For non-metallic materials, chemists try to get ultra-violet/visible spectra. In the case of semiconductors that will give an idea of the band gap.
Four-point (or five-point) probe methods are often applied either to ingots, crystals or pressed pellets to measure resistivity and the size of the Hall effect. This gives information on whether the compound is an insulator, semiconductor, semimetal or metal and upon the type of doping and the mobility in the delocalized bands (if present). So, important information is obtained on the chemical bonding in the material.
Magnetic susceptibility can be measured as function of temperature to establish whether the material is a para-, ferro- or antiferro- magnet. This tells the bonding in the material. This is particularly important for transition metal compounds. In the case of magnetic order, neutron diffraction can be used to find the magnetic structure.
Abdominal obesity
Abdominal obesity, also called central body obesity, is a condition involving excess fat surrounding the abdomen and an increase in waist size in humans. Obesity in this area is linked to Type 2 Diabetes, insulin resistance and heart disease in humans of both genders.
Alveolar consonant
An alveolar consonant is a consonant with the tongue close to the , which is the part just behind our teeth. Alveolar consonants that are pronounced with the tip of the tongue, like in English, are called while those pronounced using the blade of the tongue which is the flat part of the tongue behind the tip, are called . Alveolar consonants in English are , , , , and . The alveolar consonants , the , and , the , are the most common sounds in human languages.
The alveolar/coronal consonants identified by the IPA are:
List of programming languages
This is a list of programming languages.
John George Kemeny
John George Kemeny (31 May 1926 - 26 December 1992) developed BASIC with Thomas Eugene Kurtz at Dartmouth College, in 1964.
List of bus models
The following is a list of buses. It is not complete. The different types of bus, used in this chart, are:
There are over 300 buses in this list.
The year that is displayed refers to the first year of the model.
Year refers to the first year introduced. A range of years is the period the bus was manufactured.
Odontochelys
Odontochelys is the oldest known turtle to have been discovered. It was first described from three 220 million year-old specimens excavated in Upper Triassic rocks in Guizhou, China.
As a primitive turtle, "Odontochelys" differed from modern turtles in several ways. Modern turtles possess a horny beak without any teeth in their mouth. In contrast, "Odontochelys" fossils had teeth in their upper and lower jaws.
One of the most striking features of turtles, both modern and prehistoric alike, are their dorsal shells, forming an armored carapace over the body of the animal. "Odontochelys" only had the bottom portion of a turtle's armor, the plastron. It did not yet have a solid carapace as most other turtles do. Instead of a solid carapace, "Odontochelys" had broadened ribs like those of modern turtle embryos that still have not started developing the ossified plates of a carapace.
In a comparison of skull proportions, the skull of "Odontochelys" is far more elongated in front of the eyes compared to other turtles. The tail of the prehistoric turtle was longer in proportion to its body than other turtles. In addition, the transverse processes found in the tail are not fused such as in later turtles.
Taken together, these anatomical differences mean that "Odontochelys" has some of the most primitive features ever seen in a turtle and is somewhat of a transitional fossil. Some scientists, however, are skeptical of this idea. Reisz and Head suggest that "Odontochelys" does not represent a turtle with a partly evolved shell, but that it is a descendant of an older, land–living turtle, and that the shell became reversed. Such shells can be seen on modern turtles, like the leatherback turtles (the genus "Dermochelys").
It is likely that "Odontochelys" was aquatic, as the fossil specimens were found in marine deposits full of conodonts and ammonites. The primitive turtle swam in shallow marine waters close to shore.
The species' name, "Odontochelys semitestacea" literally means "toothed turtle with a half-shell" - an apt description of its most striking physical characteristics.
Band gap
A band gap, also called a bandgap or energy gap, is an energy range in a solid where no electron states can exist. The term is used in solid-state physics and chemistry.
Band gaps can be found in insulators and semiconductors. In graphs of the electronic band structure of solids, the band gap is the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band. This is the same as the energy needed to free an outer shell electron from its orbit about the nucleus to become a mobile charge carrier. The free electron is able to move freely within the solid material. So the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors. Conductors either have very small band gaps or no band gap if the energy levels of valence and conduction bands overlap.
Scientists use the band gap to predict if a solid will conduct electricity. Most electrons (called valence electrons) are attracted to the nucleus of just one atom. But if an electron has enough energy to fly away from its nearest nucleus, it can join in the flow of electric current across the many atoms that make up the solid. The electrons that are not tightly attached to just one nucleus are called the conduction band.
In semiconductors and insulators, quantum mechanics show that electrons are only found in a number of bands of energy. Electrons are forbidden from other energy levels. The term "band gap" refers to the energy difference between the top of the valence band and the bottom of the conduction band. Electrons are able to jump from one band to another. However, an electron needs a certain amount of energy to jump from a valence band to a conduction band. The amount of energy needed differs with different materials. Electrons can gain enough energy to jump to the conduction band by absorbing either a phonon (heat) or a photon (light).
A semiconductor is a material with a small but nonzero band gap which behaves as an insulator at absolute zero temperature (0 K) but allows heat to excite electrons enough to jump into its conduction band at temperatures which are below its melting point. In contrast, a material with a large band gap is an insulator. In conductors, the valence and conduction bands may overlap, so they may not have a band gap.
The conductivity of intrinsic semiconductors is strongly dependent on the band gap. The only available carriers for conduction are the electrons which have enough thermal energy to be excited across the band gap.
Band gap engineering is the process of controlling or altering the band gap of a material by controlling the composition of certain semiconductor alloys, such as GaAlAs, InGaAs, and InAlAs. It is also possible to construct layered materials with alternating compositions by techniques like molecular beam epitaxy. These methods are used in the design of heterojunction bipolar transistors (HBTs), laser diodes and solar cells.
It is hard to draw a line between semiconductors and insulators. One way is to think of semiconductors as a type of insulator with a narrow band gap. Insulators with a larger band gap, usually greater than 3 eV, are not put into the semiconductor group and generally do not exhibit semiconductive behavior under practical conditions. Electron mobility also plays a role in determining a material's informal grouping as a semiconductor.