HD
Huntington's disease (HD) is a progressive, inherited neurodegenerative disorder caused by an autosomal dominant mutation consisting of an expanded CAG trinucleotide repeat in the HTT gene on chromosome 4, which encodes the huntingtin protein and leads to the gradual degeneration of neurons in the brain, particularly in the striatum.[1][2][3] The condition typically manifests between ages 30 and 50, though juvenile forms exist, and is characterized by a triad of motor dysfunction (including chorea, or involuntary jerking movements), cognitive impairment (such as executive dysfunction and memory loss), and psychiatric symptoms (ranging from depression to irritability and psychosis).[4][5] With no cure available, HD inexorably progresses over 15–20 years to severe disability and death, often from complications like pneumonia or aspiration; its prevalence is estimated at 5–10 cases per 100,000 individuals worldwide, with genetic penetrance approaching 100% for repeat expansions exceeding 40 CAG units.[2][6] Diagnosis relies on clinical evaluation, family history, and confirmatory genetic testing, while management focuses on symptomatic relief through medications like tetrabenazine for chorea and supportive therapies, amid ongoing research into gene silencing and neuroprotective strategies.[7][8] Controversies surround predictive testing due to the absence of preventive treatments and ethical implications of knowing one's fate, with some affected individuals advocating for expanded access to euthanasia in jurisdictions where it is permitted, highlighting tensions between autonomy and the disease's deterministic progression.[9]Technology and media
High-definition video and television
High-definition (HD) video encompasses display and recording formats that provide substantially greater resolution than standard-definition (SD) television, which typically operates at 720x480 or 480i pixels. Common HD resolutions include 720p at 1280x720 pixels and 1080p or 1080i at 1920x1080 pixels, enabling sharper images with more detail due to increased pixel density and often a 16:9 aspect ratio.[10][11] These standards support progressive (p) or interlaced (i) scanning, with progressive offering smoother motion for video playback.[12] The development of HD video traces back to analog experiments in the 1960s by Japan's NHK, which pioneered systems like MUSE for high-resolution broadcasting. Digital HDTV advanced significantly with a fully integrated prototype demonstrated on March 30, 1995, by SRI International, paving the way for standards like ATSC in the US. Consumer HDTV sets first appeared in 1998 from manufacturers such as Panasonic and Sony, with adoption accelerating in the early 2000s as broadcasters transitioned from analog NTSC signals.[12][13][14] A key milestone in HD media distribution was the 2006-2008 format war between HD DVD (backed by Toshiba and supporting up to 30 GB per layer) and Blu-ray Disc (championed by Sony, with higher capacities up to 50 GB). The competition ended on February 19, 2008, when Toshiba announced cessation of HD DVD production, allowing Blu-ray to emerge as the dominant optical format for HD content delivery.[15][16] As of 2025, HD remains a foundational standard in broadcasting and streaming, serving as the baseline for "high-definition" content distinct from SD, even as 4K (3840x2160) and 8K (7680x4320) proliferate for premium applications requiring higher bandwidth—typically 25 Mbps or more for 4K versus less for 1080p. Many platforms, including live TV and on-demand services, default to HD for compatibility with legacy devices and to optimize data usage, with HD comprising a significant portion of non-UHD streams due to its balance of quality and efficiency.[17][18][19]Hard disk drive
A hard disk drive (HDD) is an electromechanical device for storing and retrieving digital data using magnetic storage on one or more rapidly rotating circular platters coated with ferromagnetic material.[20] The platters, typically made of aluminum or glass substrates, spin at speeds ranging from 5,400 to 15,000 revolutions per minute, while actuator arms position read/write heads to access data sectors without physical contact, relying on air-bearing surfaces for proximity.[21] This design enables random access to data, distinguishing HDDs from sequential tape storage, though mechanical components introduce latency, vibration sensitivity, and wear over time.[20] The first commercial HDD, the IBM 350 Disk Storage Unit, debuted in 1956 as part of the IBM 305 RAMAC system, offering 3.75 to 5 megabytes of capacity across 50 platters each 24 inches in diameter, with the entire unit weighing over a ton and consuming significant power.[20] [21] Subsequent innovations reduced form factors and boosted areal density through advances like thin-film heads in the 1980s and perpendicular magnetic recording in the 2000s, driving exponential capacity growth: from tens of megabytes in the 1970s to gigabyte-scale drives in personal computers by the 1990s, and terabyte drives becoming standard by the late 2000s.[22] By 2025, enterprise HDDs routinely exceed 20 terabytes per drive, incorporating technologies such as helium sealing for lower friction and higher platter counts, and shingled magnetic recording for denser packing.[23] Reliability metrics from large-scale deployments, such as Backblaze's data centers, indicate annualized failure rates (AFR) averaging 1.4% in 2024 across hundreds of thousands of drives, with variations by model and age—newer high-capacity models often showing lower rates under 1%, while older or mid-capacity units approach 2-3%.[24] [25] These rates reflect improvements in materials and error-correcting codes but highlight ongoing risks from mechanical failure, head crashes, and thermal issues, prompting redundancy practices like RAID arrays in critical applications.[24] Although solid-state drives (SSDs) have supplanted HDDs in consumer and performance-critical roles due to faster access times and shock resistance, HDDs persist in enterprise and data center settings for economical bulk storage, where cost per gigabyte remains 4-5 times lower than SSDs as of 2025.[26] [27] Hyperscale providers allocate nearly 80% of capacity to HDDs for archival and cold data tiers through at least 2028, often in hybrid systems pairing HDD arrays with SSD caches to balance cost, capacity, and speed.[28] Emerging hybrid HDD variants integrate small NAND flash caches for frequently accessed data, extending the technology's viability amid SSD price declines.[26]Medicine and biology
Huntington's disease
Huntington's disease (HD) is a progressive, autosomal dominant neurodegenerative disorder caused by an expanded CAG trinucleotide repeat in the HTT gene on the short arm of chromosome 4.[2] The mutation involves 36 or more CAG repeats, with normal alleles containing 10 to 35 repeats; repeats of 36 to 39 confer reduced penetrance, while 40 or more lead to full penetrance and inevitable disease manifestation.[29] Longer repeat lengths inversely correlate with age of onset, accelerating progression in juvenile cases (over 60 repeats, onset before age 20).[2] Symptoms typically emerge between ages 30 and 50, with a mean onset of 35 to 44 years, beginning with subtle motor abnormalities like chorea—involuntary, jerky movements—followed by cognitive decline, including executive dysfunction and memory loss, and psychiatric features such as depression, irritability, or psychosis.[2] Disease duration averages 15 to 20 years from symptom onset, culminating in severe motor impairment, dementia, and death often from secondary complications like aspiration pneumonia or infection, independent of repeat length once onset occurs.[30] Prevalence estimates range from 4 to 15 per 100,000 individuals of European descent, with lower rates in Asian and African populations, though underascertainment may inflate true figures due to undiagnosed cases with 36+ repeats.[31] Diagnosis relies on genetic testing confirming expanded CAG repeats, alongside clinical evaluation, as neuroimaging shows striatal atrophy but lacks specificity.[2] No disease-modifying treatments exist, with management limited to symptomatic relief; the FDA approved tetrabenazine in 2008 as the first agent for chorea, a vesicular monoamine transporter 2 inhibitor that depletes dopamine but carries risks of depression and parkinsonism.[32] Subsequent approvals include deutetrabenazine (2017) and valbenazine for chorea, alongside antipsychotics for behavioral symptoms and antidepressants for mood disorders, though evidence for neuroprotection remains absent.[7] Research into causal interventions targeting mutant huntingtin has yielded setbacks, exemplified by Roche's tominersen, an antisense oligonucleotide that reduced protein levels but failed to demonstrate clinical benefit in the Phase III GENERATION-HD1 trial, leading to its halt in 2021; a follow-up HD2 trial testing higher doses continues as of 2025, with completion expected in 2026.[33] Alternative approaches, such as uniQure's AMT-130 AAV-delivered RNAi gene therapy, advanced to Phase I/II in 2025 showing potential HTT lowering but require invasive intracisternal delivery and long-term safety data, with no approval yet despite slowing claims in early readouts.[34] Phase III trials of pridopidine, a sigma-1 agonist aimed at neuroprotection, reported in 2025 no significant functional improvement over placebo in early manifest HD, underscoring persistent challenges in translating genetic insights to durable outcomes.[35]Business and brands
Harley-Davidson
Harley-Davidson, Inc., commonly abbreviated as HD, is an American motorcycle manufacturer founded on September 17, 1903, in Milwaukee, Wisconsin, by William S. Harley and Arthur Davidson, with brothers Walter and William A. Davidson joining shortly thereafter.[36][37] The company originated in a backyard shed, producing its first motorcycle prototype in 1903 and establishing a formal factory by 1906 on what became Juneau Avenue.[38] Harley-Davidson gained prominence for its V-twin engines, introduced in models like the 1909 Single and later refined in the 1915 Twin, which became synonymous with the brand's distinctive rumble and torque delivery.[39] Its cruiser-style motorcycles, characterized by low-slung seating, wide handlebars, and robust frames, evolved into cultural icons emphasizing customization and long-haul touring.[40] The company achieved peak motorcycle shipments of 349,196 units in 2006, driven by strong U.S. demand for heavyweight models amid a booming economy.[41] Following the 2008 financial crisis, which halved shipments to around 250,000 units annually, Harley-Davidson rebounded through cost-cutting, including workforce reductions and production shifts, restoring profitability to $624 million by 2012—the highest since 2008—while maintaining focus on core internal combustion engine (ICE) heritage.[42][43] In 2023, the firm reported $5.836 billion in revenue, reflecting resilience in premium segments despite broader market contraction.[44] Harley-Davidson supplied over 90,000 WLA "Liberator" motorcycles to U.S. and Allied forces during World War II, earning three Army-Navy E Awards for production efficiency and adapting civilian designs for military scouting, dispatch, and escort duties.[45] Harley-Davidson's brand fosters intense loyalty within biker subcultures, exemplified by the Harley Owners Group (H.O.G.), which builds community through rallies, customization events, and shared identity tied to freedom and craftsmanship, sustaining repeat purchases and organic advocacy.[46][47] In the U.S., it holds dominant positions in heavyweight categories, such as 74.5% market share in the Touring segment in 2024, though overall unit sales declined 21% in early 2025 amid economic pressures.[48][49] Facing electric vehicle (EV) competition, Harley-Davidson launched the LiveWire brand in 2019 but prioritizes ICE models like the Milwaukee-Eight V-twin, with executives noting EVs lack sufficient range and sensory appeal for core riders, projecting a gradual shift rather than abandonment of combustion heritage.[50][51] Labor relations have included disputes, such as the 1991 strike by over 1,400 union workers at its York, Pennsylvania plant—the first in 22 years—over wages, pensions, and overtime, halting production for weeks and highlighting tensions between management efficiency drives and union demands.[52][53] Despite such challenges, the company's emphasis on quality control and innovation, including employee involvement in assembly processes during the 1980s turnaround under AMF divestiture, contributed to its recovery from near-bankruptcy.[54] Tariffs on imported components have periodically pressured costs, given reliance on global supply chains for non-core parts, though domestic assembly bolsters its "Made in America" appeal.[55]The Home Depot
The Home Depot, Inc. (NYSE: HD) is an American multinational retailer specializing in home improvement products and services, headquartered in Atlanta, Georgia.[56] Founded in 1978 by Bernie Marcus and Arthur Blank after their dismissal from a competing retailer, the company pioneered the warehouse-style home improvement superstore format, offering a wide range of building materials, tools, appliances, and services targeted at do-it-yourself (DIY) consumers and professional contractors.[57] By emphasizing low prices, broad assortments, and knowledgeable staff, it disrupted traditional smaller hardware stores and grew rapidly through organic expansion and strategic acquisitions.[58] As of the second quarter of fiscal 2025, The Home Depot operated 2,353 retail stores across North America, including all 50 U.S. states, Canada, and Mexico, making it the largest player in the U.S. home improvement sector by store count and market share.[59] The company reported fiscal 2024 net sales of $159.5 billion, driven primarily by sales to professional customers (approximately 45% of revenue) and DIY homeowners, with key product categories including lumber, appliances, and outdoor equipment.[58] It employs approximately 475,000 associates as of 2025, contributing to significant job creation in retail and logistics while facing periodic legal challenges over wage and hour practices, such as a 2023 $72.5 million settlement for uncompensated employee wait times under California labor law and a 2025 $3.35 million resolution of overtime claims for overnight shifts.[60][61][62] The Home Depot expanded its professional segment through the 2015 acquisition of Interline Brands for $1.625 billion, which enhanced its maintenance, repair, and operations (MRO) offerings and distribution network for contractors.[63] During the 2020s supply chain disruptions, including those from the COVID-19 pandemic and global logistics strains, the retailer adapted by accelerating e-commerce capabilities, with online sales growing over 10% year-over-year in multiple quarters and comprising a growing share of total revenue—reaching around 10-12% by 2024 amid investments in buy-online-pickup-in-store fulfillment and same-day delivery.[64] This digital shift supported resilience, as comparable store sales stabilized despite macroeconomic pressures like inflation and housing market slowdowns, underscoring the company's focus on operational efficiency over non-core initiatives.[58]Chemistry and materials science
Deuterium hydride
Deuterium hydride, with the molecular formula HD, is a diatomic molecule composed of one protium atom (^1H) and one deuterium atom (^2H), forming an isotopologue of molecular hydrogen (H_2).[65] The molecule features a covalent single bond arising from the overlap of 1s orbitals between the two nuclei, with a bond dissociation energy of approximately 436 kJ/mol, closely akin to that of H_2 but influenced by the reduced mass difference due to deuterium's doubled mass.[66] This mass asymmetry results in distinct vibrational frequencies and rotational constants compared to H_2; for instance, the fundamental vibrational wavenumber for HD is about 3632 cm^{-1}, lower than H_2's 4161 cm^{-1}, enabling precise studies of isotopic substitution effects in quantum mechanical models of molecular spectra.[67] In natural hydrogen reservoirs, such as atmospheric or oceanic sources, HD occurs at trace levels due to deuterium's low atomic abundance of roughly 0.0156% relative to protium.[68] Assuming statistical pairing in diatomic hydrogen, the mole fraction of HD approximates 2 \times (deuterium fraction) \times (protium fraction) \approx 312 ppm, rendering it negligible for bulk applications but detectable via high-resolution spectroscopy.[65] Laboratory synthesis typically involves equilibration of H_2 and D_2 gases over catalysts like palladium or production via electric discharge in mixtures of hydrogen isotopes, yielding purities exceeding 96 mol% HD for research purposes.[69] The molecule is stable under standard conditions, with a boiling point of 20.1 K and melting point of 14.1 K, exhibiting behavior similar to H_2 but with enhanced rotational ortho-para conversion rates due to nuclear spin differences.[66] HD holds significance in physical chemistry for probing anharmonic effects and zero-point energy variations in diatomic systems, where empirical spectra validate first-principles calculations of potential energy surfaces.[67] In astrophysics, HD emerges in primordial gas clouds post-recombination, where its formation via ion-molecule reactions (e.g., H_2^+ + D \to HD + H^+) facilitates efficient radiative cooling through rovibrational transitions, potentially lowering gas temperatures to near cosmic microwave background levels (around 2.7 K at high redshifts z > 10) in shocked regions, distinct from H_2's limitations due to ortho-para restrictions.[70] Detectable HD absorption lines against quasars or its emission in molecular clouds provide empirical constraints on deuterium fractionation and early universe chemistry, though no large-scale industrial utilization exists owing to its scarcity and specialized research role.[71]High-density polyethylene
High-density polyethylene (HDPE) is a thermoplastic polymer derived from the low-pressure catalytic polymerization of ethylene monomer, yielding a linear molecular structure with minimal branching that confers high tensile strength and rigidity.[72] Commercial production began in the 1950s following the development of Ziegler-Natta catalysts by Karl Ziegler and Giulio Natta, which enabled precise control over chain formation and marked a shift from high-pressure free-radical methods used for low-density polyethylene (LDPE).[73] [74] This process operates at pressures below 100 atmospheres and temperatures around 50–150°C, producing HDPE with a density range of 0.941–0.970 g/cm³, significantly higher than LDPE's 0.910–0.940 g/cm³ due to reduced crystallinity defects.[72] The material's mechanical properties, including tensile strength exceeding 20 MPa (compared to LDPE's approximately 10 MPa), stem from its crystalline structure (60–80% crystallinity), making it suitable for demanding applications such as pressurized pipes, chemical-resistant bottles, and geomembranes.[75] [76] HDPE outperforms LDPE in shear and abrasion resistance, justifying its use in infrastructure where load-bearing capacity and longevity are critical, as evidenced by its deployment in water distribution systems lasting decades without failure.[77] Global production reached approximately 52 million metric tons in 2024, driven by demand in packaging (30–40% share) and construction, with projections exceeding 53 million tons by 2025 amid expansions in Asia-Pacific facilities.[78] HDPE is recyclable under resin identification code 2, with closed-loop processes recovering up to 100% of material value through mechanical reprocessing, though repeated cycles degrade molecular weight and properties.[79] Its durability—resisting photodegradation and biological attack for 50+ years in service—minimizes replacement frequency and associated emissions, countering critiques of plastic persistence by prioritizing material efficiency over rapid breakdown.[80] However, abrasion in marine or terrestrial environments can generate microplastics, with studies estimating HDPE contributes 10–20% of ocean microplastic mass from wear rather than primary shedding; mitigation relies on end-of-life capture rather than inherent biodegradability, as forced degradation accelerates fragmentation without net environmental gain.[81] [82]Computing and codes
Help desk
A help desk, abbreviated as HD, functions as a centralized point of contact for users reporting technical issues related to IT infrastructure, software applications, or hardware malfunctions within organizations. This operational framework prioritizes incident logging, triage, and resolution to restore functionality swiftly, often employing ticketing systems for tracking and escalation. Formalization of help desk processes emerged in the late 1980s through the IT Infrastructure Library (ITIL), developed by the United Kingdom's Central Computer and Telecommunications Agency to standardize service management amid growing IT complexity in government operations.[83] ITIL's emphasis on service desk practices, including problem categorization and priority assignment, has since become a benchmark for enterprise IT support.[84] Performance metrics for help desks typically include first-contact resolution (FCR), defined as the percentage of incidents resolved during the initial user interaction without escalation or follow-up. Industry benchmarks target FCR rates of 70-80%, with averages around 74% reported in global service desk data, as higher rates correlate with reduced repeat calls and improved user satisfaction.[85] Other key indicators encompass average resolution time and ticket volume per agent, which guide resource allocation and process refinements under ITIL guidelines. Following the 2020 shift to widespread remote work prompted by the COVID-19 pandemic, help desks evolved to incorporate remote access tools such as screen-sharing software and virtual private networks for diagnostics, enabling support without physical presence.[86] By 2025, artificial intelligence integration, including chatbots and predictive analytics, has automated routine tasks like password resets and basic troubleshooting, with Gartner projecting that generative AI will autonomously handle up to 30% of customer interactions, thereby reducing operational costs and human ticket volumes by comparable margins through deflection of low-complexity queries.[87][88] Outsourcing help desk operations to third-party providers has faced scrutiny for inefficiencies, including communication breakdowns across time zones, cultural mismatches, and diminished institutional knowledge transfer, which can extend resolution times and elevate costs beyond initial projections.[89][90] Nevertheless, empirical assessments affirm help desks' role in curtailing IT downtime; proactive monitoring and rapid triage have been shown to lower infrastructure outages by preempting escalations, with organizations employing structured service desks reporting measurable decreases in unplanned disruptions.[91][92]Hexadecimal notation contexts
In computing, "HD" commonly abbreviates "hex dump," a textual representation of binary data using hexadecimal notation to display byte offsets, raw hexadecimal values, and corresponding ASCII interpretations, facilitating inspection of files, memory, or network packets without higher-level abstraction.[93] The hexdump utility in Unix-like operating systems, invoked ashd in many implementations, defaults to this format, printing input offsets in hexadecimal followed by grouped byte values (e.g., two-byte decimal or hexadecimal clusters) and character mappings, as standardized in POSIX specifications.[94] This notation emerged in early Unix systems for debugging purposes, where tools like [od](/page/OD) or xxd variants also produce similar outputs, emphasizing raw data parsing over formatted readability.
In low-level programming and assembly contexts, hex dumps marked by "HD" shorthand aid reverse engineering and error diagnosis, such as verifying data structures in legacy binaries or firmware.[95] For instance, invoking hd on executable files reveals embedded constants or opcodes in hexadecimal, essential for tasks like malware analysis or embedded system troubleshooting, where empirical byte-level verification trumps interpretive tools prone to abstraction errors.[96] Proprietary or system-specific extensions, such as in QNX or BS2000 environments, extend HD notation to include octal/decimal hybrids or custom delimiters, but core usage remains tied to hexadecimal for universality in cross-platform debugging.[97]
Niche applications include hardware standards like JEDEC's Serial Presence Detect (SPD) for DDR4 SDRAM, where 0xHD encodes identifiers for 32-bit SO-DIMMs with hybrid architectures, parsed in hexadecimal during BIOS/UEFI memory detection.[98] Such codes, while valid within defined namespaces, underscore HD's role in constrained notation systems rather than general-purpose literals, as standard hexadecimal restricts digits to 0-9 and A-F, rendering unbound sequences like standalone 0xHD erroneous in parsers.[93] These contexts prioritize causal data flows—e.g., firmware reading SPD bytes directly—over interpretive flexibility, with empirical validation via tools like hexdump confirming module parameters against specification hex values.