature held by the Library of Congress and the U.S. Geological Survey Library so that he was able to furnish the government an engineering field guide and a technical report about permafrost by 1943. That report coined the English term as a c... | Permafrost | Wikipedia | 407 | 157774 | https://en.wikipedia.org/wiki/Permafrost | Physical sciences | Glaciology | null |
A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a ... | Meteor shower | Wikipedia | 438 | 157819 | https://en.wikipedia.org/wiki/Meteor%20shower | Physical sciences | Planetary science | null |
Viola is a genus of flowering plants in the violet family Violaceae. It is the largest genus in the family, containing over 680 species. Most species are found in the temperate Northern Hemisphere; however, some are also found in widely divergent areas such as Hawaii, Australasia, and the Andes.
Some Viola species are... | Viola (plant) | Wikipedia | 446 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Solitary flowers end long stalks with a pair of bracteoles. The flowers have five sepals that persist after blooming, and in some species the sepals enlarge after blooming. The corolla ranges from white to yellow, orange or various shades of blue and violet or multicolored, often blue and yellow, with or without a yell... | Viola (plant) | Wikipedia | 404 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
History
First formally described by Carl Linnaeus in 1753 with 19 species, the genus Viola bears his botanical authority, L. When Jussieu established the hierarchical system of families (1789), he placed Viola in the Cisti (rock roses), though by 1811 he suggested Viola be separated from these. However, in 1802 Batsch ... | Viola (plant) | Wikipedia | 323 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Subdivision
Viola is a large genus that has traditionally been treated in sections. One of these was that of Gingins (1823), based on stigma morphology, with five sections (Nomimium, Dischidium, Chamaemelanium, Melanium, Leptidium). The extensive taxonomic studies of Wilhelm Becker, culminating in his 1925 conspectus, ... | Viola (plant) | Wikipedia | 449 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Sect. Andinium W.Becker (113) S America
Sect. Chamaemelanium Ging. s.lat. (61) N America, northeast Asia (includes Dischidium, Orbiculares)
Subsect. Chamaemelanium
Subsect. Nudicaules
Subsect. Nuttalianae
Sect. Chilenium W.Becker (8) southern S America
Sect. Danxiaviola W. B. Liao et Q. Fan (1) China
Sect. Delph... | Viola (plant) | Wikipedia | 406 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Species
The genus includes dog violets, a group of scentless species which are the most common Viola in many areas, sweet violet (Viola odorata) (named from its sweet scent), and many other species whose common name includes the word "violet". But not other "violets": Neither Streptocarpus sect. Saintpaulia ("African v... | Viola (plant) | Wikipedia | 468 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Genetics
Habitat fragmentation has been shown to have minimal effect on the genetic diversity and gene flow of the North American woodland violet Viola pubescens. This may be partially attributed to the ability of Viola pubescens to continue to persist within a largely agricultural matrix. This trend of unexpectedly hi... | Viola (plant) | Wikipedia | 339 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Ecology
Viola species are used as food plants by the larvae of some Lepidoptera species, including the giant leopard moth, large yellow underwing, lesser broad-bordered yellow underwing, high brown fritillary, small pearl-bordered fritillary, pearl-bordered fritillary, regal fritillary, cardinal, and Setaceous Hebrew c... | Viola (plant) | Wikipedia | 400 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Violet species occupy a diverse array of habitats, from bogs (Viola lanceolata) to dry hill prairies (V. pedata) to woodland understories (V. labradorica). While many of these species are indicators of high quality habitat, some violets are capable of thriving in a human altered landscape. Two species of zinc violet (V... | Viola (plant) | Wikipedia | 478 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
The modern garden pansy (V. × wittrockiana) is a plant of complex hybrid origin involving at least three species, V. tricolor (wild pansy or heartsease), V. altaica, and V. lutea (mountain pansy). The hybrid horned pansy (V. × williamsii) originates from hybridization involving garden pansy and Viola cornuta.
Bedding ... | Viola (plant) | Wikipedia | 380 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
When newly opened, Viola flowers may be used to decorate salads or in stuffings for poultry or fish. Soufflés, cream, and similar desserts can be flavoured with essence of Viola flowers. The young leaves are edible raw or cooked as a mild-tasting leaf vegetable. The flowers and leaves of the cultivar 'Rebecca', one of ... | Viola (plant) | Wikipedia | 434 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Medicinal
Many Viola species contain antioxidants called anthocyanins. Fourteen anthocyanins from V. yedoensis and V. prionantha have been identified. Some anthocyanins show strong antioxidant activities. Most violas tested and many other plants of the family Violaceae contain cyclotides, which have a diverse range of ... | Viola (plant) | Wikipedia | 510 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
Violets, and badges depicting them,
were sold in fund-raising efforts in Australia and New Zealand on and around Violet Day in commemoration of the lost soldiers of World War I. | Viola (plant) | Wikipedia | 36 | 157841 | https://en.wikipedia.org/wiki/Viola%20%28plant%29 | Biology and health sciences | Malpighiales | null |
An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system.
In higher organisms, the eye is a complex optical system that collects light from the surrounding environme... | Eye | Wikipedia | 384 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
The first proto-eyes evolved among animals about the time of the Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35 main phyla. In most vertebrates and some molluscs, the eye allo... | Eye | Wikipedia | 470 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
In contrast to compound eyes, simple eyes have a single lens. Jumping spiders have one pair of large simple eyes with a narrow field of view, augmented by an array of smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a type of simple eye (stemmata) which usually provides only a rough image... | Eye | Wikipedia | 503 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Non-compound eyes
Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustaceans and Cubozoa.
Pit eyes
Pit eyes, also known as stemmata, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye... | Eye | Wikipedia | 503 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Heterogeneous eyes have evolved at least nine times: four or more times in gastropods, once in the copepods, once in the annelids, once in the cephalopods, and once in the chitons, which have aragonite lenses. No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneo... | Eye | Wikipedia | 456 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air. In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is ... | Eye | Wikipedia | 456 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small r... | Eye | Wikipedia | 504 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Superposition eyes
The second type is named the superposition eye. The superposition eye is divided into three types:
refracting,
reflecting and
parabolic superposition
The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and re... | Eye | Wikipedia | 416 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies, have specialised zones of ommatidia organised into a fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a... | Eye | Wikipedia | 435 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Nutrients
The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium... | Eye | Wikipedia | 497 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye, and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution, despite thei... | Eye | Wikipedia | 506 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
The gap between tissue layers naturally formed a biconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This inc... | Eye | Wikipedia | 348 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey. In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipods are deep water animals that feed on organisms above them. ... | Eye | Wikipedia | 374 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Visual acuity, or resolving power, is "the ability to distinguish fine detail" and is the property of cone cells. It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measur... | Eye | Wikipedia | 426 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
"Colour vision is the faculty of the organism to distinguish lights of different spectral qualities." All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between wavelengths of 400 and 700 nm. This is a rather small section of the electromagnet... | Eye | Wikipedia | 502 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are ... | Eye | Wikipedia | 319 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells. The eyes of vertebrates usually contain ciliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with... | Eye | Wikipedia | 314 | 157898 | https://en.wikipedia.org/wiki/Eye | Biology and health sciences | Biology | null |
Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genet... | Genetic recombination | Wikipedia | 476 | 158005 | https://en.wikipedia.org/wiki/Genetic%20recombination | Biology and health sciences | Genetics | Biology |
V(D)J recombination in organisms with an adaptive immune system is a type of site-specific genetic recombination that helps immune cells rapidly diversify to recognize and adapt to new pathogens.
Synapsis
During meiosis, synapsis (the pairing of homologous chromosomes) ordinarily precedes genetic recombination.
Mech... | Genetic recombination | Wikipedia | 435 | 158005 | https://en.wikipedia.org/wiki/Genetic%20recombination | Biology and health sciences | Genetics | Biology |
Chromosomal crossover involves recombination between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. During prophase I (pachytene stage) the four available chromatids are in tight formation with one another. While in this formation, homologous sites on two chromatids can... | Genetic recombination | Wikipedia | 380 | 158005 | https://en.wikipedia.org/wiki/Genetic%20recombination | Biology and health sciences | Genetics | Biology |
In gene conversion, a section of genetic material is copied from one chromosome to another, without the donating chromosome being changed. Gene conversion occurs at high frequency at the actual site of the recombination event during meiosis. It is a process by which a DNA sequence is copied from one DNA helix (which re... | Genetic recombination | Wikipedia | 368 | 158005 | https://en.wikipedia.org/wiki/Genetic%20recombination | Biology and health sciences | Genetics | Biology |
Recombinational repair
DNA damages caused by a variety of exogenous agents (e.g. UV light, X-rays, chemical cross-linking agents) can be repaired by homologous recombinational repair (HRR). These findings suggest that DNA damages arising from natural processes, such as exposure to reactive oxygen species that are bypr... | Genetic recombination | Wikipedia | 356 | 158005 | https://en.wikipedia.org/wiki/Genetic%20recombination | Biology and health sciences | Genetics | Biology |
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes form a continuous barrier around all cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus, and m... | Lipid bilayer | Wikipedia | 408 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
The structure of biological membranes typically includes several types of molecules in addition to the phospholipids comprising the bilayer. A particularly important example in animal cells is cholesterol, which helps strengthen the bilayer and decrease its permeability. Cholesterol also helps regulate the activity of ... | Lipid bilayer | Wikipedia | 481 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
The first region on either side of the bilayer is the hydrophilic headgroup. This portion of the membrane is completely hydrated and is typically around 0.8-0.9 nm thick. In phospholipid bilayers the phosphate group is located within this hydrated region, approximately 0.5 nm outside the hydrophobic core. In some cases... | Lipid bilayer | Wikipedia | 454 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Lipid asymmetry arises, at least in part, from the fact that most phospholipids are synthesised and initially inserted into the inner monolayer: those that constitute the outer monolayer are then transported from the inner monolayer by a class of enzymes called flippases. Other lipids, such as sphingomyelin, appear to ... | Lipid bilayer | Wikipedia | 413 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
At a given temperature a lipid bilayer can exist in either a liquid or a gel (solid) phase. All lipids have a characteristic temperature at which they transition (melt) from the gel to liquid phase. In both phases the lipid molecules are prevented from flip-flopping across the bilayer, but in liquid phase bilayers a gi... | Lipid bilayer | Wikipedia | 438 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Surface chemistry
While lipid tails primarily modulate bilayer phase behavior, it is the headgroup that determines the bilayer surface chemistry. Most natural bilayers are composed primarily of phospholipids, but sphingolipids and sterols such as cholesterol are also important components. Of the phospholipids, the most... | Lipid bilayer | Wikipedia | 298 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Containment and separation
The primary role of the lipid bilayer in biology is to separate aqueous compartments from their surroundings. Without some form of barrier delineating “self” from “non-self”, it is difficult to even define the concept of an organism or of life. This barrier takes the form of a lipid bilayer i... | Lipid bilayer | Wikipedia | 421 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
The most familiar form of cellular signaling is likely synaptic transmission, whereby a nerve impulse that has reached the end of one neuron is conveyed to an adjacent neuron via the release of neurotransmitters. This transmission is made possible by the action of synaptic vesicles which are, inside the cell, loaded wi... | Lipid bilayer | Wikipedia | 476 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
The lipid bilayer is a difficult structure to study because it is so thin and fragile. To overcome these limitations, techniques have been developed to allow investigations of its structure and function.
Electrical measurements
Electrical measurements are a straightforward way to characterize an important function of... | Lipid bilayer | Wikipedia | 478 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
A new method to study lipid bilayers is Atomic force microscopy (AFM). Rather than using a beam of light or particles, a very small sharpened tip scans the surface by making physical contact with the bilayer and moving across it, like a record player needle. AFM is a promising technique because it has the potential to ... | Lipid bilayer | Wikipedia | 354 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Most polar molecules have low solubility in the hydrocarbon core of a lipid bilayer and, as a consequence, have low permeability coefficients across the bilayer. This effect is particularly pronounced for charged species, which have even lower permeability coefficients than neutral polar molecules. Anions typically hav... | Lipid bilayer | Wikipedia | 510 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Endocytosis and exocytosis
Some molecules or particles are too large or too hydrophilic to pass through a lipid bilayer. Other molecules could pass through the bilayer but must be transported rapidly in such large numbers that channel-type transport is impractical. In both cases, these types of cargo can be moved acro... | Lipid bilayer | Wikipedia | 497 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Lipid bilayers are large enough structures to have some of the mechanical properties of liquids or solids. The area compression modulus Ka, bending modulus Kb, and edge energy , can be used to describe them. Solid lipid bilayers also have a shear modulus, but like any liquid, the shear modulus is zero for fluid bilayer... | Lipid bilayer | Wikipedia | 472 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
is a measure of how much energy it takes to expose a bilayer edge to water by tearing the bilayer or creating a hole in it. The origin of this energy is the fact that creating such an interface exposes some of the lipid tails to water, but the exact orientation of these border lipids is unknown. There is some evidence ... | Lipid bilayer | Wikipedia | 288 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
There are four fundamental steps in the fusion process. First, the involved membranes must aggregate, approaching each other to within several nanometers. Second, the two bilayers must come into very close contact (within a few angstroms). To achieve this close contact, the two surfaces must become at least partially d... | Lipid bilayer | Wikipedia | 398 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
In studies of molecular and cellular biology it is often desirable to artificially induce fusion. The addition of polyethylene glycol (PEG) causes fusion without significant aggregation or biochemical disruption. This procedure is now used extensively, for example by fusing B-cells with myeloma cells. The resulting “hy... | Lipid bilayer | Wikipedia | 477 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
The first generation of drug delivery liposomes had a simple lipid composition and suffered from several limitations. Circulation in the bloodstream was extremely limited due to both renal clearing and phagocytosis. Refinement of the lipid composition to tune fluidity, surface charge density, and surface hydration resu... | Lipid bilayer | Wikipedia | 477 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
By the early twentieth century scientists had come to believe that cells are surrounded by a thin oil-like barrier, but the structural nature of this membrane was not known. Two experiments in 1925 laid the groundwork to fill in this gap. By measuring the capacitance of erythrocyte solutions, Hugo Fricke determined tha... | Lipid bilayer | Wikipedia | 348 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Around the same time, the development of model membranes confirmed that the lipid bilayer is a stable structure that can exist independent of proteins. By “painting” a solution of lipid in organic solvent across an aperture, Mueller and Rudin were able to create an artificial bilayer and determine that this exhibited l... | Lipid bilayer | Wikipedia | 204 | 158011 | https://en.wikipedia.org/wiki/Lipid%20bilayer | Biology and health sciences | Cell parts | Biology |
Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs.
This initial stage of sepsis is followed by suppression of the immune system. Common signs and symptoms include fever, increased heart rate, increased breathing rate, and co... | Sepsis | Wikipedia | 416 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Sepsis requires immediate treatment with intravenous fluids and antimicrobial medications. Ongoing care and stabilization often continues in an intensive care unit. If an adequate trial of fluid replacement is not enough to maintain blood pressure, then the use of medications that raise blood pressure becomes necessary... | Sepsis | Wikipedia | 493 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
The drop in blood pressure seen in sepsis can cause lightheadedness and is part of the criteria for septic shock.
Oxidative stress is observed in septic shock, with circulating levels of copper and vitamin C being decreased.
Diastolic blood pressure falls during the early stages of sepsis, causing a widening/increasi... | Sepsis | Wikipedia | 433 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Sepsis is caused by a combination of factors related to the particular invading pathogen(s) and the status of the immune system of the host. The early phase of sepsis characterized by excessive inflammation (sometimes resulting in a cytokine storm) may be followed by a prolonged period of decreased functioning of the i... | Sepsis | Wikipedia | 305 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
There are a number of microbial factors that may cause the typical septic inflammatory cascade. An invading pathogen is recognized by its pathogen-associated molecular patterns (PAMPs). Examples of PAMPs include lipopolysaccharides and flagellin in gram-negative bacteria, muramyl dipeptide in the peptidoglycan of the g... | Sepsis | Wikipedia | 450 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Inflammatory responses cause multiple organ dysfunction syndrome through various mechanisms as described below. Increased permeability of the lung vessels causes leaking of fluids into alveoli, which results in pulmonary edema and acute respiratory distress syndrome (ARDS). Impaired utilization of oxygen in the liver i... | Sepsis | Wikipedia | 450 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Within the first three hours of suspected sepsis, diagnostic studies should include white blood cell counts, measuring serum lactate, and obtaining appropriate cultures before starting antibiotics, so long as this does not delay their use by more than 45 minutes. To identify the causative organism(s), at least two sets... | Sepsis | Wikipedia | 401 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Previously, SIRS criteria had been used to define sepsis. If the SIRS criteria are negative, it is very unlikely the person has sepsis; if it is positive, there is just a moderate probability that the person has sepsis. According to SIRS, there were different levels of sepsis: sepsis, severe sepsis, and septic shock. T... | Sepsis | Wikipedia | 511 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Examples of end-organ dysfunction include the following:
Lungs: acute respiratory distress syndrome (ARDS) (PaO2/FiO2 ratio < 300), different ratio in pediatric acute respiratory distress syndrome
Brain: encephalopathy symptoms including agitation, confusion, and coma; causes may include ischemia, bleeding, formation... | Sepsis | Wikipedia | 217 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
More specific definitions of end-organ dysfunction exist for SIRS in pediatrics.
Cardiovascular dysfunction (after fluid resuscitation with at least 40 mL/kg of crystalloid)
hypotension with blood pressure < 5th percentile for age or systolic blood pressure < 2 standard deviations below normal for age, or
vasopresso... | Sepsis | Wikipedia | 435 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Biomarkers
Biomarkers can help with diagnosis because they can point to the presence or severity of sepsis, although their exact role in the management of sepsis remains undefined. A 2013 review concluded moderate-quality evidence exists to support the use of the procalcitonin level as a method to distinguish sepsis f... | Sepsis | Wikipedia | 467 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Early recognition and focused management may improve the outcomes of sepsis. Current professional recommendations include several actions ("bundles") to be followed as soon as possible after diagnosis. Within the first three hours, someone with sepsis should have received antibiotics, and intravenous fluids if there is... | Sepsis | Wikipedia | 490 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Several factors determine the most appropriate choice for the initial antibiotic regimen. These factors include local patterns of bacterial sensitivity to antibiotics, whether the infection is thought to be a hospital or community-acquired infection, and which organ systems are thought to be infected. Antibiotic regime... | Sepsis | Wikipedia | 474 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Intravenous fluids
The Surviving Sepsis Campaign has recommended 30 mL/kg of fluid to be given in adults in the first three hours followed by fluid titration according to blood pressure, urine output, respiratory rate, and oxygen saturation with a target mean arterial pressure (MAP) of 65 mmHg. In children an initial ... | Sepsis | Wikipedia | 349 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Blood products
The Surviving Sepsis Campaign recommended packed red blood cells transfusion for hemoglobin levels below 70 g/L if there is no myocardial ischemia, hypoxemia, or acute bleeding. In a 2014 trial, blood transfusions to keep target hemoglobin above 70 or 90 g/L did not make any difference to survival rates... | Sepsis | Wikipedia | 435 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
Norepinephrine is often used as a first-line treatment for hypotensive septic shock because evidence shows that there is a relative deficiency of vasopressin when shock continues for 24 to 48 hours. Norepinephrine raises blood pressure through a vasoconstriction effect, with little effect on stroke volume and heart rat... | Sepsis | Wikipedia | 482 | 158400 | https://en.wikipedia.org/wiki/Sepsis | Biology and health sciences | Symptoms and signs | Health |
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