Scattering of waves by an aperture in an impedance screen

The transmission and diffraction of waves by an aperture in an impedance screen is investigated. The Senior's solution of the scattering problem of waves by an impedance half-plane is transformed into a physical optics type integral. The obtained method is applied to the transmission problem of waves by a slit in an impedance screen. The results are compared with the aperture problem in black and conducting screens numerically.     

Elastic interaction of a dislocation array with a phase boundary

The equilibrium configuration of an array of dislocations in parallel equidistant slip planes under an external shear stress near a welded boundary between two isotropic half-spaces having different elastic constants is computed. For large external stress, the dislocations are arranged into an arc concave when seen from the boundary. It is concluded that such an arc is formed at the tip of a twin or of a martensitic plate near a phase boundary. The tensile stress across the boundary due to an edge dislocation array is discussed in connection with the formation of an interfacial crack.     

Direct measurement of the oscillation frequency in an optical-tweezers trap by parametric excitation

We demonstrate a novel technique for direct measurement of the oscillation frequency in an optical-tweezers trap. The technique uses the phenomenon of parametric resonance in an oscillator when the stiffness of the trapping potential is modulated. The trapped particle is a strongly damped oscillator; hence, the signature of parametric resonance is not an increase in the amplitude but an increase in the size of Brownian fluctuations. The trap frequency is measured with an accuracy of 0.1%, which is better than previous techniques and thus opens up new possibilities in experiments with optical tweezers.     

The surface energy of an electron gas in model crystals

The surface energy of an electron gas in a crystal is considered. The results obtained for a quadratic spectrum are generalized to an arbitrary energy spectrum in certain crystal models. The surface energy of an electron gas with a quadratic spectrum is found for a sample with a rough boundary when the height of irregularities is small compared with the electron wavelength.     

Vibrations of double-string complex system under moving forces. Closed solutions

In this paper the dynamic response of a double-string system traversed by a constant or a harmonically oscillating moving force is considered. The force is moving with a constant velocity on the top string. The strings are identical, parallel, one upon the other and continuously coupled by a linear Winkler elastic element. The classical solution of the response of a double-string system subjected to a force moving with a constant velocity has a form of an infinite series. The main goal of this paper is to show that in the considered case a part of the solution can be presented in a closed, analytical form instead of an infinite series. The presented method of finding the solution in a closed, analytical form is based on the observation that the solution of the system of partial differential equations in the form of an infinite series is also a solution of an appropriate system of ordinary differential equations.     

Passive and temporally continuous optical spectral analyzer of RF signals via wavelength coding

A novel approach realizing an optical spectrum analyzer for photonic detection of an unknown RF carrier signals is presented. The described module may be part of an electronic warfare system in which detection of a narrow band RF signal is required. Moreover, The RF signal is characterized by an unknown time varying carrier frequency embedded in wide band noise. The system uses a passive, fiber based photonic configuration. It allows the spectrum mapping of an incoming electronic RF signal modulated on an optical carrier. The spectral analyzer configuration uses a finite impulse response (FIR) filter that is realized by two different optical paths of parallel fibers which generate a spectral notch filter. Hence, a wavelength coding is realized by chromatic dispersion such that each wavelength is filtered by a different FIR filter. Therefore, the energy at a WDM demux output channels is actually proportional to the spectrum of the input RF signal. This spectral mapping is obtained without lose of temporal RF information.     

Employment of the scattering amplitude in solving the diffraction problems for waves in a halfspace

The problem on the diffraction of an acoustic wave by a finite-size scatterer (inclusion) located in a halfspace is considered. The method of solving this problem is based on the use of the scattering amplitude of the inclusion. A formula analogous to the Green formula is presented. It allows one to determine the scattering amplitude of the inclusion for an arbitrary incident wave (determined by the directional pattern of the source of primary waves) from the scattering amplitude corresponding to plane incident waves. The algorithm is presented for solving the problem on the operation of an acoustically opaque radiator in a halfspace whose boundary is characterized by an arbitrary reflection coefficient. As an example, the problem is solved on the generation of low-frequency oscillations by a sphere with an acoustically soft boundary near an acoustically hard or soft boundary of the halfspace.     

Linear intermode conversion of electromagnetic wave energy in a magnetically soft gyrotropic material

The excitation of axial radio-frequency (rf) magnetic induction by an axial rf current is observed in a conductor with circular magnetic anisotropy when a weak magnetizing field is applied. The conductor is an amorphous cobalt-based wire, which exhibits azimuthal magnetic anisotropy. It serves as the central conductor in a coaxial line. The axial rf magnetic induction produces an emf in an induction coil coaxial to the conductor. The induction coil is part of a matched receiving circuit. The power conversion coefficient is as high as tens of percent. The measurements demonstrate the high sensitivity of the conversion coefficient to an external field. The theory of ferromagnetic resonance faithfully describes the results of the observations. Zh. Tekh. Fiz. 69, 58–63 (March 1999)     

Diffraction of a sound wave by the open end of a flanged waveguide with impedance walls

Diffraction of a plane sound wave by the open end of an impedance-wall waveguide connected to an opening in an impedance screen is considered. The plane wave is incident on the waveguide from a free half-space. Two versions of the problem are considered: for a semi-infinite waveguide and for a finite-length waveguide with a specified bottom impedance; the impedances of the walls, screen, and waveguide bottom can be different. The finite-length waveguide can be treated as an open cavity in the impedance screen. For the cavity of zero length, the problem is reduced to the diffraction by an impedance insert in the impedance screen. The solution in the external region determines the scattered field; the solution in the internal region allows one to determine the directional pattern of an array of receivers located in the cavity. The problem is solved using the integral Helmholtz equation with a specially selected Green’s function that provides the fulfillment of the boundary conditions. Formally, the problem is reduced to an infinite system of algebraic equations. The computational results obtained for bistatic and monostatic scattering patterns are presented.     

The electromagnetic initial boundary value problem in a domain with a chiral filling

The problem of the excitation of electromagnetic oscillations by given charge and current distributions in a domain with a nonhomogeneous chiral filling is investigated. The domain where the problem is considered may be both a finite one bounded by an ideally conducting surface and an infinite supplement to an ideally conducting bounded object. The initial boundary value problem is shown to arise, for which the generalized formulation in a special functional space is given. The existence of a unique weak solution to the problem is proven using the Galerkin method.     

Persistent supercurrent atom chip

Rubidium-87 atoms are trapped in an Ioffe-Pritchard potential generated with a persistent supercurrent that flows in a loop circuit patterned on a sapphire surface. The superconducting circuit is a closed loop made of a 100 microm wide molecular-beam epitaxy-grown MgB2 stripe carrying a supercurrent of 2.5 A. To control the supercurrent in the stripe, an on-chip thermal switch operated by a focused argon-ion laser is developed. The switch operates as an on/off switch of the supercurrent or as a device to set the current to a specific value with the aid of an external magnetic field. The current can be set even without an external source if the change is in the decreasing direction.     

Acoustic energy harvesting using an electromechanical Helmholtz resonator

This paper presents the development of an acoustic energy harvester using an electromechanical Helmholtz resonator (EMHR). The EMHR consists of an orifice, cavity, and a piezoelectric diaphragm. Acoustic energy is converted to mechanical energy when sound incident on the orifice generates an oscillatory pressure in the cavity, which in turns causes the vibration of the diaphragm. The conversion of acoustic energy to electrical energy is achieved via piezoelectric transduction in the diaphragm of the EMHR. Moreover, the diaphragm is coupled with energy reclamation circuitry to increase the efficiency of the energy conversion. Lumped element modeling of the EMHR is used to provide physical insight into the coupled energy domain dynamics governing the energy reclamation process. The feasibility of acoustic energy reclamation using an EMHR is demonstrated in a plane wave tube for two power converter topologies. The first is comprised of only a rectifier, and the second uses a rectifier connected to a flyback converter to improve load matching. Experimental results indicate that approximately 30 mW of output power is harvested for an incident sound pressure level of 160 dB with a flyback converter. Such power level is sufficient to power a variety of low power electronic devices.     

Diffraction of cylindrical waves by an ideally conducting wedge in an anisotropic plasma

The problem of diffraction of cylindrical waves by an ideally conducting wedge in an anisotropic plasma is formulated and solved. The integral equations for the field are reduced to function equations, which are solved with the aid of a special function that is introduced. The properties of this function are studied. The general solution is represented as a double contour integral in the plane of a complex variable. The radiation field and surface waves for a number of special cases are analyzed: a source of cylindrical waves on an edge; at infinity; etc. Diffraction in a half-plane is studied separately.     

Modular values and weak values of quantum observables

The concept of a modular value of an observable of a pre- and postselected quantum system is introduced. It is similar in form and in some cases has a close connection to the weak value of an observable, but instead of describing an effective interaction when the coupling is weak, it describes a coupling of any strength but only to qubit meters. The generalization of the concept for a coupling of a composite system to a multiqubit meter provides an explanation of some current experiments.     

大角度蚀刻衍射光栅的模拟

研究了平面波导密集波分复用器件中很有发展潜力的蚀刻衍射光栅(EDG).小角度范围光栅的模拟通常采用高斯近似的输入光场,由于近轴的高斯光场接近实际光场,所以模拟结果很准确.但这种方法应用于大角度范围的光栅则有偏差.本文提出了大角度蚀刻衍射光栅的模拟方法,分析了这种偏差并给出了模拟结果.事实上这种方法也适合于实际任意输入光场的模拟.     

Optical theorem and Aharonov-Bohm scattering

A rigorous derivation of the optical theorem (OT) from the conservation of probability flux (CPF) is presented for scattering on an arbitrary spherically symmetric potential inN-spatial dimensions (ND). The constructed expression for the OT is found to yield the corresponding well-known results for two- and three-dimensional cases in a rather natural way. The Aharonov-Bohm (AB) effect is considered as a scattering event of an electron by a magnetic field confined in an infinitely long shielded solenoid and a similar derivation is attempted for an appropriate optical theorem. Our current understanding of the scattering theory is found to be inadequate for the purpose. The reason for this is discussed in some detail.     

Optical switch based on variable aperture

We report on a pixel whose aperture can be varied electrically. The pixel is confined by a hole-patterned polymer wall and a dielectric liquid forms a ring shape around the wall surface. Without an electric field, the pixel has the largest aperture. The applied fringing field stretches the liquid surface, leading to a decrease in the aperture size. The switchable aperture ratio of the pixel is over 80% and the response time is ~10 ms. Such a device is useful for an optical attenuator, a light shutter, an adaptive iris, and an information display.     

Analytical Approach for Piecewise Linear Coupled Map Lattices

A simple construction is presented which generalizes piecewise linear one-dimensional Markov maps to an arbitrary number of dimensions. The corresponding coupled map lattice, known as a simplicial mapping in the mathematical literature, allows for an analytical investigation. In particular, the spin Hamiltonian which is generated by the symbolic dynamics is accessible. As an example, a formal relation between a globally coupled system and an Ising mean-field model is established. The phase transition in the limit of infinite system size is analyzed and analytical results are compared with numerical simulations.     

Localization of sound in rooms. IV: The Franssen effect

The Franssen effect is an illusion that causes human listeners to make large errors in localizing a sound source. This paper describes steps taken to convert the illusion into an experiment in order to study the localization precedence effect as it operates in rooms. The results of the experiment suggest that there are two components to the illusion: The first is the inability of listeners to localize a sine tone in a room in the absence of an onset; the second is the obscuring of modulation cues by the irregular transient response of a room. Experiments show that the Franssen effect fails completely in an anechoic environment, as expected if the effect depends upon the implausibility of steady-state cues in a room. The Franssen effect also fails when the spectrum of the sound is dense.     

Ellipsoidal space-times,sources for the Kerr metric

The paper develops a systematic derivation of the Kerr metric and its possible sources in a clear geometric manner. It starts with a concise account of previous attempts at constructing an interior Kerr solution. Then a treatment of stationary-axisymmetric spacetimes, specially fitted to the needs of the following analysis, is presented. A new notion of an ellipsoidal space-time is introduced: it is a space-time in which local rest 3-spaces of some observers split naturally into congruences of concentric and coaxial ellipsoids. It is shown that these 3-spaces are natural spaces to consider the ellipsoidal figures of equilibrium. The investigation is carried out in detail for axially symmetric oblate confocal ellipsoids, but possible generalizations are indicated. The Kerr metric is found to be an ellipsoidal space-time of this special kind. Some remarks concerning an (unfound) explicit interior Kerr solution conclude the paper.