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Epoxy resin curing agents
Amines are often used as epoxy resin curing agents. These include dimethylethylamine, cyclohexylamine, and a variety of diamines such as 4,4-diaminodicyclohexylmethane. Multifunctional amines such as tetraethylenepentamine and triethylenetetramine are also widely used in this capacity. The rea... | Amine | Wikipedia | 286 | 1412 | https://en.wikipedia.org/wiki/Amine | Physical sciences | Carbon–nitrogen bond | null |
Absolute zero is the lowest limit of the thermodynamic temperature scale; a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value. The fundamental particles of nature have minimum vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. The theo... | Absolute zero | Wikipedia | 395 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
Thermodynamics near absolute zero
At temperatures near , nearly all molecular motion ceases and ΔS = 0 for any adiabatic process, where S is the entropy. In such a circumstance, pure substances can (ideally) form perfect crystals with no structural imperfections as T → 0. Max Planck's strong form of the third law of th... | Absolute zero | Wikipedia | 415 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
Using the Debye model, the specific heat and entropy of a pure crystal are proportional to T 3, while the enthalpy and chemical potential are proportional to T 4 (Guggenheim, p. 111). These quantities drop toward their T = 0 limiting values and approach with zero slopes. For the specific heats at least, the limiting va... | Absolute zero | Wikipedia | 385 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
One model that estimates the properties of an electron gas at absolute zero in metals is the Fermi gas. The electrons, being fermions, must be in different quantum states, which leads the electrons to get very high typical velocities, even at absolute zero. The maximum energy that electrons can have at absolute zero is... | Absolute zero | Wikipedia | 461 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
Absolute temperature scales
Absolute, or thermodynamic, temperature is conventionally measured in kelvin (Celsius-scaled increments) and in the Rankine scale (Fahrenheit-scaled increments) with increasing rarity. Absolute temperature measurement is uniquely determined by a multiplicative constant which specifies the si... | Absolute zero | Wikipedia | 497 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
On 3 January 2013, physicists announced that for the first time they had created a quantum gas made up of potassium atoms with a negative temperature in motional degrees of freedom.
History
One of the first to discuss the possibility of an absolute minimal temperature was Robert Boyle. His 1665 New Experiments and Ob... | Absolute zero | Wikipedia | 431 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
Values of this order for the absolute zero were not, however, universally accepted about this period. Pierre-Simon Laplace and Antoine Lavoisier, in their 1780 treatise on heat, arrived at values ranging from 1,500 to 3,000 below the freezing point of water, and thought that in any case it must be at least 600 below. J... | Absolute zero | Wikipedia | 357 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
With a better theoretical understanding of absolute zero, scientists were eager to reach this temperature in the lab. By 1845, Michael Faraday had managed to liquefy most gases then known to exist, and reached a new record for lowest temperatures by reaching . Faraday believed that certain gases, such as oxygen, nitrog... | Absolute zero | Wikipedia | 448 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
Absolute zero cannot be achieved, although it is possible to reach temperatures close to it through the use of evaporative cooling, cryocoolers, dilution refrigerators, and nuclear adiabatic demagnetization. The use of laser cooling has produced temperatures of less than a billionth of a kelvin. At very low temperature... | Absolute zero | Wikipedia | 473 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
In June 2015, experimental physicists at MIT cooled molecules in a gas of sodium potassium to a temperature of 500 nanokelvin, and it is expected to exhibit an exotic state of matter by cooling these molecules somewhat further.
In 2017, Cold Atom Laboratory (CAL), an experimental instrument was developed for launch to... | Absolute zero | Wikipedia | 170 | 1418 | https://en.wikipedia.org/wiki/Absolute%20zero | Physical sciences | Thermodynamics | null |
An adiabatic process (adiabatic ) is a type of thermodynamic process that occurs without transferring heat between the thermodynamic system and its environment. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work and/or mass flow. As a key concept in thermodynamics, the ... | Adiabatic process | Wikipedia | 413 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
The assumption of adiabatic isolation is useful and often combined with other such idealizations to calculate a good first approximation of a system's behaviour. For example, according to Laplace, when sound travels in a gas, there is no time for heat conduction in the medium, and so the propagation of sound is adiabat... | Adiabatic process | Wikipedia | 178 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
If the system has such rigid walls that work cannot be transferred in or out (), and the walls are not adiabatic and energy is added in the form of heat (), and there is no phase change, then the temperature of the system will rise.
If the system has such rigid walls that pressure–volume work cannot be done, but the wa... | Adiabatic process | Wikipedia | 446 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
The transfer of energy as work into an adiabatically isolated system can be imagined as being of two idealized extreme kinds. In one such kind, no entropy is produced within the system (no friction, viscous dissipation, etc.), and the work is only pressure-volume work (denoted by ). In nature, this ideal kind occurs on... | Adiabatic process | Wikipedia | 403 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
Adiabatic compression occurs in the Earth's atmosphere when an air mass descends, for example, in a Katabatic wind, Foehn wind, or Chinook wind flowing downhill over a mountain range. When a parcel of air descends, the pressure on the parcel increases. Because of this increase in pressure, the parcel's volume decreases... | Adiabatic process | Wikipedia | 487 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
In practice, no process is truly adiabatic. Many processes rely on a large difference in time scales of the process of interest and the rate of heat dissipation across a system boundary, and thus are approximated by using an adiabatic assumption. There is always some heat loss, as no perfect insulators exist.
Ideal ga... | Adiabatic process | Wikipedia | 469 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
The gas is now compressed to a 0.1 L (0.0001 m3) volume, which we assume happens quickly enough that no heat enters or leaves the gas through the walls. The adiabatic constant remains the same, but with the resulting pressure unknown
We can now solve for the final pressure
or 25.1 bar. This pressure increase is more ... | Adiabatic process | Wikipedia | 378 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
For an adiabatic free expansion of an ideal gas, the gas is contained in an insulated container and then allowed to expand in a vacuum. Because there is no external pressure for the gas to expand against, the work done by or on the system is zero. Since this process does not involve any heat transfer or work, the first... | Adiabatic process | Wikipedia | 499 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
Using the ideal gas law and assuming a constant molar quantity (as often happens in practical cases),
By the continuous formula,
or
Substituting into the previous expression for ,
Substituting this expression and (b1) in (b3) gives
Simplifying,
Derivation of discrete formula and work expression
The change in inte... | Adiabatic process | Wikipedia | 504 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
Etymology
The term adiabatic () is an anglicization of the Greek term ἀδιάβατος "impassable" (used by Xenophon of rivers). It is used in the thermodynamic sense by Rankine (1866), and adopted by Maxwell in 1871 (explicitly attributing the term to Rankine).
The etymological origin corresponds here to an impossibility of... | Adiabatic process | Wikipedia | 453 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
For the foundations of thermodynamics, the conceptual importance of this was emphasized by Bryan, by Carathéodory, and by Born. The reason is that calorimetry presupposes a type of temperature as already defined before the statement of the first law of thermodynamics, such as one based on empirical scales. Such a presu... | Adiabatic process | Wikipedia | 440 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
Some authors, like Pippard, recommend using "adiathermal" to refer to processes where no heat-exchange occurs (such as Joule expansion), and "adiabatic" to reversible quasi-static adiathermal processes (so that rapid compression of a gas is not "adiabatic"). And Laidler has summarized the complicated etymology of "adia... | Adiabatic process | Wikipedia | 413 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
Recent research suggests that the power absorbed from the perturbation corresponds to the rate of these non-adiabatic transitions. This corresponds to the classical process of energy transfer in the form of heat, but with the relative time scales reversed in the quantum case. Quantum adiabatic processes occur over rela... | Adiabatic process | Wikipedia | 355 | 1419 | https://en.wikipedia.org/wiki/Adiabatic%20process | Physical sciences | Thermodynamics | Physics |
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent any group, typically organyl groups or hydrogen atoms. The amide group is called a peptide bond when it is part of the main chain of a protein, and an isopeptide bond w... | Amide | Wikipedia | 427 | 1422 | https://en.wikipedia.org/wiki/Amide | Physical sciences | Carbon–nitrogen bond | null |
Amides are pervasive in nature and technology. Proteins and important plastics like nylons, aramids, Twaron, and Kevlar are polymers whose units are connected by amide groups (polyamides); these linkages are easily formed, confer structural rigidity, and resist hydrolysis. Amides include many other important biological... | Amide | Wikipedia | 478 | 1422 | https://en.wikipedia.org/wiki/Amide | Physical sciences | Carbon–nitrogen bond | null |
Basicity
Compared to amines, amides are very weak bases. While the conjugate acid of an amine has a pKa of about 9.5, the conjugate acid of an amide has a pKa around −0.5. Therefore, compared to amines, amides do not have acid–base properties that are as noticeable in water. This relative lack of basicity is explained ... | Amide | Wikipedia | 475 | 1422 | https://en.wikipedia.org/wiki/Amide | Physical sciences | Carbon–nitrogen bond | null |
Amides do not readily participate in nucleophilic substitution reactions. Amides are stable to water, and are roughly 100 times more stable towards hydrolysis than esters. Amides can, however, be hydrolyzed to carboxylic acids in the presence of acid or base. The stability of amide bonds has biological implications, si... | Amide | Wikipedia | 509 | 1422 | https://en.wikipedia.org/wiki/Amide | Physical sciences | Carbon–nitrogen bond | null |
From carboxylic acids and related compounds
Amides are usually prepared by coupling a carboxylic acid with an amine. The direct reaction generally requires high temperatures to drive off the water:
Esters are far superior substrates relative to carboxylic acids.
Further "activating" both acid chlorides (Schotten-Baum... | Amide | Wikipedia | 190 | 1422 | https://en.wikipedia.org/wiki/Amide | Physical sciences | Carbon–nitrogen bond | null |
ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the Association for Computing Machinery (ACM) in textbooks and academic sources fo... | ALGOL | Wikipedia | 495 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
John Backus developed the Backus normal form method of describing programming languages specifically for ALGOL 58. It was revised and expanded by Peter Naur for ALGOL 60, and at Donald Knuth's suggestion renamed Backus–Naur form.
Peter Naur: "As editor of the ALGOL Bulletin I was drawn into the international discussio... | ALGOL | Wikipedia | 448 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
ALGOL 60 allowed for two evaluation strategies for parameter passing: the common call-by-value, and call-by-name. Call-by-name has certain effects in contrast to call-by-reference. For example, without specifying the parameters as value or reference, it is impossible to develop a procedure that will swap the values of ... | ALGOL | Wikipedia | 426 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
procedure Absmax(a) Size:(n, m) Result:(y) Subscripts:(i, k);
value n, m; array a; integer n, m, i, k; real y;
comment The absolute greatest element of the matrix a, of size n by m,
is copied to y, and the subscripts of this element to i and k;
begin
integer p, q;
y := 0; i := k := 1;
for p :... | ALGOL | Wikipedia | 487 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
floating point algol68 test:
(
real a,b,c,d;
# printf – sends output to the file stand out. #
# printf($p$); – selects a new page #
printf(($pg$,"Enter d:"));
read(d);
for step from 0 while a:=step*d; a <= 2*pi do
printf($l$); # $l$ - selects a new line. #
b := sin(a);
c :... | ALGOL | Wikipedia | 479 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
The ICT 1900 series Algol I/O version allowed input from paper tape or punched card. Paper tape 'full' mode allowed lower case. Output was to a line printer. The open and close quote characters were represented using '(' and ')' and spaces by %.
'BEGIN'
WRITE TEXT('('HELLO%WORLD')');
'END'
ALGOL 68
ALGO... | ALGOL | Wikipedia | 377 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
1968: The "Algol 68 Report" – used extant ALGOL characters, and further adopted →, ↓, ↑, □, ⌊, ⌈, ⎩, ⎧, ○, ⊥, and ¢ characters which can be found on the IBM 2741 keyboard with typeball (or golf ball) print heads inserted (such as the APL golf ball). These became available in the mid-1960s while ALGOL 68 was being draft... | ALGOL | Wikipedia | 249 | 1453 | https://en.wikipedia.org/wiki/ALGOL | Technology | "Historical" languages | null |
The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which succeeded in landing the first men on the Moon in 1969, following Project Mercury, which put the first Americans in space. It was conceived in 1960 as a three-person spacecraft during President Dwight D.... | Apollo program | Wikipedia | 507 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Overall, the Apollo program returned of lunar rocks and soil to Earth, greatly contributing to the understanding of the Moon's composition and geological history. The program laid the foundation for NASA's subsequent human spaceflight capability and funded construction of its Johnson Space Center and Kennedy Space Cen... | Apollo program | Wikipedia | 446 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
In November 1960, John F. Kennedy was elected president after a campaign that promised American superiority over the Soviet Union in the fields of space exploration and missile defense. Up to the election of 1960, Kennedy had been speaking out against the "missile gap" that he and many other senators said had developed... | Apollo program | Wikipedia | 461 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
NASA expansion
At the time of Kennedy's proposal, only one American had flown in space—less than a month earlier—and NASA had not yet sent an astronaut into orbit. Even some NASA employees doubted whether Kennedy's ambitious goal could be met. By 1963, Kennedy even came close to agreeing to a joint US-USSR Moon mission... | Apollo program | Wikipedia | 495 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
In September 1962, by which time two Project Mercury astronauts had orbited the Earth, Gilruth had moved his organization to rented space in Houston, and construction of the MSC facility was under way, Kennedy visited Rice to reiterate his challenge in a famous speech:
The MSC was completed in September 1963. It was r... | Apollo program | Wikipedia | 410 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Organization
Administrator Webb realized that in order to keep Apollo costs under control, he had to develop greater project management skills in his organization, so he recruited George E. Mueller for a high management job. Mueller accepted, on the condition that he have a say in NASA reorganization necessary to effec... | Apollo program | Wikipedia | 351 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Once Kennedy had defined a goal, the Apollo mission planners were faced with the challenge of designing a spacecraft that could meet it while minimizing risk to human life, limiting cost, and not exceeding limits in possible technology and astronaut skill. Four possible mission modes were considered:
Direct Ascent: T... | Apollo program | Wikipedia | 378 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
In early 1961, direct ascent was generally the mission mode in favor at NASA. Many engineers feared that rendezvous and docking, maneuvers that had not been attempted in Earth orbit, would be nearly impossible in lunar orbit. LOR advocates including John Houbolt at Langley Research Center emphasized the important weigh... | Apollo program | Wikipedia | 495 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Wiesner kept up the pressure, even making the disagreement public during a two-day September visit by the President to Marshall Space Flight Center. Wiesner blurted out "No, that's no good" in front of the press, during a presentation by von Braun. Webb jumped in and defended von Braun, until Kennedy ended the squabble... | Apollo program | Wikipedia | 484 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The command module (CM) was the conical crew cabin, designed to carry three astronauts from launch to lunar orbit and back to an Earth ocean landing. It was the only component of the Apollo spacecraft to survive without major configuration changes as the program evolved from the early Apollo study designs. Its exterior... | Apollo program | Wikipedia | 375 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The Apollo Lunar Module (LM) was designed to descend from lunar orbit to land two astronauts on the Moon and take them back to orbit to rendezvous with the command module. Not designed to fly through the Earth's atmosphere or return to Earth, its fuselage was designed totally without aerodynamic considerations and was ... | Apollo program | Wikipedia | 435 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Since Apollo, like Mercury, would require a launch escape system (LES) in case of a launch failure, a relatively small rocket was required for qualification flight testing of this system. A rocket bigger than the Little Joe used by Mercury would be required, so the Little Joe II was built by General Dynamics/Convair. A... | Apollo program | Wikipedia | 384 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The Saturn IB was an upgraded version of the Saturn I. The S-IB first stage increased the thrust to by uprating the H-1 engine. The second stage replaced the S-IV with the S-IVB-200, powered by a single J-2 engine burning liquid hydrogen fuel with LOX, to produce of thrust. A restartable version of the S-IVB was used... | Apollo program | Wikipedia | 466 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The Apollo astronauts were chosen from the Project Mercury and Gemini veterans, plus from two later astronaut groups. All missions were commanded by Gemini or Mercury veterans. Crews on all development flights (except the Earth orbit CSM development flights) through the first two landings on Apollo 11 and Apollo 12, in... | Apollo program | Wikipedia | 287 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The first three lunar missions (Apollo 8, Apollo 10, and Apollo 11) used a free return trajectory, keeping a flight path coplanar with the lunar orbit, which would allow a return to Earth in case the SM engine failed to make lunar orbit insertion. Landing site lighting conditions on later missions dictated a lunar orbi... | Apollo program | Wikipedia | 461 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Preparation for crewed flight
Two crewed orbital Block I CSM missions were planned: AS-204 and AS-205. The Block I crew positions were titled Command Pilot, Senior Pilot, and Pilot. The Senior Pilot would assume navigation duties, while the Pilot would function as a systems engineer. The astronauts would wear a modifie... | Apollo program | Wikipedia | 499 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Program delays
The spacecraft for the AS-202 and AS-204 missions were delivered by North American Aviation to the Kennedy Space Center with long lists of equipment problems which had to be corrected before flight; these delays caused the launch of AS-202 to slip behind AS-203, and eliminated hopes the first crewed miss... | Apollo program | Wikipedia | 417 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The plugs-out test began on the morning of January 27, 1967, and immediately was plagued with problems. First, the crew noticed a strange odor in their spacesuits which delayed the sealing of the hatch. Then, communications problems frustrated the astronauts and forced a hold in the simulated countdown. During this hol... | Apollo program | Wikipedia | 436 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
In September 1967, Mueller approved a sequence of mission types which had to be successfully accomplished in order to achieve the crewed lunar landing. Each step had to be successfully accomplished before the next ones could be performed, and it was unknown how many tries of each mission would be necessary; therefore l... | Apollo program | Wikipedia | 448 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
This was followed on April 4, 1968, by Apollo 6 (AS-502) which carried a CSM and a LM Test Article as ballast. The intent of this mission was to achieve trans-lunar injection, followed closely by a simulated direct-return abort, using the service module engine to achieve another high-speed reentry. The Saturn V experie... | Apollo program | Wikipedia | 486 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The following March, LM flight, rendezvous and docking were successfully demonstrated in Earth orbit on Apollo 9, and Schweickart tested the full lunar EVA suit with its portable life support system (PLSS) outside the LM. The F mission was successfully carried out on Apollo 10 in May 1969 by Gemini veterans Thomas P. S... | Apollo program | Wikipedia | 362 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The contracted batch of 15 Saturn Vs was enough for lunar landing missions through Apollo 20. Shortly after Apollo 11, NASA publicized a preliminary list of eight more planned landing sites after Apollo 12, with plans to increase the mass of the CSM and LM for the last five missions, along with the payload capacity of ... | Apollo program | Wikipedia | 488 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The cutbacks forced mission planners to reassess the original planned landing sites in order to achieve the most effective geological sample and data collection from the remaining four missions. Apollo 15 had been planned to be the last of the H series missions, but since there would be only two subsequent missions lef... | Apollo program | Wikipedia | 495 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The rocks collected from the Moon are extremely old compared to rocks found on Earth, as measured by radiometric dating techniques. They range in age from about 3.2 billion years for the basaltic samples derived from the lunar maria, to about 4.6 billion years for samples derived from the highlands crust. As such, they... | Apollo program | Wikipedia | 503 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Accurate estimates of human spaceflight costs were difficult in the early 1960s, as the capability was new and management experience was lacking. Preliminary cost analysis by NASA estimated $7 billion – $12 billion for a crewed lunar landing effort. NASA Administrator James Webb increased this estimate to $20 billion b... | Apollo program | Wikipedia | 495 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
In 2008, Japan Aerospace Exploration Agency's SELENE probe observed evidence of the halo surrounding the Apollo 15 Lunar Module blast crater while orbiting above the lunar surface.
Beginning in 2009, NASA's robotic Lunar Reconnaissance Orbiter, while orbiting above the Moon, photographed the remnants of the Apollo pr... | Apollo program | Wikipedia | 426 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
The crew of Apollo 8 sent the first live televised pictures of the Earth and the Moon back to Earth, and read from the creation story in the Book of Genesis, on Christmas Eve 1968. An estimated one-quarter of the population of the world saw—either live or delayed—the Christmas Eve transmission during the ninth orbit of... | Apollo program | Wikipedia | 474 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Apollo 13 (1995)
Apollo 11 (1996)
From the Earth to the Moon (1998)
The Dish (2000)
Space Race (2005)
Moonshot (2009)
First Man (2018)
Fictional
The Apollo program has been the focus of several works of fiction, including:
Apollo 18 (2011), horror movie which was released to negative reviews.
Men in Black 3 (201... | Apollo program | Wikipedia | 201 | 1461 | https://en.wikipedia.org/wiki/Apollo%20program | Technology | Programs and launch sites | null |
Aspirin is the genericized trademark for acetylsalicylic acid (ASA), a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and inflammation, and as an antithrombotic. Specific inflammatory conditions that aspirin is used to treat include Kawasaki disease, pericarditis, and rheumatic fever.
Aspirin ... | Aspirin | Wikipedia | 466 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Brand vs. generic name
In 1897, scientists at the Bayer company began studying acetylsalicylic acid as a less-irritating replacement medication for common salicylate medicines. By 1899, Bayer had named it "Aspirin" and was selling it around the world.
Aspirin's popularity grew over the first half of the 20th century, ... | Aspirin | Wikipedia | 498 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Reaction between acetic acid and salicylic acid can also form aspirin but this esterification reaction is reversible and the presence of water can lead to hydrolysis of the aspirin. So, an anhydrous reagent is preferred.
Reaction mechanism
Formulations containing high concentrations of aspirin often smell like vinegar... | Aspirin | Wikipedia | 511 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Discovery of the mechanism
In 1971, British pharmacologist John Robert Vane, then employed by the Royal College of Surgeons in London, showed aspirin suppressed the production of prostaglandins and thromboxanes. For this discovery he was awarded the 1982 Nobel Prize in Physiology or Medicine, jointly with Sune Bergströ... | Aspirin | Wikipedia | 480 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
COX-1 and COX-2 inhibition
At least two different types of cyclooxygenases, COX-1 and COX-2, are acted on by aspirin. Aspirin irreversibly inhibits COX-1 and modifies the enzymatic activity of COX-2. COX-2 normally produces prostanoids, most of which are proinflammatory. Aspirin-modified COX-2 (aka prostaglandin-endope... | Aspirin | Wikipedia | 362 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Furthermore, aspirin, while inhibiting the ability of COX-2 to form pro-inflammatory products such as the prostaglandins, converts this enzyme's activity from a prostaglandin-forming cyclooxygenase to a lipoxygenase-like enzyme: aspirin-treated COX-2 metabolizes a variety of polyunsaturated fatty acids to hydroperoxy p... | Aspirin | Wikipedia | 454 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Aspirin is readily broken down in the body to salicylic acid, which itself has anti-inflammatory, antipyretic, and analgesic effects. In 2012, salicylic acid was found to activate AMP-activated protein kinase, which has been suggested as a possible explanation for some of the effects of both salicylic acid and aspirin.... | Aspirin | Wikipedia | 467 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
About 50–80% of salicylate in the blood is bound to human serum albumin, while the rest remains in the active, ionized state; protein binding is concentration-dependent. Saturation of binding sites leads to more free salicylate and increased toxicity. The volume of distribution is 0.1–0.2 L/kg. Acidosis increases the v... | Aspirin | Wikipedia | 255 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Salicylates are excreted mainly by the kidneys as salicyluric acid (75%), free salicylic acid (10%), salicylic phenol (10%), and acyl glucuronides (5%), gentisic acid (< 1%), and 2,3-dihydroxybenzoic acid. When small doses (less than 250mg in an adult) are ingested, all pathways proceed by first-order kinetics, with an... | Aspirin | Wikipedia | 341 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Medicines made from willow and other salicylate-rich plants appear in clay tablets from ancient Sumer as well as the Ebers Papyrus from ancient Egypt. Hippocrates referred to the use of salicylic tea to reduce fevers around 400 BC, and willow bark preparations were part of the pharmacopoeia of Western medicine in class... | Aspirin | Wikipedia | 467 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Aspirin's popularity declined after the development of acetaminophen/paracetamol in 1956 and ibuprofen in 1962. In the 1960s and 1970s, John Vane and others discovered the basic mechanism of aspirin's effects, while clinical trials and other studies from the 1960s to the 1980s established aspirin's efficacy as an anti-... | Aspirin | Wikipedia | 465 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Aspirin is an effective analgesic for acute pain, although it is generally considered inferior to ibuprofen because aspirin is more likely to cause gastrointestinal bleeding. Aspirin is generally ineffective for those pains caused by muscle cramps, bloating, gastric distension, or acute skin irritation. As with other N... | Aspirin | Wikipedia | 501 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Inflammation
Aspirin is used as an anti-inflammatory agent for both acute and long-term inflammation, as well as for the treatment of inflammatory diseases, such as rheumatoid arthritis.
Heart attacks and strokes
Aspirin is an important part of the treatment of those who have had a heart attack. It is generally not re... | Aspirin | Wikipedia | 306 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
After percutaneous coronary interventions (PCIs), such as the placement of a coronary artery stent, a U.S. Agency for Healthcare Research and Quality guideline recommends that aspirin be taken indefinitely. Frequently, aspirin is combined with an ADP receptor inhibitor, such as clopidogrel, prasugrel, or ticagrelor to ... | Aspirin | Wikipedia | 496 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
As of , the United States Preventive Services Task Force (USPSTF) determined that there was a "small net benefit" for patients aged 40–59 with a 10% or greater 10-year cardiovascular disease (CVD) risk, and "no net benefit" for patients aged over 60. Determining the net benefit was based on balancing the risk reduction... | Aspirin | Wikipedia | 507 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Some conclude the benefits are greater than the risks due to bleeding in those at average risk. Others are unclear if the benefits are greater than the risk. Given this uncertainty, the 2007 United States Preventive Services Task Force (USPSTF) guidelines on this topic recommended against the use of aspirin for prevent... | Aspirin | Wikipedia | 504 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Schizophrenia
Some researchers have speculated the anti-inflammatory effects of aspirin may be beneficial for schizophrenia. Small trials have been conducted but evidence remains lacking.
Other uses
Aspirin is a first-line treatment for the fever and joint-pain symptoms of acute rheumatic fever. The therapy often las... | Aspirin | Wikipedia | 384 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Meta-analysis and systematic reviews have concluded that laboratory confirmed aspirin resistance confers increased rates of poorer outcomes in cardiovascular and neurovascular diseases. Although the majority of research conducted has surrounded cardiovascular and neurovascular, there is emerging research into the risk ... | Aspirin | Wikipedia | 407 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
March 2009 recommendations from the USPSTF on the use of aspirin for the primary prevention of coronary heart disease encourage men aged 45–79 and women aged 55–79 to use aspirin when the potential benefit of a reduction in MI for men or stroke for women outweighs the potential harm of an increase in gastrointestinal h... | Aspirin | Wikipedia | 373 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Aspirin should not be taken by people who are allergic to ibuprofen or naproxen, or who have salicylate intolerance or a more generalized drug intolerance to NSAIDs, and caution should be exercised in those with asthma or NSAID-precipitated bronchospasm. Owing to its effect on the stomach lining, manufacturers recommen... | Aspirin | Wikipedia | 500 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Blockade of COX-1 by aspirin apparently results in the upregulation of COX-2 as part of a gastric defense. There is no clear evidence that simultaneous use of a COX-2 inhibitor with aspirin may increase the risk of gastrointestinal injury.
"Buffering" is an additional method used with the intent to mitigate gastroint... | Aspirin | Wikipedia | 512 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Reye's syndrome
Reye's syndrome, a rare but severe illness characterized by acute encephalopathy and fatty liver, can occur when children or adolescents are given aspirin for a fever or other illness or infection. From 1981 to 1997, 1207 cases of Reye's syndrome in people younger than 18 were reported to the US Center... | Aspirin | Wikipedia | 511 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Other adverse effects
Aspirin can induce swelling of skin tissues in some people. In one study, angioedema appeared one to six hours after ingesting aspirin in some of the people. However, when the aspirin was taken alone, it did not cause angioedema in these people; the aspirin had been taken in combination with anoth... | Aspirin | Wikipedia | 503 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Aspirin overdose can be acute or chronic. In acute poisoning, a single large dose is taken; in chronic poisoning, higher than normal doses are taken over a period of time. Acute overdose has a mortality rate of 2%. Chronic overdose is more commonly lethal, with a mortality rate of 25%; chronic overdose may be especiall... | Aspirin | Wikipedia | 215 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Interactions
Aspirin is known to interact with other drugs. For example, acetazolamide and ammonium chloride are known to enhance the intoxicating effect of salicylates, and alcohol also increases the gastrointestinal bleeding associated with these types of drugs. Aspirin is known to displace a number of drugs from pr... | Aspirin | Wikipedia | 472 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Infectious diseases
Several studies investigated the anti-infective properties of aspirin for bacterial, viral and parasitic infections. Aspirin was demonstrated to limit platelet activation induced by Staphylococcus aureus and Enterococcus faecalis and to reduce streptococcal adhesion to heart valves. In patients with... | Aspirin | Wikipedia | 446 | 1525 | https://en.wikipedia.org/wiki/Aspirin | Biology and health sciences | Drugs and pharmacology | null |
Acupuncture is a form of alternative medicine and a component of traditional Chinese medicine (TCM) in which thin needles are inserted into the body. Acupuncture is a pseudoscience; the theories and practices of TCM are not based on scientific knowledge, and it has been characterized as quackery.
There is a range of a... | Acupuncture | Wikipedia | 442 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
Scientific investigation has not found any histological or physiological evidence for traditional Chinese concepts such as qi, meridians, and acupuncture points, and many modern practitioners no longer support the existence of qi or meridians, which was a major part of early belief systems. Acupuncture is believed to h... | Acupuncture | Wikipedia | 476 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
Clinical practice varies depending on the country. A comparison of the average number of patients treated per hour found significant differences between China (10) and the United States (1.2). Chinese herbs are often used. There is a diverse range of acupuncture approaches, involving different philosophies. Although va... | Acupuncture | Wikipedia | 467 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
The most common mechanism of stimulation of acupuncture points employs penetration of the skin by thin metal needles, which are manipulated manually or the needle may be further stimulated by electrical stimulation (electroacupuncture). Acupuncture needles are typically made of stainless steel, making them flexible and... | Acupuncture | Wikipedia | 449 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
(; "arrival of qi") refers to a claimed sensation of numbness, distension, or electrical tingling at the needling site. If these sensations are not observed then inaccurate location of the acupoint, improper depth of needle insertion, inadequate manual manipulation, are blamed. If is not immediately observed upon need... | Acupuncture | Wikipedia | 197 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
Related practices
Acupressure, a non-invasive form of bodywork, uses physical pressure applied to acupressure points by the hand or elbow, or with various devices.
Acupuncture is often accompanied by moxibustion, the burning of cone-shaped preparations of moxa (made from dried mugwort) on or near the skin, often but... | Acupuncture | Wikipedia | 415 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
Acupuncture point injection is the injection of various substances (such as drugs, vitamins or herbal extracts) into acupoints. This technique combines traditional acupuncture with injection of what is often an effective dose of an approved pharmaceutical drug, and proponents claim that it may be more effective than ei... | Acupuncture | Wikipedia | 355 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
Efficacy
, many thousands of papers had been published on the efficacy of acupuncture for the treatment of various adult health conditions, but there was no robust evidence it was beneficial for anything, except shoulder pain and fibromyalgia. For Science-Based Medicine, Steven Novella wrote that the overall pattern o... | Acupuncture | Wikipedia | 303 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
A 2014 review in Nature Reviews Cancer found that "contrary to the claimed mechanism of redirecting the flow of qi through meridians, researchers usually find that it generally does not matter where the needles are inserted, how often (that is, no dose-response effect is observed), or even if needles are actually inser... | Acupuncture | Wikipedia | 491 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
The use of acupuncture has been criticized owing to there being little scientific evidence for explicit effects, or the mechanisms for its supposed effectiveness, for any condition that is discernible from placebo. Acupuncture has been called "theatrical placebo", and David Gorski argues that when acupuncture proponent... | Acupuncture | Wikipedia | 427 | 1537 | https://en.wikipedia.org/wiki/Acupuncture | Biology and health sciences | Alternative and traditional medicine | null |
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