Intrinsic absorption

Clinical manifestation of vitamin B 2 deficiency is usually a result of absence of the gastric absorptive (intrinsic) factor. Dietary deficiency of vitamin B 2 is uncommon and may take 20 to 30 years to develop, even in healthy adults who foUow a strict vegetarian regimen. An effective enterohepatic recycling of the vitamin plus small amounts from bacterial sources and other contaminants greatly minimizes the risk of a complete dietary deficiency. Individuals who have a defect in vitamin B 2 absorption, however, may develop a deficiency within three to seven years. 

Doubled absorption Tripled absorption Intrinsic Extrinsic (human) 30... 

We have assumed up to now that besides lattice absorption, intrinsic semiconductors were essentially transparent to photon energies less than the band gap at RT and below. Now, like electrons in metals, the free carriers in semiconductors can absorb electromagnetic radiation to increase their energies. In the calculation of the intrinsic free-carrier concentrations in the VB and CB of a semiconductor, one has to consider the effective densities of states... 

V.B12 is also known as antipemicious anemia factor. Pernicious anemia is characterized by a severely reduced production of red blood cells, deficient gastric secretion and disturbances of the nervous system. It is not usually caused by dietary deficiency of V.B]2, but by the absence of intrirrsic factor, which is required for V.B[2 absorption. Intrinsic factor is a neuraminic acid-containing glycoprotein, normally present in the gastric mucosa, which forms a pepsin-resistant complex with V.B,2, and enables V.B,2 absorption in the lower part of the intestinal traet. 

Blood lead values in childhood vary with age and differ from those of adults living in the same environment. Conventional metabolic balance studies in children have limitations for the study of factors modifying lead absorption. Feeding studies, and the use of both isolated and in-vivo gut loops in laboratory animals have shown that major minerals, lipids and proteins, modify lead uptake and absorption. Intrinsic ma-turational changes modify the response to ingested lead and are relat-... 

The fast-motional nitroxide ESR spectrum is a superposition of three Lorentzian lines of different widths and, consequently, with different amplitudes when recorded as first derivative of the absorption. Intrinsic first-derivative peak-to-peak widths of fines, A/fpp, of the three components of the nitrogen hyperfine splitting in the fast-motional nitroxide spectra can be expressed as... 

Metabolism—It is noteworthy (1) that vitamin B-12 is the only vitamin that requires a specific gastrointestinal tract secretion for its absorption (intrinsic factor) and (2) that the absorption of vitamin B-12 in the small intestine requires about 3 hours (compared to seconds for most other water-soluble vitamins). The absorption of vitamin B-12 involves the following five steps ... 

The vitamin deficiency is often due to failure to absorb B12 from the stomach and can be alleviated by giving mg doses with extracts of hog s stomach which contains the intrinsic anti-pernicious anaemia factor (a muco-protein), which promotes the absorption. 

AH intrinsic germanium metal sold is specified to be N-type with a resistivity of at least 40 H-cm at 25°C or 50 H-cm at 20°C. Germanium metal prepared for use in infrared optics is usuaHy specified to be N-type with a resistivity of 4-40 Hem, to be stress-free and fine annealed, and to have certain minimum transmission (or maximum absorption) characteristics in the 3—5 or 8—12 pm wavelength ranges. Either polycrystaHine or single-crystal material is specified. 

Hafnium tetrafluoride [13709-52-9] is one component in the cladding layer of a proposed zirconium fluoride glass optical waveguide fiber composition which is expected to have a lower intrinsic light absorption than fused quart2 optical fiber (see Glass Fiber optics Fluorine compounds, inorganic-zirconium). 

Thickness. The traditional definition of thermal conductivity as an intrinsic property of a material where conduction is the only mode of heat transmission is not appHcable to low density materials. Although radiation between parallel surfaces is independent of distance, the measurement of X where radiation is significant requires the introduction of an additional variable, thickness. The thickness effect is observed in materials of low density at ambient temperatures and in materials of higher density at elevated temperatures. It depends on the radiation permeance of the materials, which in turn is influenced by the absorption coefficient and the density. For a cellular plastic material having a density on the order of 10 kg/m, the difference between a 25 and 100 mm thick specimen ranges from 12—15%. This reduces to less than 4% for a density of 48 kg/m. References 23—27 discuss the issue of thickness in more detail. 

The amount of each element required in daily dietary intake varies with the individual bioavailabihty of the mineral nutrient. BioavailabiUty depends both on body need as deterrnined by absorption and excretion patterns of the element and by general solubiUty, and on the absence of substances that may cause formation of iasoluble products, eg, calcium phosphate, Ca2(P0 2- some cases, additional requirements exist either for transport of substances or for uptake or binding. For example, calcium-binding proteias are iavolved ia calcium transport an intrinsic factor is needed for vitamin cobalt,... 

Intrinsic Factor. Vitamin B 2 deficiency commonly is caused by inadequate absorption resulting from a lack or insufficient intrinsic factor (IF) (153). 

Ideal Performance and Cooling Requirements. Eree carriers can be excited by the thermal motion of the crystal lattice (phonons) as well as by photon absorption. These thermally excited carriers determine the magnitude of the dark current,/ and constitute a source of noise that defines the limit of the minimum radiation flux that can be detected. The dark carrier concentration is temperature dependent and decreases exponentially with reciprocal temperature at a rate that is determined by the magnitude of or E for intrinsic or extrinsic material, respectively. Therefore, usually it is necessary to operate infrared photon detectors at reduced temperatures to achieve high sensitivity. The smaller the value of E or E, the lower the temperature must be. 

Spectral Sensitization. The intrinsic absorption, and therefore the intrinsic photographic sensitivity, of silver bromide and silver iodobromide microcrystals falls off rapidly for wavelengths greater than 500 nm (see Fig. 2). In fact, silver chloride crystals have almost no sensitivity in the visible... 

In 1929, Castie (7) tied the work of Combe and Addison with that of Whipple, Miaot, and Murphy by ptoposiag that both an extrinsic factor and an intrinsic factor ate iavolved ia the coatrol of pernicious anemia. The extrinsic factor, from food, is vitamin 2- Th intrinsic factor is a specific B22-biading protein secreted by the stomach. This protein is requited for vitamin B 2 absorption. 

Radioisotope dilution assays are based on the principle of competition between radioactive labeled ( Co) vitamin B 2 and cobalamins extracted from matrices for binding sites on the intrinsic factor (a glycoprotein). Binding is in proportion to the concentration of the radioactive and nonradio active B 2 with the concentration of intrinsic factor as the limiting factor. Free cobalamins are separated from those bound on the intrinsic factor by absorption... 

Electron spin resonance (esr) (6,44) has had more limited use in coal studies. A rough estimate of the free-radical concentration or unsatisfied chemical bonds in the coal stmcture has been obtained as a function of coal rank and heat treatment. For example, the concentration increases from 2 X 10 radicals/g at 80 wt % carbon to a sharp peak of about 50 x 10 radicals/g at 95 wt % carbon content and drops almost to zero at 97 wt % carbon. The concentration of these radicals is less than that of the common functional groups such as hydroxyl. However, radical existence seems to be intrinsic to the coal molecule and may affect the reactivity of the coal as well as its absorption of ultraviolet radiation. Measurements from room... 

Substances that are intrinsically fluorescent can often be exeited with long-wavelength UV light. They absorb the radiation and then emit, usually in the visible region of the spectrum, so that they appear as bright luminous zones, whieh can frequently be differentiated by color. They, thus, set themselves apart from the multitude of substances that only exhibit absorption. This detection possibility is characterized by high specificity (Sec. 2.3). 

In situ quantitation The reagent had no advantages for the direct determination of the acids investigated the determination of the intrinsic absorption or intrinsic fluorescences was to be preferred. 

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