摘要:

A simple method is shown for calculating the relaxation time spectrum which controls the rate at which a process following simple first‐order kinetics takes place. The method involves unfolding a Fredholm equation of the first kind using least‐squares and then using a modified nonlinear regression rather than a linear least‐squares technique, thereby avoiding the highly oscillatory solutions which tend to occur with the latter with reduced mesh spacing or an increased number of bins. The validity and accuracy of the method for analyzing experimental data to reproduce various known input spectra are assessed and found to be excellent for data with no experimental error. For data with simulated experimental error with standard deviations up to &sgr;=0.05 the method provides acceptable approximate solutions even though no exact solution is expected. Increasing the magnitude of the experimental error for a single lognormal input spectrum appears to have an increasing but nonsystematic effect upon the uncertainty of the approximate solution. Effects due to increasing the number of bins in the interval over which the spectrum is calculated are assessed and shown not to appreciably change the results, even for up to 60 bins. The methods is shown to be applicable to a wide variety of input spectra including single and double lognormal and box distributions. Importantly, in each of the cases studied the approximate solution appeared both to be unique and to converge toward the known input spectrum. Based upon this validation it is concluded that this method has applicability to a wide range of problems in which simple exponential decay is occurring with a spectrum of time constants. It may also be useful for problems with different kernals than that for first order kinetics; however, careful validation will be required.

ISSN:0021-8979    

DOI:10.1063/1.332390

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Commercial manganin stress gauges are used in planar impact experiments to determine spall strengths of variously heat‐treated 2024A1 specimens. A one‐dimensional Lagrangian code is used to find the best fit of calculated versus experimental stress histories by varying the spall strength in the code and using a simple threshold criterion. We found values in the range of 1.2–1.75 GPa for spall strengths of the differently treated specimens. These values are in good agreement with published data obtained by other methods. We also confirmed the spall strength values by a series of low‐stress experiments resulting in only incipient spalls. A specimen of 2024T351 which was shocked perpendicular to the rolling direction has a lower spall strength (by about 0.3 GPa) than a specimen shocked along the rolling direction. This difference is very close to that predicted earlier.

ISSN:0021-8979    

DOI:10.1063/1.332391

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An Al/ZnSe:Mn/ITO dc‐operated electroluminescent (EL) cell was prepared by molecular beam deposition. The threshold voltage was 6–10 V, which is the lowest value in these types of EL cells reported so far. The deposited ZnSe:Mn layer was a polycrystal with only (111) orientation and exhibited sharp x‐ray diffraction and reflection high energy electron diffraction patterns which have been hardly obtained by conventional evaporation methods. This low threshold voltage EL cell has a great potential of application in panel displays because of the low cost and the large size of Indium‐Tin‐Oxide (ITO)‐coated glass substrates.

ISSN:0021-8979    

DOI:10.1063/1.332392

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The properties of Tb3+in crystals of three stoichiometric Tb compounds, viz., TbP5O14, TbLiP4O12, and TbAl3(BO3)4have been studied by spectroscopic absorption and emission methods to evaluate these materials as hosts for Tb3+laser applications. The absorption spectra between 50000 and 200 cm−1at 300 °K, the emission spectra between 27000 and 14000 cm−1at 300 °K, and the fluorescence decay characteristics of5D4emission at 300 and 5 °K are given. Because of cross relaxation, the5D3and5G6emissions in all three materials were concentration‐quenched strongly with a similar behavior observed in other hosts. Quenching in the5D4states was negligible except for TbAl3(BO3)4where moderate quenching was observed due to energy transfer to nonradiative traps. Transition rates between various states were calculated by using the Judd–Ofelt approach and a first order wavefunction set, and good fit was obtained between the calculated and experimental parameters. The transition rates were then used to find the emission cross sections of various lines.

ISSN:0021-8979    

DOI:10.1063/1.332393

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A realistic analytic central potential is used to generate wave functions for the ground and excited states of singly‐ionized beryllium. Generalized oscillator strengths and integrated cross sections from threshold to 5 keV are calculated in the Born approximation for 2s‐ns, 2s‐npand 2s‐ndexcitations. Comparison of the cross sections with experimental and theoretical data is discussed for the 2s‐2ptransition.

ISSN:0021-8979    

DOI:10.1063/1.332394

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A wave packet reflected totally at an interface between two media may undergo the Goos–Ha¨nchen shift and associated time delay. Two different theoretical approaches have been presented so far to evaluate this phenomenon. One is the stationary‐phase method and the other is the conventional energy‐flux method. In this paper, a certain deficiency existing in the conventional energy‐flux method is pointed out and a new energy‐flux method is derived based on an accurate argument of the conservation of energy flux. The new energy‐flux method confirms the consistency of the predictions by the stationary‐phase method from the point of view of the conservation of energy.

ISSN:0021-8979    

DOI:10.1063/1.332395

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Operating characteristics are described for broad contact double‐heterostructure (DH) lasers grown by molecular beam epitaxy (MBE), with In0.53Ga0.47As active layers lattice matched to InP. These were operated atT≊293 K, with (low duty cycle) pulses of current from 1.5 to 3Ith. The lowest threshold current density,Jth≊2800 A/cm2, is some 40% higher than an ideal cavity expectation. Under these strong pulse conditions, a multimode output was observed, with pronounced spatially filamentary characteristics. The output was plane polarized perpendicular to the active layer, indicative of TM mode dominance. This nontypical polarization, considered in conjunction with an indicated trend of external differential quantum efficiency increasing with length, is consistent with polarization‐selective internal losses or polarization‐dependent gain as the mode‐controlling feature, rather than facet reflection losses.

ISSN:0021-8979    

DOI:10.1063/1.332396

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The kinetics of gases due to absorption of infrared radiation on closed cells has been discussed with the use of the Einstein coefficient for emission and absorption of radiation. The expression derived for the magnitude of pressure pulse in the cell explains satisfactorily the observed characteristics of the pneumatic detector.

ISSN:0021-8979    

DOI:10.1063/1.332370

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We present calculations of electron impact collision strengths and spontaneous radiative decay rates for neon‐like krypton (Kr XXVII) for the 2s22p6, 2s22p53s, 2s22p53p, and 2s22p53dconfigurations. From these atomic data the level populations as a function of the electron density were calculated at two temperatures (Te=1×107K andTe=3×107K). The analysis of level populations shows that a volume of krypton in which a significant number of the ions are in the Kr XXVII degree of ionization can produce a significant gain in transitions between the 2s22p53sand 2s22p53pconfigurations. At an electron density of 1×1019cm−3the plasma length has to be on the order of 1 m; at a density of 1×1021cm−3the length is reduced to about 0.5 cm; and at an electron density of 1×1022cm−3the length of the plasma is further reduced to about 1 mm.

ISSN:0021-8979    

DOI:10.1063/1.332371

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A formalism is developed for describing the evolution of picosecond mode‐locked pulses in synchronously pumped dye lasers. The finite phase memory of the molecular wave functions is included, and it is found that the resultant coherence effects can be dominant for operation close to exact synchrony. Considerations of the isotropic molecular orientational distribution and the finite vibrational relaxation times are also essential in obtaining quantitative agreement with experimental results.

ISSN:0021-8979    

DOI:10.1063/1.332372

出版商:AIP    

年代:1983

数据来源: AIP