Showing papers in "International Journal of Modern Physics B in 2007"
TL;DR: In this article, the authors consider the relationship between the tight-binding Hamiltonian of the two-dimensional honeycomb lattice of carbon atoms with nearest neighbor hopping only and the 2 + 1 dimensional Hamiltonians of quantum electrodynamics, which follows in the continuum limit.
Abstract: We consider the relationship between the tight-binding Hamiltonian of the two-dimensional honeycomb lattice of carbon atoms with nearest neighbor hopping only and the 2 + 1 dimensional Hamiltonian of quantum electrodynamics, which follows in the continuum limit. We pay particular attention to the symmetries of the free Dirac fermions including spatial inversion, time reversal, charge conjugation and chirality. We illustrate the power of such a mapping by considering the effect of the possible symmetry breaking, which corresponds to the creation of a finite Dirac mass, on various optical properties. In particular, we consider the diagonal AC conductivity with emphasis on how the finite Dirac mass might manifest itself in experiment. The optical sum rules for the diagonal and Hall conductivities are discussed.
310 citations
TL;DR: In this article, the viscoelastic properties of silicone-based magnetorheological elastomer matrix composites have been investigated in terms of their storage and loss moduli.
Abstract: Magnetorheological (MR) elastomers are composite materials consisting of magnetic particles in elastomer matrices, whose mechanical properties can be influenced by applying a magnetic field. Main parameters which determine the behavior of these smart materials are the concentration of the magnetic particles and the mechanical stiffness of the elastomer matrix. The viscoelastic properties of silicone-based MR elastomers are outlined in terms of their storage and loss moduli. The mechanical behavior of the material is also influenced by a magnetic field during the curing of the elastomer matrix, which leads to materials with anisotropic microstructures. The storage modulus of soft elastomer matrix composites can be increased in the presence of a magnetic field by significantly more than one order of magnitude or several hundreds of kPa. The relative increase exceeds that of all previously reported data. A shape memory effect, i. e. the deformation of an MR elastomer in a magnetic field and its return to original shape on cessasion of the magnetic field, is described.
116 citations
TL;DR: In this article, the rheological properties and dispersion stability of MR fluids as a function of particle shape were investigated by comparing fluids made with uniform nickel spheres to those employing nickel spheres.
Abstract: We present studies of the rheological properties and dispersion stability of MR fluids as a function of particle shape by comparing fluids made with uniform nickel spheres to those employing nickel...
77 citations
TL;DR: In this paper, the influence of the surface treatment of the magnetic particle and the kind of fumed silica on the formulation of some magnetorheological suspensions (MRS) was evaluated.
Abstract: Two types of carbonyl iron powders, (CIP's, BASF AG), the HS and HS-I (I = insulated, due a coating with phosphate), and two kinds of silica, one hydrophobic (Cab-O-Sil® TS610) and other hydrophilic (Cab-O-Sil® M5), were used to evaluate the influence of the surface treatment of the magnetic particle and the kind of fumed silica on the formulation of some magnetorheological suspensions (MRS). Oscillatory measurements at no field showed an evident difference between the silicas, but not a specific interaction with the phosphate coating on HSI. On the other hand, steady flow experiments also without magnetic field showed that the kind of silica and its specific interactions with the coating on iron powder drove the rheological behavior of the MRS on all region of the shear rate. Under magnetic field, the flow curves differences will be due to the iron particles and its magnetic properties, mainly on the region of higher shear rate.
66 citations
TL;DR: The aim of this review is to provide better understanding of a few approaches that have been proposed for treating nonequilibrium (time-dependent) processes in statistical mechanics with the emphasis on the inter-relation between theories.
Abstract: The aim of this paper is to provide better understanding of a few approaches that have been proposed for treating nonequilibrium (time-dependent) processes in statistical mechanics with the emphasis on the interrelation between theories. The ensemble method, as it was formulated by Gibbs, has great generality and broad applicability to equilibrium statistical mechanics. Different macroscopic environmental constraints lead to different types of ensembles, with particular statistical characteristics. In the present work, the statistical theory of nonequilibrium processes which is based on nonequilibrium ensemble formalism is discussed. We also outline the reasoning leading to some other useful approaches to the description of the irreversible processes. The kinetic approach to dynamic many-body problems, which is important from the point of view of the fundamental theory of irreversibility, is alluded to. Appropriate references are made to papers dealing with similar problems arising in other fields. The em...
58 citations
TL;DR: In this paper, two kinds of magnetorheological elastomers (MREs) are used for adaptive tuned vibration absorbers, which will serve for vibration absorption of vehicles.
Abstract: This paper presents two kinds of magnetorheological elastomers (MREs). One is composed of appropriate silicon rubber, carbonyl iron particles and some other materials. It is cured under a strong magnetic field at a room temperature. Its shear modulus change from 0.34MPa at zero magnetic field to 3.34MPa at 1T magnetic field, the relative MR effect reaches 878%. Such high MR effect has not been reported until now. The other is composed by appropriate natural rubber, carbonyl iron particles and some other materials. After the compositions are mixed in a two-roll mill, they are cured under a strong magnetic field according to a temperature profile. The increment of its modulus reaches 3.6MPa, and the relative modulus increment is 133%. Their mechanical properties are also evaluated. All observed results show that the fabricated MREs are utilizable. They have successfully been utilized to adaptive tuned vibration absorbers, which will serve for vibration absorption of vehicles.
56 citations
TL;DR: In this paper, the authors introduce a general analysis method based on the use of a resonant tunneling phenomenon, admitting strong electron correlation in a quantum dot with degenerated states, which allows them to simulate the operation of high-performance molecular nano-devices and to design the expected function of a wide range of devices in nano-scale size.
Abstract: We introduce a general analysis method, which allows us to simulate the operation of high-performance molecular nano-devices and to design the expected function of a wide range of devices in nano-scale size The method is based on the use of a resonant tunneling phenomenon, admitting strong electron correlation in a quantum dot with degenerated states Three examples of the application of this method are given: Coulomb repulsion, uncorrelated resonant tunneling, and electron-phonon interaction It is shown that there is a good agreement with experimental data in all three cases
54 citations
TL;DR: In this article, a 3D thermal lattice Boltzmann model is proposed to simulate 3D incompressible thermal flow problem, which is based on the double-distribution function approach.
Abstract: In this paper, a three-dimensional (3D) thermal lattice Boltzmann model is proposed to simulate 3D incompressible thermal flow problem. Our model is based on the double-distribution function approach. We found that a new and simple lattice type of eight-velocity model for the internal energy density distribution function can be developed, where the viscous and compressive heating effects are negligible. Numerical results of 3D natural convection flow in a cubic cavity are presented.
46 citations
TL;DR: In this article, the electrical resistivity under pressure for an antiferromagnet CeCoGe3 without inversion symmetry in the tetragonal crystal structure was measured, and it was shown that superconductivity appears above 4.3 GPa, with a superconduting transition temperature Tsc = 0.72 K and a large upper critical field Hc2(0) = 7 T at 5.6 GPa.
Abstract: We measured the electrical resistivity under pressure for an antiferromagnet CeCoGe3 without inversion symmetry in the tetragonal crystal structure. The Neel temperature TN1 = 21 K at ambient pressure decreases monotonically with increasing pressure, and becomes zero at about 5.5 GPa. Superconductivity appears above 4.3 GPa, with a superconduting transition temperature Tsc = 0.72 K and a large upper critical field Hc2(0) = 7 T at 5.6 GPa. The large upper critical field Hc2(0)= 7 T exceeds the Pauli limitting field Hp (≃ 1.86Tsc)=1.3 T as in CePt3Si, CeRhSi3 and CeIrSi3. The large slope of Hc2 at Tsc, -dHc2/dT = 18T/K, at 5.6 GPa indicates the heavy-fermion superconductivity in CeCoGe3.
37 citations
TL;DR: In this article, the dielectric properties of three different material systems such as spherical-monodisperse polymer microspheres (PAPMMA) consisting of a poly(methyl methacrylate) (PMMA) core and a polyaniline (PANI) shell, single-doped and mesoporousdoped TiO2 system, and copper phthalocyanine-decomposition-based suspensions based ER fluid were analyzed via dielectrics spectra of permittivity and loss factor as a function of the frequency.
Abstract: Along with rheological properties, dielectric spectra of the ER fluids were found to provide additional information on both analyzing their electrical polarization properties and interpreting their flow behavior. Dielectric properties of three different material systems such as spherical-monodisperse polymer microspheres (PAPMMA) consisting of a poly(methyl methacrylate) (PMMA) core and a polyaniline (PANI) shell, single-doped and mesoporous-doped TiO2 system and copper phthalocyanine-doped mesoporous TiO2 suspensions based ER fluid were analyzed via dielectric spectra of permittivity and loss factor as a function of the frequency, and Cole-Cole plots. Polarizability which is defined as a difference of dielectric constant at both zero frequency and infinite frequency was found to be a proper parameter to understand a better ER fluid. Using the Cole-Cole plot, we were not only able to fit the dielectric spectra, but also to deduce the achievable polarizability by explaining the higher ER performance of the ER fluids.
33 citations
TL;DR: In this article, a magnetic field dependent yield stress in ferrofluids has been investigated and a special stress controlled rheometer for ferro fluids has been designed, which shows a dependence of the yield stress on magnetic field strength for different kind of ferro fluid and magnetorheological fluids.
Abstract: Recent experimental as well as theoretical investigations have shown that the formation of structures of magnetic nanoparticles has significant influence on the behaviour of ferrofluids The dependence of this structure formation on the magnetic field strength and shear stress applied to the fluid leads to strong changes of the viscosity and to the appearance of viscoelastic effects in the fluids The actual approaches for a description of the effects vary in the basic modeling of the fluid and its behaviour Some models base on microscopic assumptions, other model the fluid on a mesoscale and even macroscopic descriptions abstaining from microscopic assumptions have been suggested A point in which the predictions of the models differ is the question of an appearance of a magnetic field dependent yield stress in ferrofluids For investigations concerning the appearance and field dependence of a yield stress a special stress controlled rheometer for ferrofluids has been designed The preliminary results presented here, show a dependence of the yield stress on magnetic field strength for different kind of ferrofluids and magnetorheological fluids
TL;DR: The development of target characterization in time-reversal, with an emphasis on extracting information from small targets, is reviewed, and how the symmetry of the target is reflected in the properties of the singular value spectrum is shown.
Abstract: Over the last 15 years, there has been rapid growth in applications of time-reversal symmetry of wave propagation to enhance communications and imaging through highly scattering media. These techniques exploit both temporal and spatial reciprocity to mitigate signal distortion created from the large number of independent propagation paths between a transmitter and receiver. The time-reversal process is often described by the time-reversal operator (TRO), or equivalently by the multistatic response matrix (MRM), defined by the transmit and receive system. A singular value decomposition of this operator (or MRM) is the starting point for many of the time-reversal imaging techniques. In addition to imaging, this decomposition can also be used to extract information about objects embedded within the propagation medium, i.e., target characterization. In this paper, we review the development of target characterization in time-reversal, with an emphasis on extracting information from small targets. We will analyze the MRM for both acoustic and electromagnetic scattering and show how the symmetry of the target is reflected in the properties of the singular value spectrum. Finally, we discuss several open problems and potential applications.
TL;DR: In this paper, a number of recent interference experiments involving multiple photons are reviewed, including generalized photon bunching effects, generalized Hong-Ou-Mandel interference effects and multi-photon interferometry for demonstrations of multiphoton de Broglie wavelength.
Abstract: A number of recent interference experiments involving multiple photons are reviewed. These experiments include generalized photon bunching effects, generalized Hong-Ou-Mandel interference effects and multi-photon interferometry for demonstrations of multi-photon de Broglie wavelength. The multi-photon states used in these experiments are from two pairs of photons in parametric down-conversion. We find that the size of the interference effect in these experiments, characterized by the visibility of the interference pattern, is governed by the degree of distinguishability among different pairs of photons. Based on this discovery, we generalize the concept of multi-photon temporal distinguishability and relate it to a number of multi-photon interference effects. Finally, we make an attempt to interpret the coherence theory by multi-photon interference via the concept of temporal distinguishability of photons.
TL;DR: In this article, a model is proposed to represent the time response of the fluid to the application of the magnetic field, and the experimental data and the proposed model are used to identify the response time of fluid for each field strength.
Abstract: Magnetorheological fluids are known to respond in a matter of milliseconds to the application of a magnetic field. To date, however, very little work has been done to study the time dependence of the MR response. The purpose of this study is to investigate the response time of the fluid. Experiments were conducted on a high shear rate rheometer capable of fluid speeds in excess of 35 m/s. With an MR valve length of 6.35 mm, the resulting dwell times were as low as 0.18 ms. For each of three magnetic field strengths, a reduction in yield stress is observed as dwell time decreases. A model is proposed to represent the time response of the fluid to the application of the magnetic field. The experimental data and the proposed model are used to identify the response time of the fluid for each field strength. Results indicate that as the magnetic field increases, the response time of the MR fluid decreases. For the range of magnetic field strengths considered in this study the response time of the fluid ranged from 0.24 ms to 0.19 ms.
TL;DR: The notion of representative statistical ensembles, correctly representing statistical systems, is strictly formulated in this article, which allows for a proper description of statistical systems and avoids inconsistencies in theory.
Abstract: The notion of representative statistical ensembles, correctly representing statistical systems, is strictly formulated. This notion allows for a proper description of statistical systems, avoiding inconsistencies in theory. As an illustration, a Bose-condensed system is considered. It is shown that a self-consistent treatment of the latter, using a representative ensemble, always yields a conserving and gapless theory.
TL;DR: In this paper, the authors reviewed the recent developments of the phase string theory for doped antiferromagnets and presented the selfconsistent and systematic consequences of these phases, as well as a series of anomalous physical properties.
Abstract: The recent developments of the phase string theory for doped antiferromagnets will be briefly reviewed. Such theory is built upon a singular phase string effect induced by the motion of holes in a doped antiferromagnet, which as a precise property of the t-J model dictates the novel competition between the charge and spin degrees of freedom. A global phase diagram including the antiferromagnetic, superconducting, lower and upper pseudogap, and high-temperature "normal" phases, as well as a series of anomalous physical properties of these phases will be presented as the self-consistent and systematic consequences of the phase string theory.
TL;DR: In this paper, a superconducting open cavity was used to detect high-frequency gravitational waves (HFGWs) in GHz band, which is based upon coupling between superconducted open cavity and electromagnetic fields stored in the cavity.
Abstract: We present a detecting scheme of high-frequency gravitational waves (HFGWs) which is based upon coupling between superconducting open cavity and electromagnetic fields stored in the cavity. Utilizing zero resistance and perfect diamagnetism of the superconductors, one can obtain very large quality factor and high sensitivity for the cavity to detect the HFGWs in GHz band. In addition, we review other possible superconducting systems for detection of the HFGWs, such as superconducting resonant-mass detector, toroidal waveguide, coupled superconducting spherical cavities and superconducting quantum antennas.
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TL;DR: In this paper, a study of polyaromatic hydrocarbons by semi-empirical PM3 and ab initio methods in MINI and STO 6G-31 bases has been performed for compounds with different numbers of rings.
Abstract: A study of polyaromatic hydrocarbons by semiempirical PM3 and ab initio methods in MINI and STO 6G-31 bases has been performed for compounds with different numbers of rings. The optimized space and electronic structures have been derived. The multiplicity states effect on the energetic stability of the polyaromatic hydrocarbons is examined. It is shown that the high multiplicity states become more energetically preferable with the growth of the PAH size.
TL;DR: In this paper, the authors consider a graphene sheet folded in an arbitrary geometry, compact or with nanotube-like open boundaries, and derive an index theorem that relates the zero energy modes of the graphene sheet with the topology of the lattice.
Abstract: We consider a graphene sheet folded in an arbitrary geometry, compact or with nanotube-like open boundaries. In the continuous limit, the Hamiltonian takes the form of the Dirac operator, which provides a good description of the low energy spectrum of the lattice system. We derive an index theorem that relates the zero energy modes of the graphene sheet with the topology of the lattice. The result coincides with analytical and numerical studies for the known cases of fullerene molecules and carbon nanotubes, and it extends to more complicated molecules. Potential applications to topological quantum computation are discussed.
TL;DR: In this paper, a model is proposed based on the interaction of polar molecule-charge in between the particles, where the local electric field is much higher than the external one and can cause the polar molecules aligning.
Abstract: The static and dynamic shear stress of newly developed electrorheological (ER) fluids can reach more than 100 kPa and over 60 kPa at 3 kV/mm, respectively. The high yield stress of those ER fluids and its near linear dependence on the electric field are different from the conventional ER fluids and can not be explained with traditional dielectric theory. Experiment demonstrates that the polar molecules adsorbed on the particles play crucial role in those ER fluids, which can be named as polar molecule type electrorheological (PM-ER) fluids. To explain PM-ER effect a model is proposed based on the interaction of polar molecule-charge in between the particles, where the local electric field is much higher than the external one and can cause the polar molecules aligning. The main effective factors for achieving high-performance PM-ER fluids are discussed.
TL;DR: In this paper, a new methodology for producing magnetorheological elastomers using vacuum assisted resin transfer molding (VARTM) was investigated, which was used with a range of iron particles sizes and silicon elastomer systems and found to be effective within certain limits of applicability.
Abstract: Magnetorheological elastomers (MREs) consist of ferromagnetic particles embedded in a compliant matrix (i.e. elastomer). Due to the magnetic interaction of the ferromagnetic particles, MREs exhibit field dependent physical properties. Very significant changes in the modulus and loss factor of the elastomer can be realized. This makes MREs a promising candidate for active vibration control mechanisms. One factor currently limiting the implementation of this technology is the lack of an efficient manufacturing method that is practical for mass production. Most of the specimens created for previous MRE research were made using simple casting or mechanical mixing methods that are not ideal. In this research a new methodology for producing MREs using Vacuum Assisted Resin Transfer Molding (VARTM) was investigated. The method was used with a range of iron particles sizes and silicon elastomer systems and found to be effective within certain limits of applicability. The specimens produced were tested in compression under a range of magnetic fields to validate the presence of the MR effect. Relative changes in compressive modulus ranging from 35% to 150% (depending on volume fraction), under fields of around 0.3T were observed.
TL;DR: In this paper, the capacitance between any two arbitrary lattice sites in an infinite square lattice is studied when one bond is removed (i.e. perturbed), and a connection is made between capacitance and the lattice Green's function of the perturbed network, where they are expressed in terms of those of the perfect network.
Abstract: The capacitance between any two arbitrary lattice sites in an infinite square lattice is studied when one bond is removed (i.e. perturbed). A connection is made between the capacitance and the lattice Green's function of the perturbed network, where they are expressed in terms of those of the perfect network. The asymptotic behavior of the perturbed capacitance is investigated as the separation between the two sites goes to infinity. Finally, numerical results are obtained along different directions and a comparison is made with the perfect capacitances.
TL;DR: In this paper, the authors summarize the screening theory of the integer quantized Hall effect and emphasize its two key mechanisms: first, the existence, in certain magnetic field intervals, of incompressible strips, with integer values of the local filling factor and quantized values of longitudinal and Hall resistivity, and second, the confinement of an imposed dissipative current to these strips, leading to the quantization of the global resistances.
Abstract: We summarize the screening theory of the integer quantized Hall effect (IQHE) and emphasize its two key mechanisms: first, the existence, in certain magnetic field intervals, of incompressible strips, with integer values of the local filling factor and quantized values of longitudinal and Hall resistivity, and second, the confinement of an imposed dissipative current to these strips, leading to the quantization of the global resistances. We demonstrate that, without any localization assumption, this theory explains the enormous experimental reproducibility of the quantized resistance values, as well as experimental results on the potential distribution in narrow Hall bars. We further demonstrate that inclusion of long-range potential fluctuations allows to apply the theory to wider Hall bars, and can lead to a broadening of the quantum Hall plateaus, whereas short-range disorder tends to narrow the plateaus.
TL;DR: In this paper, a critical wave vector km is identified, which depends on one effective nonlinearity parameter, and q-breathers minimize the localization length at k 0 = km and completely delocalize in the limit k 0 → 0, π.
Abstract: Recently q-breathers - time-periodic solutions which localize in the space of normal modes and maximize the energy density for some mode vector q0 - were obtained for finite nonlinear lattices. We scale these solutions to arbitrarily large lattices in various lattice dimensions. We study the scaling consequence for previously obtained analytical estimates of the localization length of q-breathers for β-FPU and α-FPU lattices. The first finding is that the degree of localization depends only on intensive quantities and is size independent. Secondly, a critical wave vector km is identified, which depends on one effective nonlinearity parameter, q-breathers minimize the localization length at k0 = km and completely delocalize in the limit k0 → 0, π.
TL;DR: In this article, a three level atom in interaction with a two-mode quantized electromagnetic field, initially prepared in an entangled twomode coherent state, is considered, and the exact solution of the wave function in the Schrodinger picture is obtained.
Abstract: In this contribution, a three level atom in interaction with a two-mode quantized electromagnetic field, initially prepared in an entangled two-mode coherent state, is considered. Through the elimination of an intermediate level using the adiabatic elimination method, a nonlinear Stark shift is introduced. The exact solution of the wave function in the Schrodinger picture is obtained. Some statistical aspects through the effective two-level atom interacting with the two-mode and multiphotons processess with the nonlinear Stark shift are presented. The results are employed to perform a careful investigation of the temporal evolution of the atomic inversion, entropy squeezing and variance squeezing. It has been shown that the system is sensitive to any change in the parameter representation of the Stark shift. General conclusions reached are illustrated by numerical results.
TL;DR: In this paper, a photo-cathode rf gun with a solenoid magnet was used to enhance the X-ray yeild and to increase electron beam charge up to 5 nC/bunch and to make multibunch beam.
Abstract: Compact hard X-ray source via laser Compton sattering has been developed in SHI and AIST. Our system has the injector and the linac and the high power laser system. The injector has a photo-cathode rf gun with a solenoid magnet. To enhance the X-ray yeild, we are planning to increase electron beam charge up to 5 nC/bunch and to make multi-bunch beam. The beam tracking simulation in the injector have been performed by changing laser spot size, laser pulse width, rf phase and solenoid field to optimize the distance between the injector and the linac for 5 nC/bunch high charge beam. In addition, high charge multi-bunch beam simulation in rf-gun cavity have been carried out to investigate the influence by the beam loading and the wake field.
TL;DR: In this article, the authors explored the physical mechanism for the viscosity reduction method in liquid suspension by pulsed electric or magnetic field and showed that the maximum volume fraction to be available for the suspended particles in the suspension increases with the particle size and the polydispersity in particle size distribution.
Abstract: Reducing the viscosity of liquid suspensions is vital in science and engineering. This paper explores the physical mechanism for the viscosity reduction method in liquid suspension by pulsed electric or magnetic field. The key is that the maximum volume fraction to be available for the suspended particles in the suspension increases with the particle size and the polydispersity in the particle size distribution. Positive experimental results with various liquid suspensions indicate that this method, developed from the basic mechanism of viscosity, is universal and powerful for all liquid suspensions with broad applications.
TL;DR: By connecting two dissimilar anharmonic lattices exemplified by Fermi-Pasta-Ulam (FPU) model and Frenkel-kontorova (FK) model, the authors successfully build up one dimensional thermal diode.
Abstract: By connecting two dissimilar anharmonic lattices exemplified by Fermi-Pasta-Ulam (FPU) model and Frenkel-kontorova (FK) model, we successfully build up one dimensional thermal diode. We find the rectifying effect is closely related to asymmetric interface thermal resistance (Kapitza resistance). And the asymmetric thermal resistance depends on how the temperature gradient is applied. Moreover, a qualitative relationship between the thermal rectification and the phonon spectra is proposed.
TL;DR: In this article, a model inspired by quantum dots is proposed, where a short-range interaction is added to a harmonic confinement, and the level rearrangement phenomenon occurs when an attractive long range potential is perturbed by a short range attractive potential as its strength is increased.
Abstract: A presentation and a generalization are given of the phenomenon of level rearrangement. This occurs when an attractive long-range potential is perturbed by a short-range attractive potential as its strength is increased. This phenomenon was first discovered in condensed matter physics and has also been studied in the physics of exotic atoms. A similar phenomenon occurs in a model that we propose, inspired by quantum dots, where a short-range interaction is added to a harmonic confinement.