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B2

The Northrop Grumman B-2 Spirit is an American heavy strategic bomber that employs advanced low-observable stealth technology to evade sophisticated enemy air defenses, enabling deep penetration strikes with both conventional and nuclear payloads. Characterized by its distinctive flying wing configuration, which enhances aerodynamic efficiency and radar evasion, the aircraft measures 69 feet in length with a 172-foot wingspan and is powered by four turbofan engines providing over 70,000 pounds of thrust each. Capable of unrefueled intercontinental ranges exceeding 6,000 nautical miles and altitudes above 50,000 feet, it represents a pinnacle of post-Cold War aviation engineering focused on precision global strike capabilities.^[1]^[2] Development of the B-2 began in the 1980s under Northrop Corporation (later Northrop Grumman) as part of the Advanced Technology Bomber program, with the prototype's first flight occurring on July 17, 1989, and initial operational capability achieved in April 1997 at Whiteman Air Force Base, Missouri. Only 21 aircraft were produced—one for testing and 20 operational—due to escalating costs that ballooned the total program expenditure to approximately $44 billion, equating to over $2 billion per unit when accounting for research, development, and procurement. This limited fleet size, a direct result of congressional scrutiny over unit costs rising from initial estimates of around $571 million, has constrained the platform's surge capacity despite its unmatched stealth and payload versatility, which includes up to 40,000 pounds of ordnance such as Joint Direct Attack Munitions.^[1]^[3]^[4] The B-2 has demonstrated its strategic value in combat since its debut deployment during Operation Allied Force in 1999, where it flew non-stop from Missouri to targets in Kosovo, delivering 651 precision-guided bombs with a 98% hit rate and expending 11% of all NATO munitions dropped in the campaign. Subsequent missions included support for Operations Enduring Freedom and Iraqi Freedom, involving sorties from forward bases that showcased its global reach and endurance, as well as strikes in Libya in 2011. However, operational challenges persist, including high maintenance demands from specialized stealth coatings requiring climate-controlled facilities and a sortie rate historically lower than legacy bombers like the B-52, exacerbating debates over its cost-effectiveness amid evolving threats from peer adversaries.^[5]^[6]^[7]

Transportation

Aircraft

The Northrop B-2 Spirit is a heavy strategic bomber featuring a flying wing design optimized for low-observable stealth characteristics, enabling penetration of advanced air defenses. Developed under the U.S. Air Force's Advanced Technology Bomber program initiated in the early 1980s, the B-2 incorporates radar-absorbent materials and specialized coatings to minimize radar cross-section.^[1]^[3] The aircraft's first public rollout occurred on November 22, 1988, at Air Force Plant 42 in Palmdale, California, followed by its maiden flight on July 17, 1989.^[1] Production totaled 21 airframes, reduced from initial plans for 132 due to the Soviet Union's collapse and subsequent post-Cold War budget constraints, with the final delivery in 2000 and initial operational capability achieved in April 1997.^[8] Equipped with four General Electric F118-GE-100 non-afterburning turbofan engines, the B-2 achieves high subsonic speeds and an unrefueled range exceeding 6,000 nautical miles, extendable via aerial refueling for intercontinental missions.^[1]^[2] It carries a crew of two—a pilot and mission commander—and supports a maximum payload of over 40,000 pounds, including up to 80 Mk 82 JDAMs, 16 B83 nuclear gravity bombs, or AGM-158 JASSM cruise missiles, with all-altitude attack capability up to 50,000 feet.^[2]^[9] The flying wing configuration, derived from earlier Northrop designs, enhances aerodynamic efficiency while reducing infrared and visual signatures, though it demands fly-by-wire controls for stability.^[1] The B-2's combat debut occurred during Operation Allied Force in the 1999 Kosovo War, where aircraft flying from Whiteman Air Force Base, Missouri, destroyed 33% of selected Serbian targets in the initial eight weeks despite comprising less than 1% of total sorties, demonstrating long-range precision strike efficacy without losses.^[10] Subsequent deployments included 49 sorties in Operation Iraqi Freedom in 2003—22 from forward locations and 27 nonstop round-trips from the U.S.—targeting leadership and hardened facilities; noncombat strikes in Afghanistan from 2001; and suppression missions in Libya in 2011 under Operation Odyssey Dawn.^[1]^[11] The fleet has maintained zero combat losses across these operations, attributable to its stealth profile and standoff weapons, while continuing deterrence patrols against adversaries like China and Russia from bases including Diego Garcia and Andersen AFB, Guam.^[12] Unit flyaway costs averaged approximately $737 million in 1997 dollars, escalating to over $2.1 billion per aircraft when including research, development, and procurement for the low-volume fleet, drawing criticism for fiscal inefficiency compared to legacy platforms like the B-52 Stratofortress.^[8]^[13] Maintenance demands specialized climate-controlled hangars and radar-absorbent coating refurbishments every seven years, yielding operating costs of about $169,000 per flight hour—over twice the B-52's $70,000—and monthly upkeep exceeding $3 million per aircraft, prompting debates on whether the B-2's strategic niche justifies sustaining fewer than two squadrons versus expanding cheaper conventional bombers.^[14]^[15] Proponents argue its unique deep-strike capability against peer threats remains irreplaceable until the B-21 Raider enters service in the late 2020s.^[15]^[13]

Locomotives

The B2 wheel arrangement designates steam tank locomotives with a single unpowered leading axle (two wheels) and a single powered driving axle (two wheels), aligning with the Whyte 2-2-0T configuration. This setup prioritized compactness and agility for low-speed, light-duty tasks such as shunting in industrial yards or branch lines with sharp curves, where the leading wheels guided the engine without contributing to propulsion. However, the design suffered from minimal tractive effort—typically under 7,000 lbf—and inadequate stability beyond 30-40 mph due to the short wheelbase and limited weight distribution over powered axles, rendering it unsuitable for mainline or heavy freight operations.^[16]^[17] Primarily developed in early 20th-century Britain for European narrow-gauge or industrial applications, B2 locomotives exemplified empirical trade-offs in rail engineering: enhanced curve negotiation via the short rigid frame but compromised adhesion from only two driving wheels, often exacerbated by sandy or wet rails. The London and South Western Railway's C14 class, comprising 10 examples built from 1907 to 1911, represented a key instance, equipped with 12-by-18-inch cylinders and coal-water bunkers for push-pull workings on rural sidings, achieving modest hauls of 50-100 tons at slow speeds. Similarly, Aveling & Porter's TJ-class geared well-tank engines, like works No. 9449 "The Blue Circle" delivered in 1926, adapted the arrangement for cement works shunting, incorporating traction gears to boost low-speed torque despite the inherent power constraints. Few U.S. equivalents emerged, as American practice favored sturdier 0-4-0T switchers for yard work, limiting B2 adoption transatlantically.^[18] By the interwar period, operational data revealed B2 engines' vulnerability to derailments on uneven track and inefficiency in fuel consumption relative to arrangements like 0-4-0T, which doubled driving wheel contact for better grip without sacrificing maneuverability. Post-World War II dieselization accelerated obsolescence, as compact switchers like the British Rail Class 08 offered superior reliability and lower maintenance without steam's boiler demands. No preserved B2 locomotives operate today, underscoring their niche role in transitional rail history before standardized, higher-traction designs dominated.^[19]

Submarines

The designation B2 appears in historical submarine nomenclature across navies, denoting distinct classes or individual vessels optimized for patrol and reconnaissance roles amid technological constraints of their eras.^[20]^[21] In the Royal Navy, HMS B2 exemplified early 20th-century coastal defense submarines within the B class, launched on 30 October 1905 and completed on 9 December 1905 by Vickers at Barrow-in-Furness. These vessels addressed shortcomings in prior A-class designs by improving speed, endurance, and seakeeping for harbor and littoral operations. Powered by petrol engines on the surface and batteries submerged, B2 carried a crew of 16 and mounted two bow 18-inch torpedo tubes for stealthy engagements. Her operational career ended prematurely on 4 October 1912, when she was rammed and sunk by the steamer SS Amerika off Dover during exercises, resulting in 15 fatalities. The B class's petrol propulsion posed inherent risks of fire and explosion, compounded by cramped conditions and limited battery capacity that restricted submerged endurance to hours, rendering them highly vulnerable to surface threats and quickly obsolete as diesel technology advanced.^[21]^[22] The Imperial Japanese Navy's Type B2 submarines, part of the cruiser submarine lineage, represented a World War II effort to project naval power through long-range infiltration and scouting, with six I-40-class units completed between 1943 and 1944. Displacing 2,624 tons surfaced and 3,700 tons submerged, these 106.9-meter vessels featured diesel-electric propulsion delivering 11,000 shaft horsepower for 23.5 knots surfaced and 2,000 shp electric motors for 8 knots submerged, with a test dive depth of 100 meters. Armament comprised six forward 533 mm torpedo tubes (carrying 17 Type 95 torpedoes), a single 140 mm deck gun, twin 25 mm anti-aircraft mounts, and a reconnaissance seaplane (some later adapted for kaiten human torpedoes). Surfaced range reached 14,000 nautical miles at 16 knots, enabling Pacific patrols, though submerged endurance was curtailed to 96 nautical miles at 3 knots due to battery constraints. A crew of 100 operated under tactical doctrines emphasizing commerce disruption and fleet support, but inferior machinery compared to the antecedent Type B1 limited acceleration and reliability in contested waters. All six were lost by November 1944—I-40 to a U.S. submarine on 23 October 1943, I-41 to destroyer escorts on 18 November 1944, and others to aircraft or combined anti-submarine attacks—contributing to the IJN's overall submarine attrition rate exceeding 60% from depth charges, sonar advancements, and air-dropped ordnance. Maintenance in tropical humidity exacerbated battery acid corrosion and electrical failures, hastening operational degradation. By nuclear submarine standards post-1945, Type B2 designs proved tactically constrained, prioritizing surface speed over stealthy submerged persistence.^[20]

Roads

In national highway systems, B2 designations typically denote federal or trunk roads that provide secondary connectivity between urban centers, ports, and industrial areas, often featuring two-lane asphalt configurations with rural speed limits of 100 km/h for passenger vehicles.^[23] These routes play a causal role in freight logistics and regional economic integration by enabling efficient goods movement, though they experience higher congestion and maintenance challenges compared to controlled-access motorways.^[24] Germany's Bundesstraße 2 exemplifies such infrastructure, functioning as a key north-south corridor for post-war industrial revival and daily commuter flows. Recent investments, including relocations to bypass urban bottlenecks like in Fürstenfeldbruck, aim to reduce heavy truck traffic through residential zones.^[25] ^[26] In Namibia, the B2 trunk road spans approximately 395 km from Windhoek eastward to the Atlantic coast, terminating at Walvis Bay via Swakopmund, and serves as a vital artery for exporting minerals and seafood through the port.^[27] Upgrades to the coastal segment between Swakopmund and Walvis Bay, completed with N$960 million in public funding starting in 2016, enhanced capacity for trade volumes.^[28] Further rehabilitation of the Usakos-Karibib section, financed by a German government loan exceeding N$2 billion in 2022, targets improved durability and economic throughput by alleviating bottlenecks in mining logistics.^[29] These interventions underscore B2's role in fostering GDP growth through reliable inland-port links, though underfunding in non-upgraded stretches contributes to potholes and elevated accident risks relative to higher-standard highways.^[30]

Other transport

In Singapore, SMRT Buses deployed Mercedes-Benz O530 Citaro B2 low-floor single-deck city buses starting October 10, 2011, with a batch of 40 units registered between 2013 and 2015 under chassis codes SBS6342A to SBS6549X.^[31] These buses measure approximately 12 meters in length and 2.55 meters in width, accommodating up to 88 passengers including 37 seated and 51 standing, and feature three doors for efficient urban boarding.^[31] Powered by a 6,374 cc Mercedes-Benz OM 906 hLA inline-six diesel engine rated at 286 horsepower (210 kW) and 1,120 Nm torque, compliant with Euro V emission standards, they pair with a Voith DIWA 854.5 automatic transmission for smooth operation in dense traffic.^[32] In Malaysia, the B2 driver's license category authorizes operation of geared motorcycles with engine displacements up to 250 cc, targeting riders aged 16 and above who complete mandatory training including circuit and road tests.^[33] Established under the Road Transport Department (JPJ), the category requires 16 hours of practical instruction, with fees standardized at RM211 as of September 1, 2009, covering training, testing, and issuance.^[33] From October 1, 2024, holders of B2 licenses with over 10 years' experience can upgrade to B Full for unlimited capacity via a two-hour safety program, addressing progression for experienced riders while maintaining restrictions on novice access to higher-powered machines.^[34] This tiered system prioritizes safety by limiting power output for entry-level licensing, with B2 vehicles typically achieving fuel efficiencies of 30-50 km per liter in urban conditions depending on model and load.^[35]

Biology and Medicine

Vitamin B2

Vitamin B2, also known as riboflavin, is a water-soluble vitamin that serves as a precursor to the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which facilitate redox reactions in cellular metabolism.^[36] Its chemical structure consists of an isoalloxazine ring linked to a ribitol chain, with the molecular formula C17H20N4O6.^[37] These coenzymes are integral to the electron transport chain in mitochondria, where they support oxidation-reduction processes essential for ATP production and the breakdown of carbohydrates, fats, and proteins.^[38] Dietary sources of riboflavin include dairy products, meat, eggs, and leafy greens, with average daily intakes from food reaching 2.5 mg for men and 1.8 mg for women in the United States.^[39] The recommended dietary allowance (RDA) for adults is 1.3 mg per day for men and 1.1 mg per day for women, levels typically met through omnivorous diets but potentially challenged in those relying heavily on plant-based sources due to lower bioavailability of riboflavin from plants compared to animal-derived foods.^[40] ^[41] Animal products provide more readily absorbed forms, raising deficiency risks in strict vegan diets without fortification or supplementation, as evidenced by cases of severe riboflavin shortfall leading to metabolic complications.^[42] ^[43] Riboflavin deficiency, termed ariboflavinosis, manifests through cheilosis (cracks at the mouth corners), glossitis, angular stomatitis, and normocytic anemia, often alongside skin dermatitis and ocular irritation such as photophobia.^[44] These symptoms arise from impaired flavoprotein function in energy metabolism and antioxidant defenses, commonly occurring in contexts of overall B-vitamin poor intake or malabsorption rather than isolated riboflavin lack.^[45] High-dose riboflavin supplementation at 400 mg per day has demonstrated efficacy in reducing migraine frequency, duration, and severity in randomized trials involving adults, with one study reporting over 50% reduction in attack days after three months compared to placebo.^[46] ^[47] This benefit links to riboflavin's enhancement of mitochondrial energy production and neuronal redox balance, though such doses exceed RDA by orders of magnitude and yield no evidence for broader prophylactic roles beyond migraines.^[48] Excess intake poses minimal toxicity risk, as riboflavin is rapidly excreted, though it commonly causes harmless fluorescent yellow urine discoloration.^[39] Empirical data confirm no observable adverse effects from intakes many times the RDA, underscoring its safety margin in addressing deficiency or targeted therapeutic needs without unsubstantiated claims of universal metabolic enhancement.^[36]

Immunological contexts

B2 B cells, also known as conventional or follicular B cells, constitute the predominant subset of B lymphocytes, accounting for approximately 90-95% of total B cells in peripheral blood and lymphoid tissues in adults.^[49] These cells originate and mature in the bone marrow through V(D)J recombination to generate diverse B cell receptors, subsequently emigrating to secondary lymphoid organs like the spleen and lymph nodes, where they recirculate as naive cells awaiting antigen encounter.^[50] In immunological function, B2 B cells drive T cell-dependent humoral responses by capturing antigens via their B cell receptors, processing them, and presenting peptides to CD4+ T follicular helper cells, which provide cognate help to trigger proliferation, germinal center formation, somatic hypermutation, class-switch recombination, and differentiation into long-lived plasma cells and memory B cells.^[51] This yields high-affinity, isotype-switched antibodies essential for effective pathogen neutralization and immunological memory. Studies in B cell-deficient mouse models, including those with disruptions preventing mature B cell development, reveal profoundly impaired T-dependent antibody production, such as diminished IgG titers and absent germinal center reactions, underscoring B2 cells' indispensable role in adaptive immunity.^[52]^[53] Unlike B1 B cells, which arise primarily from fetal liver progenitors, self-renew in the periphery, and generate T-independent natural antibodies with innate-like properties, B2 B cells depend on T helper signals for full activation, class switching, and affinity maturation, rendering them specialized for antigen-specific adaptive responses rather than rapid, low-affinity innate defense.^[54] Recent flow cytometry analyses of vaccine-induced immunity confirm B2 B cells' dominance in generating durable responses; for example, SARS-CoV-2 mRNA vaccination elicits spike protein-specific memory B cells from the B2 lineage, persisting for at least six months and correlating with sustained neutralizing antibody efficacy against variants.^[55]^[56] While B2 B cells contribute to autoimmunity by producing high-affinity autoantibodies in dysregulated germinal centers, as seen in associations with conditions like systemic lupus erythematosus, mainstream attributions often emphasize correlations over rigorous causal demonstration, with B cell depletion therapies yielding variable outcomes that implicate additional mechanisms like antigen presentation and cytokine dysregulation.^[57]^[58]

Visas and Immigration

B-2 visa

The B-2 visa is a nonimmigrant visa issued by the United States Department of State for temporary visits primarily for tourism, pleasure, or medical treatment, including activities such as sightseeing, visiting family and friends, or participating in social events. It prohibits employment or productive work within the United States, distinguishing it from work-authorized visas, and requires applicants to demonstrate strong ties to their home country, intent to depart after the authorized stay, and sufficient funds to cover expenses without relying on U.S. employment.^[59] The initial period of stay, determined by U.S. Customs and Border Protection officers at entry, is typically up to six months, with extensions possible through U.S. Citizenship and Immigration Services via Form I-539, though such requests face heightened scrutiny to prevent abuse. Applicants must complete the online DS-160 Nonimmigrant Visa Application form, pay a $185 machine-readable visa fee (MRV fee), and attend a consular interview at a U.S. embassy or consulate, where biometrics such as fingerprints and photographs are collected to aid fraud detection.^[60]^[61] Despite technological improvements like biometric screening implemented since the early 2000s, enforcement challenges persist, including incomplete departure tracking and limited interior removal resources, which GAO reports have identified as hindering effective overstay identification and deportation.^[62]^[63] Prior to the COVID-19 pandemic, the U.S. issued approximately 8-10 million B-1/B-2 visas annually (combining business and tourist categories), with high volumes from countries like China, which accounted for over 20% of applications in peak years.^[64] In fiscal year 2023, issuances rebounded to about 5.9 million B-1/B-2 visas from 7.7 million applications processed worldwide.^[64] Overstay rates for B-1/B-2 visas average around 2% overall according to Department of Homeland Security (DHS) data, but vary significantly by nationality, reaching 10-20% or higher for certain high-risk countries such as those in parts of Africa and Asia, as detailed in annual DHS Entry/Exit Overstay Reports.^[65]^[66] These overstays contribute substantially to the unauthorized immigrant population, with DHS estimating around 500,000-700,000 suspected in-country overstays annually across nonimmigrant categories in recent fiscal years, including B-2 holders who remain beyond their admission period without departing or adjusting status.^[67] Empirical analyses, including GAO assessments, indicate that systemic overstays have fueled unauthorized labor market participation, with limited interior enforcement—due to resource constraints and prioritization of criminal removals—allowing many to evade detection and potentially sponsor further migration through family-based petitions or asylum claims post-expiry.^[63]^[68] While proponents cite tourism's economic contributions, data from DHS and GAO underscore net fiscal costs from untracked overstays, including strains on public services and wage suppression in low-skilled sectors, countering narratives that downplay long-term unauthorized presence.^[62]^[65]

Language Proficiency

CEFR B2 level

The CEFR B2 level denotes upper-intermediate proficiency, characterized by the ability to comprehend the main ideas of complex texts on concrete and abstract topics, including technical discussions within one's specialization. Users at this level interact with a degree of fluency and spontaneity that facilitates regular exchanges with native speakers without mutual strain, produce clear and detailed writing on diverse subjects, and explain viewpoints on topical issues by weighing advantages and disadvantages of options.^[69]^[70] Specific skills at B2 include listening to and participating in spontaneous debates on current affairs, reading detailed articles and reports to grasp implicit attitudes or viewpoints, and writing structured essays that present arguments coherently without excessive phrase-searching. This proficiency aligns empirically with IELTS overall bands of 5.5 to 6.5 and TOEFL iBT total scores of 72 to 94, based on score concordance studies mapping performance across frameworks.^[71]^[72] B2 certification is commonly mandated for undergraduate university admissions in the UK and many EU institutions, where it satisfies minimum English language requirements for degree-level study, as well as for professional roles in multinational firms requiring effective cross-cultural communication. Empirical data from labor market analyses in the 2020s link B2-equivalent second-language skills to wage premiums of 5-20% for multilingual workers in globalized sectors, attributable to expanded job access and productivity gains from reduced communication barriers.^[73]^[74]^[75] Assessments of B2 proficiency encounter challenges from inherent subjectivity, especially in self-evaluations versus calibrated standardized tests, with critics noting the framework's relative rigidity and limited sensitivity to contextual nuances or individual variation in aptitude. Over-dependence on B2 thresholds in policy can undervalue domain-specific competencies. Nonetheless, inter-rater reliability in rubric-guided evaluations often exceeds 80% consistency across studies employing multiple trained assessors, underscoring the value of empirical validation over anecdotal judgments.^[76]^[77]

Fictional and Cultural Uses

Star Wars characters

The B2-series super battle droid served as a heavy infantry unit for the Confederacy of Independent Systems during the Clone Wars, representing an evolution from the lighter B1 battle droid with enhanced combat capabilities. Manufactured by Baktoid Combat Automata, these droids featured integrated forearm-mounted blaster cannons, eliminating the need for separate weaponry, and possessed bulkier frames for superior strength and resilience in direct engagements. Unlike B1 models reliant on central command signals, B2 units operated with limited autonomy, enabling fearless and persistent assaults without fatigue.^[78] Measuring approximately 1.91 to 1.93 meters in height, the B2 droids deployed thick armor plating that resisted standard blaster fire, as evidenced by their performance in early conflicts. They first saw action in the First Battle of Geonosis in 22 BBY, where Separatist leaders observed their effectiveness against clone troopers and advocated for mass production to bolster droid armies. Command variants coordinated tactical maneuvers, while specialized models like the B2-RP incorporated repulsorlift jetpacks for aerial mobility and marked wrist blasters.^[78]^[79]^[80] In Star Wars media, B2 super battle droids appeared in Attack of the Clones (2002) during the Geonosis arena sequence, Revenge of the Sith (2005) aboard Separatist vessels, and the Clone Wars animated microseries (2003–2005), underscoring their role in Separatist offensives. Later depictions in the Star Wars: The Clone Wars series (2008–2020) portrayed them in diverse battles, highlighting upgrades like wrist rockets for anti-infantry suppression. Narrative analyses note their design efficiency in droid swarm tactics but point to exploitable weaknesses, such as joint articulations vulnerable to precision strikes or lightsaber severance, which often determined outcomes in fictional scenarios despite armored durability.^[78]^[81]

Card games

Big Two, also known as B2, Choh Dai Di, or Dai Di, is a shedding-type card game of Chinese origin that emerged in coastal regions around 1980.^[82]^[83] The game involves 2 to 4 players and uses a standard 52-card deck, though multiple decks may be employed for larger groups to increase hand sizes up to 13 cards per player.^[82] The primary objective is to be the first to discard all cards from one's hand by playing valid combinations that outrank the previous play in either card value or type.^[84] Gameplay proceeds clockwise, beginning with the player holding the 3 of diamonds, which must be led first as the lowest card.^[82] Cards rank from 3 (lowest) ascending to ace, with 2s as the highest; suits follow the order diamonds (lowest), clubs, hearts, and spades (highest), determining ties within the same rank.^[82] Valid plays include singles, pairs of equal rank, three-of-a-kind, straights of five or more consecutive cards (ignoring suits, with 2s breaking sequences only as high cards), full houses (three-of-a-kind plus a pair), four-of-a-kind, flushes (five cards of the same suit), straight flushes, and five-of-a-kind (rare without jokers).^[82] Each subsequent player must beat the prior combination with an equal or superior type using the same number of cards (e.g., a higher pair against a pair); failure to do so requires passing, and if all pass, the last successful player leads anew.^[82] The first player to empty their hand wins the round, often with scoring based on remaining cards in opponents' hands (e.g., face cards worth 10 points, aces 11, others by pip value).^[85] Strategic play emphasizes controlling the lead and forcing passes to disrupt opponents, with empirical patterns from competitive variants showing that retaining low cards (3s through 7s) early allows players to bait high-card expenditure from rivals while preserving 2s and suited combinations for late-game dominance.^[85] Effective blocking involves passing strategically to regain the lead with unbeatable hands like spade 2s or straight flushes, minimizing personal losses in poor draws by shedding bulk low-value cards quickly.^[86] Variants such as Vietnamese Tiến Lên introduce scoring multipliers for consecutive wins or penalties for holding 2s at round's end, altering risk assessment in multi-round sessions.^[87] The game enjoys widespread popularity across East and Southeast Asia, including Hong Kong, Taiwan, Vietnam, the Philippines (as Pusoy Dos), Indonesia, and Singapore, where it features prominently in casual gatherings and during festivals like Chinese New Year.^[82]^[88] Casino adaptations exist in Macau and online platforms, emphasizing its adaptability for both social and wagering contexts without inherent promotion of gambling.^[85]

Other Uses

Computing terms

In computing security, B2 denotes the second-highest mandatory protection division in the Trusted Computer System Evaluation Criteria (TCSEC), a U.S. Department of Defense standard formalized in 1985 for evaluating systems handling classified information. This class required structured design documentation, formal verification of trusted computing base (TCB) components, mandatory access controls with security labels on all objects, and analysis limiting covert storage and timing channels to less than 1 bit per second in aggregate. Systems achieving B2 certification, such as Multics in 1985, demonstrated non-discretionary access controls extending to user interfaces and utilities, audited changes to security levels, and trusted path mechanisms isolating sensitive operations.^[89] Historically, B2 evaluations emerged in the early 1980s amid Cold War-era needs for multilevel secure systems, building on earlier discretionary classes (C1-C2) by enforcing a reference monitor model—tamper-proof, always-invoked, and verifiable—across the TCB. Examples included embedded military applications and mainframes like the Honeywell SCOMP, but certifications were rare; by the mid-1990s, fewer than 20 commercial or government systems reached B2 or higher due to rigorous testing mandates, including design specification reviews and penetration attempts by independent teams.^[90] The standard influenced protocols in classified networks but faced criticism for its U.S.-centric focus, excluding international interoperability and underemphasizing usability, leading to high development costs—often millions per system—without proportional scalability for commercial use.^[91] Adoption waned as TCSEC proved inefficient against evolving threats like networked attacks; empirical assessments showed evaluation timelines exceeding 2-3 years per product, with compliance overhead inflating costs by factors of 5-10 compared to baseline secure development.^[92] By 1999, the NSA transitioned to the multinational Common Criteria (ISO/IEC 15408), which offered graded assurance levels (EAL1-EAL7) but relaxed some B2 rigor, such as aggregate covert channel bounds, prioritizing flexibility over exhaustive verification. B2's stringent metrics, while effective for isolated environments—evidenced by zero known exploits in certified TCBs under lab conditions—yielded diminishing returns in distributed systems, where benchmarks indicated 20-50% higher resource demands for equivalent protection under modern frameworks like SELinux or AppArmor.^[93] Today, B2 holds archival relevance in legacy DoD procurements and historical analyses of assurance, with no active certifications since the early 2000s; its principles persist indirectly in high-assurance subsets of Common Criteria EAL4+ evaluations, though without the original's mandatory covert channel quantification.^[94] Niche references appear in graph theory algorithms, such as approximations for packing "big two-bar charts" (2-BCs) in bin-packing variants, but these remain theoretical without widespread implementation.^[95] Overall, B2 exemplifies early formal methods' trade-offs, underscoring causal limits of static verification in dynamic computing paradigms.

Recent technological developments

In 2025, Unitree Robotics unveiled a fire rescue variant of its B2 industrial quadruped robot, designed for hazardous firefighting operations in environments unsafe for human teams.^[96] The B2 model features enhanced mobility, high-temperature resistance up to 100°C ambient conditions, and AI-driven sensors for autonomous navigation and obstacle avoidance, enabling it to carry payloads like hoses or cameras into burning structures.^[97] Priced at approximately $100,000 per unit, the robot supports rapid deployment for perimeter security and initial suppression tasks, though field trials have highlighted limitations such as battery endurance of under 2 hours during intensive operations.^[98] Ongoing research into B2-structured iron aluminides (FeAl alloys) has advanced their use in high-temperature structural components, building on post-2020 refinements in composition and processing to mitigate brittleness. These intermetallic materials exhibit ordered B2 crystal structures that confer oxidation resistance and mechanical stability at temperatures exceeding 1000°C, making them candidates for turbine blades and exhaust systems in aerospace and power generation.^[99] Recent alloy designs incorporate microalloying elements to enhance ductility and reduce vacancy-related defects, with tensile elongations improved to 5-10% at elevated temperatures through controlled heat treatments.^[100] However, environmental embrittlement—caused by hydrogen ingress from moisture interaction—remains a key failure mode, leading to intergranular fracture under dynamic loads, as evidenced by fracture mechanics studies.^[101] Despite these prototypes, B2-based innovations represent incremental progress rather than transformative shifts, constrained by scalability challenges including high production costs (e.g., specialized casting for aluminides) and reliability gaps in real-world variability. Empirical data from simulations and lab tests underscore practical gains in safety and efficiency, such as reduced human exposure in fire scenarios, but widespread adoption awaits cost reductions below $50,000 for robotics and embrittlement-resistant variants for materials.^[102]^[103]

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Sep 22, 2025 · With a unit cost exceeding $2 billion when adjusted for inflation, the B-2 represents a significant financial burden. Retiring it could free up ...Missing: per criticisms
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Did you know the B-52H cost per flying ... - The Aviation Geek Club
In 2016 they were quoted as $69,708 per flying hour, compared with $169,313 for the B-2A Spirit. However, the overall mission-capable rate for all three bomber ...
[15]
[PDF] NSIAD-93-209 B-2 Bomber: Comparison of Operational Capabilities ...
Aug 20, 1993 · B-2 operations and maintenance cost estimates have grown significantly from prior estimates and costs per unit will be high compared to B-1B ...
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Classification of Diesel Locomotives - Discover Live Steam Magazine
Mar 25, 2012 · "The AAR system counts axles instead of wheels. Letters refer to powered axles, and numbers to unpowered (or idler) axles. "A" refers to one ...
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Jan 5, 2023 · The first purpose built tank engines for that company appeared on the GW in 1849 - but they were for working passenger trains, not specifically ...Missing: B2 | Show results with:B2
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https://www.steamlocomotive.com/locobase.php?country=Great_Britain
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Tank locomotive types - a beginners guide - YouTube
Jan 18, 2021 · From saddletank to side tank, join us to learn the basics behind each type of tank engine style, their differences, and the reason they were ...Missing: B2 shunting history<|control11|><|separator|>
[20]
B2 Class, Japanese Submarines
The B2s were virtually identical with the B1s except for less powerful machinery. An additional eight units were projected but not authorized.
[21]
B 2 (I 22) - RN Subs
Home → Boats → Submarines → B Class → B2. B 2 (I 22). Built By: Vickers (Barrow). Build Group: B. Fate: Rammed and sunk by SS Amerika off Dover 4th October ...
[22]
ww1 british submarines - Naval Encyclopedia
Despite their limitations like petrol engines, limited armament and cramped interiors, the Type C saw active service throughout the war.
[23]
https://www.easycar.com/car-rental-guides/germany
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Speed limits in Germany – your complete travel guide - Drive - RAC
Feb 20, 2025 · The speed limit in towns and cities is 50 km/h (~31 mph) – unless otherwise stated – and 100 km/h (~62 mph) on non-urban/open roads that are not the motorway/ ...
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Fürstenfeldbruck: Bundesstraße 2 wird verlegt
May 30, 2025 · Fürstenfeldbruck hat die Verlegung der Bundesstraße 2 beschlossen, die Innenstadt soll vom Schwerverkehr entlastet werden.
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Fürstenfeldbrucker Stadtrat entscheidet: B2-Verlegung beschlossen
May 30, 2025 · Der Stadtrat Fürstenfeldbruck hat die Verlegung der Bundesstraße B2 beschlossen. Die jetzige Schwerlast-Trasse wird zur Staatsstraße.
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Distance from Walvis Bay to Windhoek
Distance between Walvis Bay and Windhoek is 268 kilometers (167 miles). Driving distance from Walvis Bay to Windhoek is 395 kilometers (246 miles).
[28]
N$960m coastal road upgrades begin - The Namibian -
Jul 4, 2016 · The ground-breaking ceremony of the N$960 million project fully funded by the taxpayer, took place near Swakopmund last Thursday, and was ...
[29]
German government loans over N$2 billion to Namibia Business ...
Dec 14, 2022 · This loan will be funding the rehabilitation and upgrading of the B2 Road section between Usakos and Karibib. The loan agreements were signed on ...Missing: impact | Show results with:impact
[30]
German investment fuels Namibian road network expansion Maria ...
Aug 11, 2025 · This can lead to increased economic activity, job creation, and higher incomes for local residents.Missing: B2 | Show results with:B2
[31]
Mercedes-Benz Citaro - Singapore - Land Transport Guru
Jan 1, 2018 · The Mercedes-Benz O530 Citaro (or simply Citaro) is a low-floor, wheelchair-accessible, single-deck city bus built by Mercedes-Benz and EvoBus GmbH.
[32]
Mercedes-Benz O530 Citaro (Batch 2) - Singapore - SgWiki
SMRT Buses. Registration no. Deployment. SBS6646Z, SLDEP SP. SBS6691S, SLDEP 242 ... Former Deployments of Mercedes-Benz O530 Citaro (Batch 2). Non-revenue buses.
[33]
Determination of Fee Rates for Class B2 Driver's Licenses, FI ... - JPJ
The training fee, test designation card and driving license for class B2 motorcycles has been reduced to RM211 with effect from 1 September 2009.
[34]
Malaysian B2 m'cycle licence conversion starts today - paultan.org
Oct 1, 2024 · Those wanting to convert their Malaysian B1 and B2 motorcycle licence to the B Full (unlimited engine capacity) class can do so from today, October 1.
[35]
B2 VS B - - Metro Driving Academy
B2 is for bikes under 250cc, B for all. B has unlimited CC, B2 only gear. B uses clutch/gear, B2 only gear. B is bigger/heavier.<|separator|>
[36]
Riboflavin | Linus Pauling Institute | Oregon State University
Riboflavin is a water-soluble B vitamin, precursor to FAD and FMN, which act as electron carriers in energy production and metabolic pathways.
[37]
Riboflavin | C17H20N4O6 | CID 493570 - PubChem - NIH
Riboflavin (vitamin B2) functions as a coenzyme for numerous oxidation-reduction reactions in several metabolic pathways and in energy production. The rate of ...
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Vitamin B2 (Riboflavin) - StatPearls - NCBI Bookshelf - NIH
Feb 1, 2024 · Riboflavin, or vitamin B2, is a water-soluble vitamin in the B complex, often prescribed to treat deficiency, and is an antioxidant.
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Riboflavin - Health Professional Fact Sheet
May 11, 2022 · Riboflavin (also known as vitamin B2) is one of the B vitamins, which are all water soluble. Riboflavin is naturally present in some foods, added to some food ...
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Riboflavin - Dietary Reference Intakes for Thiamin ... - NCBI - NIH
The RDA for riboflavin for adults is 1.3 mg/day for men and 1.1 mg/day for women. Recently, the median intake of riboflavin from food in the United States and ...
[41]
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Jul 31, 2023 · The overview of studies showed that in general, vitamins in foods originating from animals are more bioavailable than vitamins in foods sourced from plants.
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Riboflavin: a scoping review for Nordic Nutrition Recommendations ...
Dec 22, 2023 · The main dietary sources of riboflavin are animal-derived foods, suggesting that riboflavin sufficiency may be a concern among those excluding ...Missing: daily | Show results with:daily
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Life-Threatening Neonatal Complications of a Strict Vegan Diet ...
Sep 19, 2022 · We report a case of a male neonate with a life-threatening hypoglycaemia and lactic acidosis due to severe riboflavin deficiency.
[44]
Riboflavin Deficiency - StatPearls - NCBI Bookshelf
Riboflavin deficiency can cause fatigue, swollen throat, blurred vision, and depression. It can affect the skin by causing skin cracks, itching, and dermatitis ...
[45]
Riboflavin Deficiency - Medscape Reference
Aug 13, 2025 · Clinical Features of Deficiency (Ariboflavinosis) · Red, itchy eyes · Night blindness · Cataracts · Migraines · Peripheral neuropathy · Anemia ( ...
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Effect of Vitamin B2 supplementation on migraine prophylaxis
Mar 29, 2021 · Vitamin B2 400 mg/day for three months supplementation had significant effect on days, duration, frequency, and pain score of migraine attacks.
[47]
Effectiveness of high‐dose riboflavin in migraine prophylaxis A ...
We now compared riboflavin (400 mg) and placebo in 55 patients with migraine in a randomized trial of 3 months duration. Using an intention-to-treat analysis, ...
[48]
Riboflavin metabolism: role in mitochondrial function
Riboflavin is a key component of the mitochondrial respiratory chain (RC), hence is pivotal for ATP generation and sustaining energy-dependent cellular ...
[49]
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Jun 27, 2013 · A recent study concluded that human B1 cells can be identified and resolved from other human B-cell subsets by a distinct surface phenotype.
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Aug 2, 2024 · B-2 cells are the predominant subtype of B cells in adults and can be easily found in secondary lymphoid organs where they form germinal centers ...
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T cell dependent activation of B cells supports the generation of memory B cells and long-lived plasma cells secreting high affinity antibodies. This ...
[52]
Markedly impaired humoral immune response in mice deficient in ...
Nevertheless, B-cell responses to low and high doses of a T-cell-dependent antigen are impaired with decreased titers of antigen-specific IgM and IgG isotypes.
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Apr 16, 1996 · We explored the role of these receptors in the development of humoral immunity by generating CR1- and CR2-deficient mice using gene-targeting techniques.
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Evidence of SARS-CoV-2-Specific Memory B Cells Six Months After ...
These data demonstrate that mRNA BNT162b2 vaccine elicits strong B cell immunity with spike-specific memory B cells that still persist 6 months after ...
[56]
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The secondary immune response to the mRNA SARS-CoV-2 vaccine generates specific memory B cells (MBCs) and plasma cells (PCs) that are based on the proper ...
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B cells in autoimmunity - PMC - PubMed Central
B2 cells participate preferentially in T cell-dependent GC reactions, during which they can hypermutate their IgV gene rearrangements, switch Ig classes, and ...Missing: causal | Show results with:causal
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B Cells and Humoral Immunity in Atherosclerosis
May 23, 2014 · In this review, we will focus on recent insights on the role of B cells and various immunoglobulin classes and how these may mediate their effects in ...
[59]
9 FAM 402.2 [REDACTED] TOURISTS AND BUSINESS VISITORS ...
B visas are for temporary US entry for business (B-1), pleasure (B-2), or both (B-1/B-2). B-2 is for tourism, family visits, or medical reasons.
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DS-160: Online Nonimmigrant Visa Application - Travel.gov
Pay the visa application processing fee. Review country-specific instructions on the U.S. Embassy or Consulate website. More Information. A-Z Index · Latest ...
[61]
Fees for Visa Services - Travel.gov
Application for Waiver of two-year residency requirement, J Waiver, Form DS-3035. $120.00 ; Application for Waiver of visa ineligibility, Form I-601 (Collected ...Fees For Visa Services · Border Crossing Card Fees · Other Fees
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GAO-04-82, Overstay Tracking: A Key Component of Homeland ...
This is the accessible text file for GAO report number GAO-04-82 entitled 'Overstay Tracking: A Key Component of Homeland Security and a Layered Defense' ...
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Overstay Enforcement: Additional Mechanisms for Collecting ... - GAO
Apr 15, 2011 · GAO recommends, among other things, that DHS establish a time frame for completing overstay enforcement planning, performance measurement ...
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Oct 1, 2025 · In FY 2023, U.S. consulates processed a total of 7,745,109 B1/B2 visa applications worldwide. Out of these: 5,902,426 visas were issued.
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Entry/Exit Overstay Reports - Homeland Security
Sep 4, 2025 · DHS has generated this report to provide data on departures and overstays, by country, for foreign visitors to the United States who were expected to depart in ...
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[PDF] CBP Entry Exit Overstay Report FY 2024 - Homeland Security
Jul 16, 2025 · For Visa Waiver Program countries, the Fiscal Year 2024, Suspected In-Country Overstay rate is 0.43 percent of the 18,853,231 expected ...
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DHS Reports Approximately 500,000 Nonimmigrants Overstayed ...
Sep 28, 2025 · “This report presents the overstay rates of those who remained in the United States beyond their authorized period of admission with no ...
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Nonimmigrant Overstays: Overview and Policy Issues - Congress.gov
Nov 21, 2023 · An estimated 42% of the approximately 11 million unauthorized population living in the United States entered the country legally but overstayed ...Historical Overstay Estimates · Recent Overstay Trends · Overstay Enforcement
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Common European Framework of Reference for Languages (CEFR)
The descriptors specify progressive mastery of each skill, which is graded on a six-level scale (A1, A2, B1, B2, C1, C2). However, for textbook authors, ...Descriptors · Global scale · The framework · CEFR Companion Volume...
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B2 Upper intermediate | LearnEnglish - British Council Learn English
Learners who achieve B2 Upper intermediate level can understand the main ideas of complex texts. They can interact with some fluency and communicate easily.
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English levels and English proficiency scores - EF SET
Converting from one English level to another ; B2 Upper Intermediate, 51 - 60, 72 - 94, 5.5 - 6.5, 785 - 940 ; C1 Advanced, 61 - 70, 95 - 120, 7.0 - 8.0, 945 - ...Intermediate English · Advanced English · Practicing basic English skills
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CEFR vs IELTS vs TOEFL: What's the Difference? - EduSynch
Aug 17, 2025 · CEFR to IELTS and TOEFL Score Conversion ; C1, 7.0 – 8.0, 95 – 114 ; B2, 5.5 – 6.5, 72 – 94 ; B1, 4.0 – 5.0, 42 – 71 ; A2, 3.0 – 3.5, 31 – 41.
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Student visa : Knowledge of English - GOV.UK
You must prove you can read, write, speak and understand English to a certain level on the Common European Framework of Reference for Languages ( CEFR ) scale.
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Why It Pays to Be Bilingual - LTI Blog - Language Testing International
Aug 16, 2022 · Research shows that those who are bilingual or multilingual can earn 5%-20% more per hour than those who aren't.
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[PDF] Language Skills as Economic Assets: Insights from the Russian Job ...
Aug 13, 2025 · Empirical studies demonstrate that foreign language proficiency correlates with wage premiums of. 5–20%, with variation depending on both the ...
[76]
Limitations of the Common European Framework for developing ...
Aug 7, 2025 · Critics have pointed out the insufficient nuance and rigidity of the CEFR levels, which are not in principle sensitive to context of use or ...
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[PDF] Examining Rater Reliability When Using an Analytical Rubric ... - ERIC
This study examines rater reliability using an analytical rubric, finding that more raters and detailed rubrics improve reliability, and that inter-rater ...
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Super Battle Droid | Star Wars Databank | StarWars.com
Super Battle Droids are bulkier, stronger, and more advanced droids designed for combat, operating independently, and are fearless and tireless. They are not ...
[79]
B2-RP battle droid - StarWars.com
B2-RPs are modified B2 super battle droids with rocket pack and repulsorlift tech, blue and white markings, and a built-in wrist blaster. They are 1.91m tall.
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https://www.battledroids.miraheze.org/wiki/B2-series_super_battle_droid
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The B2 Super Battle Droid: The Heavy Hitter and Clone Nemesis
Jun 25, 2021 · The standard model B2 gave a decent account at the First Battle of Geonosis, but even that early in the conflict there was a variant in action.
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Big Two - card game rules - Pagat.com
Feb 18, 2022 · The object of the game is to be the first to get rid of all of your cards, by playing them to the table. Cards can be played singly or in certain combinations.Introduction · Playable Combinations · The Play · Variations
[83]
About BIG TWO
Big Two is considered one of the many Climbing card games. It was thought to have originated in coastal China around 1980.
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https://www.denexa.com/blog/big-two/
[85]
Big 2 Card Game: A Beginner's Guide | Casino.org
Aug 6, 2024 · Learn how to play the Big 2 card game in this detailed guide. Explore Big 2 card game rules, how to achieve victory, strategies, and more!
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Big Two aka Deuces, Thirteen - Discuss Draw and Other Poker Games
Apr 14, 2010 · There is a lot of strategy to it. For instance when you have a bad hand you want to go down with as much cards as possible to minimise losses, ...
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Big 2 Variations - EvenBet Gaming
Feb 21, 2025 · It is known as Capsa, Pusoy Dos, Dai Di, and Deuces depending on the region. Let's take a closer look at the most commonly recognised variations ...Missing: strategy | Show results with:strategy
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Step-by-step guide on how to play Dai Di (Big Two) - Time Out
Jan 29, 2025 · Also known as Big Two or Tai Ti, this beloved card game is a hot favourite among Singaporeans especially during Chinese New Year, where post- ...
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B2 Security Evaluation - Multics
This article describes the Multics security evaluation that led to the B2 rating in the mid 1980s, starting with the needs and context.
[90]
[PDF] Trusted Computer System Evaluation Criteria(TCSEC)
The TCSEC defines 6 evaluation classes identified by the rating scale from lowest to highest: D, C1, C2, B1,. B2, B3, and A1. An evaluated computer product ...
[91]
A Guide to Understanding Trusted Facility Management
PURPOSE An important assurance requirement of the TCSEC, which appears in all classes from B2 to A1, is trusted facility management. This refers to the ...
[92]
Evaluation Criteria of Systems Security Controls - Dummies
Aug 1, 2018 · These criteria include the Trusted Computer System Evaluation Criteria (TCSEC), Trusted Network Interpretation (TNI), European Information Technology Security ...
[93]
TCSEC- Trusted Computer System Evaluation Criteria - Quizlet
B2 - Structured Protection. Security policy model clearly defined and formally documented. DAC and MAC enforcement extended to all subjects and objects. Covert ...<|separator|>
[94]
Evaluation Criteria Mindmap: CISSP Domain 3 | DestCert
B2 means products provide security labels and verification of no covert channels. ... And ITSEC uses exactly the same functional levels as TCSEC that we just went ...
[95]
[PDF] A 4/3OPT+2/3 approximation for big two-bar charts packing problem
Dec 5, 2022 · The problem 2-BCPP> is to pack the big 2-BCs into the minimal number of bins. 2. NP-hardness of 2-BCPP>. In this section, we show that 2-BCPP> ...
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EP.63 ROBOT DOGS BECAME FIREFIGHTERS - by Lukas Ziegler
May 21, 2025 · Unitree has unveiled a fire rescue version of its B2 quadruped robot, designed to tackle dangerous environments and assist in firefighting operations.
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Unitree B2 Robot: Revolutionizing Firefighting with Agility and ...
The Unitree B2 quadruped robot, with its agile mobility, high-temperature resistance, and heavy-load capacity, serves as a "super assistant" to firefighters, ...
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Unitree B2-W Quadruped Robot - Humanoid Robots
Unitree B2 Quadruped Robot w/ Free Worldwide Delivery. US$100,000.00. Add to ... Firefighting Robots · Logistics Robots · Sports Robots · Boxing Robots ...
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Iron Aluminides - Annual Reviews
Jul 1, 2019 · 35. Liu CT, George EP, Maziasz PJ, Schneibel JH 1998. Recent advances in B2 iron aluminide alloys: deformation, fracture and alloy design.Iron Aluminides · Most Cited · Related Articles From Annual...
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Recent advances in B2 iron aluminide alloys: deformation, fracture ...
Recent advances include understanding moisture-induced embrittlement, grain-boundary weakness, and vacancies, leading to improved FeAl alloys with better ...
[101]
Recent advances in B2 iron aluminide alloys: Deformation, fracture ...
This paper reviews the deformation, fracture and alloy design of B2 iron aluminides based on FeAl. Moisture-induced environmental embrittlement is shown to ...
[102]
A Review of Recent Developments in Iron Aluminides - ResearchGate
Aug 6, 2025 · The results have shown improved aqueous corrosion resistance of B2 iron aluminide after introduction of alloying elements. Based on the ...
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Insights into Dynamic Hardness of B2 Iron Aluminide using Ultra ...
This project aims to investigate the dynamic hardness of B2-iron aluminides at high strain rates using an in situ nanomechanical tester capable of ...