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AST

Aspartate aminotransferase (AST), also known as serum glutamic-oxaloacetic (SGOT), is a pyridoxal phosphate-dependent enzyme that catalyzes the reversible transfer of an amino group between L-aspartate and α-ketoglutarate, yielding oxaloacetate and L-, thereby facilitating and the malate-aspartate shuttle for NADH transport across mitochondrial membranes. Predominantly localized in the cytosol and mitochondria of hepatocytes, cardiomyocytes, cells, renal tissue, , , and erythrocytes, AST enters the bloodstream upon cellular injury or , serving as a sensitive indicator of hepatocellular damage, , or . The , a standard component of liver function panels, quantifies activity—typically expressed in international units per liter (/L)—with reference ranges generally 10–40 /L for adults, though influenced by age, sex, and methodology. Often interpreted alongside () for diagnostic specificity, an AST/ALT ratio exceeding 2:1 suggests , while elevations without ALT predominance may point to non-hepatic sources like or strenuous exercise. Though not specific to any single , AST monitoring aids in evaluating acute , drug-induced , progression, and post-ischemic cardiac events, with rapid rises and falls reflecting acute injury dynamics.

Science and technology

Computing

An abstract syntax tree (AST) is a hierarchical data structure representing the syntactic structure of source code in a programming language, where nodes denote syntactic constructs such as expressions, statements, or declarations, and edges indicate parent-child relationships. Unlike a full parse tree, an AST omits details of concrete syntax like punctuation, whitespace, and explicit grouping symbols, focusing instead on the essential logical form to facilitate subsequent processing. In compiler design, an AST is typically constructed during the syntax analysis phase following lexical analysis, where a parser processes tokens to build either a concrete syntax tree or directly an AST by applying grammar rules and resolving operator precedences. This intermediate representation enables semantic analysis to check type compatibility and scope rules, followed by optimization passes that traverse and transform the tree—such as constant folding or dead code elimination—and ultimately code generation, where the AST guides translation to machine code or bytecode. For instance, in the Java programming language, the compiler uses ASTs to validate and optimize code before producing class files. ASTs extend beyond compilation to support tools for and transformation. Integrated development environments (IDEs) leverage ASTs for features like , error detection, and refactoring, enabling operations such as renaming variables across a codebase without altering syntax fidelity. Transpilers, like Babel for , parse into ASTs, apply modifications (e.g., converting ES6 features to ES5), and regenerate code. In research, ASTs underpin models for code comprehension, capturing syntactic patterns for tasks like bug detection or . A key distinction exists between ASTs and concrete syntax trees (CSTs), also called parse trees: CSTs mirror the input exactly, including every production rule application and terminal symbol, resulting in larger, more verbose structures suited for initial validation but cumbersome for analysis. ASTs abstract these by flattening or eliminating nodes for —e.g., treating a + (b + c) as a with + at the root and operands a, b, c—to emphasize semantic intent and improve traversal efficiency in later phases. This abstraction reduces complexity while preserving all information necessary for correct interpretation.

Medicine and biology

Aspartate aminotransferase (AST), also known as serum glutamic oxaloacetic transaminase (SGOT), is an enzyme present in various human tissues, including the liver, heart, skeletal muscle, kidneys, brain, red blood cells, pancreas, and lungs. It catalyzes the reversible transamination reaction transferring an amino group from aspartate to α-ketoglutarate, producing oxaloacetate and glutamate, which plays a role in amino acid metabolism and gluconeogenesis. In clinical medicine, AST levels are measured via blood tests to evaluate hepatocellular injury or damage to other AST-rich tissues, as the leaks into the bloodstream upon disruption. Normal AST concentrations typically range from 8 to 48 units per liter (U/L), though reference intervals vary by , , and method, with males often at 6-34 international units per liter (/L) and females at 8-40 /L. Levels below the normal range are generally not clinically significant and reflect normal physiology. Elevated AST indicates potential tissue damage, with marked increases over 10,000 IU/L signaling acute, life-threatening conditions requiring immediate intervention. Common causes include (A, B, C, D, E), , , , acetaminophen toxicity, hemochromatosis, , trauma or , and strenuous exercise. Skeletal muscle damage accounts for over half of cases with markedly elevated AST (>1,000 IU/L) in non-hepatic etiologies, followed by cardiac sources. AST is frequently assessed alongside alanine aminotransferase (ALT) in liver function panels, as ALT is more hepatospecific while AST occurs in broader tissues. An exceeding 2:1 often points to , whereas a ratio near 1 suggests or ; ratios below 1 may indicate . Mild, persistent elevations warrant monitoring and further evaluation if exceeding twice the upper limit, prioritizing exclusion of chronic alcohol use, , and metabolic disorders.

Mathematics

The , also known as Leibniz's test or the Leibniz criterion, provides a sufficient condition for the of an infinite series of the form \sum_{n=1}^{\infty} (-1)^{n+1} b_n, where b_n > 0 for all n. Specifically, if the sequence \{b_n\} is monotonically decreasing (i.e., b_{n+1} \leq b_n for all n) and \lim_{n \to \infty} b_n = 0, then the series converges. This test applies only to and does not guarantee ; for instance, the alternating harmonic series \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n} converges by the test since \frac{1}{n} decreases to 0, but its absolute value series diverges. The proof of the test relies on the and properties of partial sums. Consider the partial sums s_{2k} = \sum_{n=1}^{2k} (-1)^{n+1} b_n and s_{2k-1} = \sum_{n=1}^{2k-1} (-1)^{n+1} b_n. Due to the decreasing nature of b_n, the even partial sums form an increasing bounded above by b_1, while the odd partial sums form a decreasing bounded below by 0, ensuring both subsequences converge to the same , hence the full sequence of partial sums converges. Failure of the conditions implies the test is inconclusive; for example, if \lim b_n \neq 0, the series diverges by the divergence test, but if b_n does not decrease monotonically, further tests like the ratio or may be needed. The test extends to generalized alternating series \sum (-1)^n a_n where |a_n| decreases to 0, and it underpins the estimation theorem, which bounds the error in truncation: the remainder after n terms satisfies |R_n| \leq b_{n+1}. Historically, formulated an early version in the 17th century, though rigorous proofs emerged later with the development of by mathematicians like . In practice, the test is applied after verifying the conditions, often in to distinguish conditional from , as in for more general cases.

Physical sciences

The anamorphic stretch transform (AST) is a physics-inspired mathematical transformation that warps and stretches signals in a context-aware manner to enable efficient compression and processing, drawing from and dispersive transforms. Developed as an analog to physical and time-stretch techniques, AST selectively compresses by increasing coherence in the domain, reducing redundancy in high-dimensional datasets such as images or time-series signals. It has applications in signal analysis, where traditional uniform sampling leads to inefficiencies; for instance, discrete implementations like the discrete anamorphic stretch transform (DAST) mimic through virtual gratings to achieve ratios superior to in certain scenarios without perceptible loss. This approach addresses bottlenecks by leveraging causal physical analogies, such as non-uniform frequency sampling, validated through experimental setups. In and dynamics, the adiabatic surface temperature (AST) represents the equilibrium temperature of an idealized, infinitely thin surface exposed to convective and radiative es where net is zero, simplifying boundary condition modeling for real materials. Introduced to replace the need for separate gas and surface temperatures in simulations, AST integrates incident radiation, convection, and emission via the Stefan-Boltzmann law, with measurements approximated using plate thermometers calibrated to match theoretical values under ISO 834 curves. Empirical validations, such as those from NIST experiments, show AST predictions aligning with temperatures within 50–100°C for , enabling causal predictions of loads without solving full conduction equations. This metric supports performance-based engineering, as outlined in Eurocode standards, by providing a single-parameter input for finite element analyses of exposed structures.

Organizations and institutions

Government and military

In the United States, of Commercial Space Transportation (AST), a branch of the (FAA), regulates commercial space launches, reentries, and related operations to ensure public safety and national security. Established under the and subsequent legislation, AST issues licenses for over 1,000 commercial launches annually as of 2023, overseeing activities by entities like and while integrating with Department of Defense requirements for range safety. The U.S. Coast Guard's Atlantic Strike Team (AST), one of three regional strike teams under the National Strike Force, specializes in rapid response to oil spills, hazardous material releases, and weapons of mass destruction incidents since its formation in 1973. Comprising about 20 members trained in containment, recovery, and mitigation, the AST has supported over 500 major incidents, including the 2010 spill, coordinating with the Environmental Protection Agency and providing on-scene expertise in chemical, biological, radiological, nuclear, and explosives environments. Within the U.S. Coast Guard, Aviation Survival Technicians (ASTs), also known as rescue swimmers, perform search-and-rescue missions, deploying from helicopters to conduct swimmer rescues, hoist extractions, and medical evacuations in adverse conditions. ASTs undergo rigorous training, including a 24-week "A" School program emphasizing water survival, helicopter operations, and emergency medical response, with personnel maintaining proficiency through annual qualifications; as of 2023, approximately 100 active-duty ASTs support missions saving over 300 lives annually. U.S. Customs and Border Protection (CBP) employs Autonomous Surveillance Towers (ASTs) as a program-of-record technology for border security, deploying sensor-equipped towers with , cameras, and analytics to detect unauthorized crossings along the U.S.- border. Declared operational in 2020 after testing phases starting in 2017, the system covers over 2,000 miles with integrated data fusion to cue agents, reducing response times by up to 50% in pilot areas according to agency evaluations. In the U.S. military, AST designations include the Acquisition Support Team, which assists in and contracting processes across Department of Defense branches, and the Army Satellite Tracking Center, responsible for monitoring satellite assets. Additionally, AST refers to Air Staff Targets in joint air operations planning, denoting prioritized objectives for aerial strikes or support.

Professional associations

The Association of Surgical Technologists (AST), founded in 1969, is the primary professional organization representing surgical technologists and surgical assistants in the United States, with a mission to advance the through education, certification support, and advocacy for quality patient care in settings. It provides resources such as credits, career development tools, and guidelines for best practices, and collaborates with accrediting bodies like the Accrediting Review Council on Education in Surgical Technology and Surgical Assisting (ARC/STSA). Membership includes access to and networking opportunities, emphasizing evidence-based standards to minimize surgical risks. The American Society of Transplantation (AST), established in 1982, serves as the leading professional body for transplant physicians, surgeons, scientists, and allied health professionals in , boasting over 5,000 members dedicated to advancing through research, education, and policy influence. It organizes annual meetings like the American Transplant Congress, funds grants for clinical and basic research, and develops consensus guidelines on immunosuppressive therapies and organ allocation, drawing on empirical from member-led studies to improve graft survival rates and outcomes. The society's work prioritizes causal factors in and long-term viability, often critiquing regulatory hurdles that delay innovative protocols. The Association for Software Testing (AST) functions as a global community for software testing professionals, promoting rigorous methodologies in through conferences, certifications, and peer-reviewed resources since its inception in the early . It emphasizes empirical testing practices over unverified assumptions, offering training in techniques that rely on real-world defect reproduction rather than solely automated scripts. Membership benefits include access to specialized workshops and publications that challenge outdated paradigms in software reliability, fostering of failure modes in complex systems.

Businesses and companies

AST SpaceMobile, Inc. (: ASTS) is a satellite communications company founded in 2017 and headquartered in , specializing in the design and deployment of a space-based cellular broadband network compatible with unmodified smartphones. The company aims to provide global coverage by launching low-Earth orbit satellites, with its first five commercial BlueBird satellites deployed in September 2024 via rockets. As of October 2024, AST SpaceMobile has secured partnerships with over 45 mobile network operators worldwide, covering more than 2.8 billion subscribers, and reported a cash position of approximately $918 million following a July 2024 stock offering. AST Research, Inc., founded in 1980 in , by Albert Wong, Safi Qureshey, and Thomas Yuen, was a major manufacturer of personal computers and peripherals, initially focusing on expansion cards for PC compatibles before expanding into desktops, laptops, and servers. By the early , it ranked as the third-largest U.S. PC maker by revenue, with annual sales exceeding $2 billion in 1995, but faced challenges from Asian competitors and internal issues, leading to its acquisition by in 1997 for $130 million in cash and assumed debt. The brand was later licensed and the company effectively ceased independent operations by 1999.

Education

Qualifications and roles

The Advanced Skills Teacher (AST) designation in recognizes educators who demonstrate exceptional performance through rigorous external against national standards for excellence, including subject knowledge, , and pupil progress. Introduced in 1998 as part of the government's performance management framework, ASTs are typically experienced qualified teachers who remain primarily -based but receive additional remuneration—historically up to 25% above the upper —to disseminate best practices across schools via coaching, mentoring, or demonstrations. Eligibility for AST assessment requires at least three years of qualified experience, with candidates submitting evidence portfolios and undergoing classroom observations by independent assessors appointed under guidelines; successful ASTs must renew their status periodically through continued high performance. This role offers a non-leadership progression path, emphasizing expertise-sharing to elevate school-wide , though uptake has varied due to demands and post-2013 reforms integrating AST elements into broader upper pay scales. In the United States, particularly in Tennessee and select other states, the Associate of in Teaching (AST) is a two-year degree program at community colleges, embedding foundational coursework and partial fulfillment of state teacher licensure standards to prepare students for bachelor's degrees in elementary, secondary, or . Programs typically include 60-62 credits in , , and introductory , seamless to while addressing teacher shortages in high-need areas.

Transportation

Systems and services

Anruf-Sammel-Taxi (AST), or collective call taxi, constitutes a demand-responsive public transportation service widely implemented in to supplement fixed-route bus and rail networks in low-density areas or during off-peak hours. Passengers initiate rides by , , or online booking, typically requiring advance notice of at least 30 minutes to one hour, after which dispatch systems optimize routes to collect multiple users en route to shared destinations. Vehicles employed include minibuses or capable of accommodating several passengers, with operations extending into evenings and nights—such as from 6:00 a.m. to 1:00 a.m. in some regions—to address gaps in conventional timetables. This model prioritizes efficiency by minimizing empty runs through shared pickups, often adhering to predefined service zones while allowing route deviations for collective efficiency. AST integrates seamlessly with broader public transit ecosystems, accepting standard tickets, day passes, or subscriptions from local operators, thereby maintaining fare equity; for instance, children up to school age travel free when accompanied by adults, and reduced rates apply to seniors. Services are managed by regional transport authorities or contracted providers, such as Verkehrsverbund Bremen/Niedersachsen (VBN) in districts like Diepholz and Verden, or in , where GPS-enabled apps facilitate automated location detection for streamlined booking. Operational constraints include limited availability for telephone bookings outside core hours (e.g., 6:00 a.m. to 10:00 p.m. weekdays in some areas) and adherence to protocols, such as mandatory masking during certain periods. Distinguishing AST from related services like , which follows fixed lines with on-call timing, AST emphasizes flexible routing for grouped passengers to enhance viability in underserved locales. Deployment spans various , including , , and , often replacing or augmenting discontinued bus lines to sustain rural connectivity without subsidizing underutilized fixed services. Evaluation metrics from operators highlight improved cost-effectiveness, with shared rides reducing per-passenger expenses compared to individual taxis, though reliance on digital tools can pose barriers for non-tech-savvy users.

Timekeeping

Time zones

Atlantic Standard Time (AST) is a standard time zone used in parts of eastern North America and the Caribbean, corresponding to a fixed offset of four hours behind Coordinated Universal Time (UTC−04:00). This offset aligns approximately with solar noon for longitudes around 60° west, facilitating consistent timekeeping across regions spanning from the Canadian Maritimes to tropical islands. In , AST applies to the provinces of , , and , as well as eastern portions of (including the and ) and mainland east of approximately 63° west longitude. The does not use AST in its contiguous states but observes it in the territories of and the U.S. Virgin Islands. Numerous nations and dependencies also follow AST year-round, including , , the , , , and . Certain areas in northern , such as parts of and , occasionally reference AST equivalents, though Brazil's system varies by region and federal decree. Many AST-observing areas in transition to Atlantic Daylight Time (ADT, ) during , typically from the second in to the first in November, advancing clocks by one hour to extend evening daylight. However, , the U.S. , and most Caribbean AST users do not observe , maintaining UTC−04:00 throughout the year to avoid disruptions in and . This variation stems from local legislative decisions, with Canada's federal coordinating DST across provinces while allowing territorial exemptions. The establishment of AST as a standardized zone traces to the late 19th-century railroad-driven unification of North American timekeeping, formalized on November 18, 1883, when 100+ localities adopted four principal zones including Atlantic at to replace chaotic local times. International Railway Time conventions and subsequent national laws, such as Canada's 1918 and the U.S. of 1918, entrenched AST amid efforts to optimize rail efficiency and wartime production. Adjustments for DST originated earlier in Canada, with trialing it in 1908 and wider adoption during energy crises like , though permanent shifts have been debated and rejected in favor of seasonal changes.

Other uses

Finance and economics

Automated screen trading (AST) denotes the electronic execution of trades in securities or via computer-based interfaces, enabling automated order entry, matching, and confirmation without physical floors. This system supports continuous, 24-hour market access, contrasting with legacy methods and facilitating global participation in time-zone-spanning markets like . Early implementations, such as the Chicago Mercantile Exchange's GLOBEX platform launched in 1992, exemplified AST by digitizing futures and options trading, initially for after-hours sessions before expanding to primary trading hours. The transition to AST in markets like the London International Financial Futures and Options Exchange (LIFFE) for the contract in 1998 shifted peak trading volumes from small lots (e.g., 3 contracts pre-transition) to larger sizes, reflecting improved and efficiency. Economically, AST reduces execution costs through , with empirical studies showing negative correlations between its introduction, , and per-contract commissions in futures markets. By minimizing human intervention, it enhances and , though it has prompted regulatory scrutiny over risks and volatility amplification during events like the 1987 crash, where electronic precursors highlighted systemic interdependencies. Overall, AST's proliferation has lowered for institutional and retail traders, contributing to the and of exchanges since the 1990s.

Miscellaneous

In medicine, AST refers to (also known as or serum glutamic-oxaloacetic transaminase, SGOT), an primarily found in the liver, heart, , kidneys, , and red blood cells, which catalyzes the reversible transfer of an amino group between aspartate and glutamate. Elevated serum levels of AST, typically measured via blood tests with normal ranges under 40 IU/L for adults, indicate potential tissue damage, particularly in the liver, as the enzyme leaks into the bloodstream following cell injury from conditions such as , , alcohol-induced damage, or . AST levels are often evaluated alongside () for diagnostic specificity, though AST elevations can also arise from non-hepatic sources like muscle or . In and compiler design, AST denotes an , a -like that represents the syntactic structure of after , omitting extraneous details like parentheses or operator precedence tokens present in concrete syntax trees. ASTs facilitate subsequent phases such as semantic analysis, optimization, and by providing a simplified hierarchical model of program constructs, where nodes correspond to operators, variables, or expressions. For instance, the expression "a + b * c" might be abstracted into a tree with as a child of , enabling efficient traversal and transformation independent of the original grammar's ambiguities. Other miscellaneous applications include antibiotic susceptibility testing (AST), a laboratory method assessing bacterial sensitivity to antimicrobial agents by measuring growth inhibition zones or minimum inhibitory concentrations, guiding treatment for infections. In engineering contexts, AST can refer to atmospheric storage tanks, large vessels used in petrochemical facilities to hold liquids at ambient pressure and temperature, subject to standards for integrity and leak prevention.