摘要:

Cylindrical aluminum shells have been imploded at velocities ≳2 mm/&mgr;s in aZ‐pinch discharge driven by a 100‐kJ capacitor bank. The velocity and symmetry of the imploding liners were determined from flash x‐ray pictures, and the compression of an axial magnetic field was measured with pickup coils. The results are consistent with numerical calculations of the implosion dynamics. The implosions are symmetric and stable when strongly driven. Buckling is observed in slower implosions

ISSN:0021-8979    

DOI:10.1063/1.331599

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Voltage breakdowns of some narrow gap electrodes [2–10 mil (0.05–0.25 mm)] on polymeric insulator surfaces (epoxy‐glass and triazine) have been examined over the pressure range from atmospheric pressure to 127 Torr and are shown to be an air breakdown modified by the presence of the insulator. Breakdown values as a function of the number of the breakdown and discharge energy level were also examined. In the worst case the breakdown voltage was observed to decrease by approximately 1300 V after about five successive breakdowns. The breakdown voltage between narrowly spaced metallic contacts on dielectric surfaces has been assumed to exhibit a Gaussian distribution. Non‐Gaussian, bimodal distributions have been observed in the present work. These bimodal distributions, found on fine line epoxy‐glass and triazine printed wiring boards, and attempts for explanation in terms of the flashover discharge initiating mechanisms, including the effects of ultraviolet radiation and a negative‐ion flux on breakdown, are described. Negative ions appear to reduce the standard deviation but do not reduce the breakdown voltage. Ultraviolet radiation reduces both the standard deviation and the breakdown voltage. Increasing the conductor overlap distance (line length) reduced the breakdown voltage.

ISSN:0021-8979    

DOI:10.1063/1.331600

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A new numerical method is presented for calculating the particle‐size distribution function of dilute particle systems from Small Angle Scattering data. The size distribution function, in order to be always positive, is approximated by the square of a combination of cubicB‐splines. The coefficients of the combination are calculated in reciprocal space using the weighted least squares principle, which leads to a variational problem, solved by a Newton‐Gauss‐Marquardt iterative technique. A strategy is presented to enhance resolution in correspondence to the peaks of the distribution. Some results obtained on simulated and experimental points are presented, showing the accuracy of the method.

ISSN:0021-8979    

DOI:10.1063/1.329983

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Rietveld analyses of room‐temperature neutron powder diffraction data for seven Nd2(CoxFe1−x)17alloys (x= 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) are reported. In the ternary systems we find that thec‐type transition metal sites are preferentially occupied by Fe ions; concomitantly, thedandhsites have Co occupations larger than those predicted by stoichiometry, while thefsites deviate only slightly from random occupation. The magnetic moments obtained from the data refinements indicate a transition from a low to a high spin state on thed,  f, andhsites as Fe is incorporated into the structure; a reverse trend is exhibited by the moments on thecsite.

ISSN:0021-8979    

DOI:10.1063/1.331601

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

We apply the matrix representation technique to determine the concentrations of three dye components in the liquid‐crystal mixture needed to make a black‐and‐white guest‐host display. This method employs the Newton‐Raphson iterative process to match the tristimulus values of the mixture to the tristimulus values of the achromatic color. The color matches are thus metameric rather than spectral and hence depend upon the illuminant type. We give examples which show that practically any yellow, red, and blue dye components can be mixed to obtain a neutral color for a given illuminant, but that such mixtures generally have some coloration when viewed under other illuminant types. By extending the matrix representation technique into six dimensions, we show that it is possible to select optimum dye components according to the width and centroid wavelength of their absorption curves. These optimized components minimize the sensitivity of the neutral color to changes in illuminant type. We demonstrate that displays can be made with three optimized dye components which are achromatic under the extremes of both daylight and incandescent illumination. The absorption bands of these optimized dye components must be about 100 nm wide or wider, and the centroids of their respective absorption curves must be located within the ranges 445±10, 540±10, and 650±10 nm. We find that Heilmeier‐ and White‐and‐Taylor‐type displays generally require different dye formulations. Examples are given for both display types.

ISSN:0021-8979    

DOI:10.1063/1.331602

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Exposure of MgAl2O4crystals to137Cs &ggr; rays produces a broad absorption complex centered near 3 eV and at the same time destroys absorption at 4.8 and 6.4 eV which is attributed to charge transfer transitions on octahedral Fe3+impurity ions. Thermal and optical bleaching of the 3‐eV absorption complex in crystals with different Fe3+concentration reveal that this complex is composed of absorption bands located at 2.8, 3.1, 3.6, and possibly at 3.9 eV. Analysis of the intense, persistent afterglow and conductivity after &ggr;‐ray exposure and thermally stimulated conductivity discloses a very high concentration of shallow electron traps with a prominent set of these traps having a thermal depth of ∼0.9 eV. It is proposed that antistructure disorder, e.g., Al3+ions on tetrahedral sites, is responsible for a substantial portion of these electron traps.

ISSN:0021-8979    

DOI:10.1063/1.331603

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Dislocations in highly perfect quartz crystals have been characterized by correlating experimentally observed section patterns with computer simulations. The Burgers vector observed is the shortest translation vector of the quartz lattice. In cases, such as quartz, where the simple geometrical criteria fail, computer simulation methods are a powerful aid in establishing the Burgers vector of dislocations.

ISSN:0021-8979    

DOI:10.1063/1.331604

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Pulsed electron beam with an energy fluence of 1.0 J/cm2was irradiated on (100) and (111) Si implanted with 1×1016As+/cm2at 40 keV. Highly dopedn+layers with peak carrier concentrations of 8×1020/cm3and 7×1020/cm3for (100) and (111) samples were obtained, respectively, after electron beam irradiation. The effect of additional thermal treatment on electrical behaviors and crystalline quality of electron‐beam annealed samples has been investigated. Carrier concentration decreased with increasing additional annealing temperature up to 800 °C and it increased above 800 °C, where the system approached a thermal equilibrium and at the same time thermal diffusion of As occurs. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) observations revealed that no residual damage remained after electron beam irradiation but dislocation loops were formed during the course of additional thermal annealing.

ISSN:0021-8979    

DOI:10.1063/1.329876

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

n‐type ZnSe layers with a room‐temperature resistivity of less than 0.05 &OHgr; cm and mobilities of ∼400 cm2/(V sec) have been grown on (100) GaAs by organometallic chemical vapor deposition (OM‐CVD), using triethylaluminum as a dopant. No further treatment after the layer growth is necessary in order to achieve the high electrical conductivity. An analysis of the low‐temperature electrical transport data and of the photoluminescence data, however, suggests that the physical properties of the layers differ from those of ZnSe prepared by other methods. Charge transport occurs via impurity‐band conduction in the more heavily doped layers and via thermally activated hopping in the more lightly doped layers rather than via thermally activated extrinsic conductivity. The degree of compensation of donors is larger than 0.5. The exact nature of the compensating centers in the material prepared by OM‐CVD is uncertain at this point, although the photoluminescence data suggest the presence of Al‐VZncomplexes.

ISSN:0021-8979    

DOI:10.1063/1.329928

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The elastic constants of the Ta‐W system were determined between 4.2 and 300 K. Anomalous behavior was detected in the temperature dependence of the shear constantc44near the critical composition of about 50% W. This anomaly is attributed to certain topoligical changes in the Fermi surface of the alloys near the critical composition. The Debye temperature for the alloys was calculated from the elastic constants.

ISSN:0021-8979    

DOI:10.1063/1.329929

出版商:AIP    

年代:1982

数据来源: AIP