Hybrid Approach


Abstract. This article provides an overview of an algorithm used for the prediction of ionization constants of titratable residues in proteins. The algorithm is based on an assumption that the difference in protonation behavior of a given group in an isolated state in solution, for which the ionization constant is assumed to be known, and the protonation behavior in the protein environment is purely electrostatic in origin. Calculations of the relevant electrostatic free energies are based on the Poisson-Boltzmann (PB) model of the protein-solvent system and the finite-difference solution to the corresponding PB equation. The resultant multiple site titration problem is treated by one of two methods. The first is a hybrid approach, based on collecting ionizable groups into clusters. The second method is a Monte Carlo approach based on the Metropolis algorithm for extracting a sufficient number of low-energy ionization states out of all possible states, to obtain a correct estimation of thermodynamic properties of the system.  [c.176]

Treatment of Multiple Ionizations by a Hybrid Approach  [c.186]

A concept gaining support is a hybrid approach to making thick crystalline silicon efficient in thin layers. Although conventional crystalline silicon cells have gone from 400—600-p.m thick to 200—300-p.m, thin-film crystalline silicon cells have reached 10% efficiency while being only 10-p.m thick.  [c.471]

In general, the model-based reasoning approach is best appHed, not as a method in itself, but as an add-on to a knowledge-based system. The main reason is that modeling is hard, and problem-solving based solely on fundamental models is computationally complex (41). Using the hybrid approach can take advantage of the efficiency of compiled knowledge in rapidly focusing on the solution, while retaining the robustness of models when confronted with the need for behavioral detail. Several recent research papers in the chemical engineering Hterature have explored this hybrid problem-solving notion (42,43). For more information on model-based reasoning in general see References 44 and 45.  [c.536]

However, theories that are based on a basis set expansion do have a serious limitation with respect to the number of electrons. Even if one considers the rapid development of computer technology, it will be virtually impossible to treat by the MO method a small system of a size typical of classical molecular simulation, say 1000 water molecules. A logical solution to such a problem would be to employ a hybrid approach in which a chemical species of interest is handled by quantum chemistry while the solvent is treated classically.  [c.418]

A typical hybrid approach is the QM/MM (quanmm mechanical-molecular mechanical) simulation method [4]. In this method, the solute molecule is treated quantum mechanically, whereas surrounding solvent molecules are approximated by molecular mechanical potentials. This idea is also used in biological systems by regarding a part of the system, e.g., the activation site region of an enzyme, as a quantum solute, which is embedded in the rest of the molecule, which is represented by molecular mechanics. The actual procedure used in this method is very simple The total energy of the liquid system (or part of a protein) at an instantaneous configuration, generated by a Monte Carlo or molecular dynamics procedure, is evaluated, and the modified Schrddinger equations are solved repeatedly until sufficient sampling is accumulated. Since millions of electronic structure calculations are needed for sufficient sampling, the ab initio MO method is usually too slow to be practical in the simulation of chemical or biological systems in solution. Hence a semiempirical theory for electronic structure has been used in these types of simulations.  [c.419]

FIGURE 5-1. Example of Responsibility Matrix for Hybrid Approach  [c.99]

Keeping these variables in mind may help you consider the following discussion of some available methods for PSM systems design in terms of your company s requirements Total Quality Management (TQM) techniques, use of model programs, and business process redesign. Each of these methods has advantages and disadvantages in terms of application in fact, you may decide to adapt features of each to create your own "hybrid" approach.  [c.129]

There is no correct way to implement the integration project. You may choose a company-wide, facility-by-facility (or division-by-division) or hybrid approach. Factors that will influence your choice include  [c.74]

Hybrid approach. A hybrid approach addresses some matters centrally and some locally. For example, programs and elements may be developed locally due to significant differences in regulation and manufacturing processes, but the management systems (the framework of the integration) are developed centrally in order to establish uniform standards of performance. Management of hybrid approaches is particularly difficult and requires careful planning and well developed channels of communication.  [c.75]

Hubbard and co-workers have developed a surface imaging approach, angular-distribution Auger microscopy (ADAM), based on resolution of the angular distribution of Auger electrons [84-86]. In this method, the sample is irradiated by a beam of electrons held at a fixed angle from the surface. The energy analyzer scans the angular distribution with a resolution of 1° in about three hours [85]. Surface atoms are illuminated by Auger electrons emitted by atoms deeper in the solid. The surface structure thus appears as silhouettes or minima in Auger intensity. This technique has been used to image single crystals [84], but is best applied to monatomic layers such as silver on platinum with and without an iodine overlayer [85, 86]. The structures found from ADAM have been verified with STM and LEED.  [c.308]

The basic scheme of this algorithm is similar to cell-to-cell mapping techniques [14] but differs substantially In one important aspect If applied to larger problems, a direct cell-to-cell approach quickly leads to tremendous computational effort. Only a proper exploitation of the multi-level structure of the subdivision algorithm (also for the eigenvalue problem) may allow for application to molecules of real chemical interest. But even this more sophisticated approach suffers from combinatorial explosion already for moderate size molecules. In a next stage of development [19] this restriction will be circumvented using certain hybrid Monte-Carlo methods.  [c.110]

The Monte Carlo approach, although much slower than the Hybrid method, makes it possible to address very large systems quite efficiently. It should be noted that the Monte Carlo approach gives a correct estimation of thermodynamic properties even though the number of production steps is a tiny fraction of the total number of possible ionization states.  [c.187]

Hybrid grids are used for very complex geometries where combination of structured mesh segments joined by zones of unstructured mesh can provide the best approach for discretization of the problem domain. The flexibility gained by combining structured and unstructured mesh segments also provides a facility to improve accuracy of the numerical solutions for field problems of a complicated nature. Figure 6.3 shows an example of this type of computational mesh.  [c.194]

AH the methods described so far involve introducing the organic phase prior to the formation of a soHd phase. There is an interesting alternative to prepare a nanocomposite by a sequential approach (22). In this approach a siUca aerogel was first prepared, then carbon was deposited in it by the decomposition by hydrocarbons (eg, methane, acetylene) at a temperature range of 500—850°C. This example demonstrates the feasibiUty of preparing hybrid materials by depositing an inorganic or organic phase onto an organic or inorganic substrate, respectively.  [c.3]

The search for new high performance materials has spurred the development of composites combining high modulus /high thermal stabiUty inorganic glasses and low modulus /low thermal stabiUty polymeric glasses. Research has resulted in a novel class of amorphous polymer—glass composites referred to as organic—inorganic hybrids or inorganic—organic hybrids, depending on the component with the highest volume fraction. These materials are synthesized in a variety of ways but ultimately exhibit near-molecular-level mixing of the matrix and the filler. Hence the term hybrid. Typically, this high degree of mixing results in transparent materials which exhibit significant increases in thermomechanical properties owing to extensive interaction between the polymeric and inorganic phases. However, the relatively high volume fraction of polymer included in these materials normally limits their service temperatures to well below 400°C. One route to promoting mixed, interactive phases is the sol—gel processing of metal alkoxides, which allows the development of an inorganic, oxygen-bridging network during composite consoHdation and promotes the formation of polymeric inorganic glasses with a morphology, and consequentiy a resultant polymer—glass interface, that is a function of the traditional sol—gel processing variables and other controllable factors. In essence, this approach results in materials that can be broadly defined as amorphous, interpenetrating network stmctures.  [c.328]

Poly( phenylene vinylene). An organic—inorganic hybrid of poly(p-phenylene vinylene) (PPV) has been made utilizing a very ingenious approach (47). By mixing a sulfonium polyelectrolyte precursor for PPV and tetramethoxysilane (TMOS) together and subsequently polymerizing the organic precursor via thermolysis, a hybrid network was formed. The catalyst required for the polymerization of the TMOS was suppHed as a by-product of the thermolysis. The polymer-doped glass exhibited improved optical quaUty over that of pure PPV. Similarly, initial studies showed that the hybrid has promise as a waveguide material, although the sol—gel processing of the TMOS may result in a shortening of the conjugation length in the PPV. This is important for future nonlinear optical appHcations.  [c.329]

Hydrogels. A new approach has been taken to produce organic—inorganic hybrid interpenetrating networks using the sol—gel process, as described previously for PTMO, and y-radiation (69—70). By swelling existing organic—inorganic networks with either methacrylic acid or A/-vinylpyrrohdinone and subsequent y-polymerization of the monomers in situ IPNs which exhibit some degree of hydrogel behavior, ie, the abiUty to absorb significant amounts of moisture or preferential swelling dependent upon pH, are produced, and they possess the optical transparency of the original gels. Additionally, very significant increases in the strength (up to a factor of 50) and elongation at break, as well as the elastic and dynamic storage modulus were induced.  [c.331]

Distributed control systems (DCS) are a hybrid of the previous systems, having stand-alone computers for control and data gathering at each pilot plant together with one or more higher level computer(s) for data storage and work-up. Typically more expensive than either central systems or stand-alone computers, distributed control systems have the advantages of both systems. This approach is preferred for pilot plants when it can be economically justified, usually for larger research faciUties or very large demonstration units.  [c.42]

The gel approach offers processing advantages which are not available with the more conventional methods used to form synthetic fused siUca. The lower firing temperatures reduce energy consumption and minimize the pickup of furnace impurities. Also, near-net-shaping is possible because the gelling procedure is not limited to any particular mold configuration. Unfortunately, the gel approach has critical drying and shrinkage problems which limit the glass sizes that can be produced. The gels, fragile stmctures that tend to crack during drying owing to capillary stresses, are highly porous stmctures that shrink linearly by up to 50% upon firing. The high shrinkage makes dimension control difficult. These problems have been attacked with limited success by increasing gel strength through gel aging, additions of siUca particle fillers, etc controlling the pore size in the gel through pH control and hydrothermal aging (73) and slower, milder drying procedures (see Hydrothermal processing Sol-gel technology). In response to these processing limitations, several hybrid processes have been proposed that use sol—gel-derived powders as the feedstock for more conventional manufacturing approaches, including flame fusion and high temperature vacuum sintering (11,74).  [c.500]

One approach for ameliorating the highly brittle nature of these cements has involved the use of tougher, more ductile fillers (62,63). Another approach for improving the overall properties of traditional glass—ionomer cements involves the development of hybrid cement-composites and resin-modified cements (64—68).  [c.473]

Although the thermodynamic perturbation approach [Eq. (8)] is important conceptually, it is usually not the most efficient numerically. A more fruitful approach in practice is to introduce an explicit transformation of the potential energy function such that it is gradually changed from its starting form Up, into the final fonn (/b tlirough the variation of one or a few convenient parameters or coupling coordinates. The simplest such approach is linear interpolation between Up, and (/b, i-e., we introduce the hybrid energy function  [c.176]

To compute derivatives of F at the point (/ ii, X2, ) numerically, a simulation is performed with the hybrid energy function (7(r / ii, X2, ) and the appropriate energy derivatives are averaged. This procedure is repeated for a few discrete values of the coupling parameter(s), spanning the interval from 0 to 1. The resulting free energy derivatives are then interpolated and integrated numerically to yield Fg — F. Many applications use a linear coupling and rely only on first derivatives calculated at evenly spaced points however, efficiency can be improved by using somewhat more complicated schemes [20,24]. This general approach is known as thermodynamic integration.  [c.177]

C. The Hybrid Energy Approach  [c.255]

Roughly speaking, three types of hybrid approaches have been proposed depending on the level of coarse graining with respect to solvent coordinates. Methods based on continuum models smear all solvent coordinates and represent solvent characteristics with a single parameter, namely, a dielectric constant. Molecular simulations, on the other hand, take all solvent coordinates into account explicitly and sample many solvent configurations in order to realize meaningful statistics for the physical quantities of concern. The approach based on the statistical mechanics of molecular liquids coarse-grains solvent coordinates in a level of the (density) pair correlation functions. In what follows, we briefly outline these tliree methods.  [c.418]

Vinyl ethers can also be formulated with acryHc and unsaturated polyesters containing maleate or fumarate functionaHty. Because of their abiHty to form alternating copolymers by a free-radical polymeri2ation mechanism, such formulations can be cured using free-radical photoinitiators. With acryHc monomers and oligomers, a hybrid approach has been taken using both simultaneous cationic and free-radical initiation. A summary of these approaches can be found in Table 9.  [c.519]

One of the many advantages of an object-oriented representation is the fact that it allows representation of all the declarative information known about a process or domain in a stmctured way. Representing the domain knowledge declaratively offers the flexibiUty to choose whatever reasoning strategy is appropriate for the problem to be solved. In addition, the idea of inheritance greatly faciUtates building and maintaining systems using an object-oriented representation. On the downside, object systems do not generally come with built-in problem-solving strategies, uncertainty handling capabihty, or explanation features. This is up to the system developer to implement using a programming language. Eor a range of knowledge-based apphcations, this potential hurdle can be avoided by coupling the object system with a rule base. Many commercially available tools support this hybrid architecture. Eor other types of problems, the hybrid approach may not be sufficient, and the full power of object-oriented programming may have to be used. Eor example, knowledge-based simulation of discrete event processes can be approached in an object-oriented way (21).  [c.535]

Neither the companywide nor the fadlity-spedfic implementation model offers a magic solution. In fact, many companies incorporate elements of both strategies into a "hybrid" approach that tetter meets their individual needs. A hybrid approach addresses some PSM elements centrally and others locally, reflecting current PSM status. In many real situations, this offers the test way to take advantage of what already exists. Where the status of different elements varies (e.g., some may be poor throughout the company, while others are either strong throughout the company or at particular locations), a hybrid may be the only effective means of addressing gaps systematically.  [c.99]

MMVB is a hybrid force field, which uses MM to treat the unreactive molecular framework, combined with a valence bond (VB) approach to treat the reactive part. The MM part uses the MM2 force field [58], which is well adapted for organic molecules. The VB part uses a parametrized Heisenberg spin Hamiltonian, which can be illustrated by considering a two orbital, two electron description of a sigma bond described by the VB determinants  [c.301]

Molecular Self-Assembly. As seen in "Reductive Approaches," reductive techniques, such as those currently in use in the microelectronics industry, can produce stmctural features smaller than about 200 nm, although at great economic cost. The use of proximal probes and other nanomanipulative techniques can be considered to be a hybrid of the reductive lithographic techniques and the synthetic strategies of assembling functional nanostmctures atom by atom, or molecule by molecule. The organization of nanostmctures and devices by the self-assembly of the component atoms and molecules, a ubiquitous phenomenon in biological systems, forms the noncovalent synthetic approach to nanotechnology.  [c.207]

Yet another approach is a hybrid of the last two, and is particularly appHcable to complex processes. The overaH process, including the batching scale, is controUed by a controUer, such as a PLC. The PLC downloads the recipe to the scale and teUs it when to commence the batching is then controUed completely by the scale through its own digital I/O. The advantage is that the scale is fully integrated into the larger process without compromising speed and accuracy of the batching operation.  [c.339]

It was expected that the mixed region, the diffuse glass—polymer interface, would be responsible for many of the composites properties. Therefore, more recentiy, methods of modifying the microstmcture of these hybrids in situ have been examined (34,35). It was found that by using a strongly basic solution of ethylamine and water, the solubiUty of siUca at high pH could be used to selectively modify the interface between the organic and inorganic phases. Essentially, syneresis and ripening of the polysiUcate domains just like that experienced for traditional sol—gel-derived inorganic glasses aged at high pH could be induced, resulting in phase separation. This modification resulted in systematic changes in the strength of the hybrid. Additionally, this process has been used in the synthesis of organic—inorganic hybrid interpenetrating networks (IPN). By controlling the degree of interaction (and hence PTMO restriction), the ethylamine procedure was used to control the equiUbrium mass uptake of various vinyHc monomers absorbed by the original hybrid network. Subsequent y-radiation-induced polymerization of this absorbed monomer resulted in the formation of an IPN. Indeed, the properties of the new IPN were a function of the preirradiation, ethylamine exposure processing. These new materials were synthesized using methacrylic acid (MAA), N-vinylpyrrohdinone (NVP) and cyclohexyl methacrylate (CHMA) monomers. In particular, the PMAA and poly(N-vinylpyrrohdinone) (PVP) IPN exhibited hydrogel-hke behavior. This approach opens new potential appHcations for these hybrid glasses.  [c.329]

Distinction between pyrolytic and photochemical techniques is not clear cut. Deposition may, for example, involve thermolysis of a photochemicaHy generated intermediate or vice versa. Photochemical techniques generally have an advantage over the pyrolytic approach in that it is not necessary to subject the substrate, even locally, to the extreme temperatures (750—1400°C) used in the purely pyrolytic processes (50). Frequency-doubled Ar ion lasers (244 nm) and excimer lasers (193 and 248 nm) are used to effect the photochemistry. Laser selection may be critical in a particular appHcation. Where surface photochemistry is desired exclusively for high resolution patterning, decomposition of adsorbed Cd(CH2)2 or Zn(CH2)2 to yield the corresponding metal requires 193 nm photons from a ArF laser, even though the gas-phase decomposition of these precursors can be effected at 248 nm with a KrF laser. Surface energy relaxation pathways have been invoked to explain this difference. Metal carbonyls (qv) are also useful, especially for deposition of Ni, Fe, Cr, W, and Mo. These decompositions are often hybrid photochemical—pyrolytic (52). Noble or coinage metal films, Cu, Au, Ir, Pt, or Pd, are accessible by laser photolysis of volatile acetylacetonate (acac) or hexafluoroacetylacetonate (hfacac) complexes, again using excimer lasers. In these cases higher purity metal films are obtained by the pyrolytic, rather than the pure photochemical mechanism (48,53) surface temperatures of no more than 175—225°C are requited to decompose hfacac complexes.  [c.391]

Quantitative Structure-Activity Relationship (QSAR) Methods. These methods (62) are computer algorithms that constmct mathematical functions correlating the chemical stmcture of a compound to its biological inhibitory activity. In many cases, this has led to the prediction of a compound s biological activity after obtaining data from a series of stmcturaHy similar molecules (63,64). For one QSAR approach, the Hansch method (65—67), it is assumed that the relative potency of an analogue is related to an additive combination of terms related to its physicochemical parameters such as piQ partition coefficient, and molecular refractivity. The values of the physicochemical properties and the values of concentration necessary for eliciting a standard biological effect ate measured for a series of stmcturaHy related compounds. Next, a set of many equations with many unknowns is obtained and solved for by a least-squares multiple regression analysis. In another approach called the Free-Wilson method (68), it is assumed that the relative potency of an analogue is related to an additive combination of terms described by variables that indicate the presence or absence of functional groups. For systems that cannot be accurately described by either of these two methods alone, the methods can be combined. With hybrid Hansch—Free-Wilson equations, the effects of functional groups on biological activity that cannot be fully accounted for by the physicochemical properties alone can be quantified. Once the mathematical function has been deterrnined by one of these methods, the variables for a new but related compound can be plugged into the equation, and the equations solved for its anticipated biological potency.  [c.327]

The development of a simple and effective approach to development of new organo-inorganic nanohybrid materials in accordance with the requirements and demands of modern industrial technologies necessitates fundamental investigations in this area, in particular to obtain an in depth understanding of the factors determining the stmcture and properties of the resultant materials, in order that these can be engineered by control of suitable process parameters. These hybrid materials, possessing nanostmcture are interesting to use of them as chromatographic stationary phases for HPLC and HPTLC.  [c.253]

Finally, an alchemical free energy simulation is needed to obtain the free energy difference between any one substate of system A and any one substate of system B, e.g., Ai- In practice, one chooses two substates that resemble each other as much as possible. In the alchemical simulation, it is necessary to restrain appropriate parts of the system to remain in the chosen substate. Thus, for the present hybrid Asp/Asn molecule, the Asp side chain should be confined to the Asp substate I and the Asn side chain confined to its substate I. Flat-bottomed dihedral restraints can achieve this very conveniently [38], in such a way that the most populated configurations (near the energy minimum) are hardly perturbed by the restraints. Note that if the substates AI and BI differ substantially, the transfomnation will be difficult to perform with a single-topology approach.  [c.193]

An alternative approach to the link atom method is to use the frozen orbital approach developed by Rivail and coworkers [56] (the local self-consistent field, LSCF). The continuity of the electron density at the boundary region is maintained by a frozen orbital along the bond between the quantum and classical atoms. This frozen orbital is derived from calculaitons on model compounds, with the assumption that the orbitals from model compounds are transferable to the enzymatic system. A more generalized fonn of this implementation was presented by Gao et al. [57], in which a set of hybrid orbitals are used at the boundary region [this method is termed the generalized hybrid orbital (GHO) method by the authors]. The set is divided into auxiliary and active orbitals and acts as a basis set for the boundary atoms of the MM fragment. The active orbitals are optimized along with other orbitals on the QM atoms in the SCF cycle. In essence this method is an expansion of the approach of Rivail but has the advantage that the oribitals do not need to be parametrized for each specific problem.  [c.227]


See pages that mention the term Hybrid Approach : [c.99]    [c.378]    [c.499]    [c.146]    [c.469]    [c.604]    [c.631]    [c.155]    [c.77]   
See chapters in:

Guidelines for implementing process safety management systems  -> Hybrid Approach