摘要:

Remote sensing of brightness temperatures of a scattering medium composed of spherical scatterers beneath a homogeneous surface layer is studied by using Mie scattering functions. We illustrate the effects of a surface layer by plotting the brightness temperatures as functions of frequency and viewing angle for different layer thicknesses, dielectric constants, and fractional scattering volumes. It is found that the brightness temperature increases when the loss tangent of the surface layer is increased and when the fractional volume occupied by the scatterers is decreased. In the absence of a surface layer the brightness temperature is usually decreasing as a function of frequency. The presence of a homogeneous layer may cause the brightness temperature to increase with frequency. At all viewing angles the vertical polarization is brighter than the horizontal polarization.

ISSN:0021-8979    

DOI:10.1063/1.326255

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An expression for the energy of small‐amplitude waves in a radially inhomogeneous cold‐fluid unneutralized relativistic electron beam is obtained in terms of the wave amplitudes. The result is employed together with conservation of wave energy to determine how the axial electric field strength and beam‐edge modulation associated with slow cyclotron waves change with position in an electron beam propagating along the adiabatically spatially decreasing magnetic guide field of an autoresonant collective ion accelerator. The resulting axial profiles are found to depart markedly from those of earlier radially homogeneous beam calculations. Possible impacts of these findings on a planned autoresonant acceleration feasibility experiment are discussed.

ISSN:0021-8979    

DOI:10.1063/1.326256

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Light‐scattering properties of very thin or flat dielectric particles are approximately calculated by means of a method which combines Rayleigh‐Gans and Rayleigh scattering. For the approximation to be valid the shortest diameter of the particle,Rmin, must be small compared to the longest diameterRmaxand to the wavelength &lgr; of the incident radiation. The method is applied to needles and circular disks and yields the scattering matrix and the differential and total scattering cross section in the lowest order ofRmin/RmaxandRmin/&lgr;. For the disks the total cross section is calculated only in the limiting cases of long and short wavelengths.

ISSN:0021-8979    

DOI:10.1063/1.326257

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The results of a systematic investigation of the power flow along the Oak Ridge National Laboratory/Princeton Large Torus (ORNL/PLT) neutral beam line, using an intense modified duoPIGatron source with a 22‐cm active grid diameter and 1799 circular apertures that provide 53% transparency, are reported. The variation of power deposited on the different components of the beam line is measured over a wide range of perveance values. The maximum efficiency for beam power transmitted through a 20×25‐cm aperture located 4.1 m downstream was found to be 41%. This efficiency was raised to 53% when a voltage of about 175 V was applied to preaccelerate the ions entering the extraction apertures. Transmission efficiencies approaching 60% were obtained using shaped apertures on the plasma grid. Higher efficiencies should be attainable when used for PLT injection since the acceptance angle for the Princeton tokamak is 11% higher than that of the test facility. Detailed analysis of the results using straight circular apertures without precel voltage suggests that the power‐deposition profiles have broad wings that significantly affect the transmission efficiency. The results allow optimization of the performance of the beam line and provide guidelines for designing future multimegawatt neutral beam lines.

ISSN:0021-8979    

DOI:10.1063/1.326258

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The magnetic field detectable outside the chest arising from the heart is analyzed using Maxwell’s equations. It is shown to consist of two contributions: (i) the field arising from the heart’s electrical activity, commonly known as the magnetocardiogram, and (ii) a contribution occurring only in the presence of an external magnetic field arising from the motion of diamagnetic material, principally blood. The latter contribution has been studied by means of a superconducting gradiometer in model circulatory systems consisting of plastic or rubber ventricles filled and emptied by pumps and tubing, and has been shown to be readily detectable in magnetic fields comparable to that of the earth. The effect has also been measured with human subjects, suggesting the possibility of clinical application of our results.

ISSN:0021-8979    

DOI:10.1063/1.326259

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The properties of a physically asymmetric three‐element electrostatic lens have been calculated numerically for voltage‐symmetric and voltage‐asymmetric cases. The lens has low chromatic aberration,Cc∞/f < 0.5, when operated in the voltage‐asymmetric mode with voltage ratiosVfinal/Vinitialas low as 2. Calculations of beam diameter versus current with realistic field electron emission parameters ofdI/d&OHgr;=1 mA sr−1and &Dgr;E=2 eV at 5 kV emitter voltage show that at 30‐kV final‐beam voltage 250 nA current could be focused into a 0.25‐&mgr;m spot at 5 cm working distance, with an emitter‐lens separation of 1.5 cm. It is shown that while the two‐element immersion lens is inappropriate for high‐current microprobe applications, the three‐element asymmetric lens is well suited for this work.

ISSN:0021-8979    

DOI:10.1063/1.326260

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We performed a series of tests on the propagation of intense electron beams with &ngr;/&ggr;?0.40 and 0.85 in a vacuum (∼10−4Torr) and in a few gases (nitrogen, helium, and carbon dioxide) at pressures ranging from 50 mTorr to 1 Torr. Beam currents were recorded step by step by a Faraday cup movable along the drift‐tube axis up to about (1/2) m from the anode of the field emission diode. Current neutralization and almost complete transport of the electron beam along the drift tube occur at different pressures in different gases. Structures in the transmitted currents appear as a function of the drift distance, markedly at pressures slightly lower than that of complete neutralization of the beam. They are in good agreement with Lawson’s predictions.

ISSN:0021-8979    

DOI:10.1063/1.326261

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A Fourier‐Bessel series representation in terms ofI0Bessel functions is given for the potential distribution in certain open Einzel‐ or immersion‐type electrostatic configurations with rotational symmetry described by &fgr; (A,z) =F(z), 0<z<L; and &fgr; (A,z) =0 for allz<0 and for allz≳L.F(z) is a given function andAandLare constants. The method is a direct one—no iterations or matrix inversions are required—and a superior rate of convergence in the paraxial region is achieved through the elimination ofJ0Bessel functions. The precision reached is apparently limited by the computer word length only, programming is of a simple nature, and computer memory requirements are modest enough to allow implementation on small desk‐top computers.

ISSN:0021-8979    

DOI:10.1063/1.326245

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A simple method is presented of numerically solving inhomogeneous planar waveguide problems. The characteristic mode equation given here to determine rigorous solutions is similar to WKB’s mode equation and is solved by the step-by-step numerical method. Examples are given for the sake of comparison with other results.

ISSN:0021-8979    

DOI:10.1063/1.326246

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An accelerated aging test is performed at temperatures of 70, 110, and 140 °C to estimate the activation energy. Samples are operated in the LED mode at high temperatures of 110 and 140 °C. At 70 °C samples are operated in lasing mode of optical output 0.27 mW/&mgr;m. The laser lifetime is defined to be a time at which the cw threshold current measured at a standard temperature 25 °C reaches 1.5 times the initial value. The activation energy 0.74 eV is obtained. It is shown that the degradation does not depend on the optical output power below the power level of 0.3 mW/&mgr;m and that the activation energy is indifferent to the operation mode, LED mode, or lasing mode, at a low power level. The use of the LED mode operation and the definition of the laser lifetime in terms of the characteristics at low standard temperature enable one to perform the accelerated aging test at high temperatures above 110 °C where cw operation is almost impossible. The reliability is examined at 70 °C using 50 samples and an average laser lifetime is obtained. The application of the activation energy gives the average laser lifetime at the junction temperature of 30 °C to be 3×105h.

ISSN:0021-8979    

DOI:10.1063/1.326247

出版商:AIP    

年代:1979

数据来源: AIP