摘要:

A simple Carnot‐like irreversible power cycle is modeled with two isothermal and two adiabatic, irreversible processes. The generic source of internal irreversibility, deduced from the Clausius inequality, produces entropy at a rate proportional to the external heat conductance and the engine temperature ratio. This cycle is optimized for maximum power and maximum efficiency, and its performances compared to those of the endoreversible cycle, based on typical heat source and heat sink temperatures. Both cycles produce maximum power at the same engine temperature ratio, but the irreversible cycle prediction of maximum efficiency and heat conductance allocation between steam boiler and condenser, appear to be not only more realistic, but also more relevant to actual design considerations of power plants. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359834

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A rf excitation system that can drive a gas laser constructed of multiple wide, but narrow‐gap (slab), discharge volumes is presented. Resonant cavity techniques adopted from microwave applications are employed to provide uniform rf power division and impedance matching into each electrode channel. This approach when applied to a large radial array of gain channels can be used to create a very high‐power laser system in an unusually compact package. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359835

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the optical absorption and photorefractive properties of a series of cerium‐doped barium titanate crystals. The light‐induced absorption and the intensity‐dependent two‐beam coupling gain coefficient indicate that there are at least two active trap levels in cerium‐doped BaTiO3crystals. The total effective trap density, the Debye screening wave vector, and the intensity‐dependent factor increase with cerium‐doping concentration as well as the pump beam intensity. The positive light‐induced absorption and the negative absorption gain coefficient as the grating wave vector approaches zero indicate that the excitation cross section of shallow traps is larger than that of deep traps. One of these crystals exhibits a two‐beam coupling coefficient of 8.06 cm−1for ordinarily polarized beams, which is the highest ever reported to date. Both electro‐optic index grating and absorption grating are contributing to the coupling coefficient. The response time of as‐grown cerium‐doped BaTiO3with 15 ppm cerium is 220 ms at an intensity of 800 mW/cm2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359836

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A model of switching in ferroelectric liquid crystals is developed which represents the devices using three variables. This is a useful approach because the switching process in ferroelectric liquid crystal devices takes place through the formation and evolution of domains. The three variables used then represent the background director orientation, the director orientation within evolving domains, and the net domain area which has evolved. Setting up a system in this way allows modeling of a wide range of switching conditions in devices. The modeling is compared successfully with experimental results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359837

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Scanning optical microscopy with uncoated dielectric silica probe is used in the near field to investigate the propagation of optical modes along tapered integrated semiconductor optical amplifier devices and at larger working distances to study the electromagnetic intensity profile in the focal plane of various microlensed fibers. We show how this technique provides images of the mode structure of optoelectronic devices and profiled optical fibers with typical sizes in the range 2–10 &mgr;m, with an accuracy of 0.2 &mgr;m in beamwaist measurements. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359838

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This article gives formulas for calculating the diffraction efficiency of gratings with modulation that varies along the direction perpendicular to the grating vector. The analysis uses coupled‐wave theory for mixed (phase and absorption) hologram gratings. General solutions for diffracted (signal) and undiffracted (reference) waves are given. The diffraction efficiency calculated for some special cases is compared with that for a uniform grating. Angle and wavelength mismatch from the Bragg condition is also discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359839

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A theory for laminar flow through randomly distributed magnetic spheres which uses an effective medium treatment (EMT) is presented. In the EMT, the system of fluid and spheres is replaced by a composite sphere—a representative sphere of radiusaenclosed by a fluid shell of radiusb—embedded in an effective medium of different viscosity. The velocity fields in the fluid shell and in the effective medium as a function of sphere volume packing fraction (&ggr;3=a3/b3) or density of spheres in liquid are determined by using Green’s theorem and proper boundary conditions. The results are applied to study the capture of paramagnetic and diamagnetic particles by an assemblage of spheres. The capture radius as a function of &ggr; and applied magnetic field (H0) is obtained and compared with results from previous study based on Happel’s theory. The dependence of capture radius onH0is also given for various fixed values of &ggr;. Finally, filter efficiency is predicted for varying &ggr; andH0. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359840

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The properties of a microwave‐induced argon plasma produced by traveling surface wave at atmospheric pressure are investigated theoretically. A hydrokinetic model is elaborated to obtain the nonequilibrium one‐dimensional profiles of electron temperatureTe(average electron energy), electron densityne, and the first excited state population densityn4s, along the axis of a steady‐state discharge. A three‐level atomic structure is assumed for the argon atom. A particle balance is included through the continuity equations forneandn4s. These equations are coupled with an energy balance equation for the electrons. The effects of different parameters on the properties of the argon discharge are investigated: discharge tube radius, gas flow rate, resonant radiation‐escape factor, and neutral gas temperature. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360703

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We simulate in two dimensions the expansion of a plasma between biased plane parallel electrodes using the particle‐in‐cell method. Such a plasma is frequently created in many experiments by the interaction of a pulsed laser with atomic vapor or gas stream. We describe the motion of the electrons and ions and reproduce the experimentally observed bulk drift of the plasma toward the high potential electrode. This is explained in terms of the retrograde movement of the ion sheath boundary on one side of the plasma accompanied by ambipolar diffusion on the other. We estimate the reduced ion density in the plasma by observing oscillations in the space‐charge‐limited current. By calculating the plasma decay time constant and ambipolar diffusion coefficient, we note that computer simulation can generate data which is difficult to measure experimentally, and not possible to calculate analytically. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359841

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ion‐beam‐induced epitaxial crystallization (IBIEC) of Fe‐implanted Si(001) was studied by transmission electron microscopy and Rutherford backscattering spectrometry. For sufficiently high Fe doses, it was found that IBIEC at 320 °C results in sequential epitaxy of Fe silicide phases in Si, with a sequence of &ggr;‐FeSi2, &agr;‐FeSi2, and &bgr;‐FeSi2with increasing Fe concentration along the implantation profile. The critical concentrations for the &ggr;‐&agr; and &agr;‐&bgr; phase transitions were determined as ≊11 and 21 at. % Fe, respectively. The observed sequential phase formation can be correlated to the degree of lattice mismatch with the Si matrix and the stoichiometry of the silicide phases. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359842

出版商:AIP    

年代:1995

数据来源: AIP