利用负阻抗构成无内阻抗模拟电表

将负阻抗引入电表测量电路，可消除由内阻抗引起的系统误差，从而构成无内阻抗电表。本文分析了电表内阻引起的测量误差，介绍了利用负阻抗消除内阻影响的方法，并给出了负阻抗原理电路和实际应用电路。     

Interaction of nanosecond laser pulses with plastic foams

Some results of an experimental and theoretical study of the interaction of laser pulses with plastic foams are reported. The propagation velocity of a hydrodynamic peturbation which was initiated in foam target under the action of a laser pulse with intensityq≈2·10¹³ W/cm² and the velocity distribution function of plasma ions were measured; the preliminary results of time-integrated spectroscopic measurements of an intense red-shifted signal are also reported. A self-consistent model of the foam target’s laser plasma formed in a hydrodynamic mode was derived. The predictions of this model are consistent with experimental results. A model of microprocesses of laser plasma formation in a structured material was also developed. The results of numerical simulations by 1D and 2D computer codes are also reported. Original article submitted in English May 25, 1997.     

Self-control of chaos in neural circuits with plastic electrical synapses

Two kinds of connections are known to exist in neural circuits: electrical (also called gap junctions) and chemical. Whereas chemical synapses are known to be plastic (i. e., modifiable), but slow, electrical transmission through gap junctions is not modifiable, but is very fast. We suggest the new artificial synapse that combines the best properties of both: the fast reaction of a gap junction and the plasticity of a chemical synapse. Such a plastic electrical synapse can be used in hybrid neural circuits and for the development of neural prosthetics, i.e., implanted devices that can interact with the real nervous system. Based on the computer modelling we show that such a plastic electrical synapse regularizes chaos in the minimal neural circuit consisting of two chaotic bursting neurons.     

Experimental investigation of supersonic radiation propagation in low-density plastic and copper-doped foams

1 Introduction The investigation of supersonic radiation wave transporting in low density foam pro-duced by thermal radiation is of crucial importance in inertial confinement fusion (ICF) research[1]. When the intense radiation flux is incident in the media, first, a supersonic heat wave is formed which propagates into the undisturbed material. In time, due to the increasing mass of heated material, it slows down and is overtaken by a shock wave,thus becoming of the ablative type. Normally, …     

Quaternion-Octonion Unitary Symmetries and Analogous Casimir Operators

An attempt has been made to investigate the global SU(2) and SU(3) unitary flavor symmetries systematically in terms of quaternion and octonion respectively. It is shown that these symmetries are suitably handled with quaternions and octonions in order to obtain their generators, commutation rules and symmetry properties. Accordingly, Casimir operators for SU(2) and SU(3) flavor symmetries are also constructed for the proper testing of these symmetries in terms of quaternions and octonions.     

Quantum States Transfer by Analogous Bell States

Transmitting quantum states by channels of analogous Bell states is studied in this paper. We analyze the transmitting process. constructed the probabilitic unitary operator, and gain the largest successful transfer quantum state probability.     

Sliding backshorts for planar circuits

The Superconductor-Insulator-Superconductor (SIS) tunnel junction is an extremely sensitive heterodyne detector at millimeter and submillimeter wavelengths. The large inherent capacitance associated with this device results in a substantial impedance mismatch with typical antennas and, therefore, requires a tuning circuit for optimum results. At frequencies where waveguide dimensions are realizable, impedance matching can be accomplished by embedding the detector in a waveguide circuit with adjustable waveguide backshorts. At higher frequencies, where waveguide dimensions become prohibitively small, a planar transmission line embedding circuit provides a reasonable alternative. Typically, such planar circuits offer no post-fabrication adjustability, resulting in demanding materials and design requirements. An adjustable planar embedding circuit based on coplanar transmission lines with movable noncontacting shorting elements has been developed. The shorting elements each consist of a thin metallic plate with an optimized arrangement of rectangular holes, placed along the insulated metallic transmission line to provide a periodic variation of the line impedance. A scadel (1–5 GHz) has shown that a large reflection coefficient, |s ₁₁|–0.5 dB, can be achieved with these sliding elements. A low frequency tuning circuit incorporating these shorting elements has been tested to demonstrate practical tuning ranges.     

An elasto-visco-plastic model for immortal foams or emulsions

A variety of complex fluids consists in soft, round objects (foams, emulsions, assemblies of copolymer micelles or of multilamellar vesicles--also known as onions). Their dense packing induces a slight deviation from their prefered circular or spherical shape. As a frustrated assembly of interacting bodies, such a material evolves from one conformation to another through a succession of discrete, topological events driven by finite external forces. As a result, the material exhibits a finite yield threshold. The individual objects usually evolve spontaneously (colloidal diffusion, object coalescence, molecular diffusion), and the material properties under low or vanishing stress may alter with time, a phenomenon known as aging. We neglect such effects to address the simpler behaviour of (uncommon) immortal fluids: we construct a minimal, fully tensorial, rheological model, equivalent to the (scalar) Bingham model. Importantly, the model consistently describes the ability of such soft materials to deform substantially in the elastic regime (be it compressible or not) before they undergo (incompressible) plastic creep--or viscous flow under even higher stresses.     

An accurate von Neumann's law for three-dimensional foams

The diffusive coarsening of 2D soap froths is governed by von Neumann's law. A statistical version of this law for dry 3D foams has long been conjectured. A new derivation, based on a theorem by Minkowski, yields an explicit analytical von Neumann's law in 3D which is in very good agreement with detailed simulations and experiments. The average growth rate of a bubble with F faces is shown to be proportional to F1/2 for large F, in contrast to the conjectured linear dependence. Accounting for foam disorder in the model further improves the agreement with data.     

Permeability of aqueous foams

We perform forced-drainage experiments in aqueous foams and compare the results with data available in the literature. We show that all the data can be accurately compared together if the dimensionless permeability of the foam is plotted as a function of liquid fraction. Using this set of coordinates highlights the fact that a large part of the published experimental results corresponds to relatively wet foams ( ∼ 0.1 . Yet, most of the foam drainage models are based on geometrical considerations only valid for dry foams. We therefore discuss the range of validity of the different models in the literature and their comparison to experimental data. We propose extensions of these models considering the geometry of foam in the relatively wet-foam limit. We eventually show that if the foam geometry is correctly described, forced drainage experiments can be understood using a unique parameter --the Boussinesq number.     

Ferroelectric materials for dynamic-memory integrated circuits

The possibilities of using ferroelectric materials for new generations of integrated circuits for high-density dynamic memory (up to 1 Gbit per crystal) are discussed. The correspondence of the specific capacitance and leakage currents of thin film ferroelectric capacitors to the requirements for integrated circuits with various information capacities is examined. It is shown that the capacitance-voltage characteristic of the ferroelectric strongly influences the specific capacitance and the rate of decrease of the voltage across the capacitors when they are discharged in the process of storing information. The prospects for increasing the specific capacitance of memory capacitors using relaxor ferroelectrics are examined. Zh. Tekh. Fiz. 69, 89–92 (May 1999)     

Quantum circuits for general multiqubit gates

We consider a generic elementary gate sequence which is needed to implement a general quantum gate acting on n qubits-a unitary transformation with 4(n) degrees of freedom. For synthesizing the gate sequence, a method based on the so-called cosine-sine matrix decomposition is presented. The result is optimal in the number of elementary one-qubit gates, 4(n), and scales more favorably than the previously reported decompositions requiring 4(n)-2(n+1) controlled NOT gates.     

Mode transformer for miniaturized optical circuits

A novel mode transformer was fabricated that transforms a modal area by a factor of 100. Using the mode transformer improves the efficiency of mode transformation by an order of magnitude compared with that when no mode transformer is used. With this mode transformer, input-output coupling of miniaturized, on-chip integrated optical circuits to external optical fibers is achieved with low loss. The mode transformer's design, fabricated in silicon, is scalable to virtually any waveguide size, facilitating continuous miniaturization in silicon optoelectronics.     

Dilatancy in liquid foams

It is shown that dilatancy (a change in liquid fraction due to shear) can be a large effect in foams. Theory and simulations for the standard idealized model of a two-dimensional liquid foam are found to be in good agreement. The estimate of the maximum effect of static shear at constant osmotic pressure gives an absolute increase in liquid fraction of roughly 1.5%, halfway between the wet and the dry limits. The same theory, which uses the established dependence of shear rnodulus on liquid fraction, predicts a qualitatively and quantitatively similar behaviour in three dimensions.     

Optical techniques for active integratedantenna circuits

This paper reviews some of the recent efforts in the area of microwave–optical interactions applied to active integrated antennas and arrays. Two optical–microwave techniques and examples of their application are presented. First, antenna remoting via optical means is discussed. Second, optical control of microwave devices in active antenna circuits is demonstrated.     

Adjustable tuning for planar millimeter-wave circuits

At millimeter wavelengths uncontrollable parasitics are of ten large enough to significantly degrade circuit performance when they are not compensated by adjustable elements. It is difficult to add adjustable elements to planar millimeter-wave circuits without increasing their size, weight, and cost. In this paper we investigate three adjustable elements, all involving movement of a short along a section of coplanar waveguide (CPW). These tuners are incorporated in a planar detector circuit for purposes of demonstration and characterization. Their losses are determined. The precision with which they can be adjusted is also considered. Of the three, a tuner based on the laser-assisted etching of molybdenum is shown to have the highest performance at millimeter wavelengths. This tuner employs laser direct write etching¹ with a recently developed photochemical reaction for trimming molybdenum.University of California, Berkeley Berkeley, California 94720M.I.T. Lincoln Laboratory 244 Wood St. Lexington, Massachusetts 0217     

Effective theories for circuits and automata

Abstracting an effective theory from a complicated process is central to the study of complexity. Even when the underlying mechanisms are understood, or at least measurable, the presence of dissipation and irreversibility in biological, computational, and social systems makes the problem harder. Here, we demonstrate the construction of effective theories in the presence of both irreversibility and noise, in a dynamical model with underlying feedback. We use the Krohn-Rhodes theorem to show how the composition of underlying mechanisms can lead to innovations in the emergent effective theory. We show how dissipation and irreversibility fundamentally limit the lifetimes of these emergent structures, even though, on short timescales, the group properties may be enriched compared to their noiseless counterparts.     

Application of multi-layered polyurethane foams for flat-walled anechoic linings

Previous work demonstrated that a multi-objective evolutionary algorithm could be successfully employed as an optimiser to make the design of flat-walled multi-layered anechoic linings more efficient. In the present work, such an algorithm is employed to investigate the practical aspects of the application of multi-layered polyurethane foams as the flat-walled anechoic lining. The investigation includes aspects such as the efficacy of a single layer of material, the minimum number of layers of linings to achieve the minimum overall thickness for low (100 Hz), mid (250 Hz) and high (500 Hz) cut-off frequencies, the use of the three-layered lining composite for low to mid cut-off frequencies and the effect of air gaps.