CH
CH is an abbreviation or initialism with multiple meanings in various fields. For the mathematical concept, see [[Continuum hypothesis]].Arts and entertainment
Literature
In literary contexts, "CH" commonly appears as an abbreviation for "chapter," a standard convention used in book citations, tables of contents, and textual references to denote divisions within a work. This shorthand, often rendered as "Ch." with a period, facilitates precise navigation in scholarly and general reading, as outlined in major style guides such as the MLA Handbook, which lists "ch." among approved abbreviations for structural elements like chapters and sections.[1] Similarly, the Chicago Manual of Style permits "ch." or "chap." for abbreviating "chapter" in footnotes and bibliographies, emphasizing its role in maintaining conciseness without ambiguity.[2] A notable historical instance of "CH" in literature involves a collection of fifteen French lyrics preserved in University of Pennsylvania MS French 15, a 15th-century anthology where the poems are headed by the initials "Ch." Scholar James I. Wimsatt, in his edited volume Chaucer and the Poems of "CH", argues that these lyrics, composed around 1368–1369, are attributable to Geoffrey Chaucer based on linguistic, thematic, and paleographical evidence linking them to his early career influences from French courtly poetry. The manuscript's "Ch" signature reflects medieval scribal practices for attributing anonymous or pseudonymous works, positioning these poems as a bridge between Chaucer's French sources and his later English compositions, such as those in The Canterbury Tales. Wimsatt's analysis highlights their stylistic alignment with Chaucer's known oeuvre, including shared motifs of love and fortune, and traces the manuscript's provenance to French origins before its arrival in England.[3] This "CH" attribution has sparked ongoing debate in Chaucer studies, underscoring the fluidity of authorship in medieval literary anthologies.[4]Film and television
In film, C.H.U.D. (1984) is an American independent horror movie directed by Douglas Cheek, depicting a police captain and a photographer investigating disappearances linked to toxic waste creating cannibalistic humanoid underground dwellers in New York City's sewers.[5] The film stars John Heard and Daniel Stern and critiques 1980s urban decay and environmental neglect, grossing over $3.3 million on a modest budget and gaining cult status for its practical effects and social commentary. In television, Chosen (2013–2014) is an American action-thriller web series created by Ben Ketai and Ryan Lewis, stylized onscreen as CH:OS:EN with a ticking sound effect to evoke a countdown. Airing on Crackle for three seasons (18 episodes total), it follows attorney Ian Mitchell (Chad Michael Murray) who receives a mysterious box containing a gun, a photo of a target, and instructions for an assassination, pulling him into a shadowy organization's deadly game; the series blends high-stakes suspense with themes of family protection and moral dilemmas, produced by Sony Pictures Television.[6] In Canada, CH Morning Live is a long-running morning television program that premiered on February 13, 2001, on CHCH-TV in Hamilton, Ontario, offering news, weather, traffic, lifestyle segments, and community features to inform and engage local audiences.[7] Initially co-hosted by Cathy Wegner and later by Bob Cowan until his retirement in 2022, with Tim Bolen as co-anchor until leaving in January 2025, the show runs weekdays from 6 to 10 a.m. EST, emphasizing educational content on health, finance, and regional events as part of CHCH's commitment to accessible broadcasting since 1954.[8] The procedural drama CSI: Crime Scene Investigation features the episode "Ch-Ch-Changes" (season 5, episode 8, aired November 18, 2004), directed by Kenneth Fink and written by Naren Shankar, where the Las Vegas team probes the brutal stabbing of Wendy Sentori, a woman undergoing sex reassignment surgery.[9] The plot delves into the city's underground transgender community and black-market hormone trade, with Gil Grissom (William Petersen) and Catherine Willows (Marg Helgenberger) uncovering family secrets and surgical complications as key motives; guest starring Kate Walsh as the victim Mimosa, the episode highlights forensic techniques like luminol testing and DNA analysis while addressing social stigma, earning a 7.8/10 rating from viewers for its sensitive handling of identity themes.[10] Production involved consultations with medical experts for accuracy in depicting gender-affirming procedures, reflecting the show's emphasis on scientific investigation in episodic case files abbreviated in titles like "CH" for narrative shorthand.[11]Music
Canadian rapper Choclair released his debut studio album Ice Cold in 2000, marking a significant entry in the Canadian hip-hop scene with its blend of smooth flows, introspective lyrics, and collaborations featuring artists like Saukrates and Jully Black. The album, produced primarily by Saukrates and others, showcases Choclair's signature style rooted in Toronto's urban sound, emphasizing themes of perseverance and street life. It achieved commercial success, peaking at number 5 on the RPM Canadian Albums Chart and earning Choclair his first Juno Award nomination for Rap Recording of the Year in 2001.[12][13] The track listing includes:- "Intro" (featuring Manal "Prima" Hajj)
- "Ice Cold"
- "Let's Ride" (featuring Saukrates)
- "Rubbin'" (featuring Jully Black)
- "Takin' It In" (featuring Mase and Jully Black)
- "Hate Me" (featuring Solitair)
- "Get Up" (featuring Saukrates)
- "I Know" (featuring Kardinal Offishall)
- "Flavours" (featuring Jully Black)
- "Off the Record"
- "The Life"
- "In the Music"
- "Fifty"
- "Skunk" (featuring Kurupt)
- "21 Years"
Businesses and organizations
Companies
CH is a diffusion line of the Carolina Herrera fashion house, launched in 1986 as a more accessible secondary collection featuring less expensive fabrics while maintaining the designer's signature elegance and sophistication.[19] The brand was reintroduced in 2001 as CH Carolina Herrera, expanding into a lifestyle collection that includes ready-to-wear apparel for men, women, and children, along with handcrafted accessories such as bags and leather goods produced in Spain.[20] CH Carolina Herrera's product lines emphasize versatile, modern pieces blending classic tailoring with contemporary details, and it has become known for fragrances like CH for Women (2007) and CH Men (2009), which contribute to its broad appeal.[21] With a global presence spanning 105 countries and over 15,000 points of distribution, the brand operates more than 350 retail locations, including standalone boutiques and shop-in-shops, underscoring its role in democratizing luxury fashion.[22] CHS Inc. is a farmer-owned cooperative headquartered in Inver Grove Heights, Minnesota, established in 1931 as the Farmers Union Central Exchange to support agricultural marketing and supply needs in the Upper Midwest.[23] The company has grown into a diversified agribusiness giant, operating across agriculture segments like agronomy, grains, oilseed processing, and foods, as well as energy sectors including renewable fuels, lubricants, and transportation.[23] In fiscal year 2025 (ended August 31, 2025), CHS reported revenues of $35.5 billion and net income of $597.9 million, reflecting its scale as one of the largest farmer-owned cooperatives in the United States with operations in 19 countries and serving over 500,000 member-owners.[24] Its business model emphasizes returning value to farmers through patronage dividends and equity redemptions, with $600 million distributed to owners in 2025 amid stable demand in global grain and energy markets.[25][26] C.H. Robinson Worldwide, Inc. is a global logistics provider founded in 1905 in Grand Forks, North Dakota, initially as a produce brokerage firm by Charles Henry Robinson to connect farmers with wholesalers.[27] Over the decades, it evolved into a third-party logistics leader offering multimodal freight transportation, supply chain management, and consulting services across North America, Europe, Asia, and other regions, handling over 19 million shipments annually.[28] In 2025, the company expanded its capabilities through initiatives like the launch of the Always-on Logistics Planner, an AI-powered tool for 24/7 supply chain execution, and significant growth in global forwarding, where volumes tripled and gross profits rose from $150 million to $800 million over the prior decade.[29] Additionally, C.H. Robinson broadened its healthcare logistics support by expanding ISO 9001:2015 certification and investing in specialized cold chain and regulatory compliance services.[30] These expansions contributed to strong third-quarter 2025 results, with income from operations up 22.6% to $220.8 million, driven by AI integration and margin improvements.[31]Other organizations
In Switzerland, the abbreviation "CH" derives from Confoederatio Helvetica, the Latin term for the Swiss Confederation, serving as an official shorthand for the country's federal government and its institutions. This usage avoids linguistic biases among the nation's German, French, Italian, and Romansh-speaking populations and appears on passports, vehicle license plates, coins, and international standards like the ISO 3166-1 alpha-2 code. The term reflects Switzerland's historical identity as a confederation dating back to 1291, with "Helvetica" referencing the ancient Roman province of Helvetia.[32] Several nonprofit foundations dedicated to pediatric care operate under or are associated with the "CH" acronym, focusing on supporting children's hospitals through fundraising, program development, and community outreach. For instance, the Children's Hospital Foundation, linked to the Children's Hospital of Richmond at VCU (CHoR), traces its origins to 1920 when the original children's hospital was incorporated on Brook Road in Richmond, Virginia, evolving into a key supporter of comprehensive pediatric services. The foundation funds initiatives such as child life programs that help young patients and families manage hospital stays, alongside expansions like the 500,000-square-foot Children's Tower, which enhances operating rooms, emergency departments, and family amenities to serve over 80,000 children annually with treatments ranging from routine care to complex conditions like cancer.[33][34] Another example is the Children's Health Foundation (CHF), a 501(c)(3) organization that partners with pediatricians to advance child health outcomes through quality improvement collaboratives and resource sharing. Established to foster collaboration among healthcare providers, it offers project management support, learning sessions, and expertise in pediatric care systems, emphasizing actionable measures to enhance preventive and treatment services for children in communities in Oregon.[35][36] The Chemical Heritage Foundation (CHF), originally founded in 1982 as the Center for the History of Chemistry through a partnership between the University of Pennsylvania and the American Chemical Society, preserved and promoted the history of chemical sciences via archives, fellowships, and public programs. Renamed the Science History Institute in 2018 to encompass broader scientific histories including biology and technology, the organization continues its mission with initiatives such as the annual Curious Histories Fest, which explores science's cultural impacts through exhibitions and events. As of 2024–2025, it supports ongoing research via the Beckman Center for the History of Chemistry, hosting postdoctoral and senior fellows to study topics like molecular biology and underrepresented scientists' contributions, while planning new exhibits on topics such as reproductive health technologies set to open in May 2025.[37][38][39][40]Language and linguistics
Digraphs
In English, the digraph "ch" most commonly represents the voiceless postalveolar affricate /tʃ/, as in words like "church" and "chair". This pronunciation predominates in both native Germanic words and loanwords from Romance languages. Historically, the /tʃ/ sound in Old English was typically spelled with a single "c" before front vowels, as in cirice (modern "church"), but following the Norman Conquest in 1066, the digraph "ch" entered English via Old French influences, initially for borrowed terms like "chance" and later extending to native vocabulary for clarity in spelling.[41] In certain Greek-derived words, such as "chorus" or "echo," "ch" is instead pronounced as /k/, reflecting the original Greek chi (χ).[42] In German, the digraph "ch" denotes two distinct fricative sounds depending on the preceding vowel: the voiceless palatal fricative /ç/ (known as the ich-laut, similar to a soft "sh" but more hissing) after front vowels like i, e, ä, ö, or ü, as in ich ("I"); and the voiceless velar or uvular fricative /x/ (the ach-laut, a guttural rasp like Scottish "loch") after back vowels like a, o, or u, as in ach ("oh"). This dual pronunciation arose from High German consonant shifts around the 8th century, distinguishing regional dialects.[43][44] In Spanish, "ch" consistently represents the voiceless postalveolar affricate /tʃ/, akin to the English "church," as in chico ("boy") or mucho ("much"). This sound has remained stable since the digraph's adoption in medieval Castilian orthography to distinguish it from single "c" or "ç," and it was historically treated as a distinct letter in the Spanish alphabet until the 2010 reform.[45] Regional variations exist, such as a sibilant /ʃ/ in parts of Andalusia or the Andes, but the standard pronunciation is /tʃ/.[46] In Welsh, "ch" stands for the voiceless uvular fricative /χ/, a harsh, throaty sound produced at the back of the throat, as in bach ("small") or llyn (with mutation to chlyn). This pronunciation, akin to the "ch" in Scottish Gaelic loch, dates to Proto-Celtic origins and is treated as a single letter in the Welsh alphabet, affecting sorting and mutation rules.[47] The digraph "ch" is generally encoded as separate Unicode characters U+0063 LATIN SMALL LETTER C and U+0068 LATIN SMALL LETTER H in modern digital text, allowing for standard rendering. However, historical ligature forms exist in medieval scripts, represented in extensions like U+F1BB LATIN SMALL LIGATURE CH in the Private Use Area for scholarly reproductions. In languages like Czech and Slovak, the related /tʃ/ sound uses the single grapheme č (U+010D LATIN SMALL LETTER C WITH CARON) instead of the digraph.[48]Abbreviations
In various linguistic and documentary contexts, "CH" serves as an abbreviation for "chapter," particularly in publishing and legal texts where it denotes a division within a larger work. According to standard English dictionaries, this usage is recognized alongside variants like "ch." or "chap.," and it appears in bibliographic references and annotations to streamline citations. For instance, in academic publishing guidelines such as those from the Modern Language Association (MLA), "ch." is employed to abbreviate chapter numbers in works cited, reflecting a convention that prioritizes brevity while maintaining clarity.[49][1] The abbreviation "CH" is commonly used to represent Switzerland in informal settings, such as travel guides, vehicle license plates, and casual correspondence, deriving from the Latin Confoederatio Helvetica (Helvetic Confederation). This shorthand distinguishes itself from more formal multilingual terms like "Schweiz" or "Suisse" and is prevalent in non-official contexts to evoke the country's neutral identity without favoring any national language. While it aligns with the official ISO 3166-1 alpha-2 code, its informal application extends to everyday items like stamps and domain names (.ch), making it a practical identifier for international travelers and expatriates.[50] In trade and commerce, "CH" abbreviates "Customs House," referring to the official buildings or offices responsible for processing imports and exports, as noted in standard lexicographical references. This usage dates back to historical mercantile practices where Customs Houses served as hubs for tariff collection and documentation, and it persists in modern shipping glossaries to denote related administrative functions.[49] "CH" also functions as an abbreviation for "Chief" in certain titles, both historically and in contemporary usage, such as in honors. For example, in the United Kingdom's Order of the Companions of Honour, established in 1917, recipients append "CH" as a post-nominal honor for distinguished public service, as documented in peerage and etiquette authorities.[49][51]Science and technology
Chemistry
In chemistry, the methylidyne radical, denoted as CH or CH•, is a highly reactive diatomic species consisting of a carbon atom bonded to a hydrogen atom with an unpaired electron in its ground state (X²Π). It was first identified in 1937 through spectroscopic analysis of interstellar absorption lines by Swings and Rosenfeld.[52] The laboratory spectrum of CH was subsequently observed in 1953 by Norrish and coworkers using flash photolysis of acetylene in the presence of NO₂.[53] Due to its exceptional reactivity, the CH radical acts as a key intermediate in hydrocarbon combustion, participating in chain-branching reactions and contributing to the formation of pollutants like NOx.[54] In organic chemistry, the methylene group (–CH₂–) represents a fundamental bivalent structural unit where a carbon atom is bonded to two hydrogen atoms and connected to two other atoms or groups, commonly appearing in aliphatic hydrocarbons. This group features a carbon atom in sp³ hybridization, forming tetrahedral geometry with bond angles near 109.5° and C–H bond lengths of approximately 1.09 Å. For instance, in methane (CH₄), the simplest hydrocarbon, a central carbon atom is bonded to four hydrogen atoms in a symmetric tetrahedral arrangement, exemplifying saturated C–H bonding with all single bonds and no methylene groups per se, but serving as the building block for more complex alkanes containing –CH₂– units, such as ethane (CH₃–CH₃) or propane (CH₃–CH₂–CH₃).[55] The notation "CH" in chemical formulas emerged from advancements in nomenclature during the late 18th century, when Antoine Lavoisier and collaborators, including Berthollet and de Fourcroy, proposed a systematic naming system based on elemental composition in their 1787 work Méthode de nomenclature chimique, emphasizing compounds of carbon and hydrogen as a class of substances.[56] This foundation enabled the later introduction of abbreviated symbols by Jöns Jacob Berzelius in 1814, who assigned "C" for carbon and "H" for hydrogen, allowing concise representations like CH₄ for methane and facilitating the documentation of hydrocarbons.[57]Mathematics and computing
In set theory, the continuum hypothesis (CH) posits that there is no infinite set of real numbers whose cardinality is strictly greater than that of the natural numbers and strictly less than that of the continuum. Formally, it states that the cardinality of the continuum, denoted $2^{\aleph_0}, equals \aleph_1, the smallest uncountable cardinal number. This hypothesis, first proposed by Georg Cantor in 1878, was shown to be independent of the standard Zermelo–Fraenkel set theory with the axiom of choice (ZFC) through landmark results: Kurt Gödel proved in 1940 that CH is consistent with ZFC by constructing the inner model L (the constructible universe) where CH holds, while Paul Cohen demonstrated in 1963 using forcing that the negation of CH is also consistent with ZFC. These proofs established CH as undecidable within standard axiomatic set theory, influencing subsequent research in descriptive set theory and large cardinals. The hyperbolic cosine function, denoted \cosh x or sometimes ch(x), is defined as \cosh x = \frac{e^x + e^{-x}}{2} for real x. This even function has a graph that resembles a parabola opening upwards, with a minimum value of 1 at x = 0, and it grows exponentially as |x| increases. Hyperbolic cosine arises naturally as a solution to certain second-order linear differential equations, such as y'' - y = 0, where the general solution is y = A \cosh x + B \sinh x./03%3A_Higher_Order_Equations/3.05%3A_Homogeneous_Linear_Equations_with_Constant_Coefficients) Applications include modeling the shape of a hanging chain (catenary curve, y = a \cosh(x/a)) and in solutions to wave equations in hyperbolic geometries. In computing, "CH" commonly abbreviates "channel," a fundamental data structure for interprocess communication and synchronization in concurrent programming. In the Go programming language, channels (often namedch in code) enable safe data exchange between goroutines without shared memory, using the syntax ch := make(chan T) to create a channel of type T, with operations like ch <- v for sending and v := <-ch for receiving. This design, inspired by Communicating Sequential Processes (CSP), prevents race conditions and supports patterns like fan-in/fan-out for multiplexing multiple inputs. Additionally, channel allocation algorithms in wireless networks optimize frequency assignment to minimize interference, as in dynamic channel allocation (DCA) schemes where channels are reused based on real-time traffic and co-channel constraints.[58]
Medicine
In medicine, "CH" commonly abbreviates congenital hypothyroidism, a condition characterized by deficient thyroid hormone production present at birth, affecting approximately 1 in 2,000 to 4,000 newborns worldwide.[59] If untreated, it leads to growth retardation, intellectual disability, and other developmental issues due to impaired metabolism and brain maturation.[60] Symptoms in affected infants may include prolonged jaundice, poor feeding, constipation, hypotonia, hoarse cry, and macroglossia, though many cases are subclinical and detected only through screening.[61] Newborn screening protocols, implemented globally since the 1970s, involve heel-prick blood tests measuring thyroid-stimulating hormone (TSH) levels, typically performed between 24 and 72 hours after birth to enable early intervention. Elevated TSH prompts confirmatory serum free thyroxine (FT4) and TSH testing, with treatment initiated immediately upon diagnosis to prevent irreversible damage.[59] Treatment for congenital hypothyroidism consists of lifelong oral levothyroxine (L-T4) replacement therapy, starting at 10-15 mcg/kg/day for newborns, adjusted based on serial TSH and FT4 monitoring to maintain levels within age-specific normal ranges. Early initiation, ideally within two weeks of birth, normalizes growth and cognitive outcomes in most cases, with reassessment for transient forms recommended around age 3 if doses are low.[62] Current guidelines from organizations like the American Academy of Pediatrics emphasize prompt screening and therapy, though no specific World Health Organization update occurred in 2024; instead, WHO endorses universal newborn screening aligned with regional protocols for endocrine disorders.[59] Long-term management includes annual evaluations to titrate dosing as the child grows, minimizing risks like overtreatment-induced hyperthyroidism. Another significant medical use of "CH" refers to the total hemolytic complement (CH50) assay, which evaluates the functional activity of the classical complement pathway, including the C1q subcomponent—a key recognition protein in the innate immune system.[63] C1q, a 460 kDa hexameric glycoprotein composed of 18 polypeptide chains (six each of A, B, and C subunits), features collagen-like stalks and globular heads that bind to antibody-antigen complexes, initiating complement activation and opsonization to clear pathogens and apoptotic cells.[64] This structure enables C1q to bridge innate and adaptive immunity by recognizing diverse ligands, such as immune complexes and microbial surfaces, promoting phagocytosis and inflammation modulation.[65] Deficiencies in C1q, often hereditary and autosomal recessive, result in low or absent CH50 levels and predispose individuals to severe autoimmune diseases, particularly systemic lupus erythematosus (SLE)-like syndromes in over 90% of cases, alongside recurrent infections due to impaired immune complex clearance.[66] Acquired C1q deficiencies can also occur in SLE via anti-C1q autoantibodies.[67] Assays for C1q include quantitative serum immunoassays measuring protein levels (normal range: 70-140 mg/L) and functional CH50 tests, which quantify the dilution of serum required to lyse 50% of antibody-coated sheep erythrocytes, serving as a sensitive screen for classical pathway defects.[68] C1q-binding assays detect circulating immune complexes by measuring C1q precipitation, aiding diagnosis of complement-related disorders like hypocomplementemic urticarial vasculitis.[69] These tests guide management, such as immunosuppressive therapy for autoimmune manifestations or vaccination against encapsulated bacteria in deficient patients.[70] Historically in pharmacology, "CH" has abbreviated cholesterol, a sterol essential for cell membrane integrity and hormone synthesis, with notations appearing in early 20th-century medical records and lipid profiles to denote total cholesterol levels.[71] This usage facilitated monitoring in treatments for hypercholesterolemia, where drugs like bile acid sequestrants (e.g., cholestyramine, introduced in the 1950s) targeted CH reduction to prevent atherosclerosis, as evidenced in pivotal trials like the Lipid Research Clinics Coronary Primary Prevention Trial of 1984.[72] Though modern pharmacology favors "Chol" or "TC" for precision, "CH" variants persisted in abbreviated notations for cholesterol/triglyceride ratios until standardized reporting in the late 20th century.[73]Military technology
In military aviation nomenclature, particularly under the 1962 United States Tri-Service aircraft designation system, "CH" denotes a cargo helicopter designed for heavy-lift transport of troops, equipment, and supplies.[74] This prefix distinguishes such aircraft from utility (UH), attack (AH), or observation (OH) helicopters, emphasizing their role in logistical support during operations. The Boeing CH-47 Chinook exemplifies this designation as a tandem-rotor heavy-lift helicopter that entered U.S. Army service in 1962, initially as the CH-47A model.[75] Capable of transporting up to 33 troops plus three crew members or a sling-load payload of 26,000 pounds, it has been pivotal in conflicts from Vietnam to modern deployments, with variants like the CH-47F featuring upgraded avionics, digital cockpits, and enhanced engines for improved reliability.[76] Ongoing upgrades, including the CH-47F Block II recapitalization, incorporate strengthened fuselages, redesigned fuel systems, and advanced drivetrains to extend service life beyond 2025, with the U.S. Army contracting for additional units in October 2025 to bolster fleet capacity.[77][78] The "CH" prefix also appears in Chinese military designations for unmanned aerial vehicles (UAVs), such as the CH-4 Rainbow, a medium-altitude long-endurance (MALE) drone developed by the China Aerospace Science and Technology Corporation (CASC) in the early 2010s. The CH-4B variant supports reconnaissance and strike missions with a 345 kg payload across six hardpoints for air-to-ground munitions, 40-hour endurance, and a cruising altitude up to 5,000 meters, enabling persistent surveillance and precision attacks.[79] Post-2010 deployments include exports to Saudi Arabia for operations in the Yemeni Civil War starting in 2015, where CH-4s conducted armed strikes against Houthi targets, and to Iraq for counter-ISIS missions, demonstrating its role in asymmetric warfare.[80] More recently, the Democratic Republic of Congo acquired nine CH-4 units in 2023 to combat M23 rebels in eastern conflicts, highlighting its proliferation in African theaters.[81] Historically, "CH" referred to the Chain Home (CH) radar network, a British early-warning system of coastal stations developed in the late 1930s and operational by World War II.[82] These RDF (radio direction finding) installations detected incoming Luftwaffe aircraft at ranges up to 150 miles, providing critical intelligence that integrated with fighter command during the Battle of Britain in 1940, where CH signals enabled the RAF to scramble interceptors effectively and inflict decisive losses on German bombers.[83] While not involving encryption per se, CH operations employed secure radio protocols to relay detections, contributing to Allied air superiority without advanced cipher methods beyond standard signal authentication.[84]Other sciences
In physics, the Chandrasekhar limit, often denoted as M_\text{CH} in stellar evolution models, is the maximum stable mass for a white dwarf star, approximately 1.4 times the mass of the Sun (M_\odot). Beyond this limit, the degeneracy pressure of electrons can no longer support the star against gravitational collapse, leading to further evolution into a neutron star or trigger for a type Ia supernova explosion. Subrahmanyan Chandrasekhar derived this limit in the 1930s by applying special and general relativity to the equation of state for a degenerate Fermi gas of electrons, providing a cornerstone for understanding binary star systems and cosmic nucleosynthesis.[85]Places and geography
Country codes and regions
The two-letter code "CH" designates Switzerland in the ISO 3166-1 alpha-2 standard, derived from the Latin Confoederatio Helvetica, the formal name for the Swiss Confederation. This code was introduced in the initial edition of ISO 3166, published in 1974, and remains the official identifier for the country in international contexts. It is employed by the United Nations for statistical and diplomatic purposes.[86][87][88] Switzerland's 26 cantons are codified under ISO 3166-2 by appending the national "CH" prefix to a unique two-letter regional identifier, enabling granular referencing in global databases, logistics, and administrative systems. For instance, CH-ZH represents the canton of Zürich, the most populous region, while CH-GE denotes Geneva. These codes support applications such as geospatial mapping and economic reporting, ensuring consistency across borders without favoring any of Switzerland's four official languages.[89] In vehicle registration, Swiss license plates prominently feature the cantonal code—such as ZH for Zürich or VD for Vaud—followed by a serial number of up to six digits, reflecting the decentralized federal structure. To comply with international road traffic agreements like the 1968 Vienna Convention, vehicles must display a separate "CH" country emblem sticker when traveling abroad, distinguishing Swiss-registered cars from those of those of other nations. This practice underscores the code's role in mobility and trade, with approximately 6.1 million registered vehicles in Switzerland as of 2023.[90][91][92]Settlements
In the Andean highlands of Bolivia and Peru, the prefix "Ch'"—representing a glottal stop in the Aymara language—appears in numerous place names for towns and villages, often denoting qualities like clarity, purity, or natural elements central to indigenous cosmovision. For instance, Chuquisaca, the historical Quechua name for the city now known as Sucre in Bolivia's Chuquisaca Department, derives from terms meaning "silver mountain" or "headquarters of the Charcas," reflecting the region's mineral wealth and pre-colonial indigenous governance structures.[93][94] Similarly, Chucuito, a town on the shores of Lake Titicaca in southern Peru's Puno Region, serves as a key Aymara settlement, underscoring the community's enduring cultural practices tied to the lake's spiritual significance.[95] These naming conventions preserve Aymara linguistic heritage and emphasize a worldview that integrates human habitation with environmental stewardship, as seen in rituals and oral traditions passed down through generations.[96] In the United Kingdom, "CH" functions as the postcode prefix for the Chester area, encompassing much of Cheshire county in northwest England and parts of northeast Wales, with CH1 specifically designating central Chester.[97] This system originated from the national postcode initiative developed by the General Post Office in the 1950s, with initial trials launched in Norwich in 1959 to mechanize mail sorting and improve delivery efficiency amid rising postal volumes.[98] The CH codes were rolled out as part of the broader alphanumeric format introduced progressively from 1959 onward, assigning "CH" to the historic county of Cheshire based on its central sorting office in Chester, thereby facilitating organized urban and rural addressing in a region known for its medieval architecture and agricultural heritage.[99]Natural features
Ch'alla Jawira is a river in the La Paz Department of western Bolivia, serving as a right tributary of the Aqhuya Jawira, which ultimately drains into the Desaguadero River and contributes to the Lake Titicaca basin.[100] This highland river system plays a key ecological role in the Altiplano region by facilitating water flow that sustains wetlands, supports endemic fish species like the pejerrey, and enables raised-field agriculture in surrounding areas.[101] Its tributaries, including smaller streams from the Andean foothills, enhance biodiversity by providing habitats for migratory birds and amphibians adapted to intermittent flows in the semi-arid plateau. The Challenger Deep, the deepest point on Earth's seafloor, is situated at the southern end of the Mariana Trench in the western Pacific Ocean approximately 322 km southwest of Guam.[102] The site's depth measures 10,935 ± 6 meters below sea level, as determined by submersible transects conducted in 2020 and revised in a 2021 study.[103] Formed by the subduction of the Pacific Plate beneath the Mariana Plate, this hadal zone features extreme pressure, near-freezing temperatures, and complete darkness, hosting unique ecosystems with chemosynthetic bacteria and specialized invertebrates like amphipods. Exploration began with soundings by HMS Challenger in 1875, which first identified the deep as nearly 8,200 meters.[104] The first manned descent occurred in 1960 via the Bathyscaphe Trieste, reaching about 10,911 meters with Jacques Piccard and Don Walsh aboard. Subsequent expeditions include the 2012 solo submersible descent by James Cameron to 10,908 meters, and Victor Vescovo's 2019 dive to 10,927 meters using the Limiting Factor, which also collected biological samples revealing plastic pollution at hadal depths. In 2025, Japan developed an autonomous unmanned probe intended for the Challenger Deep to gather seafloor samples and assess mineral resources, marking a shift toward robotic exploration for sustained study.[105] Ch'aki Qucha comprises a series of peaks in the Potosí Range of the Andes, located in the Potosí Department of southern Bolivia near the border with Argentina. The primary summit reaches an elevation of 4,628 meters and overlooks a high-altitude lake of the same name, characteristic of glacial cirques in the region. These peaks formed through ongoing tectonic uplift driven by the subduction of the Nazca Plate under the South American Plate, a process that initiated around 200 million years ago and accelerated during the Miocene epoch about 25-10 million years ago, resulting in folded sedimentary and volcanic rocks. The geological structure includes quartzite layers and intrusive granites, contributing to the rugged terrain that influences local microclimates and supports sparse alpine vegetation such as tussock grasses and cushion plants adapted to thin soils and high winds.Other uses
Computing and internet
The .ch is the country code top-level domain (ccTLD) for Switzerland, introduced on May 20, 1987.[106] It is delegated to SWITCH, the Swiss Education and Research Network, which has managed registrations since 1990 under the technical oversight of the Internet Assigned Numbers Authority (IANA), part of ICANN.[106] As of Q3 2025, there are approximately 2.7 million active .ch domains, reflecting steady growth driven by Switzerland's digital economy and international business presence.[107] In programming contexts, "ch" refers to the Ch shell, an embeddable interpreter for C and C++ that supports interactive execution and scripting on Linux and other Unix-like systems. The "ch" command launches this environment, allowing users to run C code as shell scripts or interactively, combining the power of C with shell-like utilities for tasks such as numerical computing and system automation. Basic syntax isch [options] [file], where common options include -d for debugging mode, -l to load libraries, and -s for safe execution without file I/O; for example, ch -d script.c executes a C script with debugging enabled.[108]
Chameleon hash (CH) functions are trapdoor-based cryptographic primitives that enable collision generation with a secret key while remaining collision-resistant otherwise, finding key applications in blockchain for features like redactable transactions and privacy-preserving commitments. Originally proposed by Krawczyk and Rabin in 2000, post-2020 advancements include lattice-based constructions for post-quantum resistance, such as those achieving full collision resistance from simpler assumptions, and policy-based variants that allow fine-grained control over hash rewriting in decentralized ledgers. These developments enhance blockchain scalability and compliance, as seen in frameworks for dynamic redaction without consensus forks.[109]