Carrier, elemental

All carrier solutions should be properly labeled to indicate the carrier element (e.g., Sr, Y). Also on the label should be the concentration of the carrier with its standard deviation, the concentration and the chemical form of the solution (e.g., 0.01M HN03), the date of preparation and the initials of the analyst. An example is given in Fig. 5.1. 

Figure 24 X-ray maps of trace elements and Ca from garnet-bearing quartzite, showing spatially coincident, pronounced spikes. The location of these spikes is systematically different in different-sized garnets, relative to Fe-Mg-Mn systematics (Chernoff and Carlson, 1997,1999). Diffusionally produced haloes around growing crystals can cause sudden stabilization or destabilization of minerals (Johnson and Carlson, 1990). The coincidence of spikes in many trace elements as well as Ca is interpreted to reflect modal changes in a mineral like apatite or allanite. A common, diffusional mechanism for intergranular diffusion of trace elements and Ca may also be required, possibly by complexing with a common, slow-diffusing carrier element (Chernoff and Carlson, 1999) (reproduced by permission of GSA from Geology, 1999, 27, 555-558).

The chemical separation methods of activation analysis in which the radionuclides of interest are chemically isolated follow the schemes usually used in inorganic quantitative analysis. After the sample has been activated, it is decomposed or solubilized in the presence of a known weight of a nonradioactive chemical carrier, that is, a known amount of the stable element of interest. The addition of the carrier and the initiation of chemical reactions that permit an exchange of the radioactive and nonradioactive species is followed by a chemical isolation of the two species in a suitable stoichiometric form and the ultimate determination of the amount of carrier element (and thus the radioactive element) recovered. This type of separation does not need to be quantitative because the radioactivity measurements can be corrected for the measured yield of the carrier recovered from the chemical separation. 

Horizontal systems have been used mainly for heterogeneous bioassay where the separation of the free and bound labeled molecules is accomplished by capillary migrations through the carrier element. 

Several decorating processes use heat to transfer a decoration or a printed image to the plastic part surface. These techniques usually use a carrier element, the decorative media, and an adhesive. In certain... 

With the increasing mass of the carrier construction, the acceleration acting on the aggregate is reduced. Here one speaks of the so-called inertia of the carrier elements. 

An alternative form of distribution coefficient (Henderson and Kracek Formula) which has been comparatively little used in geochemistry, introduces the concept of carrier elements which can be thoiight of as the major elements for which the trace element... 

Initially, the only means of obtaining elements higher than uranium was by a-particle bombardment of uranium in the cyclotron, and it was by this means that the first, exceedingly minute amounts of neptunium and plutonium were obtained. The separation of these elements from other products and from uranium was difficult methods were devised involving co-precipitation of the minute amounts of their salts on a larger amount of a precipitate with a similar crystal structure (the carrier ). The properties were studied, using quantities of the order of 10 g in volumes of... 

We can descnbe the major elements of fatty acid biosynthesis by considering the for mation of butanoic acid from two molecules of acetyl coenzyme A The machinery responsible for accomplishing this conversion is a complex of enzymes known as fatty acid synthetase Certain portions of this complex referred to as acyl carrier protein (ACP), bear a side chain that is structurally similar to coenzyme A An important early step m fatty acid biosynthesis is the transfer of the acetyl group from a molecule of acetyl coenzyme A to the sulfhydryl group of acyl carrier protein... 

There are many potential advantages to kinetic methods of analysis, perhaps the most important of which is the ability to use chemical reactions that are slow to reach equilibrium. In this chapter we examine three techniques that rely on measurements made while the analytical system is under kinetic rather than thermodynamic control chemical kinetic techniques, in which the rate of a chemical reaction is measured radiochemical techniques, in which a radioactive element s rate of nuclear decay is measured and flow injection analysis, in which the analyte is injected into a continuously flowing carrier stream, where its mixing and reaction with reagents in the stream are controlled by the kinetic processes of convection and diffusion. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Molybdenum hexafluoride can be prepared by the action of elemental fluorine on hydrogen-reduced molybdenum powder (100—300 mesh (ca 149—46 l-lm)) at 200°C. The reaction starts at 150°C. Owing to the heat of reaction, the temperature of the reactor rises quickly but it can be controlled by increasing the flow rate of the carrier gas, argon, or reducing the flow of fluorine. 

Wire Interconnect Materials. Wire-bonding is accompHshed by bringing the two conductors to be joined into such intimate contact that the atoms of the materials interdiffuse (2). Wire is a fundamental element of interconnection, providing electrical connection between first-level (ie, the chip or die) and second-level (ie, the chip carrier, or the leadframe in a single-chip carrier) packages. 

Atoms of elements that are characterized by a valence greater than four, eg, phosphoms or arsenic (valence = 5), are one type of dopant. These high valence dopants contribute free electrons to the crystal and are cabed donor dopants. If one donor atom is incorporated in the lattice, four of the five valence electrons of donor dopants are covalentiy bonded, but the fifth electron is very weakly bound and can be detached by only ca 0.03 eV of energy. Once it is detached, it is available as a free electron, ie, a carrier of electric current. A sibcon crystal with added donor dopants has excess electron carriers and is cabed n-ty e (negative) sibcon (Fig. Ic). 

When a sibcon crystal is doped with atoms of elements having a valence of less than four, eg, boron or gallium (valence = 3), only three of the four covalent bonds of the adjacent sibcon atoms are occupied. The vacancy at an unoccupied covalent bond constitutes a hole. Dopants that contribute holes, which in turn act like positive charge carriers, are acceptor dopants and the resulting crystal is -type (positive) sibcon (Fig. Id). 

The catalyst combines two essential ingredients found in eadier catalysts, vanadium oxide and titanium dioxide, which are coated on an inert, nonporous carrier in a layer 0.02- to 2.0-mm thick (13,16). Other elements such as phosphoms are also used. Ring-shaped supports are used instead of spherical supports to give longer catalyst life, less pressure drop though the reactor, and higher yields (17,18). Half rings are even better and allow more catalyst to be loaded (18). 

A widely used procedure for determining trace amounts of selenium involves separating selenium from solution by reduction to elemental selenium using tellurium (as a carrier) and hypophosphorous acid as reductant. The precipitated selenium, together with the carrier, are collected by filtration and the filtered soflds examined directly in the wavelength-dispersive x-ray fluorescence spectrometer (70). Numerous spectrophotometric and other methods have been pubHshed for the deterruination of trace amounts of selenium (71—88). 

The variations in D and D and the much larger value for In show the limitations of a simple hydrogen atom model. Other elements, particularly transition metals, tend to introduce several deep levels in the energy gap. For example, gold introduces a donor level 0.54 eV below D and an acceptor level 0.35 eV above D in siHcon. Because such impurities are effective aids to the recombination of electrons and holes, they limit carrier lifetime. 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

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