Positioning the carrier

The width of the frequency window in an FT NMR experiment is the digitizing rate if the folding problems are ignored. 

Since the carrier is the reference frequency in the detection process, it becomes the origin for the frequency scale after the Fourier transform. It is strictly arbitrary whether the frequency scale runs left to right or conversely but the usual convention is to plot the spectra so that the frequency increases to the left. This is equivalent to the laboratory field increasing to the right in cw NMR, an even older convention. 

The spins resonating upfield experience a smaller fraction of the applied field than those downfield because they are shielded better, i.e., their atomic electrons contribute induced fields opposed to the laboratory field. Thus, an alternative description for these cases is that the well-shielded spins are diamagnetically shifted and, conversely, the less- 

In any event, the spectrum moves back and forth in the window when the carrier frequency is changed. Assuming the conventional spectral representation discussed above, increasing the carrier frequency causes the window to move toward higher frequencies relative to the spectrum so that the spectrum will move to the right. Likewise, decreasing the carrier frequency will move the spectrum to the left. 

If the window is not large enough to contain the entire spectrum, any lines which lie outside it will be folded back into the window an equal distance from the edge. Such folded lines can be so identified in two ways. First, they will not phase properly so that the correction giving the correct phase for the rest of the spectrum will not be correct for the folded lines. Secondly, the folded lines will move in the wrong direction when the carrier frequency is moved. Whenever there is a possibility of folded lines, increase the digitizing rate to increase the window width or change the carrier to move the window. 

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In the bypass position, the carrier solution flows through the bypass loop and across the ISFET. The sample is injected into the sampling valve and is introduced into the carrier solution. The bypass loop has a high hydrodynamic resistance and thus the solution proceeds to the detector. The reference electrode is always immersed only in the carrier solution and is electrically connected with the ISFET through the solutioa The apparatus is regularly calibrated by K, Ca and pH standard solutions. 

An injection system A six-way rotary valve (three inlets and three outlets) that can adopt two positions—in the filling position the sample fills the loop in the injecting position, the carrier sweeps the sample toward the reactor)... 

A practical solution consists of a carousel line with a row of service positions where the operators can work on moulds that have been temporarily taken off-line (see Figure 3.13). When the press leaves the curing area, it passes in front of the first free operator and is automatically disengaged by the dragging system. The moulds can be serviced, taking all the time required, then, when the textile inserts have been positioned, the carrier can be reinserted in the first available position in the line. 

The uncertainty principle, according to which either the position of a confined microscopic particle or its momentum, but not both, can be precisely measured, requires an increase in the carrier energy. In quantum wells having abmpt barriers (square wells) the carrier energy increases in inverse proportion to its effective mass (the mass of a carrier in a semiconductor is not the same as that of the free carrier) and the square of the well width. The confined carriers are allowed only a few discrete energy levels (confined states), each described by a quantum number, as is illustrated in Eigure 5. Stimulated emission is allowed to occur only as transitions between the confined electron and hole states described by the same quantum number. 

Initiators. The degree of polymerization is controlled by the addition rate of initiator(s). Initiators (qv) are chosen primarily on the basis of half-life, the time required for one-half of the initiator to decay at a specified temperature. In general, initiators of longer half-Hves are chosen as the desired reaction temperature increases they must be well dispersed in the reactor prior to the time any substantial reaction takes place. When choosing an initiator, several factors must be considered. For the autoclave reactor, these factors include the time permitted for completion of reaction in each zone, how well the reactor is stirred, the desired reaction temperature, initiator solubiUty in the carrier, and the cost of initiator in terms of active oxygen content. For the tubular reactors, an additional factor to take into account is the position of the peak temperature along the length of the tube (9). 

Based on the Monte Carlo simulations, it is seen that the presence of positional disorder causes the mobiUty to decrease with increasing field at low fields (37). This is the case because the introduction of positional disorder into the system provides the carrier with energetically more favorable routes, which occasionally are against the field direction. These detour routes are most efficient at low fields, but are eliminated at high fields. This rationalizes the decrease of hole mobilities with increasing field. 

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 electrical conductivity in the solid state is determined by the product of the carrier concentration and the carrier mobility. In conjugated polymers both entities are material dependent and, i.e., are different for electrons and holes. Electrons or holes placed on a conjugated polymer lead to a relaxation of the surrounding lattice, forming so-called polarons which can be positive or negative. Therefore, the conductivity, o, is the sum of both the conductivity of positive (P+) and negative polarons (P ) ... 

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