摘要:

A procedure for synthesizing the x‐ray intensity profile for x‐ray optical systems employing curved diffractors is presented. The synthesis takes account of the effects of misalignment, the solid angle, and the convergence or divergence of the diffracted x rays. Broadening effects due to finite source size, wavelength spread, and presence of polychromatic radiation have also been included. The broadening effects on the intensity profile are demonstrated analytically. By comparing experimental results with results from the synthesis method, curved diffractor’s parameters (rocking curve width and peak reflectivity) were quantitatively evaluated for mica, silicon, graphite, and LiF crystals at three x‐ray wavelengths.

ISSN:0021-8979    

DOI:10.1063/1.354615

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The chemical species of the neutral radicals in the methane microwave (MW) discharge plasma were studied by quadrupole mass spectrometry in combination with a Li+ion attachment technique. The approach is to have a MW discharge flow pass a lithium ion emitter and then to analyze, by quadrupole mass spectrometry, all ions formed by lithium ion attachment. Mainly, radicals such as CnH2n+1(n=2–11) and CnH2n−1(n=2–11) were detected. Species such as C4H3, C5H5, and C6H5may also be produced in the process. Many such species have been identified for the first time. The presence of these species is evaluated by comparison with results from optical spectroscopy and threshold ionization mass spectrometry.

ISSN:0021-8979    

DOI:10.1063/1.354616

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

By comparing the radiated energy densities in the Fresnel’s region due to excitations by a cw (continuous wave) sin &ohgr;0tand a single‐cycle sin &ohgr;0t, it is shown that the single‐cycle pulse is more efficient in collimating (or focusing) the energy in the vicinity of the disk axis. We have also considered a single‐cycle cos &ohgr;0tpulse as an exciting source, which may be more academic than realistic. Nonetheless, the results shed some light in showing clearly that the shorter the rise time of a pulse, the slower is the decay of the radiated energy, and hence, it is highly efficient in focusing the energy in front of the radiating device. It follows then that whenever the transmission of a collimated beam of energy to a large distance along the axis of the radiating aperture is desired, it can be accomplished more efficiently by using a short pulse, instead of a cw source.

ISSN:0021-8979    

DOI:10.1063/1.354617

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An investigation of a chalcogenide glass thin‐film Fabry–Perot cavity has been performed in picosecond time regime. Nonlinear behavior of the structure derives from both nonlinear absorption of the material and changes in the resonance conditions of the cavity. The conditions to have bistable behavior have been established.

ISSN:0021-8979    

DOI:10.1063/1.354618

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A high frequency, piezoelectric, laminated plate theory is developed and presented for the purpose of modeling and analyzing piezoelectric thin‐film resonators and filters. The laminated plate equations are extensions of anisotropic composite plate theories to include piezoelectric effects and capabilities for modeling harmonic overtones of thickness‐shear vibrations. Two‐dimensional equations of motion for piezoelectric laminates were deduced from the three‐dimensional equations of linear piezoelectricity by expanding the mechanical displacements and electric potential in a series of trigonometric function, and obtaining stress resultants by integrating through the plate thickness. Relations for handling the mechanical and electrical effects of platings on the top and bottom surfaces of the laminate are derived. A new matrix method of correcting the cutoff frequencies is presented. This matrix method could also be used to efficiently correct the cutoff frequencies of anynth order plate laminate theories which employ Mindlin’s form of polynomial expansion of mechanical displacements and electric potential through the plate thickness. The first order laminated plate theory with correction factors for cutoff frequencies and slope of the flexural branch at large frequencies was applied to a 2‐layer, zinc oxide‐silicon strip, and a 3‐layer, zinc oxide‐zinc oxide‐silicon strip. Open circuit, dispersion relations were generated for a range of volume fractions and compared to the exact dispersion relations.Both the 2‐layer and 3‐layer strip show similar qualitative comparison: The present theory compares fairly well with the exact dispersion relation for real wave numbers and nonpropagating (imaginary) wave numbers which are smaller than 0.5i. The extensional branch, and thickness‐shear branches begin to deviate from the exact solution when the nondimensionalized frequency is greater than one. Consequently, to maintain accuracy of solutions when using the present first order laminated plate theory, one should limit the calculation of resonant, nondimensionalized frequencies to less than 1.1. Results for the frequency spectrum in the vicinity of the open circuit, fundamental thickness‐shear frequency, and modes shapes were presented for the 2‐layer strip with fixed edges, and a volume fraction of silicon equal to 0.2. The technically important fundamental thickness‐shear mode is found to have the shear component strongly coupled with extensional component.

ISSN:0021-8979    

DOI:10.1063/1.354619

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Thermal diffusivities of high quality (‐)2‐(&agr;‐methylbenzylamino)‐5‐nitropyridine (MBANP) single crystals were measured in different directions by the flash diffusivity method. The complete thermal conductivity tensor at temperatures of 295, 323, and 349 K was then obtained for this monoclinic crystal from the thermal diffusivity, specific heat, and density data. For instance, the thermal conductivity coefficients at 295 K arek1=0.27 W/mK,k2=0.29 W/mK, andk3=0.20 W/mK. The peak melting point of MBANP lies at 357.3 K, whereas the corresponding enthalpy of melting &Dgr;Hmhas a value 67.2 J/g.  

ISSN:0021-8979    

DOI:10.1063/1.354620

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Quality and pumping of an electron beam by means of the inhomogeneous electrostatic field at an anode aperture are investigated using numerical simulation. A specially developed relativistic particle‐in‐cell code, described here, is employed. The longitudinal velocity spread and the pitch ratio of the beam electrons are derived for different aperture radii and cathode‐aperture distances. The presented results could be practically useful for operation of high‐power cyclotron resonance masers with a sharpened cathode and an anode aperture. The beam pumping in such devices is typically achieved by more complicated systems (pumping magnet, adiabatically changing magnetic field, etc.). The numerical simulations show a significant pumping effect coming from the anode aperture itself.

ISSN:0021-8979    

DOI:10.1063/1.355320

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Radiation from 8 to 60 GHz is generated by injecting counterstreaming, high‐power (up to 50 keV and 4 A) electron beams into an unmagnetized, plasma‐loaded waveguide. The radiation is emitted at twice the plasma frequency and is amplitude modulated on the ion plasma frequency time scale. The beam‐to‐millimeter‐wave power conversion efficiency at 31 GHz is ≳0.04%. A turbulence theory model is consistent with the radiation characteristics and power scalings.

ISSN:0021-8979    

DOI:10.1063/1.354621

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A steep plasma edge in infrared reflectivity spectra of Hg1−xCdxTe and HgSe:Fe has been observed. It is predicted that the edge is sensitive to the variation of carrier concentration, which indicates the possibility of developing a fast light‐controlled switch for infrared radiation as well as a new approach of infrared modulation and detection. The modulation gain in power and detectivity limited by the generation‐recombination process has been calculated and compared with the photoconductive counterpart.

ISSN:0021-8979    

DOI:10.1063/1.354622

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The transfer of energy between the plasma and the iron anode and the evaporation of metal were taken into account in modeling a short free‐burning arc in argon at atmospheric pressure. The presence of metal vapor in the plasma modifies the electrical conductivity and the radiated power and leads to arc cooling in the anode region. In return, the arc cooling modifies the rate of vaporization of the anode and thus the calculated concentration of iron vapor in the arc.

ISSN:0021-8979    

DOI:10.1063/1.354624

出版商:AIP    

年代:1993

数据来源: AIP