MediaTek Inc. (Chinese: 聯發科技股份有限公司; pinyin: Liánfā Kējì Gǔfèn Yǒuxiàn Gōngsī) is a Taiwanese fabless semiconductor company that provides chips for wireless communications, high-definition television, handheld mobile devices like ...
- as A Pigment
- Role in Human Eyes
- in Diet
- Commercial Value
- See Also
This xanthophyll, like its sister compound zeaxanthin, has primarily been used in food and supplement manufacturing as a colorant due to its yellow-red color. Lutein absorbs blue light and therefore appears yellowat low concentrations and orange-red at high concentrations. Many songbirds (like golden oriole, evening grosbeak, yellow warbler, common yellowthroat and Javan green magpie, but not American goldfinch or yellow canaries) deposit lutein obtained from the diet into growing tissues to color their feathers.
Although lutein is concentrated in the macula – a small area of the retinaresponsible for three-color vision – the precise functional role of retinal lutein has not been determined.
Lutein is a natural part of a human diet found in orange-yellow fruits and flowers, and in leafy vegetables. According to the NHANES 2013-2014 survey, adults in the United States consume on average 1.7 mg/day of lutein and zeaxanthin combined. No recommended dietary allowance currently exists for lutein. Some positive health effects have been seen at dietary intake levels of 6–10 mg/day. The only definitive side effect of excess lutein consumption is bronzing of the skin (carotenodermia). As a food additive, lutein has the E number E161b (INS number 161b) and is extracted from the petals of African marigold (Tagetes erecta). It is approved for use in the EU and Australia and New Zealand. In the United States lutein may not be used as a food coloring for foods intended for human consumption, but can be added to animal feed and is allowed as a human dietary supplement often in combination with zeaxanthin. Example: lutein fed to chickens will show up in skin color and...
The lutein market is segmented into pharmaceutical, dietary supplement, food, pet food, and animal and fish feed. The pharmaceutical market for lutein is estimated to be about US$190 million, and the nutraceutical and food categories are estimated to be about US$110 million. Pet food and other animal applications for lutein are estimated at US$175 million annually. This includes chickens (usually in combination with other carotenoids), to get color in egg yolks, and fish farms to color the flesh closer to wild-caught color. In the dietary supplement industry, the major market for lutein is for products with claims of helping maintain eye health.Newer applications are emerging in oral and topical products for skin health. Skin health via orally consumed supplements is one of the fastest growing areas of the US$2 billion carotenoid market.
- 568.871 g/mol
- 190 °C (374 °F; 463 K)
- Physics of Semiconductors
- Early History of Semiconductors
- See Also
- Further Reading
- External Links
Variable electrical conductivity
Semiconductors in their natural state are poor conductors because a current requires the flow of electrons, and semiconductors have their valence bands filled, preventing the entire flow of new electrons. Several developed techniques allow semiconducting materials to behave like conducting materials, such as doping or gating. These modifications have two outcomes: n-type and p-type. These refer to the excess or shortage of electrons, respectively. An unbalanced number of electrons would cause...
Heterojunctions occur when two differently doped semiconducting materials are joined together. For example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials. The n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. The transfer occurs until an equilibrium is reached by a process called recombination, which causes the...
A difference in electric potential on a semiconducting material would cause it to leave thermal equilibrium and create a non-equilibrium situation. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion. Whenever thermal equilibrium is disturbed in a semiconducting material, the number of holes and electrons changes. Such disruptions can occur as a result of a temperature difference or photons, which can enter the system and create electrons...
A large number of elements and compounds have semiconducting properties, including: 1. Certain pure elements are found in Group 14 of the periodic table; the most commercially important of these elements are silicon and germanium. Silicon and germanium are used here effectively because they have 4 valence electrons in their outermost shell which gives them the ability to gain or lose electrons equally at the same time. 2. Binary compounds, particularly between elements in Groups 13 and 15, such as gallium arsenide, Groups 12 and 16, groups 14 and 16, and between different group 14 elements, e.g. silicon carbide. 3. Certain ternary compounds, oxides, and alloys. 4. Organic semiconductors, made of organic compounds. 5. Semiconducting Metal-organic frameworks. The most common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are also known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of...
Energy bands and electrical conduction
Semiconductors are defined by their unique electric conductive behavior, somewhere between that of a conductor and an insulator. The differences between these materials can be understood in terms of the quantum states for electrons, each of which may contain zero or one electron (by the Pauli exclusion principle). These states are associated with the electronic band structure of the material. Electrical conductivity arises due to the presence of electrons in states that are delocalized (exten...
The partial filling of the states at the bottom of the conduction band can be understood as adding electrons to that band. The electrons do not stay indefinitely (due to the natural thermal recombination) but they can move around for some time. The actual concentration of electrons is typically very dilute, and so (unlike in metals) it is possible to think of the electrons in the conduction band of a semiconductor as a sort of classical ideal gas, where the electrons fly around freely without...
The conductivity of semiconductors may easily be modified by introducing impurities into their crystal lattice. The process of adding controlled impurities to a semiconductor is known as doping. The amount of impurity, or dopant, added to an intrinsic (pure) semiconductor varies its level of conductivity. Doped semiconductors are referred to as extrinsic.By adding impurity to the pure semiconductors, the electrical conductivity may be varied by factors of thousands or millions. A 1 cm3 specim...
The history of the understanding of semiconductors begins with experiments on the electrical properties of materials. The properties of the time-temperature coefficient of resistance, rectification, and light-sensitivity were observed starting in the early 19th century. Thomas Johann Seebeck was the first to notice an effect due to semiconductors, in 1821. In 1833, Michael Faraday reported that the resistance of specimens of silver sulfide decreases, when they are heated. This is contrary to the behavior of metallic substances such as copper. In 1839, Alexandre Edmond Becquerel reported observation of a voltage between a solid and a liquid electrolyte, when struck by light, the photovoltaic effect. In 1873, Willoughby Smith observed that selenium resistors exhibit decreasing resistance, when light falls on them. In 1874, Karl Ferdinand Braun observed conduction and rectification in metallic sulfides, although this effect had been discovered much earlier by Peter Munck af Rosenschold...A. A. Balandin & K. L. Wang (2006). Handbook of Semiconductor Nanostructures and Nanodevices (5-Volume Set). American Scientific Publishers. ISBN 978-1-58883-073-9.Sze, Simon M. (1981). Physics of Semiconductor Devices (2nd ed.). John Wiley and Sons (WIE). ISBN 978-0-471-05661-4.Turley, Jim (2002). The Essential Guide to Semiconductors. Prentice Hall PTR. ISBN 978-0-13-046404-0.Yu, Peter Y.; Cardona, Manuel (2004). Fundamentals of Semiconductors : Physics and Materials Properties. Springer. ISBN 978-3-540-41323-3.
This Kanji index method groups together the kanji that are written with the same number of strokes. Currently, there are 2,187 individual kanji listed. Characters followed by an alternate in (parentheses) indicate a difference between the ...