Steady-state free procession

In imaging, faster accumulation by means of the steady-state free procession (SSFP) has been used successfully for 15N, but the method has so far not been reported for spectroscopy, although it should prove useful there also, provided proper attention is paid to phasing problems. 

The steady-state free-procession (SSFP) technique was used with no NOE, and in the case of aniline the T of the 15N was reduced by addition of chromium acetylacetate as a relaxation reagent to the sample. The 15N spectrum of aniline showed a single broad line (Avi/2 = 42 Hz) in which, because of proton exchange125,126, there is no evidence of N H coupling (J = 80 Hz). 

Description. The model organism is a free-floating unicellular sphere with characteristics selected, where possible, to match those of a phytoplankton cell. The organism and its environment (Figure Ic) are divided into four concentric zones -the bulk solution, the diffusion layer, the containing membrane and the cell concents. We will assume that the species taken up by the cell is the free metal ion since most of the studies of the uptake of B-subgroup metals by organisms support this hypothesis Z . 5 steady-state transport processes are... 

A steady-state free-radical styrene polymerization process is being controlled such that the rate of polymerization is constant at 1.79 g of monomer/ml-min. The initiator concentration is 6.6 x 10 molAnl. 

We have explored the possibility that deactivation of polydimethylsiloxane-hydrophobed silica antifoams by disproportionation is a consequence of the random distribution of particles across the drops formed when the antifoam is dispersed to achieve a steady state by processes of drop splitting and coalescence. Simple mass balance considerations permit the estimation of the composition of deactivated antifoam dispersions if we assume they are made up of particle-free drops together with particle-rich drops and agglomerates of known silica content From that composition, it is possible to calculate the ratio of the number of particles to the number of drops, NM, in a deactivated antifoam if the distribution of particles across drops is assumed to be random. This analysis reveals that for monodisperse particles and drops where NIM < 1 this necessarily implies a proportion of particle-free drops irrespective of the nature of any distribution If, on the other hand, NIM > 1, then the probability of finding particle-free drops is always vanishingly small. 

The emission signal corresponding to benzene confirms that it is formed by a free-radical process. As in steady-state EPR experiments, the enhanced emission and absorption are observed only as long as the reaction is proceeding. When the reaction is complete or is stopped in some way, the signals rapidly return to their normal intensity, because equilibrium population of the two spin states is rapidly reached. 

In the pneumatic conveying process the flow around the particle is not uni form, the particle is not in steady-state motion, and the flow contains turbulence which is not merely generated by the particles. Thus the use of Eqs. (14.23)-(14.29) is of course rather restricted. Despite these limitations we will now esti mate the free-falling velocity of a set of different-sized particles based on the assumption that we know the free-falling velocity of each single particle. 

Most vibration programs that use microprocessor-based analyzers are limited to steady-state data. Steady-state vibration data assumes the machine-train or process system operates in a constant, or steady-state, condition. In other words, the machine is free of dynamic variables such as load, flow, etc. This approach further assumes that all vibration frequencies are repeatable and maintain a constant relationship to the rotating speed of the machine s shaft. 

In the normal acquisition process, the analyzer acquires multiple blocks of data. As part of the process, the microprocessor compares each block of data as it is acquired. If a block contains a transient that is not included in subsequent blocks, the block containing the event is discarded and replaced with a transient-free block. As a result, steady-state analysis does not detect random events that may have a direct, negative effect on equipment reliability. 

Achieving steady-state operation in a continuous tank reactor system can be difficult. Particle nucleation phenomena and the decrease in termination rate caused by high viscosity within the particles (gel effect) can contribute to significant reactor instabilities. Variation in the level of inhibitors in the feed streams can also cause reactor control problems. Conversion oscillations have been observed with many different monomers. These oscillations often result from a limit cycle behavior of the particle nucleation mechanism. Such oscillations are difficult to tolerate in commercial systems. They can cause uneven heat loads and significant transients in free emulsifier concentration thus potentially causing flocculation and the formation of wall polymer. This problem may be one of the most difficult to handle in the development of commercial continuous processes. 

The steady-state balance of the Ca pump and plasma membrane leaks of Ca determines the resting intracellular free Ca concentration. Kinetically, all the other membrane bound compartments and their transport processes are analogous to buffer systems with various rates of binding and release. The essential point is that all the other pools must come to steady-state with the intracellular free concentration. Thus, the plasma membrane Ca -pump for the Ca economy of the cell has primacy. 

In reality, many other chemical and photochemical processes take place leading to a sort of steady-state concentration of O3 which is a sensitive function of height. To be accurate, it is necessary to include the reactions of nitrogen oxides, chlorine- and hydrogen-containing free radicals (molecules containing an unpaired electron). However, occurrence of a layer due to the altitude dependence of the photochemical processes is of fundamental geochemical importance and can be demonstrated simply by the approach of Chapman (1930). 

Figure 9 illustrates the fret that the release of biocide from the carriers is a dynamic process. Here a quantity of loaded carrier was slurried with a fixed volume of water and aliquots taken after 1 hour. From previous experiments it was found that after an initial period of rapid release, a steady-state concentration of free biocide was present in the aqueous extract. To probe the effects of repetitive extraction, the carrier was filtered from the slurry, the water replenished and the process repeated. It can be seen that only after ten successive extractions does the amount of the biocide OIT released by the carrier fall below the MIC. It should be noted that the conditions employed to illustrate this continuous release are rather more severe than would be experienced when the loaded carrier is incorporated in a coating (see Section 2.5). 

Because there are two positive terms in the denominator of equation 4.2.85 (either of which may be associated with the dominant termination process), this equation leads to two explosion limits. At very low pressures the mean free path of the molecules in the reactor is quite long, and the radical termination processes occur primarily on the surfaces of the reaction vessel. Under these conditions gas phase collisions leading to chain breaking are relatively infrequent events, and fst fgt. Steady-state reaction conditions can prevail under these conditions if fst > fb(a — 1). 

As the pressure in the reaction vessel increases, the mean free path of the gaseous molecules will decrease and the ease with which radicals can reach the surfaces of the vessel will diminish. Surface termination processes will thus occur less frequently fst will decline and may do so to the extent that fst + fgt becomes equal to fb oc — 1). At this point an explosion will occur. This point corresponds to the first explosion limit shown in Figure 4.1. If we now jump to some higher pressure at which steady-state reaction conditions can again prevail, similar... 

Since operation in an autothermal mode implies a feedback of energy to preheat the feed, provision must be made for ignition of the reactor in order to attain steady-state operation. The ordinary gas burner and many other rapid combustion reactions are examples of autothermal reactions in which the reactants are preheated to the reaction temperature by thermal conduction and radiation. (Back diffusion of free radicals also plays an important role in many combustion processes.)... 

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