Separation in space

In a mass spectrometer, ions can arrive at a multipoint collector as a spatially dispersed beam. This means that all ions of different m/z values arrive simultaneously but separated in space according to each m/z value. Each element of the array, depending on its position in space, detects one particular m/z value (see Chapter 29, Array Collectors ). 

Dielectric Constant The dielectric constant of material represents its ability to reduce the electric force between two charges separated in space. This propei ty is useful in process control for polymers, ceramic materials, and semiconduc tors. Dielectric constants are measured with respect to vacuum (1.0) typical values range from 2 (benzene) to 33 (methanol) to 80 (water). TEe value for water is higher than for most plastics. A measuring cell is made of glass or some other insulating material and is usually doughnut-shaped, with the cylinders coated with metal, which constitute the plates of the capacitor. 

Figure 6.21a) comprising two domains separated by a long straight a helix, similar in shape to troponin-C described in Chapter 2 (see Figure 2.13c). Each domain comprises two EF hands (see Figure 2.13a), each of which binds a calcium atom. The two domains are clearly separated in space at the two ends of the a helix linker. 

If the three light pulses of the pulse sequence are only separated in time, and not separated in space (i.e. if the velocity of the atoms is parallel to the laser beams), the interferometer is in a gravimeter or accelerometer configuration. In a uniformly accelerating frame with the atoms, the frequency of the driving... 

In semiconductors, which have a bandgap, recombination of the excited carriers— return of the electrons from the conduction band to vacancies in the valence band—is greatly delayed, and the lifetime of the excited state is much longer than in metals. Moreover, in n-type semiconductors with band edges bent upward, excess electrons in the conduction band will be driven away from the surface into the semiconductor by the electrostatic held, while positive holes in the valence band will be pushed against the solution boundary (Fig. 29.3). The electrons and holes in the pairs produced are thus separated in space. This leads to an additional stabihzation of the excited state, to the creation of some steady concentration of excess electrons in the conduction band inside the semiconductor, and to the creation of excess holes in the valence band at the semiconductor-solution interface. 

The H-bonding in the anhydrous 1 Im (Table 24) has topologic properties (Fig. 46) similar to those in the alcohol coordinatoclathrates of 1 with 1 2 host guest stoichiometry (cf. Fig. 17 a). Assuming a perfectly ordered crystal lattice, the resulting central loop of H-bonds should appear to have homodromic directionality with the donor/acceptor functions separated in space. This contrasts to the behavior in the dihydrated l Im where no such characteristic loops are formed. Involvement of the C—H hydrogen atoms of the imidazole molecule, however, is similar in both cases. 

During catabolic and anabolic processes, a renovation of the molecular cellular components takes place. It should be emphasized that the catabolic and anabolic pathways are independent of each other. Be these pathways coincident and differing in the cycle direction only, the metabolism would have been side-tracked to the so-called useless, or futile, cycles. Such cycles arise in pathology, where a useless turnover of metabolites may occur. To avoid this undesirable contingency, the synthetic and degradative routes in the cell are most commonly separated in space. For example, the oxidation of fatty acids occurs in the mitochondria, while the synthesis thereof proceeds extramitochondrially, in the microsomes. 

A two-dimensional cartoon is helpful in understanding overlap relationships between the important phase spaces /, and /. As illustrated in Fig. 6.1, there are four possible ways that /, and / can be related (a) / can form a subset of /, (b) /, and r may almost coincide, i.e., have complete overlap (c) T( and / may have partial overlap and (d) / and r may have no overlap. For simplicity, in Fig. 6.1 we have only considered the case in which / is continuous in space but the same principle applies to more-complicated situations, in which regions of / are separated in space. 

The DNA of advanced organisms is broken up into chromosomes so that there has to be cooperative connections between stretches of DNA well separated in space. 

Spatial resolution The ability of a telescope or other optical system to resolve sources separated in space - the eye can reveal features some 200 km apart on the surface of the moon. 

Focal plane detectors are used primarily to detect ions separated in space by, for example, magnetic sector analyzers (see Section 2.2.2). The objective of an ideal focal plane detector is to simultaneously record the location of every ion in the spectrum. In many ways the photoplate (see Section 2.3.1) is the original focal plane detector, but it has today been more or less replaced with designs that rely on EM detectors (see Section 2.3.3). A common arrangement is to allow the spatially disperse ion beams simultaneously to impinge on an MCP (see Section 2.3.3.2). The secondary electrons generated by the ion impacts then strike a one- or two-dimensional array of metal strips and the current from the individual electrodes is recorded. A tutorial on the fundamentals of focal plane detectors is found in Reference 283. Reference 284 provides a relatively recent review of MS detector-array technology. 

Hexanitrostilbene or HNS (C14H6N6012) is a heat-resistant yellow crystalline solid explosive. HNS is also resistant to radiation, insensitive to electric sparks, and less sensitive to impact than tetryl. It is used in heat-resistant booster explosives and has been used in stage separations in space rockets and for seismic experiments on the moon. Its melting temperature is 316 °C.12... 

Keeping in view, this specific, rigid and stringent requirement, the separation-in-space method is found to be normally of lower precision and accuracy than the separation-in time-method. 

Evidently, the optical choppers are quite expensive, and therefore, the instrument manufacturers very often utilize the separation-in-space method for the routine measurement spectrophotometers. 

Let us continue with the example of copper ions in contact with copper metal and zinc ions in contact with zinc metal. This combination is usually referred to as the Darnell cell or zinc/copper couple(Fig. 6.5a). For this electrochemical cell the reduction and oxidation processes responsible for the overall reaction are separated in space one half reaction taking place in one electrode compartment and the other takes place in the other compartment. 

One striking characteristic of the coupling ATPase of energy-transducing membranes, apart from the extraordinarily large number of different polypeptide subunits, is the existence of two different polypeptides involved in the response of the enzyme to the inhibitor oligomycin. One binds the inhibitor, the other, separated in space from the former by possibly as much as 10 to 15 A, confers oligomycin sensitivity to the entire enzyme complex. How could the transfer of information between these two polypeptide subunits and their concerted interaction with the ATPase proper be visualized ... 

Hexanitroshlbene (HNS) has been reported for use in achieving stage separation in space rockets and also as a component of heat-resistant compositions employed in the Apollo spaceship and for seismic experiments on the moon [107]. Similar to HNS, 3,3 -diamino-2,2, 4,4, 6,6 -hexanitrodiphenyl (DIPAM) has also been reported for such applications [108]. 

Diamino-2,2, 4,4 6,6 -hexanitrodiphenyl (DIPAM) [Structure (2.30)] is extremely insensitive to electrostatic discharge, requiring more than 32 kj for initiation. In addition, it has good thermal stability (m.p. ca. 304 °C) and has been used to achieve stage separation in space rockets and for seismic experiments on the moon in a manner similar to HNS [74]. 

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