Experiments to study the confinement of a target plasma in a magnetic trap with inverse plugs and circular multipole walls

In order to neutralize beams of high-energy negative ions, it is convenient to use a plasma target. It is necessary to confine a target plasma within a magnetic trap. It is of importance to restrict the escape of a plasma from the inlet and outlet holes in the target. It is proposed to confine a target plasma in a magnetic trap with a weak longitudinal field with circular multipole walls and with inverse plugs (with an inverse field). Experiments in which a plasma is confined in an axisymmetric trap of this type with one double inverse plug, which restricts longitudinal plasma outflow, are described. A cathode pellet emitting accelerated electrons for plasma production by gas ionization is installed at the opposite end face of the trap on the axis. The experiment shows that inverse plugs suppress strongly the plasma outflow into the end-face hole. The mechanism of this suppression is revealed. It is found that electrons are confined within a trap predominantly by magnetic fields.     

Evolution of Classical and Quantum States in the Groupoid Picture of Quantum Mechanics

The evolution of states of the composition of classical and quantum systems in the groupoid formalism for physical theories introduced recently is discussed. It is shown that the notion of a classical system, in the sense of Birkhoff and von Neumann, is equivalent, in the case of systems with a countable number of outputs, to a totally disconnected groupoid with Abelian von Neumann algebra. The impossibility of evolving a separable state of a composite system made up of a classical and a quantum one into an entangled state by means of a unitary evolution is proven in accordance with Raggio’s theorem, which is extended to include a new family of separable states corresponding to the composition of a system with a totally disconnected space of outcomes and a quantum one.     

一种新型的水下低频共鸣器*

该文旨在宽开口的共鸣腔内嵌入聚氨酯泡沫来设计一种新型的水下低频共鸣器。首先通过水池实验测定聚氨酯泡沫板的声速。然后基于此建立镶嵌聚氨酯泡沫共鸣器的理论模型获得声阻抗率,通过与直口结构以及棒纵振动模型对比,验证理论模型的正确性,并建立集中参数系统,分析内嵌聚氨酯泡沫能够降低共鸣器共振频率的原因。最后通过有限元仿真软件进行计算,检验理论模型的正确性,与无聚氨酯泡沫镶嵌的共鸣器相比,镶嵌聚氨酯泡沫的共鸣器在维持较低品质因素的同时实现了共振频率大幅降低。     

High-frequency resonant blockade in one-dimensional quantum pump with oscillating potential wells

The conductance and the stationary current are studied in a one-dimensional quantum wire with a harmonically oscillating delta-potential barrier or well. It is shown that, in the structure with a single well, the conductance vanishes at certain parameters. This phenomenon is associated with the occurrence of quasi-energy states corresponding to the total and elastic reflection of particles from the well. The stationary photovoltaic current under an alternating field in a double-well structure is considered. It is shown that the derivative of the photovoltaic current with respect to the Fermi energy vanishes under the same conditions. The results for a system with a single well are generalized to the case of a one-dimensional lattice in the tight binding model with an oscillating level of one of its sites. It is shown that the problem of particle scattering by a three-dimensional short-range center with an oscillating potential is reduced to the corresponding one-dimensional problem.     

A simple method to simulate diffraction and speckle patterns with a PC

A simple, intuitive and pedagogical method is proposed in order to simulate the phenomenon of light diffraction in simple cases. A diffracting plane obstacle is simulated by means of a model with a variable transmittance from one point to another. A numerical matrix is built with transmittance values at those points taken as samples. The matrix is handled with the Matlab program, and the Fraunhofer approximation is used. The method is applied to variable module and constant phase transmittance obstacles in single slit, double slit, square window and round window cases. The method is also applied to an obstacle with a constant reflectance module and random variable phase with Gaussian statistics, which gives rise to speckle phenomenon.     

Features of electron-phonon interaction in nanotubes with chiral symmetry placed in a magnetic field

The interaction of electrons with acoustic phonons is considered in a nanotube with chiral symmetry placed in a magnetic field parallel to the nanotube axis. It is shown that in such a system, the electronic energy spectrum is not invariant under electron wavevector reversal and, therefore, the electron-phonon interaction is different for identical phonons with oppositely directed wavevectors. This phenomenon leads to the occurrence of an electromotive force during spatially homogeneous heating of an electron gas and to the presence of a term quadratic in current in the current-voltage characteristic of a nanotube.     

The effect of flow on the piston problem of acoustics

A compressible fluid, bounded on one side by an infinite plane, flows with constant subsonic speed U parallel to the plane, and acoustic disturbances are caused by a small amplitude vibration of a circular piston set in the plane. The effect of the mean flow on this classical radiation problem is investigated and the distant field is expressed in elementary form. For the compact piston, whose radius is small compared with a wavelength, it is confirmed (in agreement with earlier work) that the distant field is not simply that of a point source with strength equal to the displaced volume flux since the piston has an additional blockage effect on the mean flow. The total excess energy flow is calculated for the compact piston with any subsonic mean flow (and also for the non-compact piston with low Mach number mean flow) and is compared with that for the complementary problem of a moving piston in a quiescent fluid. Since this is the previous problem referred to a reference frame that moves with the mean flow, the pressure and velocity fluctuations are as before, but the energy balance is different since the drag force on the piston does work in the latter case.     

Limit of hanger linearity in suspension footbridge dynamics: A new section model

The mechanical behaviour of suspension bridges is characterised by nonlinearities due to the main cables geometric effects and to the inability of the hangers to sustain compressive loads. The nonlinear effects due to hanger slackening are expected to increase in suspension footbridges due to lightweight decks, that is, low dead to live load ratio, and to shallow plate-girder decks with very low flexural and torsional stiffness. In this paper a new section model is proposed to study the limit of hanger linearity in lightweight suspension footbridges. The model is inspired to a four degrees-of-freedom model already proposed in the literature, but is expressed with a new formalism that allows some interesting properties to be outlined. Specifically, the expression of a particular frequency, herein called relative antiresonance frequency, as a function of the model generalised properties is derived: if the system is loaded with a harmonic force having that frequency, the linear behaviour of the hangers is assured for every value of the force amplitude. The proposed section model is applied to a footbridge benchmark subject to the pedestrian harmonic load and results are compared with those obtained through a nonlinear dynamic analysis on a 3D Finite Element model of the bridge.     

Theoretical investigation of hydrodynamic surface mode in a lined duct with sheared flow and comparison with experiment

A spectral collocation method is used to solve the linearized Euler equations in a duct with shear flow and lined walls in order to identify a possible hydrodynamic instability observed in published experiments. This method is first checked against a reference test case in a cylindrical duct. Then a theoretical test case in a plane bi-dimensional duct with no-slip flow is considered: the Briggs-Bers stability criterion is proved to be valid and it shows that the hydrodynamic instability does correspond to a right-running amplified wave. Eigenmode analyses are then performed on the experimental configuration. An unstable hydrodynamic surface mode is found, with an axial wavenumber and velocity eigenfunctions which are in good agreement with the experimental ones. Acoustic energy calculations show that the hydrodynamic instability paradoxically carries noticeable levels of acoustic energy in the upstream direction. Finally, the influence of Mach number and frequency is investigated.     

On the sound field of a resilient disk in free space

Radiation characteristics are calculated for a circular planar sound source in free space with a uniform surface pressure distribution, which can be regarded as a freely suspended membrane with zero mass and stiffness. This idealized dipole source is shown to have closed form solutions for its far-field pressure response and radiation admittance. The latter is found to have a simple mathematical relationship with the radiation impedance of a rigid piston in an infinite baffle. Also, a single expansion is derived for the near-field pressure field, which degenerates to a closed form solution on the axis of symmetry. From the normal gradient of the surface pressure, the surface velocity is calculated. The near-field expression is then generalized to an arbitrary surface pressure distribution. It is shown how this can be used as a simplified solution for a rigid disk in free space or a more realistic sound source such as pre-tensioned membrane in free space with non-zero mass and a clamped rim.     

Bifurcations in a model of magnetoconvection

Bifurcations from oscillatory solutions are studied in a truncated model of two-dimensional Boussinesq magnetoconvection. The fifth order system of nonlinear differential equations is integrated numerically and in certain parameter regimes there is a bifurcation from symmetrical to asymmetrical oscillations followed by a period-doubling cascade. After the accumulation point there is a semiperiodic cascade leading to chaotic behaviour. Then the semiperiodic cascade is repeated in reverse, followed by a period-halving cascade and a bifurcation back to symmetry. Finally, the branch of oscillatory solutions terminates with a symmetrical heteroclinic orbit that connects two saddle-foci. The interval with aperiodic solutions contains many pairs of narrow windows with asymmetrical or symmetrical periodic solutions, each with its own cascade. This pattern of behaviour is likely to occur when a periodic orbit approaches a symmetrical pair of saddle-foci with eigenvalues that satisfy Shil'nikov's inequality.     

Pattern of flow around a sphere oscillating an neutrally buoyancy horizon in a continuously stratified fluid

The flow pattern produced by a sphere freely sinking to the neutral buoyancy horizon in a continuously stratified liquid is visualized with different schlieren methods. Dispersion of light in the brine produces colouring of conventional schlieren images when cutting diaphragm is at the edge of blade or thread and is used to form “natural rainbow” colour schlieren image. With sensitive schlieren methods a new structural element is distinguished in the flow pattern. That is a narrow jet covered with a high gradient envelope forming in the neighbourhood of the turning points on the trajectory of the oscillating body. Due to the interaction of the body with the emitted internal waves, and also with the wake and secondary jets, the rate of amplitude damping decreases with time     

Permittivity and permeability of pentagon configuration molecules with different symmetry breaking and their applications

In nature, some molecules have broken conjugate symmetry configurations, which might result in a special optical phenomenon called negative refraction. Under such circumstances, both permittivity and permeability are negative simultaneously. When light at certain frequency is transmitted through a transparent medium (e.g., slide glass) in which a psychoactive drug with negative indexes has been deposited, the refracted light is detected at different locations in the transparent medium. This is because the refracted light travels in a direction opposite to the expected path when it passes through material with a negative index. Using this method, it is possible to distinguish synthetic cannabinoids from other abusive psychoactive drugs in the UV-vis region. In this study, we use a tight-binding model to calculate the permittivity and permeability of pentagonal configurations with different broken symmetries. Furthermore, a qualitative analysis of the negative refraction with respect to heptagonal models is discussed.     

Renormalizable models with simple symmetry breaking

If to a Lagrangian density with invariance under a continuous group of linear transformations of the fields a term linear or bilinear in the fields is added, the symmetry is in general reduced and the currents associated with the original symmetry are only partially conserved. If the theory without the added term is renormalizable, the theory with that term also is, and the needed renormalization conditions are the essential content of the appropriate Ward-Takahashi-Kazes-Rivers identities. The case of symmetry breaking by a term linear in Bose fields (source term) is here analysed completely, in particular with respect to the nonsymmetric limit of vanishing source term, a particular Goldstone mode, and with respect to properties of the ground state energy density as a function of the strength of the source term. Induced and spontaneous breaking of a discrete symmetry are also treated.     

Kinetic features of the deformation of solids in nano-and microscopic volumes

The deformation dynamics of nanovolumes in crystalline, quasicrystalline, and amorphous solids is studied experimentally using continuous nanoindentation with a resolution of 0.1 nm. The elastic limits of some materials are determined in a nanocontact region. A jumplike transition to a plastic flow (which is equivalent to a drop in yield in uniaxial macroscopic tests) is revealed and studied. The dynamics and statistics of an unstable plastic flow in strain-aging alloys are analyzed. The specific features of a local stress-strain curve associated with a phase transformation under an indenter and with microcrack nucleation are revealed. The load-carrying ability of a material upon nanocontact loading is shown to be many times its macroscopic yield strength and to approach the theoretical ultimate strength even in plastic materials. The relaxation processes occurring in submicrovolumes after unloading are found to induce an elastic aftereffect that is much larger than that in macroscopic tests. In Si and Ge single crystals, the effect of a jumplike increase in the cracking resistance with the strain rate is detected.     

A frequency domain numerical method for airfoil broadband self-noise prediction

This paper describes a numerical approach, based in the frequency domain, for predicting the broadband self-noise radiation due to an airfoil situated in a smooth mean flow. Noise is generated by the interaction between the boundary layer turbulence on the airfoil surface and the airfoil trailing edge. Thin airfoil theory is used to deduce the unsteady blade loading. In this paper, the important difference with much of the previous work dealing with trailing edge noise is that the integration of the surface sources for computation of the radiated sound field is evaluated on the actual airfoil surface rather than in the mean-chord plane. The assumption of flat plate geometry in the calculation of radiation is therefore avoided. Moreover, the solution is valid in both near and far fields and reduces to the analytic solution due to Amiet when the airfoil collapses to a flat plate with large span, and the measurement point is taken to the far field.Predictions of the airfoil broadband self-noise radiation presented here are shown to be in reasonable agreement with the predictions obtained using the Brooks approach, which are based on a comprehensive database of experimental data. Also investigated in this paper is the effect on the broadband noise prediction of relaxing the ‘frozen-gust’ assumption, whereby the turbulence at each frequency comprises a continuous spectrum of streamwise wavenumber components. It is shown that making the frozen gust assumption yields an under-prediction of the noise spectrum by approximately 2dB compared with that obtained when this assumption is relaxed, with the largest occurring at high frequencies.This paper concludes with a comparison of the broadband noise directivity for a flat-plat, a NACA 0012 and a NACA 0024 airfoil at non-zero angle of attack. Differences of up to 20 dB are predicted, with the largest difference occurring at a radiation angle of zero degrees relative to the airfoil mean centre line.     

Geometro-Differential Conception of Extended Particles and the Semigroup of Trajectories in Minkowski Space-Time

The semigroup of trajectories in Minkowski space-time and its induced representations are constructed as a generalization of the Galilei case. They describe relativistic pointlike particles and yield the free propagator as a path integral in the space of trajectories parametrized by a fifth parameter. This non physical propagator in a five-dimensional space is integrated over the fifth parameter to yield the physical propagator in Minkowski space. Thereafter, this notion is applied to a model of extended particles with internal Poincaré symmetry and moving in an external Minkowski space. The geometrical structure is of Hilbert bundles and the interaction is introduced as a connection. The propagator is a path integral with respect to either the internal and external trajectories and reduces to a product of an internal and an external propagator when the interaction is ignored, just as has been found in a previous work with representations of the group rather than those of the semigroup.     

Electrodynamics of hyperbolically accelerated charges V. The field of a charge in the Rindler space and the Milne space

We describe the electromagnetic field of a uniformly accelerated charge in its co-moving Rindler frame. It is shown that the electrical field lines coincide with the trajectories of photons. The self force of a charged particle at rest in Rindler space, and the increase of its weight due to its charge, is calculated. The general case of an accelerated charge in Rindler space is also considered. It is shown that the electrical field inside a uniformly charged spherical shell can be used as a measure of it 4-acceleration. A result that has earlier been deduced in a different way by Fugmann and Kretzschmar is confirmed, namely that the intensity of radiation from a point charge instantaneously at rest in an accelerated frame is proportional to the square of the relative acceleration of the charge and the observer. In particular it is shown that a freely falling charge in Rindler space radiates in accordance with Larmor’s formula. In this case the radiation energy is taken from the Schott energy. The energy of the electromagnetic field is analysed from the point of view of the Hirayama-separation, which generalizes the Teitelboim-separation to non-inertial frames, of the field in a bound part and an unbound part. A detailed account, with reference to the Rindler frame, of the field energy and particle energy is given for the case of a charge entering and leaving a region with hyperbolic motion. We also consider the electromagnetic field of a uniformly accelerated charge with reference to the Milne frame, which covers a different part of spacetime than the Rindler frame. The radiating part of the electromagnetic field is found in the Milne sector of spacetime.     

利用几何特性及神经网络进行人脸探测技术的研究

在人脸识别过程中 ,首先也是最重要的一个环节是人脸探测 ,因为一旦从图像中定位并提取到了人脸 ,那么下一步的人脸识别工作就变得非常容易。眼睛是人脸图像中最容易探测的部位 ,而且通过探测双眼来发现人脸最符合人的视觉习惯。提出了一种基于几何特征分析和人工神经网络的由粗到细的两级人脸探测方法。在第一级中 ,眼睛和脸是通过测量眼睛的尺寸和眼睛与脸的位置关系探测到的 ,第一级的输出是一个尺寸归一化的人脸 ,但偶尔也伴随着一个或多个因对复杂背景中与眼睛类似的物体的误判而得到的非人脸图像 ;第二级神经网络正是用来过滤掉第一级中被误判的人脸。实验表明 ,这种由粗到细的两级人脸探测系统具有很高的稳定性和探测正确率