Electrical resistivity and conductivityElectrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm-metre (Ω⋅m).
Nutrient pollutionNutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Raw sewage is a large contributor to cultural eutrophication since sewage is high in nutrients.
NitriteThe nitrite ion has the chemical formula NO2-. Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite also refers to organic compounds having the –ONO group, which are esters of nitrous acid. Sodium nitrite is made industrially by passing a mixture of nitrogen oxides into aqueous sodium hydroxide or sodium carbonate solution: The product is purified by recrystallization.
ContinentA continent is any of several large geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be a single landmass or a part of a very large landmass, as in the case of Asia or Europe. Due to this, the number of continents varies; up to seven or as few as four geographical regions are commonly regarded as continents. Most English-speaking countries recognize seven regions as continents.
Australia (continent)The continent of Australia, sometimes known in technical contexts by the names Sahul (səˈhuːl), Australia-New Guinea, Australinea, Meganesia, or Papualand to distinguish it from the country of Australia, is located within the Southern and Eastern hemispheres. The name "Sahul" takes its name from the Sahul Shelf, which is a part of the continental shelf of the Australian continent. The continent includes mainland Australia, Tasmania, the island of New Guinea (Papua New Guinea and Western New Guinea), the Aru Islands, the Ashmore and Cartier Islands, most of the Coral Sea Islands, and some other nearby islands.
OrganophosphateIn organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered as esters of phosphoric acid. Like most functional groups, organophosphates occur in a diverse range of forms, with important examples including key biomolecules such as DNA, RNA and ATP, as well as many insecticides, herbicides, nerve agents and flame retardants.
Boundaries between the continentsDetermining the boundaries between the continents is generally a matter of geographical convention. Several slightly different conventions are in use. The number of continents is most commonly considered seven (in English-speaking countries) but may range as low as four when Afro-Eurasia and the Americas are both considered as single continents. An island can be considered to be associated with a given continent by either lying on the continent's adjacent continental shelf (e.g.
Kjeldahl methodThe Kjeldahl method or Kjeldahl digestion (ˈkhelˌtɛˀl) in analytical chemistry is a method for the quantitative determination of nitrogen contained in organic substances plus the nitrogen contained in the inorganic compounds ammonia and ammonium (NH3/NH4+). Without modification, other forms of inorganic nitrogen, for instance nitrate, are not included in this measurement. Using an empirical relation between Kjeldahl nitrogen content and protein content it is an important method for analyzing proteins.
