All articles starting with H

Hydrography

Hydrography is the applied science of measuring and describing the physical features of oceans, seas, coastal waters, lakes, and rivers, chiefly to chart hazards and support safe navigation.

Hydrohalogenation

Hydrohalogenation is the addition of a hydrogen halide (HCl, HBr, or HI) across the π bond of an alkene or alkyne, giving alkyl or vinyl halides with Markovnikov regiochemistry.

Hydroid, Inc.

Hydroid, Inc. is an American manufacturer of autonomous underwater vehicles, best known for the REMUS family, founded in 2001 and acquired by HII in 2020.

Hydrokinetic turbine

A hydrokinetic turbine, also called a kinetic or free-flow turbine, generates electricity directly from moving water such as river or tidal currents without a dam, like an underwater wind turbine.

Hydrolethalus syndrome (HLS, OMIM 236680/614120), a lethal autosomal recessive Finnish-enriched ciliopathy from HYLS1 or KIF7 mutations, causing hydrocephalus, keyhole occipital defect, polydactyly, cleft palate, and heart defects.

Hydrologic balance

Hydrologic balance (water balance): accounting where storage change equals precipitation minus evapotranspiration and runoff; basis of catchment hydrology, the Budyko framework, and water balance models.

Hydrologic regions of California

Hydrologic regions of California: ten DWR drainage-basin divisions (North Coast through Colorado River) plus Delta and Mountain Counties overlay areas, used for the Water Plan, Bulletin 118, and Calwater watershed mapping.

Hydrological model

A hydrological model, also called a hydrological transport model, is a mathematical representation of water movement in a catchment, supporting flood forecasting and water resource management.

Hydrology

Hydrology, or hydrologic science, is the science of Earth's water, studying its occurrence, movement, and properties through the water cycle, from precipitation and runoff to evaporation.

Hydrolycus scomberoides

Hydrolycus scomberoides, the payara (basionym Hydrocyon scomberoides Cuvier 1819), is a fanged piscivorous characiform fish of the Amazon basin, family Cynodontidae, IUCN Least Concern, max 117 cm TL and 17.8 kg.

Hydrolysed proteins

Hydrolysed proteins (protein hydrolysates) are peptide and amino acid mixtures from hydrolysed animal or plant proteins, used as an EU low-risk pesticide active substance (insect attractant), as plant biostimulants, and in infant formula and sports nutrition.

Hydrolysis

Hydrolysis is a chemical reaction in which water breaks a bond in a molecule, covering salt pH changes, ester saponification, polymer degradation, and ATP-driven cell reactions.

Hydrolyzed pork cartilage

Hydrolyzed pork cartilage (hydrolyzed porcine trachea cartilage, Peptan II) is a type II collagen and chondroitin sulfate food ingredient, GRAS under FDA GRN 713 by Rousselot, used at 1.2–2 g per serving.

Hydrolyzed poultry protein

Hydrolyzed poultry protein, a peptide-rich ingredient from enzymatically hydrolyzed poultry protein or by-products, used as protein source and flavoring; GRAS via GRN 1132 (Norilia AS), FDA no questions Jan 29, 2024.

Hydrolyzed sardine protein

Hydrolyzed sardine protein, also called sardine peptide (Valtyron), is an enzyme-hydrolyzed sardine muscle protein ingredient; GRAS via FDA GRN 360 (Senmi Ekisu, 2011), EFSA-safe to 0.6 g/serving.

Hydrolyzed yeast

Hydrolyzed yeast, including enzymatically hydrolyzed and autolyzed Saccharomyces cerevisiae products such as DNF-10, is yeast broken into peptides and amino acids for flavoring, nutrition, feed, and cosmetics; FDA issued no-questions letter GRN 1033 in 2023.

Hydromantes

Hydromantes (web-toed salamanders), genus of lungless plethodontid salamanders; five species in northern California, closely allied to the eight European cave salamanders (Speleomantes); known for a ballistic tongue, webbed climbing feet, and Miocene fossils from Slovakia.

Hydromedusa

Hydromedusa: a genus of two South American snake-necked side-necked turtles (H. maximiliani, H. tectifera) in Chelidae; also hydromedusae, the medusa stage of hydrozoan cnidarians, over 3,600 planktonic species.

Oct 22, 2026

Hydrometallurgical lithium-ion battery recycling

Hydrometallurgical lithium-ion battery recycling recovers metals from spent lithium-ion batteries by leaching cathode material in acid and separating lithium, nickel, and cobalt, recovering over 95% of lithium.

Hydrometer

A hydrometer, also spelled areometre, is an instrument that measures a liquid's density or specific gravity by floating in it, used in brewing, battery testing, and petroleum measurement.

Hydromethylthionine

Hydromethylthionine (leucomethylene blue, LMTM, TRx0237) is the reduced form of methylene blue, an oral tau aggregation inhibitor developed by TauRx for Alzheimer's disease and frontotemporal dementia; investigational, MHRA review expected 2026.

Hydromorphone

Hydromorphone (Dilaudid), a semisynthetic Schedule II opioid agonist derived from morphine, two to eight times morphine's potency, no active metabolites, used for moderate to severe postoperative and cancer pain.

Hydronephrosis

Hydronephrosis is swelling of the kidney from urine build-up, dilating the renal pelvis and calices. Causes include stones, pregnancy, and prostate enlargement; it does not always mean obstruction, and treatment ranges from drainage to surgery.

Hydronephrosis with ureteropelvic junction obstruction

Hydronephrosis with ureteropelvic junction obstruction (ICD-11 GB56.0): urine outflow blocked where the renal pelvis joins the ureter, dilating the kidney. Incidence 1:1,500, male predominance, treated by pyeloplasty with about 95% success.

Hydronium

Hydronium, also known as the hydroxonium ion, is the cation H3O+ formed when a proton bonds to a water molecule; it is the form all hydrogen ions take in water.

Oct 22, 2026

Hydropathes

The Hydropathes were a Parisian literary club founded by Émile Goudeau in 1878, whose Left Bank café readings and journal L'Hydropathe helped launch the cabaret culture later carried on by Le Chat Noir.

Hydropeaking

Hydropeaking is the rapid fluctuation of river flow and water level downstream of hydropower plants, caused by turbine releases timed to meet peak electricity demand.

Hydroperoxy

Hydroperoxy refers to the univalent –OOH group, formed by replacing one hydrogen atom of hydrogen peroxide; its ROOH compounds are hydroperoxides, and the neutral radical HOO• is the hydroperoxyl radical, HO2.

Hydroperoxyl

Hydroperoxyl, also called the perhydroxyl radical and written HO2, is the protonated form of the superoxide anion and a key radical in atmospheric oxidation and combustion chemistry.