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where:
nA is the number density of A in the gas in units of m−3.
nB is the number density of B in the gas in units of m−3. E.g. for a gas mixture with gas A concentration 0.1 mol⋅L−1 and B concentration 0.2 mol⋅L−1, the number of density of A is 0.1×6.02×1023÷10−3 = 6.02×1025 m−3, the number of density of B is 0.2×6... | Collision theory | Wikipedia | 365 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
In collision theory it is considered that two particles A and B will collide if their nuclei get closer than a certain distance. The area around a molecule A in which it can collide with an approaching B molecule is called the cross section (σAB) of the reaction and is, in simplified terms, the area corresponding to a ... | Collision theory | Wikipedia | 439 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
where:
Z is the collision frequency with unit s−1⋅m−3. The z is Z without [A][B].
is the steric factor, which will be discussed in detail in the next section,
Ea is the activation energy (per mole) of the reaction in unit J/mol,
T is the absolute temperature in unit K,
R is the gas constant in unit J/mol/K.
[A] i... | Collision theory | Wikipedia | 509 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
Usually, the more complex the reactant molecules, the lower the steric factor. Nevertheless, some reactions exhibit steric factors greater than unity: the harpoon reactions, which involve atoms that exchange electrons, producing ions. The deviation from unity can have different causes: the molecules are not spherical, ... | Collision theory | Wikipedia | 320 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
{| class="wikitable"
|+ Experimental rate constants compared to the ones predicted by collision theory for reactions in solution
|-
! Reaction
! Solvent
! A, 1011 s−1⋅M−1
! Z, 1011 s−1⋅M−1
! Steric factor
|-
| C2H5Br + OH− || ethanol || 4.30 || 3.86 || 1.11
|-
| C2H5O− + CH3I || ethanol ||2.42 || 1.93 || 1.25
|-
| ClC... | Collision theory | Wikipedia | 411 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
For a diluted solution in the gas or the liquid phase, the collision equation developed for neat gas is not suitable when diffusion takes control of the collision frequency, i.e., the direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecu... | Collision theory | Wikipedia | 360 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
In 2022, Chen rationales that because the diffusive flux is evolving over time and the distance between the molecules has a finite value at a given concentration, there should be a critical time to cut off the evolution of the flux that will give a value much larger than the infinite solution Smoluchowski has proposed.... | Collision theory | Wikipedia | 285 | 1427763 | https://en.wikipedia.org/wiki/Collision%20theory | Physical sciences | Kinetics | Chemistry |
In biology, stolons (from Latin stolō, genitive stolōnis – "branch"), also known as runners, are horizontal connections between parts of an organism. They may be part of the organism, or of its skeleton. Typically, animal stolons are exoskeletons (external skeletons).
In botany
In botany, stolons are plant stems which... | Stolon | Wikipedia | 494 | 1430910 | https://en.wikipedia.org/wiki/Stolon | Biology and health sciences | Plant anatomy and morphology: General | Biology |
T. Holm (1929) restricted the term rhizome to a horizontal, usually subterranean, stem that produces roots from its lower surface and green leaves from its apex, developed directly from the plumule of the embryo. He recognized stolons as axillary, subterranean branches that do not bear green leaves but only membranaceo... | Stolon | Wikipedia | 490 | 1430910 | https://en.wikipedia.org/wiki/Stolon | Biology and health sciences | Plant anatomy and morphology: General | Biology |
An agrochemical or agrichemical, a contraction of agricultural chemical, is a chemical product used in industrial agriculture. Agrichemical typically refers to biocides (pesticides including insecticides, herbicides, fungicides and nematicides) alongside synthetic fertilizers. It may also include hormones and other che... | Agrochemical | Wikipedia | 457 | 1431156 | https://en.wikipedia.org/wiki/Agrochemical | Technology | Pest and disease control | null |
Many agrochemicals are toxic, and agrichemicals in bulk storage may pose significant environmental and/or health risks, particularly in the event of accidental spills. In many countries, use of agrichemicals is highly regulated. Government-issued permits for purchase and use of approved agrichemicals may be required. S... | Agrochemical | Wikipedia | 468 | 1431156 | https://en.wikipedia.org/wiki/Agrochemical | Technology | Pest and disease control | null |
In mathematics and mathematical physics, potential theory is the study of harmonic functions.
The term "potential theory" was coined in 19th-century physics when it was realized that two fundamental forces of nature known at the time, namely gravity and the electrostatic force, could be modeled using functions called ... | Potential theory | Wikipedia | 434 | 1431342 | https://en.wikipedia.org/wiki/Potential%20theory | Mathematics | Harmonic analysis | null |
As for symmetry in the usual sense of the term, we may start with the theorem that the symmetries of the -dimensional Laplace equation are exactly the conformal symmetries of the -dimensional Euclidean space. This fact has several implications. First of all, one can consider harmonic functions which transform under irr... | Potential theory | Wikipedia | 371 | 1431342 | https://en.wikipedia.org/wiki/Potential%20theory | Mathematics | Harmonic analysis | null |
Two dimensions
From the fact that the group of conformal transforms is infinite-dimensional in two dimensions and finite-dimensional for more than two dimensions, one can surmise that potential theory in two dimensions is different from potential theory in other dimensions. This is correct and, in fact, when one realiz... | Potential theory | Wikipedia | 474 | 1431342 | https://en.wikipedia.org/wiki/Potential%20theory | Mathematics | Harmonic analysis | null |
One important use of these inequalities is to prove convergence of families of harmonic functions or sub-harmonic functions, see Harnack's theorem. These convergence theorems are used to prove the existence of harmonic functions with particular properties.
Spaces of harmonic functions
Since the Laplace equation is li... | Potential theory | Wikipedia | 131 | 1431342 | https://en.wikipedia.org/wiki/Potential%20theory | Mathematics | Harmonic analysis | null |
A correlation coefficient is a numerical measure of some type of linear correlation, meaning a statistical relationship between two variables. The variables may be two columns of a given data set of observations, often called a sample, or two components of a multivariate random variable with a known distribution.
Seve... | Correlation coefficient | Wikipedia | 486 | 29018709 | https://en.wikipedia.org/wiki/Correlation%20coefficient | Mathematics | Probability | null |
The two variables were measured on a continuous scale, instead of as ordered-category variables.
The two continuous variables followed a bivariate normal distribution.
When both variables are dichotomous instead of ordered-categorical, the polychoric correlation coefficient is called the tetrachoric correlation coeff... | Correlation coefficient | Wikipedia | 108 | 29018709 | https://en.wikipedia.org/wiki/Correlation%20coefficient | Mathematics | Probability | null |
In algebraic geometry, a lemniscate ( or ) is any of several figure-eight or -shaped curves. The word comes from the Latin , meaning "decorated with ribbons", from the Greek (), meaning "ribbon", or which alternatively may refer to the wool from which the ribbons were made.
Curves that have been called a lemniscate i... | Lemniscate | Wikipedia | 484 | 5210590 | https://en.wikipedia.org/wiki/Lemniscate | Mathematics | Two-dimensional space | null |
In 1694, Johann Bernoulli studied the lemniscate case of the Cassini oval, now known as the lemniscate of Bernoulli (shown above), in connection with a problem of "isochrones" that had been posed earlier by Leibniz. Like the hippopede, it is an algebraic curve, the zero set of the polynomial . Bernoulli's brother Jacob... | Lemniscate | Wikipedia | 414 | 5210590 | https://en.wikipedia.org/wiki/Lemniscate | Mathematics | Two-dimensional space | null |
Clothes moth or clothing moth is the common name for several species of moth considered to be pests, whose larvae eat animal fibres (hairs), including clothing and other fabrics.
These include:
Tineola bisselliella, the common clothes moth or webbing clothes moth
Tinea pellionella, the case-bearing clothes moth. Obs... | Clothes moth | Wikipedia | 490 | 5217516 | https://en.wikipedia.org/wiki/Clothes%20moth | Biology and health sciences | Lepidoptera | Animals |
To control an infestation, all items from the area should be removed and cleaned by using a strong-suctioned vacuum, or soapy water and a washing machine to launder items in hot water for 20–30 minutes to kill eggs.
Among other methods, recommendations to protect heritage collections of textiles include checking the u... | Clothes moth | Wikipedia | 134 | 5217516 | https://en.wikipedia.org/wiki/Clothes%20moth | Biology and health sciences | Lepidoptera | Animals |
Optical computing or photonic computing uses light waves produced by lasers or incoherent sources for data processing, data storage or data communication for computing. For decades, photons have shown promise to enable a higher bandwidth than the electrons used in conventional computers (see optical fibers).
Most rese... | Optical computing | Wikipedia | 440 | 2878626 | https://en.wikipedia.org/wiki/Optical%20computing | Technology | Computer architecture concepts | null |
Controversy
There are some disagreements between researchers about the future capabilities of optical computers; whether or not they may be able to compete with semiconductor-based electronic computers in terms of speed, power consumption, cost, and size is an open question. Critics note that real-world logic systems r... | Optical computing | Wikipedia | 510 | 2878626 | https://en.wikipedia.org/wiki/Optical%20computing | Technology | Computer architecture concepts | null |
Time delays optical computing
The basic idea is to delay light (or any other signal) in order to perform useful computations. Of interest would be to solve NP-complete problems as those are difficult problems for the conventional computers.
There are two basic properties of light that are actually used in this approa... | Optical computing | Wikipedia | 331 | 2878626 | https://en.wikipedia.org/wiki/Optical%20computing | Technology | Computer architecture concepts | null |
The light will enter in Start node. It will be divided into two (sub)rays of smaller intensity. These two rays will arrive into the second node at moments a1 and 0. Each of them will be divided into two subrays which
will arrive in the third node at moments 0, a1, a2 and a1 + a2. These represents the all subsets of the... | Optical computing | Wikipedia | 506 | 2878626 | https://en.wikipedia.org/wiki/Optical%20computing | Technology | Computer architecture concepts | null |
The travelling salesman problem has been solved by Shaked et al. (2007) by using an optical approach. All possible TSP paths have been generated and stored in a binary matrix which was multiplied with another gray-scale vector containing the distances between cities. The multiplication is performed optically by using a... | Optical computing | Wikipedia | 378 | 2878626 | https://en.wikipedia.org/wiki/Optical%20computing | Technology | Computer architecture concepts | null |
The Hass avocado is a variety of avocado with dark green, bumpy skin. It was first grown and sold by Southern California mail carrier and amateur horticulturist Rudolph Hass, who also gave it his name.
The Hass avocado is a large-sized fruit weighing 200 to 300 grams (7 to 10 oz). When ripe, the skin becomes a dark pu... | Hass avocado | Wikipedia | 323 | 2882046 | https://en.wikipedia.org/wiki/Hass%20avocado | Biology and health sciences | Other culinary fruits | Plants |
In 1926, at his 1.5-acre grove at 430 West Road, La Habra Heights, California, Hass planted three seeds he had bought from Rideout, which yielded one strong seedling. After trying and failing at least twice to graft the seedling with branches from Fuerte avocado trees (the leading commercial cultivar at the time), Hass... | Hass avocado | Wikipedia | 371 | 2882046 | https://en.wikipedia.org/wiki/Hass%20avocado | Biology and health sciences | Other culinary fruits | Plants |
The mother tree
Owing to later suburban sprawl in Southern California, the mother tree stood for many years in front of a residence in La Habra Heights. The tree died when it was 76 years old and was cut down on 11 September 2002 after a ten-year fight with phytophthora (root rot), which often kills avocado trees. Two... | Hass avocado | Wikipedia | 470 | 2882046 | https://en.wikipedia.org/wiki/Hass%20avocado | Biology and health sciences | Other culinary fruits | Plants |
Avocados have diverse fats. For a typical avocado:
About 75% of an avocado's energy comes from fat, most of which (67% of total fat) is monounsaturated fat as oleic acid.
Other predominant fats include palmitic acid and linoleic acid.
The saturated fat content amounts to 14% of the total fat.
Typical total fat comp... | Hass avocado | Wikipedia | 128 | 2882046 | https://en.wikipedia.org/wiki/Hass%20avocado | Biology and health sciences | Other culinary fruits | Plants |
Planetary boundaries are a framework to describe limits to the impacts of human activities on the Earth system. Beyond these limits, the environment may not be able to self-regulate anymore. This would mean the Earth system would leave the period of stability of the Holocene, in which human society developed. The frame... | Planetary boundaries | Wikipedia | 372 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
In 2015, several of the scientists in the original group published an update, bringing in new co-authors and new model-based analysis. According to this update, four of the boundaries were crossed: climate change, loss of biosphere integrity, land-system change, altered biogeochemical cycles (phosphorus and nitrogen). ... | Planetary boundaries | Wikipedia | 481 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
The scientists outlined how breaching the boundaries increases the threat of functional disruption, even collapse, in Earth's biophysical systems in ways that could be catastrophic for human wellbeing. While they highlighted scientific uncertainty, they indicated that breaching boundaries could "trigger feedbacks that ... | Planetary boundaries | Wikipedia | 371 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
climate change (CO2 concentration in the atmosphere < 350 ppm and/or a maximum change of +1 W/m2 in radiative forcing);
ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels);
stratospheric ozone depletion (less than 5% reduction in total atmospheric O3 f... | Planetary boundaries | Wikipedia | 472 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
For several of the processes in the planetary boundaries framework, it is difficult to locate individual points that mark the threshold shift away from Holocene-like conditions. This is because the Earth system is complex and the scientific evidence base is still partial and fragmented. Instead, the planetary boundarie... | Planetary boundaries | Wikipedia | 338 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
There are many many interactions among the processes in the planetary boundaries framework. While these interactions can create both stabilizing and destabilizing feedbacks in the Earth system, the authors suggested that a transgressed planetary boundary will reduce the safe operating space for other processes in the f... | Planetary boundaries | Wikipedia | 440 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
In 2015, a second paper was published in Science to update the Planetary Boundaries concept. The update concluded four boundaries had now been transgressed: climate, biodiversity, land use and biogeochemical cycles. The 2015 paper emphasized interactions of the nine boundaries and identified climate change and loss of ... | Planetary boundaries | Wikipedia | 465 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
The ocean chemist Peter Brewer queries whether it is "truly useful to create a list of environmental limits without serious plans for how they may be achieved ... they may become just another stick to beat citizens with. Disruption of the global nitrogen cycle is one clear example: it is likely that a large fraction of... | Planetary boundaries | Wikipedia | 462 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
Freshwater
The freshwater cycle is another boundary significantly affected by climate change. Overexploitation of freshwater occurs if a water resource is mined or extracted at a rate that exceeds the recharge rate. Water pollution and saltwater intrusion can also turn much of the world's underground water and lakes i... | Planetary boundaries | Wikipedia | 503 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
A Bayesian emulator for persistent organic pollutants has been developed which can potentially be used to quantify the boundaries for chemical pollution. To date, critical exposure levels of polychlorinated biphenyls (PCBs) above which mass mortality events of marine mammals are likely to occur, have been proposed as a... | Planetary boundaries | Wikipedia | 491 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
The "Limits to Growth" (1972) and Gaia theory
The idea that there are limits to the burden placed upon our planet by human activities has been around for a long time. The Planetary Boundaries framework acknowledges the influence of the 1972 study, The Limits to Growth, that presented a model in which exponential growt... | Planetary boundaries | Wikipedia | 329 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
Another key idea influencing the Planetary Boundaries framework is the Gaia theory or hypothesis. In the 1970s, James Lovelock and microbiologist Lynn Margulis presented the idea that all organisms and their inorganic surroundings on Earth are integrated into a single self-regulating system. The system has the ability ... | Planetary boundaries | Wikipedia | 453 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
Various biophysical processes that are important in maintaining the resilience of the Earth system are also undergoing large and rapid change because of human actions. For example, since the advent of the Anthropocene, the rate at which species are going extinct has increased over 100 times, and humans are now the driv... | Planetary boundaries | Wikipedia | 506 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
Boundaries related to agriculture and food consumption
Human activities related to agriculture and nutrition globally contribute to the transgression of four out of nine planetary boundaries. Surplus nutrient flows (N, P) into aquatic and terrestrial ecosystems are of highest importance, followed by excessive land-sy... | Planetary boundaries | Wikipedia | 468 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
In 2011, at their second meeting, the High-level Panel on Global Sustainability of the United Nations had incorporated the concept of planetary boundaries into their framework, stating that their goal was: "To eradicate poverty and reduce inequality, make growth inclusive, and production and consumption more sustainabl... | Planetary boundaries | Wikipedia | 396 | 24458151 | https://en.wikipedia.org/wiki/Planetary%20boundaries | Physical sciences | Earth science basics: General | Earth science |
A hazard is a potential source of harm. Substances, events, or circumstances can constitute hazards when their nature would potentially allow them to cause damage to health, life, property, or any other interest of value. The probability of that harm being realized in a specific incident, combined with the magnitude of... | Hazard | Wikipedia | 504 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
In defining hazard Keith Smith argues that what may be defined as the hazard is only a hazard if there is the presence of humans to make it a hazard. In this regard, human sensitivity to environmental hazards is a combination of both physical exposure (natural and/or technological events at a location related to their ... | Hazard | Wikipedia | 511 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
Risk and vulnerability
The terms hazard and risk are often used interchangeably. However, in terms of risk assessment, these are two very distinct terms. A hazard is an agent that can cause harm or damage to humans, property, or the environment. Risk is the probability that exposure to a hazard will lead to a negativ... | Hazard | Wikipedia | 463 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
Hazards may be grouped according to their characteristics. These factors are related to geophysical events, which are not process specific:
Areal extent of damage zone
Intensity of impact at a point
Duration of impact at a point
Rate of onset of the event
Predictability of the event
By causing actor
Natural haza... | Hazard | Wikipedia | 506 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
Anthropogenic hazard
Anthropogenic hazards, or human-induced hazards, are "induced entirely or predominantly by human activities and choices". These can be societal, technological or environmental hazards.
Technological hazard
Technological hazards are created by the possibility of failure associated with human tech... | Hazard | Wikipedia | 421 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
Waste disposal
In managing waste many hazardous materials are put in the domestic and commercial waste stream. In part this is because modern technological living uses certain toxic or poisonous materials in the electronics and chemical industries. Which, when they are in use or transported, are usually safely contain... | Hazard | Wikipedia | 502 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
Biological hazards include pathogenic microorganisms, such as viruses and bacteria, epidemics, pandemics, parasites, pests, animal attacks, venomous animals, biological toxins and foodborne illnesses.
For example, naturally occurring bacteria such as Escherichia coli and Salmonella are well known pathogens, and a var... | Hazard | Wikipedia | 491 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
A variety of chemical hazards have been identified. However, every year companies produce more new chemicals to fill new needs or to take the place of older, less effective chemicals. Laws, such as the Federal Food, Drug, and Cosmetic Act and the Toxic Substances Control Act in the US, require protection of human healt... | Hazard | Wikipedia | 496 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
Casualties resulting from fires, regardless of their source or initial cause, can be aggravated by inadequate emergency preparedness. Such hazards as a lack of accessible emergency exits, poorly marked escape routes, or improperly maintained fire extinguishers or sprinkler systems may result in many more deaths and inj... | Hazard | Wikipedia | 450 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
By status
Hazards are sometimes classified into three modes or statuses:
Dormant—The situation environment is currently affected. For instance, a hillside may be unstable, with the potential for a landslide, but there is nothing below or on the hillside that could be affected.
Armed—People, property, or environment ... | Hazard | Wikipedia | 134 | 24462957 | https://en.wikipedia.org/wiki/Hazard | Biology and health sciences | Health and fitness: General | Health |
A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The heavy water coolant is kept under pressure to avoid boiling, allowing it to... | Pressurized heavy-water reactor | Wikipedia | 449 | 33087778 | https://en.wikipedia.org/wiki/Pressurized%20heavy-water%20reactor | Technology | Power generation | null |
The trick to achieving criticality using only natural or low enriched uranium, for which there is no "bare" critical mass, is to slow down the emitted neutrons (without absorbing them) to the point where enough of them may cause further nuclear fission in the small amount of 235U which is available. (238U which is the ... | Pressurized heavy-water reactor | Wikipedia | 416 | 33087778 | https://en.wikipedia.org/wiki/Pressurized%20heavy-water%20reactor | Technology | Power generation | null |
One complication of this approach is the need for uranium enrichment facilities, which are generally expensive to build and operate. They also present a nuclear proliferation concern; the same systems used to enrich the 235U can also be used to produce much more "pure" weapons-grade material (90% or more 235U), suitabl... | Pressurized heavy-water reactor | Wikipedia | 495 | 33087778 | https://en.wikipedia.org/wiki/Pressurized%20heavy-water%20reactor | Technology | Power generation | null |
Disadvantages
Pressurised heavy-water reactors do have some drawbacks. Heavy water generally costs hundreds of dollars per kilogram, though this is a trade-off against reduced fuel costs. The reduced energy content of natural uranium as compared to enriched uranium necessitates more frequent replacement of fuel; this i... | Pressurized heavy-water reactor | Wikipedia | 306 | 33087778 | https://en.wikipedia.org/wiki/Pressurized%20heavy-water%20reactor | Technology | Power generation | null |
Nuclear proliferation
While prior to India's development of nuclear weapons (see below), the ability to use natural uranium (and thus forego the need for uranium enrichment which is a dual use technology) was seen as hindering nuclear proliferation, this opinion has changed drastically in light of the ability of severa... | Pressurized heavy-water reactor | Wikipedia | 499 | 33087778 | https://en.wikipedia.org/wiki/Pressurized%20heavy-water%20reactor | Technology | Power generation | null |
The proliferation risk of heavy-water reactors was demonstrated when India produced the plutonium for Operation Smiling Buddha, its first nuclear weapon test, by extraction from the spent fuel of a heavy-water research reactor known as the CIRUS reactor. | Pressurized heavy-water reactor | Wikipedia | 47 | 33087778 | https://en.wikipedia.org/wiki/Pressurized%20heavy-water%20reactor | Technology | Power generation | null |
Cirrostratus nebulosus is a type of high-level cirrostratus cloud. The name cirrostratus nebulosus is derived from Latin, the adjective nebulosus meaning "full of vapor, foggy, cloudy, dark". Cirrostratus nebulosus is one of the two most common forms that cirrostratus often takes, with the other being cirrostratus fibr... | Cirrostratus nebulosus | Wikipedia | 205 | 33092462 | https://en.wikipedia.org/wiki/Cirrostratus%20nebulosus | Physical sciences | Clouds | Earth science |
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of transmission may be divided into communication channels for multiplexing, allo... | Telecommunications | Wikipedia | 484 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Telecommunication is a compound noun of the Greek prefix tele- (τῆλε), meaning distant, far off, or afar, and the Latin verb communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was fir... | Telecommunications | Wikipedia | 508 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Besides beacons and pigeons, long-distance communication used sounds like coded drumbeats, the blowing of horns, and whistles.
Telegraph and telephone
On July 25, 1837, the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke and English scientist Sir Charles Wheatst... | Telecommunications | Wikipedia | 430 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated the development of radio for the wartime purposes of aircraft and land communica... | Telecommunications | Wikipedia | 471 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
In the 1940s, the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, cheaper, and more efficient, reliable, and durable than thermionic tubes. Starting in the mid-1960s, thermionic tubes were replaced with the transistor. Thermionic tubes still have some applications ... | Telecommunications | Wikipedia | 473 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Basic elements
Telecommunication technologies may primarily be divided into wired and wireless methods. Overall, a basic telecommunication system consists of three main parts that are always present in some form or another:
A transmitter that takes information and converts it to a signal
A transmission medium, also ... | Telecommunications | Wikipedia | 428 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Analogue versus digital communications
Communications can be encoded as analogue or digital signals, which may in turn be carried by analogue or digital communication systems. Analogue signals vary continuously with respect to the information, while digital signals encode information as a set of discrete values (e.g.,... | Telecommunications | Wikipedia | 442 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
The other meaning of the term channel in telecommunications is seen in the phrase communications channel, which is a subdivision of a transmission medium so that it can be used to send multiple streams of information simultaneously. For example, one radio station can broadcast radio waves into free space at frequencies... | Telecommunications | Wikipedia | 366 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
The shaping of a signal to convey information is known as modulation. Modulation can be used to represent a digital message as an analogue waveform. This is commonly called "keying"—a term derived from the older use of Morse Code in telecommunications—and several keying techniques exist (these include phase-shift keyin... | Telecommunications | Wikipedia | 463 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Societal impact
Telecommunication has a significant social, cultural and economic impact on modern society. In 2008, estimates placed the telecommunication industry's revenue at US$4.7 trillion or just under three per cent of the gross world product (official exchange rate). Several following sections discuss the impa... | Telecommunications | Wikipedia | 445 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Social impact
Telecommunication has played a significant role in social relationships. Nevertheless, devices like the telephone system were originally advertised with an emphasis on the practical dimensions of the device (such as the ability to conduct business or order home services) as opposed to the social dimensio... | Telecommunications | Wikipedia | 422 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Many countries have enacted legislation which conforms to the International Telecommunication Regulations established by the International Telecommunication Union (ITU), which is the "leading UN agency for information and communication technology issues". In 1947, at the Atlantic City Conference, the ITU decided to "af... | Telecommunications | Wikipedia | 435 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
, the landline telephones in most residential homes are analogue—that is, the speaker's voice directly determines the signal's voltage. Although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting the signals to digital signals f... | Telecommunications | Wikipedia | 449 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Assisting communication across many modern optical fibre networks is a protocol known as Asynchronous Transfer Mode (ATM). The ATM protocol allows for the side-by-side data transmission mentioned in the second paragraph. It is suitable for public telephone networks because it establishes a pathway for data through the ... | Telecommunications | Wikipedia | 303 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
The broadcast media industry is at a critical turning point in its development, with many countries moving from analogue to digital broadcasts. This move is made possible by the production of cheaper, faster and more capable integrated circuits. The chief advantage of digital broadcasts is that they prevent a number of... | Telecommunications | Wikipedia | 479 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
However, despite the pending switch to digital, analog television remains being transmitted in most countries. An exception is the United States that ended analog television transmission (by all but the very low-power TV stations) on 12 June 2009 after twice delaying the switchover deadline. Kenya also ended analog tel... | Telecommunications | Wikipedia | 455 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
The Internet works in part because of protocols that govern how the computers and routers communicate with each other. The nature of computer network communication lends itself to a layered approach where individual protocols in the protocol stack run more-or-less independently of other protocols. This allows lower-lev... | Telecommunications | Wikipedia | 362 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
At the transport layer, most communication adopts either the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP). TCP is used when it is essential every message sent is received by the other computer whereas UDP is used when it is merely desirable. With TCP, packets are retransmitted if they are los... | Telecommunications | Wikipedia | 476 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Local area networks and wide area networks
Despite the growth of the Internet, the characteristics of local area networks (LANs)—computer networks that do not extend beyond a few kilometres—remain distinct. This is because networks on this scale do not require all the features associated with larger networks and are o... | Telecommunications | Wikipedia | 444 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
Despite the modest popularity of Token Ring in the 1980s and 1990s, virtually all LANs now use either wired or wireless Ethernet facilities. At the physical layer, most wired Ethernet implementations use copper twisted-pair cables (including the common 10BASE-T networks). However, some early implementations used heavie... | Telecommunications | Wikipedia | 146 | 33094374 | https://en.wikipedia.org/wiki/Telecommunications | Technology | Media and communication | null |
A sungrazing comet is a comet that passes extremely close to the Sun at perihelion – sometimes within a few thousand kilometres of the Sun's surface. Although small sungrazers can completely evaporate during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong ev... | Sungrazing comet | Wikipedia | 440 | 930437 | https://en.wikipedia.org/wiki/Sungrazing%20comet | Physical sciences | Planetary science | Astronomy |
Pre-19th century
One of the first comets to have its orbit computed was the sungrazing comet (and Great Comet) of 1680, now designated C/1680 V1. It was observed by Isaac Newton and he published the orbit results in 1687. Later, in 1699, Jacques Cassini proposed that comets could have relatively short orbital periods... | Sungrazing comet | Wikipedia | 471 | 930437 | https://en.wikipedia.org/wiki/Sungrazing%20comet | Physical sciences | Planetary science | Astronomy |
In an attempt to link the 1843 and 1880 comets to the comet in 1106 and 371 BC, Kreutz measured the fragments of the 1882 comet and determined that it was likely a fragment of the 1106 comet. He then designated that all sungrazing comets with similar orbital characteristics as these few comets would be part of the Kre... | Sungrazing comet | Wikipedia | 423 | 930437 | https://en.wikipedia.org/wiki/Sungrazing%20comet | Physical sciences | Planetary science | Astronomy |
In 1987 and 1988 it was first observed by SMM that there could be pairs of sungrazing comets that can appear within very short time periods ranging from a half of a day up to about two weeks. Calculations were made to determine that the pairs were part of the same parent body but broke apart at tens of AU from the Sun.... | Sungrazing comet | Wikipedia | 493 | 930437 | https://en.wikipedia.org/wiki/Sungrazing%20comet | Physical sciences | Planetary science | Astronomy |
Apart from Comet Lovejoy, none of the sungrazers seen by SOHO has survived its perihelion passage; some may have plunged into the Sun itself, but most are likely to have simply evaporated away completely.
Other sungrazers
About 83% of the sungrazers observed with SOHO are members of the Kreutz group. The other 17% ... | Sungrazing comet | Wikipedia | 413 | 930437 | https://en.wikipedia.org/wiki/Sungrazing%20comet | Physical sciences | Planetary science | Astronomy |
Tropical rainforests are dense and warm rainforests with high rainfall typically found between 10° north and south of the Equator. They are a subset of the tropical forest biome that occurs roughly within the 28° latitudes (in the torrid zone between the Tropic of Cancer and Tropic of Capricorn). Tropical rainforests a... | Tropical rainforest | Wikipedia | 496 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Tropical rainforests are hot and wet. Mean monthly temperatures exceed during all months of the year. Average annual rainfall is no less than and can exceed although it typically lies between and . This high level of precipitation often results in poor soils due to leaching of soluble nutrients in the ground.
Trop... | Tropical rainforest | Wikipedia | 467 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Moist seasonal tropical forests receive high overall rainfall with a warm summer wet season and a cooler winter dry season. These forests usually fall under tropical monsoon or tropical savanna climates. Some trees in these forests drop some or all of their leaves during the winter dry season, thus they are sometimes c... | Tropical rainforest | Wikipedia | 446 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
The understory layer lies between the canopy and the forest floor. The understory is home to a number of birds, small mammals, insects, reptiles, and predators. Examples include leopard (Panthera pardus), poison dart frogs (Dendrobates sp.), ring-tailed coati (Nasua nasua), boa constrictor (Boa constrictor), and many s... | Tropical rainforest | Wikipedia | 509 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
The emergent layer contains a small number of very large trees, called emergents, which grow above the general canopy, reaching heights of 45–55m, although on occasion a few species will grow to 70–80m tall. Some examples of emergents include: Hydrochorea elegans, Dipteryx panamensis, Hieronyma alchorneoides, Hymenolob... | Tropical rainforest | Wikipedia | 492 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Soil types
Soil types are highly variable in the tropics and are the result of a combination of several variables such as climate, vegetation, topographic position, parent material, and soil age. Most tropical soils are characterized by significant leaching and poor nutrients, however there are some areas that contain... | Tropical rainforest | Wikipedia | 473 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
This high rate of decomposition is the result of phosphorus levels in the soils, precipitation, high temperatures and the extensive microorganism communities. In addition to the bacteria and other microorganisms, there are an abundance of other decomposers such as fungi and termites that aid in the process as well. Nut... | Tropical rainforest | Wikipedia | 503 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Forest succession
Succession is an ecological process that changes the biotic community structure over time towards a more stable, diverse community structure after an initial disturbance to the community. The initial disturbance is often a natural phenomenon or human caused event. Natural disturbances include hurrica... | Tropical rainforest | Wikipedia | 489 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Tropical rainforests have harboured human life for many millennia, with many Indigenous people in South and Central America, who belong to the Indigenous peoples of the Americas, the Congo Pygmies in Central Africa, and several tribes in Southeast Asia, like the Dayak people and the Penan people in Borneo. Food resourc... | Tropical rainforest | Wikipedia | 485 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Some notable indigenous peoples of the Americas, or Amerindians, include the Huaorani, Ya̧nomamö, and Kayapo people of the Amazon. The traditional agricultural system practiced by tribes in the Amazon is based on swidden cultivation (also known as slash-and-burn or shifting cultivation) and is considered a relatively b... | Tropical rainforest | Wikipedia | 396 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
In addition to extractive human uses, rain forests also have non-extractive uses that are frequently summarized as ecosystem services. Rain forests play an important role in maintaining biological diversity, sequestering and storing carbon, global climate regulation, disease control, and pollination. Half of the rainfa... | Tropical rainforest | Wikipedia | 484 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Deposits of precious metals (gold, silver, coltan) and fossil fuels (oil and natural gas) occur underneath rainforests globally. These resources are important to developing nations and their extraction is often given priority to encourage economic growth. Mining and drilling can require large amounts of land developmen... | Tropical rainforest | Wikipedia | 451 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
Declining populations
Some species of fauna show a trend towards declining populations in rainforests, for example, reptiles that feed on amphibians and reptiles. This trend requires close monitoring. The seasonality of rainforests affects the reproductive patterns of amphibians, and this in turn can directly affect t... | Tropical rainforest | Wikipedia | 157 | 931370 | https://en.wikipedia.org/wiki/Tropical%20rainforest | Physical sciences | Forests | null |
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