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SAR

Synthetic aperture (SAR) is a form of technology that utilizes the relative motion between a radar platform and a to synthesize a large aperture, enabling the production of high-resolution two- or three-dimensional images of , objects, or structures. Unlike passive optical , SAR operates as an active sensor by transmitting pulses and measuring the backscattered echoes, allowing it to function independent of and penetrate atmospheric obscurants such as clouds, smoke, or darkness. Developed in the 1950s through innovations that compensate for the small physical size of real , SAR achieves resolutions approaching centimeters from airborne or spaceborne platforms, far exceeding what a static of equivalent size could provide. SAR's defining characteristics include its side-looking geometry, where the beam illuminates perpendicular to the flight path, and advanced processing algorithms that correct for Doppler shifts and phase differences across multiple pulses to form coherent images. Key applications span , such as detecting or oil spills; , including mapping and damage assessment; and military reconnaissance for target identification, owing to its all-weather reliability and resistance to . Notable achievements include its integration into satellite constellations like NASA's NISAR for and commercial systems providing near-real-time data for and , demonstrating SAR's evolution from specialized defense tools to ubiquitous assets. While primarily valued for empirical utility in data-driven fields, SAR data interpretation requires accounting for speckle noise and geometric distortions inherent to microwave interactions with surfaces, underscoring the technology's reliance on rigorous for accurate causal inference in imaging.

Places

Administrative regions

Special administrative regions (SARs) designate territories granted a degree of within a sovereign nation, often featuring independent legal, economic, and administrative frameworks distinct from the . This status enables retention of pre-existing systems, such as in former colonies, while integrating into the broader state structure. The model emphasizes autonomy in internal affairs, with central authority retained over defense and . In the , SARs embody the "" principle, allowing capitalist economies and separate governance in designated areas. SAR was formally established on July 1, 1997, upon handover from British sovereignty, preserving its system, free port status, and independent judiciary under the . SAR followed on December 20, 1999, after transfer from Portuguese administration, maintaining its tradition, gambling industry dominance, and separate currency via the for Macau. Both regions issue their own passports, currencies ( and ), and participate in international organizations under China's representation, though recent legislation in has centralized certain oversight functions. The SAR framework in supports economic continuity, with serving as a global financial hub and as a tourism and gaming center, contributing significantly to national GDP despite comprising less than 0.1% of 's land area. Population figures stand at approximately 7.5 million for and 700,000 for as of 2023. Outside , the SAR designation appears in limited contexts, such as Russia's special administrative regions in and , established in 2018 to attract relocated businesses with favorable tax regimes, though these lack the comprehensive autonomy of Chinese SARs.

Geographical locations

The Sar River is a waterway in the region of northwestern . Originating near the city of at an elevation of approximately 500 meters, it flows southward through the A Maía valley for more than 30 kilometers before merging with the Ulla River near Valga. The river's covers an area of about 656 square kilometers and supports local and ecosystems in province. Several villages and settlements named Sar exist in Iran, primarily in provinces such as East Azerbaijan, , and Semnan, often situated in rural or mountainous terrain. These locations, typically small population centers, derive their names from terms but lack extensive documentation on specific geographical attributes beyond coordinates.

Currency and finance

Saudi Arabian Riyal

The (SAR) is the official of , subdivided into 100 halalas. It bears the code SAR (numeric: 682) and is symbolized as ر.س in or SR/SAR in Latin characters. Managed by the (SAMA), the riyal serves as the primary in the kingdom's oil-driven economy, where foreign exchange inflows are predominantly denominated in U.S. dollars. The riyal was established in 1932 following the under King Abdulaziz, replacing disparate regional currencies such as the Hejazi riyal and Hajr riyal. A single national currency was formalized in 1952, with SAMA (originally the Saudi Arabian Monetary Agency) assuming issuance responsibilities from 1952 onward. Prior to mid-1981, the riyal operated under a loose (±7.5%) to the IMF's basket; from 1981 to 1986, it floated against the U.S. dollar before adopting a fixed in 1986 at 3.75 SAR per USD, a rate unchanged since to anchor amid volatile revenues. This , defended through SAMA's interventions and backed by reserves exceeding $400 billion as of recent data, has ensured stability, with the rate holding within 3.75-3.76 SAR per USD through economic cycles including the 2014-2016 oil price collapse. Banknotes circulate in denominations of 1, 5, 10, 20, 50, 100, 200, and 500 riyals, featuring portraits of monarchs (e.g., King Abdulaziz on the 1-riyal note) alongside Islamic and national motifs, with enhanced security elements like holograms introduced in series updates. Coins include 1, 5, 10, 25, 50, and 100 halalas, plus 1- and 2-riyal pieces, minted primarily in base metals. The fixed facilitates trade predictability, as over 90% of exports (chiefly ) are USD-settled, minimizing risk exposure for the kingdom's $1 trillion-plus non-oil GDP as of 2024 estimates.

Stock appreciation rights

Stock appreciation rights (SARs) grant employees the right to receive payment equal to the increase in value of a designated number of shares of , measured from a predetermined exercise price—typically the on the —to the on the exercise date, without requiring the employee to purchase the underlying shares. This compensation mechanism aligns employee incentives with stock performance, often over a period such as three to five years, after which eligible participants may exercise the rights within a specified window, usually up to ten years from . Upon exercise, the payout equals the appreciation per share multiplied by the number of , settled either in cash or equivalent shares, depending on the plan design. SARs differ from actual by providing only the economic benefit of price appreciation, functioning as a or stock equivalent tied to relative performance rather than absolute rights like or dividends. -settled SARs, common in private companies, deliver a direct monetary , avoiding share issuance and dilution, while stock-settled variants distribute shares valued at the appreciated amount, potentially conferring upon . For issuers, cash settlement preserves structure but may impact , whereas stock settlement dilutes existing shareholders proportionally to the payout. Compared to traditional stock options, SARs eliminate the need for employees to fund the exercise price, enabling receipt of the full intrinsic value without out-of-pocket costs, which reduces for participants but forgoes the of options where post-exercise share appreciation could yield capital gains. Options compel share purchase at , often leading to and potential eligibility, whereas SARs typically yield or equivalent without such benefits unless stock-settled and held post-exercise. Both instruments share similar vesting schedules and expiration terms under U.S. regulations, but SARs offer issuers flexibility in settlement to manage cash flow or dilution, particularly pre-IPO, as seen in plans adopted by companies like and to incentivize retention without immediate grants. In the United States, SARs are treated as nonqualified under rules, with employees recognizing ordinary income on the full appreciation amount at exercise, subject to withholding for income and employment taxes, while issuers claim a corresponding . To avoid penalties under 409A, plans must specify fixed exercise prices and terms at , prohibiting later reductions that could defer taxation. companies disclose SAR grants in proxy statements and filings per requirements, including valuation assumptions like Black-Scholes models for expense recognition under ASC 718. Advantages include motivational alignment without employee capital outlay and administrative simplicity for cash payouts, though drawbacks encompass potential cash strain on issuers and ordinary income taxation limiting after-tax returns compared to qualified options. SARs prove particularly useful for closely held firms transitioning ownership or startups preserving share pools, as evidenced in agreements facilitating key employee incentives without diluting founder control.

Computing and telecommunications

Segmentation and reassembly

Segmentation and reassembly (SAR) refers to the process in (ATM) networks where higher-layer protocol data units (PDUs) of variable length are divided into fixed-length cells of 53 bytes—comprising a 5-byte header and 48-byte —for transmission across the ATM layer, with subsequent reconstruction at the receiving end. This mechanism ensures efficient multiplexing and switching in ATM, which relies on uniform cell sizes to avoid variable delays in hardware processing. The SAR function is primarily handled by the ATM Adaptation Layer (AAL), divided into convergence and SAR sublayers, where the SAR sublayer specifically fragments the incoming PDU into segments that fit the 48-byte , appending ATM cell headers before passing them to the ATM layer for transmission. At the receiver, the SAR sublayer collects these cells, verifies sequence integrity (via mechanisms like sequence numbers in certain AAL types), and reassembles the original PDU, discarding any or trailers added during segmentation. Different AAL types implement SAR variably: AAL1 for constant bit rate services adds timing stamps and sequence checks for real-time reassembly, while AAL5, optimized for data traffic like over ATM, uses a simple trailer with length and (CRC) fields in the final cell for error detection and minimal overhead. In practice, SAR offloads processing from endpoints to network interfaces or switches, reducing CPU burden on devices like routers; for instance, Cisco's software SAR implementation on platforms such as the 2600 series enables handling of voice and data over without dedicated hardware accelerators. This approach contrasts with variable-length packet networks like Ethernet, where fragmentation occurs at higher layers (e.g., ), but 's cell-based SAR provides deterministic latency critical for applications like video streaming in early deployments during the . Despite 's decline in favor of -based technologies, SAR principles influence modern protocols, such as segmentation in MPLS or mesh networks for handling oversized messages.

Other computing protocols

In wireless ad hoc networks, the Security-Aware (SAR) protocol integrates metrics, such as levels derived from and intrusion detection capabilities, into the route process to select paths that balance and performance. Proposed in 2002, SAR modifies on-demand mechanisms like AODV by incorporating route requests that propagate requirements, enabling nodes to evaluate paths based on cumulative attributes rather than solely hop or . This approach addresses vulnerabilities in open ad hoc environments, where intermediate nodes may be compromised, by enforcing predefined thresholds during path formation. For wireless sensor networks, a Self-Adaptive and Reliable (SAR) transport protocol ensures end-to-end delivery of data by dynamically adjusting retransmission strategies based on channel conditions and packet priorities, using techniques like selective acknowledgments and avoidance to minimize and use. Introduced around 2015, this SAR variant prioritizes reliable transport over unreliable links by predicting and adapting sending rates, outperforming static protocols in heterogeneous sensor deployments. In networks, a receiver-driven SAR transport , detailed in 2024 research, mitigates micro-bursts from short flows by having receivers forecast and throttle long-flow rates accordingly, achieving up to 66% reduction in average flow completion time compared to baselines like DCTCP in simulations and testbeds. This leverages explicit feedback from switches to enable proactive rate adjustment, enhancing throughput in incast-prone environments without sender-side modifications.

Public safety and emergency response

Search and rescue operations

(SAR) operations encompass the systematic efforts to detect, locate, and provide assistance to persons in distress or facing imminent peril, spanning diverse environments including , aeronautical, inland, and settings. These missions prioritize rapid response to mitigate risks from hazards such as shipwrecks, aircraft incidents, mishaps, or structural collapses, with responders often enduring extreme conditions to effect recoveries. Core phases of SAR include size-up for situational assessment and planning, systematic search to identify victims using techniques like patterns or signal detection, and rescue execution involving stabilization, extraction, and initial medical care. Procedures emphasize safety protocols, such as avoiding entanglement risks with retrieval lines and employing like helmets and gloves in dynamic hazards. Internationally, maritime SAR is standardized under the 1979 International Convention on Maritime Search and Rescue, adopted in on April 27, 1979, and effective from July 22, 1985, mandating coordinated global plans to aid distressed persons at sea irrespective of nationality or status. The convention delineates search regions, promotes cooperation among states, and requires shore-based facilities for coordination, influencing operations worldwide. In the United States, the National Plan, established via interagency agreement among federal entities including the U.S. and Air Force Rescue Coordination , outlines responsibilities for coordinating civil SAR across , inland, and aeronautical domains to address domestic emergencies efficiently. This framework integrates resources under the National Response Framework, specifying lead agencies like the for surface s and FEMA for urban disaster responses. SAR variants include (USAR) for rubble-penetrating operations in earthquakes or building failures, wilderness SAR for remote terrain navigation, and specialized inland types like swiftwater or recovery, each demanding tailored expertise. Equipment commonly deployed features and imaging for victim detection, and for aquatic or aerial searches, concrete-cutting tools and hydraulic lifts for structural breaches, and or specialized vehicles for access in inaccessible areas. Operational challenges arise from environmental perils, such as rising floodwaters precluding safe searches or confined spaces heightening rescuer risks, compounded by the need for multi-agency and time-critical decisions in low-visibility scenarios. Effectiveness hinges on pre-established coordination, as uncoordinated efforts can exacerbate outcomes in high-stakes incidents.

Science and engineering

Synthetic aperture radar

Synthetic aperture radar (SAR) is an active technique that utilizes the relative motion between a and a target to achieve high imaging, simulating a large through coherent rather than relying solely on physical size. pulses are transmitted toward the Earth's surface or other targets, and the backscattered echoes are recorded as the —typically an aircraft, drone, or —moves along its flight path. This motion enables the synthesis of an extended , often spanning kilometers, which dramatically improves azimuthal to levels comparable to the physical length divided by two, independent of to the target. The core principles rely on range , determined by the transmitted pulse bandwidth, and azimuth , enhanced by exploiting Doppler frequency shifts in the returns from scatterers at different angular positions relative to the flight path. As the platform advances, phase differences in echoes from the same point target over multiple pulses are coherently summed, effectively focusing the energy as if from a much larger stationary . SAR operates in side-looking to maximize the synthetic aperture length while minimizing range migration effects, with processing algorithms such as range-Doppler or back-projection correcting for nonlinear trajectories and compensating for Earth's curvature in spaceborne systems. Frequencies typically range from P-band (0.3-1 GHz) for deep to X-band (8-12 GHz) for fine detail, with varying from meters in spaceborne configurations to centimeters in high-resolution modes. SAR's primary advantages stem from its active nature and wavelengths, allowing imaging independent of , through clouds, , and , with penetration into dry or depending on —longer wavelengths like L-band (1-2 GHz) enabling subsurface detection up to several meters in arid conditions. It overcomes limitations of passive optical sensors by providing polarimetric data, which reveals surface properties such as roughness, moisture, and dielectric constants via backscattering coefficients. However, challenges include speckle noise from coherent , requiring multi-look processing that trades for reduced granularity; geometric distortions like foreshortening, , and shadow effects in sloped terrain; and high computational demands for raw data focusing, often exceeding terabytes per mission for global coverage. Applications encompass for monitoring dynamic processes, including surface deformation via differential interferometry (InSAR), which measures millimeter-scale changes from differences between repeat passes—used, for instance, in tracking or volcanic activity. In , SAR derives wave spectra, current velocities, and wind fields from Doppler and hydrodynamic modulation effects; benefits from mapping snow wetness and ice velocity; employs it for estimation and via models. Disaster management leverages rapid revisit capabilities for extent delineation and mapping, while applications include classification and through . Spaceborne systems like NASA's upcoming NISAR mission, planned for L- and S-band operation with 5-10 meter resolution, aim to provide 12-day global revisits starting in 2024, enhancing causal understanding of geophysical phenomena through time-series analysis.

Specific absorption rate

The (SAR) quantifies the rate at which radiofrequency (RF) energy is absorbed by biological , expressed as the power deposited per unit in watts per (W/). It serves as a primary metric for evaluating potential thermal effects from RF exposure in devices such as mobile phones, wireless routers, and equipment like MRI scanners. SAR is calculated using the SAR = (σ |E|^2) / ρ, where σ represents the electrical conductivity of the (in per meter), |E| is the magnitude of the internal (in volts per meter), and ρ is the of the (in kilograms per cubic meter). This formulation derives from electromagnetic principles, linking absorbed power to the squared strength modulated by properties. Measurement of SAR typically involves laboratory simulations using anthropomorphic phantoms filled with tissue-equivalent liquids that mimic human head or body dielectric properties at specific frequencies. For mobile devices, probes scan the phantom to map distributions, with SAR computed numerically or via finite-difference time-domain methods, ensuring compliance testing adheres to standardized protocols like IEEE 1528 or IEC 62209. Testing positions include , tilt, and body-worn configurations, with maximum values reported for head and trunk exposure. Regulatory limits on SAR aim to prevent excessive tissue heating, based on thresholds where core body temperature rises less than 1°C. In the United States, the Federal Communications Commission (FCC) enforces a limit of 1.6 W/kg averaged over 1 gram of tissue for partial-body exposure, adopted in 1996 following IEEE C95.1 standards. Internationally, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends 2 W/kg averaged over 10 grams of tissue for localized exposure, as updated in its 2020 guidelines covering frequencies from 100 kHz to 300 GHz. The European Union aligns with ICNIRP via the Radio Equipment Directive (RED 2014/53/EU), requiring SAR certification for marketed devices since 2016. These limits originated in the 1990s from industry and health organizations like IEEE and ANSI, emphasizing thermal bioeffects while incorporating safety factors of 50 from established adverse effect levels. SAR regulations have evolved with technological advancements, including efforts in the early for methods and expansions to address emerging sources like 5G mmWave frequencies. Compliance is mandatory for in most jurisdictions, with devices exceeding limits barred from sale; for instance, FCC rules mandate SAR reporting in user manuals. While SAR focuses on acute thermal risks, some peer-reviewed analyses question whether limits adequately account for prolonged low-level exposures or non-thermal mechanisms, though regulatory bodies maintain they protect against established hazards based on epidemiological and dosimetric evidence.

Structure-activity relationship

The structure-activity relationship (SAR) describes the correlation between a molecule's chemical structure and its biological or pharmacological activity, where modifications to specific structural features predictably alter potency, selectivity, or toxicity. This principle underpins medicinal chemistry by enabling chemists to systematically vary substituents on a lead compound and measure resulting changes in bioactivity through in vitro assays or animal models, revealing causal links such as how electron-withdrawing groups enhance receptor binding affinity. Empirical data from such iterative testing, rather than theoretical assumptions, drives SAR analyses, as biological activity often stems from precise intermolecular interactions like hydrogen bonding or hydrophobic contacts at the target site. In , SAR guides lead optimization by identifying "hotspots" where structural tweaks maximize therapeutic efficacy while minimizing off-target effects; for instance, truncating a might retain activity against a but reduce metabolic . This qualitative approach contrasts with quantitative SAR (QSAR), which employs mathematical models to numerically predict activity from descriptors like molecular weight, , or topological indices, using techniques on datasets of hundreds to thousands of analogs. QSAR models, validated via cross-validation metrics like R² > 0.7 or Q² > 0.5, accelerate but require high-quality, diverse training data to avoid , as poor descriptor selection can inflate apparent predictivity without reflecting true causal mechanisms. Recent advances integrate into QSAR for handling complex datasets, improving accuracy in predicting ADMET properties, though limitations persist in extrapolating to novel scaffolds. SAR studies emphasize causal realism by prioritizing experimentally verified trends over correlative artifacts; for example, isosteric replacements (e.g., for ) test hypotheses about steric or electronic influences on activity, with failures highlighting multifactorial determinants like conformational dynamics. In practice, SAR matrices tabulate activity across analog series to visualize trends, aiding decisions on evolution, as seen in optimizing antibiotics where ring modifications correlate with MIC reductions against resistant strains. Despite biases in academic datasets toward certain chemotypes, rigorous SAR demands orthogonal validation, such as confirming modes, to ensure predictions align with biophysical reality rather than artifacts.

Other scientific applications

In , SAR denotes the successive register, a key component in successive-approximation analog-to-digital converters (SAR ADCs). This iteratively refines a of an input analog voltage by comparing it against a digitally controlled reference via a feedback loop involving a (DAC) and . The process begins with the most significant bit (MSB) set to 1 and proceeds bit-by-bit, typically achieving resolutions from 8 to 18 bits with sampling rates up to 5 MSPS in modern implementations. SAR ADCs incorporating this register are favored for their , as scales with sampling rate rather than resolution, making them suitable for battery-powered devices and precision instrumentation. These converters operate through a : the register initializes the DAC output to half the full-scale range, compares it to the sampled input, and adjusts subsequent bits accordingly, converging on the digital code in N cycles for an N-bit . Introduced in the 1950s for early systems, SAR-based ADCs gained prominence in the 1970s with advancements, enabling applications in interfaces, logging, and systems where medium-speed (under 10 MSPS) and low are required. Typical performance metrics include signal-to-noise ratios exceeding 90 dB for 16-bit devices and below 1 LSB, though susceptibility to clock limits high-frequency use. Beyond ADCs, the successive approximation register principle extends to optimization algorithms in and control systems, where iterative refinement minimizes errors in parameter estimation. In scientific , such as oscilloscopes and peripherals, SAR ADCs provide accurate of transient signals, supporting research in fields like and materials testing.

Organizations and societies

Patriotic and historical groups

The (NSSAR), commonly known as the SAR, is a lineage-based fraternal dedicated to honoring ancestors who aided the American cause during the (1775–1783). Established nationally on April 30, 1889—coinciding with the centennial of Washington's inauguration as president—it originated from earlier local groups, including one formed in as the Sons of Revolutionary Sires. The society's core objectives encompass perpetuating the memory of these patriots, fostering patriotism, preserving historical records, and educating members and the public on the founding principles of liberty and constitutional governance. Federally chartered by the U.S. on June 9, 1906, under President (himself a member), the NSSAR operates as a 501(c)(3) nonprofit headquartered at 809 West Main Street in , since acquiring the property in 1978. It maintains over 575 chapters nationwide, with membership totaling around 38,000 individuals who must demonstrate direct lineal descent from a verified via documented genealogical evidence, including recent allowances for DNA testing in cases of incomplete records. Eligibility is restricted to males aged 18 or older, irrespective of race, religion, or ethnicity, emphasizing civic heritage over political partisanship. The NSSAR conducts diverse activities to advance its mission, including youth-oriented programs such as the Knight Essay Contest, George S. & Stella M. Knight Patriotic Essay Contest, and Joseph S. Rumbaugh Historical Oration Contest, which engage students in researching and presenting on Revolutionary-era topics. It also honors achievements like Boy Scout Eagle Awards with medals and scholarships, organizes grave-marking ceremonies for over 140,000 documented patriot burial sites, and fields color guards for parades, wreath-layings at memorials (e.g., on and Independence Day), and reenactments. Educational initiatives feature outreach lesson plans covering events from the through the Declaration of Independence, a genealogical with 732,000 records, and support for veterans via volunteer services. Notable members have included 16 U.S. presidents and figures such as , underscoring the society's historical prestige. The NSSAR remains distinct from the General Society of the , founded in 1876 as a separate patriotic entity focused on similar lineage but with different and scope. Affiliated youth groups, like the National Society of the Children of the American Revolution (NSCAR, established 1895), extend SAR principles to those under 22 through service, patriotism, and heritage education, though they operate independently.

Transportation entities

The Saudi Arabia Railways (SAR) is the state-owned national railway operator of Saudi Arabia, responsible for freight and passenger rail services across the kingdom. Established in 2006 under the ownership of the Public Investment Fund (PIF), SAR manages a network that includes both legacy lines dating back to the mid-20th century and modern high-speed infrastructure, positioning it as the largest railway operator in the Middle East by route length and capacity. The company's formation consolidated rail assets to support economic diversification, logistics enhancement, and pilgrimage transport, with operations focused on mineral export, intercity connectivity, and urban links. SAR's primary freight corridor is the North-South Railway, a 2,750-kilometer electrified line extending from to the Gulf coast at Ras Al Khair, facilitating the transport of over 70 million tons of minerals annually, including and from Ma'aden facilities. Passenger services are anchored by the Haramain High-Speed Railway, operational since 2018, which spans 453 kilometers between , , and at speeds up to 300 km/h, serving approximately 60 million passengers per year during peak and seasons. This line features advanced signaling, 35 stations, and integration with goals for tourism and mobility. In addition to core operations, SAR oversees maintenance depots, terminals, and expansion projects, including potential extensions to connect with rail networks. The entity employs modern , such as electric locomotives for freight and high-speed trainsets for Haramain, emphasizing safety standards aligned with international benchmarks from bodies like the (UIC). As of 2023, SAR reported transporting billions in cargo value, contributing to Saudi Arabia's non-oil export growth amid global shifts.

Military and defense units

The United States Coast Guard operates the Office of Search and Rescue (CG-SAR), a specialized component established to coordinate national maritime and aeronautical search and rescue efforts, minimizing loss of life through rapid response capabilities including helicopters, cutters, and fixed-wing aircraft deployed across 95,000 miles of coastline and inland waterways. CG-SAR maintains three Rescue Coordination Centers (RCCs) in Miami, Cleveland, and Alameda, integrating data from the Automated Mutual-Assistance Vessel Rescue (AMVER) system to facilitate international coordination, with over 20,000 SAR cases handled annually as of 2023. The Air Force's Air Force Rescue Coordination Center (AFRCC), located at , , serves as the single federal agency for coordinating inland operations across the 48 contiguous states, , and , employing pararescue jumpers and HH-60 Pave Hawk helicopters for missions that rescued over 1,200 lives in fiscal year 2022. This unit evolved from World War II-era efforts and now integrates civil-military partnerships under the National Search and Rescue Plan, responding to distress signals via the U.S. Air Force Rescue Coordination Center's 24/7 operations center. United States Navy search and rescue units, such as those at Naval Air Station Lemoore, deploy MH-60S Seahawk helicopters crewed by pilots, aircrewmen, and medical technicians for both peacetime and combat operations, conducting over 100 missions yearly with specialized equipment for swimmer rescues and medical evacuations. These detachments support broader personnel recovery doctrines, including combat search and rescue (CSAR), where units like Helicopter Sea Combat Squadrons extract downed pilots in hostile environments using tactics refined since the Vietnam War era. Internationally, militaries maintain analogous units; for instance, the Canadian Armed Forces' operates SAR squads with CH-146 Griffon helicopters, covering regions and averaging 5,000 flight hours annually for rescues as of 2024. Similarly, the Royal Australian Air Force's No. 114 Mobile Control Centre coordinates SAR within its air combat group, leveraging P-8A Poseidon aircraft for surveillance and recovery in the theater. These defense-oriented SAR entities prioritize operational readiness, with training emphasizing (SERE) protocols to ensure mission success in austere conditions.

Other uses

Medical and biological terms

In , (SAR) refers to a broad-spectrum, long-lasting induced defense mechanism activated following localized or exposure to specific chemical elicitors, enhancing in distal tissues against subsequent attacks by , viruses, and fungi. This response involves the accumulation of (SA), which acts as a key signaling molecule, leading to the upregulation of pathogenesis-related () proteins and other defense genes. SAR differs from (HR), which is localized , by providing whole-plant protection without in systemic tissues. The molecular pathway of SAR includes SA biosynthesis via the isochorismate or routes, transport of or as mobile signals, and priming of immune responses for faster activation upon reinfection. Studies since the have shown SAR effectiveness in crops like , , and , with applications in for reducing use through chemical inducers like benzothiadiazole. However, SAR can incur fitness costs, such as reduced growth in non-stressed conditions. In medical and pharmacovigilance contexts, SAR denotes serious adverse reaction, defined as an unintended, harmful response to a medicinal product or that meets criteria for —such as resulting in death, being life-threatening, requiring or prolonging hospitalization, causing persistent , or necessitating to prevent such outcomes—and where a reasonable possibility of exists. This distinguishes SAR from serious adverse events (SAEs), which lack implied relatedness. SARs are monitored in clinical trials and post-marketing surveillance to assess drug safety, with expedited reporting required for suspected unexpected serious adverse reactions (SUSARs) to regulatory bodies like the . Reporting of SARs follows international standards, such as those from the International Council for Harmonisation (ICH E2A), emphasizing causality assessment via algorithms like or WHO-UMC scales. In blood transfusion medicine, SAR specifically applies to reactions linked to component administration, prompting investigations into hemovigilance systems.

Environmental metrics

The species-area relationship (SAR) quantifies the empirical pattern in ecology where species richness increases with sampled habitat area, serving as a core metric for assessing biodiversity patterns and informing environmental management. Typically expressed in power-law form as S = c A^z, where S is species number, A is area, c is a scaling constant, and z (often 0.1–0.3 for continental scales or higher for islands) reflects the rate of species accumulation, this relationship derives from extensive field data across taxa and biomes. Empirical validation spans decades, with nested sampling designs showing consistent logarithmic increases in species count as area expands, driven by probabilistic sampling of individuals rather than deterministic niche filling alone. In environmental metrics, SAR enables estimation of baselines and loss projections from alteration. For instance, it underpins targets by extrapolating retention in reduced land classes; a analysis of South African biomes used SAR to recommend protecting 20–44% of land per type to maintain 90% of , aligning with global standards. Applications extend to fragmented landscapes, where the -fragmented area relationship adjusts for isolation effects, revealing that aggregation of remnants can mitigate predicted extinctions beyond simple area-based models. However, empirical tests indicate classic SARs may overestimate losses in human-modified matrices, as matrix-tolerant persist, reducing effective z values by up to 50% in forested conversions. Variations in SAR slope arise from environmental heterogeneity and , with steeper curves (z > 0.25) in heterogeneous or isolated systems like habitat islands, versus shallower ones in continuous mainland s. Recent modeling with refines predictions by incorporating rare species distributions, improving fits to global datasets from sources like GBIF across continents and taxa. In practice, SAR informs metrics like habitat connectivity indices and reserve design, though passive sampling hypotheses emphasize that area alone captures only baseline accumulation, not dynamic processes like dispersal or .

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