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AutoCAD LT
AutoCAD LT is the lower-cost version of AutoCAD, with reduced capabilities, first released in November 1993. Autodesk developed AutoCAD LT to have an entry-level CAD package to compete in the lower price level. Priced at $495, it became the first AutoCAD product priced below $1000. It was sold directly by Au... | AutoCAD | Wikipedia | 462 | 2753 | https://en.wikipedia.org/wiki/AutoCAD | Technology | Science and Engineering | null |
AutoCAD WS began with a version for the iPhone and subsequently expanded to include versions for the iPod Touch, iPad, Android phones, and Android tablets. Autodesk released the iOS version in September 2010, following with the Android version on April 20, 2011. The program is available via download at no cost from the... | AutoCAD | Wikipedia | 327 | 2753 | https://en.wikipedia.org/wiki/AutoCAD | Technology | Science and Engineering | null |
Student versions
AutoCAD is licensed, for free, to students, educators, and educational institutions, with a 12-month renewable license available. Licenses acquired before March 25, 2020, were a 36-month license, with its last renovation on March 24, 2020. The student version of AutoCAD is functionally identical to the... | AutoCAD | Wikipedia | 197 | 2753 | https://en.wikipedia.org/wiki/AutoCAD | Technology | Science and Engineering | null |
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individua... | Asexual reproduction | Wikipedia | 437 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Some cells divide by budding (for example baker's yeast), resulting in a "mother" and a "daughter" cell that is initially smaller than the parent. Budding is also known on a multicellular level; an animal example is the hydra, which reproduces by budding. The buds grow into fully matured individuals which eventually br... | Asexual reproduction | Wikipedia | 340 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Many multicellular organisms produce spores during their biological life cycle in a process called sporogenesis. Exceptions are animals and some protists, which undergo meiosis immediately followed by fertilization. Plants and many algae on the other hand undergo sporic meiosis where meiosis leads to the formation of h... | Asexual reproduction | Wikipedia | 338 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. Fragmentation is seen in many organisms. Animals that reproduce asexually include planarians, many annelid worms including polychaetes and some oligocha... | Asexual reproduction | Wikipedia | 486 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
In facultative parthenogenesis, females can reproduce both sexually and asexually. Because of the many advantages of sexual reproduction, most facultative parthenotes only reproduce asexually when forced to. This typically occurs in instances when finding a mate becomes difficult. For example, female zebra sharks will ... | Asexual reproduction | Wikipedia | 421 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Apomixis in plants is the formation of a new sporophyte without fertilization. It is important in ferns and in flowering plants, but is very rare in other seed plants. In flowering plants, the term "apomixis" is now most often used for agamospermy, the formation of seeds without fertilization, but was once used to incl... | Asexual reproduction | Wikipedia | 492 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Male apomixis
Other type of androgenesis is the male apomixis or paternal apomixis is a reproductive process in which a plant develops from a sperm cell (male gamete) without the participation of a female cell (ovum). In this process, the zygote is formed solely with genetic material from the father, resulting in offsp... | Asexual reproduction | Wikipedia | 497 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Other species where androgenesis has been observed naturally are the stick insects Bacillus rossius and Bassillus Grandii, the little fire ant Wasmannia auropunctata, Vollenhovia emeryi, Paratrechina longicornis, occasionally in Apis mellifera, the Hypseleotris carp gudgeons, the parasitoid Venturia canescens, and occa... | Asexual reproduction | Wikipedia | 450 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
The slime mold Dictyostelium undergoes binary fission (mitosis) as single-celled amoebae under favorable conditions. However, when conditions turn unfavorable, the cells aggregate and follow one of two different developmental pathways, depending on conditions. In the social pathway, they form a multi-cellular slug whic... | Asexual reproduction | Wikipedia | 502 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Polyembryony is a widespread form of asexual reproduction in animals, whereby the fertilized egg or a later stage of embryonic development splits to form genetically identical clones. Within animals, this phenomenon has been best studied in the parasitic Hymenoptera. In the nine-banded armadillos, this process is oblig... | Asexual reproduction | Wikipedia | 386 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
Adaptive significance of asexual reproduction
A complete lack of sexual reproduction is relatively rare among multicellular organisms, particularly animals. It is not entirely understood why the ability to reproduce sexually is so common among them. Current hypotheses suggest that asexual reproduction may have short t... | Asexual reproduction | Wikipedia | 197 | 2756 | https://en.wikipedia.org/wiki/Asexual%20reproduction | Biology and health sciences | Biological reproduction | null |
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.
The International Union of Pure and Applied Chemistry (IUPAC) recommends using the name "alkene" only for acycl... | Alkene | Wikipedia | 454 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
: ethylene only
: propylene only
: 3 isomers: 1-butene, 2-butene, and isobutylene
: 5 isomers: 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene
: 13 isomers: 1-hexene, 2-hexene, 3-hexene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-methyl-2-pentene, 3-methyl-2-pentene... | Alkene | Wikipedia | 467 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Rotation about the carbon–carbon double bond is restricted because it incurs an energetic cost to break the alignment of the p orbitals on the two carbon atoms. Consequently cis or trans isomers interconvert so slowly that they can be freely handled at ambient conditions without isomerization. More complex alkenes may ... | Alkene | Wikipedia | 462 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
For there to be cis- and trans- configurations, there must be a carbon chain, or at least one functional group attached to each carbon is the same for both. E- and Z- configuration can be used instead in a more general case where all four functional groups attached to carbon atoms in a double bond are different. E- and... | Alkene | Wikipedia | 463 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
NMR spectroscopy
In 1H NMR spectroscopy, the hydrogen bonded to the carbon adjacent to double bonds will give a δH of 4.5–6.5 ppm. The double bond will also deshield the hydrogen attached to the carbons adjacent to sp2 carbons, and this generates δH=1.6–2. ppm peaks. Cis/trans isomers are distinguishable due to differ... | Alkene | Wikipedia | 443 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Similarly, halogenation involves the addition of a halogen molecule, such as Br2, resulting in a dihaloalkane. The equation of bromination of ethylene to form ethane is:
H2C=CH2 + Br2→H2CBr−CH2Br
Unlike hydrogenation, these halogenation reactions do not require catalysts. The reaction occurs in two steps, with a haloni... | Alkene | Wikipedia | 497 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
For ethylene, the epoxidation is conducted on a very large scale industrially using oxygen in the presence of silver-based catalysts:
Alkenes react with ozone, leading to the scission of the double bond. The process is called ozonolysis. Often the reaction procedure includes a mild reductant, such as dimethylsulfide... | Alkene | Wikipedia | 487 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Allylic substitution
The presence of a C=C π bond in unsaturated hydrocarbons weakens the dissociation energy of the allylic C−H bonds. Thus, these groupings are susceptible to free radical substitution at these C-H sites as well as addition reactions at the C=C site. In the presence of radical initiators, allylic C-... | Alkene | Wikipedia | 498 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Catalytic synthesis of higher α-alkenes (of the type RCH=CH2) can also be achieved by a reaction of ethylene with the organometallic compound triethylaluminium in the presence of nickel, cobalt, or platinum.
Elimination reactions
One of the principal methods for alkene synthesis in the laboratory is the elimination re... | Alkene | Wikipedia | 481 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Alkenes can be prepared indirectly from alkyl amines. The amine or ammonia is not a suitable leaving group, so the amine is first either alkylated (as in the Hofmann elimination) or oxidized to an amine oxide (the Cope reaction) to render a smooth elimination possible. The Cope reaction is a syn-elimination that occurs... | Alkene | Wikipedia | 489 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
A pair of ketones or aldehydes can be deoxygenated to generate an alkene. Symmetrical alkenes can be prepared from a single aldehyde or ketone coupling with itself, using titanium metal reduction (the McMurry reaction). If different ketones are to be coupled, a more complicated method is required, such as the Barton–Ke... | Alkene | Wikipedia | 512 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Rearrangements and related reactions
Alkenes can be synthesized from other alkenes via rearrangement reactions. Besides olefin metathesis (described above), many pericyclic reactions can be used such as the ene reaction and the Cope rearrangement.
In the Diels–Alder reaction, a cyclohexene derivative is prepared from ... | Alkene | Wikipedia | 344 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
For straight-chain alkenes with 4 or more carbon atoms, that name does not completely identify the compound. For those cases, and for branched acyclic alkenes, the following rules apply:
Find the longest carbon chain in the molecule. If that chain does not contain the double bond, name the compound according to the a... | Alkene | Wikipedia | 462 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
More generally, cis–trans isomerism will exist if each of the two carbons of in the double bond has two different atoms or groups attached to it. Accounting for these cases, the IUPAC recommends the more general E–Z notation, instead of the cis and trans prefixes. This notation considers the group with highest CIP pr... | Alkene | Wikipedia | 192 | 2761 | https://en.wikipedia.org/wiki/Alkene | Physical sciences | Hydrocarbons | null |
Acetylene
Propyne
1-Butyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula . Alkynes are traditionally kno... | Alkyne | Wikipedia | 485 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
Terminal alkynes have the formula , where at least one end of the alkyne is a hydrogen atom. An example is methylacetylene (propyne using IUPAC nomenclature). They are often prepared by alkylation of monosodium acetylide. Terminal alkynes, like acetylene itself, are mildly acidic, with pKa values of around 25. They ar... | Alkyne | Wikipedia | 399 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
In chemistry, the suffix -yne is used to denote the presence of a triple bond. In organic chemistry, the suffix often follows IUPAC nomenclature. However, inorganic compounds featuring unsaturation in the form of triple bonds may be denoted by substitutive nomenclature with the same methods used with alkynes (i.e. the ... | Alkyne | Wikipedia | 430 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
From calcium carbide
Classically, acetylene was prepared by hydrolysis (protonation) of calcium carbide (Ca2+[:C≡C:]2–):
Ca^{2+}[C#C]^2- + 2 HOH -> HC#CH + Ca^{2+}[(HO^{-})2]
which was in turn synthesized by combining quicklime and coke in an electric arc furnace at 2200 °C:
CaO + 3 C (amorphous) -> CaC2 + CO
This... | Alkyne | Wikipedia | 493 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
Dehydrohalogenation and related reactions
Alkynes are prepared from 1,1- and 1,2-dihaloalkanes by double dehydrohalogenation. The reaction provides a means to generate alkynes from alkenes, which are first halogenated and then dehydrohalogenated. For example, phenylacetylene can be generated from styrene by bromination... | Alkyne | Wikipedia | 500 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
The largest scale application of this technology is the conversion of acetylene to ethylene in refineries (the steam cracking of alkanes yields a few percent acetylene, which is selectively hydrogenated in the presence of a palladium/silver catalyst). For more complex alkynes, the Lindlar catalyst is widely recommended... | Alkyne | Wikipedia | 481 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
Isomerization to allenes
Alkynes can be isomerized by strong base or transition metals to allenes. Due to their comparable thermodynamic stabilities, the equilibrium constant of alkyne/allene isomerization is generally within several orders of magnitude of unity. For example propyne can be isomerized to give an equil... | Alkyne | Wikipedia | 489 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
This reactivity exploits the fact that terminal alkynes are weak acids, whose typical pKa values around 25 place them between that of ammonia (35) and ethanol (16):
RC#CH + MX -> RC#CM + HX
where MX = NaNH2, LiBu, or RMgX.
The reactions of alkynes with certain metal cations, e.g. and also gives acetylides. Thus, few... | Alkyne | Wikipedia | 338 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
Alkynes in nature and medicine
According to Ferdinand Bohlmann, the first naturally occurring acetylenic compound, dehydromatricaria ester, was isolated from an Artemisia species in 1826. In the nearly two centuries that have followed, well over a thousand naturally occurring acetylenes have been discovered and reporte... | Alkyne | Wikipedia | 423 | 2763 | https://en.wikipedia.org/wiki/Alkyne | Physical sciences | Hydrocarbons | null |
The Anatomical Therapeutic Chemical (ATC) Classification System is a drug classification system that classifies the active ingredients of drugs according to the organ or system on which they act and their therapeutic, pharmacological and chemical properties. Its purpose is an aid to monitor drug use and for research to... | Anatomical Therapeutic Chemical Classification System | Wikipedia | 505 | 2770 | https://en.wikipedia.org/wiki/Anatomical%20Therapeutic%20Chemical%20Classification%20System | Biology and health sciences | General concepts_2 | Health |
First level
The first level of the code indicates the anatomical main group and consists of one letter. There are 14 main groups:
Example: C Cardiovascular system
Second level
The second level of the code indicates the therapeutic subgroup and consists of two digits.
Example: C03 Diuretics
Third level
The third ... | Anatomical Therapeutic Chemical Classification System | Wikipedia | 474 | 2770 | https://en.wikipedia.org/wiki/Anatomical%20Therapeutic%20Chemical%20Classification%20System | Biology and health sciences | General concepts_2 | Health |
ATC follows guidelines in creating new codes for newly approved drugs. An application is submitted to WHO for ATC classification and DDD assignment. A preliminary or temporary code is assigned and published on the website and in the WHO Drug Information for comment or objection. New ATC/DDD codes are discussed at the ... | Anatomical Therapeutic Chemical Classification System | Wikipedia | 191 | 2770 | https://en.wikipedia.org/wiki/Anatomical%20Therapeutic%20Chemical%20Classification%20System | Biology and health sciences | General concepts_2 | Health |
Parallel ATA (PATA), originally , also known as Integrated Drive Electronics (IDE), is a standard interface designed for IBM PC-compatible computers. It was first developed by Western Digital and Compaq in 1986 for compatible hard drives and CD or DVD drives. The connection is used for storage devices such as hard disk... | Parallel ATA | Wikipedia | 507 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
The first version of what is now called the ATA/ATAPI interface was developed by Western Digital under the name Integrated Drive Electronics (IDE). Together with Compaq (the initial customer), they worked with various disk drive manufacturers to develop and ship early products with the goal of remaining software compat... | Parallel ATA | Wikipedia | 508 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
In 1994, about the same time that the ATA-1 standard was adopted, Western Digital introduced drives under a newer name, Enhanced IDE (EIDE). These included most of the features of the forthcoming ATA-2 specification and several additional enhancements. Other manufacturers introduced their own variations of ATA-1 such a... | Parallel ATA | Wikipedia | 443 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
The SCSI commands and responses used by each class of ATAPI device (CD-ROM, tape, etc.) are described in other documents or specifications specific to those device classes and are not within ATA/ATAPI or the T13 committee's purview. One commonly used set is defined in the MMC SCSI command set.
ATAPI was adopted as pa... | Parallel ATA | Wikipedia | 479 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
Owing to a lack of foresight by motherboard manufacturers, the system BIOS was often hobbled by artificial C/H/S size limitations due to the manufacturer assuming certain values would never exceed a particular numerical maximum.
The first of these BIOS limits occurred when ATA drives reached sizes in excess of 504 MiB... | Parallel ATA | Wikipedia | 493 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
Some operating systems, including Windows XP pre-SP1, and Windows 2000 pre-SP3, disable LBA48 by default, requiring the user to take extra steps to use the entire capacity of an ATA drive larger than about 137 gigabytes.
Older operating systems, such as Windows 98, do not support 48-bit LBA at all. However, members of... | Parallel ATA | Wikipedia | 392 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
Interface
Parallel ATA cables transfer data 16 bits at a time. The traditional cable uses 40-pin female insulation displacement connectors (IDC) attached to a 40- or 80-conductor ribbon cable. Each cable has two or three connectors, one of which plugs into a host adapter interfacing with the rest of the computer syste... | Parallel ATA | Wikipedia | 478 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
ATA's cables have had 40 conductors for most of its history (44 conductors for the smaller form-factor version used for 2.5" drives—the extra four for power), but an 80-conductor version appeared with the introduction of the UDMA/66 mode. All of the additional conductors in the new cable are grounds, interleaved with t... | Parallel ATA | Wikipedia | 444 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
The mode that a device must use is often set by a jumper setting on the device itself, which must be manually set to Device 0 (Master) or Device 1 (Slave). If there is a single device on a cable, it should be configured as Device 0. However, some certain era drives have a special setting called Single for this configur... | Parallel ATA | Wikipedia | 161 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
There are many debates about how much a slow device can impact the performance of a faster device on the same cable. On early ATA host adapters, both devices' data transfers can be constrained to the speed of the slower device, if two devices of different speed capabilities are on the same cable. For all modern ATA hos... | Parallel ATA | Wikipedia | 506 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
If two drives are configured as Device 0 and Device 1 manually, this configuration does not need to correspond to their position on the cable. Pin 28 is only used to let the drives know their position on the cable; it is not used by the host when communicating with the drives. In other words, the manual master/slave se... | Parallel ATA | Wikipedia | 493 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
The ATA-4 and subsequent versions of the specification have included an "overlapped feature set" and a "queued feature set" as optional features, both being given the name "Tagged Command Queuing" (TCQ), a reference to a set of features from SCSI which the ATA version attempts to emulate. However, support for these is ... | Parallel ATA | Wikipedia | 460 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
A device can be locked in two modes: High security mode or Maximum security mode. Bit 8 in word 128 of the IDENTIFY response shows which mode the disk is in: 0 = High, 1 = Maximum. In High security mode, the device can be unlocked with either the User or Master password, using the "SECURITY UNLOCK DEVICE" ATA command. ... | Parallel ATA | Wikipedia | 492 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
External hard disk drives or optical disk drives that have an internal PATA interface, use some other interface technology to bridge the distance between the external device and the computer. USB is the most common external interface, followed by Firewire. A bridge chip inside the external devices converts from the USB... | Parallel ATA | Wikipedia | 445 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
Only the Ultra DMA modes use CRC to detect errors in data transfer between the controller and drive. This is a 16-bit CRC, and it is used for data blocks only. Transmission of command and status blocks do not use the fast signaling methods that would necessitate CRC. For comparison, in Serial ATA, 32-bit CRC is used fo... | Parallel ATA | Wikipedia | 444 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
There are two variants of ARMD, ARMD-FDD and ARMD-HDD. Originally ARMD caused the devices to appear as a sort of very large floppy drive, either the primary floppy drive device 00h or the secondary device 01h. Some operating systems required code changes to support floppy disks with capacities far larger than any stand... | Parallel ATA | Wikipedia | 449 | 2778 | https://en.wikipedia.org/wiki/Parallel%20ATA | Technology | Computer hardware | null |
Astrobiology (also xenology or exobiology) is a scientific field within the life and environmental sciences that studies the origins, early evolution, distribution, and future of life in the universe by investigating its deterministic conditions and contingent events. As a discipline, astrobiology is founded on the pre... | Astrobiology | Wikipedia | 480 | 2787 | https://en.wikipedia.org/wiki/Astrobiology | Physical sciences | Astronomy basics | Astronomy |
Astrobiology is a rapidly developing field with a strong interdisciplinary aspect that holds many challenges and opportunities for scientists. Astrobiology programs and research centres are present in many universities and research institutions around the world, and space agencies like NASA and ESA have dedicated depar... | Astrobiology | Wikipedia | 326 | 2787 | https://en.wikipedia.org/wiki/Astrobiology | Physical sciences | Astronomy basics | Astronomy |
The modern field of astrobiology can be traced back to the 1950s and 1960s with the advent of space exploration, when scientists began to seriously consider the possibility of life on other planets. In 1957, the Soviet Union launched Sputnik 1, the first artificial satellite, which marked the beginning of the Space Age... | Astrobiology | Wikipedia | 441 | 2787 | https://en.wikipedia.org/wiki/Astrobiology | Physical sciences | Astronomy basics | Astronomy |
Carbon and Organic Compounds: Carbon is the fourth most abundant element in the universe and the energy required to make or break a bond is at just the appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the buil... | Astrobiology | Wikipedia | 407 | 2787 | https://en.wikipedia.org/wiki/Astrobiology | Physical sciences | Astronomy basics | Astronomy |
The anthropic principle, also known as the observation selection effect, is the proposition that the range of possible observations that could be made about the universe is limited by the fact that observations are only possible in the type of universe that is capable of developing intelligent life. Proponents of the a... | Anthropic principle | Wikipedia | 415 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
The anthropic principle has given rise to some confusion and controversy, partly because the phrase has been applied to several distinct ideas. All versions of the principle have been accused of discouraging the search for a deeper physical understanding of the universe. Critics of the weak anthropic principle point ou... | Anthropic principle | Wikipedia | 503 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
The observed values of the dimensionless physical constants (such as the fine-structure constant) governing the four fundamental interactions are balanced as if fine-tuned to permit the formation of commonly found matter and subsequently the emergence of life. A slight increase in the strong interaction (up to 50% for ... | Anthropic principle | Wikipedia | 411 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
One reason this is plausible is that there are many other places and times in which humans could have evolved. But when applying the strong principle, there is only one universe, with one set of fundamental parameters, so what exactly is the point being made? Carter offers two possibilities: First, humans can use their... | Anthropic principle | Wikipedia | 460 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Ludwig Boltzmann may have been one of the first in modern science to use anthropic reasoning. Prior to knowledge of the Big Bang Boltzmann's thermodynamic concepts painted a picture of a universe that had inexplicably low entropy. Boltzmann suggested several explanations, one of which relied on fluctuations that could ... | Anthropic principle | Wikipedia | 474 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Strong anthropic principle (SAP) (Barrow and Tipler): "The Universe must have those properties which allow life to develop within it at some stage in its history."This looks very similar to Carter's SAP, but unlike the case with Carter's SAP, the "must" is an imperative, as shown by the following three possible elabora... | Anthropic principle | Wikipedia | 385 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Strong self-sampling assumption (SSSA) (Bostrom): "Each observer-moment should reason as if it were randomly selected from the class of all observer-moments in its reference class." Analysing an observer's experience into a sequence of "observer-moments" helps avoid certain paradoxes; but the main ambiguity is the sele... | Anthropic principle | Wikipedia | 503 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Although philosophers have discussed related concepts for centuries, in the early 1970s the only genuine physical theory yielding a multiverse of sorts was the many-worlds interpretation of quantum mechanics. This would allow variation in initial conditions, but not in the truly fundamental constants. Since that time a... | Anthropic principle | Wikipedia | 478 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Paul Davies's book The Goldilocks Enigma (2006) reviews the current state of the fine-tuning debate in detail, and concludes by enumerating the following responses to that debate:
The absurd universe: Our universe just happens to be the way it is.
The unique universe: There is a deep underlying unity in physics that ... | Anthropic principle | Wikipedia | 465 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Observational evidence
No possible observational evidence bears on Carter's WAP, as it is merely advice to the scientist and asserts nothing debatable. The obvious test of Barrow's SAP, which says that the universe is "required" to support life, is to find evidence of life in universes other than ours. Any other unive... | Anthropic principle | Wikipedia | 505 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
One thing that would not count as evidence for the anthropic principle is evidence that the Earth or the Solar System occupied a privileged position in the universe, in violation of the Copernican principle (for possible counterevidence to this principle, see Copernican principle), unless there was some reason to thin... | Anthropic principle | Wikipedia | 299 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Don Page criticized the entire theory of cosmic inflation as follows. He emphasized that initial conditions that made possible a thermodynamic arrow of time in a universe with a Big Bang origin, must include the assumption that at the initial singularity, the entropy of the universe was low and therefore extremely impr... | Anthropic principle | Wikipedia | 485 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Jürgen Schmidhuber (2000–2002) points out that Ray Solomonoff's theory of universal inductive inference and its extensions already provide a framework for maximizing our confidence in any theory, given a limited sequence of physical observations, and some prior distribution on the set of possible explanations of the un... | Anthropic principle | Wikipedia | 385 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
In 1920, Paul Ehrenfest showed that if there is only a single time dimension and more than three spatial dimensions, the orbit of a planet about its Sun cannot remain stable. The same is true of a star's orbit around the center of its galaxy. Ehrenfest also showed that if there are an even number of spatial dimensions,... | Anthropic principle | Wikipedia | 493 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Metaphysical interpretations
Some of the metaphysical disputes and speculations include, for example, attempts to back Pierre Teilhard de Chardin's earlier interpretation of the universe as being Christ centered (compare Omega Point), expressing a creatio evolutiva instead the elder notion of creatio continua. From a ... | Anthropic principle | Wikipedia | 480 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Seeing little sense in a principle requiring intelligent life to emerge while remaining indifferent to the possibility of its eventual extinction, Barrow and Tipler propose the final anthropic principle (FAP): Intelligent information-processing must come into existence in the universe, and, once it comes into existence... | Anthropic principle | Wikipedia | 417 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Critics of the Barrow and Tipler SAP claim that it is neither testable nor falsifiable, and thus is not a scientific statement but rather a philosophical one. The same criticism has been leveled against the hypothesis of a multiverse, although some argue that it does make falsifiable predictions. A modified version of ... | Anthropic principle | Wikipedia | 492 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Lee Smolin has offered a theory designed to improve on the lack of imagination that has been ascribed to anthropic principles. He puts forth his fecund universes theory, which assumes universes have "offspring" through the creation of black holes whose offspring universes have values of physical constants that depend o... | Anthropic principle | Wikipedia | 176 | 2792 | https://en.wikipedia.org/wiki/Anthropic%20principle | Physical sciences | Physical cosmology | Astronomy |
Aerodynamics ( aero (air) + (dynamics)) is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an important domain of study in aeronautics. The term aerodynamics is oft... | Aerodynamics | Wikipedia | 491 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
In 1799, Sir George Cayley became the first person to identify the four aerodynamic forces of flight (weight, lift, drag, and thrust), as well as the relationships between them, and in doing so outlined the path toward achieving heavier-than-air flight for the next century. In 1871, Francis Herbert Wenham constructed t... | Aerodynamics | Wikipedia | 496 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
By the time the sound barrier was broken, aerodynamicists' understanding of the subsonic and low supersonic flow had matured. The Cold War prompted the design of an ever-evolving line of high-performance aircraft. Computational fluid dynamics began as an effort to solve for flow properties around complex objects and ha... | Aerodynamics | Wikipedia | 510 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
Compressible flow accounts for varying density within the flow. Subsonic flows are often idealized as incompressible, i.e. the density is assumed to be constant. Transonic and supersonic flows are compressible, and calculations that neglect the changes of density in these flow fields will yield inaccurate results.
Vis... | Aerodynamics | Wikipedia | 507 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
Conservation laws
The assumption of a fluid continuum allows problems in aerodynamics to be solved using fluid dynamics conservation laws. Three conservation principles are used:
Conservation of mass Conservation of mass requires that mass is neither created nor destroyed within a flow; the mathematical formulation o... | Aerodynamics | Wikipedia | 410 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
Aerodynamic problems are classified by the flow environment or properties of the flow, including flow speed, compressibility, and viscosity. External aerodynamics is the study of flow around solid objects of various shapes. Evaluating the lift and drag on an airplane or the shock waves that form in front of the nose of... | Aerodynamics | Wikipedia | 439 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
Subsonic flow
Subsonic (or low-speed) aerodynamics describes fluid motion in flows which are much lower than the speed of sound everywhere in the flow. There are several branches of subsonic flow but one special case arises when the flow is inviscid, incompressible and irrotational. This case is called potential flow a... | Aerodynamics | Wikipedia | 444 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
The term Transonic refers to a range of flow velocities just below and above the local speed of sound (generally taken as Mach 0.8–1.2). It is defined as the range of speeds between the critical Mach number, when some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, ... | Aerodynamics | Wikipedia | 511 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
Associated terminology
The incompressible and compressible flow regimes produce many associated phenomena, such as boundary layers and turbulence.
Boundary layers
The concept of a boundary layer is important in many problems in aerodynamics. The viscosity and fluid friction in the air is approximated as being signif... | Aerodynamics | Wikipedia | 393 | 2819 | https://en.wikipedia.org/wiki/Aerodynamics | Physical sciences | Fluid mechanics | null |
Ash is the solid remnants of fires. Specifically, ash refers to all non-aqueous, non-gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash is the non-gaseous, non-liquid residue after complete combustion.
Ashes as the end product ... | Ash | Wikipedia | 496 | 2822 | https://en.wikipedia.org/wiki/Ash | Physical sciences | Salts and ions: General | Chemistry |
For example, ash collected from wood boilers is composed of
17–33% calcium in the form of calcium oxide ()
2–6% potassium in the form of potassium oxide ()
2.5–4.6% magnesium in the form of magnesium oxide ()
1–6% phosphorus in the form of phosphorus pentoxide ()
3% in total of oxides such as iron oxide, manganese... | Ash | Wikipedia | 431 | 2822 | https://en.wikipedia.org/wiki/Ash | Physical sciences | Salts and ions: General | Chemistry |
Cremation ashes
Cremation ashes, also called cremated remains or "cremains," are the bodily remains left from cremation. They often take the form of a grey powder resembling coarse sand. While often referred to as ashes, the remains primarily consist of powdered bone fragments due to the cremation process, which elimi... | Ash | Wikipedia | 491 | 2822 | https://en.wikipedia.org/wiki/Ash | Physical sciences | Salts and ions: General | Chemistry |
Others
Ashes from
Stubble burning
Open burning of waste
Cigarette or cigar ash
Incinerator bottom ash, a form of ash produced in incinerators
Products of coal combustion
Bottom ash
Fly ash
Volcanic ash, ash that consists of fragmented glass, rock, and minerals that appears during an eruption.
Wood ash
Other ... | Ash | Wikipedia | 391 | 2822 | https://en.wikipedia.org/wiki/Ash | Physical sciences | Salts and ions: General | Chemistry |
In calculus, an antiderivative, inverse derivative, primitive function, primitive integral or indefinite integral of a continuous function is a differentiable function whose derivative is equal to the original function . This can be stated symbolically as . The process of solving for antiderivatives is called antidif... | Antiderivative | Wikipedia | 495 | 2823 | https://en.wikipedia.org/wiki/Antiderivative | Mathematics | Integral calculus | null |
If is an antiderivative of , and the function is defined on some interval, then every other antiderivative of differs from by a constant: there exists a number such that for all . is called the constant of integration. If the domain of is a disjoint union of two or more (open) intervals, then a different const... | Antiderivative | Wikipedia | 365 | 2823 | https://en.wikipedia.org/wiki/Antiderivative | Mathematics | Integral calculus | null |
The linearity of integration (which breaks complicated integrals into simpler ones)
Integration by substitution, often combined with trigonometric identities or the natural logarithm
The inverse chain rule method (a special case of integration by substitution)
Integration by parts (to integrate products of functions... | Antiderivative | Wikipedia | 376 | 2823 | https://en.wikipedia.org/wiki/Antiderivative | Mathematics | Integral calculus | null |
A necessary, but not sufficient, condition for a function to have an antiderivative is that have the intermediate value property. That is, if is a subinterval of the domain of and is any real number between and , then there exists a between and such that . This is a consequence of Darboux's theorem.
The set o... | Antiderivative | Wikipedia | 364 | 2823 | https://en.wikipedia.org/wiki/Antiderivative | Mathematics | Integral calculus | null |
Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion and plasticizers, silicone oils, defoamers, stabilizers, or metal soaps. Most acrylic paints are water-based, but become water-resistant when dry. Depending on how much the paint is diluted with water, or modified with acrylic ge... | Acrylic paint | Wikipedia | 400 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Soon after the water-based acrylic binders were introduced as house paints, artists and companies alike began to explore the potential of the new binders. Diego Rivera, David Alfaro Siqueiros, and José Clemente Orozco were the first ones who experimented with acrylic paint. This is because they were very impressed with... | Acrylic paint | Wikipedia | 458 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Painting with acrylics
Acrylic painters can modify the appearance, hardness, flexibility, texture, and other characteristics of the paint surface by using acrylic medium or simply by adding water. Watercolor and oil painters also use various mediums, but the range of acrylic mediums is much greater. Acrylics have the ... | Acrylic paint | Wikipedia | 386 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Acrylic artists' paints may be thinned with water or acrylic medium and used as washes in the manner of watercolor paints, but unlike watercolor the washes are not rehydratable once dry. For this reason, acrylics do not lend themselves to the color lifting techniques of gum arabic-based watercolor paints. Instead, the ... | Acrylic paint | Wikipedia | 434 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
An acrylic sizing should be used to prime canvas in preparation for painting with acrylic paints, to prevent Support Induced Discoloration (SID). Acrylic paint contains surfactants that can pull up discoloration from a raw canvas, especially in transparent glazed or translucent gelled areas. Gesso alone will not stop S... | Acrylic paint | Wikipedia | 278 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
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