Core sizing

It must always be borne in mind that when capillary condensation takes place during the course of isotherm determination, the pore walls are already covered with an adsorbed him, having a thickness t determined by the value of the relative pressure (cf. Chapter 2). Thus capillary condensation occurs not directly in the pore itself but rather in the inner core (Fig. 3.7). Consequently the Kelvin equation leads in the first instance to values of the core size rather than the pore size. The conversion of an r value to a pore size involves recourse to a model of pore shape, and also a knowledge of the angle of contact 0 between the capillary condensate and the adsorbed film on the walls. The involvement of 0 may be appreciated by consideration... 

The curve for core size distribution—Foster s plot of 6 j6r against r —is also shown, as Curve D, in Fig. 3.18. It differs markedly from the pore size distribution curves, clearly showing that the corrections for the film thinning effect which have become possible since Foster s day, are of first-order importance. 

The accuracy of a VT depends upon its leakage reactance and the winding resistance. It determines the voltage and the phase errors of a transformer and varies with the VA on the secondary side. With the use of better core material (for permeability) (Section 1.9) and better heat dissipation, one can limit the excitation cunent and reduce the error. A better core lamination can reduce the core size and improve heat dissipation. 

Determine whether an airgap is needed and calculate the number of turns needed for each winding. Then determine whether the accuracy of the output voltages meets the needs of the requirements and whether the winding actually fit into the selected core size (Sections 3.5.3 through 3.5.7). 

Each manufacturer uses different core sizing procedures. Some use graphs, others simply state how much power each core can handle for a particular application, and some use cryptic equations that are confused by the mixture of unrelated units. The following two procedures are generalized approaches for estimating the initial core size. 

Table 3-4 Approximate Core Size versus Output Power...

If you desire to use the core manufacturer s own method of determining core size, then feel free to do so. This phase of the transformer design is a gross estimation. 

A ferrite toroid or E core can be used for a drive transformer. No gap is needed since the input coupling capacitor guarantees that the core will operate in a bipolar fashion. A high permeability core is also suitable for this purpose. The wire that is going to be used will be in the range of 32 to 36 AWG. The core size will be approximately 0.4 to 0.6 inches (10 to 15mm). 

I will use an MPP toroid core. The core sizing procedure is contained in Section 3.5.5. Estimate the core size required ... 

The estimated core size for this application is approximately 1.3 inches (33 mm) on each side. The closest sized core is Magnetics part number F-43515. I will request that core and also F-44317, which is the next core size larger, just in case the windings grow beyond the limits of the window area. 

Determining the core size. TDK rates its cores by the amount of power that can be handled by the core in a one-transistor forward converter. Its volume requirements are very similar to a flyback converter. The EPC core that rated at 15 W or greater is the EPC 17 core size. The part numbers for this assembly are core, PC40EPC17-Z bobbin,BER17-llllCPH and clamp, FEPC17-A. 

Fig. 24. Calculation of the conformational energy of Valinomycin as a function of the size of the polar core which contains the ion. This uses the structure of Fig. 20. The verticle lines are the optimal core sizes for the indicated ions. Based on the conformational energy component, selectivity for K+ and Rb+ would be similar and Cs+ less favored. Na+ is off the curve suggesting that this conformation cannot form a polar core small enough to complex Na+ by means of this conformation. Adapted with permission from Ref.

Light wave technologies provide a number of special challenges for polymeric materials. Polymer fibers offer the best potential for optical communications in local area network (LAN) applications, because their large core size makes it relatively cheap to attach connectors to them. There is a need for polymer fibers that have low losses and that can transmit the bandwidths needed for LAN applications the aciylate and methacrylate polymers now under study have poor loss and bandwidth performance. Research on monomer purification, polymerization to precise molecular-size distributions, and weU-controlled drawing processes is relevant here. There is also a need for precision plastic molding processes for mass prodnction of optical fiber connectors and splice hardware. A tenfold reduction in the cost of fiber and related devices is necessaiy to make the utilization of optical fiber and related devices economical for local area networks and tlie telecommunications loop. 

The premise of this review is that synthetic procedures for very mixed"-metal clusters are comparatively well understood, but that reactivity and physical properties are less well studied. Metal core transformations (modifications of a preexisting cluster) fall into both the synthesis and reactivity categories. A summary is presented here, but as they have been reviewed elsewhere (see Refs. 4, 107-109), the account below is necessarily brief. Section lI.E. 1. considers core transformations where the cluster core nuclearity is pre.served, whereas Section 11.E.2. summarizes reactions involving a change in core size. 

Generally, MPCs are prepared by chemical reduction of gold ions in the presence of thiols. The average core size can be controlled in the range of 2-10 nm by controlling the preparation conditions, such as the molar ratios of gold ions and RSH. However, control of size at an atomic resolution is not feasible by this approach. 

TEM is conventionally used as a tool to evaluate the size and shape of the cores by direct imaging. However, the core size cannot be determined with atomic resolution from low contrast and 2-D projection of the 3-D core. There are several subjective factors in the estimation of size e.g., how to select the area from which the core size is derived and how to measure this precisely from the vague projections of cores in the TEM micrographs. 

Our approach is similar to that employed in research of free cluster ions in the gas phase, where various measurements are conducted on the cluster which is mass selected out of the size-distributed clusters generated by laser sputtering. Based on the chemical compositions of the isolated MFCs, we discuss the determining factors of core size in connection with the formation processes. Some core-size dependent properties of the MFCs are also presented. 

Core Sizes of Au. SR Clusters Formed by Reductive Decomposition of Au(I) SR Polymer... 

As demonstrated in Section 3.1.1, the Au SR clusters formed in reaction (1) correspond to trapped intermediates of the growing clusters and are thus not always thermodynamically stable. The stabilities of the Au SG clusters (1-9) are acutely dependent on the core sizes. The Aui8(SG)i4 Au25(SG)i8, and Au39(SG)24 clusters were found to be stable when allowed to stand in aqueous solution while other Au SG clusters were degraded into smaller clusters (Figure 7a) [16]. 

Simple material balance programs requiring only a relatively small core size. 

The benefit of the LbL technique is that the properties of the assemblies, such as thickness, composition, and function, can be tuned by varying the layer number, the species deposited, and the assembly conditions. Further, this technique can be readily transferred from planar substrates (e.g., silicon and quartz slides) [53,54] to three-dimensional substrates with various morphologies and structures, such as colloids [55] and biological cells [56]. Application of the LbL technique to colloids provides a simple and effective method to prepare core-shell particles, and hollow capsules, after removal of the sacrificial core template particles. The properties of the capsules prepared by the LbL procedure, such as diameter, shell thickness and permeability, can be readily adjusted through selection of the core size, the layer number, and the nature of the species deposited [57]. Such capsules are ideal candidates for applications in the areas of drug delivery, sensing, and catalysis [48-51,57]. 

FIGURE 3.11 Core definition. After redistribution of energy at the molecular scale, core size is suggested by the distance at which energy transported by secondary electrons just exceeds that due to every other channel (see text for details). From Mozumder and La Verne (1987). 

Generally, gold nanoparticles have been used for most biomedical applications. Gold nanoparticles with varying core sizes are usually prepared by the reduction of... 

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