High Quality Content by WIKIPEDIA articles! Heavy crude oil or extra heavy crude oil is any type of crude oil which does not flow easily. It is referred to as "heavy" because its density or specific gravity is higher than that of light crude oil. Heavy crude oil has been defined as any liquid petroleum with an API gravity less than 20°. Extra heavy oil is defined with API gravity below 10.0 °API (i.e. with density greater than 1000 kg/m3 or, equivalently, a specific gravity greater than 1). With a specific gravity of greater than 1, extra heavy crude is present as a dense non-aqueous phase liquid in ambient conditions.
High Quality Content by WIKIPEDIA articles! The Heck reaction (also called the Mizoroki-Heck reaction) is the chemical reaction of an unsaturated halide (or triflate) with an alkene and a base and palladium catalyst to form a substituted alkene. Together with the other palladium-catalyzed cross-coupling reactions, this reaction is of great importance, as it allows one to do substitution reactions on planar centers. It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry for the discovery and development of this reaction.
High Quality Content by WIKIPEDIA articles! Helium-3 (He-3, sometimes called tralphium) is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research. The abundance of helium-3 is thought to be greater on the Moon (embedded in the upper layer of regolith by the solar wind over billions of years) and the solar system`s gas giants (left over from the original solar nebula), though still low in quantity (28 ppm of lunar regolith is helium-4 and from 1 ppb to 50 ppb is helium-3).
High Quality Content by WIKIPEDIA articles! Hemerdon Mine, alternatively known as the Hemerdon Ball or Hemerdon Bal Mine, is a historic tungsten and tin mine. It is located 11 km (7 miles) NE of Plymouth, near Plympton, in Devon, England. It lies to the north of the villages of Sparkwell and Hemerdon and adjacent to the large china clay pits near Lee Moor. The mine, which has been out of operation since 1944, except for the brief operation of a trial mine in the 1980s, hosts one of the largest tungsten and tin deposits in the world.
High Quality Content by WIKIPEDIA articles! The Heslington Brain is a 2,600-year-old human brain found inside a skull buried in a pit in Heslington, Yorkshire, in England. It is the oldest preserved brain ever found in Europe or Asia, and is believed to be the best-preserved ancient brain in the world. The skull was discovered during an archaeological dig commissioned by the University of York on the site of its new campus on the outskirts of the city of York. The area was found to have been the site of well-developed permanent habitation between 2,000–3,000 years before the present day. A number of possibly ritualistic objects were found to have been deposited in several pits, including the skull, which had belonged to a man probably...
High Quality Content by WIKIPEDIA articles! A Heusler alloy is a ferromagnetic metal alloy based on a Heusler phase. Heusler phases are intermetallics with particular composition and face-centered cubic crystal structure. They are ferromagnetic—even though the constituting elements are not—as a result of the double-exchange mechanism between neighboring magnetic ions. The latter are usually manganese ions, which sit at the body centers of the cubic structure and carry most of the magnetic moment of the alloy. (See the Bethe-Slater curve for more info on why this happens.)
High Quality Content by WIKIPEDIA articles! Hexachlorophene, also known as Nabac, is a disinfectant. The compound occurs as a white to light-tan crystalline powder, which either is odorless or produces a slightly phenolic odor. In medicine, hexachlorophene is very useful as a topical anti-infective, anti-bacterial agent, often used in soaps and toothpaste. It is also used in agriculture as a soil fungicide, plant bactericide, and acaricide.
High Quality Content by WIKIPEDIA articles! Hexafluoroacetone is a chemical compound with the formula CF3-CO-CF3. It is structurally similar to acetone, however its reactivity is markedly different. It comes in the form of a colourless, hygroscopic, nonflammable, highly reactive gas characterized by a musty odour. The most common form of this substance is hexafluoroacetone sesquihydrate (1.5 H2O), which is a gem-diol.
High Quality Content by WIKIPEDIA articles! The High Flux Isotope Reactor (or HFIR) is a nuclear research reactor located at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, United States. Operating at 85 MW, HFIR is one of the highest flux reactor-based sources of neutrons for condensed matter research in the United States, and it provides one of the highest steady-state neutron fluxes of any research reactor in the world. The thermal and cold neutrons produced by HFIR are used to study physics, chemistry, materials science, engineering, and biology. The intense neutron flux, constant power density, and constant-length fuel cycles are used by more than 500 researchers each year for neutron scattering research into the...
High Quality Content by WIKIPEDIA articles! Hillforts in Britain refers to the various hillforts within the island of Great Britain. Although the earliest such constructs fitting this description come from the Neolithic period, with a few also dating to the later Bronze Age, British hill forts were primarily constructed during the Iron Age. Some of these were apparently abandoned in the southern areas that were a part of Roman Britain, although at the same time, those areas of northern Britain that remained free from Roman occupation saw an increase in their construction. Some hillforts were reused in the Early Mediaeval period, and in some rarer cases, into the Later Mediaeval period as well. By the Early Modern period these had...
High Quality Content by WIKIPEDIA articles! Hipposudoric acid is a red pigment found in the skin secretions of the hippopotamus; although the secretions are often known as "blood sweat" (thus the name "hipposudoric", referring to "hippo sweat"), they are neither blood nor sweat.
High Quality Content by WIKIPEDIA articles! The history of the periodic table reflects over a century of growth in the understanding of chemical properties, and culminates with the publication of the first actual periodic table by Dmitri Mendeleev in 1869. While Mendeleev built upon earlier discoveries by such scientists as Antoine-Laurent de Lavoisier and Stanislao Cannizzaro, the Russian scientist is generally given sole credit for development of the actual periodic table itself.
High Quality Content by WIKIPEDIA articles! History of metallurgy in the Indian subcontinent began during the 2nd millennium BCE and continued well into the British Raj.Metals and related concepts were mentioned in various early Vedic age texts. The Rigveda already uses the Sanskrit term Ayas (metal). The Indian cultural and commercial contacts with the Near East and the Greco-Roman world enabled an exchange of metallurgic sciences. With the advent of the Mughals, India`s Mughal Empire (established: April 21, 1526—ended: September 21, 1857) further improved the established tradition of metallurgy and metal working in India.
High Quality Content by WIKIPEDIA articles! The history of Cluj-Napoca covers the time from the Roman conquest of Dacia, when it was known as Napoca, through its flourishing as the main cultural and religious center in the historic province of Transylvania, until its modern existence as a city, the seat of Cluj County in north-western Romania.
High Quality Content by WIKIPEDIA articles! Hordenine, or N,N-dimethyltyramine, is an alkaloid of the phenethylamine class that occurs naturally in a variety of plants, taking its name from one of the commonest, barley (Hordeum species). Chemically, hordenine is the N-methyl derivative of N-methyltyramine, and the N,N-dimethyl derivative of the well-known biogenic amine tyramine, from which it is biosynthetically derived and with which it shares some pharmacological properties (see below). Currently, hordenine is widely sold as an ingredient of "nutritional supplements", with the claims that it is a "stimulant", of the central nervous system or otherwise, and has the ability to promote weight loss by enhancing metabolism. In experimental...
High Quality Content by WIKIPEDIA articles! Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood.
High Quality Content by WIKIPEDIA articles! The Hydra is a 22 person hydrogen ship, power-assisted by an electric motor that gets its electricity from a fuel cell. The debut was in June 2000 on the Rhine near Bonn, Germany.