System selection factors

Original Mixture (Ref) Micellar System Selectivity Factor... 

Additional Selection Factors. System characteristics and physical and chemical properties can be principal considerations in reactor... 

The discussion of materials selection factors is naturally divided into three parts (1) overall factors pertinent to selection of the composite material itself, (2) factors governing the selection of the fibers, and (3) factors essential to selection of the matrix system. Those three types of selection trade-offs will be described, followed by summary remarks on the process of selecting a suitable composite material. 

The rotative speed of a pump is dependent upon the impeller characteristics, type fluid, NPSH available and other factors for its final determination. The most direct method is by reference to manufacturer s performance curves. VVTien a seemingly reasonable selection has been made, the effect of this selected speed on the factors such as NPSH required, suction head or lift, fluid erosion and corrosion, etc., must be evaluated. For many systems these factors are of no concern or consequence. 

Steuber, A., Consider These Factors for Optimum Vacuum System Selection, Llydw Proc., V. 61, No. 9, 1982, p. 267. 

System cost Cost should not be the primary deciding factor in system selection. The capabilities of the various systems vary greatly and so does the cost. Care should be taken to ensure a fair comparison of the total system capability and price is made before selection of your system. 

Acquiring accurate vibration and process data will require several types of transducers. Therefore, the system must be able to accept input from as many different types of transducers as possible. Any limitation of compatible transducers can become a serious limiting factor. This should eliminate systems that will accept inputs from a single type of transducer. Other systems are limited to a relatively small range of transducers that will also prohibit maximum utilization of the system. Selection of the specific transducers required to monitor the mechanical condition, i.e. vibration, and process parameters, i.e. flow, pressure, etc., will also deserve special consideration and will be discussed latter. 

Selection of inspection points therefore, should be based on a thorough knowledge of process conditions, materials of construction, geometry of the system, external factors and historical records. Some of these factors may not be present, for example, when new plant is commissioned. There is greater knowledge now available concerning hydromechanics of fluid flows which should be considered when installation is planned. 

In sharp contrast, Bartoli showed that the (salen) Co catalyst system could be applied to the kinetic resolution of terminal epoxides with unprotected tert-butyl carbamate as nucleophile with extraordinarily high selectivity factors (Scheme 7.40) [72]. Excellent yields and selectivities are also obtained with use of ethyl, Cbz,... 

Sigman et al. have optimized their system too [45]. A study of different solvents showed that the best solvent was f-BuOH instead of 1,2-dichloroethane, which increased the conversion and the ee. To ensure that the best conditions were selected, several other reaction variables were evaluated. Reducing the catalyst loading to 2.5 mol % led to a slower conversion, and varying temperature from 50 °C to 70 °C had little effect on the selectivity factor s. Overall, the optimal conditions for this oxidative kinetic resolution were 5 mol % of Pd[(-)-sparteine]Cl2, 20 mol % of (-)-sparteine, 0.25 M alcohol in f-BuOH, molecular sieves (3 A) at 65 °C under a balloon pressure of O2. 

In conclusion, both systems presented by both teams are rather competitive, even if the selectivity factors given by the system of Stoltz is better for a given set of substrates. In the case of 1-phenylethanol, Stoltz s system led to a 99% ee and s of 31, while in Sigman s procedure the resolution led to a 98.5% ee and s of 19. Both teams synthesized a range of model substrates that gave good ee s and good selectivity factors [44,45,49]. 

The system selected here was also a tablet formulation. The five independent variables or formulation factors selected for this study are shown in Table 2. The dependent variables are listed in Table 3. Since each dependent variable is considered separately, any number could have been included. 

M. Eigen describes this process roughly as follows let us consider a self-replicating system which is characterized by a quantity of information equal to N bits. The probability that a bit is incorrectly copied is w, and the selection reacts to errors by means of a selection factor S. In other words an error-free system has a selection advantage S over a system with an error. The survival criterion is then ... 

If kinetic resolution is being studied, the ratio of pseudo-e nantiomers can be measured by MS, allowing for the determination of ee-values (and/or of selectivity factors E). The same applies to the reaction of pseudo prochiral compounds. This system has been used successfully in the directed evolution of enantioselective enzymes. However, it should work equally well in the case of asymmetric transition metal catalyzed reactions. In the original version about 1,000 ee-deter-minations were possible per day (Figure 6).94 The second-generation version based on an 8-channel multiplexed spray system enables about 10,000 samples to be handled per day, the sensitivity being 2% ee.96... 

Several other approaches to solve the quantitation problem have been proposed. Hoppe et al. [2] determined y/ by calibrating it against constructs with known FRET efficiency. We and others [3, 6] have used data from a cell before and after acceptor photobleaching to relate the FRET-induced sensitized emission in the S channel to the loss of donor emission in the D channel by factors termed or G, respectively. For the CFP/YFP pair this works very well on confocal microscopes with a 514-nm Argon ion laser line, but on wide-held systems, selective acceptor photobleaching reportedly causes problems [ 14]. F inally, G can also be determined by comparison of several constructs that differ in FRET efficiency, a bit analogous to the Yellow Cameleon calibration described above [10,14],... 

After the initial volume estimate has been determined, testing of a pilot recovery system should be initiated to evaluate recovery rates. However, factors that significantly affect recovery rates include the areal distribution and geometry of the free-hydrocarbon product plume, type(s) and design of recovery system selected, and the performance and efficiency of the system with time. 

A very minor effect on shape selectivity has been observed for changes in mobile phase composition [109]. Shape selectivity increased slightly with an increase in percent organic modifier for water-organic mobile phase systems and increased in order of methanol acetonitrile < ethanol. Changes in the shape selectivity factor... 

The selected factors are either mixture-related, quantitative (continuous), or qualitative (discrete).A mixture-related factor is, for instance, the fraction organic solvent in the buffer system. Examples of quantitative factors are the electrolyte concentration, the buffer pH, the capillary temperature, and the voltage, and of qualitative factors the manufacturer or the batch number of a reagent, solvent, or capillary. Sample concentration (see Table 1) is a factor sometimes included. However, the aim of the method tested is to determine this concentration through the measured signal, from a calibration procedure. Thus, one evaluates the influence of the sample concentration on the sample concentration, which we do not consider a good idea. 

The reactor system selected will influence the economics of the process by dictating the size of the units needed and by fixing the ratio of products formed. The first factor, reactor size, may well vary a hundredfold among competing designs while the second factor, product distribution, is usually of prime consideration where it can be varied and controlled. 

It is clear that all three types of selectivity are relevant to catalytic hydrogenation reactions and from a consideration of the reaction scheme for alkyne hydrogenation (Fig. 4), it can be deduced that all three factors may be operative simultaneously. Clearly, the selectivity for the formation of the alkene relative to alkane will depend upon a number of factors. If both the alkene and the alkane are formed during one residence of the parent molecule on the surface, the selectivity will depend upon the relative values of k, and k2 (Type II selectivity) and upon the ratio kjk4 (Type II selectivity). Since both of these depend upon the specific properties of the catalyst, they have been termed the mechanistic selectivity factor [38], Once the alkene is produced, the system contains another potential adsorbate and Type I selectivity must be taken into account. It... 

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