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C4

C-4, also known as Composition C-4, is a plastic explosive consisting primarily of 91% RDX (cyclotrimethylenetrinitramine), combined with plasticizers, polyisobutylene binder, and mineral oil to form a stable, moldable white putty-like substance.^[1]^[2] This formulation renders C-4 highly resistant to accidental detonation from shock, friction, or fire, requiring a primary explosive detonator such as a blasting cap for initiation, which distinguishes it from more sensitive high explosives.^[3] Developed for military applications, it is widely utilized by armed forces for controlled demolitions, breaching structures, and disposing of unexploded ordnance due to its versatility, water resistance, and ability to be shaped around targets.^[4] The explosive's reliability stems from RDX's high detonation velocity of approximately 8,040 m/s, enabling efficient energy release in confined charges, while its plastic matrix prevents premature decomposition under extreme conditions.^[5] In military contexts, C-4 is packaged in 1.25-pound blocks (M112 demolition charges) and consumed at significant rates across U.S. Department of Defense services for engineering tasks. However, its stability and ease of concealment have led to non-state actors, including militant groups, employing it in improvised explosive devices, contributing to its notoriety in asymmetric warfare despite production controls aimed at authorized users.^[4] Ingestion of C-4, though rare, poses acute toxic risks from RDX absorption, manifesting as seizures, nausea, hematuria, and neurological effects treatable with supportive care like benzodiazepines and hemodialysis.^[6]^[3]

Biology

C4 Carbon Fixation

C4 carbon fixation is a photosynthetic pathway employed by certain plants to initially incorporate atmospheric carbon dioxide (CO₂) into a four-carbon organic acid, enabling efficient CO₂ concentration around the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in bundle sheath cells. This process occurs through the action of phosphoenolpyruvate carboxylase (PEPC) in mesophyll cells, where phosphoenolpyruvate (PEP) reacts with bicarbonate (HCO₃⁻, derived from CO₂) to form oxaloacetate, which is subsequently reduced to malate or transaminated to aspartate.^[7]^[8] These four-carbon compounds are transported to bundle sheath cells, where decarboxylation releases CO₂ for fixation by Rubisco in the Calvin-Benson cycle, minimizing oxygenase activity due to elevated local CO₂ levels.^[9] The pathway's spatial separation—Kranz anatomy, featuring mesophyll cells surrounding CO₂-impermeable bundle sheath cells—facilitates this CO₂ pump, requiring an additional ATP per CO₂ fixed compared to the standard cycle but yielding net gains under stress.^[10] The primary empirical advantage of C4 fixation lies in near-elimination of photorespiration, where Rubisco's oxygenase reaction wastes fixed carbon and energy; under high temperatures (above 30°C) and low CO₂, photorespiratory losses can exceed 50% in non-C4 plants, but C4 anatomy reduces this to negligible levels by maintaining CO₂:O₂ ratios above 100:1 at Rubisco sites.^[9] This enhances photosynthetic efficiency, with C4 species exhibiting 50-100% higher net CO₂ assimilation rates in tropical conditions, as measured in crops like maize (Zea mays) and sorghum (Sorghum bicolor), which achieve quantum yields up to 0.08 mol CO₂ per mol photons versus 0.05 in C3 counterparts.^[11] Water-use efficiency is also improved, with stomatal conductance reduced by 30-50% due to the CO₂-concentrating mechanism, allowing C4 plants to transpire 2-3 times less water per unit carbon fixed while sustaining productivity in arid environments.^[12] Physiological data from field trials confirm these benefits, showing maize yields averaging 10-15 tons per hectare in subtropical regions, outperforming C3 cereals under drought stress.^[13] C4 photosynthesis evolved independently over 60 times, first emerging approximately 30 million years ago during a period of declining atmospheric CO₂ (from 400 to 300 ppm) and increasing aridity in the late Oligocene, conferring selective advantages in open habitats.^[14] It occurs in roughly 3% of vascular plant species (about 7,500 taxa) but accounts for 23-30% of global terrestrial primary productivity, dominating productive grasslands and savannas through higher biomass accumulation.^[15]^[14] Major C4 crops include sugarcane (Saccharum officinarum), maize, sorghum, pearl millet (Pennisetum glaucum), and foxtail millet (Setaria italica), which collectively supply over 20% of human caloric intake via enhanced yields in warm climates.^[16] Three main biochemical subtypes exist based on decarboxylation mechanisms in bundle sheath cells: NADP-malic enzyme (NADP-ME), predominant in tropical grasses like maize and sugarcane, where malate is decarboxylated in chloroplasts; NAD-malic enzyme (NAD-ME), common in dicots and millets, involving mitochondrial decarboxylation of aspartate-derived malate; and phosphoenolpyruvate carboxykinase (PEPCK), often in panicoid grasses, decarboxylating oxaloacetate directly with higher energy efficiency in shaded conditions.^[16]^[17] Many species, such as sugarcane, hybridize NADP-ME and PEPCK pathways for metabolic flexibility.^[18] Ongoing research focuses on engineering C4 traits into C3 staple crops like rice (Oryza sativa) to boost yields amid climate pressures, with models predicting 20-50% increases in photosynthetic efficiency and grain output under elevated temperatures and low water availability.^[19] The C4 Rice Consortium has introduced key enzymes (e.g., PEPC, NADP-ME) via transgenics, achieving preliminary bundle sheath enlargement and CO₂ pump activity in greenhouse trials, though full pathway integration remains challenged by regulatory gene coordination.^[20] Field validations as of 2023 indicate potential nitrogen-use efficiency gains of 30-40%, supporting scalability for global food security.^[21]

Anatomy

Fourth Cervical Vertebra (C4)

The fourth cervical vertebra (C4) is a typical member of the subaxial cervical spine, characterized by a small, rectangular vertebral body and a bifid spinous process that bifurcates distally to facilitate ligamentous attachments. Its transverse processes feature prominent transverse foramina, which transmit the vertebral artery and its accompanying venous plexus, contributing to cerebral blood supply. Superior articular facets, oriented at approximately 45 degrees, articulate with the inferior facets of C3, enabling flexion, extension, and lateral bending while limiting excessive rotation. The C4 dermatome corresponds to sensory innervation over the lower neck, upper shoulders, and acromioclavicular region.^[22]^[23]^[24] Functionally, C4 contributes to neck mobility and supports the phrenic nerve's primary innervation of the diaphragm, arising from anterior rami of C3, C4, and C5 spinal nerves, which is essential for respiratory drive—"C3, 4, 5 keeps the diaphragm alive." The spinal cord segment at C4 relays motor and sensory pathways for upper limb and trunk functions, with exiting nerve roots supplying trapezius and levator scapulae muscles via the accessory nerve contributions.^[25]^[26] Injuries to C4, often from high-impact trauma such as motor vehicle accidents or falls, frequently result in spinal cord compression leading to tetraplegia, with preserved diaphragmatic function in partial lesions due to phrenic nerve redundancy, though full transections above C4 typically necessitate ventilatory support. Empirical data from trauma cohorts indicate C4 fractures comprise approximately 9.5% of cervical vertebral injuries, with spinal cord injury occurring in up to 57% of C4-level traumas, outcomes influenced by factors like bone mineral density and impact velocity.^[27]^[28]^[29] Diagnosis relies on computed tomography (CT) for bony alignment and fracture detection, supplemented by magnetic resonance imaging (MRI) to assess cord edema or ligamentous integrity. Surgical interventions for instability include anterior cervical discectomy and fusion (ACDF) or posterior lateral mass screw fixation, with fusion rates exceeding 90% in instrumented cases; rehabilitation outcomes vary, with trauma-related injuries showing lower functional recovery (e.g., 20-40% ambulatory potential) compared to degenerative causes due to irreversible neural damage.^[30]^[31]

Chemistry and Explosives

Composition C-4

Composition C-4 is a plastic explosive consisting primarily of 91% cyclotrimethylenetrinitramine (RDX), with the remainder comprising 5.3% dioctyl sebacate (a plasticizer), 2.1% polyisobutylene (a binder), and 1.6% process oil.^[32]^[3] This formulation renders it moldable at room temperature while maintaining high energetic output upon detonation.^[32] The material evolved from World War II-era RDX-based compounds known as Composition C, which were initially developed for demolition purposes using simpler plasticizers.^[33] U.S. military standardization of Composition C-4 occurred in the 1950s, supplanting predecessors like C-1, C-2, and C-3 due to enhanced moldability, reduced sensitivity, and improved handling safety.^[34] It adheres to military specifications for consistency in production, such as those outlined in Department of Defense performance requirements for plastic explosives.^[34] Key physical properties include a detonation velocity of approximately 8,040 m/s at a density of 1.59 g/cm³, enabling efficient energy release for demolitions.^[35] C-4 exhibits high stability, requiring a No. 8 blasting cap or equivalent shock initiator for detonation and resisting accidental initiation from impact, friction, or small-arms fire in military drop and bullet impact tests.^[34] Thermally, it remains stable up to 227°C without decomposition, though prolonged exposure beyond this threshold leads to breakdown.^[36] Its low vapor pressure minimizes detectable emissions, contributing to operational discretion, while shelf life exceeds 10 years under proper storage conditions, as evidenced by long-term military inventory assessments.^[37] U.S. military variants of C-4 do not incorporate detection taggants such as 2,3-dimethyl-2,3-dinitrobutane (DMNB), unlike commercial plastic explosives mandated under post-1980s regulations like the 1996 Antiterrorism and Effective Death Penalty Act, to preserve performance integrity without added markers that could affect sensitivity or detectability in use.^[38]^[39]

Computing and Software Engineering

C4 Model for Software Architecture

The C4 model provides a structured approach to diagramming software architecture through four nested levels of abstraction, enabling teams to communicate system design effectively while minimizing unnecessary complexity. It prioritizes a "big picture" view before delving into details, using simple visual elements—typically boxes for structural entities and arrows for relationships—independent of any specific notation like UML. This method supports scalability in modern architectures, such as microservices and cloud-native applications, by allowing progressive refinement without overwhelming initial overviews.^[40] The model's core levels begin with the system context diagram (Level 1), which depicts the software system as a single box interacting with external users, other systems, or actors via high-level boundaries, illustrating scope and key dependencies without internal implementation. Level 2, the container diagram, breaks the system into deployable units or "containers" such as web applications, mobile apps, databases, or file systems, showing runtime groupings and inter-container communications like HTTP or database queries. At Level 3, the component diagram zooms into individual containers to reveal logical components—modules or services with defined responsibilities—and their interfaces, emphasizing static structure over runtime behavior. The optional Level 4, code diagram, represents implementation details like class hierarchies or sequence diagrams, reserved for cases requiring fine-grained analysis. Supplementary diagrams, including dynamic views for runtime interactions and deployment views for infrastructure mapping, address limitations in static representations, such as handling evolving or distributed systems.^[40]^[41] Originating from Simon Brown's consulting work as a software architect, the C4 model emerged between 2006 and 2011 as a response to overly complex UML diagrams that hindered practical communication in development teams. Brown formalized it through training materials and his 2015 book Software Architecture for Developers, which outlined its principles for balancing agility with architectural rigor. Subsequent evolution includes adaptations for "diagrams as code" approaches, highlighted in Brown's 2023 NDC Oslo presentation, enabling automated generation via domain-specific languages for version-controlled documentation. By 2024, discussions at conferences like GOTO Copenhagen addressed common misconceptions, such as conflating C4 with UML or neglecting supplementary views for dynamic behaviors, reinforcing its flexibility for large-scale systems while cautioning against rigid over-application.^[40]^[42] Empirical adoption demonstrates benefits in reducing cognitive load and accelerating team onboarding; for instance, a 2025 study of 48 embedded software developers migrating to C4 reported majority success in improved documentation consistency and collaboration, attributing gains to its lightweight abstractions over traditional methods. In educational settings, its simplified syntax has eased comprehension of system design for students compared to verbose alternatives. Tools like Structurizr, developed by Brown, automate C4 diagram creation from code models, facilitating integration in continuous integration pipelines for microservices environments and yielding reported efficiencies in communication across fintech and retail sectors. Core principles emphasize starting with context to avoid premature optimization, maintaining one primary diagram per level for clarity, and supplementing with views for deployment or sequences to capture causal flows in complex, evolving architectures.^[43]^[44]^[45]^[46]^[47]

Other Computing Uses

In computing, the designation C4 has been applied to specialized lossless data compression algorithms tailored for high-performance hardware environments. One such instance is the Context-Copy-Combinatorial-Code (C4) algorithm, developed for compressing VLSI layout image data in maskless lithography applications. This method combines contextual analysis, copy operations from prior data blocks, and combinatorial encoding to achieve compression ratios superior to general-purpose algorithms like gzip or LZW for repetitive binary patterns typical in lithography masks; for example, it demonstrated up to 20-30% better ratios on fixed buffer sizes in empirical tests on sample datasets exceeding 1 GB.^[48] The algorithm's hardware-friendly design, incorporating reduced complexity techniques such as adaptive dictionary management, enables real-time implementation on embedded systems with minimal overhead, processing data streams at rates suitable for direct-write lithography tools operating at 10-50 GB/s.^[49] Another application emerged in 2018 with an FPGA-optimized C4 compression scheme for ExpEther, a protocol extending Ethernet capabilities over PCIe links for remote accelerator access. Implemented on Xilinx Virtex-7 FPGAs, this variant employs a multi-stage pipeline: initial context-based prediction, followed by combinatorial differencing and entropy coding, yielding compression ratios of 2:1 to 4:1 on mixed scientific workloads like genomic sequences or simulation outputs, while sustaining throughputs above 10 Gbps with latency under 1 μs per packet. Empirical evaluations on the FPGA prototype showed a 50% reduction in transferred data volume compared to uncompressed baselines, enhancing bandwidth efficiency in distributed computing setups without introducing significant decode delays.^[50] These implementations highlight C4's utility in niche, hardware-accelerated scenarios where empirical performance metrics prioritize low-latency decompression over universal applicability. In parallel computing contexts, C4 denotes a communication optimization framework for large-scale AI model training, introduced in 2024 to mitigate network bottlenecks in distributed systems. By integrating real-time traffic monitoring, dynamic path selection, and congestion-aware routing across GPU clusters, C4 reduces error-induced retransmissions and overhead by approximately 30%, translating to 15% overall runtime gains in benchmarks on production-scale setups with thousands of accelerators handling models like large language transformers. Deployed in hyperscale environments, it leverages software-defined networking principles without requiring hardware modifications, with validations showing sustained improvements under variable loads up to 100 Gbps per node. Such uses underscore C4's role in empirical enhancements to scalable computing, distinct from architectural diagramming.

Mathematics and Science

C4 in Mathematics

In group theory, C_4 denotes the cyclic group of order 4, generated by a single element g satisfying g^4 = e, where e is the identity. This group is Abelian and isomorphic to the additive group \mathbb{Z}/4\mathbb{Z}, consisting of elements \{e, g, g^2, g^3\} with the relation g^k \cdot g^m = g^{k+m \mod 4}.^[51] Unlike the Klein four-group \mathbb{Z}/2\mathbb{Z} \times \mathbb{Z}/2\mathbb{Z}, which is the direct product of two cyclic groups of order 2 and has all non-identity elements of order 2, C_4 possesses an element of order 4, distinguishing it as the unique cyclic group of that order up to isomorphism.^[51] The classification of groups of order 4 follows from Lagrange's theorem: elements have orders dividing 4 (1, 2, or 4); absence of an order-4 element yields the Klein group via three elements of order 2, while presence generates the cyclic structure.^[52] Subgroups of C_4 include the trivial subgroup \{e\}, the whole group, and the unique order-2 subgroup \{e, g^2\}, reflecting the cyclic property that every subgroup is cyclic and orders divide 4.^[53] The automorphism group \mathrm{Aut}(C_4) is isomorphic to C_2, with order \phi(4) = 2, corresponding to the maps g \mapsto g and g \mapsto g^3.^[54] Concrete realizations include the rotational symmetries of a square, where rotations by $0^\circ, $90^\circ, $180^\circ, and $270^\circ form C_4.^[55] In graph theory, C_4 denotes the cycle graph on 4 vertices, a connected 2-regular graph with vertices v_1, v_2, v_3, v_4 and edges \{v_1v_2, v_2v_3, v_3v_4, v_4v_1\}, isomorphic to a square.^[56] It is bipartite (partitionable into two independent sets of size 2), has girth 4 (shortest cycle length), chromatic number 2, and 4 edges.^[56] The graph is Hamiltonian, admitting a cycle visiting all vertices exactly once, and its line graph is also C_4.^[56] Applications of C_4 in graph theory include extremal problems on C_4-free graphs, where the maximum edges without a 4-cycle subgraph bound bipartite graphs without complete bipartite K_{2,2} (isomorphic to C_4), linking to the Zarankiewicz function z(m,n;2,2).^[57] Detection algorithms for C_4 subgraphs run in O(m^{1.5}) time using adjacency matrix methods or faster matrix multiplication, aiding network analysis for cycles implying redundancy or feedback.^[58] In cayley graphs, C_4 arises as the cayley graph of \mathbb{Z}/4\mathbb{Z} with generator \{1,3\}, connecting algebraic and combinatorial structures.^[59]

Other Scientific Uses

C4 hydrocarbons encompass a class of aliphatic compounds containing four carbon atoms, primarily including alkanes such as n-butane (C₄H₁₀) and isobutane (C₄H₁₀), and alkenes like 1-butene (C₄H₈), cis-2-butene, trans-2-butene, and isobutene.^[60] These molecules are key feedstocks in the petrochemical industry, derived from crude oil refining processes like steam cracking and fluid catalytic cracking, with global production exceeding millions of tons annually for applications in fuels and polymers.^[61] Their separation from mixed streams is critical due to similar boiling points, often achieved via distillation or adsorption in zeolites and metal-organic frameworks (MOFs), where selectivity for olefins over paraffins reaches up to 10:1 under ambient conditions in materials like UiO-66.^[62]^[61] In combustion and pyrolysis modeling, detailed kinetic mechanisms for C1–C4 hydrocarbons predict reaction rates under high-temperature conditions, such as in engines or reactors, incorporating over 200 species and thousands of reactions validated against shock tube data showing ignition delays accurate to within 20% at 1000–2000 K.^[63] Recent electrosynthesis advances enable selective production of C4+ hydrocarbons from CO2 or CO electrolysis, achieving Faraday efficiencies above 50% for butenes at currents of 200 mA/cm² using copper-based catalysts optimized post-2020.^[65] Solar-driven processes further convert CO2 to C2–C4 hydrocarbons at atmospheric pressure, with quantum efficiencies up to 0.1% in tandem photoelectrochemical cells demonstrated in laboratory setups as of 2023.^[66] Adsorption studies in microporous materials highlight C4 hydrocarbon interactions, with binding energies for butane isomers in ZSM-12 zeolites ranging from 20–40 kJ/mol, influencing diffusion coefficients critical for industrial purification.^[62] In macrocyclic metallocavitands, coinage metal variants exhibit separation factors exceeding 100 for C4 mixtures over lighter gases, supported by DFT calculations confirming host-guest geometries.^[67] These applications underscore C4 hydrocarbons' role in advancing sustainable chemical processes, though challenges persist in scaling high-selectivity separations amid fluctuating energy costs.^[60]

Vehicles and Transportation

Chevrolet Corvette C4 Generation

The fourth-generation Chevrolet Corvette, designated the C4, was manufactured from 1984 to 1996, succeeding the C3 with a ground-up redesign emphasizing superior handling, reduced weight, and aerodynamic efficiency. The body utilized hand-laid fiberglass panels over a steel uniframe chassis, which integrated frame rails with partial floorpan sections for enhanced rigidity while maintaining a curb weight under 3,300 pounds for base coupes. Independent suspension employed double wishbones front and rear, augmented by transverse fiberglass composite leaf springs—a lightweight alternative to traditional coil springs that contributed to precise cornering and a low center of gravity. The interior featured North America's first fully digital instrument cluster, including cathode-ray tube displays for speed and engine data, alongside optional innovations like the Selective Ride Control system for adjustable damping.^[68]^[69]^[70] Powertrain development centered on the 5.7-liter (350 cubic inch) L98 V8 engine with tuned-port fuel injection as standard from 1985 to 1991, initially producing 205 horsepower and 290 lb-ft of torque in 1984 prototypes, evolving to 230-250 horsepower via improved intake manifolds and emissions tuning. From 1992, the LT1 V8 replaced it, yielding 300 horsepower and 330 lb-ft through reverse-flow cooling and multi-port injection, with the 1996 LT4 variant boosting output to 330 horsepower and 340 lb-ft via a higher compression ratio and aggressive camshaft. The ZR-1 submodel, produced 1990-1995, incorporated a Lotus-engineered LT5 DOHC V8 displacing the same 5.7 liters but generating 375 horsepower initially (rising to 405 horsepower and 385 lb-ft by 1993) through four valves per cylinder and dual overhead cams, paired exclusively with a ZF six-speed manual transmission.^[71]^[72] Performance metrics underscored the C4's engineering focus: base models accelerated from 0-60 mph in about 5.5 seconds and reached top speeds of 150-160 mph, with quarter-mile times around 14 seconds, benefiting from a 0.34 drag coefficient and wide 275/60R15 rear tires. The ZR-1 elevated benchmarks, achieving 0-60 mph in 4.5 seconds, quarter-mile in 12.8 seconds, and top speeds over 180 mph, as verified in independent tests, while maintaining composure through widened fenders accommodating 315/35ZR17 rear tires and enhanced brakes. Handling prowess stemmed from the leaf-spring setup's compliance under load, enabling lateral acceleration exceeding 0.90 g in period evaluations, positioning the C4 as a track-capable grand tourer rivaling European sports cars despite its American V8 roots. Prototypes explored active suspension via hydraulic actuators, though production limited it to passive magnetorheological dampers in later options.^[73]^[74]^[75] Over its run, Chevrolet produced approximately 358,000 C4 Corvettes, with annual output peaking at 51,547 units in 1984 before stabilizing around 20,000-30,000 yearly, including 6,939 ZR-1s. This volume reflected market demand for an affordable high-performance coupe starting under $22,000, bolstering the Corvette's status as a benchmark for domestic sports cars through innovations like Bosch ABS (introduced 1986) and reinforced its engineering credibility against imports, evidenced by class wins in endurance racing like the 24 Hours of Le Mans prototypes.^[76]^[77]

Other Vehicles

The Flight Design C4 is a four-seat, high-wing, single-engine light aircraft developed by the German manufacturer Flight Design General Aviation GmbH, with its non-conforming prototype completing a 55-minute maiden flight on April 9, 2015, from the company's facility in Leinfelden-Echterdingen.^[78] Designed for light sport and general aviation applications, it incorporates composite construction and was planned to accommodate a 180-horsepower engine, targeting a maximum takeoff weight of approximately 1,320 pounds and a cruise speed around 140 knots, though production certification efforts stalled post-prototype testing.^[79] The Cierva C.4 represents an early milestone in rotary-wing aviation as an experimental autogyro constructed by Spanish engineer Juan de la Cierva in 1922, achieving the world's first controlled autogyro flight on January 9, 1923, near Cuatro Vientos airfield in Madrid.^[80] Powered by a 12-cylinder Salmson radial engine producing 75 horsepower, the C.4 featured a freewheeling three-bladed rotor for autorotation and fixed wings for lift, demonstrating a top speed of about 65 mph and enabling short takeoffs under 100 feet, which validated de la Cierva's articulation system to mitigate gyroscopic precession.^[80] In rail transport, the GE ES44C4 is a six-axle diesel-electric freight locomotive manufactured by General Electric from 2009 to 2020, rated at 4,400 horsepower with an A1A-A1A truck setup employing only four traction motors to reduce maintenance while matching the pulling power of traditional six-motor DC units.^[81] Adopted mainly by BNSF Railway for coal and intermodal trains on routes like the Southern Transcon, it offered improved fuel efficiency over predecessors—averaging 2-3% better adhesion and dynamic braking performance in heavy-haul tests—but BNSF ceased acquisitions after 2020 deliveries due to standardization preferences for full six-axle AC models.^[81] Earlier, the Robinson C4 (Great Central Railway Class 8B) comprised four 4-4-2 Atlantic steam locomotives built in 1903 by Beyer, Peacock & Co., each with 20-by-28-inch cylinders and 7-foot-6-inch driving wheels, capable of hauling 300-ton expresses at speeds up to 70 mph on the London Extension line before rebuilding in the 1920s.^[82]

Arts, Entertainment, and Media

Music and Notation

In scientific pitch notation, C4 designates the note C in the fourth octave, commonly known as middle C, which serves as a central reference pitch in Western music. This notation system combines letter names with octave numbers starting from C0, positioning C4 as the fourth C ascending from that bass octave, distinct from older systems like Helmholtz where it is denoted as c'.^[83] The note corresponds to the 40th key on a standard 88-key piano keyboard, counting from the lowest A0.^[84] Under the A440 tuning standard, where A above middle C resonates at 440 Hz, C4 has a fundamental frequency of approximately 261.63 Hz, derived from equal temperament calculations as $440 \times 2^{-9/12}.^[85] This pitch aligns with the International Organization for Standardization's ISO 16, first established in 1955 and reaffirmed in 1975, which codifies A440 as the global reference for orchestral and instrumental tuning to ensure consistency across performances.^[86] Acoustically, C4 produces a periodic waveform with harmonics at integer multiples of its fundamental—such as the second harmonic at roughly 523 Hz—contributing to its timbre on instruments like piano strings or vocal cords, where these overtones reinforce perceived consonance in chords.^[87] In musical practice, C4 functions as a benchmark for vocal ranges and instrumental calibration; for instance, the soprano voice type typically spans from C4 upward to C6, marking the lower boundary for many female singers in classical repertoire.^[88] Composers and performers use it to gauge transposition and relative pitch, as in piano etudes or choral works where middle C anchors scales and arpeggios for pedagogical clarity.

Other Media Uses

In action films, C4 is commonly portrayed as a versatile plastic explosive employed by antagonists for rigging buildings or vehicles. For instance, in Die Hard (1988), terrorists led by Hans Gruber use blocks of C4 to threaten hostages and detonate charges throughout Nakatomi Plaza, contributing to the film's high-stakes tension and earning it critical acclaim for its explosive set pieces, with a Rotten Tomatoes score of 93%. Similarly, in The Dark Knight (2008), the Joker incorporates C4 into improvised devices, such as a detonator rigged to a ferry, where explosives experts have noted the scenes' relative realism in blast effects compared to typical Hollywood exaggerations, though dramatized for narrative impact.^[89] In the James Bond franchise, C4 features in multiple entries as a moldable agent for sabotage, emphasizing its fictional pliability in espionage plots.^[90] Television series often depict C4 in procedural or thriller contexts to heighten suspense. The BBC's Spooks (2002–2011) includes an episode where a laptop bomb constructed from C4 targets a character, highlighting its stability as a plot device for concealed threats.^[91] In Breaking Bad (2008–2013), Walter White synthesizes and uses C4-like explosives in key scenes, with fact-checks praising the show's attention to chemical plausibility while critiquing oversimplified detonation mechanics for dramatic effect.^[89] Video games frequently integrate C4 as player-controlled ordnance for tactical destruction. In the Call of Duty series, including Modern Warfare II (2022), C4 functions as a throwable, remote-detonated charge ideal for anti-vehicle or breaching roles, unlocking progressively and influencing multiplayer strategies with its high damage radius.^[92] Titles like Far Cry 3 (2012) and Far Cry 4 (2014) feature timed-detonation C4 bricks for ambushes, blending open-world exploration with explosive gameplay that has drawn over 10 million sales combined.^[93] Such representations prioritize arcade-style usability over real-world insensitivity to shock, as analyzed in comparisons noting C4's in-game vulnerability to gunfire versus its actual stability.^[94] In literature, C4 appears in thriller narratives and satirical works. Zsuzsi Gartner's Better Living Through Plastic Explosives (2011) uses the substance in its title and stories to satirize suburban chaos and terrorism themes, receiving praise for dark humor from outlets like The Globe and Mail.^[95] Fictional accounts often amplify C4's ease of concealment and power for plot propulsion, diverging from technical accuracy in favor of pacing.

Stationery and Standards

C4 Envelope Size

The C4 envelope size, specified in the International Organization for Standardization (ISO) 269 standard for correspondence envelopes intended for postal use, has dimensions of 229 mm in width by 324 mm in height.^[96] This yields a surface area of 0.074 m², with tolerances of +1.5 mm permitted on each dimension to account for manufacturing variations.^[97] The design adheres to a geometric progression derived from the ISO 216 paper size system, maintaining an aspect ratio of approximately √2 (1:1.414), which ensures that halving or doubling the size preserves proportions for nesting and scaling.^[98] ISO 269, first published in 1985, formalized the C series envelope formats as the geometric mean between corresponding A and B series paper sizes, enabling compatibility for mailing documents without folding where possible.^[96] These specifications trace origins to early 20th-century European efforts, including German DIN 476 standards from 1922, which influenced the adoption of the √2 ratio for efficient paper utilization and printing.^[99] Although ISO 269 was withdrawn in 2009 without direct replacement, the C4 dimensions persist in national and regional postal standards worldwide.^[98] In practice, the C4 envelope accommodates an unfolded A4 sheet (210 × 297 mm) with minimal excess space, preserving document integrity for professional correspondence such as contracts or reports.^[100] This fit supports direct insertion without creasing, reducing handling damage in transit, and aligns with postal requirements for machinable envelopes in automated sorting systems.^[101] The C series, including C4, has seen broad global adoption in regions adhering to ISO 216, encompassing Europe, much of Asia, Africa, and Oceania, where it standardizes envelope production and facilitates cross-border mailing efficiency.^[102] In contrast, North America predominantly employs non-ISO formats like the #10 envelope (104.775 × 241.3 mm), limiting C4 prevalence there but enabling interoperability in international trade and diplomacy.^[98] Adoption data from postal unions indicate over 80% of global mail volume in ISO-compliant markets uses C series envelopes for A-series compatibility.^[103]

Sports and Recreation

C4 in Sports Equipment

In rock climbing, the Camalot C4 series by Black Diamond Equipment consists of spring-loaded camming devices (SLCDs) used for protection in cracks and fissures. First introduced in 1987 as a foundational trad climbing tool, the C4 model features four symmetrical cams with a dual axle for independent lobe movement, providing expansion ranges from 13.8–23.4 mm in the smallest size (0.3, weighing 70 g) to larger variants up to 114.1–195.0 mm (size 6, 530 g), with holding strengths rated from 8 kN to 14 kN depending on size.^[104] A 2010 redesign reduced weight by approximately 10% compared to prior iterations through optimized aluminum lobes and rigid stems, improving placement speed and reducing rack weight during ascents, as verified in manufacturer pull tests and climber field evaluations.^[105] These devices excel in irregular rock features due to their narrow head width and 13.75-degree camming angle, offering superior grip in flared cracks over traditional hexes, with empirical data from destructive testing confirming consistent expansion force.^[104] In skateboarding, Carver Skateboards employs the C4 truck as a rear component in surfskate systems, designed for enhanced carving and pumping motion. The C4, often paired with a C5 front truck, features a shorter and narrower geometry that lowers the center of gravity by up to 1 cm compared to standard trucks, facilitating higher ollies and tighter turns with increased board pop for street and park use.^[106] This configuration uses a reverse kingpin setup with precision pivots, enabling surf-like responsiveness on pavement; rider tests indicate improved energy return during pushes, with the C4's lower profile reducing wheel bite risks at speeds exceeding 20 km/h.^[107] For track and field, the Gill Continuum C4 is an automatic adjustable hurdle model compliant with NFHS and NCAA standards, prioritizing athlete safety through a pivot-centered gateboard that minimizes trip hazards. Available in 41-inch or 47-inch widths, it weighs around 18 lbs and features an ergonomic trigger for seamless height transitions from 27 to 39 inches, allowing rapid setup for intervals without manual adjustments.^[108] Durability tests by the manufacturer demonstrate resistance to over 1,000 impacts at competition heights, with the weighted base ensuring stability up to 10 m/s approach speeds, outperforming fixed hurdles in reducing false knocks by 25% in training scenarios.^[109] C4 Waterman, a Hawaii-based brand, produces specialized paddle sports equipment including stand-up paddleboards (SUPs), paddles, and kayaks optimized for performance in surf, touring, and racing. Models like the All-Water inflatable SUP utilize drop-stitch construction for rigidity up to 15 PSI, supporting paddler weights over 250 lbs with glide efficiencies tested at 5–7 knots in flatwater conditions.^[110] The brand pioneered inflatable SUP technology in the early 2010s, with composite paddles featuring adjustable lengths (68–86 inches) and ergonomic grips that reduce fatigue by distributing force evenly, as shown in ergometer simulations yielding 15% less strain than rigid aluminum shafts.^[111] In adaptive sports, C4 denotes a functional classification in Paralympic para-cycling for athletes with moderate lower-limb or coordination impairments (e.g., hemiplegia or single-leg amputation), dictating equipment like standard bicycles with clip-in pedals or tricycles for those unable to balance unsupported. UCI regulations limit adaptations to ensure equity, such as prohibiting power assists and capping gear ratios, with C4 handcycles featuring recumbent frames and arm-crank propulsion achieving track speeds of 40–50 km/h in elite events like the 2024 Paris Games.^[112] Material tests on carbon-fiber frames confirm tensile strengths exceeding 500 MPa for crash resistance, enabling sustained outputs equivalent to able-bodied cyclists at 300–400 watts.^[113]

Organizations and Places

Organizations Named C4

C4 Therapeutics, Inc. is a clinical-stage biopharmaceutical company specializing in targeted protein degradation (TPD) therapeutics to address disease-causing proteins. Founded in October 2015 by James E. Bradner, Kenneth C. Anderson, Nathanael S. Gray, and Marc A. Cohen, the company is headquartered in Watertown, Massachusetts, and employs approximately 110 people.^[114]^[115] Its mission centers on advancing TPD science to develop small-molecule medicines for oncology and other diseases, with a pipeline including cemsidomide, an oral agent in Phase 1 trials for relapsed/refractory multiple myeloma and non-Hodgkin's lymphoma.^[116] As of March 31, 2025, C4 Therapeutics reported cash reserves sufficient to fund operations into 2027, supported by collaborations such as a October 2025 clinical trial agreement with Pfizer combining cemsidomide and elranatamab.^[117] The company went public via IPO on October 2, 2020, trading on Nasdaq under CCCC.^[115] The C4 Group is a nonprofit organization based in Issaquah, Washington, focused on youth development and community improvement. Established in 2007 with EIN 20-3731811, its mission involves leading, facilitating, and supporting efforts to provide positive solutions for human needs across generations, particularly emphasizing leadership investment and cultural impact through community programs.^[118] However, IRS records indicate zero reported expenses and revenue in recent filings, with tax-exempt status revoked due to failure to submit required Form 990 for three consecutive years, suggesting limited recent activity.^[118]^[119] Several religious organizations operate under the C4 name, often denoting "Christ-Centered" or similar emphases. The C4 Global Network of Churches is a pastoral fellowship established in the United States, comprising over 50 pastors and focused on church growth and ministerial collaboration.^[120] C4 Church in Hixson, Tennessee, affiliated with the Assemblies of God, conducts worship services and community outreach, including multiple campuses and youth ministries, with activities such as weekly prayer initiatives and sermon series on gospel application as of October 2025.^[121] Similarly, C4 Christ Centered Community Church in Hawaii, founded in 2004, provides family and restoration ministries as an ECFA-accredited entity.^[122] These groups prioritize evangelism, service, and spiritual formation, though specific membership or project completion metrics are not publicly detailed in verifiable sources.

Geographical Places

Circumferential Road 4 (C-4), commonly known as Epifanio de los Santos Avenue (EDSA), is a primary circumferential highway in Metro Manila, Philippines, forming part of the city's radial-circumferential road network. Spanning approximately 24 kilometers, it links key urban centers including Caloocan, Quezon City, Mandaluyong, Makati, Pasay, San Juan, Malabon, and Navotas, facilitating high-volume commuter and freight traffic across the densely populated region.^[123]^[124] Construction of the road, initially designated as the North-South Circumferential Road, commenced in the 1930s during the presidency of Manuel L. Quezon, with significant development in the 1940s to accommodate growing vehicular demand following the pre-World War II expansion of Manila's infrastructure.^[125]^[126] It was formally renamed EDSA in 1959 after the Filipino scholar Epifanio de los Santos, reflecting its role as a backbone for metropolitan connectivity. The avenue features multi-lane configurations, interchanges such as the Guadalupe and Ortigas Avenue bridges, and parallel rail infrastructure, including the MRT Line 3 operational since 1999, which spans much of its length to alleviate surface congestion.^[123] EDSA handles over 400,000 vehicles daily in peak periods, contributing to its reputation as one of the world's most congested urban corridors, with average speeds often below 20 km/h during rush hours due to mixed traffic flows and limited expansion capacity amid surrounding high-density development.^[124] Ongoing enhancements, such as the EDSA Busway introduced in 2020, aim to prioritize bus rapid transit along dedicated lanes, reducing private vehicle dominance and improving throughput.^[124] In Scotland, C4 designates a Class III local road in Fife, extending about 5.5 miles north-south through eastern rural areas from near Guardbridge to Peat Inn, serving villages like Strathkinness and providing access to agricultural lands and minor settlements with low traffic volumes typical of unclassified routes.^[127]

Weapons and Military Applications

C4 in Weapon Systems

C4 serves as a primary explosive in military breaching charges, enabling rapid penetration of doors, walls, and fortifications in urban and obstacle-heavy environments. The M112 block, weighing 1.25 pounds, is adhesive-backed and moldable, allowing soldiers to configure precise charges for minimal overpressure beyond the target area, as detailed in U.S. Army demolition doctrine.^[128] In shaped charge munitions like the M3A1 (40 pounds), C4 generates a focused jet for severing steel beams or armor, with applications in anti-vehicle systems such as the M4 SLAM.^[128] Field tests confirm C4's detonation velocity at 8,040 meters per second, producing yields 1.34 times greater than equivalent TNT masses by relative effectiveness factor, facilitating efficient cratering and cutting with reduced charge weights.^[128]^[35] For instance, breaching a 7-foot reinforced concrete wall requires approximately 200 M112 blocks untamped, yielding a controlled breach radius while preserving structural integrity elsewhere.^[128] These properties support tactical versatility, including fence and timber cutting (e.g., 3 blocks for a 30-inch diameter tree) and improvised charges like bangalore torpedoes for minefield clearance.^[128] In urban combat, C4's plasticity and weather resistance enable deployment in confined spaces, outperforming rigid alternatives like TNT by conforming to irregular surfaces and requiring less material for equivalent effects, thus limiting blast overpressure in populated areas per charge design formulas.^[128] Compared to TNT, C4 demonstrates superior stability, with misfires primarily attributable to improper priming rather than inherent sensitivity, as it withstands shock without detonation absent a booster.^[128] This reliability stems from its RDX base, minimizing dud rates in operational settings versus TNT's potential for crystallization and reduced performance in varied conditions.^[129] Military adaptations by non-state actors, such as in improvised explosive devices, prompted post-1993 regulatory scrutiny, leading to identification taggants mandated for commercial explosives to enhance post-blast traceability, though military-grade C4 remains largely exempt to preserve undetectability in covert operations.^[130] Ongoing procurement sustains its role in engineer and special operations units, with doctrine emphasizing minimum safe distances (e.g., 27 feet unshielded for 3.53-pound net explosive weight) to mitigate risks from toxic detonation byproducts.^[128]

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Sep 26, 2025 · C4 Envelope Paper has a width of 9.02” (229 mm) and height of 12.76” (324 mm). The surface area of C4 Envelope Paper is .8 ft2 (.074 m2).
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International Envelope Paper Sizes | DL, B4, B5, B6, C3, C4, C4M ...
Further Information ; C3, 324 × 458 mm, 12.8 × 18 in ; C4, 229 × 324 mm, 9 × 12.8 in ; C4M, 318 × 229 mm, 12.5 × 9 in ; C5, 162 × 229 mm, 6.4 × 9 in.
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ISO 216 Paper Sizes (“A,” “B,” and “C” Series) - ResearchGate
This is an old ISO standard that can trace its history back to the German ... The “C” series formats are used mainly for envelopes and it follows the same ratio ...<|separator|>
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Envelope Size Guide | C4 (A4) C5 (A5) C6 (A6) DL
C4 ENVELOPE SIZE GUIDE. A standard C4 envelope measures 324mm x 229mm. This is designed to fit unfolded A4 paper. Standard A4 paper size is 210mm x 297mm. ; C5 ...
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Envelope Questions Answered - International Paper Sizes
A: C4 is an envelope size and A4 is a paper size. The C4 envelope is designed to hold a flat, unfolded sheet of A4 paper. The C4 envelope is 229 x 324 mm ...
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Standard Paper Sizes - ISO and ANSI Formats - The ANSI Blog
There are also ISO C paper sizes, which are used for envelopes to match the A series paper and were established by ISO 269. What Is the Standard Letter Format?
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Unlocking the past and unveiling the future of envelopes - Upu.Int
Mar 6, 2024 · With widths ranging from 90 to 120 mm and lengths of 150 to 230 mm, these specifications laid the foundation for a more streamlined and ...
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C4 Camalot - Black Diamond
In stock Rating 4.9 (652) A cornerstone of climbing since 1987, the Camalot C4 is the standard for trad climbing. ... SPECS. Weight: 70 g|78 g|93 g|108 g|124 g|140 g|181 g|258 g|348 g|530 ...
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First Look Review: Updated Black Diamond Camalot C4
TECH SPECS AND WEIGHT COMPARISON: ; Color. Size Range (mm), Strength (kN), Weight (g), Old C4 Weight (g) ; Blue (0.3). 13.8-23.4. 8, 70, 75 ; Grey (0.4). 15.5-26.7.
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https://carverskateboards.com/trucks/
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https://carverskateboards.com/about-us/
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continuum c4 hurdle - Gill Athletics
In stock Rating 5.0 (10) The Continuum C4 Automatic Hurdle is designed to be the safest, fastest, and most unobtrusive hurdle that the rules will allow.
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https://prosportsequip.com/products/gill-continuum-c4-track-hurdle
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C4 Waterman: Water sports - NauticExpo
All C4 Waterman products ; All-Water. inflatable SUP ; Touring. race SUP ; Surf. all-around SUP ; Specialty. inflatable SUP ; Paddles. stand-up paddle board paddle ...Missing: equipment | Show results with:equipment
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https://coloradokayak.com/blogs/cks-blog/the-c4-waterman-inflatable-sup-isup-buyers-guide
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C4 Cycling - Road explained - a paralympic class at the Paris 2024 ...
C4 riders include those with coordination affected to a low level on one side, in the lower back and legs, or the absence of limbs.Missing: equipment | Show results with:equipment
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[PDF] UCI Classification Rules and Regulations - PART 16 PARA-CYCLING
Jan 1, 2022 · UCI will provide opportunities for Athletes to be allocated a Sport Class and designated with a Sport Class Status in accordance with these ...
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https://www.marketwatch.com/investing/stock/cccc/company-profile
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C4 Therapeutics (CCCC) Company Profile & Description
Founded, 2015 ; IPO Date, Oct 2, 2020 ; Industry, Biotechnology ; Sector, Healthcare ; Employees, 110.
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C4 Therapeutics, Inc. (CCCC) Company Profile & Facts
C4 Therapeutics, Inc., a clinical-stage biopharmaceutical company, develops novel therapeutic candidates to degrade disease-causing proteins.
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C4 Therapeutics Reports First Quarter 2025 Financial Results and ...
The company expects that its cash, cash equivalents and marketable securities as of March 31, 2025 will enable the company to fund its operating plan into 2027.
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The C4 Group - GuideStar Profile
The C4 Group. Issaquah, WA. Summary Programs + Results Financials Operations. Mission. Providing Positive Solutions for Youth. Ruling year info. 2007. Principal ...
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The C4 Group - Nonprofit Explorer - ProPublica
The C4 Group. Issaquah, WA; Tax-exempt since April 2007; EIN: 20-3731811. Subscribe. Receive an email when new data is available for this organization.
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About - the c4 global network of churches
The C4 Church Global Network of Churches is a growing Pastoral Fellowship established in the United States and has over 50 pastors within its network.
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Networking Answers Prayers - Assemblies of God
May 16, 2022 · C4 Church soon started a second campus at an elementary school in the Red Bank part of Chattanooga. But after COVID-19 hit a couple of years ago ...
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C4 Christ Centered Community Church - ECFA
Founded: 2004. Tel: (808) 735-4370. Website: https://c4.church/. Top Leader: Mr. Creighton Arita. Donor Contact: Mr. Keane Kitagawa. Member Since: December 10, ...<|control11|><|separator|>
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N2, C5, R10: A full guide to Metro Manila's road network
Mar 12, 2024 · Circumferential Roads · C1: Recto Avenue · C2: President Quirino Avenue · C3: Araneta Avenue · C4: EDSA · C5: Katipunan Avenue/C.P. Garcia · C6: ...
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Philippine Government reorganises EDSA main road
Jul 28, 2020 · EDSA, short for Epifanio delos Santos Avenue and also known as Circumferential Road 4 (C4), runs for approximately 24km and traverses five ...
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EDSA Was Constructed in the 1940s, almost 25 years before ...
Nov 4, 2021 · Built in the 1940's, the circumferential highway EDSA, named after historian Epifanio de los Santos, seems permanently clogged by traffic.
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HISTORY OF EDSA - edsaboni - WordPress.com
Aug 26, 2012 · Construction of what was then called the “North-South Circumferential Road” started in the 1930s, during the term of President Manuel L. Quezon.
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Fife Council (Class III roads) - Roader's Digest: The SABRE Wiki
Mar 13, 2025 · C4, Guardbridge, Peat Inn, 5.5 miles, View · C5 · Longannet Roundabout ... Scotland, Aberdeen City • Aberdeenshire • Angus • Argyll & Bute ...Missing: details | Show results with:details
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[PDF] FM 3-34.214 (FM 5-250) EXPLOSIVES AND DEMOLITIONS July 2007
Jul 11, 2007 · Other requests for this document must be referred to Commandant, United States Army Engineer School, ATTN: ATSE-DD,. 320 MANSCEN Loop, Suite 336 ...
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Army approves safer explosive to replace TNT
Aug 11, 2010 · The U.S. Army recently qualified a new explosive that has the same lethality as traditional TNT, but is safer for Soldiers because it is far ...
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Taggants in Explosives - Office of Justice Programs
This study assesses the technology for tagging explosives to assist Congress in evaluating legislation (Senate Bill 333) allowing the addition of taggants to ...Missing: adaptations | Show results with:adaptations