摘要:

We regard a magnetic inverse problem as a spatial optimum allocation problem of currents and use a Hopfield neural network for solving this optimization problem. Because the Hopfield neural network has an initial state problem that the optimum solution cannot be obtained unless an initial state of network is set up suitably, adoption of a genetic algorithm is proposed for solving this initial state problem of Hopfield neural network. The effectiveness of proposed method is confirmed by computational simulations. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360946

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The equivalent circuit model is used to describe analytically the coupling process of the center of mass motion of a cloud of particles in a Penning trap. From the response of this coupled circuit to white noise a way of nondestructively diagnosing the number of trapped particles is given which is valid for all values of this quantity. Experimental results are presented and compared with this analysis. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360947

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The differential cross sections for16O(He,He)16O resonant elastic scattering at 3.034 and 3.078 MeV have been measured using stoichiometric thin (100 A˚) and thick (6000 A˚) SiO2layers formed on Si(100) wafers by thermal oxidation at 900 °C under H2and O2flows. We have determined the resonance widths (&Ggr;) and interaction radii (a), which are the parameters defining the cross sections in the partial wave analysis, by best fitting the angular and energy dependent scattering yields from oxygen. A computer simulation program for Rutherford backscattering including the16O(He,He)16O resonant scattering has been synthesized and applied to the elemental analysis of thin YBa2Cu4O8and Nd1+xBa2−xCu3O7−&dgr;films grown on SrTiO3substrates. The present elemental analysis is compared with the transition temperatures of superconductivity (Tc) in the context of the oxygen deficiency. The accuracy of oxygen content is estimated to be better than 0.1 (a few %). How to improve the accuracies of the elemental analysis, in particular the oxygen content, is discussed in detail. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360948

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The time‐varying electric and magnetic fields inside a solenoidal coil have recently been calculated by Harmon. He modeled the coil by a cylindrical current sheet, used a physical approach starting from the Maxwell equations, and found results very different from what was believed from circuit theory since the 1920’s. Harmon’s derivation neglects the electric field‐current relation in the wire, i.e., it violates Ohm’s law. In this article, the fields are derived from the Maxwell equations with this omission amended. Instead of the current, the terminal voltage of the coil is taken as the independent input. The relation between the current and the electric field in the coil wire constitutes an additional boundary condition. It allows as additional variable an energy influx from the power source, whereas Harmon considered radiation from the coil outward only. With these modifications, the old circuit theory results are recovered again. Implications are outlined for the physical legitimacy of other models involving a given current sheet. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360949

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects connected with the dynamical scattering of electromagnetic waves by weakly curved periodic layered media are discussed. A simple physical model is used to take into account the effects of the curvature in the framework of the dynamical theory of diffraction. A peculiar effect consisting of the possibility of a continuous sweep of the direction of the diffracted beam over a relatively wide angular range, under the control of the frequency of the incident wave, is seen and analyzed. The design of a device realizing such a frequency‐direction conversion in the frequency range of 82–107 GHz is presented and discussed as a prototype of a new possible class of instruments. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360950

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a method to calculate the electrostatic field between a metallic tip of arbitrary shape and a sample surface. The basic idea is to replace the electrodes by a set of ‘‘image’’ charges. These charges are adjusted in order to fit the boundary conditions on the surfaces. As an application of the method, we describe the field characteristics of a field‐emission diode as a function of the gap between electrodes for different tip shapes. A comparison between numerical and analytical results is presented. The results do not depend on the overall tip geometry only for gap distances smaller than ≊1/2 the tip radius. The field enhancement factor due to the presence of small protrusions on the tip apex is calculated and their influence in near‐field‐emission scanning tunneling microscopy is also discussed. We show that the electron‐field emission from the sample is stable against tip‐shape changes due to adsorbate diffusion or atomic rearrangements. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360951

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Using a longitudinally mode‐controlled transversely excited atmospheric CO2laser, we studied the conversion characteristics of single‐, two‐, and multimode pump pulses in a para‐H2Raman laser. In the small signal region, two‐ and multimode pump pulses showed higher Raman conversion efficiencies. In the saturation region, however, output energies pumped with single‐ and two‐mode pulses exceeded those pumped with multimode pulses. Consequently, the two‐mode pumping was the most efficient within the limit of pump energies used in the experiment. The results are explained in relation to the mode‐mixing effect for the correlated pump and Stokes beams. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360952

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Liquid phase epitaxial growth of Te‐compensated GaSb results in a very low dopedn−GaSb epilayer (n≊1015cm−3). Be+‐implanted photodiodes produced from this material exhibit voltage breakdown values reaching 70 V. Generation‐recombination lifetimes in the space charge region around 10−8s have been deduced from these diode photoelectrical properties. The high value of the space charge width leads to an efficient redshift due to the electroabsorption. The variation of the absorption coefficient value is 1350 cm−1at 1.72 &mgr;m for a variation of the electric field maximum of 1.2×105V/cm. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360789

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A complex‐coupled distributed feedback laser using a novel mechanism for creating a periodic gain is investigated. A one‐dimensional longitudinal analysis is developed to predict the change in the coupling strength when the carrier density is perturbed. Earlier reports have shown that this differential coupling affects the linewidth, with negative differential coupling offering the possibility for the most significant reductions in the linewidth enhancement factor. The analysis predicts that the linewidth enhancement factor can be reduced by about a factor of 2 because of the negative differential coupling for the particular design studied. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360790

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The excess noise of semiconductor lasers has been reduced mostly with the help of the self‐sustained pulsation in experiments. A theoretical analysis is given for mechanisms of the noise generation and the reduction method basing on the mode competition theory. Basic equations of these dynamics are given in the form of rate equations, where the nonlinear gain terms and Langevin noise sources are included. Effect of the optical feedback is introduced to give changes in the threshold gain level and by building of external cavity modes formed by the facet of the laser and the reflecting surface. The self‐sustained pulsation phenomena are examined in the narrow stripe structure geometries having the saturable absorbing region beside the active region. The amount of noise is expressed relating to time averaged values of the photons and the carrier densities in laser, whose levels are modified by the pulsation. It is shown that the excess noise due to mode competition among the internal cavity modes is well suppressed by the self‐sustained pulsation, while noise due to mode competition among the external cavity modes is mostly suppressed but sometimes not suppressed. More general discussions for the mechanisms are also given qualitatively by help of topological charts for dynamics. Three types of mode competitions are indicated. The first one is with a bistable state due to the symmetric profile of gain suppression for wavelength distribution. The second one is with an elliptic eddy motion of dynamics due to weak asymmetric property of the gain suppression. The third one is with a circular eddy motion of dynamics due to the strong asymmetric property of the gain suppression. Some difficulty in the noise reduction in the case of the strong asymmetric property of the gain suppression is mentioned. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360791

出版商:AIP    

年代:1996

数据来源: AIP