Science terms starting with L

480 terms

Lateral moraine Ridge-like pile of sediment along the side of a glacier.
Latite An igneous, volcanic (extrusive) rock.
Latitude (abbrev. LAT) The location north or south in reference to the equator, which is designated at zero (0) degrees.
Lattice The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.
Laurentide ice sheet the ice sheet that grew over a large part of North America during the last glacial period.
Lava Magma that reaches the Earth's surface and issues from volcanoes.
Lava flow An outpouring of lava onto the land surface from a vent or fissure. Also, a solidified tongue-like or sheetlike body formed by outpouring lava.
Lava tubes Natural conduits through which lava moves beneath the surface of a lava flow during a volcanic eruption.
Law of the River A complex body of laws, court decrees, contracts, agreements, regulations and an international treaty used to govern allocation and management of Colorado…
Law(s) of Thermodynamics The first law states that energy can not be created or destroyed; the second law states that when a free exchange of heat occurs between two materials…
LAWEB (Great Lakes Weather Broadcast) - A National Weather Service product containing an observation summary prepared to provide Great Lakes mariners with a…
Lawn A uniform and uninterrupted laver of bacterial growth, in which individual colonies cannot be observed.
Laydown area An area that has been cleared for the temporary storage of equipment and supplies.
Layer Composite Reflectivity Average This WSR-88D radar product displays the average reflectivities for a layer. Data is taken from all elevation angles contained in a given layer for each…
Layer Composite Reflectivity Maximum This WSR-88D radar product displays the maximum reflectivities for a layer. Data is taken from all elevation angles contained in a given layer for each…
Layered Haze Haze produced when air pollution from multiple line, area or point sources is transported long distances to form distinguishable layers of discoloration…
layering A technique for vegetative propagation, in which new plants produce adventitious roots before being severed from the parent plant.
LCD (Local Climatological Data) This National Climatic Data Center (NCDC) publication is produced monthly and annually for some 270 United States cities and it's territories.
LCL 1. Abbreviation for "local" or "locally" 2. Lifting Condensation Level - the level at which a parcel of moist air becomes saturated when it is lifted dry…
LCR Abbreviation for ligase chain reaction.
LD50 Abbreviation for lethal dose50%. The amount of a substance required to kill 50% of the test population.
LDS Lightning Detection System
LDT Local Daylight Time.
Leach To remove components from the soil by the action of water trickling through.
Leachate A liquid that results from water collecting contaminants as it trickles through wastes, agricultural pesticides or fertilizers.
Leachates Liquids percolated through waste piles. Leachate can include various minerals, organic matter, or other contaminants and can contaminate surface water or…
Leaching Removal of soluble material from soil or other permeable material by the passage of water through it.
Leaching field (leaching cesspool) A lined or partially lined underground pit into which raw household water (sewage) is discharged and from which the liquid seeps into the surrounding soil.
Leaching requirement Quantity of irrigation water required for transporting salts through the soil profile to maintain a favorable salt balance in the root zone for plant…
Lead A gray-white metal that is listed as a criteria air pollutant. Health effects from exposure to lead include brain and kidney damage and learning…
Lead Acid Battery An electrochemical battery that uses lead and lead oxide for electrodes and sulfuric acid for the electrolyte.
lead compound A chemical that has demonstrated promising biological activity in preliminary assays.
Lead time Time available for Decision Makers to determine if conditions at a dam and reservoir, or in the basin, warrant declaration of a specific emergency…
Leader The streamer which initiates the first phase of each stroke of a lightning discharge.
leader peptide See: signal sequence.
leader sequence A variable length sequence of nucleotides at the 5' end of an mRNA molecule that precedes the AUG initiation codon where translation begins and is not…
Leader Spot In solar-terrestrial terms, in a magnetically bipolar or multipolar sunspot group, the western part precedes and the main spot in that part is called the…
Leadership in Energy and Environmental Design (LEED) Green Building Rating System is a nationally accepted benchmark for the design, construction, and operation of high performance green buildings.
Leading Edge In reference to a wind energy conversion system, the area of a turbine blade surface that first comes into contact with the wind.
leading strand The strand of DNA that is synthesized continuously during replication.
leaf blade The usually flattened portion of the leaf.
leaf bud cutting A cutting that includes a short section of stem with attached leaf.
leaf margin The edge of a leaf.
leaf primordium A lateral outgrowth from the apical meristem, which will become a leaf when fully developed and expanded.
leaf roll A symptom of some virus diseases, characterized by curling of the leaves. Can also occur as a response to water stress.
leaf scar Mark left on a stem after leaf abscission.
leaflet Expanded leaf-like part of a compound leaf.
Leak Uncontrolled loss of water by flow through a hole or crack.
Leakage Free flow loss of water through a hole or crack.
Leaking Electricity Related to stand-by power, leaking electricity is the power needed for electrical equipment to remain ready for use while in a dormant mode or operation.
leaky mutant A mutant in which the gene product still retains some biological activity.
Leapfrog Development Development that occurs beyond the limits of existing development and creates areas of vacant land between areas of developed land.
Leasable minerals Federal minerals such as coal, oil shale, oil, gas, phosphate, potash, sodium, tar sands, geothermal resources, potassium, asphaltic materials, and all…
Lease A contract transferring the use of property or occupancy of land, space, structures, or equipment in consideration of a payment (e.g., rent).
Lease of power privilege Contractual right given to a non-Federal entity to utilize, consistent with project purposes, water power head and storage from Reclamation projects for…
Least cost planning (integrated resource planning) A method of power planning that recognizes load uncertainty, embodies an emphasis on risk management, and reviews all…
lectin A complex molecule that has both protein and sugars. Lectins are able to bind to the outside of a cell and cause biochemical changes in it.
Lee The side or part that is sheltered or turned away from the wind, such as with a mountain.
Lee Wave The wavelike effect, characterized by severe updrafts and downdrafts, that occurs in the lee of a mountain range when rapidly flowing air is lifted up the…
LEED "Plus" Created by the Massachusetts Sustainable Design Roundtable to address shortcomings with standard LEED certification these standards apply to construction…
Leeside Low Extratropical cyclones that form on the downwind (lee) side of a mountain chain.
Leeward The side away from the wind. Compare windward.
Left Abutment See abutment.
Left Exit Region Used interchangably with Left Front Quadrant; the area downstream from and to the left of an upper-level jet max (as would be viewed looking along the…
Left Front Quadrant Used interchangably with Left Exit Region; the area downstream from and to the left of an upper-level jet max (as would be viewed looking along the…
Left Mover A thunderstorm which moves to the left relative to the steering winds, and to other nearby thunderstorms; often the northern part of a splitting storm.
Left or right designation In the context of dams and river channels, the designation of left or right is made with the observer looking in the downstream direction.
Left-lateral fault See Fault, left-lateral
Lefty A developmental factor that helps determine right-left asymmetry in vertebrates.
Leg A side post in tunnel timbering.
Legacy Chargers Legacy electric charging systems such as inductive paddles. Learn more about types of chargers.
Legume A member of the pea family that possesses root nodules containing nitrogen-fixing bacteria.
Lek A communal mating area within which males of certain species hold small territories, which they use solely for courtship and copulation.
Length The distance in the direction of flow between two specific points along a river, stream, or channel.
Length of dam. See crest length.
Lentic Still water systems such as lakes and reservoirs.
Lentic environment An aquatic ecosystem in which the water is still and not rapidly moving, such as is found in ponds and swamps.
Lentic System A nonflowing or standing body of fresh water, such as a lake or pond. Compare lotic system.
Lenticular Cloud A very smooth, round or oval, lens-shaped cloud that is often seen, singly or stacked in groups, near or in the lee of a mountain ridge.
Leptin A hormone produced by the placenta and fetal tissues that acts as a growth factor and modulator of metabolic and immune functions.
leptonema Stage in meiosis immediately preceding synapsis and post DNA replication, in which the chromosomes appear as single, fine, threadlike structures.
leptotene (adj.) See: leptonema.
lethal allele A mutant form of a gene that, in the homozygous state, is fatal.
lethal gene See: lethal allele.
lethal mutation See: lethal allele.
Lethe A measure of air purity that is equal to one complete air change (in an interior space).
Letter of Agreement (LOA). See Memorandum of Understanding (MOU).
leukemia (loo-KEE-mee-uh) Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of blood cells to be produced and enter the…
Leukemia inhibitory factor A cell messenger protein originally noted for inhibition of mouse M1 myeloid leukemia cells that also has effects including inhibiting differentiation to…
Leukemia inhibitory factor (LIF) A growth factor necessary for maintaining mouse embryonic stem cells in a proliferative, undifferentiated state.
Leukocyte (LOO-koh-site) A white blood cell. Refers to a blood cell that does not contain hemoglobin.
Leukocyte (White Blood Cell) The general name for a white blood cell. Leukocytes are responsible for maintaining the immune system's response to foreign substances and infection.
Leukocyte common antigen Cell-surface molecule found on white blood cells and white blood cell progenitors. Also referred to as CD45.
Levee A natural or man-made barrier that helps keep rivers from overflowing their banks. See dike.
Levee (Dike) A long, low embankment usually built along a watercourse to protect land from flooding.
Level The number of values used in a card counting system. A level one counting system only uses +1 and -1, but a level two system would use +1, +2, -1 and -2…
Level of Free Convection (LFC) - The level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely.
Level of protection (LOP) As used in the evaluation process, it is the level of loading selected to which corrective actions will be designed to prevent dam failure.
Level of Service (LOS) A qualitative measure describing operational conditions within a traffic stream in terms of speed and travel time, freedom to maneuver, traffic…
Levelized Life Cycle Cost A total life cycle cost divided into equal amounts.