Home About us Contact
|
Home About us Contact | ||
|
|
||
Physical Meaning (physical + meaning)
Selected AbstractsA reduced-order modeling technique for tall buildings with active tuned mass damperEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2001Zu-Qing Qu Abstract It is impractical to install sensors on every floor of a tall building to measure the full state vector because of the large number of degrees of freedom. This makes it necessary to introduce reduced-order control. A kind of system reduction scheme (dynamic condensation method) is proposed in this paper. This method is iterative and Guyan condensation is looked upon as an initial approximation of the iteration. Since the reduced-order system is updated repeatedly until a desired one is obtained, the accuracy of the reduced-order system resulting from the proposed method is much higher than that obtained from the Guyan condensation method. Another advantage of the method is that the reduced-order system is defined in the subspace of the original physical space, which makes the state vectors have physical meaning. An eigenvalue shifting technique is applied to accelerate the convergence of iteration and to make the reduced system retain all the dynamic characteristics of the full system within a given frequency range. Two schemes to establish the reduced-order system by using the proposed method are also presented and discussed in this paper. The results for a tall building with active tuned mass damper show that the proposed method is efficient for the reduced-order modelling and the accuracy is very close to exact only after two iterations. Copyright © 2001 John Wiley & Sons, Ltd. [source] An approach to the non-active power concept in terms of the poynting-park vectorEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2001A. Ferrero This paper reconsiders the approach to the electric systems in terms of Maxwell equations, and reconsiders in particular the energy transfer involved in an electric system in terms of the flux of the Poynting vector. This approach is extended to the three-phase systems, and the Park transformation is reconsidered by applying it to the Poynting vector. In this way a correct physical meaning can be assigned to the non-active components of the Park instantaneous power by tracing them back to the components of the Poynting vector. [source] Damage analysis of laminated composites using a new coupled micro-meso approachFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2010A. FARROKHABADI ABSTRACT In this study, the simplicity and strong physical meaning of micromechanics approach and capability of mesomechanics approach for damage analysis of structures with complex loadings are employed to develop a new micro-meso approach. For this purpose, a new micromechanics model is developed to predict the matrix cracking initiation and evolution in laminated composites. These damage initiation and evolution are replaced with the damage criteria and flow rule in the continuum damage approach, respectively. The results of this procedure are used in the FEM damage analyses of laminated composites to predict constitutive response of layered composites. It is shown that, the predicted stress distribution and strain energy in a lamina unit cell are in good agreement with the finite element results. Furthermore, it is shown that the predicted stress,strain behaviours are in good agreement with the available experimental results for various laminates with different lay-ups. [source] Examination of fatigue crack driving force parameterFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2008Y. XIONG ABSTRACT Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter Kop in Elber's effective SIF range ,Keff(=Kmax,Kop). However, the parameters that replaced the traditional parameter Kop were based on different measurements or theoretical calculations, so it is difficult to distinguish their differences. This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip; the tests were carried out under different amplitude loading for structural steel. Based on these test results, differences of several parameter ,Keff in literature are analysed and an improved two-parameter driving force ,Kdrive(=(Kmax)n(,K,)1-n) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the ,Kdrive parameter was equally effective or better than ,K(=Kmax,Kmin), ,Keff(=Kmax,Kop) and ,K*(= (Kmax),(,K+)1,,) in correlating and predicting the R -ratio effects on fatigue crack growth rate. [source] Consistency of the spatial autocorrelation method with seismic interferometry and its consequenceGEOPHYSICAL PROSPECTING, Issue 3 2008Toshiaki Yokoi ABSTRACT We have cross-checked the conventional theory of the spatial autocorrelation method and the consequence of seismic interferometry: the retrieval of the elastodynamic Green's function. Their mutual consistency is almost complete. The basic formulas of the conventional spatial autocorrelation theory can be derived by an alternative approach based on the retrieval of the elastodynamic Green's function. The only discrepancy is found with the average of the complex coherence function over azimuth in a wavefield dependent on azimuth. It is hypothesized, in discussion, that this discrepancy is due to the way of representing the wavefield in the background theory of seismic interferometry that can produce only wavefields moderately dependent on azimuth and that the mentioned consequence of seismic interferometry can also only make sense in a wavefield moderately dependent on azimuth. Our field experiment with a wavefield dependent on azimuth showed that the consequence of seismic interferometry in the logical framework of the conventional spatial autocorrelation theory is appropriate under such degrees of approximation as the measure proposed in this study, i.e., the deviation of the total dispersion curves is between about 10 and 16 per cent at the maximum from those averaged over azimuth. The acceptance of the retrieval of Green's function gives a proper physical meaning to the complex coherence function: the real part of the elastodynamic Green's function normalized by its zero-offset version. This makes it possible to take a deterministic approach rather than the statistical one on which the conventional spatial autocorrelation method is based and gives fruitful new aspects and perspectives. For example, the formula for the multi-mode case is given and the possibility of exploration of two or three dimensional velocity structures is suggested. [source] Monotonic and cyclic modeling of interface between geotextile and gravelly soilINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2010Ga Zhang Abstract This paper describes a modified elasto-plasticity damage model to capture monotonic and cyclic behavior of the interface between a geotextile and gravelly soil. New damage variable and shear strength criterion are introduced on the basis of test observations. The formulations of the modified model are obtained by extending those of the original interface model. The model parameters with physical meaning are easily determined from a group of cyclic shear tests and a confining compression test. The model predictions are compared with the results of a series of direct shear tests and large-scale pullout tests. The comparison results demonstrate that the model accurately describes the monotonic and cyclic stress,strain relationship of the interface between a geotextile and gravelly soil while capturing new characteristics: (1) the strength that is nonlinearly dependent on the normal stress; (2) significant shear strain-softening; (3) the comprehensive volumetric strain response with dependency on the shear direction; and (4) the evolution of behavior associated with the changes in the physical state that includes the geotextile damage. This model is used in a finite element analysis of pullout tests, indicating that the tensile modulus of a geotextile has a significant effect on the response of the geotextile,gravel system. Copyright © 2009 John Wiley & Sons, Ltd. [source] A small-strain overlay modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2009T. Benz Abstract The paper begins with a discussion of the phenomenon of small-strain stiffness and presents the small-strain overlay model, a simple model that takes into account the non-linear stiffness of soils at small strains. The new model can enhance already established elastoplastic formulations for non-linear stiffness variation at small strains in a similar way that intergranular strain enhances the hypoplastic model. The overlay model is driven by the material's strain history and only two additional material constants, both with clear physical meaning. Therefore, the proposed model is a step towards the incorporation of small-strain stiffness into routine design. In this paper, the new small-strain overlay model is formulated. Its ability to take into account the influence of various strain histories on soil stiffness is illustrated in several examples. Copyright © 2008 John Wiley & Sons, Ltd. [source] Modelling of hygro-thermal behaviour and damage of concrete at temperature above the critical point of waterINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2002D. Gawin Abstract In this paper, a model for the analysis of the behaviour of concrete at temperature largely exceeding critical point of water, is presented. In this temperature range liquid phase, i.e. capillary phase, and gas phase cannot be distinguished and only the latter exists. Consequently, capillary pressure has no more physical meaning above this point and liquid water is present only as physically adsorbed water. In this work, we give a different physical interpretation to the capillary pressure and use it still for the description of the hygrometric state of concrete in the zone, where temperature exceeds the critical point of water. Considerable thermal dilatation of the liquid water and the real behaviour of water vapour close to critical temperature are taken into account. Moreover, a special switching procedure in order to avoid the Stefan-like problem, which subsequently arises, is described and employed in the calculations. Finally, several numerical examples demonstrating the robustness of the adopted solution have been shown. Copyright © 2002 John Wiley & Sons, Ltd. [source] A finite element formulation for thermoelastic damping analysisINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2009Enrico Serra Abstract We present a finite element formulation based on a weak form of the boundary value problem for fully coupled thermoelasticity. The thermoelastic damping is calculated from the irreversible flow of entropy due to the thermal fluxes that have originated from the volumetric strain variations. Within our weak formulation we define a dissipation function that can be integrated over an oscillation period to evaluate the thermoelastic damping. We show the physical meaning of this dissipation function in the framework of the well-known Biot's variational principle of thermoelasticity. The coupled finite element equations are derived by considering harmonic small variations of displacement and temperature with respect to the thermodynamic equilibrium state. In the finite element formulation two elements are considered: the first is a new 8-node thermoelastic element based on the Reissner,Mindlin plate theory, which can be used for modeling thin or moderately thick structures, while the second is a standard three-dimensional 20-node iso-parametric thermoelastic element, which is suitable to model massive structures. For the 8-node element the dissipation along the plate thickness has been taken into account by introducing a through-the-thickness dependence of the temperature shape function. With this assumption the unknowns and the computational effort are minimized. Comparisons with analytical results for thin beams are shown to illustrate the performances of those coupled-field elements. Copyright © 2008 John Wiley & Sons, Ltd. [source] A finite element solution of acoustic propagation in rigid porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2005A. Bermúdez Abstract This paper deals with the acoustical behaviour of a rigid porous material. A finite element method to compute both the response to an harmonic excitation and the free vibrations of a three-dimensional finite multilayer system consisting of a free fluid and a rigid porous material is considered. The finite element used is the lowest order face element introduced by Raviart and Thomas, that eliminates the spurious or circulation modes with no physical meaning. For the porous medium a Darcy's like model and the Allard,Champoux model are taken into account. The numerical results show that the finite element method allows us to compute the response curve for the coupled system and the complex eigenfrequencies. Some of them have a small imaginary part but there are also overdamped modes. Copyright © 2004 John Wiley & Sons, Ltd. [source] Geometrical properties of nodal surfaces of many-electron wave functionsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2010Nikolai D. Chuvylkin Abstract Hypothesis of the exclusion of equipotential surfaces for many-electron wave functions (MWF) has been enunciated. This hypothesis clarifies the physical meaning of the Pauli exclusion principle and opens the way for future progress of new quantum-chemical methods for the construction of approximate MWFs differing from the traditional Hartree,Fock approximation. The equipotential surface exclusion principle has been tested on traditional representative "test systems" of quantum mechanics: the helium atom, the lithium atom, and the hydrogen molecule. Judging by the results of these tests, the use of the suggested approach can lead to a considerable increase in the efficiency of high-accuracy quantum-chemical calculations. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] From quantum chemistry and the classical theory of polar liquids to continuum approximations in molecular mechanics calculations,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Sergio A. Hassan Abstract Biological macromolecules and other polymers belong to the class of mesoscopic systems, with characteristic length scale of the order of a nanometer. Although microscopic models would be the preferred choice in theoretical calculations, their use in computer simulations becomes prohibitive for large systems or long simulation times. On the other hand, the use of purely macroscopic models in the mesoscopic domain may introduce artifacts, with effects that are difficult to assess and that may compromise the reliability of the calculations. Here is proposed an approach with the aim of minimizing the empirical nature of continuum approximations of solvent effects within the scope of molecular mechanics (MM) approximations in mesoscopic systems. Using quantum chemical methods, the potential generated by the molecular electron density is first decomposed in a multicenter-multipole expansion around predetermined centers. The monopole and dipole terms of the expansion at each site create electric fields that polarize the surrounding aqueous medium whose dielectric properties can be described by the classical theory of polar liquids. Debye's theory allows a derivation of the dielectric profiles created around isolated point charges and dipoles that can incorporate Onsager reaction field corrections. A superposition of screened Coulomb potentials obtained from this theory makes possible a simple derivation of a formal expression for the total electrostatic energy and the polar component of the solvation energy of the system. A discussion is presented on the physical meaning of the model parameters, their transferability, and their convergence to calculable quantities in the limit of simple systems. The performance of this continuum approximation in computer calculations of amino acids in the context of an atomistic force field is discussed. Applications of a continuum model based on screened Coulomb potentials in multinanosecond simulations of peptides and proteins are briefly reviewed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Role of transcription factors Ad4bp/SF-1 and DAX-1 in steroidogenesis and spermatogenesis in human testicular development and idiopathic azoospermiaINTERNATIONAL JOURNAL OF UROLOGY, Issue 6 2006YOSHIYUKI KOJIMA Background:, Ad4bp/SF-1 and DAX-1 are orphan members of the nuclear hormone receptor superfamily of transcription factors. In order to obtain better understandings of human testicular steroidogenesis and spermatogenesis, we examined the expression levels of both factors in human normal and idiopathic azoospermic testes and investigated their physical meaning. Methods:, First, we examined the expression level of Ad4bp/SF-1 and DAX-1 by quantitative reverse transcription,polymerase chain reaction (RT,PCR), immunohistochemistry and western blotting analysis using eight normal human testicular tissues from infants to adults. Second, we performed quantitative RT,PCR using testicular biopsy samples obtained from 22 idiopathic azoospermic patients to examine the expression of Ad4bp/SF-1 and DAX-1, and analysed the correlation between the expression levels of both factors and the serum hormone levels or histological evaluation to study their potential correlation with steroidogenesis and spermatogenesis on idiopathic azoospermia. Results:, The expression levels of both factors in the normal testes increased with testicular development. Ad4bp/SF-1 was abundantly expressed in Leydig cell, whereas DAX-1 was expressed in Sertoli cells. The expression level of Ad4bp/SF-1 in idiopathic azoospermic patients testes positively correlated with serum testosterone (P < 0.05). The average expression levels of DAX-1 mRNA for patients with maturation arrest (0.39 ± 0.19) and Sertoli cell-only syndrome (0.13 ± 0.08) were lower than that with hypospermatogenesis (1.60 ± 1.32) and normal spermatogenesis (1.30 ± 1.41). Conclusion:, Ad4bp/SF-1 is important for the maintenance of steroidogenesis in the human testis. DAX-1 plays a critical role in spermatogenesis in the human testis, and Sertoli cell-only syndrome and maturation arrest may result from abnormal Sertoli cell function that disrupts the normal progression of spermatogenesis. [source] Inductive effect of uncharged groups: dependence on electronegativityJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2006Otto Exner Abstract Substituent effects in rigid non-conjugated systems were followed on the series of 3-substituted 1-fluoro-bicyclo[1.1.1]pentanes and 2-substituted 1-fluoroethanes in the fixed ap conformation. Their energies were calculated within the framework of the density functional theory at the B3LYP/6-311++G(3df,3pd)//B3LYP/6-311++G(3df,3pd) level and the substituent effects were expressed in terms of isodesmic homodesmotic reactions. The results were confirmed by the energies of 1,4-disubstituted bicyclo[2.2.2]octanes reported in the literature and calculated at a lower level. Interaction of two common substituents of low or medium polarity cannot be described as the classical inductive effect by one term, proportional in all series, but an additional parameter is necessary, which depends only on the first atom of the substituent and may be identified with its electronegativity. The second term decreases with the distance more steeply than the first term and is always much less important. Nevertheless its statistical significance was proved by several sensitive tests at the highest level used in statistics. When one of the substituents is charged (or at least strongly polar as NO2 or CN), the first term is much increased and the second becomes less significant or insignificant. Therefore, the standard definition of the inductive effect with a uniform, universally valid constant can be retained as far as one treats only the ionization equilibria, both in solution and in the gas phase, or kinetics with a strongly polar transition state. In contrast to the firm statistical proofs, the physical meaning of the electronegativity term was not established. Any relation to various group electronegativities does not exist, similarity to the 13C NMR shifts is merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd. [source] Conjugation of two functional groups through an unsaturated systemJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2006Otto Exner Abstract Energies of 51 1-(E),4-(E)-disubstituted 1,3-butadienes (1), 36 1,4-disubstituted benzenes (2) and 36 (E)-1,2-disubstituted ethenes (3) with dipolar substituents were calculated at the B3LYP/6,311,+,G(d,p) level and evaluated in terms of isodesmic reactions expressing the interaction of substituents through the conjugated system. The energy of interaction reaches up to 40,kJ,mol,1, it is roughly similar in the three series and most regular in the series 1. While its correlation within the framework of dual substituent parameter analysis lacks physical meaning, it is possible to separate the conjugative (resonance) component by subtracting the inductive component with reference to 1,4-disubstituted bicyclo[2.2.2]octanes 4. The conjugative interaction is strongly stabilizing for the combination acceptor,donor and destabilizing for two donors; in these cases it is parallel to changes of geometry as they are predicted by the common resonance equations. Interaction of two acceptors is weak; in addition, there are groups that cannot be classified either as donors or as acceptors. Therefore, one can construct a scale of the resonance ability of donors in conjugation with an acceptor and vice versa, but it is not possible to express the interaction of two donors or of two acceptors on a unified scale for all substituents. The resonance description is certainly appropriate for the typical examples (interaction of NO2 and NH2) but should not be generalized to all possible structures. Copyright © 2005 John Wiley & Sons, Ltd. [source] Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2003Maria Bercea Abstract This is the first of two parts investigating the Flory-Huggins interaction parameter, ,, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients, A2, in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for ,o, the , value in range of pair interaction: ,o,=,,,,,,,,. The parameter , measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter , quantifies the contributions of the conformational changes taking place in response to dilution; , becomes zero for theta conditions. The influences of M are exclusively contained in the parameter , The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of ,o with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between , and ,. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail. Conformational response, ,, as a function of ,, the interaction parameter for fixed conformation. [source] Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small-Angle X-Ray ScatteringMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Arben Jusufi Abstract Summary: We performed molecular dynamics simulation of a charged colloidal particle with explicit counterions. Our work provides a direct comparison between simulations and ASAXS-experiments, offering insight into the counterion distribution of charged colloidal suspensions. We give a detailed constitution of the appearing scattering terms with their physical meaning. It is shown that the cross-correlation between a macroion and its counterions gives the meanfield approximation of the counterion density even if the counterion system is highly fluctuating. Furthermore, it is shown that cross-correlations can be negative due to oscillations of the density amplitudes of the macroion and counterions and, therefore, must be distinguished from other scattering contributions. These oscillations become more pronounced if the counterions exhibit a fixed shape and if the size of the macroion and that of the counterion system are different. Simulation sanpshot of a charged colloid (big central sphere) with counterions (small spheres). [source] On a hierarchy of models for electrical conduction in biological tissuesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 7 2006M. Amar Abstract In this paper we derive a hierarchy of models for electrical conduction in a biological tissue, which is represented by a periodic array of period , of conducting phases surrounded by dielectric shells of thickness ,, included in a conductive matrix. Such a hierarchy will be obtained from the Maxwell equations by means of a concentration process , , 0, followed by a homogenization limit with respect to ,. These models are then compared with regard to their physical meaning and mathematical issues. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kirschning and Jansen computer-aided design formulae for the analysis of parallel coupled linesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2009J. A. Brandão Faria Abstract Among the many computer-aided design (CAD) formulae used for the calculation of the wave parameters of coupled microstrip lines where fringing field effects occur, the Kirschning and Jansen equations are the most utilized ones, not only because of their high accuracy, but also because of their wide range of application. Here, we show that, despite the aforementioned advantages, such equations may lack physical meaning. We prove, for the first time, that the utilization of these widespread CAD equations can lead to positive valued mutual capacitances, an unacceptable result from the viewpoint of electromagnetic theory. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2466,2470, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24659 [source] The lack of large compact symmetric objectsASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009P. Augusto Abstract In recent years, ,baby' (<103 yr) and ,young' (103,105 yr) radio galaxies have been found and classified, although their numbers are still small (tens). Also, they have many different names, depending on the type of survey and scientific context in which they were found: compact steep spectrum sources (CSS), giga-Hertz peaked spectrum sources (GPS) and compact-medium symmetric objects (C-MSO). The latter have the radio galaxy structure more obvious and correspond to the ,babies' (CSOs; < 1 kpc) and ,young' (MSOs; 1,15 kpc) radio galaxies. The log-size distribution of CSOs shows a sharp drop at 0.3 kpc. This trend continues through flat-spectrum MSOs (over the full 1,15 kpc size range). In order to find out if this lack of large CSOs and flat-spectrum MSOs is due to poor sampling (lack of surveys that probe efficiently the 0.3,15 kpc size range) and/or has physical meaning (e.g. if the lobes of CSOs expand as they grow and age, they might become CSSs, ,disappearing' from the flat-spectrum MSO statistics), we have built a sample of 157 flat-spectrum radio sources with structure on ,0.3,15 kpc scales. We are using new, archived and published data to produce and inspect hundreds of multi-frequency multi-instrument maps and models. We have already found 13 new secure CSO/MSOs. We expect to uncover ,30,40 new CSOs and MSOs, most on the 0.3,15 kpc size range, when our project is complete (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A molecular viewer for the analysis of TLS rigid-body motion in macromoleculesACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2005Jay Painter TLS (translation/libration/screw) models describe rigid-body vibrational motions of arbitrary objects. A single-group TLS model can be used to approximate the vibration of an entire protein molecule within a crystal lattice. More complex TLS models are broadly applicable to describing inter-domain and other internal vibrational modes of proteins. Such models can be derived and refined from crystallographic data, but they can also be used to describe the vibrational modes observed through other physical techniques or derived from molecular dynamics. The use of TLS models for protein motion has been relatively limited, partly because the physical meaning of the refined TLS parameters is not intuitive. Here, a molecular viewer, TLSView, is introduced using OpenGL and based on the mmLib library for describing and manipulating macromolecular structural models. This visualization tool allows an intuitive understanding of the physical significance of TLS models derived from crystallographic or other data and may be used as an interactive tool to display and interpret inter-domain or other motions in protein structural models. TLSView may also be used to prepare, analyze and validate TLS models for crystallographic refinement. [source] Flat bulk-solvent model: obtaining optimal parametersACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2002Andrei Fokine A bulk-solvent correction is regularly used for macromolecular refinement. The flat model of the bulk solvent is considered to be the most reliable. It is shown that the standard procedure does not always result in the optimal values of the bulk-solvent correction parameters. A method to obtain the best values for parameters ksol and Bsol of the flat-solvent model is discussed. The values of correctly determined parameters for crystallographic structures deposited in the Protein Data Bank are clustered around ksol = 0.35,e,Å,3 and Bsol = 46,Å2, which have a reasonable physical meaning. Such a distribution allows the use of these mean values of solvent parameters for many practical applications when refined parameters cannot be obtained, especially when an atomic model in the unit cell is not yet known. [source] Numerical Simulation of the Hydrodynamics of Gas/Solid Two-Phase Flow in a Circulating Fluidized Bed with Different Inlet ConfigurationsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2009Y. Li Abstract The gas/solid flow characteristics in a circulating fluidized bed with two different inlet configurations were investigated by numerical simulation based on an Eulerian approach. In order to describe the interaction between the gas phase and the solid phase and the influence of the solid phase on the gas turbulence, a source term formulation with a more reasonable physical meaning was introduced. The simulation results were validated by the experimental data; then, the model was employed to examine the effect of the inlet configuration on the gas and solid feeding. The simulation results showed that, using the side feeding system, the distributions of solid flow and concentration were highly variable both over the column cross-section and along the column height. However, such variations can be improved by using the elbow inlet system where the gas and solid are fed from the bottom. [source] Development in modeling cyclic loading of sands based on kinematic hardeningINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2009Mohammad Maleki Abstract In this paper, there is presented an elastoplastic constitutive model to predict sandy soils behavior under monotonic and cyclic loadings. This model is based on an existing model (Cambou-Jafari-Sidoroff) that takes into account deviatoric and isotropic mechanisms of plasticity. The flow rule used in the deviatoric mechanism is non-associated and a mixed hardening law controls the evolution of the yield surface. In this research the critical state surface and history surface, which separates the virgin and cyclic states in stress space, are defined. Kinematic hardening modulus and stress,dilatancy law for monotonic and cyclic loadings are effectively modified. With taking hardening modulus as a function of deviatoric and volumetric plastic strain and with defining the history surface and stress reversal, the model has the ability to predict the sandy soils' behavior. All of the model parameters have clear physical meanings and can be determined from usual laboratory tests. In order to validate the model, the results of homogeneous tests on Hostun and Toyoura sands are used. The results of validation show a good capability of the proposed model. Copyright © 2009 John Wiley & Sons, Ltd. [source] Why do we need a biomechanical approach to the ocular rigidity concept?ACTA OPHTHALMOLOGICA, Issue 2009KE KOTLIAR Ocular rigidity in ophthalmology is generally assumed to be a measurable surrogate parameter related to the biomechanical properties of the whole globe. Clinical tonometry and tonography, as well as recently developed methods to assess the ocular pulse amplitude and pulsatile ocular blood flow and measurements with the ocular response analyzer are based on the concept of ocular rigidity. Clinical concepts of ocular rigidity describe a resulting effect without considerations of possible diverse morphology and material properties of the different ocular tissues. It is commonly accepted that ocular rigidity is related to the elasticity of the sclera. Many formulations are however dependent on the internal volume of the globe, intraocular pressure, corneal biomechanics and thickness of the corneoscleral shell. Sometimes this is extended to biomechanical properties of the ocular vasculature and perfusion pressure. Therefore ocular rigidity is expressed in various units and has different physical meanings but the same name is used which is confusing. Ocular biomechanics introduces parameters of elasticity and viscoelasticity of the sclera, cornea and other tissues which consider the morphology of the different tissues describing their mechanical properties such as: Young's modules of the sclera and Poisson's ratios of the cornea. When applying these rigorous statements and methods of biomechanical modeling a unified concept for ocular rigidity can be developed in order to link the limited clinical concepts, to improve them and to better understand the results of clinical measurements. [source] | ||||||||||||||||||||||