text
stringlengths 9
2.4k
|
|---|
The fermentation of urine by bacteria produces a solution of ammonia; hence fermented urine was used in Classical Antiquity to wash cloth and clothing, to remove hair from hides in preparation for tanning, to serve as a mordant in dying cloth, and to remove rust from iron. It was also used by ancient dentists to wash teeth.
In the form of sal ammoniac (نشادر, "nushadir"), ammonia was important to the Muslim alchemists. It was mentioned in the "Book of Stones", likely written in the 9th century and attributed to Jābir ibn Hayyān. It was also important to the European alchemists of the 13th century, being mentioned by Albertus Magnus. It was also used by dyers in the Middle Ages in the form of fermented urine to alter the colour of vegetable dyes. In the 15th century, Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal ammoniac. At a later period, when sal ammoniac was obtained by distilling the hooves and horns of oxen and neutralizing the resulting carbonate with hydrochloric acid, the name 'spirit of hartshorn' was applied to ammonia.
|
Gaseous ammonia was first isolated by Joseph Black in 1756 by reacting "sal ammoniac" (ammonium chloride) with "calcined magnesia" (magnesium oxide). It was isolated again by Peter Woulfe in 1767, by Carl Wilhelm Scheele in 1770 and by Joseph Priestley in 1773 and was termed by him 'alkaline air'. Eleven years later in 1785, Claude Louis Berthollet ascertained its composition.
The production of ammonia from nitrogen in the air (and hydrogen) was invented by Fritz Haber and Robert LeRossignol. The patent was sent in 1909 (USPTO Nr 1,202,995) and awarded in 1916. Later, Carl Bosch developed the industrial method for ammonia production (Haber–Bosch process). It was first used on an industrial scale in Germany during World War I, following the allied blockade that cut off the supply of nitrates from Chile. The ammonia was used to produce explosives to sustain war efforts. The Nobel Prize in Chemistry 1918 was awarded to Fritz Haber "for the synthesis of ammonia from its elements".
Before the availability of natural gas, hydrogen as a precursor to ammonia production was produced via the electrolysis of water or using the chloralkali process.
|
With the advent of the steel industry in the 20th century, ammonia became a byproduct of the production of coking coal.
Applications.
Fertiliser.
In the US , approximately 88% of ammonia was used as fertilisers either as its salts, solutions or anhydrously. When applied to soil, it helps provide increased yields of crops such as maize and wheat. 30% of agricultural nitrogen applied in the US is in the form of anhydrous ammonia, and worldwide, 110 million tonnes are applied each year.
Solutions of ammonia ranging from 16% to 25% are used in the fermentation industry as a source of nitrogen for microorganisms and to adjust pH during fermentation.
Refrigeration–R717.
Because of ammonia's vapourization properties, it is a useful refrigerant. It was commonly used before the popularisation of chlorofluorocarbons (Freons). Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. It suffers from the disadvantage of toxicity, and requiring corrosion resistant components, which restricts its domestic and small-scale use. Along with its use in modern vapour-compression refrigeration it is used in a mixture along with hydrogen and water in absorption refrigerators. The Kalina cycle, which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia–water mixture.
|
Ammonia coolant is also used in the radiators aboard the International Space Station in loops that are used to regulate the internal temperature and enable temperature-dependent experiments. The ammonia is under sufficient pressure to remain liquid throughout the process. Single-phase ammonia cooling systems also serve the power electronics in each pair of solar arrays.
The potential importance of ammonia as a refrigerant has increased with the discovery that vented CFCs and HFCs are potent and stable greenhouse gases.
Antimicrobial agent for food products.
As early as in 1895, it was known that ammonia was 'strongly antiseptic; it requires 1.4 grams per litre to preserve beef tea (broth).' In one study, anhydrous ammonia destroyed 99.999% of zoonotic bacteria in three types of animal feed, but not silage. Anhydrous ammonia is currently used commercially to reduce or eliminate microbial contamination of beef.
Lean finely textured beef (popularly known as 'pink slime') in the beef industry is made from fatty beef trimmings (c. 50–70% fat) by removing the fat using heat and centrifugation, then treating it with ammonia to kill "E. coli". The process was deemed effective and safe by the US Department of Agriculture based on a study that found that the treatment reduces "E. coli" to undetectable levels. There have been safety concerns about the process as well as consumer complaints about the taste and smell of ammonia-treated beef.
|
Fuel.
Ammonia has been used as fuel, and is a proposed alternative to fossil fuels and hydrogen. Being liquid at ambient temperature under its own vapour pressure and having high volumetric and gravimetric energy density, ammonia is considered a suitable carrier for hydrogen, and may be cheaper than direct transport of liquid hydrogen.
Compared to hydrogen, ammonia is easier to store. Compared to hydrogen as a fuel, ammonia is much more energy efficient, and could be produced, stored and delivered at a much lower cost than hydrogen, which must be kept compressed or as a cryogenic liquid. The raw energy density of liquid ammonia is 11.5 MJ/L, which is about a third that of diesel.
Ammonia can be converted back to hydrogen to be used to power hydrogen fuel cells, or it may be used directly within high-temperature solid oxide direct ammonia fuel cells to provide efficient power sources that do not emit greenhouse gases. Ammonia to hydrogen conversion can be achieved through the sodium amide process or the catalytic decomposition of ammonia using solid catalysts.
|
Ammonia engines or ammonia motors, using ammonia as a working fluid, have been proposed and occasionally used. The principle is similar to that used in a fireless locomotive, but with ammonia as the working fluid, instead of steam or compressed air. Ammonia engines were used experimentally in the 19th century by Goldsworthy Gurney in the UK and the St. Charles Streetcar Line in New Orleans in the 1870s and 1880s, and during World War II ammonia was used to power buses in Belgium.
Ammonia is sometimes proposed as a practical alternative to fossil fuel for internal combustion engines. However, ammonia cannot be easily used in existing Otto cycle engines because of its very narrow flammability range. Despite this, several tests have been run. Its high octane rating of 120 and low flame temperature allows the use of high compression ratios without a penalty of high production. Since ammonia contains no carbon, its combustion cannot produce carbon dioxide, carbon monoxide, hydrocarbons, or soot.
Ammonia production currently creates 1.8% of global emissions. 'Green ammonia' is ammonia produced by using green hydrogen (hydrogen produced by electrolysis with electricity from renewable energy), whereas 'blue ammonia' is ammonia produced using blue hydrogen (hydrogen produced by steam methane reforming (= SMR) where the carbon dioxide has been captured and stored (cfr. carbon capture and storage = CCS).
|
Rocket engines have also been fueled by ammonia. The Reaction Motors XLR99 rocket engine that powered the hypersonic research aircraft used liquid ammonia. Although not as powerful as other fuels, it left no soot in the reusable rocket engine, and its density approximately matches the density of the oxidiser, liquid oxygen, which simplified the aircraft's design.
In 2020, Saudi Arabia shipped 40 metric tons of liquid 'blue ammonia' to Japan for use as a fuel. It was produced as a by-product by petrochemical industries, and can be burned without giving off greenhouse gases. Its energy density by volume is nearly double that of liquid hydrogen. If the process of creating it can be scaled up via purely renewable resources, producing green ammonia, it could make a major difference in avoiding climate change. The company ACWA Power and the city of Neom have announced the construction of a green hydrogen and ammonia plant in 2020.
Green ammonia is considered as a potential fuel for future container ships. In 2020, the companies DSME and MAN Energy Solutions announced the construction of an ammonia-based ship, DSME plans to commercialize it by 2025. The use of ammonia as a potential alternative fuel for aircraft jet engines is also being explored.
|
Japan intends to implement a plan to develop ammonia co-firing technology that can increase the use of ammonia in power generation, as part of efforts to assist domestic and other Asian utilities to accelerate their transition to carbon neutrality.
In October 2021, the first International Conference on Fuel Ammonia (ICFA2021) was held.
In June 2022, IHI Corporation succeeded in reducing greenhouse gases by over 99% during combustion of liquid ammonia in a 2,000-kilowatt-class gas turbine achieving truly -free power generation.
In July 2022, Quad nations of Japan, the U.S., Australia and India agreed to promote technological development for clean-burning hydrogen and ammonia as fuels at the security grouping's first energy meeting. , however, significant amounts of are produced. Nitrous oxide may also be a problem as it is a "greenhouse gas that is known to possess up to 300 times the Global Warming Potential (GWP) of carbon dioxide".
The IEA forecasts that ammonia will meet approximately 45% of shipping fuel demands by 2050.
|
At high temperature and in the presence of a suitable catalyst ammonia decomposes into its constituent elements. Decomposition of ammonia is a slightly endothermic process requiring 23 kJ/mol (5.5 kcal/mol) of ammonia, and yields hydrogen and nitrogen gas.
Other.
Remediation of gaseous emissions.
Ammonia is used to scrub from the burning of fossil fuels, and the resulting product is converted to ammonium sulfate for use as fertiliser. Ammonia neutralises the nitrogen oxide () pollutants emitted by diesel engines. This technology, called SCR (selective catalytic reduction), relies on a vanadia-based catalyst.
Ammonia may be used to mitigate gaseous spills of phosgene.
Stimulant.
Ammonia, as the vapour released by smelling salts, has found significant use as a respiratory stimulant. Ammonia is commonly used in the illegal manufacture of methamphetamine through a Birch reduction. The Birch method of making methamphetamine is dangerous because the alkali metal and liquid ammonia are both extremely reactive, and the temperature of liquid ammonia makes it susceptible to explosive boiling when reactants are added.
|
Textile.
Liquid ammonia is used for treatment of cotton materials, giving properties like mercerisation, using alkalis. In particular, it is used for prewashing of wool.
Lifting gas.
At standard temperature and pressure, ammonia is less dense than atmosphere and has approximately 45–48% of the lifting power of hydrogen or helium. Ammonia has sometimes been used to fill balloons as a lifting gas. Because of its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquefied aboard an airship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast).
Fuming.
Ammonia has been used to darken quartersawn white oak in Arts & Crafts and Mission-style furniture. Ammonia fumes react with the natural tannins in the wood and cause it to change colour.
Safety.
The US Occupational Safety and Health Administration (OSHA) has set a 15-minute exposure limit for gaseous ammonia of 35 ppm by volume in the environmental air and an 8-hour exposure limit of 25 ppm by volume. The National Institute for Occupational Safety and Health (NIOSH) recently reduced the IDLH (Immediately Dangerous to Health or Life, the level to which a healthy worker can be exposed for 30 minutes without suffering irreversible health effects) from 500 ppm to 300 ppm based on recent more conservative interpretations of original research in 1943. The 1 hour IDLH limit is still 500 ppm. Other organisations have varying exposure levels. US Navy Standards [U.S. Bureau of Ships 1962] maximum allowable concentrations (MACs): for continuous exposure (60 days) is 25 ppm; for exposure of 1 hour is 400 ppm.
|
Ammonia vapour has a sharp, irritating, pungent odor that acts as a warning of potentially dangerous exposure. The average odor threshold is 5 ppm, well below any danger or damage. Exposure to very high concentrations of gaseous ammonia can result in lung damage and death. Ammonia is regulated in the US as a non-flammable gas, but it meets the definition of a material that is toxic by inhalation and requires a hazardous safety permit when transported in quantities greater than .
Liquid ammonia is dangerous because it is hygroscopic and because it can cause caustic burns. See for more information.
Toxicity.
The toxicity of ammonia solutions does not usually cause problems for humans and other mammals, as a specific mechanism exists to prevent its build-up in the bloodstream. Ammonia is converted to carbamoyl phosphate by the enzyme carbamoyl phosphate synthetase, and then enters the urea cycle to be either incorporated into amino acids or excreted in the urine. Fish and amphibians lack this mechanism, as they can usually eliminate ammonia from their bodies by direct excretion. Ammonia even at dilute concentrations is highly toxic to aquatic animals, and for this reason it is classified as "dangerous for the environment". Atmospheric ammonia plays a key role in the formation of fine particulate matter.
|
Ammonia is a constituent of tobacco smoke.
Coking wastewater.
Ammonia is present in coking wastewater streams, as a liquid by-product of the production of coke from coal. In some cases, the ammonia is discharged to the marine environment where it acts as a pollutant. The Whyalla Steelworks in South Australia is one example of a coke-producing facility that discharges ammonia into marine waters.
Aquaculture.
Ammonia toxicity is believed to be a cause of otherwise unexplained losses in fish hatcheries. Excess ammonia may accumulate and cause alteration of metabolism or increases in the body pH of the exposed organism. Tolerance varies among fish species. At lower concentrations, around 0.05 mg/L, un-ionised ammonia is harmful to fish species and can result in poor growth and feed conversion rates, reduced fecundity and fertility and increase stress and susceptibility to bacterial infections and diseases. Exposed to excess ammonia, fish may suffer loss of equilibrium, hyper-excitability, increased respiratory activity and oxygen uptake and increased heart rate. At concentrations exceeding 2.0 mg/L, ammonia causes gill and tissue damage, extreme lethargy, convulsions, coma, and death. Experiments have shown that the lethal concentration for a variety of fish species ranges from 0.2 to 2.0 mg/L.
|
During winter, when reduced feeds are administered to aquaculture stock, ammonia levels can be higher. Lower ambient temperatures reduce the rate of algal photosynthesis so less ammonia is removed by any algae present. Within an aquaculture environment, especially at large scale, there is no fast-acting remedy to elevated ammonia levels. Prevention rather than correction is recommended to reduce harm to farmed fish and in open water systems, the surrounding environment.
Storage information.
Similar to propane, anhydrous ammonia boils below room temperature when at atmospheric pressure. A storage vessel capable of is suitable to contain the liquid. Ammonia is used in numerous different industrial applications requiring carbon or stainless steel storage vessels. Ammonia with at least 0.2% by weight water content is not corrosive to carbon steel. carbon steel construction storage tanks with 0.2% by weight or more of water could last more than 50 years in service. Experts warn that ammonium compounds not be allowed to come in contact with bases (unless in an intended and contained reaction), as dangerous quantities of ammonia gas could be released.
|
Laboratory.
The hazards of ammonia solutions depend on the concentration: 'dilute' ammonia solutions are usually 5–10% by weight (< 5.62 mol/L); 'concentrated' solutions are usually prepared at >25% by weight. A 25% (by weight) solution has a density of 0.907 g/cm3, and a solution that has a lower density will be more concentrated. The European Union classification of ammonia solutions is given in the table.
The ammonia vapour from concentrated ammonia solutions is severely irritating to the eyes and the respiratory tract, and experts warn that these solutions only be handled in a fume hood. Saturated ('0.880'–see "") solutions can develop a significant pressure inside a closed bottle in warm weather, and experts also warn that the bottle be opened with care. This is not usually a problem for 25% ('0.900') solutions.
Experts warn that ammonia solutions not be mixed with halogens, as toxic and/or explosive products are formed. Experts also warn that prolonged contact of ammonia solutions with silver, mercury or iodide salts can also lead to explosive products: such mixtures are often formed in qualitative inorganic analysis, and that it needs to be lightly acidified but not concentrated (<6% w/v) before disposal once the test is completed.
|
Laboratory use of anhydrous ammonia (gas or liquid).
Anhydrous ammonia is classified as toxic (T) and dangerous for the environment (N). The gas is flammable (autoignition temperature: 651 °C) and can form explosive mixtures with air (16–25%). The permissible exposure limit (PEL) in the United States is 50 ppm (35 mg/m3), while the IDLH concentration is estimated at 300 ppm. Repeated exposure to ammonia lowers the sensitivity to the smell of the gas: normally the odour is detectable at concentrations of less than 50 ppm, but desensitised individuals may not detect it even at concentrations of 100 ppm. Anhydrous ammonia corrodes copper- and zinc-containing alloys, which makes brass fittings not appropriate for handling the gas. Liquid ammonia can also attack rubber and certain plastics.
Ammonia reacts violently with the halogens. Nitrogen triiodide, a primary high explosive, is formed when ammonia comes in contact with iodine. Ammonia causes the explosive polymerisation of ethylene oxide. It also forms explosive fulminating compounds with compounds of gold, silver, mercury, germanium or tellurium, and with stibine. Violent reactions have also been reported with acetaldehyde, hypochlorite solutions, potassium ferricyanide and peroxides.
|
Production.
Ammonia has one of the highest rates of production of any inorganic chemical. Production is sometimes expressed in terms of 'fixed nitrogen'. Global production was estimated as being 160 million tonnes in 2020 (147 tons of fixed nitrogen). China accounted for 26.5% of that, followed by Russia at 11.0%, the United States at 9.5%, and India at 8.3%.
Before the start of World War I, most ammonia was obtained by the dry distillation of nitrogenous vegetable and animal waste products, including camel dung, where it was distilled by the reduction of nitrous acid and nitrites with hydrogen; in addition, it was produced by the distillation of coal, and also by the decomposition of ammonium salts by alkaline hydroxides such as quicklime:
For small scale laboratory synthesis, one can heat urea and calcium hydroxide or sodium hydroxide:
Electrochemical.
The electrochemical synthesis of ammonia involves the reductive formation of lithium nitride, which can be protonated to ammonia, given a proton source. The first use of this chemistry was reported in 1930, where lithium solutions in ethanol were used to produce ammonia at pressures of up to 1000 bar, with ethanol acting as the proton source. Beyond simply mediating proton transfer to the nitrogen reduction reaction, ethanol has been found to play a multifaceted role, influencing electrolyte transformations and contributing to the formation of the solid electrolyte interphase, which enhances overall reaction efficiency
|
In 1994, Tsuneto et al. used lithium electrodeposition in tetrahydrofuran to synthesize ammonia at more moderate pressures with reasonable Faradaic efficiency. Subsequent studies have further explored the ethanol–tetrahydrofuran system for electrochemical ammonia synthesis.
In 2020, a solvent-agnostic gas diffusion electrode was shown to improve nitrogen transport to the reactive lithium. production rates of up to and Faradaic efficiencies of up to 47.5 ± 4% at ambient temperature and 1 bar pressure were achieved.
In 2021, it was demonstrated that ethanol could be replaced with a tetraalkyl phosphonium salt. The study observed production rates of at 69 ± 1% Faradaic efficiency experiments under 0.5 bar hydrogen and 19.5 bar nitrogen partial pressure at ambient temperature. Technology based on this electrochemistry is being developed for commercial fertiliser and fuel production.
In 2022, ammonia was produced via the lithium mediated process in a continuous-flow electrolyzer also demonstrating the hydrogen gas as proton source. The study synthesized ammonia at 61 ± 1% Faradaic efficiency at a current density of −6 mA/cm2 at 1 bar and room temperature.
|
Biochemistry and medicine.
Ammonia is essential for life. For example, it is required for the formation of amino acids and nucleic acids, fundamental building blocks of life. Ammonia is however quite toxic. Nature thus uses carriers for ammonia. Within a cell, glutamate serves this role. In the bloodstream, glutamine is a source of ammonia.
Ethanolamine, required for cell membranes, is the substrate for ethanolamine ammonia-lyase, which produces ammonia:
Ammonia is both a metabolic waste and a metabolic input throughout the biosphere. It is an important source of nitrogen for living systems. Although atmospheric nitrogen abounds (more than 75%), few living creatures are capable of using atmospheric nitrogen in its diatomic form, gas. Therefore, nitrogen fixation is required for the synthesis of amino acids, which are the building blocks of protein. Some plants rely on ammonia and other nitrogenous wastes incorporated into the soil by decaying matter. Others, such as nitrogen-fixing legumes, benefit from symbiotic relationships with rhizobia bacteria that create ammonia from atmospheric nitrogen.
|
In humans, inhaling ammonia in high concentrations can be fatal. Exposure to ammonia can cause headaches, edema, impaired memory, seizures and coma as it is neurotoxic in nature.
Biosynthesis.
In certain organisms, ammonia is produced from atmospheric nitrogen by enzymes called nitrogenases. The overall process is called nitrogen fixation. Intense effort has been directed toward understanding the mechanism of biological nitrogen fixation. The scientific interest in this problem is motivated by the unusual structure of the active site of the enzyme, which consists of an ensemble.
Ammonia is also a metabolic product of amino acid deamination catalyzed by enzymes such as glutamate dehydrogenase 1. Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to urea (by liver), which is much less toxic, particularly less basic. This urea is a major component of the dry weight of urine. Most reptiles, birds, insects, and snails excrete uric acid solely as nitrogenous waste.
Physiology.
Ammonia plays a role in both normal and abnormal animal physiology. It is biosynthesised through normal amino acid metabolism and is toxic in high concentrations. The liver converts ammonia to urea through a series of reactions known as the urea cycle. Liver dysfunction, such as that seen in cirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase, lead to hyperammonemia. Hyperammonemia contributes to the confusion and coma of hepatic encephalopathy, as well as the neurological disease common in people with urea cycle defects and organic acidurias.
|
Ammonia is important for normal animal acid/base balance. After formation of ammonium from glutamine, α-ketoglutarate may be degraded to produce two bicarbonate ions, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across the renal tubules, combine with a hydrogen ion, and thus allow for further acid excretion.
Excretion.
Ammonium ions are a toxic waste product of metabolism in animals. In fish and aquatic invertebrates, it is excreted directly into the water. In mammals, sharks, and amphibians, it is converted in the urea cycle to urea, which is less toxic and can be stored more efficiently. In birds, reptiles, and terrestrial snails, metabolic ammonium is converted into uric acid, which is solid and can therefore be excreted with minimal water loss.
Extraterrestrial occurrence.
Ammonia has been detected in the atmospheres of the giant planets Jupiter, Saturn, Uranus and Neptune, along with other gases such as methane, hydrogen, and helium. The interior of Saturn may include frozen ammonia crystals. It is found on Deimos and Phobos–the two moons of Mars.
|
Interstellar space.
Ammonia was first detected in interstellar space in 1968, based on microwave emissions from the direction of the galactic core. This was the first polyatomic molecule to be so detected. The sensitivity of the molecule to a broad range of excitations and the ease with which it can be observed in a number of regions has made ammonia one of the most important molecules for studies of molecular clouds. The relative intensity of the ammonia lines can be used to measure the temperature of the emitting medium.
The following isotopic species of ammonia have been detected: , , , and . The detection of triply deuterated ammonia was considered a surprise as deuterium is relatively scarce. It is thought that the low-temperature conditions allow this molecule to survive and accumulate.
Since its interstellar discovery, has proved to be an invaluable spectroscopic tool in the study of the interstellar medium. With a large number of transitions sensitive to a wide range of excitation conditions, has been widely astronomically detected–its detection has been reported in hundreds of journal articles. Listed below is a sample of journal articles that highlights the range of detectors that have been used to identify ammonia.
|
The study of interstellar ammonia has been important to a number of areas of research in the last few decades. Some of these are delineated below and primarily involve using ammonia as an interstellar thermometer.
Interstellar formation mechanisms.
The interstellar abundance for ammonia has been measured for a variety of environments. The []/[] ratio has been estimated to range from 10−7 in small dark clouds up to 10−5 in the dense core of the Orion molecular cloud complex. Although a total of 18 total production routes have been proposed, the principal formation mechanism for interstellar is the reaction:
The rate constant, "k", of this reaction depends on the temperature of the environment, with a value of formula_1 at 10 K. The rate constant was calculated from the formula . For the primary formation reaction, and . Assuming an abundance of formula_2and an electron abundance of 10−7 typical of molecular clouds, the formation will proceed at a rate of in a molecular cloud of total density .
All other proposed formation reactions have rate constants of between two and 13 orders of magnitude smaller, making their contribution to the abundance of ammonia relatively insignificant. As an example of the minor contribution other formation reactions play, the reaction:
|
has a rate constant of 2.2. Assuming densities of 105 and []/[] ratio of 10−7, this reaction proceeds at a rate of 2.2, more than three orders of magnitude slower than the primary reaction above.
Some of the other possible formation reactions are:
Interstellar destruction mechanisms.
There are 113 total proposed reactions leading to the destruction of . Of these, 39 were tabulated in extensive tables of the chemistry among C, N and O compounds. A review of interstellar ammonia cites the following reactions as the principal dissociation mechanisms:
with rate constants of 4.39×10−9 and 2.2×10−9, respectively. The above equations (, ) run at a rate of 8.8×10−9 and 4.4×10−13, respectively. These calculations assumed the given rate constants and abundances of []/[] = 10−5, []/[] = 2×10−5, []/[] = 2×10−9, and total densities of "n" = 105, typical of cold, dense, molecular clouds. Clearly, between these two primary reactions, equation () is the dominant destruction reaction, with a rate ≈10,000 times faster than equation (). This is due to the relatively high abundance of .
|
Single antenna detections.
Radio observations of from the Effelsberg 100-m Radio Telescope reveal that the ammonia line is separated into two components–a background ridge and an unresolved core. The background corresponds well with the locations previously detected CO. The 25 m Chilbolton telescope in England detected radio signatures of ammonia in H II regions, HNH2O masers, H–H objects, and other objects associated with star formation. A comparison of emission line widths indicates that turbulent or systematic velocities do not increase in the central cores of molecular clouds.
Microwave radiation from ammonia was observed in several galactic objects including W3(OH), Orion A, W43, W51, and five sources in the galactic centre. The high detection rate indicates that this is a common molecule in the interstellar medium and that high-density regions are common in the galaxy.
Interferometric studies.
VLA observations of in seven regions with high-velocity gaseous outflows revealed condensations of less than 0.1 pc in L1551, S140, and Cepheus A. Three individual condensations were detected in Cepheus A, one of them with a highly elongated shape. They may play an important role in creating the bipolar outflow in the region.
|
Extragalactic ammonia was imaged using the VLA in IC 342. The hot gas has temperatures above 70 K, which was inferred from ammonia line ratios and appears to be closely associated with the innermost portions of the nuclear bar seen in CO. was also monitored by VLA toward a sample of four galactic ultracompact HII regions: G9.62+0.19, G10.47+0.03, G29.96-0.02, and G31.41+0.31. Based upon temperature and density diagnostics, it is concluded that in general such clumps are probably the sites of massive star formation in an early evolutionary phase prior to the development of an ultracompact HII region.
Infrared detections.
Absorption at 2.97 micrometres due to solid ammonia was recorded from interstellar grains in the Becklin–Neugebauer Object and probably in NGC 2264-IR as well. This detection helped explain the physical shape of previously poorly understood and related ice absorption lines.
A spectrum of the disk of Jupiter was obtained from the Kuiper Airborne Observatory, covering the 100 to 300 cm−1 spectral range. Analysis of the spectrum provides information on global mean properties of ammonia gas and an ammonia ice haze.
|
A total of 149 dark cloud positions were surveyed for evidence of 'dense cores' by using the (J,K) = (1,1) rotating inversion line of NH3. In general, the cores are not spherically shaped, with aspect ratios ranging from 1.1 to 4.4. It is also found that cores with stars have broader lines than cores without stars.
Ammonia has been detected in the Draco Nebula and in one or possibly two molecular clouds, which are associated with the high-latitude galactic infrared cirrus. The finding is significant because they may represent the birthplaces for the Population I metallicity B-type stars in the galactic halo that could have been borne in the galactic disk.
Observations of nearby dark clouds.
By balancing and stimulated emission with spontaneous emission, it is possible to construct a relation between excitation temperature and density. Moreover, since the transitional levels of ammonia can be approximated by a 2-level system at low temperatures, this calculation is fairly simple. This premise can be applied to dark clouds, regions suspected of having extremely low temperatures and possible sites for future star formation. Detections of ammonia in dark clouds show very narrow linesindicative not only of low temperatures, but also of a low level of inner-cloud turbulence. Line ratio calculations provide a measurement of cloud temperature that is independent of previous CO observations. The ammonia observations were consistent with CO measurements of rotation temperatures of ≈10 K. With this, densities can be determined, and have been calculated to range between 104 and 105 cm−3 in dark clouds. Mapping of gives typical clouds sizes of 0.1 pc and masses near 1 solar mass. These cold, dense cores are the sites of future star formation.
|
UC HII regions.
Ultra-compact HII regions are among the best tracers of high-mass star formation. The dense material surrounding UCHII regions is likely primarily molecular. Since a complete study of massive star formation necessarily involves the cloud from which the star formed, ammonia is an invaluable tool in understanding this surrounding molecular material. Since this molecular material can be spatially resolved, it is possible to constrain the heating/ionising sources, temperatures, masses, and sizes of the regions. Doppler-shifted velocity components allow for the separation of distinct regions of molecular gas that can trace outflows and hot cores originating from forming stars.
Extragalactic detection.
Ammonia has been detected in external galaxies, and by simultaneously measuring several lines, it is possible to directly measure the gas temperature in these galaxies. Line ratios imply that gas temperatures are warm (≈50 K), originating from dense clouds with sizes of tens of parsecs. This picture is consistent with the picture within our Milky Way galaxyhot dense molecular cores form around newly forming stars embedded in larger clouds of molecular material on the scale of several hundred parsecs (giant molecular clouds; GMCs).
|
Amethyst
Amethyst is a violet variety of quartz. The name comes from the Koine Greek from - , "not" and (Ancient Greek) / (Modern Greek), "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.
Amethyst, a semiprecious stone, is often used in jewelry.
Structure.
Amethyst is a violet variety of quartz () and owes its violet color to irradiation, impurities of iron () and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions.
The irradiation causes the iron ions that replace Si in the lattice to lose an electron and form a color center.
Amethyst is a three-dimensional network of tetrahedra where the silicon atoms are in the center and are surrounded by four oxygen atoms located at the vertices of a tetrahedron. This structure is quite rigid and results in quartz's hardness and resistance to weathering. The hardness of the mineral is the same as quartz, thus making it suitable for use in jewelry.
|
Hue and tone.
Amethyst occurs in primary hues from a light lavender or pale violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue.
High-quality amethyst can be found in Siberia, Sri Lanka, Brazil, Uruguay, and the Far East. The ideal grade, called "Deep Siberian", has a primary purple hue of around 75–80%, with 15–20% blue and (depending on the light source) red secondary hues.
"Rose de France" is defined by its markedly light shade of the purple, reminiscent of a lavender / lilac shade. These pale colors were once considered undesirable, but have recently become popular due to intensive marketing.
Green quartz is sometimes called "green amethyst"; the scientific name is prasiolite.
Other names for green quartz are "vermarine" and "lime citrine".
Amethyst frequently shows color zoning, with the most intense color typically found at the crystal terminations. One of gem cutters' tasks is to make a finished product with even color. Sometimes, only a thin layer of a natural, uncut amethyst is violet colored, or the color is very uneven. The uncut gem may have only a small portion that is suitable for faceting.
|
The color of amethyst has been demonstrated to result from substitution by irradiation of trivalent iron (Fe3+) for silicon in the structure, in the presence of trace elements of large ionic radius, and to a certain extent, the amethyst color can naturally result from displacement of transition elements even if the iron concentration is low. Natural amethyst is dichroic in reddish violet and bluish violet, but when heated, turns yellow-orange, yellow-brown, or dark brownish and may resemble citrine, but loses its dichroism, unlike genuine citrine. When partially heated, amethyst can result in ametrine.
Amethyst can fade in tone if overexposed to light sources, and can be artificially darkened with adequate irradiation. It does not fluoresce under either short-wave or long-wave UV light.
Geographic distribution.
Amethyst is found in many locations around the world. Between 2000 and 2010, the greatest production was from Marabá and Pau d'Arco, Pará, and the Paraná Basin, Rio Grande do Sul, Brazil; Sandoval, Santa Cruz, Bolivia; Artigas, Uruguay; Kalomo, Zambia; and Thunder Bay, Ontario. Lesser amounts are found in many other locations in Africa, Brazil, Spain, Argentina, Russia, Afghanistan, South Korea, Mexico, and the United States.
|
Amethyst is produced in abundance in the state of Rio Grande do Sul in Brazil where it occurs in large geodes within volcanic rocks.
Many of the hollow agates of southwestern Brazil and Uruguay contain a crop of amethyst crystals in the interior. Artigas, Uruguay and neighboring Brazilian state Rio Grande do Sul are large world producers, with lesser quantities mined in Minas Gerais and Bahia states.
Amethyst is also found and mined in South Korea. The large opencast amethyst vein at Maissau, Lower Austria, was historically important, but is no longer included among significant producers. Much fine amethyst comes from Russia, especially near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks. Amethyst was historically mined in many localities in south India, though these are no longer significant producers. One of the largest global amethyst producers is Zambia in southern Africa, with an annual production around 1000 tons.
Amethyst occurs at many localities in the United States. The most important production is at Four Peaks, Gila and Maricopa Counties, Arizona, and Jackson's Crossroads, Wilkes County, Georgia.
|
Smaller occurrences have been reported in the Red Feather Lakes, near Fort Collins, Colorado; Amethyst Mountain, Texas; Yellowstone National Park; Delaware County, Pennsylvania; Haywood County, North Carolina; Deer Hill and Stow, Maine, and in the Lake Superior region of Minnesota, Wisconsin, and Michigan.
Amethyst is relatively common in the Canadian provinces of Ontario and Nova Scotia. The largest amethyst mine in North America is located in Thunder Bay, Ontario.
Amethyst is the official state gemstone of South Carolina. Several South Carolina amethysts are on display at the Smithsonian Museum of Natural History.
History.
Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglio engraved gems.
The ancient Greeks believed amethyst gems could prevent intoxication,
while medieval European soldiers wore amethyst amulets as protection in battle in the belief that amethysts heal people and keep them cool-headed.
Beads of amethyst were found in Anglo-Saxon graves in England.
|
Anglican bishops wear an episcopal ring often set with an amethyst, an allusion to the description of the Apostles as "not drunk" at Pentecost in Acts 2:15.
A large geode, or "amethyst-grotto", from near Santa Cruz in southern Brazil was presented at a 1902 exhibition in Düsseldorf, Germany.
Synthetic amethyst.
Synthetic (laboratory-grown) amethyst is produced by a synthesis method called hydrothermal growth, which grows the crystals inside a high-pressure autoclave.
Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are the same as those of natural amethyst, and it cannot be differentiated with absolute certainty without advanced gemmological testing (which is often cost-prohibitive). One test based on "Brazil law twinning" (a form of quartz twinning where right- and left-hand quartz structures are combined in a single crystal) can be used to identify most synthetic amethyst rather easily. Synthesizing twinned amethyst is possible, but this type is not available in large quantities in the market.
|
Treated amethyst is produced by gamma ray, X-ray, or electron-beam irradiation of clear quartz (rock crystal), which has been first doped with ferric impurities. Exposure to heat partially cancels the irradiation effects and amethyst generally becomes yellow or even green. Much of the citrine, cairngorm, or yellow quartz of jewelry is said to be merely "burnt amethyst".
Cultural history.
Ancient Greece.
The Greek word may be translated as "not drunken", from Greek , "not" + , "intoxicated". Amethyst was considered to be a strong antidote against drunkenness.
In his poem "L'Amethyste, ou les Amours de Bacchus et d'Amethyste" (Amethyst or the loves of Bacchus and Amethyste), the French poet Rémy Belleau (1528–1577) invented a myth in which Bacchus, the god of intoxication, of wine, and grapes was pursuing a maiden named Amethyste, who refused his affections. Amethyste prayed to the gods to remain chaste, a prayer which the chaste goddess Diana answered, transforming her into a white stone. Humbled by Amethyste's desire to remain chaste, Bacchus poured wine over the stone as an offering, dyeing the crystals purple.
|
Variations of the story include that Dionysus had been insulted by a mortal and swore to slay the next mortal who crossed his path, creating fierce tigers to carry out his wrath. The mortal turned out to be a beautiful young woman, Amethystos, who was on her way to pay tribute to Artemis. Her life was spared by Artemis, who transformed the maiden into a statue of pure crystalline quartz to protect her from the brutal claws. Dionysus wept tears of wine in remorse for his action at the sight of the beautiful statue. The god's tears then stained the quartz purple.
This myth and its variations are not found in classical sources. However, the goddess Rhea does present Dionysus with an amethyst stone to preserve the wine-drinker's sanity in historical text.
Other cultural associations.
Tibetans consider amethyst sacred to the Buddha and make prayer beads from it. Amethyst is considered the birthstone of February.
In the Middle Ages, it was considered a symbol of royalty and used to decorate English regalia. In the Old World, amethyst was considered one of the cardinal gems, in that it was one of the five gemstones considered precious above all others, until large deposits were found in Brazil.
|
Value.
Until the 18th century, amethyst was included in the cardinal, or most valuable, gemstones (along with diamond, sapphire, ruby, and emerald), but since the discovery of extensive deposits in locations such as Brazil, it has lost most of its value. It is now considered a semiprecious stone.
Collectors look for depth of color, possibly with red flashes if cut conventionally.
As amethyst is readily available in large structures, the value of the gem is not primarily defined by carat weight. This is different from most gemstones, since the carat weight typically exponentially increases the value of the stone. The biggest factor in the value of amethyst is the color displayed.
The highest-grade amethyst (called "deep Russian") is exceptionally rare. When one is found, its value is dependent on the demand of collectors; however, the highest-grade sapphires or rubies are still orders of magnitude more expensive than amethyst.
Handling and care.
The most suitable setting for gem amethyst is a prong or a bezel setting. The channel method must be used with caution.
Amethyst has a good hardness, and handling it with proper care will prevent any damage to the stone. Amethyst is sensitive to strong heat and may lose or change its colour when exposed to prolonged heat or light. Polishing the stone or cleaning it by ultrasonic or steamer must be done with caution.
|
Albertosaurus
Albertosaurus (; meaning "Alberta lizard") is a genus of large tyrannosaurid theropod dinosaur that lived in northwestern North America during the early to middle Maastrichtian age of the Late Cretaceous period, about 71 million years ago. The type species, "A. sarcophagus", was apparently restricted in range to the modern-day Canadian province of Alberta, after which the genus is named, although an indeterminate species ("cf. "Albertosaurus" sp.") has been discovered in the Corral de Enmedio and Packard Formations of Mexico. Scientists disagree on the content of the genus and some recognize "Gorgosaurus libratus" as a second species.
As a tyrannosaurid, "Albertosaurus" was a bipedal predator with short arms, two-fingered hands, and a massive head with dozens of large, sharp teeth, a strong sense of smell, powerful binocular vision, and a bone crushing bite force. It may have even been the apex predator in its local ecosystem. While "Albertosaurus" was certainly large for a theropod, it was still much smaller than its larger and more famous relative "Tyrannosaurus rex", growing up to in length and weighing .
|
Since the first discovery in 1884, fossils of more than 30 individuals have been recovered that provide scientists with a more detailed knowledge of "Albertosaurus" anatomy than what is available for most other tyrannosaurids. The discovery of 26 individuals in one particular site provides evidence of gregarious behavior and allows for studies of ontogeny and population biology. These are near impossible with lesser-known dinosaurs because their remains are rarer and more fragmentary when compared to those of "Albertosaurus".
History of discovery.
Naming.
"Albertosaurus" was named by Henry Fairfield Osborn in a one-page note at the end of his 1905 description of "Tyrannosaurus rex". Its namesake is Alberta, the Canadian province established the very same year where the first remains were found. The generic name also incorporates the Greek word /"sauros", meaning "lizard", which is the most common suffix in dinosaur names. The type species is "Albertosaurus sarcophagus" and the specific name is derived from the Ancient Greek term σαρκοφάγος ('), meaning "flesh-eating", and having the same etymology as the funeral container with which it shares its name, which is a combination of the Greek words σαρξ/' ("flesh") and /"" ("to eat"). More than 30 specimens of all ages are known to science.
|
Early discoveries.
The type specimen is a partial skull collected on June 9, 1884, from an outcrop of the Horseshoe Canyon Formation alongside the Red Deer River in Alberta. It was recovered by an expedition of the Geological Survey of Canada, led by the famous geologist Joseph Burr Tyrrell. Due to a lack of specialised equipment, the almost complete skull could only be partially secured. In 1889, Tyrrell's colleague Thomas Chesmer Weston found an incomplete smaller skull associated with some skeletal material at a location nearby. The two skulls were assigned to the preexisting species "Laelaps incrassatus" by Edward Drinker Cope in 1892. Although the name "Laelaps" was preoccupied by a genus of mite and had been changed to "Dryptosaurus" in 1877 by Othniel Charles Marsh, Cope stubbornly refused to recognize the new name created by his archrival. However, Lawrence Lambe used the name "Dryptosaurus incrassatus" instead of "Laelaps incrassatus" when he described the remains in detail in 1903 and 1904, which was a combination first coined by Oliver Perry Hay in 1902.
|
Shortly later, Osborn pointed out that "D. incrassatus" was based on generic tyrannosaurid teeth, so the two Horseshoe Canyon skulls could not be confidently referred to that species. The Horseshoe Canyon skulls also differed markedly from the remains of "D. aquilunguis", type species of "Dryptosaurus", so Osborn gave them the new name "Albertosaurus sarcophagus" in 1905. He did not describe the remains in any great detail, citing Lambe's complete description the year before. Both specimens, the holotype CMN 5600 and the paratype CMN 5601, are stored in the Canadian Museum of Nature in Ottawa. By the early twenty-first century, some concerns had arisen that, due to the damaged state of the holotype, "Albertosaurus" might be a "nomen dubium" that could only be used for the type specimen itself because other fossils could not reliably be assigned to it. However, in 2010, Thomas Carr established that the holotype, the paratype, and comparable later finds all shared a single common unique trait, or autapomorphy. The possession of an enlarged pneumatic opening in the back rim of the side of the palatine bone proves that "Albertosaurus" is a valid taxon.
|
Dry Island bone bed.
On August 11, 1910, American paleontologist Barnum Brown discovered the remains of a large group of "Albertosaurus" at another quarry alongside the Red Deer River. Because of the large number of bones and the limited time available, Brown's party did not collect every specimen, but made sure to collect remains from all of the individuals that they could identify in the bone bed. Among the bones deposited in the American Museum of Natural History collections in New York City are seven sets of right metatarsals, along with two isolated toe bones that did not match any of the metatarsals in size. This indicated the presence of at least nine individuals in the quarry. Palaeontologist Philip J. Currie of the Royal Tyrrell Museum of Palaeontology rediscovered the bonebed in 1997 and resumed fieldwork at the site, which is now located inside Dry Island Buffalo Jump Provincial Park. Further excavation from 1997 to 2005 turned up the remains of 13 more individuals of various ages, including a diminutive two-year-old and a very old individual estimated at over long. None of these individuals are known from complete skeletons and most are represented by remains in both museums. Excavations continued until 2008, when the minimum number of individuals present had been established at 12 (on the basis of preserved elements that occur only once in a skeleton) and at 26 if mirrored elements were counted when differing in size due to ontogeny. A total of 1,128 "Albertosaurus" bones had been secured, which is the largest concentration of large theropod fossils known from the Cretaceous.
|
Other discoveries.
In 1911, Barnum Brown, during the second year of the American Museum of Natural History's operations in Alberta, uncovered a fragmentary partial "Albertosaurus" skull at the Red Deer River near Tolman Bridge (specimen AMNH 5222).
William Parks described a new species in 1928, "Albertosaurus arctunguis", based on a partial skeleton lacking a skull that was excavated by Gus Lindblad and Ralph Hornell near the Red Deer River in 1923, but this species has been considered identical to "A. sarcophagus" since 1970. Parks' specimen (ROM 807) is housed in the Royal Ontario Museum in Toronto.
No "Albertosaurus" fossils were found from 1926 to 1972, but there has been an increase in findings since then. Apart from the Dry Island bonebed, six more skulls and skeletons have since been discovered in Alberta and are housed in various Canadian museums. Specimen RTMP 81.010.001 was found in 1978 by amateur paleontologist Maurice Stefanuk. RTMP 85.098.001 was found by Stefanuk on June 16, 1985. RTMP 86.64.001 was found in December 1985. RTMP 86.205.001 was found in 1986. RTMP 97.058.0001 was found in 1996 and then there is CMN 11315. Unfortunately, none of these skeletons were found with complete skulls. Fossils have also been reported from the American states of Montana, New Mexico, Wyoming, and Missouri, but they are doubted to be from "A. sarcophagus" and may not even belong to the genus "Albertosaurus".
|
Two specimens from "cf "Albertosaurus" ".sp" have been found in Mexico (Packard Formation and Corral de Enmedio Formation).
"Gorgosaurus libratus".
In 1913, paleontologist Charles H. Sternberg recovered another tyrannosaurid skeleton from the slightly older Dinosaur Park Formation in Alberta. Lawrence Lambe named this dinosaur "Gorgosaurus libratus" in 1914. Other specimens were later found in Alberta and the US state of Montana. Finding no significant differences to separate the two taxa (due mostly to a lack of good "Albertosaurus" skull material), Dale Russell declared the name "Gorgosaurus" a junior synonym of "Albertosaurus", which had been named first, and "G. libratus" was renamed "Albertosaurus libratus" in 1970. A species distinction was maintained because of the age difference. The addition extended the temporal range of the genus "Albertosaurus" earlier by several million years and its geographic range southwards by hundreds of kilometres.
In 2003, Philip J. Currie, benefiting from much more extensive finds and a general increase in anatomical knowledge of theropods, compared several tyrannosaurid skulls and came to the conclusion that the two species are more distinct than previously thought. As the two species are sister taxa, they are more closely related to each other than to any other species of tyrannosaurid. Recognizing this, Currie nevertheless recommended that "Albertosaurus" and "Gorgosaurus" be kept as separate genera, as he concluded that they were no more similar than "Daspletosaurus" and "Tyrannosaurus", which are almost always separated. In addition to this, several albertosaurine specimens have been recovered from Alaska and New Mexico. Currie suggested that the "Albertosaurus"-"Gorgosaurus" situation may be clarified once these are fully described. Most authors have followed Currie's recommendation, but some have not.
|
Other species.
In 1930, Anatoly Nikolaevich Riabinin named "Albertosaurus pericolosus" based on a tooth from China that probably belonged to "Tarbosaurus". In 1932, Friedrich von Huene renamed "Dryptosaurus incrassatus", not considered a "nomen dubium" by him, to "Albertosaurus incrassatus". Because he had identified "Gorgosaurus" with "Albertosaurus", in 1970, Russell also renamed "Gorgosaurus sternbergi" (Matthew & Brown 1922) into "Albertosaurus sternbergi" and "Gorgosaurus lancensis" (Gilmore 1946) into "Albertosaurus lancensis". The former species is today seen as a juvenile form of "Gorgosaurus libratus" and the latter is seen as either identical to "Tyrannosaurus" or representing a separate genus, "Nanotyrannus". In 1988, Gregory S. Paul based "Albertosaurus megagracilis" on a small tyrannosaurid skeleton, specimen LACM 28345, from the Hell Creek Formation of Montana. It was renamed "Dinotyrannus" in 1995, but is now thought to represent a juvenile "Tyrannosaurus rex". Also in 1988, Paul renamed "Alectrosaurus olseni" (Gilmore 1933) into "Albertosaurus olseni", but this has found no general acceptance. In 1989, "Gorgosaurus novojilovi" (Maleev 1955) was renamed by Bryn Mader and Robert Bradley as "Albertosaurus novojilovi".
|
On two occasions, species based on valid "Albertosaurus" material were reassigned to a different genus, "Deinodon". In 1922, William Diller Matthew renamed "A. sarcophagus" into "Deinodon sarcophagus". In 1939, German paleontologist Oskar Kuhn renamed "A. arctunguis" into "Deinodon arctunguis".
Description.
"Albertosaurus" was a fairly large bipedal predator, but smaller than "Tarbosaurus" and "Tyrannosaurus rex". Typical "Albertosaurus" adults measured up to long and weighed between in body mass.
"Albertosaurus" shared a similar body appearance with all other tyrannosaurids, "Gorgosaurus" in particular. Typical for a theropod, "Albertosaurus" was bipedal and balanced its large, heavy head and torso with a long, muscular tail. However, tyrannosaurid forelimbs were extremely small for their body size and retained only two functional fingers, the second being longer than the first. The legs were long and ended in a four-toed foot on which the first toe, the hallux, was very short and did not reach the ground. The third toe was longer than the rest. "Albertosaurus" may have been able to reach walking speeds of 14–21 km/hour (8–13 mi/hour). At least for the younger individuals, a high running speed is plausible.
|
Two skin impressions from "Albertosaurus" are known, and both show scales. One patch was found associated with some gastralic ribs and the impression of a long, unknown bone, indicating that the patch is from the belly. The scales are pebbly and gradually become larger and somewhat hexagonal in shape. Also preserved are two larger feature scales, placed 4.5 cm apart from each other, making "Albertosaurus", along with "Carnotaurus", the only known theropods with preserved feature scales. Another skin impression is from an unknown part of the body. These scales are small, diamond-shaped, and arranged in rows.
Skull and teeth.
The massive skull of "Albertosaurus", which was perched on a muscular, short, S-shaped neck, was about long in the largest adults. Wide openings in the skull, called fenestrae, provided space for muscle attachment sites and sensory organs that reduced its overall weight. Its long jaws contained, both sides combined, 58 or more banana-shaped teeth. Larger tyrannosaurids possessed fewer teeth, but "Gorgosaurus" had 62. Unlike most theropods, "Albertosaurus" and other tyrannosaurids were heterodont, with teeth of different forms depending on their position in the mouth. The premaxillary teeth at the tip of the upper jaw, four per side, were much smaller than the rest, more closely packed, and D-shaped in cross section. Like with "Tyrannosaurus rex", the maxillary (cheek) teeth of "Albertosaurus" were adapted in general form to resist lateral forces exerted by a struggling prey animal. The bite force of "Albertosaurus" was less formidable, however, with the maximum force, by the back teeth, reaching 3,413 Newtons. Above the eyes were short bony crests that may have been brightly coloured in life and possibly used, by males in particular, in courtship to attract a mate.
|
In 2001, William Abler observed that "Albertosaurus" tooth serrations resemble a crack in the tooth ending in a round void called an ampulla. Tyrannosaurid teeth were used as holdfasts for pulling flesh off a body, so when a tyrannosaur pulled back on a piece of meat, the tension could cause a purely crack-like serration to spread through the tooth. However, the presence of the ampulla distributed these forces over a larger surface area and lessened the risk of damage to the tooth under strain. The presence of incisions ending in voids has parallels in human engineering. Guitar makers use incisions ending in voids to, as Abler describes, "impart alternating regions of flexibility and rigidity" to wood that they work on. The use of a drill to create an "ampulla" of sorts and prevent the propagation of cracks through material is also used to protect aircraft surfaces. Abler demonstrated that a plexiglass bar with incisions called "kerfs" and drilled holes was more than 25% stronger than one with only regularly placed incisions. Unlike tyrannosaurs, more ancient predators, like phytosaurs and "Dimetrodon", had no adaptations to prevent the crack-like serrations of their teeth from spreading when subjected to the forces of feeding.
|
Classification and systematics.
"Albertosaurus" is a member of the theropod family Tyrannosauridae, specifically the subfamily Albertosaurinae. Its closest relative is the slightly older "Gorgosaurus libratus" (sometimes called "Albertosaurus libratus"; see below). These two species are the only described albertosaurines, but other undescribed species may exist. Thomas Holtz found "Appalachiosaurus" to be an albertosaurine in 2004, but his more recent unpublished work places it as a basal eotyrannosaurian just outside of Tyrannosauridae, in agreement with other authors.
The other major subfamily of tyrannosaurids is Tyrannosaurinae, which includes members like "Daspletosaurus", "Tarbosaurus", and "Tyrannosaurus". Compared with the more robust tyrannosaurines, albertosaurines had slender builds, with proportionately smaller skulls and longer bones of the lower legs (tibia) and feet (metatarsals and phalanges).
Below is the cladogram of Tyrannosauridae based on the phylogenetic analysis conducted by Loewen "et al." in 2013.
|
Palaeobiology.
Growth pattern.
Most age categories of "Albertosaurus" are represented in the fossil record. Using bone histology, the age of an individual animal at the time of death can often be determined, allowing growth rates to be estimated and compared with other species. The youngest known "Albertosaurus" is a two-year-old discovered in the Dry Island bonebed, which would have weighed about 50 kilograms (110 lb) and measured slightly more than long. The specimen from the same quarry is 28 years old, the oldest and largest one known. When specimens of intermediate age and size are plotted on a graph, an "S"-shaped growth curve results, with the most rapid growth occurring in a four-year period ending around the sixteenth year of life, a pattern also seen in other tyrannosaurids. The growth rate during this phase was per year, based on an adult weighing 1.3 tonnes. Other studies have suggested higher adult weights, which would affect the magnitude of the growth rate, but not the overall pattern. Tyrannosaurids similar in size to "Albertosaurus" had similar growth rates, although the much larger "Tyrannosaurus rex" grew at almost five times this rate ( per year) at its peak. The end of the rapid growth phase suggests the onset of sexual maturity in "Albertosaurus", although growth continued at a slower rate throughout the animals' lives. Sexual maturation while still actively growing appears to be a shared trait among small and large dinosaurs, as well as in large mammals like humans and elephants. This pattern of relatively early sexual maturation differs strikingly from the pattern in birds, which delay their sexual maturity until after they have finished growing.
|
During growth, thickening of the tooth morphology changed so much that, had the association of young and adult skeletons on the Dry Island bonebed not proven that they belonged to the same taxon, the teeth of juveniles would likely have been identified by statistical analysis as those of a different species.
Life history.
Most known "Albertosaurus" individuals were aged 14 years or older at the time of death. Juvenile animals are rarely fossilized for several reasons, mainly preservation bias, where the smaller bones of younger animals were less likely to be preserved by fossilization than the larger bones of adults, and collection bias, where smaller fossils are less likely to be noticed by collectors in the field. Young "Albertosaurus" are relatively large for juvenile animals, but their remains are still rare in the fossil record when compared to adults. It has been suggested that this phenomenon is a consequence of life history, rather than bias, and that fossils of juvenile "Albertosaurus" are rare because they simply did not die as often as adults did.
|
A hypothesis of "Albertosaurus" life history postulates that hatchlings died in large numbers, but have not been preserved in the fossil record because of their small size and fragile construction. After just two years, juveniles were larger than any other predator in the region, aside from adult "Albertosaurus", and more fleet-footed than most of their prey animals. This resulted in a dramatic decrease in their mortality rate and a corresponding rarity of fossil remains. Mortality rates doubled at age twelve, perhaps the result of the physiological demands of the rapid growth phase, and then doubled again with the onset of sexual maturity between the ages of fourteen and sixteen. This elevated mortality rate continued throughout adulthood, perhaps due to the high physiological demands of procreation, including stress and injuries received during intraspecific competition for mates and resources, and the eventual, ever-increasing effects of senescence. The higher mortality rate in adults may explain their more common preservation. Very large animals were rare because few individuals survived long enough to attain such size. High infant mortality rates, followed by reduced mortality among juveniles and a sudden increase in mortality after sexual maturity, with very few animals reaching maximum size, is a pattern observed in many modern large mammals, including elephants, African buffalo, and rhinoceros. The same pattern is also seen in other tyrannosaurids. The comparison with modern animals and other tyrannosaurids lends support to this life history hypothesis, but bias in the fossil record may still play a large role, especially since more than two-thirds of all "Albertosaurus" specimens are known from the exact same locality.
|
Social behaviour.
The Dry Island bonebed discovered by Barnum Brown and his crew contains the remains of 26 "Albertosaurus", the most individuals found in one locality of any large Cretaceous theropod and the second-most of any large theropod dinosaur behind the "Allosaurus" assemblage at the Cleveland-Lloyd Dinosaur Quarry in Utah. The group seems to be composed of one very old adult, eight adults between 17 and 23 years old, seven sub-adults undergoing their rapid growth phases at between 12 and 16 years old, and six juveniles between the ages of 2 and 11 years old that had not yet reached the growth phase.
The near-absence of herbivore remains and the similar state of preservation common to the many individuals at the "Albertosaurus" bonebed quarry led Currie to conclude that the locality was not a predator trap, such as the La Brea Tar Pits in California, and that all of the preserved animals died at the same time. Currie claims this as evidence of pack behavior. Other scientists are skeptical, observing that the animals may have been driven together by a drought, flood, or other reasons.
|
There is plentiful evidence for gregarious behaviour among herbivorous dinosaurs, including ceratopsians and hadrosaurs. However, only rarely are so many dinosaurian predators found at the same site. Small theropods, like "Deinonychus" and "Coelophysis", have been found in aggregations, as have larger predators, such as "Allosaurus" and "Mapusaurus". There is some evidence of gregarious behaviour in other tyrannosaurids as well, as fragmentary remains of smaller individuals were found alongside "Sue", the "Tyrannosaurus" mounted in the Field Museum of Natural History in Chicago, and a bonebed in the Two Medicine Formation of Montana contains at least three specimens of "Daspletosaurus" preserved alongside several hadrosaurs. These findings may corroborate the evidence for social behaviour in "Albertosaurus", although some or all of the above localities may represent temporary or unnatural aggregations. Others have speculated that, instead of social groups, at least some of these finds represent Komodo dragon-like mobbing of carcasses, where aggressive competition leads to some of the predators being killed and even cannibalized. The evidence of cannibalism was later reported in 2024 by Coppock and Currie.
|
Currie has also speculated on the pack-hunting habits of "Albertosaurus". The leg proportions of the smaller individuals were comparable to those of ornithomimids, which were probably among the fastest dinosaurs. Younger "Albertosaurus" were probably equally fleet-footed or at least faster than their prey. Currie hypothesized that the younger members of the pack may have been responsible for driving their prey towards the adults, who were larger and more powerful, but also slower. Juveniles may also have had different lifestyles than adults, filling predator niches between the enormous adults and the smaller contemporaneous theropods, the largest of which were two orders of magnitude smaller than adult "Albertosaurus" in mass. A similar situation is observed in modern Komodo dragons, with hatchlings beginning life as small insectivores before growing to become the dominant predators on their islands. However, as the preservation of behaviour in the fossil record is exceedingly rare, these ideas cannot readily be tested. In 2010, Currie, though still favouring the hunting pack hypothesis, admitted that the concentration could have been brought about by other causes, such as a slowly rising water level during an extended flood.
|
Palaeopathology.
In 2009, researchers hypothesized that smooth-edged holes found in the fossil jaws of tyrannosaurid dinosaurs, such as "Albertosaurus", were caused by a parasite similar to "Trichomonas gallinae", which infects birds. They suggested that tyrannosaurids transmitted the infection by biting each other and that the infection impaired their ability to eat.
In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior. They found that only one of the 319 "Albertosaurus" foot bones checked for stress fractures actually had them and none of the four hand bones did. The scientists found that stress fractures were "significantly" less common in "Albertosaurus" than in the carnosaur "Allosaurus". ROM 807, the holotype of "A. arctunguis" (now referred to "A. sarcophagus"), had a deep hole in the iliac blade, although the describer of the species did not recognize this as pathological. The specimen also contains some exostosis on the fourth left metatarsal. In 1970, two of the five "Albertosaurus sarcophagus" specimens with humeri were reported by Dale Russel as having pathological damage to them.
|
In 2010, the health of the Dry Island "Albertosaurus" assembly was reported upon. Most specimens showed no sign of disease. On three phalanges of the foot, strange bony spurs that consisted of abnormal ossifications of the tendons, so-called enthesophytes, were present, but their cause is unknown. Two ribs and a belly-rib showed signs of breaking and healing. One adult specimen had a left lower jaw showing a puncture wound and both healed and unhealed bite marks. The low number of abnormalities compares favourably with the health condition of a "Majungasaurus" population of which it was established, in 2007, that 19% of individuals showed bone pathologies.
Palaeoecology.
Most fossils of "Albertosaurus sarcophagus" are known from the upper Horseshoe Canyon Formation in Alberta. These younger units of this geologic formation date to the early Maastrichtian age of the Late Cretaceous period, about 70 to 68 million years ago. Immediately below this formation is the Bearpaw Shale, a marine formation representing a section of the Western Interior Seaway. The Inland Sea was receding as the climate cooled and sea levels subsided towards the end of the Cretaceous, thus exposing land that had previously been underwater. It was not a smooth process, however, and the seaway would periodically rise to cover parts of the region throughout Horseshoe Canyon before finally receding altogether in the years after. Due to the changing sea levels, many different environments are represented in the Horseshoe Canyon Formation, including offshore and near-shore marine habitats and coastal habitats, such as lagoons, estuaries, and tidal flats. Numerous coal seams represent ancient peat swamps. Like most of the other vertebrate fossils from the formation, "Albertosaurus" remains are found in deposits laid down in the deltas and floodplains of large rivers during the later half of Horseshoe Canyon times.
|
The fauna of the Horseshoe Canyon Formation is well-known, as vertebrate fossils, including those of dinosaurs, are very common. Sharks, rays, sturgeons, bowfins, gars, and the gar-like "Aspidorhynchus" made up the fish fauna. Mammals included multituberculates and the marsupial "Didelphodon". The saltwater plesiosaur "Leurospondylus" has been found in marine sediments in the Horseshoe Canyon, while freshwater environments were populated by turtles, "Champsosaurus", and crocodilians like "Leidyosuchus" and "Stangerochampsa". Dinosaurs dominate the fauna, especially hadrosaurs, which make up half of all dinosaurs known. These include the genera "Edmontosaurus", "Saurolophus", and "Hypacrosaurus". Ceratopsians and ornithomimids were also very common, together making up another third of the known fauna. Along with much rarer ankylosaurians and pachycephalosaurs, all of these animals would have been prey for a diverse array of carnivorous theropods, including troodontids, dromaeosaurids, and caenagnathids. Intermingled with the "Albertosaurus" remains of the Dry Island bonebed, the bones of the small theropod "Albertonykus" were found. Adult "Albertosaurus" were the apex predators in their environment, with intermediate niches possibly filled by juvenile "Albertosaurus".
|
Assembly language
In computer programming, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence between the instructions in the language and the architecture's machine code instructions. Assembly language usually has one statement per machine instruction (1:1), but constants, comments, assembler directives, symbolic labels of, e.g., memory locations, registers, and macros are generally also supported.
The first assembly code in which a language is used to represent machine code instructions is found in Kathleen and Andrew Donald Booth's 1947 work, "Coding for A.R.C.". Assembly code is converted into executable machine code by a utility program referred to as an "assembler". The term "assembler" is generally attributed to Wilkes, Wheeler and Gill in their 1951 book "The Preparation of Programs for an Electronic Digital Computer", who, however, used the term to mean "a program that assembles another program consisting of several sections into a single program". The conversion process is referred to as "assembly", as in "assembling" the source code. The computational step when an assembler is processing a program is called "assembly time".
|
Because assembly depends on the machine code instructions, each assembly language is specific to a particular computer architecture.
Sometimes there is more than one assembler for the same architecture, and sometimes an assembler is specific to an operating system or to particular operating systems. Most assembly languages do not provide specific syntax for operating system calls, and most assembly languages can be used universally with any operating system, as the language provides access to all the real capabilities of the processor, upon which all system call mechanisms ultimately rest. In contrast to assembly languages, most high-level programming languages are generally portable across multiple architectures but require interpreting or compiling, much more complicated tasks than assembling.
In the first decades of computing, it was commonplace for both systems programming and application programming to take place entirely in assembly language. While still irreplaceable for some purposes, the majority of programming is now conducted in higher-level interpreted and compiled languages. In "No Silver Bullet", Fred Brooks summarised the effects of the switch away from assembly language programming: "Surely the most powerful stroke for software productivity, reliability, and simplicity has been the progressive use of high-level languages for programming. Most observers credit that development with at least a factor of five in productivity, and with concomitant gains in reliability, simplicity, and comprehensibility."
|
Today, it is typical to use small amounts of assembly language code within larger systems implemented in a higher-level language, for performance reasons or to interact directly with hardware in ways unsupported by the higher-level language. For instance, just under 2% of version 4.9 of the Linux kernel source code is written in assembly; more than 97% is written in C.
Assembly language syntax.
Assembly language uses a mnemonic to represent, e.g., each low-level machine instruction or opcode, each directive, typically also each architectural register, flag, etc. Some of the mnemonics may be built-in and some user-defined. Many operations require one or more operands in order to form a complete instruction. Most assemblers permit named constants, registers, and labels for program and memory locations, and can calculate expressions for operands. Thus, programmers are freed from tedious repetitive calculations and assembler programs are much more readable than machine code. Depending on the architecture, these elements may also be combined for specific instructions or addressing modes using offsets or other data as well as fixed addresses. Many assemblers offer additional mechanisms to facilitate program development, to control the assembly process, and to aid debugging.
|
Some are column oriented, with specific fields in specific columns; this was very common for machines using punched cards in the 1950s and early 1960s. Some assemblers have free-form syntax, with fields separated by delimiters, e.g., punctuation, white space. Some assemblers are hybrid, with, e.g., labels, in a specific column and other fields separated by delimiters; this became more common than column-oriented syntax in the 1960s.
Key concepts.
Assembler.
An assembler program creates object code by translating combinations of mnemonics and syntax for operations and addressing modes into their numerical equivalents. This representation typically includes an "operation code" ("opcode") as well as other control bits and data. The assembler also calculates constant expressions and resolves symbolic names for memory locations and other entities. The use of symbolic references is a key feature of assemblers, saving tedious calculations and manual address updates after program modifications. Most assemblers also include macro facilities for performing textual substitution – e.g., to generate common short sequences of instructions as inline, instead of "called" subroutines.
|
Some assemblers may also be able to perform some simple types of instruction set-specific optimizations. One concrete example of this may be the ubiquitous x86 assemblers from various vendors. Called jump-sizing, most of them are able to perform jump-instruction replacements (long jumps replaced by short or relative jumps) in any number of passes, on request. Others may even do simple rearrangement or insertion of instructions, such as some assemblers for RISC architectures that can help optimize a sensible instruction scheduling to exploit the CPU pipeline as efficiently as possible.
Assemblers have been available since the 1950s, as the first step above machine language and before high-level programming languages such as Fortran, Algol, COBOL and Lisp. There have also been several classes of translators and semi-automatic code generators with properties similar to both assembly and high-level languages, with Speedcode as perhaps one of the better-known examples.
There may be several assemblers with different syntax for a particular CPU or instruction set architecture. For instance, an instruction to add memory data to a register in a x86-family processor might be codice_1, in original "Intel syntax", whereas this would be written codice_2 in the "AT&T syntax" used by the GNU Assembler. Despite different appearances, different syntactic forms generally generate the same numeric machine code. A single assembler may also have different modes in order to support variations in syntactic forms as well as their exact semantic interpretations (such as FASM-syntax, TASM-syntax, ideal mode, etc., in the special case of x86 assembly programming).
|
Number of passes.
There are two types of assemblers based on how many passes through the source are needed (how many times the assembler reads the source) to produce the object file.
In both cases, the assembler must be able to determine the size of each instruction on the initial passes in order to calculate the addresses of subsequent symbols. This means that if the size of an operation referring to an operand defined later depends on the type or distance of the operand, the assembler will make a pessimistic estimate when first encountering the operation, and if necessary, pad it with one or more
"no-operation" instructions in a later pass or the errata. In an assembler with peephole optimization, addresses may be recalculated between passes to allow replacing pessimistic code with code tailored to the exact distance from the target.
The original reason for the use of one-pass assemblers was memory size and speed of assembly – often a second pass would require storing the symbol table in memory (to handle forward references), rewinding and rereading the program source on tape, or rereading a deck of cards or punched paper tape. Later computers with much larger memories (especially disc storage), had the space to perform all necessary processing without such re-reading. The advantage of the multi-pass assembler is that the absence of errata makes the linking process (or the program load if the assembler directly produces executable code) faster.
|
Example: in the following code snippet, a one-pass assembler would be able to determine the address of the backward reference BKWD when assembling statement S2, but would not be able to determine the address of the forward reference FWD when assembling the branch statement S1; indeed, FWD may be undefined. A two-pass assembler would determine both addresses in pass 1, so they would be known when generating code in pass 2.
B
EQU *
EQU *
B
High-level assemblers.
More sophisticated high-level assemblers provide language abstractions such as:
See Language design below for more details.
Assembly language.
A program written in assembly language consists of a series of mnemonic processor instructions and meta-statements (known variously as declarative operations, directives, pseudo-instructions, pseudo-operations and pseudo-ops), comments and data. Assembly language instructions usually consist of an opcode mnemonic followed by an operand, which might be a list of data, arguments or parameters. Some instructions may be "implied", which means the data upon which the instruction operates is implicitly defined by the instruction itself—such an instruction does not take an operand. The resulting statement is translated by an assembler into machine language instructions that can be loaded into memory and executed.
|
For example, the instruction below tells an x86/IA-32 processor to move an immediate 8-bit value into a register. The binary code for this instruction is 10110 followed by a 3-bit identifier for which register to use. The identifier for the "AL" register is 000, so the following machine code loads the "AL" register with the data 01100001.
10110000 01100001
This binary computer code can be made more human-readable by expressing it in hexadecimal as follows.
B0 61
Here, codice_3 means "Move a copy of the following value into "AL"", and codice_4 is a hexadecimal representation of the value 01100001, which is 97 in decimal. Assembly language for the 8086 family provides the mnemonic MOV (an abbreviation of "move") for instructions such as this, so the machine code above can be written as follows in assembly language, complete with an explanatory comment if required, after the semicolon. This is much easier to read and to remember.
MOV AL, 61h ; Load AL with 97 decimal (61 hex)
In some assembly languages (including this one) the same mnemonic, such as MOV, may be used for a family of related instructions for loading, copying and moving data, whether these are immediate values, values in registers, or memory locations pointed to by values in registers or by immediate (a.k.a. direct) addresses. Other assemblers may use separate opcode mnemonics such as L for "move memory to register", ST for "move register to memory", LR for "move register to register", MVI for "move immediate operand to memory", etc.
|
If the same mnemonic is used for different instructions, that means that the mnemonic corresponds to several different binary instruction codes, excluding data (e.g. the codice_5 in this example), depending on the operands that follow the mnemonic. For example, for the x86/IA-32 CPUs, the Intel assembly language syntax codice_6 represents an instruction that moves the contents of register "AH" into register "AL". The hexadecimal form of this instruction is:
88 E0
The first byte, 88h, identifies a move between a byte-sized register and either another register or memory, and the second byte, E0h, is encoded (with three bit-fields) to specify that both operands are registers, the source is "AH", and the destination is "AL".
In a case like this where the same mnemonic can represent more than one binary instruction, the assembler determines which instruction to generate by examining the operands. In the first example, the operand codice_5 is a valid hexadecimal numeric constant and is not a valid register name, so only the codice_3 instruction can be applicable. In the second example, the operand codice_9 is a valid register name and not a valid numeric constant (hexadecimal, decimal, octal, or binary), so only the codice_10 instruction can be applicable.
|
Assembly languages are always designed so that this sort of lack of ambiguity is universally enforced by their syntax. For example, in the Intel x86 assembly language, a hexadecimal constant must start with a numeral digit, so that the hexadecimal number 'A' (equal to decimal ten) would be written as codice_11 or codice_12, not codice_9, specifically so that it cannot appear to be the name of register "AH". (The same rule also prevents ambiguity with the names of registers "BH", "CH", and "DH", as well as with any user-defined symbol that ends with the letter "H" and otherwise contains only characters that are hexadecimal digits, such as the word "BEACH".)
Returning to the original example, while the x86 opcode 10110000 (codice_3) copies an 8-bit value into the "AL" register, 10110001 (codice_15) moves it into "CL" and 10110010 (codice_16) does so into "DL". Assembly language examples for these follow.
MOV AL, 1h ; Load AL with immediate value 1
MOV CL, 2h ; Load CL with immediate value 2
MOV DL, 3h ; Load DL with immediate value 3
|
The syntax of MOV can also be more complex as the following examples show.
MOV EAX, [EBX] ; Move the 4 bytes in memory at the address contained in EBX into EAX
MOV [ESI+EAX], CL ; Move the contents of CL into the byte at address ESI+EAX
MOV DS, DX ; Move the contents of DX into segment register DS
In each case, the MOV mnemonic is translated directly into one of the opcodes 88-8C, 8E, A0-A3, B0-BF, C6 or C7 by an assembler, and the programmer normally does not have to know or remember which.
Transforming assembly language into machine code is the job of an assembler, and the reverse can at least partially be achieved by a disassembler. Unlike high-level languages, there is a one-to-one correspondence between many simple assembly statements and machine language instructions. However, in some cases, an assembler may provide "pseudoinstructions" (essentially macros) which expand into several machine language instructions to provide commonly needed functionality. For example, for a machine that lacks a "branch if greater or equal" instruction, an assembler may provide a pseudoinstruction that expands to the machine's "set if less than" and "branch if zero (on the result of the set instruction)". Most full-featured assemblers also provide a rich macro language (discussed below) which is used by vendors and programmers to generate more complex code and data sequences. Since the information about pseudoinstructions and macros defined in the assembler environment is not present in the object program, a disassembler cannot reconstruct the macro and pseudoinstruction invocations but can only disassemble the actual machine instructions that the assembler generated from those abstract assembly-language entities. Likewise, since comments in the assembly language source file are ignored by the assembler and have no effect on the object code it generates, a disassembler is always completely unable to recover source comments.
|
Each computer architecture has its own machine language. Computers differ in the number and type of operations they support, in the different sizes and numbers of registers, and in the representations of data in storage. While most general-purpose computers are able to carry out essentially the same functionality, the ways they do so differ; the corresponding assembly languages reflect these differences.
Multiple sets of mnemonics or assembly-language syntax may exist for a single instruction set, typically instantiated in different assembler programs. In these cases, the most popular one is usually that supplied by the CPU manufacturer and used in its documentation.
Two examples of CPUs that have two different sets of mnemonics are the Intel 8080 family and the Intel 8086/8088. Because Intel claimed copyright on its assembly language mnemonics (on each page of their documentation published in the 1970s and early 1980s, at least), some companies that independently produced CPUs compatible with Intel instruction sets invented their own mnemonics.
|
Two examples of CPUs that have two different sets of mnemonics are the Intel 8080 family and the Intel 8086/8088. Because Intel claimed copyright on its assembly language mnemonics (on each page of their documentation published in the 1970s and early 1980s, at least), some companies that independently produced CPUs compatible with Intel instruction sets invented their own mnemonics. The Zilog Z80 CPU, an enhancement of the Intel 8080A, supports all the 8080A instructions plus many more; Zilog invented an entirely new assembly language, not only for the new instructions but also for all of the 8080A instructions. For example, where Intel uses the mnemonics "MOV", "MVI", "LDA", "STA", "LXI", "LDAX", "STAX", "LHLD", and "SHLD" for various data transfer instructions, the Z80 assembly language uses the mnemonic "LD" for all of them. A similar case is the NEC V20 and V30 CPUs, enhanced copies of the Intel 8086 and 8088, respectively. Like Zilog with the Z80, NEC invented new mnemonics for all of the 8086 and 8088 instructions, to avoid accusations of infringement of Intel's copyright.
|
Like Zilog with the Z80, NEC invented new mnemonics for all of the 8086 and 8088 instructions, to avoid accusations of infringement of Intel's copyright. (It is questionable whether such copyrights can be valid, and later CPU companies such as AMD and Cyrix republished Intel's x86/IA-32 instruction mnemonics exactly with neither permission nor legal penalty.) It is doubtful whether in practice many people who programmed the V20 and V30 actually wrote in NEC's assembly language rather than Intel's; since any two assembly languages for the same instruction set architecture are isomorphic (somewhat like English and Pig Latin), there is no requirement to use a manufacturer's own published assembly language with that manufacturer's products.
|
"Hello, world!" on x86 Linux.
In 32-bit assembly language for Linux on an x86 processor, "Hello, world!" can be printed like this.
section .text
global _start
_start:
mov edx,len ; length of string, third argument to write()
mov ecx,msg ; address of string, second argument to write()
mov ebx,1 ; file descriptor (standard output), first argument to write()
mov eax,4 ; system call number for write()
int 0x80 ; system call trap
mov ebx,0 ; exit code, first argument to exit()
mov eax,1 ; system call number for exit()
int 0x80 ; system call trap
section .data
msg db 'Hello, world!', 0xa
len equ $ - msg
Language design.
Basic elements.
There is a large degree of diversity in the way the authors of assemblers categorize statements and in the nomenclature that they use. In particular, some describe anything other than a machine mnemonic or extended mnemonic as a pseudo-operation (pseudo-op). A typical assembly language consists of 3 types of instruction statements that are used to define program operations:
|
Opcode mnemonics and extended mnemonics.
Instructions (statements) in assembly language are generally very simple, unlike those in high-level languages. Generally, a mnemonic is a symbolic name for a single executable machine language instruction (an opcode), and there is at least one opcode mnemonic defined for each machine language instruction. Each instruction typically consists of an "operation" or "opcode" plus zero or more "operands". Most instructions refer to a single value or a pair of values. Operands can be immediate (value coded in the instruction itself), registers specified in the instruction or implied, or the addresses of data located elsewhere in storage. This is determined by the underlying processor architecture: the assembler merely reflects how this architecture works. "Extended mnemonics" are often used to specify a combination of an opcode with a specific operand, e.g., the System/360 assemblers use as an extended mnemonic for with a mask of 15 and ("NO OPeration" – do nothing for one step) for with a mask of 0.
|
"Extended mnemonics" are often used to support specialized uses of instructions, often for purposes not obvious from the instruction name. For example, many CPU's do not have an explicit NOP instruction, but do have instructions that can be used for the purpose. In 8086 CPUs the instruction is used for , with being a pseudo-opcode to encode the instruction . Some disassemblers recognize this and will decode the instruction as . Similarly, IBM assemblers for System/360 and System/370 use the extended mnemonics and for and with zero masks. For the SPARC architecture, these are known as "synthetic instructions".
Some assemblers also support simple built-in macro-instructions that generate two or more machine instructions. For instance, with some Z80 assemblers the instruction is recognized to generate followed by . These are sometimes known as "pseudo-opcodes".
Mnemonics are arbitrary symbols; in 1985 the IEEE published Standard 694 for a uniform set of mnemonics to be used by all assemblers. The standard has since been withdrawn.
|
Data directives.
There are instructions used to define data elements to hold data and variables. They define the type of data, the length and the alignment of data. These instructions can also define whether the data is available to outside programs (programs assembled separately) or only to the program in which the data section is defined. Some assemblers classify these as pseudo-ops.
Assembly directives.
Assembly directives, also called pseudo-opcodes, pseudo-operations or pseudo-ops, are commands given to an assembler "directing it to perform operations other than assembling instructions". Directives affect how the assembler operates and "may affect the object code, the symbol table, the listing file, and the values of internal assembler parameters". Sometimes the term "pseudo-opcode" is reserved for directives that generate object code, such as those that generate data.
The names of pseudo-ops often start with a dot to distinguish them from machine instructions. Pseudo-ops can make the assembly of the program dependent on parameters input by a programmer, so that one program can be assembled in different ways, perhaps for different applications. Or, a pseudo-op can be used to manipulate presentation of a program to make it easier to read and maintain. Another common use of pseudo-ops is to reserve storage areas for run-time data and optionally initialize their contents to known values.
|
Symbolic assemblers let programmers associate arbitrary names ("labels" or "symbols") with memory locations and various constants. Usually, every constant and variable is given a name so instructions can reference those locations by name, thus promoting self-documenting code. In executable code, the name of each subroutine is associated with its entry point, so any calls to a subroutine can use its name. Inside subroutines, GOTO destinations are given labels. Some assemblers support "local symbols" which are often lexically distinct from normal symbols (e.g., the use of "10$" as a GOTO destination).
Some assemblers, such as NASM, provide flexible symbol management, letting programmers manage different namespaces, automatically calculate offsets within data structures, and assign labels that refer to literal values or the result of simple computations performed by the assembler. Labels can also be used to initialize constants and variables with relocatable addresses.
Assembly languages, like most other computer languages, allow comments to be added to program source code that will be ignored during assembly. Judicious commenting is essential in assembly language programs, as the meaning and purpose of a sequence of binary machine instructions can be difficult to determine. The "raw" (uncommented) assembly language generated by compilers or disassemblers is quite difficult to read when changes must be made.
|
Macros.
Many assemblers support "predefined macros", and others support "programmer-defined" (and repeatedly re-definable) macros involving sequences of text lines in which variables and constants are embedded. The macro definition is most commonly a mixture of assembler statements, e.g., directives, symbolic machine instructions, and templates for assembler statements. This sequence of text lines may include opcodes or directives. Once a macro has been defined its name may be used in place of a mnemonic. When the assembler processes such a statement, it replaces the statement with the text lines associated with that macro, then processes them as if they existed in the source code file (including, in some assemblers, expansion of any macros existing in the replacement text). Macros in this sense date to IBM autocoders of the 1950s.
Macro assemblers typically have directives to, e.g., define macros, define variables, set variables to the result of an arithmetic, logical or string expression, iterate, conditionally generate code. Some of those directives may be restricted to use within a macro definition, e.g., MEXIT in HLASM, while others may be permitted within open code (outside macro definitions), e.g., AIF and COPY in HLASM.
|
In assembly language, the term "macro" represents a more comprehensive concept than it does in some other contexts, such as the pre-processor in the C programming language, where its #define directive typically is used to create short single line macros. Assembler macro instructions, like macros in PL/I and some other languages, can be lengthy "programs" by themselves, executed by interpretation by the assembler during assembly.
Since macros can have 'short' names but expand to several or indeed many lines of code, they can be used to make assembly language programs appear to be far shorter, requiring fewer lines of source code, as with higher level languages. They can also be used to add higher levels of structure to assembly programs, optionally introduce embedded debugging code via parameters and other similar features.
|
Macros were used to customize large scale software systems for specific customers in the mainframe era and were also used by customer personnel to satisfy their employers' needs by making specific versions of manufacturer operating systems. This was done, for example, by systems programmers working with IBM's Conversational Monitor System / Virtual Machine (VM/CMS) and with IBM's "real time transaction processing" add-ons, Customer Information Control System CICS, and ACP/TPF, the airline/financial system that began in the 1970s and still runs many large computer reservation systems (CRS) and credit card systems today.
It is also possible to use solely the macro processing abilities of an assembler to generate code written in completely different languages, for example, to generate a version of a program in COBOL using a pure macro assembler program containing lines of COBOL code inside assembly time operators instructing the assembler to generate arbitrary code. IBM OS/360 uses macros to perform system generation. The user specifies options by coding a series of assembler macros. Assembling these macros generates a job stream to build the system, including job control language and utility control statements.
|
This is because, as was realized in the 1960s, the concept of "macro processing" is independent of the concept of "assembly", the former being in modern terms more word processing, text processing, than generating object code. The concept of macro processing appeared, and appears, in the C programming language, which supports "preprocessor instructions" to set variables, and make conditional tests on their values. Unlike certain previous macro processors inside assemblers, the C preprocessor is not Turing-complete because it lacks the ability to either loop or "go to", the latter allowing programs to loop.
Despite the power of macro processing, it fell into disuse in many high level languages (major exceptions being C, C++ and PL/I) while remaining a perennial for assemblers.
Macro parameter substitution is strictly by name: at macro processing time, the value of a parameter is textually substituted for its name. The most famous class of bugs resulting was the use of a parameter that itself was an expression and not a simple name when the macro writer expected a name. In the macro:
|
foo: macro a
load a*b
the intention was that the caller would provide the name of a variable, and the "global" variable or constant b would be used to multiply "a". If foo is called with the parameter codice_17, the macro expansion of codice_18 occurs. To avoid any possible ambiguity, users of macro processors can parenthesize formal parameters inside macro definitions, or callers can parenthesize the input parameters.
Support for structured programming.
Packages of macros have been written providing structured programming elements to encode execution flow. The earliest example of this approach was in the Concept-14 macro set, originally proposed by Harlan Mills (March 1970), and implemented by Marvin Kessler at IBM's Federal Systems Division, which provided IF/ELSE/ENDIF and similar control flow blocks for OS/360 assembler programs. This was a way to reduce or eliminate the use of GOTO operations in assembly code, one of the main factors causing spaghetti code in assembly language. This approach was widely accepted in the early 1980s (the latter days of large-scale assembly language use). IBM's High Level Assembler Toolkit includes such a macro package.
|
Another design was A-Natural, a "stream-oriented" assembler for 8080/Z80 processors from Whitesmiths Ltd. (developers of the Unix-like Idris operating system, and what was reported to be the first commercial C compiler). The language was classified as an assembler because it worked with raw machine elements such as opcodes, registers, and memory references; but it incorporated an expression syntax to indicate execution order. Parentheses and other special symbols, along with block-oriented structured programming constructs, controlled the sequence of the generated instructions. A-natural was built as the object language of a C compiler, rather than for hand-coding, but its logical syntax won some fans.
There has been little apparent demand for more sophisticated assemblers since the decline of large-scale assembly language development. In spite of that, they are still being developed and applied in cases where resource constraints or peculiarities in the target system's architecture prevent the effective use of higher-level languages.
|
Assemblers with a strong macro engine allow structured programming via macros, such as the switch macro provided with the Masm32 package (this code is a complete program):
include \masm32\include\masm32rt.inc ; use the Masm32 library
.code
demomain:
REPEAT 20
switch rv(nrandom, 9) ; generate a number between 0 and 8
mov ecx, 7
case 0
print "case 0"
case ecx ; in contrast to most other programming languages,
print "case 7" ; the Masm32 switch allows "variable cases"
case 1 .. 3
.if eax==1
print "case 1"
.elseif eax==2
print "case 2"
.else
print "cases 1 to 3: other"
.endif
case 4, 6, 8
print "cases 4, 6 or 8"
default
mov ebx, 19 ; print 20 stars
.Repeat
print "*"
dec ebx
.Until Sign? ; loop until the sign flag is set
endsw
print chr$(13, 10)
ENDM
exit
end demomain
Use of assembly language.
When the stored-program computer was introduced programs were written in machine code, and loaded into the computer from punched paper tape or toggled directly into memory from console switches. Kathleen Booth "is credited with inventing assembly language" based on theoretical work she began in 1947, while working on the ARC2 at Birkbeck, University of London following consultation by Andrew Booth (later her husband) with mathematician John von Neumann and physicist Herman Goldstine at the Institute for Advanced Study.
|
In late 1948, the Electronic Delay Storage Automatic Calculator (EDSAC) had an assembler (named "initial orders") integrated into its bootstrap program. It used one-letter mnemonics developed by David Wheeler, who is credited by the IEEE Computer Society as the creator of the first "assembler". Reports on the EDSAC introduced the term "assembly" for the process of combining fields into an instruction word. SOAP (Symbolic Optimal Assembly Program) was an assembly language for the IBM 650 computer written by Stan Poley in 1955.
Assembly languages eliminated much of the error-prone, tedious, and time-consuming first-generation programming needed with the earliest computers, freeing programmers from tedium such as remembering numeric codes and calculating addresses. They were once widely used for all sorts of programming. By the late 1950s their use had largely been supplanted by higher-level languages in the search for improved programming productivity. Today, assembly language is still used for direct hardware manipulation, access to specialized processor instructions, or to address critical performance issues. Typical uses are device drivers, low-level embedded systems, and real-time systems (see ).
|
Numerous programs were written entirely in assembly language. The Burroughs MCP (1961) was the first computer for which an operating system was not developed entirely in assembly language; it was written in Executive Systems Problem Oriented Language (ESPOL), an Algol dialect. Many commercial applications were written in assembly language as well, including a large amount of the IBM mainframe software developed by large corporations. COBOL, FORTRAN and some PL/I eventually displaced assembly language, although a number of large organizations retained assembly-language application infrastructures well into the 1990s.
Assembly language was the primary development language for 8-bit home computers such as the Apple II, Atari 8-bit computers, ZX Spectrum, and Commodore 64. Interpreted BASIC on these systems did not offer maximum execution speed and full use of facilities to take full advantage of the available hardware. Assembly language was the default choice for programming 8-bit consoles such as the Atari 2600 and Nintendo Entertainment System.
|
Key software for IBM PC compatibles such as MS-DOS, Turbo Pascal, and the Lotus 1-2-3 spreadsheet was written in assembly language. As computer speed grew exponentially, assembly language became a tool for speeding up parts of programs, such as the rendering of "Doom", rather than a dominant development language. In the 1990s, assembly language was used to maximise performance from systems such as the Sega Saturn, and as the primary language for arcade hardware using the TMS34010 integrated CPU/GPU such as "Mortal Kombat" and "NBA Jam".
Current usage.
There has been debate over the usefulness and performance of assembly language relative to high-level languages.
Although assembly language has specific niche uses where it is important (see below), there are other tools for optimization.
, the TIOBE index of programming language popularity ranks assembly language at 11, ahead of Visual Basic, for example. Assembler can be used to optimize for speed or optimize for size. In the case of speed optimization, modern optimizing compilers are claimed to render high-level languages into code that can run as fast as hand-written assembly, despite some counter-examples. The complexity of modern processors and memory sub-systems makes effective optimization increasingly difficult for compilers and assembly programmers alike. Increasing processor performance has meant that most CPUs sit idle most of the time, with delays caused by predictable bottlenecks such as cache misses, I/O operations and paging, making raw code execution speed a non-issue for many programmers.
|
There are still certain computer programming domains in which the use of assembly programming is more common:
Assembly language is still taught in most computer science and electronic engineering programs. Although few programmers today regularly work with assembly language as a tool, the underlying concepts remain important. Such fundamental topics as binary arithmetic, memory allocation, stack processing, character set encoding, interrupt processing, and compiler design would be hard to study in detail without a grasp of how a computer operates at the hardware level. Since a computer's behaviour is fundamentally defined by its instruction set, the logical way to learn such concepts is to study an assembly language. Most modern computers have similar instruction sets. Therefore, studying a single assembly language is sufficient to learn the basic concepts, recognize situations where the use of assembly language might be appropriate, and to see how efficient executable code can be created from high-level languages.
|
Ambrosia
In the ancient Greek myths, ambrosia (, ) is the food or drink of the Greek gods, and is often depicted as conferring longevity or immortality upon whoever consumed it. It was brought to the gods in Olympus by doves and served either by Hebe or by Ganymede at the heavenly feast.
Ancient art sometimes depicted ambrosia as distributed by the nymph named Ambrosia, a nurse of Dionysus.
Definition.
Ambrosia is very closely related to the gods' other form of sustenance, "nectar". The two terms may not have originally been distinguished; though in Homer's poems nectar is usually the drink and ambrosia the food of the gods; it was with ambrosia that Hera "cleansed all defilement from her lovely flesh", and with ambrosia Athena prepared Penelope in her sleep, so that when she appeared for the final time before her suitors, the effects of years had been stripped away, and they were inflamed with passion at the sight of her. On the other hand, in Alcman, nectar is the food, and in Sappho and Anaxandrides, ambrosia is the drink. A character in Aristophanes' "Knights" says, "I dreamed the goddess poured ambrosia over your head—out of a ladle." Both descriptions could be correct, as ambrosia could be a liquid considered a food (such as honey).
|
The consumption of ambrosia was typically reserved for divine beings. Upon his assumption into immortality on Olympus, Heracles is given ambrosia by Athena, while the hero Tydeus is denied the same thing when the goddess discovers him eating human brains. In one version of the myth of Tantalus, part of Tantalus' crime is that after tasting ambrosia himself, he attempts to steal some to give to other mortals. Those who consume ambrosia typically have ichor, not blood, in their veins.
Both nectar and ambrosia are fragrant, and may be used as perfume: in the "Odyssey" Menelaus and his men are disguised as seals in untanned seal skins, "and the deadly smell of the seal skins vexed us sore; but the goddess saved us; she brought ambrosia and put it under our nostrils." Homer speaks of ambrosial raiment, ambrosial locks of hair, even the gods' ambrosial sandals.
Among later writers, ambrosia has been so often used with generic meanings of "delightful liquid" that such late writers as Athenaeus, Paulus and Dioscurides employ it as a technical term in contexts of cookery, medicine, and botany. Pliny used the term in connection with different plants, as did early herbalists.
|
Additionally, some modern ethnomycologists, such as Danny Staples, identify ambrosia with the hallucinogenic mushroom "Amanita muscaria": "it was the food of the gods, their ambrosia, and nectar was the pressed sap of its juices", Staples asserts.
W. H. Roscher thinks that both nectar and ambrosia were kinds of honey, in which case their power of conferring immortality would be due to the supposed healing and cleansing powers of honey, and because fermented honey (mead) preceded wine as an entheogen in the Aegean world; on some Minoan seals, goddesses were represented with bee faces (compare Merope and Melissa).
Etymology.
The concept of an immortality drink is attested in at least two ancient Indo-European languages: Greek and Sanskrit. The Greek ἀμβροσία ("ambrosia") is semantically linked to the Sanskrit ("amṛta") as both words denote a drink or food that gods use to achieve immortality. The two words appear to be derived from the same Indo-European form *"ṇ-mṛ-tós", "un-dying" ("n-": negative prefix from which the prefix "a-" in both Greek and Sanskrit are derived; "mṛ": zero grade of *"mer-", "to die"; and "-to-": adjectival suffix). A semantically similar etymology exists for nectar, the beverage of the gods (Greek: νέκταρ "néktar") presumed to be a compound of the PIE roots "*nek-", "death", and "-*tar", "overcoming".
Ambrosia (nymph).
Lycurgus, king of Thrace, forbade the cult of Dionysus, whom he drove from Thrace, and attacked the gods' entourage when they celebrated the god. Among them was Ambrosia, who turned herself into a grapevine to hide from his wrath. Dionysus, enraged by the king's actions, drove him mad. In his fit of insanity he killed his son, whom he mistook for a stock of ivy, and then himself.
|
Ambrose
Ambrose of Milan (; 4 April 397), venerated as Saint Ambrose, was a theologian and statesman who served as Bishop of Milan from 374 to 397. He expressed himself prominently as a public figure, fiercely promoting Roman Christianity against Arianism and paganism. He left a substantial collection of writings, of which the best known include the ethical commentary "De officiis ministrorum" (377–391), and the exegetical (386–390). His preaching, his actions and his literary works, in addition to his innovative musical hymnography, made him one of the most influential ecclesiastical figures of the 4th century.
Ambrose was serving as the Roman governor of Aemilia-Liguria in Milan when he was unexpectedly made Bishop of Milan in 374 by popular acclamation. As bishop, he took a firm position against Arianism and attempted to mediate the conflict between the emperors Theodosius I and Magnus Maximus. Tradition credits Ambrose with developing an antiphonal chant, known as Ambrosian chant, and for composing the "Te Deum" hymn, though modern scholars now reject both of these attributions. Ambrose's authorship on at least four hymns, including the well-known "Veni redemptor gentium", is secure; they form the core of the Ambrosian hymns, which includes others that are sometimes attributed to him. He also had a notable influence on Augustine of Hippo (354–430), whom he helped convert to Christianity.
|
Western Christianity identified Ambrose, along with Augustine, Jerome and pope Gregory the Great, as one of the four Great Latin Church Fathers, declared Doctors of the Church in 1298. He is considered a saint by the Catholic Church, Eastern Orthodox Church, Anglican Communion, and various Lutheran denominations, and venerated as the patron saint of Milan and beekeepers.
Background and career.
Legends about Ambrose had spread through the empire long before his biography was written, making it difficult for modern historians to understand his true character and fairly place his behaviour within the context of antiquity. Most agree he was the personification of his era. This would make Ambrose a genuinely spiritual man who spoke up and defended his faith against opponents, an aristocrat who retained many of the attitudes and practices of a Roman governor, and also an ascetic who served the poor.
Early life.
Ambrose was born into a Roman Christian family, of Greek descent, in the year 339. Ambrose himself wrote that he was 53 years old in his letter number 49, which has been dated to 392. He began life in Augusta Treverorum (modern Trier) the capital of the Roman province of Gallia Belgica in what was then northeastern Gaul and is now in the Rhineland-Palatinate in Germany. Scholars disagree on who exactly his father was. His father is sometimes identified with Aurelius Ambrosius, a praetorian prefect of Gaul; but some scholars identify his father as an official named Uranius who received an imperial constitution dated 3 February 339 (addressed in a brief extract from one of the three emperors ruling in 339, Constantine II, Constantius II, or Constans, in the "Codex Theodosianus", book XI.5). What does seem certain is that Ambrose was born in Trier and his father was either the praetorian prefect or part of his administration.
|
A legend about Ambrose as an infant recounts that a swarm of bees settled on his face while he lay in his cradle, leaving behind a drop of honey. His father is said to have considered this a sign of his future eloquence and honeyed tongue. Bees and beehives often appear in the saint's symbology.
Ambrose's mother was a woman of intellect and piety. It was probable that she was a member of the Roman family "Aurelii Symmachi", which would make Ambrose a cousin of the orator Quintus Aurelius Symmachus. The family had produced one martyr (the virgin Soteris) in its history. Ambrose was the youngest of three children. His siblings were Satyrus, the subject of Ambrose's "De excessu fratris Satyri", and Marcellina, who made a profession of virginity sometime between 352 and 355; Pope Liberius himself conferred the veil upon her. Both Ambrose's siblings also became venerated as saints.
Sometime early in the life of Ambrose, his father died. At an unknown later date, his mother left Trier with her three children, and the family moved to Rome. There Ambrose studied literature, law, and rhetoric. He then followed in his father's footsteps and entered public service. Praetorian Prefect Sextus Claudius Petronius Probus first gave him a place as a judicial councillor, and then in about 372 made him governor of the province of Liguria and Emilia, with headquarters in Milan.
|
Bishop of Milan.
In 374 the bishop of Milan, Auxentius, an Arian, died, and the Arians challenged the succession. Ambrose went to the church where the election was to take place to prevent an uproar which seemed probable in this crisis. His address was interrupted by a call, "Ambrose, bishop!", which was taken up by the whole assembly.
Ambrose, though known to be Nicene Christian in belief, was considered acceptable to Arians due to the charity he had shown concerning their beliefs. At first, he energetically refused the office of bishop, for which he felt he was in no way prepared: Ambrose was a relatively new Christian who was not yet baptized nor formally trained in theology. Ambrose fled to a colleague's home, seeking to hide. Upon receiving a letter from the Emperor Gratian praising the appropriateness of Rome appointing individuals worthy of holy positions, Ambrose's host gave him up. Within a week, he was baptized, ordained and duly consecrated as the new bishop of Milan. This was the first time in the West that a member of the upper class of high officials had accepted the office of bishop.
|
As bishop, he immediately adopted an ascetic lifestyle, apportioned his money to the poor, donating all of his land, making only provision for his sister Marcellina. While Bishop of Milan, Ambrose carefully cultivated practices that respected local customs and that reflected his spiritual beliefs. He understood the link between a religious leader's life and their ability to model morality for congregants. In his work "De Officiis" (377-391), he asked, "How can you consider a man to be better than you when it comes to giving advice if you see that he is worse than you when it comes to morality?" His humble and upright ways raised his standing among his people even further; it was his popularity with the people that gave him considerable political leverage throughout his career. Upon the unexpected appointment of Ambrose to the episcopate, his brother Satyrus resigned a prefecture in order to move to Milan, where he took over managing the diocese's temporal affairs.
Arianism.
Arius (died 336) was a Christian priest who around the year 300 asserted that God the Father must have created the Son, indicating that the Son was a lesser being who was not eternal and of a different "essence" from God the Father. This Christology, though contrary to tradition, quickly spread through Egypt, Libya and other Roman provinces. Bishops engaged in the dispute, and the people divided into parties, sometimes demonstrating in the streets in support of one side or the other.
|
Arianism appealed to many high-level leaders and clergy in both the Western and Eastern empires. Although the western Emperor Gratian () supported orthodoxy, his younger half brother Valentinian II, who became his colleague in the empire in 375, adhered to the Arian creed. Ambrose sought to refute Arian propositions theologically, but Ambrose did not sway the young prince's position. In the East, Emperor Theodosius I () likewise professed the Nicene creed; but there were many adherents of Arianism throughout his dominions, especially among the higher clergy.
In this state of religious ferment, two leaders of the Arians, bishops Palladius of Ratiaria and Secundianus of Singidunum, confident of numbers, prevailed upon Gratian to call a general council from all parts of the empire. This request appeared so equitable that Gratian complied without hesitation. However, Ambrose feared the consequences and prevailed upon the emperor to have the matter determined by a council of the Western bishops. Accordingly, a synod composed of thirty-two bishops was held at Aquileia in the year 381. Ambrose was elected president and Palladius, being called upon to defend his opinions, declined. A vote was then taken and Palladius and his associate Secundianus were deposed from their episcopal offices.
|
Ambrose struggled with Arianism for over half of his term in the episcopate. Ecclesiastical unity was important to the church, but it was no less important to the state, and as a Roman, Ambrose felt strongly about that. Conflict over heresies loomed large in an age of religious ferment comparable to the Reformation of the fourteenth and fifteenth centuries. Orthodox Christianity was determining how to define itself as it faced multiple challenges on both a theological and a practical level, and Ambrose exercised crucial influence at a crucial time.
Imperial relations.
Ambrose had good relations and varying levels of influence with the Roman emperors Gratian, Valentinian II and Theodosius I, but exactly how much influence, what kind of influence, and in what ways, when, has been debated in the scholarship of the late twentieth and early twenty-first centuries.
Gratian.
It has long been convention to see Gratian and Ambrose as having a personal friendship, putting Ambrose in the dominant role of spiritual guide, but modern scholars now find this view hard to support from the sources. The ancient Christian historian Sozomen () is the only ancient source that shows Ambrose and Gratian together in any personal interaction. In that interaction, Sozomen relates that, in the last year of Gratian's reign, Ambrose intruded on Gratian's private hunting party in order to appeal on behalf of a pagan senator sentenced to die. After years of acquaintance, according to professor Neil B. McLynn, this indicates that Ambrose could not take for granted that Gratian would see him, so instead, Ambrose had to resort to such manoeuvrings to make his appeal.
|
Gratian was personally devout long before meeting Ambrose. Modern scholarship indicates Gratian's religious policies do not evidence capitulation to Ambrose more than they evidence Gratian's own views. Gratian's devotion did lead Ambrose to write a large number of books and letters of theology and spiritual commentary dedicated to the emperor. The sheer volume of these writings and the effusive praise they contain has led many historians to conclude that Gratian was dominated by Ambrose, and it was that dominance that produced Gratian's anti-pagan actions. McLynn asserts that effusive praises were common in everyone's correspondence with the crown. He adds that Gratian's actions were determined by the constraints of the system as much as "by his own initiatives or Ambrose's influence".
McLynn asserts that the largest influence on Gratian's policy was the profound change in political circumstances produced by the Battle of Adrianople in 378. Gratian had become involved in fighting the Goths the previous year and had been on his way to the Balkans when his uncle and the "cream of the eastern army" were destroyed at Adrianople. Gratian withdrew to Sirmium and set up his court there. Several rival groups, including the Arians, sought to secure benefits from the government at Sirmium. In an Arian attempt to undermine Ambrose, whom Gratian had not yet met, Gratian was "warned" that Ambrose's faith was suspect. Gratian took steps to investigate by writing to Ambrose and asking him to explain his faith.
|
Ambrose and Gratian first met, after this, in 379 during a visit to Milan. The bishop made a good impression on Gratian and his court, which was pervasively Christian and aristocratic – much like Ambrose himself. The emperor returned to Milan in 380 to find that Ambrose had complied with his request for a statement of his faith – in two volumes – known as "De Fide": a statement of orthodoxy and of Ambrose' political theology, as well as a polemic against the Arian heresy – intended for public discussion. The emperor had not asked to be instructed by Ambrose, and in "De Fide" Ambrose states this clearly. Nor was he asked to refute the Arians. He was asked to justify his own position, but in the end, he did all three.
It seems that by 382 Ambrose had replaced Ausonius to become a major influence in Gratian's court. Ambrose had not yet become the "conscience" of kings he would in the later 380s, but he did speak out against reinstating the Altar of Victory. In 382, Gratian was the first to divert public financial subsidies that had previously supported Rome's cults. Before that year, contributions in support of the ancient customs had continued unchallenged by the state.
|
Valentinian II.
The childless Gratian had treated his younger brother Valentinian II like a son. Ambrose, on the other hand, had incurred the lasting enmity of Valentinian II's mother, the Empress Justina, in the winter of 379 by helping to appoint a Nicene bishop in Sirmium. Not long after this, Valentinian II, his mother, and the court left Sirmium; Sirmium had come under Theodosius' control, so they went to Milan which was ruled by Gratian.
In 383 Gratian was assassinated at Lyon, in Gaul (France) by Magnus Maximus. Valentinian was twelve years old, and the assassination left his mother, Justina, in a position of something akin to a regent. In 385 (or 386) the emperor Valentinian II and his mother Justina, along with a considerable number of clergy, the laity, and the military, professed Arianism. Conflict between Ambrose and Justina soon followed.
The Arians demanded that Valentinian allocate to them two churches in Milan: one in the city (the Basilica of the Apostles), the other in the suburbs (St Victor's). Ambrose refused to surrender the churches. He answered by saying that "What belongs to God, is outside the emperor's power." In this, Ambrose called on an ancient Roman principle: a temple set apart to a god became the property of that god. Ambrose now applied this ancient legal principle to the Christian churches, seeing the bishop, as a divine representative, as guardian of his god's property.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.