深海海底山环境下声传播水平折射效应研究

声波在深海海底山环境中传播时,海底山会对声传播产生重要影响.2016年在南海深海进行了一次海底山环境下的声传播实验,观测到了由海底山引起的三维声传播效应,本文利用BELLHOP射线理论解释了海底山环境下的三维声传播机理.结果表明：声波在传播过程中与海底山作用后破坏了深海会聚区结构,导致传播损失增大,在海底山后形成具有明显边界的声水平折射区,利用二维声传播模型无法解释实验现象,海底山后声水平折射区实验测量的声场结构与N×2D模型计算结果存在明显差异,实验的传播损失比N×2D模型计算结果大10 dB.通过三维射线模型分析N×2D模型计算结果与实验结果存在明显差异产生的原因,发现由于声波水平折射作用,部分声线无法到达接收器,使得三维声传播效应对海底山后一定角度范围内声场影响较为明显.因此,深海海底山会引起明显的三维水平折射效应,应在水下目标探测和定位等应用中给予重视.     

Influence of gate engineering on the optical characteristics of a double gate FinFET

In this paper, the potential benefit of short channel triple material double gate (TM-DG) FinFET on the optical performance characteristics considering quantum mechanical effects has been theoretically examined and analyzed. The device characteristics are obtained from the self-consistent solution of 3D Poisson–Schrödinger equation using Leibmann's iteration method and provided the reasons for improved performance. The drain and transfer characteristics, electric field, transconductance and mobility of the device have been estimated and the results were compared with the device simulator results. The effect of different length ratios of three channel regions related to three different materials of TM-DG FinFET structure on the optical characteristics have also been discussed. The model is purely a physics based one and overcomes the major limitations of the existing 2D/3D analytical models by providing a more accurate result. The results obtained for dark and illuminated conditions are used to examine the performance of the device for its suitable use as a photodetector.     

The order parameter for the superconducting phases of UPt3

I review the principal theories that have been proposed for the superconducting phases of UPt₃. The detailed H-T phase diagram places constraints on any theory for the multiple superconducting phases. Much attention has been given to the Ginzberg-Landau region of the phase diagram where the phase boundaries of three phases appear to meet at a tetracritical point. It has been argued that the existence of a tetracritical point for all field orientations eliminates the two-dimensional (2D) orbital representations coupled to a symmetry-breaking field (SBF) as a viable theory of these phases and favours either a theory based on two primary order parameters belonging to different irreducible representations that are accidentally degenerate, as described by Chen and Garg 1993, or a spin-triplet, orbital one-dimensional representation with non spin-orbit coupling in the pairing channel, as described by Machida and Ozaki 1991. I comment on the limitations of the models proposed so far for the superconducting phases of UPt₃. I also find that a theory in which the order parameter belongs to an orbital 2D representation coupled to a SBF is a viable model for the phases of UPt₃, based on the existing body of experimental data. Specifically, I show that the existing phase diagram (including an apparent tetracritical point for all field orientations), the anisotropy of the upper critical field over the full temperature range, the correlation between superconductivity and basal plane antiferromagnetism and the low-temperature power laws in the transport and thermodynamic properties can be explained qualitatively, and in many respects quantitatively, by an odd-parity E_2u order parameter with a pair spin projection of zero along the ?c axis. The coupling of an antiferromagnetic moment to the superconducting order parameter acts as a SBF which is responsible for the apparent tetracritical point, in addition to the zero-field double transition. The new results presented here for the E_2u representation are based on an analysis of the material parameters calculated within the Bardeen-Cooper-Schrieffer theory for the 2D representations, and a refinement of the SBF model given by Hess et al. (1989). I also discuss possible experiments to test the symmetry of the order parameter.     

Differential model for 2D turbulence

We present a phenomenological model for 2D turbulence in which the energy spectrum obeys a nonlinear fourth-order differential equation. This equation respects the scaling properties of the original Navier-Stokes equations, and it has both the −5/3 inverse-cascade and the −3 direct-cascade spectra. In addition, our model has Raleigh-Jeans thermodynamic distributions as exact steady state solutions. We use the model to derive a relation between the direct-cascade and the inverse-cascade Kolmogorov constants, which is in good qualitative agreement with the laboratory and numerical experiments. We discuss a steady state solution where both the enstrophy and the energy cascades are present simultaneously, and we discuss it in the context of the Nastrom-Gage spectrum observed in atmospheric turbulence. We also consider the effect of the bottom friction on the cascade solutions and show that it leads to an additional decrease and finite-wavenumber cutoffs of the respective cascade spectra, which agrees with the existing experimental and numerical results. The text was submitted by the authors in English.     

Study of superstructure II in multiferroic BiMnO3

The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4×4×4 times as large as the distorted perovskite subcell. The [111] and [101] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional （3D） structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.     

Three-dimensional experimental spatial dynamics modelling of a reciprocating Freon compressor housing

Experimental spatial dynamics modelling encompasses the modelling, postprocessing, and visualization of 3D spatial dynamic response of structures as statistically-qualified complex-valued continuous vector fields derived from experimental structural dynamics testing. A weighted least-squares discrete finite element formulation has been developed to reconstruct the continuous 3D velocity response fields from experimental dynamics data. Dynamic 3D rotations, displacements, and accelerations were naturally derived from the full field velocity response model. Also, dynamic strain and stress fields across the shell elements were extracted by directly postprocessing the dynamic response. A Scanning Laser Doppler Vibrometer (SLDV) was used to measure a single frequency of the 3D dynamic response in an in situ test of an operating reciprocating Freon compression. The SLDV measured the velocity response at thousands of locations on the compressor housing from multiple, positionally-registered locations. The geometry from a preexisting finite element model provided the shape model of the compressor. An experimentally derived spatial dynamics model of the compressor housing was solved and postprocessed results were obtained.     

泡沫硅橡胶冲击压缩性实验研究

 采用锰铜计技术，通过测量冲击波压力获得材料雨贡纽数据的技术路线，给出了初始密度为0.92 g/cm³的泡沫硅橡胶在6~33 GPa范围内的雨贡纽关系，精度优于国内外相关工作。对本实验锰铜计的典型信号作了较为详细的分析，通过数值模拟很好地重现了该非常规信号。此外，采用先前Wu等建立的疏松材料雨贡纽模型进行了预估计算，预估结果与实验结果符合很好，表明该模型不但适用于金属、岩石矿物等，亦可广泛应用于高聚物疏松材料的冲击压缩性研究。     

Fully three-dimensional accurate modeling of scattering loss in optical waveguides

Scattering loss in high-index-contrast optical waveguides has been modeled by a rigorous 3D numerical algorithm based on volume current method. The electromagnetic field generated by the wire current distribution simulating sidewalls roughness has been calculated by 3D finite element method. The developed modeling technique does not introduce any approximation in radiated power estimation. Numerical results obtained by our model have been compared with some experimental results reported in literature for four typical sub-micrometer high-index-contrast waveguides realized by different technologies and a very good agreement (relative error less than 3%) has been demonstrated. Closed-form expressions for scattering loss in low-index-contrast waveguides have been also derived and discussed. Developed modeling technique has been compared with other three-dimensional algorithms for scattering loss estimation and its advantages in terms of accuracy, computation time and generality have been pointed out. Scattering loss dependence on the parameters of the roughness distribution has been finally discussed.     

Memorino on the ‘1/2 versus 3/2 puzzle’ in B̄→lν̄X<Subscript>c</Subscript> – a year later and a bit wiser

The OPE treatment that has been so successful in describing inclusive B̄→lν̄X_c decays yields sum rules (in particular the Uraltsev sum rule and its higher moments) implying the dominance of the P wave j_q=3/2 charm states in X_c over their j_q=1/2 counterparts. This prediction is supported by other general arguments as well as quark model calculations, which illustrate the OPE results, and by preliminary lattice findings. Its failure would indicate a significant limitation in our theoretical understanding of B̄→lν̄X_c. Some experimental issues have been clarified since a preliminary version of this note had appeared; yet, the verdict on the composition of the final states beyond D, D^* and the two narrow j_q=3/2 resonances remains unsettled. Establishing which hadronic configurations – D/D^*+π,D/D^*+2π,... – contribute, what their quantum numbers are, and their mass distributions will require considerable experimental effort. We explain the theoretical issues involved and why a better understanding of them will be of considerable value. Having significant contributions from a mass continuum distribution below 2.5 GeV raises serious theoretical questions for which we have no good answer. Two lists are given, one with measurements that need to be done and one with items of theoretical homework. Some of the latter can be done by employing existing theoretical tools, whereas others need new ideas.     

Experiment and Lattice Boltzmann numerical study on nanofluids flow in a micromodel as porous medium

Al₂O₃ nanofluids flow has been studied in etched glass micromodel which is idealization of porous media by using a pseudo 2D Lattice Boltzmann Method (LBM). The predictions were compared with experimental results. Pressure drop / flow rate relations have been measured for pure water and Al₂O₃ nanofluids. Because the size of Al₂O₃ nanoparticles is tiny enough to permit through the pore throats of the micromodel, blockage does not occur and the permeability is independent of the nanofluid volume fraction. Therefore, the nanofluid behaves as a single phase fluid, and a single phase LBM is able to simulate the results of this experiment. Although the flow in micromodels is 3D, we showed that 2D LBM can be used provided an effective viscous drag force, representing the effect of the third dimension, is considered. Good qualitative and quantitative agreement is seen between the numerical and experimental results.     

A relaxation times coupling method to construct acoustic relaxation calibration for two-frequency measuring gas compositions

In our previous work (Hu et al., 2014), a method has been proposed to detect gas compositions by locating the acoustic spectral peaks, which can be detected only by two-frequency acoustic measurements in practice. However, as a ‘Detection Calibration’, the effective relaxation area (ERA) constructed by existing theoretical model cannot match the two-frequency measurements when there are more than one strong relaxational components in gas mixtures. This paper proposes a method to construct the ERA by coupling the decoupled single relaxation times together to a whole relaxation time. For gas mixtures with only one single relaxation process, the predicted ERA results match with the experimental data better than those predicted by the existing model. Moreover, for gas mixtures in which more than one relaxation process are significant, the ERA results predicted by the proposed method also match with the detection results of two-frequency measurements better than the existing model. This relaxation time coupling based ERA constructing method is validated by the application in low-quality natural gas detection.     

Modelling of Photonic Wire Bragg Gratings

Some important properties of photonic wire Bragg grating structures have been investigated. The design, obtained as a generalisation of the full-width gap grating, has been modelled using 3D finite-difference time-domain simulations. Different types of stop-band have been observed. The impact of the grating geometry on the lowest order (longest wavelength) stop-band has been investigated – and has identified deeply indented configurations where reduction of the stop-bandwidth and of the reflectivity occurred. Our computational results have been substantially validated by an experimental demonstration of the fundamental stop-band of photonic wire Bragg gratings fabricated on silicon-on-insulator material. The accuracy of two distinct 2D computational models based on the effective index method has also been studied – because of their inherently much greater rapidity and consequent utility for approximate initial designs. A 2D plan-view model has been found to reproduce a large part of the essential features of the spectral response of full 3D models.     

Localized electron states and magnetic properties at the interface of a two-dimensional graphene/MnO(001) system

The results of a density functional theory study of the band structure of two-dimensional (2D) graphene/MnO(001), new materials for spintronics, with an antiferromagnetic type of ordering are presented. The regularities of the change of the valence band electron structure in the 3D MnO → 2D MnO → 2D graphene/MnO(001) series have been studied in a comparison with X-ray photoelectron spectra. The stability of the system has been established, and the energy of chemical binding has been determined using the calculation of the structural energy of 2D graphene/MnO(001). The features of the spin state in the valence band—in particular, at the Fermi level—as well as interatomic interaction in 2D graphene/MnO(001) have been discussed in comparison with 2D and 3D MnO systems with antiferromagnetic ordering. The magnetic moment of the Mn atom in all considered systems has been estimated and compared with the experimental one. The effect of the spin polarization for the oxygen and carbon atoms has been detected. The nature of this effect has been considered.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

Heterogeneous dynamics at the glass transition in van der Waals liquids, in the bulk and in thin films

It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous dynamics close to T _g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T _g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T _g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation. Received 21 March 2000 and Received in final form 4 December 2000     

Magnetic relaxation of interacting co clusters: crossover from two- to three-dimensional lattices

The influence that dipole-dipole interactions exert on the dynamics of the magnetization of nanometer-sized Co clusters has been studied by means of ac and dc susceptibility experiments. These clusters grow in a quasiordered layered structure, where all relevant parameters can be tailored and measured independently. Our data show without ambiguity that the magnetic relaxation becomes slower as the degree of interaction increases. The effective activation energy increases linearly with the number of nearest neighbor clusters, evolving from the value for a 2D layer to the fully 3D behavior, which is nearly reached for five layers. The experimental results agree quantitatively with the predictions of a simple model.     

3D multi-directional sensor with pyramid mirror and structured light

Structured-light-based 3D multi-directional sensors are widely used due to their flexible field of view (FOV), which is a significant benefit. Nevertheless, existing 3D multi-directional sensors based on linear lasers are only capable of measuring a slice of a 3D scene at low resolution. In addition, other 3D multi-directional sensors are capable of measuring 3D scenes by shooting 2D structured light patterns in different directions through curved mirrors. However, the projected and captured structured light patterns are blurred due to the optical aberration property of curved mirrors, resulting in inaccurate 3D reconstruction. This paper proposes a 3D, high-resolution, high-accuracy, real-time multi-directional sensor that utilizes pyramid mirrors to decompose the FOVs into different directions and reduce the optical aberration phenomenon. The mathematical model of the 3D sensor is presented, and the FOV is analyzed. A dual-frequency phase-shifting fringe pattern is used for 3D reconstruction in real time. Moreover, the sensor is calibrated using a planar circle calibration gauge and the Householder reflection constraint. Finally, the experimental results demonstrate that the measurement error of the 3D multi-directional sensor is less than 1 mm and 0.03 rad, thus verifying the method's feasibility.     

Properties of Proton in Diquark-Quark Model

The properties of the proton has been investigated considering a proton as diquark-quark system. A model for diquark has been suggested in an analogy with the quasi-particle in a crystal lattice. The mass of the diquark obtained in the present model has been found to be in good agreement with other theoretical predictions. The binding energy of proton, compressibility and the excitation energy for the Roper Resonance have been estimated in the context of the proposed model. The results are found to be in agreement with the existing theoretical and experimental findings.     

Vibration-inversion-rotation spectra of ammonia: A vibration-inversion-rotation Hamiltonian for NH2D and ND2H

The model Hamiltonian developed previously for ammonia NH₃ has been used to study the vibration-inversion-rotation energy levels of the isotopic species of ammonia NH₂D and ND₂H. In this model the inversion motion is removed from the vibrational problem by allowing the molecular reference configuration to be a function of the large amplitude motion coordinate.The ground state inversion-rotation energy levels of NH₂D and ND₂H have been calculated with the use of the zeroth-order inversion-rotation Hamiltonian, and the calculated transition frequencies have been compared with the experimental data.