Science terms starting with H

545 terms

101. Heat Advisory Issued within 12 hours of the onset of the following conditions: heat index of at least 105°F but less than 115°F for less than 3 hours per day, or…
102. Heat Balance Energy output from a system that equals energy input.
103. Heat balance of the Earth-atmosphere system Heat balance of the Earth-atmosphere system The equilibrium that exists on the average between the radiation received by the Earth and atmosphere from the…
104. Heat budget Heat budget Relation between fluxes of heat into and out of a given region or body and the heat stored by the system.
105. heat capacity The ratio of the heat absorbed (or released) by a system to the corresponding temperature rise (or fall).
106. Heat Content The amount of heat in a quantity of matter at a specific temperature and pressure.
107. Heat Engine A device that produces mechanical energy directly from two heat reservoirs of different temperatures.
108. Heat Exchanger A device used to transfer heat from a fluid (liquid or gas) to another fluid where the two fluids are physically separated.
109. Heat Exhaustion A mild form of heat stroke, characterized by faintness, dizziness, and heavy sweating.
110. Heat flux Heat flux Amount of heat, transferred in a liquid, in particular in the atmosphere, per unit of time through a unit area.
111. Heat Gain The amount of heat introduced to a space from all heat producing sources, such as building occupants, lights, appliances, and from the environment, mainly…
112. Heat Index The Heat Index (HI) or the "Apparent Temperature" is an accurate measure of how hot it really feels when the Relative Humidity (RH) is added to the actual…
113. heat index (HI) An index that combines air temperature and relative humidity to determine an apparent temperature-how hot it actually feels.
114. Heat Lightning Lightning that occurs at a distance such that thunder is no longer audible.
115. Heat Loss The heat that flows from the building interior, through the building envelope to the outside environment.
116. Heat Pipe A device that transfers heat by the continuous evaporation and condensation of an internal fluid.
117. Heat Pump An electricity powered device that extracts available heat from one area (the heat source) and transfers it to another (the heat sink) to either heat or…
118. Heat Pump Water Heaters A water heater that uses electricity to move heat from one place to another instead of generating heat directly.
119. Heat rate The ratio of fuel energy input as heat per unit of net work output; a measure of a power plant thermal efficiency, generally expressed as Btu per net…
120. Heat Recovery Ventilator A device that captures the heat from the exhaust air from a building and transfers it to the supply/fresh air entering the building to preheat the air and…
121. Heat Register The grilled opening into a room by which the amount of warm air from a furnace can be directed or controlled; may include a damper.
122. heat shock protein (... PROH-teen) One of a group of proteins that help protect cells from stresses such as heat, cold, and low amounts of oxygen or glucose (sugar).
123. Heat Sink A structure or media that absorbs heat.
124. Heat Source A structure or media from which heat can be absorbed or extracted.
125. Heat Storage A device or media that absorbs heat for storage for later use.
126. Heat Storage Capacity The amount of heat that a material can absorb and store.
127. Heat Stroke A condition resulting from excessive exposure to intense heat, characterized by high fever, collapse, and sometimes convulsions or coma.
128. heat therapy See: thermotherapy.
129. Heat Transfer The flow of heat from one area to another by conduction, convection, and/or radiation. Heat flows naturally from a warmer to a cooler material or space.
130. Heat transfer efficiency The useful heat output released to a room divided by the actual heat produced in the firebox.
131. Heat Transfer Fluid A gas or liquid used to move heat energy from one place to another; a refrigerant.
132. Heat transfer fluid (HTF) Fluids that transfer heat generated at the solar collectors to a heat exchanger where steam is produced to run a steam generator.
133. Heat Transmission Coefficient Any coefficient used to calculate heat transmission by conduction, convection, or radiation through materials or structures.
134. Heat Wave A period of abnormally and uncomfortably hot and unusually humid weather. Typically a heat wave lasts two or more days.
135. Heating Capacity (Also specific heat) The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree.
136. Heating Degree Day(s) (HDD) The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature…
137. Heating Degree Days (abbrev. HDD) A form of degree day used to estimate energy requirements for heating.
138. Heating degree days (HDD) A measure of heating demand equal to the number of degrees a location’s mean daily temperature was below 65 degrees Fahrenheit.
139. Heating Fuel Units Standardized weights or volumes for heating fuels.
140. Heating Fuels Any gaseous, liquid, or solid fuel used for indoor space heating.
141. Heating Load The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour.
142. Heating Season The coldest months of the year; months where average daily temperatures fall below 65 degrees Fahrenheit creating demand for indoor space heating.
143. Heating Seasonal Performance Factor (HSPF) The measure of seasonal or annual efficiency of a heat pump operating in the heating mode.
144. Heating Value The amount of heat produced from the complete combustion of a unit of fuel. The higher (or gross) heating value is that when all products of combustion…
145. Heating, Ventilation, and Air-Conditioning (HVAC) System All the components of the appliance used to condition interior air of a building.
146. Heave The upward movement of land surfaces or structures due to subsurface expansion of soil or rock, or vertical faulting of rock.
147. Heavenly Bodies Any mass or object in space, including nebulas, planets, moons, stars, pulsars, quasars and so on.
148. Heavy Freezing Spray An accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind…
149. Heavy Freezing Spray Warning A warning that may be issued within the Offshore Waters Forecast, the Coastal Waters Forecast, the Nearshore Marine Forecast, and the Open Lake Forecast…
150. Heavy metals Metallic elements with high atomic weights (e.g., mercury, chromium, cadmium, arsenic, and lead); can damage living things at low concentrations and tend…
151. Heavy Snow This generally means... snowfall accumulating to 4" or more in depth in 12 hours or less; or snowfall accumulating to 6" or more in depth in 24 hours or…
152. Heavy Snow Warning Issued by the National Weather Service when snowfall of 6 inches (15 cm) or more in 12 hours or 8 inches (20 cm) or more in 24 hours is imminent or…
153. Heavy Surf Advisory An advisory issued by the National Weather Service for fast moving deep water waves which can result in big breaking waves in shallow water (the surf…
154. Hectare An area equal to 2.47 acres. There are 100 hectares in 1 square kilometer.
155. Hectopascal A unit of pressure equal to a millibar (1 hPa = 1 mb). Abbreviated hPa.
156. Hedging Hedging is an investment technique designed to offset a potential loss on one investment by purchasing a second investment that you expect to perform in…
157. Hedonic – (modeling approach) The hedonic method is a regression technique used to estimate the prices of qualities or models that are not available on the market in particular…
158. Hedonic statistical framework A method of assessing the impact of various structural (number of bedrooms, bathrooms, square footage, age, etc.
159. Heel of Dam The junction of the upstream face of a concrete gravity dam or arch dam with the ground surface.
160. Height In meteorology, usually a reference to Geopotential Height; roughly the height above sea level of a pressure level.
161. Height of dam. See hydraulic height or structural height.
162. Heinrich Events periods of increased discharge of icebergs from the margin of ice sheets into the North Atlantic Ocean during the last glacial.
163. Helical Spiral.
164. Helicity A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve.
165. Heliocentric A model of the universe published by Nicolaus Copernicus, and proven by Galileo (who viewed the phases of venus with his telescope), which puts our sun at…
166. Heliochemical Process The utilization of solar energy through photosynthesis.
167. Heliodon A device used to simulate the angle of the sun for assessing shading potentials of building structures or landscape features.
168. Heliosphere A huge magnetic bubble containing the solar wind and the entire solar magnetic field.
169. Heliostat A device that tracks the movement of the sun; used to orient solar concentrating systems.
170. Heliothermal Any process that uses solar radiation to produce useful heat.
171. Heliothermic Site planning that accounts for natural solar heating and cooling processes and their relationship to building shape, orientation, and siting.
172. Heliothermometer An instrument for measuring solar radiation.
173. Heliotropic Any device (or plant) that follows the sun's apparent movement across the sky.
174. helix A structure with a spiral shape. The normal state of double-stranded DNA is in the form of a double helix.
175. helminth A class of parasitic worms, especially those which are internal parasites of man and animals.
176. helper cell T cells that assist in stimulating B and T lymphocyte s to develop into antibody-producing plasma cells and killer T cells, respectively.
177. helper plasmid A plasmid that provides a function or functions to another plasmid in the same cell.
178. helper T cell A type of white blood cell that helps stimulate immune system reactions. Helper T cells help activate cytotoxic T cells and macrophages by secreting…
179. helper T lymphocyte See: helper cell.
180. helper virus A virus that provides a function or functions to another virus in the same cell.
181. Hematological Oncologist A medical doctor who specializes in diagnosing and treating malignancies, or cancers, of the blood and blood- forming tissues.
182. Hematologist (HEE-muh-TAH-loh-jist) A doctor who specializes in treating blood disorders.
183. Hematopoiesis (hee-MA-toh-poy-EE-sus) The formation of new blood cells.
184. Hematopoietic cell transplantation The transplantation of hematopoietic stem cells with blood-forming potential. Hematopoietic stem cells provide rapid and sustained reconstitution of blood…
185. Hematopoietic stem cell An unspecialized precursor cell that will develop into a mature blood cell. See also cell
186. Hematopoietic stem cell (HSC) A stem cell from which all red and white blood cells evolve.
187. Hematopoietic stem cells The precursors of mature blood cells that are defined by their ability to replace the bone marrow system following its obliteration (for example, by…
188. hemicellulase An enzyme that catalyses the degradation of hemicellulose.
189. hemicellulose Any cellulose-like carbohydrate, but excluding cellulose itself. Together with pectin and lignin, hemicelluloses form the cell wall matrix.
190. Hemispherical Bowl Technology A solar energy concentrating technology that uses a linear receiver that tracks the focal area of a reflector or array of reflectors.
191. Hemizygous The condition in which genes are present only once in the genotype and not in pairs.
192. hemoglobin (HEE-moh-GLOH-bin) The substance inside red blood cells that binds to oxygen in the lungs and carries it to the tissues.
193. hemolymph See: haemolymph.
194. hemophilia Group of hereditary disorders in which affected individuals fail to make enough of certain proteins needed to form blood clots.
195. Henry Hub A location near the coastal town of Egan, LA and the Texas border where more than a dozen major natural gas pipelines converge and exchange gas.
196. HEPA filter Abbreviation for high efficiency particulate air filter. A filter capable of excluding particles larger than 0.3ìm.
197. Hepatic (hih-PA-tik) Refers to the liver.
198. Hepatocyte (HEP-a-toe-site) A liver cell.
199. Herbaceous The plant strata that contain soft, not woody, stemmed plants that die to the ground in winter.
200. herbaceous energy crops Perennial non-woody crops that are harvested annually, though they may take two to three years to reach full productivity.