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Segment

A segment is a portion or section of a whole, often used in geometry, biology, linguistics, and other fields to describe divided parts of a structure or concept. The term has various specific meanings depending on the context, including in business and technology. For other uses, see the sections below on geometry, biology, linguistics, computing and communications, business and economics, and other fields.

Geometry

Line segment

In Euclidean geometry, a line segment is the finite portion of a straight line connecting two distinct points, known as its endpoints, and comprising all points on the line between them inclusive. It represents the shortest path between these endpoints. This concept is rooted in Euclid's Elements, where the first postulate states that a straight line segment can be drawn joining any two points, ensuring the existence and uniqueness of such a connection in the plane. Euclid described a line as "breadthless length," with the segment denoting its bounded extent between points.^[1]^[2] Line segments possess a finite length and are conventionally denoted by their endpoints, such as \overline{AB}. In the coordinate plane, the length of a line segment joining points (x_1, y_1) and (x_2, y_2) is computed via the distance formula, derived from the Pythagorean theorem:

d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}.

The midpoint M of the segment, which divides it into two equal parts, is found using the formula

M = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right).

These properties enable precise measurement and division of segments in geometric figures.^[3] Line segments form the foundational elements in geometric constructions, such as drawing figures with straightedge and compass, and in proofs of figure congruence. They are central to triangle congruence criteria, including SSS (side-side-side), which requires three pairs of corresponding line segments to be equal in length, and SAS (side-angle-side), which specifies two equal adjacent sides enclosing a congruent angle. Additionally, line segments underpin vector representations and coordinate systems, where they quantify displacements between points. The concept of the line segment originated in Euclidean geometry around 300 BCE, as systematized in Euclid's Elements, which established it as a primitive building block for plane geometry.

Circular segment

A circular segment is the region of a disk bounded by a chord and the arc subtended by that chord on the circumference of the circle. It is typically defined for the smaller portion when the central angle is less than 180 degrees (π radians), distinguishing it from the full disk or semicircle.^[4] Circular segments are classified into two types based on the central angle θ subtended by the chord at the circle's center: a minor segment where θ < π (less than a semicircle), and a major segment where θ > π (greater than a semicircle, encompassing the larger portion of the disk). The formulas below apply primarily to the minor segment; for the major segment, the area is obtained by subtracting the minor segment area from the full circle area πr².^[4] The area A of a circular segment is given by
A = \frac{r^2}{2} (\theta - \sin \theta),
where r is the radius of the circle and θ is the central angle in radians. The height (sagitta) h of the segment, measured from the chord to the arc's midpoint, is
h = r \left(1 - \cos \frac{\theta}{2}\right).
The chord length c is
c = 2 r \sin \frac{\theta}{2}. ^[4] This area formula is derived by subtracting the area of the isosceles triangle formed by the two radii to the chord endpoints from the area of the circular sector bounded by the arc and the two radii. The sector area is \frac{1}{2} r^2 \theta, and the triangle area is \frac{1}{2} r^2 \sin \theta, yielding the segment area as their difference.^[4] In engineering, circular segments are applied to calculate areas in designs involving curved boundaries, such as lenses in optical systems and dome sections in architectural structures. They also facilitate computations for fluid volumes in partially filled cylindrical tanks, where the segment height corresponds to the liquid level.^[5]

Polyhedral segment

A portion of a polyhedron cut off by a plane, sometimes referred to as a polyhedral segment or cap, is the smaller solid bounded by the cutting plane and parts of the original faces. When the cutting plane is parallel to the base, this is specifically known as a frustum. The intersection forms a polygonal base, and the resulting figure has modified faces, edges, and vertices.^[6] The properties include truncated faces where the plane intersects, with the new face being a polygon from the intersection lines. Non-intersected faces remain if they bound the segment. The resulting solid retains convexity if the original polyhedron is convex. The volume can be computed using Cavalieri's principle, by decomposition into simpler shapes like pyramids or tetrahedra, or by numerical integration of cross-sections. For a frustum of a pyramid with height h, parallel bases of areas A_1 and A_2, the volume V is

V = \frac{1}{3} h (A_1 + A_2 + \sqrt{A_1 A_2}).

This formula applies to pyramidal frustums with any polygonal bases. For non-parallel cuts, the resulting irregular polyhedron requires more general methods.^[6] Such cut portions, exemplified by pyramidal frustums, are used in architecture for truncated forms enhancing stability and aesthetics, such as the modular frustum clusters atop the Restaurant of Metasequoia Grove in Suzhou, China, inspired by tree forms for shaded canopies. In 3D modeling and computer-aided design, plane clipping generates these segments for complex polyhedra in simulations and manufacturing.^[7]

Biology

Animal body segmentation

Animal body segmentation, also known as metamerism, is a fundamental biological process in which the body of certain animals is divided into a linear series of repeating units called somites or metameres, both externally and internally. This serial repetition of body parts enables greater flexibility in movement and allows for the specialization of segments for different functions, such as locomotion, reproduction, or excretion. Metamerism is particularly prominent in three major animal phyla: Annelida, Arthropoda, and Chordata, where it contributes to diverse body plans adapted to various environments.^[8]^[9] In annelids, such as earthworms, the body typically consists of approximately 100 segments, each containing repeated structures like coelomic compartments, nephridia for excretion, and sets of circular and longitudinal muscles that facilitate burrowing and peristaltic movement. Arthropods exhibit segmentation in their exoskeleton and appendages, with insects displaying a modified form called tagmosis, where segments fuse into functional regions like the head, thorax, and abdomen to support specialized activities such as flight and feeding. In chordates, including vertebrates, segmentation manifests in the formation of somites during embryonic development, which give rise to vertebral columns, ribs, and muscle blocks, enabling coordinated swimming or walking through vertebral flexibility.^[8]^[9]^[10] The development of body segmentation is tightly regulated by genetic mechanisms, including Hox genes, which establish the anterior-posterior identity of each segment by activating specific transcription factors in precise domains along the body axis. In vertebrates, somitogenesis—the process of somite formation—is further governed by a "segmentation clock," an oscillating network of gene expression involving genes like hairy and enhancer of split (Hes), which creates rhythmic waves in the presomitic mesoderm to ensure sequential segment addition at regular intervals. These molecular controls link segmentation to overall body patterning, with disruptions leading to congenital defects like scoliosis.^[11]^[12]^[13] Evolutionarily, metamerism provides key advantages, including enhanced locomotion through independent segment movement and muscle coordination, which improves efficiency in crawling, swimming, or flying compared to non-segmented bodies. It also promotes organ specialization, as seen in annelids where each segment houses a nephridium for localized waste removal, increasing resilience to injury since damage to one segment does not compromise the entire organism. This body plan first emerged during the Cambrian period around 540 million years ago, as evidenced by fossilized annelids and early arthropod-like forms in deposits like the Burgess Shale, potentially contributing to the diversification during the Cambrian explosion by enabling more complex and adaptable morphologies.^[14]^[15]^[16]

Plant anatomy segments

In plant anatomy, segments primarily refer to internodes, which are the elongated regions of stems located between successive nodes, where leaves, buds, or branches attach.^[17] These internodes form the structural backbone of shoots, varying in length and girth to support growth and environmental adaptation. Phyllotactic arrangements further define segments by organizing the angular positioning of leaves or other appendages around the stem axis, influencing overall plant architecture.^[18] Examples of segmentation differ across plant types; in monocot stems, vascular bundles—comprising xylem and phloem for water and nutrient transport—are scattered diffusely throughout the internodal segments, providing uniform support.^[19] In contrast, dicot stems feature vascular bundles arranged in a distinct ring within the segments, enclosed by a cambium layer that enables secondary thickening.^[19] Rhizomes, underground horizontal stems, exhibit similar segmentation with nodes and internodes that produce adventitious roots and shoots, facilitating clonal spread in species like ginger or irises.^[20] These segments play key functional roles in plant development, including the mediation of apical dominance, where auxins produced at the shoot tip are transported downward through the internodes in a polar manner, inhibiting lateral bud outgrowth to prioritize vertical growth.^[21] Auxin gradients along segments also coordinate hormone signaling for cell elongation and vascular differentiation, supporting modular growth that allows plants to respond to environmental cues by branching or elongating specific internodes.^[22] In reproduction, stem segments enable vegetative propagation; cuttings from internodes with nodes are rooted to generate genetically identical plants, a method widely used in horticulture for species like roses or sugarcane.^[23] A notable aspect of plant segmentation is the prevalence of phyllotaxy patterns, such as Fibonacci spirals, where leaves emerge at angles approximating the golden ratio (approximately 137.5 degrees), optimizing space utilization and sunlight capture in species like sunflowers or pinecones.^[24] This mathematical arrangement minimizes shading and maximizes photosynthetic efficiency across successive leaf segments.^[24]

Cellular and molecular segments

In biology, cellular and molecular segments refer to the partitioning of cells or genetic material into discrete, functional units that enable organized development, replication, and inheritance across organisms. At the cellular level, segmentation manifests during processes such as the cell cycle phases, where mitosis divides the cell into daughter units, or in early embryogenesis through cleavage, which rapidly partitions the zygote into blastomeres without net growth.^[25] At the molecular level, DNA is segmented into functional regions, including chromosome arms, regulatory elements, and protective caps like telomeres, which consist of repetitive nucleotide sequences (e.g., TTAGGG in humans) that safeguard linear chromosome ends from degradation and fusion.^[26] Key examples of molecular segmentation include DNA segments in genetic recombination, where homologous chromosomes exchange material via Holliday junctions—four-way branched DNA intermediates formed during meiotic crossing over. These structures, first proposed in 1964 but structurally characterized in the 1980s, facilitate precise genetic diversity by resolving into crossover or non-crossover products.^[27] In cellular contexts, segmentation is evident in embryogenesis cleavage stages, where the fertilized egg undergoes successive mitotic divisions to form a multicellular blastula; for instance, in mammals, this progresses from a 2-cell to an 8- to 16-cell morula within days, establishing foundational tissue layers.^[25] Mechanisms underlying these segments often involve gene regulatory networks and structural proteins. In Drosophila embryogenesis, pair-rule genes such as even-skipped and fushi tarazu orchestrate molecular segmentation by activating in seven stripes along the anterior-posterior axis, subdividing the embryo into double-segment primordia; these genes were identified through saturation mutagenesis screens in the early 1980s, revealing their role in translating maternal gradients into periodic patterns.^[28] Telomere segments, maintained by the enzyme telomerase, prevent end-to-end chromosome fusions; telomerase adds repetitive sequences to maintain telomere length, a process discovered in the 1980s when reverse transcriptase activity was identified in Tetrahymena extracts.^[26] These concepts advanced significantly in the 1980s through molecular biology techniques like DNA sequencing and gel electrophoresis, which enabled the visualization and manipulation of genetic segments.^[29] In biotechnology applications, such as CRISPR-Cas9 gene editing, specific DNA segments are targeted for precise cuts or insertions; the Cas9 nuclease, guided by RNA, binds and cleaves user-defined sequences, revolutionizing therapies for genetic disorders by enabling segmental modifications with high fidelity.^[30]

Linguistics

Phonological segments

In phonology, segments are defined as the smallest discrete units of sound structure within a language, primarily consisting of consonants and vowels that function as phonemes to distinguish meaning.^[31] These units form the building blocks of words and are analyzed through their sequential organization into larger structures such as syllables, where consonants typically occupy margins and vowels form nuclei.^[32] For instance, the English word "cat" is transcribed in the International Phonetic Alphabet (IPA) as /kæt/, comprising three distinct segments: the velar stop /k/, the low front vowel /æ/, and the alveolar stop /t/.^[33] Key properties of phonological segments include articulatory and acoustic features, such as place and manner of articulation, voicing, and nasality, which allow segments to be systematically described and contrasted.^[34] Segmental phonology, the branch focused on these units, contrasts with suprasegmental phonology, which examines features like stress, tone, and intonation that extend across multiple segments to influence rhythm and prosody.^[35] In suprasegmental analysis, for example, primary stress in English words like "record" (as a noun /ˈrɛk.ɔɹd/ versus verb /rɪˈkɔɹd/) alters emphasis without changing the underlying segments.^[33] A foundational theory of segments arises in generative phonology, as developed by Noam Chomsky and Morris Halle in their 1968 work The Sound Pattern of English, where segments are decomposed into binary distinctive features—such as [+consonantal] or [-nasal]—that capture universal patterns of sound distribution and rules of alternation.^[34] These features enable predictive models of phonological processes, emphasizing how abstract representations underlie surface forms across languages. Importantly, phonological segments are abstract mental constructs rather than direct physical sounds, as actual speech production involves continuous acoustic variation that linguists idealize into discrete units for analysis.^[36]

Segmentation in syntax

In syntax, segmentation refers to the division of linguistic units into discrete, meaningful components such as morphemes, phrases, and clauses, which function as the foundational building blocks for constructing sentences and conveying grammatical relations. This concept underscores how syntax organizes smaller units hierarchically to form larger structures, ensuring coherence and interpretability in language. The approach originated in structural linguistics, where Leonard Bloomfield's seminal 1933 work emphasized empirical analysis of form and arrangement in grammar, treating syntax as the ordering of linguistic forms into sequences.^[37] Bloomfield's framework laid the groundwork by distinguishing syntax from morphology and phonology, focusing on how forms combine to create meaningful expressions.^[38] A key example of segmentation is word segmentation in languages without orthographic word boundaries, such as Chinese, where continuous strings of characters must be parsed into morphemes and words to reveal syntactic roles; for instance, the sequence "北京大学" (Běijīng dàxué) is segmented into "北京" (Beijing, a noun phrase) and "大学" (university, a noun) to form a proper noun denoting Peking University.^[39] Another illustrative tool is the phrase structure tree, a diagrammatic representation that depicts the hierarchical segmentation of sentences into constituents; in the English sentence "The cat sleeps," the tree branches from the sentence (S) node to a noun phrase (NP: "The cat") and verb phrase (VP: "sleeps"), clarifying embedding and dominance relations among segments.^[40] Central to modern syntactic theory is X-bar theory, which formalizes segmentation by proposing a universal template for phrases across categories, where each phrase (XP) includes a head (X), an optional complement forming the intermediate projection (X'), and an optional specifier; for example, in the noun phrase "the big house," "house" is the head (N), "big" the specifier (adjunct), and the structure projects to NP.^[41] Developed by Ray Jackendoff in 1977 as an extension of Noam Chomsky's earlier ideas, X-bar theory captures endocentricity—the idea that phrases are projections of their heads—and accounts for cross-linguistic consistencies in how segments like specifiers and complements integrate.^[42] This theory highlights segments as relational nodes in syntactic trees, enabling precise modeling of phrase-internal organization. Segmentation plays a pivotal role in natural language processing (NLP), particularly in syntactic parsing algorithms that segment input text into parse trees to facilitate downstream tasks like semantic analysis and machine translation; for example, dependency parsers identify morpheme-to-phrase relations to resolve ambiguities in sentences.^[43] In computational models, such as those using probabilistic context-free grammars, accurate segmentation improves parsing accuracy.^[44] These applications extend Bloomfield's structural insights into automated systems, bridging theoretical syntax with practical language technologies.

Computing and communications

Memory segments

In computer architecture, memory segmentation refers to a memory management technique that divides the physical or virtual memory into variable-sized, logical units called segments, each serving a specific purpose such as code, data, or stack. This approach allows for efficient organization of programs by grouping related information together, facilitating relocation and protection without requiring fixed-size allocations. Segments are particularly prominent in the x86 architecture, where they enable addressing a larger memory space than the register width would otherwise permit.^[45] The concept of memory segmentation was introduced with the Intel 8086 microprocessor in 1978, which used a 20-bit address bus to access 1 MB of memory despite 16-bit registers, by employing segment registers to form effective addresses as segment base plus offset. Over time, segmentation evolved in subsequent x86 processors, incorporating protected mode in the Intel 80286 (1982) for enhanced features like descriptor tables, and further refined in IA-32 and Intel 64 architectures to support both segmented and flat memory models. Modern operating systems, such as Windows and Linux, predominantly utilize a flat memory model with paging for simplicity, relegating segmentation primarily to compatibility and specific protection mechanisms.^[46]^[45] Mechanisms for segmentation in x86 include six segment registers—CS (code segment), DS (data segment), SS (stack segment), ES (extra segment), FS, and GS—which hold selectors indexing into descriptor tables like the Global Descriptor Table (GDT) or Local Descriptor Table (LDT). Addressing combines a segment base address with an offset to compute the linear address, while protection is enforced through segment descriptors specifying attributes such as size (limit), access rights (read/write/execute), and privilege levels to prevent unauthorized access. This base-limit checking and descriptor-based validation provide isolation between segments, supporting multitasking by restricting code execution or data modification.^[45] Key advantages of memory segmentation include improved isolation for security and fault tolerance, as segments can be relocated independently without affecting others, and reduced internal fragmentation by allowing variable sizes tailored to program needs. However, it introduces drawbacks such as external fragmentation, where free memory holes become unusable due to size mismatches, and overhead from managing descriptor tables and handling protection violations, often manifesting as general protection faults in x86 systems.^[47] A representative example in x86 is the code segment, loaded into the CS register, which holds executable instructions and is typically marked read-only or execute-only to protect against self-modification; conversely, the data segment in the DS register stores variables and global data, permitting read-write access for program operations.^[45]

Network segments

Network segments refer to isolated portions of a computer network designed to manage traffic flow and enhance security by dividing the overall infrastructure into smaller, controlled subnetworks. These segments are typically created using devices such as bridges, routers, or virtual local area networks (VLANs), which limit the scope of communication and prevent unrestricted data propagation across the entire network.^[48] Two primary types of network segments are collision domains and broadcast domains. A collision domain, often synonymous with an Ethernet segment, is a network section where data packets from multiple devices can collide if transmitted simultaneously, leading to retransmissions and potential performance degradation. In contrast, a broadcast domain encompasses the portion of the network where broadcast messages—intended for all devices—are forwarded, which can cause unnecessary traffic if not properly segmented.^[49]^[50] Key protocols facilitate segmentation in local area networks (LANs). Carrier Sense Multiple Access with Collision Detection (CSMA/CD) governs access in traditional Ethernet segments by allowing devices to listen before transmitting and detect collisions within a collision domain, thereby minimizing interference in shared media environments. For broader internetworking, subnetting using Classless Inter-Domain Routing (CIDR) divides IP networks into smaller subnets; for example, a /24 subnet mask (255.255.255.0) allocates 256 addresses, with 254 usable for hosts, enabling efficient traffic isolation.^[51]^[52] Segmentation provides significant benefits, including reduced network congestion by localizing traffic to specific segments and improved security through mechanisms like firewalls placed between segments to block unauthorized access or contain threats. By limiting the lateral movement of malware or attackers, it shrinks the effective attack surface while optimizing overall performance.^[53]^[54] The concept of network segments originated in the ARPANET era of the 1970s, where early packet-switched networks demonstrated the value of dividing communications for reliability, and was later standardized through IEEE 802 protocols in the 1980s for local area networking.^[55]^[56]

Business and economics

Market segmentation

Market segmentation is the process of dividing a heterogeneous market into smaller, homogeneous subsets of consumers or businesses based on shared characteristics, such as needs, preferences, or behaviors, to enable more effective marketing strategies.^[57] This approach allows companies to identify distinct groups and tailor products, pricing, promotion, and distribution accordingly. The concept was formally introduced by Wendell R. Smith in 1956, who defined it as "viewing a heterogeneous market [as] a number of smaller homogeneous markets, in response to differing product preferences and buying rates or rates of usage."^[58] A key framework for applying market segmentation is the STP model, which stands for Segmentation, Targeting, and Positioning. Segmentation divides the market using variables including demographics (e.g., age, income, gender), psychographics (e.g., lifestyles, attitudes, values), behavioral factors (e.g., purchase frequency, brand loyalty), and geographic elements (e.g., region, climate).^[59] Targeting then evaluates these segments for viability based on size, accessibility, and profitability, selecting the most attractive ones. Positioning involves creating a distinct image or value proposition for the chosen segments through customized marketing mixes.^[59] Prominent models for segmentation include the VALS (Values and Lifestyles) framework, developed by SRI International in 1978, which categorizes consumers into eight psychographic types based on primary motivations (e.g., ideals, achievement, self-expression) and resource levels (e.g., income, education).^[60] Another widely used method is cluster analysis, a statistical technique that groups similar data points—such as customer profiles—into clusters by minimizing intra-group variance and maximizing inter-group differences, often applied in data-driven segmentation to uncover hidden patterns.^[61] The primary benefits of market segmentation include more precise targeting, which enhances customer satisfaction and loyalty through personalized offerings, and improved return on investment (ROI) by reducing wasted marketing spend on irrelevant audiences.^[62] For instance, Nike employs psychographic segmentation to differentiate between athletic performance-oriented consumers seeking high-functionality gear and lifestyle segments preferring athleisure for casual, fashion-driven use, enabling targeted campaigns that boost engagement and sales efficiency.^[63] Overall, segmentation supports higher conversion rates and competitive advantage by aligning resources with specific consumer needs.^[62]

Financial segments

In financial reporting, segments refer to distinct components of a business entity that generate their own revenues and expenses, allowing for separate identification and evaluation of operational performance. Under International Financial Reporting Standards (IFRS) 8, an operating segment is defined as a component of an entity that engages in business activities from which it may earn revenues and incur expenses, whose operating results are regularly reviewed by the entity's chief operating decision maker (CODM) to make decisions about resources and assess performance, and for which discrete financial information is available.^[64] Similarly, the U.S. Financial Accounting Standards Board (FASB) under Accounting Standards Codification (ASC) 280 requires public entities to report information about their operating segments, which are components about which separate financial information is available and evaluated regularly by the CODM.^[65] The identification of reportable segments is guided by specific criteria to ensure materiality and relevance. Quantitatively, a segment is considered reportable if it meets the 10% threshold test, meaning its reported revenue (internal and external) is at least 10% of the combined revenue of all operating segments, or its profit or loss is 10% of the greater of the combined reported profit of all profitable segments or the combined reported loss of all loss-making segments, or its assets are 10% of the combined assets of all operating segments.^[65]^[64] Qualitatively, segments must also consider whether they involve different products, services, or geographic areas that expose the entity to distinct risks and returns, even if they do not meet the numerical thresholds; if the total external revenue of non-reportable segments exceeds 75% of the entity's total revenue, additional segments must be identified until this threshold is met.^[65]^[64] For reporting purposes, entities disclose segment-specific information including revenues, profit or loss measures (such as segment margins), assets, liabilities, and other key metrics like capital expenditures and depreciation, often reconciled to the consolidated financial statements. As amended by FASB ASU 2023-07 (effective for fiscal years beginning after December 15, 2023), ASC 280 also requires disclosure of significant segment expenses regularly provided to the CODM and an explanation of how the CODM uses the information to assess performance and allocate resources.^[66] For example, General Electric (GE) historically reported distinct segments for aviation (including jet engines and aftermarket services) and healthcare (encompassing medical imaging and diagnostics), highlighting how aviation generated higher margins from long-term service contracts compared to healthcare's reliance on equipment sales. This granular disclosure enables stakeholders to assess the performance and risks of individual business units without aggregating dissimilar operations. The primary purpose of financial segment reporting is to enhance investor transparency by providing insights into the composition of earnings and the allocation of resources across diverse operations, facilitating better performance evaluation and strategic decision-making. Post-Enron scandals in the early 2000s, regulatory reforms such as the Sarbanes-Oxley Act of 2002 in the U.S. mandated more robust segment disclosures to prevent opaque financial reporting and restore public trust in corporate governance.

Other fields

Road and transportation segments

In transportation engineering, segments refer to linear divisions of infrastructure such as roads, rail tracks, or airways, delineated based on factors like design specifications, operational functions, or jurisdictional boundaries to facilitate analysis, maintenance, and safety management.^[67] These divisions allow for standardized treatment of homogeneous sections, where characteristics like geometry, traffic volume, or environmental conditions remain consistent within each segment. For instance, road segments are typically bounded by intersections, changes in alignment, or control devices, enabling precise evaluation of performance metrics.^[68] Common types of transportation segments include highway segments, which encompass sections of interstates or freeways defined by uniform design elements such as lane configuration or speed limits; rail segments, often classified by track conditions and load capacities that dictate maximum train speeds; and flight segments in aviation, representing point-to-point portions of a route between airports or waypoints.^[68]^[69]^[70] Highway examples include basic freeway segments without access points and weaving areas near ramps, while rail segments may be restricted to 286,000-pound car capacities on certain tracks.^[71] Flight segments, by contrast, focus on non-stop operational units, such as takeoff to cruise phases.^[72] Standards for these segments are established by organizations like the American Association of State Highway and Transportation Officials (AASHTO), which provides guidelines in its Policy on Geometric Design of Highways and Streets (commonly called the Green Book) for defining segment lengths based on sight distance, curvature, and superelevation to ensure safe vehicle operation.^[73] For highway segments, AASHTO recommends minimum lengths for passing zones of 400 feet and advises limiting homogeneous segments to at least 0.10 miles to reduce analysis errors in safety assessments.^[74]^[75] Signage standards, also per AASHTO and the Manual on Uniform Traffic Control Devices (MUTCD), require clear delineation at segment transitions, such as curve warnings or lane drops, to maintain driver expectancy.^[76] Rail segments follow Federal Railroad Administration (FRA) track classifications for speed and safety, while aviation segments adhere to International Civil Aviation Organization (ICAO) protocols for waypoint-based routing.^[77] These segments are applied in traffic modeling to simulate flow dynamics, predict congestion, and evaluate infrastructure capacity, as seen in network-level analyses where segment-level data informs demand forecasting.^[78] In maintenance scheduling, segments enable targeted interventions, such as pavement upgrades timed to minimize user delays, optimizing life-cycle costs across networks like Interstate 95 (I-95), where the North Carolina segment—spanning over 180 miles from Virginia to South Carolina—undergoes periodic resurfacing based on condition assessments.^[79] For rail and air, segment-based scheduling supports predictive maintenance on tracks or aircraft routing to avoid overload.^[80] Safety considerations for segments emphasize location-specific hazards, with road curves and intersections posing elevated risks due to reduced sight distances and higher crash frequencies; for example, horizontal curves account for a disproportionate share of run-off-road incidents, mitigated by high-friction surface treatments.^[76]^[81] Intersections on curved segments amplify collision probabilities, particularly single-vehicle crashes on rural highways.^[82] Rail segments face derailment risks from track defects or misalignments, while flight segments during climb phases are vulnerable to engine-out scenarios, requiring adherence to minimum climb gradients for obstacle clearance.^[83]^[84]

Medical anatomy segments

In medical anatomy, segments refer to functional divisions within organs that are defined by their vascular, biliary, or bronchial supply, allowing for independent perfusion and enabling precise surgical interventions. These divisions facilitate the understanding of organ architecture and are crucial for procedures like resections in oncology and transplantation. The concept emphasizes how organs are compartmentalized into self-contained units that can be isolated without compromising the function of adjacent areas.^[85] A prominent example is the liver, where the Couinaud classification divides the organ into eight segments based on the branching patterns of the portal vein, hepatic veins, and bile ducts. Established by French anatomist Claude Couinaud in his 1957 publication Le Foie: Études Anatomiques et Chirurgicales, this system identifies segments I through VIII, with segment I corresponding to the caudate lobe and the others arranged around the principal hepatic veins. This classification is widely used in hepatic surgery to guide resections, such as in hepatocellular carcinoma, where removing a single segment preserves maximal liver function.^[86]^[87] In the lungs, bronchopulmonary segments represent another key anatomical division, with each segment supplied by a tertiary bronchus, segmental pulmonary artery, and vein, forming pyramidal units that are aerated and perfused independently. The right lung typically comprises 10 such segments (three in the upper lobe, two in the middle lobe, and five in the lower lobe), while the left lung has eight to nine (four in the upper lobe and four to five in the lower lobe, due to the absence of a middle lobe). These segments are clinically significant in procedures like segmentectomy, a parenchyma-sparing surgery for early-stage non-small cell lung cancer, which offers comparable oncologic outcomes to lobectomy while preserving pulmonary reserve, particularly in patients with limited lung function.^[88]^[89] Spinal segments, associated with dermatomes, delineate areas of skin innervated by specific spinal nerves originating from the 31 pairs of spinal cord segments (eight cervical, 12 thoracic, five lumbar, five sacral, and one coccygeal). Each dermatome receives sensory input from the dorsal root of a single spinal nerve, forming a predictable map used to localize neurological deficits, such as in herpes zoster or nerve root compression. These segments arise embryonically from somites, paired blocks of paraxial mesoderm that segment sequentially along the neural tube starting around the third week of gestation; the somites differentiate into sclerotomes (forming vertebrae), myotomes (muscles), and dermatomes (skin), establishing the metameric pattern of the spine and its sensory distribution.^[85]^[90] Clinically, anatomical segmentation across organs supports advanced imaging techniques like computed tomography (CT) and magnetic resonance imaging (MRI), which delineate boundaries for targeted therapies, and underscores the rationale for segment-specific interventions to minimize morbidity in conditions like tumors or infections.^[87]^[89]

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Segmentation divides a computer network into smaller parts. The purpose is to improve network performance and security.
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