Vacuum is space devoid of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists discuss ideal test results that would occur in a perfect vacuum, which they sometimes call "vacuum" or free space, use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure; the Latin term in vacuo is used to describe an object, surrounded by a vacuum. The quality of a partial vacuum refers to how it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Much higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry and engineering, operate below one trillionth of atmospheric pressure, can reach around 100 particles/cm3.
Outer space is an higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. According to modern understanding if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays and other phenomena in quantum physics. In the study of electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of a field. Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, inverting it in a bowl to contain the mercury.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, on life forms in general; the word vacuum comes from Latin, meaning'an empty space, void', noun use of neuter of vacuus, meaning "empty", related to vacare, meaning "be empty". Vacuum is one of the few words in the English language that contains two consecutive letters'u'. There has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite nothing at all, which cannot rightly be said to exist.
Aristotle believed that no void could occur because the denser surrounding material continuum would fill any incipient rarity that might give rise to a void. In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD, it was European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century who focused considerable attention on these issues. Following Stoic physics in this instance, scholars from the 14th century onward departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion acknowledged by the 17th century, which helped to segregate natural and theological concerns.
Two thousand years after Plato, René Descartes proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. In the medieval Middle Eastern world, the physicist and Islamic scholar, Al-Farabi, conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water, he concluded that air's volume can expand to fill available space, he suggested that the concept of perfect vacuum was incoherent. However, according to Nader El-Bizri, the physicist Ibn al-Haytham and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, they supported the existence of a void.
Using geometry, Ibn al-Haytham mathematically demonstrated that place is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī states that "there is no observable
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
Earthquake prediction is a branch of the science of seismology concerned with the specification of the time and magnitude of future earthquakes within stated limits, "the determination of parameters for the next strong earthquake to occur in a region. Earthquake prediction is sometimes distinguished from earthquake forecasting, which can be defined as the probabilistic assessment of general earthquake hazard, including the frequency and magnitude of damaging earthquakes in a given area over years or decades. Prediction can be further distinguished from earthquake warning systems, which upon detection of an earthquake, provide a real-time warning of seconds to neighboring regions that might be affected. In the 1970s, scientists were optimistic that a practical method for predicting earthquakes would soon be found, but by the 1990s continuing failure led many to question whether it was possible. Demonstrably successful predictions of large earthquakes have not occurred and the few claims of success are controversial.
For example, the most famous claim of a successful prediction is that alleged for the 1975 Haicheng earthquake. A study said that there was no valid short-term prediction. Extensive searches have reported many possible earthquake precursors, but, so far, such precursors have not been reliably identified across significant spatial and temporal scales. While part of the scientific community hold that, taking into account non-seismic precursors and given enough resources to study them extensively, prediction might be possible, most scientists are pessimistic and some maintain that earthquake prediction is inherently impossible. Predictions are deemed significant. Therefore, methods of statistical hypothesis testing are used to determine the probability that an earthquake such as is predicted would happen anyway; the predictions are evaluated by testing whether they correlate with actual earthquakes better than the null hypothesis. In many instances, the statistical nature of earthquake occurrence is not homogeneous.
Clustering occurs in both time. In southern California about 6% of M≥3.0 earthquakes are "followed by an earthquake of larger magnitude within 5 days and 10 km." In central Italy 9.5 % of M ≥ 3.0 earthquakes are followed by a larger event within 30 km. While such statistics are not satisfactory for purposes of prediction they will skew the results of any analysis that assumes that earthquakes occur randomly in time, for example, as realized from a Poisson process, it has been shown that a "naive" method based on clustering can predict about 5% of earthquakes. As the purpose of short-term prediction is to enable emergency measures to reduce death and destruction, failure to give warning of a major earthquake, that does occur, or at least an adequate evaluation of the hazard, can result in legal liability, or political purging. For example, it has been reported that members of the Chinese Academy of Sciences were purged for "having ignored scientific predictions of the disastrous Tangshan earthquake of summer 1976."
Wade 1977. Following the L'Aquila earthquake of 2009, seven scientists and technicians in Italy were convicted of manslaughter, but not so much for failing to predict the 2009 L'Aquila Earthquake as for giving undue assurance to the populace – one victim called it "anaesthetizing" – that there would not be a serious earthquake, therefore no need to take precautions, but warning of an earthquake that does not occur incurs a cost: not only the cost of the emergency measures themselves, but of civil and economic disruption. False alarms, including alarms that are canceled undermine the credibility, thereby the effectiveness, of future warnings. In 1999 it was reported that China was introducing "tough regulations intended to stamp out ‘false’ earthquake warnings, in order to prevent panic and mass evacuation of cities triggered by forecasts of major tremors." This was prompted by "more than 30 unofficial earthquake warnings... in the past three years, none of, accurate." The acceptable trade-off between missed quakes and false alarms depends on the societal valuation of these outcomes.
The rate of occurrence of both must be considered. In a 1997 study of the cost-benefit ratio of earthquake prediction research in Greece, Stathis Stiros suggested that a excellent prediction method would be of questionable social utility, because "organized evacuation of urban centers is unlikely to be accomplished", while "panic and other undesirable side-effects can be anticipated." He found that earthquakes kill less than ten people per year in Greece, that most of those fatalities occurred in large buildings with identifiable structural issues. Therefore, Stiros stated that it would be much more cost-effective to focus efforts on identifying and upgrading unsafe buildings. Since the death toll on Greek highways is more than 2300 per year on average, he argued that more lives would be saved if Greece's entire budget for earthquake prediction had been used for street and highway safety instead. Earthquake prediction is an immature science—it has not yet led to a successful prediction of an earthquake from first physical principles.
Research into methods of prediction therefore focus on empirical analysis, with two general approaches: either identifying distinctive precursors to earthquakes, or identifying some kind of geophysical trend or pattern in seismicity that might precede a large earthquake. Precursor methods are pursu
Fault mechanics is a field of study that investigates the behavior of geologic faults. Behind every good earthquake is some weak rock. Whether the rock remains weak becomes an important point in determining the potential for bigger earthquakes. On a small scale, fractured rock behaves the same throughout the world, in that the angle of friction is more or less uniform. A small element of rock in a larger mass responds to stress changes in a well defined manner: if it is squeezed by differential stresses greater than its strength, it is capable of large deformations. A band of weak, fractured rock in a competent mass can deform to resemble a classic geologic fault. Using seismometers and earthquake location, the requisite pattern of micro-earthquakes can be observed. For earthquakes, it all starts with an embedded penny-shaped crack as first envisioned by Brune; as illustrated, an earthquake zone may start as a single crack, growing to form many individual cracks and collections of cracks along a fault.
The key to fault growth is the concept of a "following force", as conveniently provided for interplate earthquakes, by the motion of tectonic plates. Under a following force, the seismic displacements form a topographic feature, such as a mountain range. Intraplate earthquakes do not have a following force, are not associated with mountain building. Thus, there is the puzzling question of. For, in a solid stressed plate, every seismic displacement acts to relieve stress. One can see this type of arching "lockup" in many natural processes. In fact, the seismic zone is ensured eternal life by the action of water; as shown, if we add the equivalent of a giant funnel to the crack, it becomes the beneficiary of stress corrosion. If there is a continuing supply of new water, the system does not come to equilibrium, but continues to grow relieving stress from a larger and larger volume, thus the prerequisite for a continuing seismically active interior zone is the presence of water, the ability of the water to get down to the fault source, the usual high horizontal interior stresses of the rock mass.
All small earthquake zones have the potential to grow to resemble New Charlevoix. Active fault – A geological fault to be the source of an earthquake sometime in the future Orogeny – The formation of mountain ranges James N. Brune, Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res. 75:4997-5009, 1970. Review written in 1987. Http://www.garfield.library.upenn.edu/classics1987/A1987J040600001.pdf retrieved Aug. 01, 2005 Arches National Park, http://www.exploratorium.edu/ronh/adventure/arches.html retrieved Aug. 01,2005 Stress Corrosion Cracking of Rock in a Chemical Environment, https://web.archive.org/web/20051217222420/http://www.nire.go.jp/annual/1998/28.htm retrieved Dec. 9, 2005 Maurice Lamontagne, last modified 2003-12-22, The Charlevoix-Kamouraska* Seismic Zone, Canada - Natural Resources, https://web.archive.org/web/20050308030140/http://www.seismo.nrcan.gc.ca/historic_eq/charpage_e.php Retrieved Aug. 01,2005
Cold welding or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint. Cold welding was first recognized as a general materials phenomenon in the 1940s, it was discovered that two clean, flat surfaces of similar metal would adhere if brought into contact under vacuum. Newly discovered micro- and nano-scale cold welding has shown great potential in the latest nanofabrication processes; the reason for this unexpected behavior is that when the atoms in contact are all of the same kind, there is no way for the atoms to “know” that they are in different pieces of copper. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the atoms “know” when they are not on the same part. Applications include electrical connections. Mechanical problems in early satellites were sometimes attributed to cold welding.
In 2009 the European Space Agency published a peer reviewed paper detailing why cold welding is a significant issue that spacecraft designers need to consider. The paper cites a documented example from 1991 with the Galileo spacecraft high-gain antenna. One source of difficulty is that cold welding does not exclude relative motion between the surfaces that are to be joined; this allows the broadly defined notions of galling, sticking and adhesion to overlap in some instances. For example, it is galling. Galling and cold welding, are not mutually exclusive. Unlike cold welding process at macro-scale which requires large applied pressures, scientists discovered that single-crystalline ultrathin gold nanowires can be cold-welded together within seconds by mechanical contact alone, under remarkably low applied pressures. High-resolution transmission electron microscopy and in-situ measurements reveal that the welds are nearly perfect, with the same crystal orientation and electrical conductivity as the rest of the nanowire.
The high quality of the welds is attributed to the nanoscale sample dimensions, oriented-attachment mechanisms and mechanically assisted fast surface diffusion. Nanoscale welds were demonstrated between gold and silver, silver and silver, indicating that the phenomenon may be applicable and therefore offer an atomistic view of the initial stages of macroscopic cold welding for either bulk metals or metallic thin film. Abutment Gauge block Molecular attraction Nanoimprint lithography Tribology Vacuum cementing Optical contact bonding Sinha, K.. D.. F. J.. J.. "Influence of fabrication parameters on bond strength of adhesively bonded flip-chip interconnects". Journal of Adhesion Science and Technology. 28: 1167–1191. Doi:10.1080/01694243.2014.891349. Kalpakjian. Manufacturing Engineering and Technology. Prentice Hall. P. 981. ISBN 978-0-13-148965-3
Water is a transparent, tasteless and nearly colorless chemical substance, the main constituent of Earth's streams and oceans, the fluids of most living organisms. It is vital for all known forms of life though it provides no calories or organic nutrients, its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient pressure, it forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of its solid state; when finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is water vapor. Water moves continually through the water cycle of evaporation, condensation and runoff reaching the sea. Water covers 71% of the Earth's surface in seas and oceans. Small portions of water occur as groundwater, in the glaciers and the ice caps of Antarctica and Greenland, in the air as vapor and precipitation.
Water plays an important role in the world economy. 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a major source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers and canals. Large quantities of water and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of chemical substances. Water is central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, sport fishing, diving; the word water comes from Old English wæter, from Proto-Germanic *watar, from Proto-Indo-European *wod-or, suffixed form of root *wed-. Cognate, through the Indo-European root, with Greek ύδωρ, Russian вода́, Irish uisce, Albanian ujë; the identification of water as a substance Water is a polar inorganic compound, at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue.
This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life", it is the only common substance to exist as a solid and gas in normal terrestrial conditions. Water is a liquid at the pressures that are most adequate for life. At a standard pressure of 1 atm, water is a liquid between 0 and 100 °C. Increasing the pressure lowers the melting point, about −5 °C at 600 atm and −22 °C at 2100 atm; this effect is relevant, for example, to ice skating, to the buried lakes of Antarctica, to the movement of glaciers. Increasing the pressure has a more dramatic effect on the boiling point, about 374 °C at 220 atm; this effect is important in, among other things, deep-sea hydrothermal vents and geysers, pressure cooking, steam engine design. At the top of Mount Everest, where the atmospheric pressure is about 0.34 atm, water boils at 68 °C. At low pressures, water cannot exist in the liquid state and passes directly from solid to gas by sublimation—a phenomenon exploited in the freeze drying of food.
At high pressures, the liquid and gas states are no longer distinguishable, a state called supercritical steam. Water differs from most liquids in that it becomes less dense as it freezes; the maximum density of water in its liquid form is 1,000 kg/m3. The density of ice is 917 kg/m3. Thus, water expands 9% in volume as it freezes, which accounts for the fact that ice floats on liquid water; the details of the exact chemical nature of liquid water are not well understood. Pure water is described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths, frogs are known to be able to smell it. However, water from ordinary sources has many dissolved substances, that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water by avoiding water, too salty or putrid; the apparent color of natural bodies of water is determined more by dissolved and suspended solids, or by reflection of the sky, than by water itself.
Light in the visible electromagnetic spectrum can traverse a couple meters of pure water without significant absorption, so that it looks transparent and colorless. Thus aquatic plants and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them. Water vapour is invisible as a gas. Through a thickness of 10 meters or more, the intrinsic color of water is visibly turquoise, as its absorption spectrum has
Pseudotachylite or Pseudotachylyte is a cohesive glassy or fine-grained rock that occurs as veins and contains inclusions of wall-rock fragments. Pseudotachylite is dark in color, it was named after its appearance resembling tachylyte. The glass is devitrified into fine-grained material with radial and concentric clusters of crystals; the glass may contain crystals with quench textures that formed via crystallization from the melt. Chemical composition of pseudotachylyte reflects the local bulk chemistry. Pseudotachylyte may form via frictional melting of faults, in large-scale landslides, by impact processes. Many researchers define the rock as one formed via the melting. However, the original description/definition by Shand did not include interpretation about its generation, it is suggested that there are pseudotachylytes formed via comminution without melting, it is found either along fault surfaces, as the matrix to a fault breccia, or as veins injected into the walls of the fault. In most cases, researchers search for and describe good evidence that the pseudotachylite formed by frictional melting of the wall rocks during rapid fault movement associated with a seismic event.
This has caused them to be termed "fossil earthquakes". The thickness of the pseudotachylite zone is indicative of the magnitude of the associated displacement and the general magnitude of the paleoseismic event; some pseudotachylites have been interpreted as forming by comminution rather than melting. They have a similar occurrence to melt-derived pseudotachylites but lack clear indications of a melt origin. Pseudotachylite has been found at the base of some large landslides involving the movement of large coherent blocks, such as the one that moved Heart Mountain in the U. S. state of Wyoming to its present location, the largest known landslide in history on land. Pseudotachylite is associated with impact structures. In an impact event, melting forms as part of the shock metamorphic effects. Pseudotachylite veins associated with impacts are much larger than those associated with faults. Impact-generated veins form by frictional effects within the crater floor and below the crater during the initial compression phase of the impact and the subsequent formation of the central uplift.
The most extensive examples of impact related pseudotachylites come from impact structures that have been eroded to expose the floor of the crater, such as Vredefort crater, South Africa and the Sudbury Basin, Canada. The first described pseudotachylyte is of this type. Lechatelierite Suevite Wieland, F. Chapter 4: Pseudotachylitic breccias, other breccias and veins. Structural analysis of impact-related deformation in the collar rocks of the Vredefort Dome, South Africa. Unpublished PhD. dissertation. School of Geosciences, University of the Witwatersrand, South Africa