All articles starting with H

Hyperparameter optimization

Hyperparameter optimization, also called hyperparameter tuning, is the process of searching for machine learning settings, like learning rate or network size, that give the best performance, usually judged by cross-validation.

Sep 29, 2026

Hyperparameter search

Hyperparameter search is a machine learning method that automatically tunes a model's hyperparameters, such as learning rate or regularization strength, by evaluating candidate configurations and selecting those that optimize validation performance.

Hyperparathyroidism

Hyperparathyroidism is a condition that occurs when the parathyroid glands excessively secrete parathyroid hormone. It can manifest in primary, secondary, or tertiary forms, impacting calcium levels.

Hyperparathyroidism-jaw tumor syndrome

Hyperparathyroidism-jaw tumor syndrome (HPT-JT, OMIM 145001) is a rare autosomal dominant CDC73/parafibromin disorder causing primary hyperparathyroidism, jaw ossifying fibromas, renal and uterine tumors, and parathyroid carcinoma risk.

Oct 20, 2026

Hyperphenylalaninemia due to tetrahydrobiopterin deficiency

Hyperphenylalaninemia due to tetrahydrobiopterin deficiency (BH4 deficiency, atypical/malignant PKU): rare autosomal recessive disorders of GCH1, PTS, QDPR, or PCBD1 causing elevated phenylalanine plus dopamine and serotonin deficiency, treated with BH4, L-dopa, and 5-hydroxytryptophan.

Hyperphosphatasia-intellectual disability syndrome

Hyperphosphatasia-intellectual disability syndrome (Mabry syndrome, HPMRS, ORPHA:247262) is a rare autosomal recessive GPI-anchor glycosylation disorder with intellectual disability, seizures, facial dysmorphism, and elevated alkaline phosphatase from PIGV, PIGO, PGAP2, PGAP3, PIGW, or PIGY variants.

HyperPhysics

HyperPhysics is a free web-based physics reference built as concept maps of linked cards, created by Georgia State University physicist Rod Nave and online since 1998.

Hyperpigmentation

Hyperpigmentation: excess melanin causing darker skin patches, mainly melasma and postinflammatory hyperpigmentation (PIH). Most common in Fitzpatrick phototypes III-VI; treated with sunscreen, hydroquinone, azelaic acid, retinoids, tranexamic acid, and procedures.

Hyperplane

A hyperplane is a subspace of one dimension less than its space: a plane in 3D, a line in 2D, generalizing the plane to any dimension.

Hyperplane arrangement

A hyperplane arrangement is a finite collection of hyperplanes, codimension-one affine subspaces, in a space like R^d, studied for how they cut space into regions.

Hyperplasia

Hyperplasia is an increase in the number of cells in an organ or tissue, making it larger; the cells look normal and are not cancer, though some forms may become cancer.

Hyperplasia of appendix

Hyperplasia of appendix (ICD-11 DB11.1) is benign, reactive proliferation of appendiceal lymphoid tissue that can obstruct the lumen, mimic appendicitis, and be mistaken histologically for LAMN.

Hyperplastic duodenal polyp

Hyperplastic duodenal polyp (過形成性十二指腸ポリープ), ICD-11 DA53.0: a rare benign non-neoplastic duodenal epithelial growth, serrated microvesicular histology, often linked to H. pylori and gastroduodenal disease, treated by endoscopic resection.

Hyperpolarization (biology)

Hyperpolarization (biology): shift of a cell's membrane potential to a more negative value, caused by K+ efflux or Cl- influx; underlies IPSPs, the afterhyperpolarization, and hyperpolarization-activated HCN/I_h currents.

Hyperpolarized carbon-13 pyruvate

Hyperpolarized carbon-13 pyruvate is a nonradioactive metabolic imaging agent, magnetically polarized and injected intravenously, imaged with MRI to measure real-time metabolism in tumors and heart tissue.

Hyperpolarized MRI

Hyperpolarized MRI is a molecular imaging technique that boosts the carbon-13 MRI signal over 10,000-fold, letting scans map enzyme-driven metabolism, most often with injected pyruvate, in real time.

Hyperpolarized MRI of inhaled xenon

Hyperpolarized MRI of inhaled xenon is an MRI technique in which magnetically prepared xenon-129 gas is inhaled to map lung ventilation and gas exchange without ionizing radiation.

Hyperpop

Hyperpop: maximalist internet pop genre with pitched-up vocals, distorted 808s, and bright synths, rooted in PC Music, SOPHIE, and 100 gecs' 1000 gecs, named by Spotify's 2019 playlist.

Hyperprolactinaemia

Hyperprolactinaemia (hyperprolactinemia) is abnormally high serum prolactin, caused by prolactinomas, drugs, hypothyroidism, or macroprolactin; treated with dopamine agonists such as cabergoline, with special pregnancy management.

Hyperprolinemia type 1

Hyperprolinemia type 1 (HPI, proline oxidase deficiency, OMIM 239500) is a rare autosomal recessive PRODH disorder at 22q11.21 causing high blood proline without urinary P5C; often asymptomatic, occasionally seizures, schizophrenia, or nephropathy.

Hyperprolinemia type 2

Hyperprolinemia type 2 (HPII, ALDH4A1 hyperprolinemia, delta-1-pyrroline-5-carboxylate dehydrogenase deficiency) is an autosomal recessive proline metabolism disorder causing proline 10-15x normal with elevated P5C, sometimes seizures and intellectual disability, often benign.

Hyperreal number

Hyperreal numbers, also called nonstandard real numbers or hyperreals, are an ordered field extending the real numbers with infinitesimals, used in Abraham Robinson's nonstandard analysis.

Hyperrealism (visual arts)

Hyperrealism (also super-realism) is a visual-arts trend from late-1960s America: photorealist-precision painting and lifelike figure sculpture by Chuck Close, Richard Estes, Duane Hanson, John de Andrea, Ron Mueck; term coined 1973 by Isy Brachot.

Hyperreality

Hyperreality: Baudrillard's condition in which simulations, copies without originals, are experienced as more real than the real; also used by Umberto Eco (Travels in Hyperreality). Distinguished from spectacle, simulation, and simulacra.

Hypersalivation

Hypersalivation (sialorrhea, ptyalism, drooling): excessive salivary flow from overproduction or, more often, impaired swallowing, common in Parkinson's disease, cerebral palsy, and clozapine therapy; treated behaviorally, with anticholinergics, botulinum toxin, or surgery.

Hyperscaler AI capital expenditure

Hyperscaler AI capital expenditure is the data center, chip, and power spending of Microsoft, Amazon, Alphabet, Meta, and Oracle, which has grown almost fivefold since ChatGPT's 2022 launch.

Oct 20, 2026

Hypersecretion of calcitonin

Hypersecretion of calcitonin (ICD-11 5A04) is excessive release of the 32-amino-acid thyroid C-cell hormone; its main cause is medullary thyroid carcinoma, and elevated serum calcitonin serves as that cancer's key tumor marker.

Hypersensitivity

Hypersensitivity, also known as the Gell-Coombs classification, is an excessive immune response that damages tissue, classically divided into four types by Gell and Coombs in 1963.

Hypersensitivity myocarditis

Hypersensitivity myocarditis (allergic myocarditis, ICD-11 BC42.2) is a drug- or vaccine-triggered eosinophilic inflammation of the heart muscle, diagnosed by endomyocardial biopsy, treated by drug withdrawal plus corticosteroids.