Black box approach

A Generalized Design Approach to Power Supplies Introducing the Building-block Approach to Power Supply Design  [c.8]

The Building-block Approach to PWM Switching Power Supply Design  [c.26]

Building-block Approach to Switching Power Supply Design  [c.27]

A Generalized Approach to Power Supplies Introducing the Building-block Approach to Power Supply Design 8  [c.271]

The Building-block Approach to PWM Switching Power Supply Design 26  [c.271]

An approach developed by Guggenheim [106] avoids the somewhat artificial concept of the Gibbs dividing surface by treating the surface region as a bulk phase whose upper and lower limits lie somewhere in the bulk phases not far from the interface.  [c.76]

This description is traditional, and some further comment is in order. The flat region of the type I isotherm has never been observed up to pressures approaching this type typically is observed in chemisorption, at pressures far below P. Types II and III approach the line asymptotically experimentally, such behavior is observed for adsorption on powdered samples, and the approach toward infinite film thickness is actually due to interparticle condensation [36] (see Section X-6B), although such behavior is expected even for adsorption on a flat surface if bulk liquid adsorbate wets the adsorbent. Types FV and V specifically refer to porous solids. There is a need to recognize at least the two additional isotherm types shown in Fig. XVII-8. These are two simple types possible for adsorption on a flat surface for the case where bulk liquid adsorbate rests on the adsorbent with a finite contact angle [37, 38].  [c.618]

A quite different approach was adopted by Robinson and Stokes [8], who emphasized, as above, that if the solute dissociated into ions, and a total of h molecules of water are required to solvate these ions, then the real concentration of the ions should be corrected to reflect only the bulk solvent. Robinson and Stokes derive, with these ideas, the following expression for the activity coefficient  [c.584]


The microscopic understanding of tire chemical reactivity of surfaces is of fundamental interest in chemical physics and important for heterogeneous catalysis. Cluster science provides a new approach for tire study of tire microscopic mechanisms of surface chemical reactivity [48]. Surfaces of small clusters possess a very rich variation of chemisoriDtion sites and are ideal models for bulk surfaces. Chemical reactivity of many transition-metal clusters has been investigated [49]. Transition-metal clusters are produced using laser vaporization, and tire chemical reactivity studies are carried out typically in a flow tube reactor in which tire clusters interact witli a reactant gas at a given temperature and pressure for a fixed period of time. Reaction products are measured at various pressures or temperatures and reaction rates are derived. It has been found tliat tire reactivity of small transition-metal clusters witli simple molecules such as H2 and NH can vary dramatically witli cluster size and stmcture [48, 49, M and 52].  [c.2393]

A logical departure point for tlie syntliesis of nanocrystals is to view tlie problem as one of limiting tlie growtli of a bulk crystal tliis is challenging because tlie large surface free energy of a nanocrystal makes it a metastable system, highly prone to fusion and aggregation. One particularly elegant and versatile solution is to precipitate solids inside reactors which are tliemselves of nanometre scale [24, 25, 26, 27 and 28]. Such nanometre-scale reaction environments can be foniied by mixing water, surfactant and oil to create inverse micelles [29, 30]. These water pools have diameters tliat can be tuned from 5 to 60 A in radius by varying tlie water/surfactant molar ratio, tlius providing a direct avenue for size control [31, 32 and 33]. Ionic salts can be solvated in tlie inverse micelles when such solutions are exposed to a counterion which foniis an insoluble solid witli tlie original salt, small crystals of tlie solid fonii witliin tlie micelle environment. This process, referred to as arrested precipitation, can be used to grow nanocrystals witli sizes which are roughly equivalent to tlie original micellar size. Surface control can be achieved by adding organic capping agents to tlie final solutions. Depending on tlie solubility and capping group affinity, tlie nanocrystals may directly precipitate out of tlie micellar solution [34, 35] or may be recovered as a powder after tlie micelle phase is dismpted by tlie addition of an alcohol [36, 37]. The advantage of tliis approach is  [c.2900]

The first step in designing a precursor synthesis is to pick precursor molecules that, when combined in organic solvents, yield the bulk crystalline solid. For metals, a usual approach is to react metal salts with reducing agents to produce bulk metals. The main challenge is to find appropriate metal salts that are soluble in an organic phase.  [c.2901]

In modelling energy transfer in a bulk medium containing more tlian two chromophores or molecules, one has to consider all tire individual pairwise processes and conduct tire appropriate averaging. Such an approach is valid when excitation can be localized on individual molecules. This is called localized excitation , tire localized energy is tenned a localized exciton. The process of energy migration is tlien known as incoherent energy transfer, and tire jump of an exciton from one molecule to anotlier is a good way to describe it. The physical condition for incoherent energy transfer is weak coupling between tire donor and acceptor species.  [c.3017]

Experimental techniques based on the application of mechanical forces to single molecules in small assemblies have been applied to study the binding properties of biomolecules and their response to external mechanical manipulations. Among such techniques are atomic force microscopy (AFM), optical tweezers, biomembrane force probe, and surface force apparatus experiments (Binning et al., 1986 Block and Svoboda, 1994 Evans et ah, 1995 Israelachvili, 1992). These techniques have inspired us and others (see also the chapters by Eichinger et al. and by Hermans et al. in this volume) to adopt a similar approach for the study of biomolecules by means of computer simulations.  [c.40]

This approach is based on the scheme suggested by Taylor et al [12] and Plimpton [28]. The force matrix is divided into y/P x y/P blocks, where P is number of processors. The processors are conceptually thought of as having a two-dimensional mesh topology, that is, y/P x V -mesh. Note that this is not the physical architecture of the parallel system. This arrangement is used only to describe the algorithm. Since the force matrix has N(N — 1) pairs to be computed, each processor is assigned x interactions, contained within a single (i,j)-block of the force matrix. Let us use Pij to denote the processor that is assigned the (i, j)-block, and Pji to denote its transpose processor. As indicated in the the preceding sections, the force matrix is skew symmetric, therefore, only the upper (or lower) triangular part of the force matrix must be used in order to remove unnecessary calculations. In light of this, the interactions in a given block of the force matrix are distributed to the processor and its transpose processor. Inter-processor communications are done only among processors in the same row and transpose processors. Note that the processors on the diagonal are responsible for necessary interactions in the diagonal blocks, since they do not have transpose processors.  [c.486]

These molds can be either finished bar-shape molds or large blocks. Finished bar-shape molds can be either a mated two-piece design or a five-sided, open-top design. Upon cooling the soHd bar is removed from the mold and packaged as desired. For the large blocks, the mold is pulled apart and the block of soHd soap is removed. Wire cutters are employed to cut the blocks first into slabs, then into stripes, and finally into rectangular bricks representing the finished size of the bar. The rectangular brick is finished by a final stamping step which typically embosses the logo and any shape modifications into the brick. This large-block approach is only suitable for brick-like shapes, whereas the finished bar-shape molds allow for the production of much more complex shapes.  [c.156]

These images cannot be studied with classical approach. The analysis of the matrix based on the blocks Bl and B4 cannot be exploited. The objects can even be present in the bloek B2 andB3.  [c.235]

A more elaborate treatment of ester hydrolysis was attempted by Davies and Rideal [308] in the case of the alkaline hydrolysis of monolayers of monocetyl-succinate ions. The point in mind was that since the interface was charged, the local concentration of hydroxide ions would not be the same as in the bulk substrate. The surface region was treated as a bulk phase 10 A thick and, using the Donnan equation, actual concentrations of ester and hydroxide ions were calculated, along with an estimate of their activity coefficients. Similarly, the Donnan effect of added sodium chloride on the hydrolysis rates was measured and compared with the theoretical estimate. The computed concentrations in the surface region were rather high (1-3 M), and since the region is definitely not isotropic because of orientation effects, this type of approach would seem to be semiempirical in nature. On the other hand, there was quite evidently an electrostatic exclusion of hydroxide ions from the charged monocetyl-succinate film, which could be predicted approximately by the Donnan relationship.  [c.154]

A somewhat different point of view is the following. Since 7sv and 7sl always occur as a difference, it is possible that it is this difference (the adhesion tension) that is the fundamental parameter. The adsorption isotherm for a vapor on a solid may be of the form shown in Fig. X-1, and the asymptotic approach to infinite adsorption as saturation pressure is approached means that at the solid is in equilibrium with bulk liquid. As Deijaguin and Zorin [144] note (see also Refs. 10 and 18S), in a contact angle system, the adsorption isotherm must cross the line and have an unstable region, as illustrated in Fig. X-IS. See Section XVII-12. A Gibbs integration to the first crossing gives  [c.374]

This insulation does, in fact, seem to occur. It was remarked on in connection with Fig. XVII-21 and was very explicitly shown in some results of Dubinin and coworkers [139]. Nitrogen adsorption isotherms at -185°C were determined for a carbon black having various amounts of preadsoibed benzene. After only about 1.5 statistical monolayers of benzene, no further change took place in the nitrogen isotherm. A similar behavior was reported by Halsey and co-workers [140] for Ar and N2 adsorption on Ti02 having increasing amounts of preadsorbed water. In this case, a limiting isotherm was reached with about four statistical layers of water, the approach to the limiting form being approximately exponential. Interestingly, the final isotherm, in the case of  [c.654]

In principle, simulation teclmiques can be used, and Monte Carlo simulations of the primitive model of electrolyte solutions have appeared since the 1960s. Results for the osmotic coefficients are given for comparison in table A2.4.4 together with results from the MSA, PY and HNC approaches. The primitive model is clearly deficient for values of r. close to the closest distance of approach of the ions. Many years ago, Gurney [H] noted that when two ions are close enough together for their solvation sheaths to overlap, some solvent molecules become freed from ionic attraction and are effectively returned to the bulk [12].  [c.583]

The are essentially adjustable parameters and, clearly, unless some of the parameters in A2.4.70 are fixed by physical argument, then calculations using this model will show an improved fit for purely algebraic reasons. In principle, the radii can be fixed by using tables of ionic radii calculations of this type, in which just the A are adjustable, have been carried out by Friedman and co-workers using the HNC approach [12]. Further rermements were also discussed by Friedman [F3], who pointed out that an additional temi is required to account for the fact that each ion is actually m a cavity of low dielectric constant, e, compared to that of the bulk solvent, e. A real difficulty discussed by Friedman is that of making the potential continuous, since the discontinuous potentials above may lead to artefacts. Friedman [F3] addressed this issue and derived  [c.583]

Surface waves at an interface between two innniscible fluids involve effects due to gravity (g) and surface tension (a) forces. (In this section, o denotes surface tension and a denotes the stress tensor. The two should not be coiifiised with one another.) In a hydrodynamic approach, the interface is treated as a sharp boundary and the two bulk phases as incompressible. The Navier-Stokes equations for the two bulk phases (balance of macroscopic forces is the mgredient) along with the boundary condition at the interface (surface tension o enters here) are solved for possible hamionic oscillations of the interface of the fomi, exp [-(iu + s)t + i V-.r], where m is the frequency, is the damping coefficient, s tlie 2-d wavevector of the periodic oscillation and. ra 2-d vector parallel to the surface. For a liquid-vapour interface which we consider, away from the critical point, the vapour density is negligible compared to the liquid density and one obtains the hydrodynamic dispersion relation for surface waves + s>tf. The temi gq in the dispersion relation arises from  [c.725]

How are fiindamental aspects of surface reactions studied The surface science approach uses a simplified system to model the more complicated real-world systems. At the heart of this simplified system is the use of well defined surfaces, typically in the fonn of oriented single crystals. A thorough description of these surfaces should include composition, electronic structure and geometric structure measurements, as well as an evaluation of reactivity towards different adsorbates. Furthemiore, the system should be constructed such that it can be made increasingly more complex to more closely mimic macroscopic systems. However, relating surface science results to the corresponding real-world problems often proves to be a stumbling block because of the sheer complexity of these real-world systems.  [c.921]

Ulness D J and Albrecht A C 1996 Four-wave mixing in a Bloch two-level system with incoherent laser light having a Lorentzian spectral density analytic solution and a diagrammatic approach Rhys. Rev. A 53 1081-95  [c.1229]

This Liouville-space equation of motion is exactly the time-domain Bloch equations approach used in equation (B2.4.13). The magnetizations are arrayed in a vector, and anything that happens to them is represented by a matrix. In frequency units (1i/2ti = 1), the fomial solution to equation (B2.4.26) is given by equation (B2.4.27) (compare equation (B2.4.14H.  [c.2099]

The Bloch equation approach (equation (B2.4.6)) calculates the spectrum directly, as the portion of the spectrum that is linear in a observing field. Binsch generalized this for a frilly coupled system, using an exact density-matrix approach in Liouville space. His expression for the spectrum is given by equation (B2.4.42). Note that this is fomially the Fourier transfomi of equation (B2.4.32). so the time domain and frequency domain are coimected as usual.  [c.2104]

We have developed a different first-principles embedding theory that combines DFT with explicit correlation methods. We sought to develop a mediod for treating bulk or surface phases that is more accurate than current implementations of DFT. The idea is to provide more accurate predictions for local energetics, such as chemisorption binding energies and adsorbate electronic excitation energies. To achieve this, our theory improves upon the DFT description of electron correlation in a local region. This is accomplished by an embedding theory that treats a small region within an accurate quantum chemistry approach [190. 191], which interacts with its surroundings via an embedding potential, embedW- TW is derived from a periodic  [c.2227]

Simulation of both bulk phases iu a single box, separated by an interface, is closest to what we do in real life. It is necessary to establish a well defined interface, most often a planar one between two phases in slab geometry. A large system is required, so that one can characterize the two phases far Irom the interface, and read off the corresponding bulk properties. Naturally, this is the approach of choice if the interfacial properties (for example, the surface tension) are themselves of interest. The first stage in such a simulation is to prepare bulk samples of each phase, as close to the coexisting densities as possible, in ciiboidal periodic boundaries, iismg boxes whose cross sections match. The two boxes are brought together, to make a single longer box, giving the desired slab arrangement with two planar interfaces. There must then follow a period of equilibration, with mass transfer between the phases if the initial densities were not quite right.  [c.2271]

Although most transition-metal atoms have unpaired d-electrons and are magnetic, very few bulk transition-metal crystals are magnetic. Therefore, it is of great interest to understand how the magnetic properties of transition metals develop (diminish) as cluster size increases. The magnetic properties of transition-metal clusters have been investigated using tire Stem-Gerlach molecular beam deflection metliod. Magnetic properties of clusters of tire tliree bulk ferromagnetic materials, Fe, Co and Ni have been extensively studied [95, 96, 92, 98 and 99]- These clusters are found to be superiDaramagnetic witli strong size-dependent magnetic moments. Figure Cl. 1.5 shows tire measured magnetic moments of small Ni clusters as a function of size [99]- The dramatic size dependence of tire cluster magnetic moments is inteiyDreted to be due to a surface enhancement tire mimima correspond to clusters witli closed geometrical shells and maxima to clusters witli relatively open stmctures. Small clusters generally possess much higher moments tlian tire bulk materials, and tire moments approach bulk values in tire size range of about 500 atoms. Magnetism has also been detected in clusters of Arose elements whose bulk crystals are nonmagnetic [100].  [c.2396]

Abstract. The paper presents basic concepts of a new type of algorithm for the numerical computation of what the authors call the essential dynamics of molecular systems. Mathematically speaking, such systems are described by Hamiltonian differential equations. In the bulk of applications, individual trajectories are of no specific interest. Rather, time averages of physical observables or relaxation times of conformational changes need to be actually computed. In the language of dynamical systems, such information is contained in the natural invariant measure (infinite relaxation time) or in almost invariant sets ("large finite relaxation times). The paper suggests the direct computation of these objects via eigenmodes of the associated Probenius-Perron operator by means of a multilevel subdivision algorithm. The advocated approach is different from both Monte-Carlo techniques on the one hand and long term trajectory simulation on the other hand in our setup long term trajectories are replaced by short term sub-trajectories, Monte-Carlo techniques are connected via the underlying Probenius-Perron structure. Numerical experiments with the suggested algorithm are included to illustrate certain distinguishing properties.  [c.98]

See pages that mention the term Black box approach : [c.486]    [c.112]    [c.199]    [c.1164]    [c.1248]    [c.1265]    [c.1283]    [c.2202]    [c.2213]    [c.2222]    [c.2222]    [c.2223]    [c.2225]    [c.2226]    [c.2601]    [c.642]   
Advanced control engineering (2001) -- [ c.358 ]