Volume selection

Recovery factor Reduced column length Reduced plate height Reduced velocity Relative retention ratio Retardation factor d Retention time Retention volume Selectivity coefficient Separation factor... 

Federal Carrier Cases, Commerce Clearing House, Inc., Chicago, HI. Continuing series of volumes selectively reporting decisions of ICC and U.S. federal and state courts pertaining to motor carrier, water carrier, and domestic freight forwarder regulation. 

From Figure 5-26 and the inlet volume, select an initial impeller diameter. d2 = 17.3 inches impeller diameter... 

Heterogeneity, nonuniformity and anisotropy are based on the probability density distribution of permeability of random macroscopic elemental volumes selected from the medium, where the permeability is expressed by the one-dimensional form of Darcy s law. 

In order to have effective exchange of air in important locations in a room, the age of the air in those locations should be low. The basis for comparison is the complete mixing scenario. That scenario gives the same age for any air volume selected in the room, identical to the nominal time constant for the ventilation airflow,. A steady-state scenario is assumed. See Sutcliffe for an overview of definitions related to age of air. The various air exchange efficiency indices are presented in Table 8.6. 

Lyophillzation Hater sample is frozen and pure water is removed by sublimation under vacuum. Nonvolatile organics Can handle large sample volumes. Selective loss of volatile organics. Inorganic constituents concentrated simultaneously. 

Another approach to obtain spatially selective chemical shift information is, instead of obtaining the entire image, to select only the voxel of interest of the sample and record a spectrum. This method called Volume Selective spectroscopY (VOSY) is a ID NMR method and is accordingly fast compared with a 3D sequence such as the CSI method displayed in Figure 1.25(a). In Figure 1.25(b), a VOSY sequence based on a stimulated echo sequence is displayed, where three slice selective pulses excite coherences only inside the voxel of interest. The offset frequency of the slice selective pulse defines the location of the voxel. Along the receiver axis (rx) all echoes created by a stimulated echo sequence are displayed. The echoes V2, VI, L2 and L3 can be utilized, where such multiple echoes can be employed for signal accumulation. 

In the following sections (Sections 5.5.2.2 and 5.5.2.3), two approaches to spatially resolving chemical conversion within a reactor are demonstrated (a) n-dimensional Chemical Shift Imaging (CSI), and (b) volume selective spectroscopy. 

Exploring Spatial Heterogeneity in Conversion Volume Selective Imaging... 

Figure 5.5.8 shows the volume selective spectroscopy pulse sequence used. This pulse sequence combines elements of NMR spectroscopy and MRI pulse sequences three slice selective rf pulses are applied in three orthogonal directions to obtain 1H spectra from pre-determined local volumes within the sample [30]. In this particular application, spectra were recorded from local volumes of dimension 1.5 mm x 1.5 mm x 0.5 mm within the fixed bed the data acquisition time for each spectrum was 3 min. Figure 5.5.9(a) shows the local volumes selected within slice 3 of the bed, as identified in Figure 5.5.7. In Figure 5.5.9(b) the 1H spectra recorded from within these volumes are shown data are presented only for the range of... 

Fig. 5.5.8 The volume selective spectroscopy rf pulse sequence used to acquire the data shown in Figures 5.5.9-5.5.11. Magnetic field gradients applied alongthex, y and zdirections enable localized spectra to be recorded from...

Fig. 5.5.9 Volume selective spectroscopy within the fixed-bed reactor, (a) The location of the ten selected volumes within image slice 3 (see Figure 5.5.7) are identified, (b) It is clearly seen that the chemical shifts of peak B obtained from the spectra recorded from the selected volumes occur at significantly different values...

Studies of this reaction have recently been extended to acquisition of a 3(4)D CSI dataset, shown in Figure 5.5.12 the grey scale indicates the extent of conversion. As expected from the 1(2)D CSI and volume selective imaging studies discussed earlier, conversion is seen to be heterogeneous within transverse sections through the bed at any position along the direction of superficial flow. 

Let us see how to represent changes in properties for a system volume to property changes for a control volume. Select a control volume (CV) to be identical to volume V t) at time t, but to have a different velocity on its surface. Call this velocity, w. Hence, the volume will move to a different location from the system volume at a later time. For example, for fluid flow in a pipe, the control volume can be selected as stationary (w = 0) between locations 1 and 2 (shown in Figure 3.4, but the system moves to a new location later in time. Let us apply the Reynolds transport theorem, Equation (3.9), twice once to a system volume, V(t), and second to a control volume, CV, where CV and V are identical at time t. Since Equation (3.9) holds for any well-defined volume and surface velocity distribution, we can write for the system... 

Since diffusional effects are most important, we wish to emphasize these processes in the gas phase. For the control volume selected in Figure 9.7, the bold assumption is made that transport processes across the lateral faces in the x direction do not change - or change very slowly. Thus we only consider changes in the y direction. This approximation is known as the stagnant layer model since the direct effect of the main flow velocity (it) is not expressed. A differential control volume Ay x Ax x unity is selected. 

Figure 9.20 Control volumes selected in the condensed phase...

In this pulse sequence the attributes of NMR spectroscopy and MR imaging are again combined. In this case three slice-selective r.f. pulses are applied in three orthogonal directions to obtain H spectra from predetermined local volumes within the sample.27 A typical volume-selective spectroscopy pulse sequence is shown in... 

Fig. 9 A volume-selective spectroscopy r.f. pulse sequence. Magnetic field gradients applied along x-, y-, and z-directions enable recording of localized spectra from pre-defined local volume elements within the sample.

Fig. 12. Sequences for volume selective single voxel spectroscopy. Both techniques work with three slice-selective RF-pulses. (a) The Point RESolved Spectroscopy (PRESS) sequence generates a volume selective double spin-echo. The entire time delay between the initial 90° excitation and the echo is sensitive to transverse relaxation, (b) The Stimulated Echo Acquisition Mode (STEAM) sequence generates a stimulated echo. Maximal signal intensity (without relaxation effects) is only half the signal intensity of PRESS under comparable conditions, but slice profiles are often better (only 90° pulses instead of 180° pulses) and the TM interval is not susceptible to transverse relaxation, (c) The recorded echo signal is only generated in a volume corresponding to the intersection of all three slices.

Relaxation times, MT ratios, and diffusion properties allow insight into the microstructure of various tissues. Determination of these parameters is possible by recording and analysing of a series of volume selective spectra, even for metabolites with relatively low concentrations in vivo. For recording series of spectra usually one parameter is changeable (e.g., inversion time TI for Ti measurements, echo time TE for T2 measurements, MT preparation for assessment of spin transfer and chemical reaction rates, or diffusion sensitizing gradients for assessment of apparent diffusion coefficients or even diffusion... 

Since the beginning of the Series in 1964, two main developments have occurred. The first of these is the publication of supplementary volumes which contain material relating to several kindred functional groups (Supplements A, B, C, D, E, F and S). The second ramification is the publication of a series of Updates , which contain in each volume selected and related chapters, reprinted in the original form in which they were published, together with an extensive updating of the subjects, if possible, by the authors of the original chapters. A complete list of all above mentioned volumes is available from the publisher. Unfortunately, the publication of the Updates has been discontinued for economic reasons. 

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