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Selected AbstractsDispersion of Dust Acoustic Modes and Perturbations of Plasma Flux BalanceCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2007V. Tsytovich Abstract Previous considerations of dust acoustic waves is demonstrated to be inconsistent - the required equilibrium state for perturbations was not defined since balance of plasma fluxes was neglecting. The self-consistent treatment shows that plasma flux perturbations are accompanying any collective waves propagating in dusty plasmas and can play an important role in wave dispersion, wave damping and can create instabilities. This is illustrated by the derivation of dispersion relation for dust acoustic modes taking into account the plasma flux balances and plasma flux perturbations by waves. The result of this approach shows that the dust acoustic waves with linear dependence of wave frequency on the wave number exist only in restricted range of the wave numbers. Only for wave numbers larger than some critical wave number for low frequency modes the frequency can be have approximately a linear dependence on wave number and can be called as dust acoustic wave but the phase velocity of these waves is different from that which can be obtained neglecting the flux balance and depends on grain charge variations which are determined by the balance of fluxes. The presence of plasma fluxes previously neglected is the main typical feature of dusty plasmas. The dispersion relation in the range of small wave numbers is found to be mainly determined by the change of the plasma fluxes and is quite different from that of dust acoustic type, namely it is found to have the same form as the well known dispersion relation for the gravitational instability. This result proves in general way the existence of the collective grain attractions of negatively charged grains for for large distances between them and for any source of ionization. The attraction of grains found from dispersion relation of the dust acoustic branch coincides with that found previously for pair grain interactions using some models for the ionization source. For the existing experiments the effective Jeans length for such attraction is estimated to be about 8 , 10 times larger than the ion Debye length and the effective gravitational constant for the grain attraction is estimated to be several orders of magnitude larger than the usual gravitational constant. The grain attraction at large inter-grain distances described by the gravitationlike grain instability is considered as the simplest explanation for observed dust cloud clustering, formation of dust structures including the plasma crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Three-dimensional VS profiling using microtremors in Kushiro, JapanEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2008Hiroshi Arai Abstract A practical method is presented for determining three-dimensional S-wave velocity (VS) profile from microtremor measurements. Frequency,wave number (f,k) spectral analyses of microtremor array records are combined, for this purpose, with microtremor horizontal-to-vertical (H/V) spectral ratio techniques. To demonstrate the effectiveness of the proposed method, microtremor measurements using arrays of sensors were conducted at six sites in the city of Kushiro, Japan. The spectral analyses of the array records yield dispersion characteristics of Rayleigh waves and H/V spectra of surface waves, and joint inversion of these data results in VS profiles down to bedrock at the sites. Conventional microtremor measurements were performed at 230 stations within Kushiro city, resulting in the H/V spectra within the city. Three-dimensional VS structure is then estimated from inversion of the H/V spectra with the VS values determined from the microtremor array data. This reveals three-dimensional VS profile of Kushiro city, together with an unknown hidden valley that crosses the central part of the city. The estimated VS profile is consistent with available velocity logs and results of subsequent borings, indicating the effectiveness of the proposed method. Copyright © 2008 John Wiley & Sons, Ltd. [source] Errors of kinematic wave and diffusion wave approximations for time-independent flows with infiltration and momentum exchange includedHYDROLOGICAL PROCESSES, Issue 9 2005V. P. Singh Abstract Error equations for kinematic wave and diffusion wave approximations were derived for time-independent flows on infiltrating planes and channels under one upstream boundary and two downstream boundary conditions: zero flow at the upstream boundary, and critical flow depth and zero depth gradient at the downstream boundary. These equations specify error in the flow hydrograph as a function of space. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors below 2% for values of KF (e.g. KF , 7·5), where K is the kinematic wave number and F is the Froude number. Even for small values of KF (e.g. KF = 2·5), the errors were typically less than 3%. The accuracy of the diffusive approximation was greatly influenced by the downstream boundary condition. For critical flow depth downstream boundary condition, the error of the kinematic wave approximation was found to be less than 10% for KF , 7·5 and greater than 20% for smaller values of KF. This error increased with strong downstream boundary control. The analytical solution of the diffusion wave approximation is adequate only for small values of K. Copyright © 2005 John Wiley & Sons, Ltd. [source] Dynamic response of a soft soil layer to flow and periodical disturbanceINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2003Ping-Cheng Hsieh Abstract The dynamic response of a soft soil layer of finite thickness under the mutual effects of flow and periodical disturbance at the free surface is discussed in this work. The homogeneous water is governed by potential theory and the soil layer obeys Biot's theory of poroelasticity. The boundary-value problem is solved by an analytical algorithm, in which the wave number is found first. Secondly, the closed form solutions are found by a two-parameter perturbation method with the boundary-layer correction. The results are also compared with those of the poroelastic soil layer of infinite thickness to show the impermeable rigid boundary effect. Copyright © 2003 John Wiley & Sons, Ltd. [source] Quasi optimal finite difference method for Helmholtz problem on unstructured gridsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2010Daniel T. Fernandes Abstract A quasi optimal finite difference method (QOFD) is proposed for the Helmholtz problem. The stencils' coefficients are obtained numerically by minimizing a least-squares functional of the local truncation error for plane wave solutions in any direction. In one dimension this approach leads to a nodally exact scheme, with no truncation error, for uniform or non-uniform meshes. In two dimensions, when applied to a uniform cartesian grid, a 9-point sixth-order scheme is derived with the same truncation error of the quasi-stabilized finite element method (QSFEM) introduced by Babu,ka et al. (Comp. Meth. Appl. Mech. Eng. 1995; 128:325,359). Similarly, a 27-point sixth-order stencil is derived in three dimensions. The QOFD formulation, proposed here, is naturally applied on uniform, non-uniform and unstructured meshes in any dimension. Numerical results are presented showing optimal rates of convergence and reduced pollution effects for large values of the wave number. Copyright © 2009 John Wiley & Sons, Ltd. [source] Exponential basis functions in solution of static and time harmonic elastic problems in a meshless styleINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2010B. Boroomand Abstract In this paper, exponential basis functions (EBFs) are used in a boundary collocation style to solve engineering problems whose governing partial differential equations (PDEs) are of constant coefficient type. Complex-valued exponents are considered for the EBFs. Two-dimensional elasto-static and time harmonic elasto-dynamic problems are chosen in this paper. The solution procedure begins with first finding a set of appropriate EBFs and then considering the solution as a summation of such EBFs with unknown coefficients. The unknown coefficients are determined by the satisfaction of the boundary conditions through a collocation method with the aid of a consistent and complex discrete transformation technique. The basis and various forms of the transformation have been addressed and discussed. We shall propose several strategies for selection of EBFs with the aid of the basis explained for the transformation. While using the transformation, the number of EBFs should not necessarily be equal to (or less than) the number of boundary information data. A library of EBFs has also been presented for further use. The effect of body forces is included in the solution via construction of particular solution by the use of the discrete transformation and another series of EBFs. A number of sample problems are solved to demonstrate the capabilities of the method. It has been shown that the time harmonic problems with high wave number can be solved without much effort. The method, categorized in meshless methods, can be applied to many other problems in engineering mechanics and general physics since EBFs can easily be found for almost all problems with constant coefficient PDEs. Copyright © 2009 John Wiley & Sons, Ltd. [source] Dispersion analysis of the meshfree radial point interpolation method for the Helmholtz equationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2009Christina Wenterodt Abstract When numerical methods such as the finite element method (FEM) are used to solve the Helmholtz equation, the solutions suffer from the so-called pollution effect which leads to inaccurate results, especially for high wave numbers. The main reason for this is that the wave number of the numerical solution disagrees with the wave number of the exact solution, which is known as dispersion. In order to obtain admissible results a very high element resolution is necessary and increased computational time and memory capacity are the consequences. In this paper a meshfree method, namely the radial point interpolation method (RPIM), is investigated with respect to the pollution effect in the 2D-case. It is shown that this methodology is able to reduce the dispersion significantly. Two modifications of the RPIM, namely one with polynomial reproduction and another one with a problem-dependent sine/cosine basis, are also described and tested. Numerical experiments are carried out to demonstrate the advantages of the method compared with the FEM. For identical discretizations, the RPIM yields considerably better results than the FEM. Copyright © 2008 John Wiley & Sons, Ltd. [source] The performance of spheroidal infinite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001R. J. Astley Abstract A number of spheroidal and ellipsoidal infinite elements have been proposed for the solution of unbounded wave problems in the frequency domain, i.e solutions of the Helmholtz equation. These elements are widely believed to be more effective than conventional spherical infinite elements in cases where the radiating or scattering object is slender or flat and can therefore be closely enclosed by a spheroidal or an ellipsoidal surface. The validity of this statement is investigated in the current article. The radial order which is required for an accurate solution is shown to depend strongly not only upon the type of element that is used, but also on the aspect ratio of the bounding spheroid and the non-dimensional wave number. The nature of this dependence can partially be explained by comparing the non-oscillatory component of simple source solutions to the terms available in the trial solution of spheroidal elements. Numerical studies are also presented to demonstrate the rates at which convergence can be achieved, in practice, by unconjugated-(,Burnett') and conjugated (,Astley-Leis')-type elements. It will be shown that neither formulation is entirely satisfactory at high frequencies and high aspect ratios. Copyright © 2001 John Wiley & Sons, Ltd. [source] Numerical study of particulate suspension flow through wavy-walled channelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2006R. Usha Abstract The particulate suspension flow in a channel whose walls describe a travelling wave motion is examined numerically. A perturbation method is employed and the primitive variables are expanded in a series with the wall amplitude as the perturbation parameter. The boundary conditions are applied at the mean surface of the channel and the first-order perturbation quantities are numerically determined by solving the governing system of ordinary differential equations by shooting technique. The present approach does not impose any restriction on the Reynolds number of the flow and the wave number and frequency of the wavy-walled channel, although it is limited by the linear analysis. The wall shear stress and the positions of flow separation and reattachment points are computed and the influence of the volume fraction density of the particles is examined. The variations of velocity and pressure of the particulate suspension flow with frequency of excitation are also presented. Copyright © 2005 John Wiley & Sons, Ltd. [source] Variability in the characteristics of cut-off low pressure systems over subtropical southern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2007A. T. Singleton Variability in the characteristics of cut-off low pressure systems over subtropical southern Africa is examined for the 1973,2002 period. These characteristics include their seasonality, frequency, duration, location and size. It is found that on average 11 cut-off lows occur over southern Africa south of 20°S per year and are most common in the March-May season. Potential relationships between the number of cut-off lows over southern Africa with the El Niño Southern Oscillation (ENSO), the Pacific South America pattern, the wave number 3 pattern and the semi-annual oscillation (SAO) are discussed. La Niña years appear to be associated with above average annual frequencies of cut-off lows but the reverse is generally not true for El Niño years. There was a shift in the preferred season for cut-off lows from March,May to June,August in the 1980s, which coincided with a weakening of the SAO and a shift in zonal wave number 3. This period also showed a change in the preferred location of these systems from southwestern subtropical southern Africa to the northeast of the region. The results suggest that there may be a relationship between cut-off lows over subtropical southern Africa, the wave number 3 pattern in the Southern Hemisphere and the SAO. Copyright © 2006 Royal Meteorological Society. [source] Theoretical ab initio study of NO and CO depollution reaction catalyzed by copperINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2001O. Bouhlel Abstract The reaction between NO and CO leading to N2 and CO2 is the most studied depollution process of the former molecules. An ab initio study of a multistage mechanism of this reaction catalyzed by copper was performed at SCF level. Many intermediates intervene in the proposed mechanism, such as CuCO, CuNO, CuO, and NCO. Geometrical parameters, atomic charge, dipole moment, vibrational normal mode wave number, and dissociation energy of intervening molecules were calculated. Thermochemistry parameters (,H, ,G, ,S) were also obtained. Transition state has also been determined and has allowed us to discuss the reaction mechanism. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source] Laser induced negative conductivity of diamondLASER PHYSICS LETTERS, Issue 12 2006A. S. Baturin Abstract We consider the negative mobility of electrons in diamond excited by a picosecond laser pulse at low temperatures, due to the inelastic electron-phonon collisions. For the first time the dependence of the deformation potential on the phonon wave number has been taken into account. This dependence changes significantly the region of the negative electron mobility as a function of the phonon temperature. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Invertibility of Helmholtz operators for nonhomogeneous mediasMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 4 2010Vladimir Rabinovich Abstract The paper is devoted to the investigation of the Helmholtz operators (1) describing the propagation of acoustic waves in non-homogeneous space. We consider the operator A with a wave number k such that where k0 is a positive function, k± are complex constants with ,(k)>0. The Helmholtz operator A with such wave number describes the propagation of acoustic waves in the waveguides being no homogeneous layer between two absorbing half-space. We prove that the operator A has an inverse operator A - 1 bounded in the Hilbert space L2(,n). Our proof is based on the limit operators method. We also consider the construction of the inverse operator for the Helmholtz operator A, with the density , = ,(xn) depending on xn only and wave number k0 = k0(,x,, xn) depending on a small parameter ,>0 which characterizes the slowness of variation of the wave number in the horizontal direction. Copyright © 2009 John Wiley & Sons, Ltd. [source] Combined far-ield operators in electromagnetic inverse scattering theoryMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2003Fioralba Cakoni Abstract We consider the inverse scattering problem of determining the shape of a perfect conductor D from a knowledge of the scattered electromagnetic wave generated by a time-harmonic plane wave incident upon D. By using polarization effects we establish the validity of the linear sampling method for solving this problem that is valid for all positive values of the wave number. We also show that it suffices to consider incident directions and observation angles that are restricted to a limited aperture. Copyright © 2003 John Wiley & Sons, Ltd. [source] Pressure-induced structural transitions in multi-walled carbon nanotubesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2009Hiroyuki Shima Abstract We demonstrate a novel cross-sectional deformation, called the radial corrugation, of multi-walled carbon nanotubes (MWNTs) under hydrostatic pressure. Theoretical analyses based on the continuum elastic approximation have revealed that MWNTs consisting of more than ten concentric walls undergo elastic deformations at critical pressure , above which the circular shape of the cross-section becomes radially corrugated. Various corrugation modes have been observed by tuning the innermost tube diameter and the number of constituent walls, which is a direct consequence of the core,shell structure of MWNTs. Cross-sectional views of MWNT under high hydrostatic pressure: elliptic deformation with the mode index n,=,2 (left), and radial corrugations with n,=,5 (center), and n,=,6 (right). The index n indicates the circumferential wave number of the deformed cross-section. [source] Multifrequency Analysis for the Helmholtz EquationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003M. Köhl This paper is a brief review of a new numerical method for the multifrequency analysis of the three-dimensional Helmholtz equation. We describe the principles of this method which is based on the identity of the Fourier transform with respect to the wave number. Some numerical examples for the solution were presented at the oral session. [source] Nonlinear simulations of magnetic instabilities in stellar radiation zones: The role of rotation and shearASTRONOMISCHE NACHRICHTEN, Issue 10 2007A.S. Brun Abstract Using the 3-dimensional ASH code, we have studied numerically the instabilities that occur in stellar radiation zones in presence of large-scale magnetic fields, rotation and large-scale shear. We confirm that some configurations are linearly unstable, as predicted by Tayler and collaborators, and we determine the saturation level of the instability. We find that rotation modifies the peak of the most unstable wave number of the poloidal instability but not its growth rate as much as in the case of the m = 1 toroidal instability for which it is changed to , = /,. Further in the case with rotation and shear, we found no sign of the dynamo mechanism suggested recently by Spruit even though we possess the essential ingredients (Tayler's m = 1 instability and a large scale shear) supposedly at work. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of ELF magnetic field on membrane protein structure of living HeLa cells studied by Fourier transform infrared spectroscopyBIOELECTROMAGNETICS, Issue 7 2003Toshitaka Ikehara Abstract The effects of exposure to a 50 Hz magnetic field (maximum of 41.7 to 43.6 mT) on the membrane protein structures of living HeLa cells were studied using attenuated total reflection infrared spectroscopy. One min of such exposure shifted peak absorbance of the amide I band to a smaller wave number, reduced peak absorbance of the amide II band, and increased absorbance at around 1600 cm,1. These results suggest that exposure to the ELF magnetic field has reversible effects on the N,H inplane bending and C,N stretching vibrations of peptide linkages, and changes the secondary structures of ,-helix and ,-sheet in cell membrane proteins. Bioelectromagnetics 24:457,464, 2003. © 2003 Wiley-Liss, Inc. [source] Wave packet pseudomodes of twisted Toeplitz matricesCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 9 2004Lloyd N. Trefethen The pseudospectra of banded, nonsymmetric Toeplitz or circulant matrices with varying coefficients are considered. Such matrices are characterized by a symbol that depends on both position (x) and wave number (k). It is shown that when a certain winding number or twist condition is satisfied, related to Hörmander's commutator condition for partial differential equations, ,-pseudoeigenvectors of such matrices for exponentially small values of , exist in the form of localized wave packets. The symbol need not be smooth with respect to x, just differentiable at a point (or less). © 2004 Wiley Periodicals, Inc. [source] Dispersion of Dust Acoustic Modes and Perturbations of Plasma Flux BalanceCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2007V. Tsytovich Abstract Previous considerations of dust acoustic waves is demonstrated to be inconsistent - the required equilibrium state for perturbations was not defined since balance of plasma fluxes was neglecting. The self-consistent treatment shows that plasma flux perturbations are accompanying any collective waves propagating in dusty plasmas and can play an important role in wave dispersion, wave damping and can create instabilities. This is illustrated by the derivation of dispersion relation for dust acoustic modes taking into account the plasma flux balances and plasma flux perturbations by waves. The result of this approach shows that the dust acoustic waves with linear dependence of wave frequency on the wave number exist only in restricted range of the wave numbers. Only for wave numbers larger than some critical wave number for low frequency modes the frequency can be have approximately a linear dependence on wave number and can be called as dust acoustic wave but the phase velocity of these waves is different from that which can be obtained neglecting the flux balance and depends on grain charge variations which are determined by the balance of fluxes. The presence of plasma fluxes previously neglected is the main typical feature of dusty plasmas. The dispersion relation in the range of small wave numbers is found to be mainly determined by the change of the plasma fluxes and is quite different from that of dust acoustic type, namely it is found to have the same form as the well known dispersion relation for the gravitational instability. This result proves in general way the existence of the collective grain attractions of negatively charged grains for for large distances between them and for any source of ionization. The attraction of grains found from dispersion relation of the dust acoustic branch coincides with that found previously for pair grain interactions using some models for the ionization source. For the existing experiments the effective Jeans length for such attraction is estimated to be about 8 , 10 times larger than the ion Debye length and the effective gravitational constant for the grain attraction is estimated to be several orders of magnitude larger than the usual gravitational constant. The grain attraction at large inter-grain distances described by the gravitationlike grain instability is considered as the simplest explanation for observed dust cloud clustering, formation of dust structures including the plasma crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comparison of two wave element methods for the Helmholtz problemINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2009T. Huttunen Abstract In comparison with low-order finite element methods (FEMs), the use of oscillatory basis functions has been shown to reduce the computational complexity associated with the numerical approximation of Helmholtz problems at high wave numbers. We compare two different wave element methods for the 2D Helmholtz problems. The methods chosen for this study are the partition of unity FEM (PUFEM) and the ultra-weak variational formulation (UWVF). In both methods, the local approximation of wave field is computed using a set of plane waves for constructing the basis functions. However, the methods are based on different variational formulations; the PUFEM basis also includes a polynomial component, whereas the UWVF basis consists purely of plane waves. As model problems we investigate propagating and evanescent wave modes in a duct with rigid walls and singular eigenmodes in an L-shaped domain. Results show a good performance of both methods for the modes in the duct, but only a satisfactory accuracy was obtained in the case of the singular field. On the other hand, both the methods can suffer from the ill-conditioning of the resulting matrix system. Copyright © 2008 John Wiley & Sons, Ltd. [source] Dispersion analysis of the meshfree radial point interpolation method for the Helmholtz equationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2009Christina Wenterodt Abstract When numerical methods such as the finite element method (FEM) are used to solve the Helmholtz equation, the solutions suffer from the so-called pollution effect which leads to inaccurate results, especially for high wave numbers. The main reason for this is that the wave number of the numerical solution disagrees with the wave number of the exact solution, which is known as dispersion. In order to obtain admissible results a very high element resolution is necessary and increased computational time and memory capacity are the consequences. In this paper a meshfree method, namely the radial point interpolation method (RPIM), is investigated with respect to the pollution effect in the 2D-case. It is shown that this methodology is able to reduce the dispersion significantly. Two modifications of the RPIM, namely one with polynomial reproduction and another one with a problem-dependent sine/cosine basis, are also described and tested. Numerical experiments are carried out to demonstrate the advantages of the method compared with the FEM. For identical discretizations, the RPIM yields considerably better results than the FEM. Copyright © 2008 John Wiley & Sons, Ltd. [source] A hybrid Padé ADI scheme of higher-order for convection,diffusion problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2010Samir KaraaArticle first published online: 8 SEP 200 Abstract A high-order Padé alternating direction implicit (ADI) scheme is proposed for solving unsteady convection,diffusion problems. The scheme employs standard high-order Padé approximations for spatial first and second derivatives in the convection-diffusion equation. Linear multistep (LM) methods combined with the approximate factorization introduced by Beam and Warming (J. Comput. Phys. 1976; 22: 87,110) are applied for the time integration. The approximate factorization imposes a second-order temporal accuracy limitation on the ADI scheme independent of the accuracy of the LM method chosen for the time integration. To achieve a higher-order temporal accuracy, we introduce a correction term that reduces the splitting error. The resulting scheme is carried out by repeatedly solving a series of pentadiagonal linear systems producing a computationally cost effective solver. The effects of the approximate factorization and the correction term on the stability of the scheme are examined. A modified wave number analysis is performed to examine the dispersive and dissipative properties of the scheme. In contrast to the HOC-based schemes in which the phase and amplitude characteristics of a solution are altered by the variation of cell Reynolds number, the present scheme retains the characteristics of the modified wave numbers for spatial derivatives regardless of the magnitude of cell Reynolds number. The superiority of the proposed scheme compared with other high-order ADI schemes for solving unsteady convection-diffusion problems is discussed. A comparison of different time discretizations based on LM methods is given. Copyright © 2009 John Wiley & Sons, Ltd. [source] Benzonitriles: Survey of their importance and scaling of their vibrational frequenciesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2003M. Alcolea Palafox Abstract This work provides a short survey of the studies carried out on benzonitrile and its derivatives, with special attention on a spectroscopic point of view. The importance and main applications of these molecules are also briefly indicated. For an accurate assignment of their vibrational spectra, the scaling procedures for the wave numbers are described. For this purpose, the performance of semiempirical, ab initio, and density functional methods, with different basis sets, is determined. A "resume" of the main scaling factors to be used in the calculated wave numbers is shown. The results obtained for several benzene derivatives, and in particular for four benzonitriles, are analyzed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 189,204, 2003 [source] On wave diffraction by a half-plane with different face impedancesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2007L. P. Castro Abstract The impedance wave diffraction problem by a half-plane screen is revisited in view of its well-posedness upon different impedance and wave parameters. The problem is analysed with the help of potential and pseudo-differential operators. Seven conditions between the impedance and wave numbers are found under which the problem will be well-posed in Bessel potential spaces. In addition, an improvement of the regularity of the solutions is shown for the previous seven conditions. Copyright © 2006 John Wiley & Sons, Ltd. [source] Guided modes in a grounded slab waveguide of uniaxially anisotropic left-handed materialMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007Songhua Liu Abstract The guidance conditions of TE and TM waves with both real and imaginary transverse wave numbers in a grounded slab waveguide of uniaxially anisotropic left-handed material are derived. The mode properties for guided TE waves, such as the existence of guided modes, the number of possible modes and the mode cutoffs are analyzed in different cases graphically. Furthermore, we come into some new conclusions different from the mode properties in an isotropic LHM slab. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1644,1648, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22531 [source] Theoretical study of the electronic structure and the totally symmetric vibrations of selected CoMoCat carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008Kürti Abstract In situ Raman spectroelectrochemical studies of CoMo-Cat single-walled carbon nanotubes enriched in (6,5) tubes have been carried out recently. We performed calculations on the density functional level using local density approximation for the electronic and vibrational properties of the most abundant tubes in these samples. The following chiral semiconducting tubes were investigated: (6,4), (7,3), (6,5), (9,1), (8,3) and (7,5). The calculated and the measured frequencies of the RBM and G, modes agree within several wave numbers. The calculated E11, E22 transition energies -after 30% and 20% upscaling, respectively- are comparable with the experimental values. The quenching of the RBM band with p- and n-doping can be interpreted within the rigid band approximation. The validity of the rigid band approximation was shown by calculating the density of states for neutral and charged tubes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preface: phys. stat. sol. (b) 245/3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2008Christopher W. Smith This is the third Special Issue of physica status solidi (b) focusing on materials with a negative Poisson's ratio or other ,anomalous' physical properties. This issue contains selected papers from the First International Conference on Auxetics and Anomalous Systems held at the University of Exeter, UK, on 4,6 September 2006. Around 50 participants from all over the world as well as from a wide range of scientific and engineering disciplines contributed to what was a highly successful conference. This conference follows in the footsteps of two previous workshops held at the Mathematical Research and Conference Centre in B,dlewo near Pozna,, Poland, in 2004 and 2005 [1, 2]. The papers selected for this issue publish recent results obtained for ,anomalous systems' in experiment, theory and computer simulations. In the following we summarize very briefly their contents. Alderson and Coenen compare the performance of auxetic composites to similar systems with conventional positive Poisson's ratios. They find that there are indeed differences which appear to arise from the change of the overall Poisson's ratio of the composite, some beneficial like a rise in impact tolerance at low impact rates, and others deleterious such as the reduced tolerance at higher impact rates. This is one of the first investigations of possible applications for auxetic materials. The two papers by Gaspar and Koenders both examine the effects of disorder upon anomalous properties, especially negative Poisson's ratio. In the first one Gaspar demonstrates how a mean strain estimate fails to predict negative values of Poisson's ratio because of an inability to account for local fluctuations in elastic properties. For instance it is shown that the volume fraction of auxetic regions in an globally auxetic material (measured experimentally) are smaller than a mean strain homogenisation would require. Koenders and Gaspar explore the elastic properties, and especially Poisson's ratio, of a heterogeneous 2D network of bending beams. They predict auxetic behaviour arising from localised disorder in the packing, and therefore effective locally aggregated elastic properties of the beams. In the three articles by Gatt et al. and Grima et al. models based on simple geometry are used to explain the behaviour of seemingly disparate systems, i.e. 2D honeycombs systems and zeolite SiO2 networks. Two papers concerning honeycombs demonstrate relationships between elastic properties and structure and the bounds for auxetic behaviour. The paper concerning the zeolite Natrolite uses numerical force field based energy minimisation methods to simulate the response of this particular zeolite to applied forces and then simplifies the predicted properties even further by considering structural units as rigid 2D polyhedra linked by flexible hinges. In a similar vein, though using a different approach and concerning a very different form of matter, Heyes shows how the heterogeneity in an assembly of particles in a liquid can affect the elastic properties of a liquid and notably the infinite frequency Poisson's ratio. Heyes uses the Molecular Dynamics approach to simulate a Lennard,Jones fluid under various pressures, notably comparing behaviour under positive and negative pressures. In their first paper Jasiukiewicz and co-authors derive elastic constants of 2D crystals for all four classes of 2D crystalline solids: hexagonal (isotropic), quadratic, rectangular, and oblique systems. In their second paper they demonstrate conditions required for auxetic behaviour of 2D crystals. Auxetic solids are further divided into those with some negative Poisson's ratios (auxetic), all negative Poisson's ratios (completely auxetic) and no negative Poisson's ratios (non-auxetic). Lakes and Wojciechowski consider counterintuitive properties of matter, like negative compressibility, negative Poisson's ratio, negative thermal expansion, negative specific heat, and negative pressure. They present and interpret experimental observations of negative bulk modulus in pre-strained foams. They propose also a constrained microscopic model which exhibits negative compressibility. Finally, they solve a very simple thermodynamic model with negative thermal expansion. Martin et al. take a long stride toward a real world application of auxetic materials with a wide ranging study starting with numerical modelling of a wingbox section to experimental testing in a wind tunnel. They show that an auxetic core in a wing box section can allow a passive aero-elastic response which can be tailored by careful design of the core so that camber, and thus drag, is reduced with increasing airspeed but without sacrificing structural integrity. Miller et al. consider another anomalous physical property, negative thermal expansivity, and its application in the form of particulate composites for amelioration of stresses arising from thermal mismatch. They show via experiments that particles with a negative coefficient of thermal expansion may be used as a composite reinforcer to reduce overall thermal expansion and behave according to the standard volume fraction based models. Narojczyk and Wojciechowski examine the effects of disorder upon the bulk elastic properties of 3D fcc soft sphere systems in terms of particle size. Systems, such as colloids, can be thought of in such terms. The study shows that higher order moments of probability distribution do not influence the bulk elastic properties much, but that lower moments such as the standard deviation of particle size influence the elastic properties greatly. The "hardness" of the particle interaction potential is also important in this context. In general, it is shown that the effect of increasing polydispersity is to increase the Poisson's ratio, except the [110] [10] directions. Scarpa and Malischewsky in their paper on Rayleigh waves in auxetic materials show how the Rayleigh wave speed is affected by the Poisson's ratio. The behaviour is complex and depends upon the homogeneity within the material, for instance slowing with decreasing Poisson's ratio in isotropic solids, but showing the reverse trend and increased sensitivity to Poisson's ratio in laminate composites. Scarpa et al. explore the buckling behaviour of auxetic tubes via three types of model, a simple beam mechanics and Eulerian buckling model, a 3D linear elastic FE model and a bespoke non-linear continuum model. The more sophisticated models provide increasing insight into the buckling behaviour though the simple beam model predicts reasonably well in the pre-buckling linear region. Some unexpected and interesting behaviour is predicted by the continuum model as the Poisson's ratio approaches the isotropic limit of ,1, including increasing sensitivity to Poisson's ratio and rapid mode jumping between integer wave numbers. The paper by Shilko et al. presents an analysis of a particular kind of friction joint, a double lap joint, and explores the effects of altering the elastic properties of one component, in particular it's Poisson's ratio. The manuscript introduces the evolution of smart materials from monolithic materials, and the classification of composites exhibiting negative Poisson's ratios. The paper then presents the case of a double lap joint and performs a sensitivity type study, via a 2D FE model, of the effects of changing the elastic properties and degree of anisotropy of one section of the model on various parameters defining the limits of functionality of the joint. The main finding is that an enhanced shear modulus, via a negative Poisson's ratio, can endow such a friction joint with superior performance. Manufacturing of auxetic materials on a commercial scale has proved to be the largest obstacle to their fuller exploitation. The paper by Simkins et al. explores one route for post processing of auxetic polymers fibres produced by a conventional melt extrusion route. Simkins et al. showed that a post process thermal annealing treatment, with carefully optimised parameters, was able to even out otherwise inhomogenous auxetic properties, and moreover improve other elastic and fracture properties often sacrificed for auxetic behaviour. We gratefully acknowledge the support given by the sponsors of the conference, namely the EPSRC of the UK and Auxetic Technologies Ltd. (UK). We also thank the Scientific Committee, the Organising Committee, and all the participants of the conference. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Number of Follicular Waves and Their Effect on Pregnancy Rate in the CowREPRODUCTION IN DOMESTIC ANIMALS, Issue 2 2005HA Çelik Contents In the study, the relationship of follicular growth waves, oestradiol and pregnancy rates were investigated during oestrus cycle in cows. A total of 22, Brown Swiss cows (3,5 years old) were used for the study. The ovaries of animals were examined from sixth day of cycle to next oestrus by ultrasound. The follicles that were present in the ovarium were recorded. Follicular growth was observed every day by means of ultrasound examination. The blood samples were taken for analysis of oestradiol simultaneously with ultrasound examinations. The oestrus animals were inseminated. Each animal that inseminated was examined by ultrasound on day 28 after insemination for pregnancy diagnosis. Two follicular growth waves were observed in nine of 22 (40.9%), three waves in 13 of 22 (59.1%) animals. The oestradiol was found in the same concentration but in different release patterns between two and three waves animals. Pregnancy rate in cows with three and two follicular waves did not differ. In conclusion, emergence of three waves of follicular growth was higher in Brown Swiss cows, the analysis of oestradiol could be used for determination of the wave numbers and the animals with different waves may have had the same pregnancy rates. [source] Experimental research on drag reduction by polymer additives in a turbulent pipe flowTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2002Shao Xueming Abstract In order to investigate the effects of injection position on drag reduction as well as further the effects of polymer additives on turbulent structures, LDA measurements of turbulent pipe flows were conducted. The results show that the amount of drag reduction grows with the increase of the Reynolds number, and injecting the polymer at the centre of pipe is more effective than at the wall. Due to the addition of polymer solution, the axial, radial r.m.s. velocity fluctuations and Reynolds stress decrease over the entire pipe cross-section, the time auto-correlation coefficients of axial and radial velocity fluctuation at the centre of pipe decay more slowly, the number of spectrum peaks is decreased, and the peak shifts towards lower wave numbers. The results also reveal that, due to the addition of polymer solution, the large-scale vortices are enhanced and small-scale vortices are suppressed. On a effectué des mesures par anémométrie laser Doppler d'écoulements turbulents dans des conduites afin d'étudier l'effet de la position de l'injection et l'effet de l'ajout d'additifs à base de polymères sur la réduction de traînée. Les résultats montrent que la réduction de traînée augmente avec le nombre de Reynolds et qu'il est plus efficace d'injecter le polymère au centre de la conduite qu'à la paroi. Du fait de l'ajout d'une solution de polymères, les fluctuations de vitesse efficace radiale et axiale et la contrainte de Reynolds diminuent sur toute la section transversale de la conduite, les coefficients d'auto-corrélation de temps de la fluctuation de vitesse efficace radiale et axiale au centre de la conduite décroissent plus lentement, le nombre de pics du spectre diminue et les pics tendent à avoir un nombre d'ondes moins grand. Les résultats montrent également que, grâce à l'ajout de la solution de polymères, les tourbillons de grande échelle sont plus nombreux tandis que les tourbillons de petite eéhelle disparaissent. [source] | |||||||||||||||||||||||||