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External Field (external + field)
Selected AbstractsDiffusion-Influenced Reversible Trapping Problem in the Presence,of,an,External FieldCHEMISTRY - AN ASIAN JOURNAL, Issue 1-2 2006Soohyung Park Abstract We investigate the field effect on the diffusion-influenced reversible trapping problem in one dimension. The exact Green function for a particle undergoing diffusive motion between two static reversible traps with a constant external field is obtained. From the Green function, we derive the various survival probabilities. Two types of trap distribution for the many-body problem are considered, the periodic and random distributions. The mean survival probability is obtained for the crossing-forbidden case for the two types of trap distribution. For the periodic distribution it decays exponentially. For the random trap distribution, similar to the irreversible case, there exists a critical field strength at which the long time asymptotic behavior undergoes a kinetic transition from the power law to exponential behaviors. The difference between equilibrium concentrations for the two types of trap distribution due to the fluctuation effect of trap concentration vanishes as the field strength increases. [source] Visualization of the distant dipolar field: A numerical studyCONCEPTS IN MAGNETIC RESONANCE, Issue 6 2009Stefan Kirsch Abstract The magnetization of liquid water in an external field generates an intrinsic magnetic field in the sample called the distant dipolar field (DDF). To visualize the spatial distribution of the DDF a numerical study was performed for the case of liquid,state 1H NMR at 7 T. 2D maps of the frequency offset caused by the DDF in pure water were calculated for homogenously magnetized spherical and cylindrical samples as well as for the case of a spatially modulated magnetization distribution occurring e.g., in CRAZED (Cosy Revamped by Asymmetric Z-Gradient Echo Detection) experiments. The calculation yielded DDF induced frequency offsets in the range of 0.58 Hz to 10.24 Hz inside the homogeneously magnetized cylinders, while DDF-induced frequency offsets ,10,5 Hz were obtained inside the sphere. The calculated frequency offsets were in good agreement with analytical results available for a sphere and an infinitely long cylinder. In the case of a spatially modulated magnetization distribution, DDF-induced frequency offsets with maximum values of +0.83 Hz were obtained inside the sphere. The presented 2D maps of the DDF-induced frequency offset have tutorial character and may help to visualize this phenomenon in a direct manner. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A:357,364, 2009. [source] Sum rules and exact relations for quantal Coulomb systemsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-6 2003V.M. Adamyan Abstract A complex response function describing a reaction of a multi-particle system to a weak alternating external field is the boundary value of a Nevanlinna class function (i.e. a holomorphic function with non-negative imaginary part in the upper half-plane). Attempts of direct calculations of response functions based on standard approximations of the kinetic theory for real Coulomb condensed systems often result in considerable discrepancies with experiments and computer simulations. At the same time a relatively simple approach using only the exact values of leading asymptotic terms of the response function permits to restrict essentially a subset of Nevanlinna class functions containing this response function, and in this way to obtain sufficient data to explain and predict experimental results. Mathematical details of this approach are demonstrated on an example with the response function being the (external) dynamic electrical conductivity of cold dense hydrogen-like plasmas. In particular, the exact values of the leading terms of asymptotic expansions of the conductivity are calculated. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pillared Layered Metal Phosphonates Showing Field-Induced Magnetic TransitionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2010Peng-Fei Wang Abstract The first examples of metal phosphonates based on 6-phosphononicotinic acid (pnaH3), namely, M3(pna)2(H2O)2 {1: M = CuII, 2: M = CoII} are reported. Both possess pillared layered structures. Within the inorganic layer, chains made up of dimers of edge-sharing {M2O6} octahedra and {M1O6} octahedra through O(1W), O,P,O, and O,C,O units are interconnected by {PO3C} tetrahedra. The pyridyl groups of pna3, serve as the pillars. An antiferromagnetic ground state is found for each compound. When the external field reaches critical points at low temperature, compound 1 features a spin flop transition, whereas 2 shows metamagnetic behavior. [source] Bulk Nanostructured Materials: Non-Mechanical Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Yulia Ivanisenko An overview of the synthesis and processing techniques for bulk nanostructured materials that are based on "bottom-up" approaches is presented. Typically, these processes use nanoparticles, which can be produced by a variety of methods in the gas, liquid or solid state, as the basic building blocks. Their assembly into bulk nanostructured materials requires at least one more processing step, such as compaction or the formation of thick films. For certain nanostructures, film deposition techniques can also be employed. A wide range of nanostructures , from thick films with theoretical density to bulk nanocrystalline materials with nanoporosity , exhibiting novel structural and functional properties useful in many fields of applications are presented. Additionally, the properties of these bulk nanostructured materials can be categorized as either tailored, i.e., microstructure-dependent and inherently irreversible, or tunable, i.e., reversible by the application of an external field. Examples of both categories of properties are presented and the special role of the synthesis and processing routes to achieve the necessary nanostructures is emphasized. [source] Quantum cosmology and tachyonsFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 4-5 2008D.D. Dimitrijevic Abstract We discuss the relevance of the classical and quantum rolling tachyons inflation in the frame of the standard, p -adic and adelic minisuperspace quantum cosmology. The field theory of tachyon matter proposed by Sen in a zero-dimensional version suggested by Kar leads to a model of a particle moving in a constant external field with quadratic damping. We calculate the exact quantum propagator of the model, as well as, the vacuum states and conditions necessary to construct an adelic generalization. [source] Modelling electromagnetic responses of 2-D structures due to spatially non-uniform inducing fields.GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003Analysis of magnetotelluric source effects at coastlines SUMMARY In previous works, we presented 2-D and 3-D magnetotelluric modelling methods based on Rayleigh,Fourier expansions. These methods are an alternative to finite-element and finite-difference techniques and are especially suitable for modelling multilayered structures, with smooth irregular boundaries. Here we generalize the 2-D method for the calculation of the electromagnetic response of 2-D structures to arbitrary, spatially non-uniform 2-D and 3-D inducing magnetic fields. These fields are characteristic of low- and high-latitude regions. We calculate the response to different 2-D and 3-D sources, of a 2-D structure representative of the conductivity distribution which could be found at a coastline, which includes deep conductive anomalies in the lower crust and upper mantle. Then, we investigate source effects, comparing these responses to that obtained for a uniform source. These effects become noticeable for periods greater than approximately 6 h and increase with the period of the source. They are highly dependent on the morphology of the source and also on the orientation of the external field relative to the strike direction of the structure. In various cases, they totally mask the uniform source response. [source] Magnetic Hydrogel Particles: Microfluidic Assembly of Magnetic Hydrogel Particles with Uniformly Anisotropic Structure (Adv. Mater.ADVANCED MATERIALS, Issue 31 200931/2009) The inside cover shows magnetic hydrogel particles with uniform anisotropic features, synthesized using double emulsions as templates, as reported by Adam Abate and co-workers on p.3201. Microfluidic assembly using flow-focusing double emulsion drop makers provides excellent control over the size, morphology, and monodispersity of the products. The particles exhibit excellent rotational control under an external field, with a possibility of eccentric rotation inducing a significant localized shear flow, and have promise for a variety of biomedical applications. [source] Quantum bits with polyacetyleneJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2002Andre Elvas Pereira Da Silva Abstract The dynamics of a polyacetylene single chain as a system for possible physical implementations of quantum bits is determined. This novel proposition is studied by varying intensity and duration of application of an electric field as well as the intensity, number, and position in the polymer chain of impurity molecules. The behavior of soliton pairs, whose associated energy levels form the quantum bit, is analyzed. The chain is modeled by a modified Pariser,Parr,Pople Hamiltonian extended to include the effects of an external electric field and the parameters of the impurity molecules. The effect of the variation of the field and impurities on the separation of the energy levels associated with soliton pairs is analyzed by numerical integration of the equations of motion. Two different approaches for controlling the separation of levels are presented, and their features compared. First, the use of changes in the electric field to control the distance (and ultimately coupling) between two solitons moving freely on the chain or captured by the potential generated by the impurity molecules. Second, the change in the intensity of the impurities alone, with no application of an external field. We have found that the effect of the use of the field on the separation of levels is much smaller than the one obtained by changes in the parameters of the impurity molecules, which eventually led us to achieve quantum bit behavior in a polyacetylene chain. The influence of the field and impurity parameters in the energy levels is determined, as well as their role in the coupling of the two solitons on the chain. Critical values for distance between solitons, intensity of field, and impurities that determine whether a pair of solitons can work as a quantum bit are obtained. © 2002 Wiley Periodicals, Inc. J Comput Chem 9: 870,873, 2002 [source] Spontaneous bremsstrahlung effect in the nonrelativistic electron scattering by a nucleus in the field of pulsed light waveLASER PHYSICS LETTERS, Issue 6 2009A.A. Lebed' Abstract The theory of nonresonant spontaneous bremsstrahlung by a nonrelativistic electron scattered by a nucleus in the field of a pulsed light wave is developed. The electron interaction with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation), and the interaction with an external pulsed field is taken into account accurately. The approximation is examined when the pulsewidth is considerably greater than the characteristic time of wave oscillations. For the range of moderately strong fields the analytic expression for the nonresonant differential cross-section was obtained, which has the form of a sum over partial differential crosssections. It is shown, that in the case of nonrelativistic electron energy the partial cross-section is not factorable on the crosssection of electron-nucleus spontaneous bremsstrahlung in the absence of the external field and the emission-absorption probability of a certain number of wave photons. It is concluded, that the total cross-section of spontaneous bremsstrahlung of an electron scattered by a nucleus in the field of pulsed light wave summing over all possible partial processes differs essentially from the cross-section of electron-nucleus spontaneous bremsstrahlung in the absence of the external field. (© 2009 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Alignment of voids in the cosmic webMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Erwin Platen ABSTRACT We investigate the shapes and mutual alignment of voids in the large-scale matter distribution of a , cold dark matter (,CDM) cosmology simulation. The voids are identified using the novel watershed void finder (WVF) technique. The identified voids are quite non-spherical and slightly prolate, with axis ratios in the order of c : b : a, 0.5 : 0.7 : 1. Their orientations are strongly correlated with significant alignments spanning scales >30 h,1 Mpc. We also find an intimate link between the cosmic tidal field and the void orientations. Over a very wide range of scales we find a coherent and strong alignment of the voids with the tidal field computed from the smoothed density distribution. This orientation,tide alignment remains significant on scales exceeding twice the typical void size, which shows that the long-range external field is responsible for the alignment of the voids. This confirms the view that the large-scale tidal force field is the main agent for the large-scale spatial organization of the cosmic web. [source] 55Mn NMR study in magnetically ordered state of perovskite manganitesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2004K. Shimizu Abstract We present NMR results of Pr1,xSrxMnO3 and their lacunar samples, and also present results of the single crystalline layered manganites La1.2Sr1.8Mn2O7 and La1.2Sr1.6Ca0.2Mn2O7. In Pr1,xSrxMnO3, a single resonance line is observed for 0.27 , x , 0.4, which indicates the sample to be in a metallic state. In the Pr and Sr deficient samples, the NMR line arising from Mn2+ is observed. Introducing deficiency to Pr or Sr sites, a charge disproportionation of the type 2Mn3+, Mn2+ + Mn4+ probably occurs. For La1.2Sr1.8Mn2O7 and La1.2Sr1.6Ca0.2Mn2O7 compounds, the NMR spectra under an external field of 1.5 T are broad and spread with several distinct lines in the frequency range 310,420 MHz. This is different from the results of La1,xSrxMnO3 and Pr1,xSrxMnO3 with a metallic state, where a single line has been observed. The distinct NMR lines are ascribed to Mn4+, Mn3+ and metallic phase, taking account of the results for La1,xSrxMnO3 and Pr1,xSrxMnO3. In addition to the NMR line from the metallic phase, the observation of Mn3+ and Mn4+ lines suggests a phase separation at low temperature in La1.2Sr1.8Mn2O7 and La1.2Sr1.6Ca0.2Mn2O7. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bond models in linear and nonlinear opticsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010D. E. Aspnes Abstract Atomic-scale descriptions of linear-optical properties such as reflection are nearly a century old, but surprisingly, analogous models describing nonlinear-optical (NLO) properties as the natural dynamic response of bond charges driven by an external field are a recent development. These bond-charge models have proven to be particularly useful in describing the relevant physics of second-, third-, and fourth-harmonic generation, identifying previously unrecognized contributions to NLO responses, and uncovering well-disguised correlations in tensor parameters determined phenomenologically from symmetry conditions. Current capabilities are discussed, and opportunities for improved understanding noted. [source] Magnetic anisotropy studies on FeNiCo/Ta/FeNiCo three layers film by layer sensitive ferromagnetic resonance techniquePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004F. Yildiz Abstract Two ferromagnetic layers that are separated by a non-magnetic spacer have been deposited in the presence of an external Dc magnetic field that has been applied in a mutually perpendicular direction during the deposition of each layer. This thin three-layer film of FeNiCo/Ta/FeNiCo was then studied by electron spin resonance (ESR) technique for different directions of the external magnetic field with respect to the film plane. Beside very anisotropic and strong two main modes, relatively well-resolved and very weak subsidiary peaks in ESR spectra were observed on low field side of the main modes for almost every direction of the external field. The anisotropic behavior as the field is rotated from the film normal towards to the film plane is due to strong demagnetizing field. However, two fold (axial) small anisotropies having 90 degrees phase shifts with respect to the peaks from two different layers were seen to originate from field-induced anisotropy. The small peaks are attributed to magnetostatics modes as well. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Decoherence of quantum tunneling by coherent phonon modes in symmetric double-well systemPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004Akira Igarashi Abstract We investigate effect of the decoherence in quantum tunneling in one-dimensional symmetric double-well potential with coherent or stochastic perturbation. A coupling with some vibrational modes can cause the decoherence in the wavepacket dynamics. Furthermore, we discuss the controllability of the quantum tunneling by external field based on optimal control theory. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic-field-induced switching of spin injectionin Zn1,xMnxTe/ZnTe double quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004S. Shirotori Abstract Magnetic-field-induced switching of the spin configuration and the resultant spin injection direction have been studied in a Zn1,xMnxTe/ZnTe double quantum well. The up- and down-spin excitons are injected from the Zn1,xMnxTe layers to the ZnTe well in weak magnetic fields, where both exciton energies in the Zn1,xMnxTe layer are higher than those in the ZnTe. Above the level crossing field, the down-spin exciton energy in the Zn1,xMnxTe layers becomes lower due to the giant Zeeman effect. Therefore, the up- and down-spin excitons are spatially separated in each layer and the down-spin exciton in the ZnTe layer is injected to the Zn1,xMnxTe. It means that the direction of the excitonic spin injection can be switched by the external field. The injection time increases from 12 psec to 300 psec toward the level crossing field of 2.5 T, since the spin-polarized excitons in those layers are associated and can cause reverse spin injection processes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Scalar Aharonov-Bohm effect in the presence of a topological defectANNALEN DER PHYSIK, Issue 7 2010K. Bakke Abstract In this paper we study the scalar Aharonov-Bohm effect for a neutral particle possessing a magnetic dipole moment in the presence of a cosmic string. We study the phase shift acquired by the wave function of the neutral particle in the presence of this topological defect, investigate this phase shift within nonrelativistic and relativistic quantum descriptions considering two distinct magnetic field configurations and find that the scalar Aharonov-Bohm effect is composed by two contributions, with the first one arises due to the interaction of a magnetic dipole with an external field, and other one arises due to the presence of the cosmic string. The nondispersivity of this effect is also discussed. [source] Optically driven Mott-Hubbard systems out of thermodynamic equilibriumANNALEN DER PHYSIK, Issue 12 2009A. Lubatsch Abstract We consider the Hubbard model at half filling, driven by an external, stationary laser field. This stationary, but periodic in time, electromagnetic field couples to the charge current, i.e. it induces an extra contribution to the hopping amplitude in the Hubbard Hamiltonian (photo-induced hopping). We generalize the dynamical mean-field theory (DMFT) for nonequilibrium with periodic-in-time external fields, using a Floquet mode representation and the Keldysh formalism. We calculate the non-equilibrium electron distribution function, the density of states and the optical DC conductivity in the presence of the external laser field for laser frequencies above and below the Mott-Hubbard gap. The results demonstrate that the system exhibits an insulator-metal transition as the frequency of the external field is increased and exceeds the Mott-Hubbard gap. This corresponds to photo-induced excitations into the upper Hubbard band. [source] Electric/magnetic flux tube on the background of magnetic/electric fieldANNALEN DER PHYSIK, Issue 5 2004V. Dzhunushaliev Abstract It is argued that the phenomenon of a flux tube in quantum chromodynamics is closely connected with a spontaneously symmetry breakdown of gauge theory. It is shown that in the presence of a mass term in the SU(2) gauge theory the Nielsen-Olesen equations describe the flux tube surrounded by an external field. [source] Diffusion-Influenced Reversible Trapping Problem in the Presence,of,an,External FieldCHEMISTRY - AN ASIAN JOURNAL, Issue 1-2 2006Soohyung Park Abstract We investigate the field effect on the diffusion-influenced reversible trapping problem in one dimension. The exact Green function for a particle undergoing diffusive motion between two static reversible traps with a constant external field is obtained. From the Green function, we derive the various survival probabilities. Two types of trap distribution for the many-body problem are considered, the periodic and random distributions. The mean survival probability is obtained for the crossing-forbidden case for the two types of trap distribution. For the periodic distribution it decays exponentially. For the random trap distribution, similar to the irreversible case, there exists a critical field strength at which the long time asymptotic behavior undergoes a kinetic transition from the power law to exponential behaviors. The difference between equilibrium concentrations for the two types of trap distribution due to the fluctuation effect of trap concentration vanishes as the field strength increases. [source] Universality in the two-matrix model: a Riemann-Hilbert steepest-descent analysisCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 8 2009Maurice Duits The eigenvalue statistics of a pair (M1, M2) of n × n Hermitian matrices taken randomly with respect to the measure can be described in terms of two families of biorthogonal polynomials. In this paper we give a steepest-descent analysis of a 4 × 4 matrix-valued Riemann-Hilbert problem characterizing one of the families of biorthogonal polynomials in the special case W(y) = y4/4 and V an even polynomial. As a result, we obtain the limiting behavior of the correlation kernel associated to the eigenvalues of M1 (when averaged over M2) in the global and local regime as n , , in the one-cut regular case. A special feature in the analysis is the introduction of a vector equilibrium problem involving both an external field and an upper constraint. © 2008 Wiley Periodicals, Inc. [source] The mean-field approximation in quantum electrodynamics: The no-photon caseCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 4 2007Christian Hainzl We study the mean-field approximation of quantum electrodynamics (QED) by means of a thermodynamic limit. The QED Hamiltonian is written in Coulomb gauge and does not contain any normal ordering or choice of bare electron/positron subspaces. Neglecting photons, we properly define this Hamiltonian in a finite box [,L/2; L/2)3, with periodic boundary conditions and an ultraviolet cutoff ,. We then study the limit of the ground state (i.e., the vacuum) energy and of the minimizers as L goes to infinity, in the Hartree-Fock approximation. In the case with no external field, we prove that the energy per volume converges and obtain in the limit a translation-invariant projector describing the free Hartree-Fock vacuum. We also define the energy per unit volume of translation-invariant states and prove that the free vacuum is the unique minimizer of this energy. In the presence of an external field, we prove that the difference between the minimum energy and the energy of the free vacuum converges as L goes to infinity. We obtain in the limit the so-called Bogoliubov-Dirac-Fock functional. The Hartree-Fock (polarized) vacuum is a Hilbert-Schmidt perturbation of the free vacuum and it minimizes the Bogoliubov-Dirac-Fock energy. © 2006 Wiley Periodicals, Inc. [source] Nonequilibrium statistical mechanics of swarms of driven particlesCOMPLEXITY, Issue 4 2003Werner Ebeling Abstract As a rough model for the collective motions of cells and organisms we develop here the statistical mechanics of swarms of self-propelled particles. Our approach is closely related to the recently developed theory of active Brownian motion and the theory of canonical-dissipative systems. Free motion and motion of a swarms confined in an external field is studied. Briefly, the case of particles confined on a ring and interacting by repulsive forces is studied. In more detail we investigate self-confinement by Morse-type attracting forces. We begin with pairs N = 2; the attractors and distribution functions are discussed, then the case N > 2 is discussed. Simulations for several dynamical modes of swarms of active Brownian particles interacting by Morse forces are presented. In particular we study rotations, drift, fluctuations of shape, and cluster formation. © 2003 Wiley Periodicals, Inc. [source] Magnetic susceptibility: Further insights into macroscopic and microscopic fields and the sphere of LorentzCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003C.J. Durrant Abstract To make certain quantitative interpretations of spectra from NMR experiments carried out on heterogeneous samples, such as cells and tissues, we must be able to estimate the magnetic and electric fields experienced by the resonant nuclei of atoms in the sample. Here, we analyze the relationships between these fields and the fields obtained by solving the Maxwell equations that describe the bulk properties of the materials present. This analysis separates the contribution to these fields of the molecule in which the atom in question is bonded, the "host" fields, from the contribution of all the other molecules in the system, the "external" fields. We discuss the circumstances under which the latter can be found by determining the macroscopic fields in the sample and then removing the averaged contribution of the host molecule. We demonstrate that the results produced by the, so-called, "sphere of Lorentz" construction are of general validity in both static and time-varying cases. This analytic construct, however, is not "mystical" and its justification rests not on any sphericity in the system but on the local uniformity and isotropy, i.e., spherical symmetry, of the medium when averaged over random microscopic configurations. This local averaging is precisely that which defines the equations that describe the macroscopic fields. Hence, the external microscopic fields, in a suitably averaged sense, can be estimated from the macroscopic fields. We then discuss the calculation of the external fields and that of the resonant nucleus in NMR experiments. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 18A: 72,95, 2003 [source] Screening Breakdown in a Plasma by Two Laser Fields and Strong DC Magnetic FieldCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005D. F. Miranda Abstract The effective static dielectric constant of an electron plasma system in the simultaneous presence of two electromagnetic waves and a strong DC magnetic field is calculated. It is found that as the difference ,, of the two electromagnetic wave frequencies matches the plasma frequency ,, a breakdown in screening occurs thereby increasing the plasma heating rate via the external fields due to inverse Bremmstrahlung. An application is made by considering the typical parameters of a hot plasma. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dynamic Magnetic Properties of Ferroic Films, Multilayers, and Patterned ElementsADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Robert L. Stamps Abstract Modification and control of material properties through careful manipulation of geometry on nano- and sub-nanometer length scales is a cornerstone of modern materials science and technology. An exciting area in which these concepts have provided exceptional advances has been magnetoelectronics and nanomagnetism. Important scales in magnetic metals are conduction spin diffusion lengths and distances over which local moments correlate. Advanced techniques now allow for the creation of structures patterned on these length scales in three dimensions. The focus of this article is on magnetic structures whose dynamic properties can be strongly modified by ion bombardment and lithographic patterning. Examples are given of how microwave frequency properties can be tuned with external fields, how factors controlling magnetic switching can be controlled, and how manipulation of magnetic domain walls can be used to reveal new and surprising phenomena. [source] Numerical solutions of liquid metal flows by incompressible magneto-hydrodynamics with heat transferINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2009Kenan, entürk Abstract A two-dimensional incompressible magneto-hydrodynamic code is presented in order to solve the steady state or transient magnetized or neutral convection problems with the effect of heat transfer. The code utilizes a numerical matrix distribution scheme that runs on structured or unstructured triangular meshes and employs a dual time-stepping technique with multi-stage Runge,Kutta algorithm. The code can be used to simulate the natural convection with internal heat generation and absorption and nonlinear time-dependent evolution of heated and magnetized liquid metals exposed to external fields. Copyright © 2008 John Wiley & Sons, Ltd. [source] Modified method of characteristics for solving population balance equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003Laurent Pilon Abstract This paper presents a new numerical method for solving the population balance equation using the modified method of characteristics. Aggregation and break-up are neglected but the density function variations in the three-dimensional space and its dependence on the external fields are accounted for. The method is an interpretation of the Lagrangian approach. Based on a pre-specified grid, it follows the particles backward in time as opposed to forward in the case of traditional method of characteristics. Unlike the direct marching method, the inverse marching method uses a fixed grid thus, making it compatible with other numerical schemes (e.g. finite-volume, finite elements) that may be used to solve other coupled equations such as the mass, momentum, and energy conservation equations. The numerical solutions are compared with the exact analytical solutions for simple one-dimensional flow cases. Very good agreement between the numerical and the theoretical solutions has been obtained confirming the validity of the numerical procedure and the associated computer program. Copyright © 2003 John Wiley & Sons, Ltd. [source] Semiconductor Nanorod Liquid Crystals and Their Assembly on a Substrate,ADVANCED MATERIALS, Issue 5 2003L.-S. Li The macroscopic alignment and superlattice structures of CdSe nanorods in a nematic liquid-crystalline (LC) phase are determined by the phases that form prior to complete solvent evaporation (e.g., vortex structures in linear arrays, see Figure). By controlling the phase of the LC solution and its orientation using pretreated surfaces or external fields, it may be possible to achieve fine control of order in deposited nanorod films. [source] Time-dependent density functional theory for nonadiabatic processesISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2005Roi Baer Time-dependent density functional theory (TDDFT) is a general and robust method allowing the study of electron dynamics whether induced by nuclear motion or by external fields. We give a brief overview of the theory and some numerical methods together with recent applications stressing the generality and wide applicability of the method. We also discuss recent attempts to extend the present TDDFT by incorporating memory terms into the exchange correlation potentials. [source] | |||||||||||||||||||||||||||||||