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1.
A method is described for the non-destructive and accurate determination of the isotopic composition of uranium by activation
analysis. The high resolving power of Ge(Li) detectors permits easy identification on a single gamma spectrum of the gamma
peaks of239Np formed from238U by activation and those of fission products formed from235U. The ratio of the peak intensities is proportional to the238U/235U ratio in the sample. A precision of ±0.6% has been obtained. 相似文献
2.
A procedure is developed for the experimental determination of the nonlinear shear behavior of fiber-reinforced composites by testing angle-ply laminates. It is shown that, for the E glass/epoxy used in this work, the popular ±45 deg specimens fail prematurely due to transverse stresses, thus limiting the range for which the shear stress-strain curve can be obtained. By selecting an appropriate fiber orientation, ±41 deg in the present work, premature failure can be prevented and the nonlinear shear response can be obtained almost to shear failure. The experimental program involved four groups of tensile specimens (±30 deg, ±35 deg ±41 deg and ±45 deg) tested under impact conditions using a drop weight testing machine. Analysis was performed using classical plate theory and an incremental loading procedure. Some problems involved in conducting dynamic tests are discussed and a solution is presented. 相似文献
3.
W. Westmeier U. Reus R. A. Esterlund J. Gilat P. Patzelt 《Zeitschrift für Physik A Hadrons and Nuclei》1981,299(3):277-278
Thin targets of natural Fe have been irradiated with132xe ions at beam energies of 5.00, 5.90, and 7.15 MeV/u. Mass yields for projectile-like and symmetric products were evaluated, and their ratio as a function of beam energy determined. The results are consistent with previously-determined thick-target radiochemical data, and are not consistent with published on-line counter data for the same system. 相似文献
4.
David Gilat 《Israel Journal of Mathematics》1988,63(3):270-280
For eachp>1, the supremum,S, of the absolute value of a martingale terminating at a random variableX inL
p, satisfiesES≦(Γ(q))1/q‖X‖p (q=p(p-1)-1).The maximum,M, of a mean-zero martingale which starts at zero and terminates atX, satisfiesES≦(Γ(q))1/q‖X‖p (q=p(p-1)-1), whereσ
q is the unique solution of the equationt = ‖Z −t ‖
q
for an exponentially distributed random variableZ with mean 1.σ
p has other characterizations and satisfies lim
p‖
q
− 1
σ
q =c withc determined byce
c+1 = 1. Equalities in (1) and (2) are attainable by appropriate martingales which can be realized as stopped segments of Brownian
motion. A presumably new property of the exponential distribution is obtained en route to inequality (2). 相似文献
5.
J. Aaronson R. Burton H. Dehling D. Gilat T. Hill B. Weiss 《Transactions of the American Mathematical Society》1996,348(7):2845-2866
Strong laws of large numbers are given for -statistics (linear combinations of order statistics) and for -statistics (averages of kernels of random samples) for ergodic stationary processes, extending classical theorems of Hoeffding and of Helmers for iid sequences. Examples are given to show that strong and even weak convergence may fail if the given sufficient conditions are not satisfied, and an application is given to estimation of correlation dimension of invariant measures.
6.
G. Gilat 《Solid State Communications》1974,14(3):263-265
Derivatives of spectral functions play a central role in the calculation of modulation spectroscopy. The general expressions for these derivatives are obtained. Transition probabilities and lifetime effects are also treated and incorporated in the general framework of the Brillouin zone integration of these derivatives. 相似文献
7.
G. Gilat 《Foundations of Physics Letters》1990,3(2):189-196
A new concept of quantitative measure of the amount of structural asymmetry is introduced and defined by maximal overlap between two enantiomers of the same chiral body. This concept is to be called chiral coefficient, and it can readily be extended to physical properties such as mass or electronic wave-function distributions over chiral objects such as molecules or unit cells in crystals. The mathematical aspects of these coefficients are discussed. There exist two cases of maximal overlaps, symmetric and asymmetric, where for the asymmetric case there exist two positions of maximal overlap. It is also shown that there always exists a natural directionz for every asymmetric body for any physical property treated. The possibility of quantizing structural asymmetry is discussed, and, if it exists, it may be associated with the naturalz axis of the chiral system. Possible applications of asymmetry quantification are discussed. 相似文献
8.
M. Hokka J. Kokkonen J. Seidt T. Matrka A. Gilat V.-T. Kuokkala 《Experimental Mechanics》2012,52(2):195-203
Mechanical properties of most metallic materials can be improved by reducing their grain size. One of the methods used to
reduce the grain size even to the nanometer level is the severe plastic deformation processing. Equal Channel Angular Pressing
(ECAP) is one of the most promising severe plastic deformation processes for the nanocrystallization of ductile metals. Nanocrystalline
and ultrafine grained metals usually have significantly higher strength properties but lower tensile ductility compared to
the coarse grained metals. In this work, the torsion properties of ECAP processed ultrafine grained pure 1070 aluminum were
studied in a wide range of strain rates using both servohydraulic materials testing machines and Hopkinson Split Bar techniques.
The material exhibits extremely high ductility in torsion and the specimens did not fail even after 300% of strain. Pronounced
yield point behavior was observed at strain rates 500 s−1 and higher, whereas at lower strain rates the yielding was continuous. The material showed slight strain softening at the
strain rate of 10−4 s−1, almost ideally plastic behavior at strain rates between 10−3 s−1 and 500 s−1, and slight but increasing strain hardening at strain rates higher than that. The tests were monitored using digital cameras,
and the strain distributions on the surface of the specimens were calculated using digital image correlation. The strain in
the specimen localized very rapidly after yielding at all strain rates, and the localization lead to the development of a
shear band. At high strain rates the shear band developed faster than at low strain rates. 相似文献
9.
罗亦孝 J.H.Hamilton J.O.Rasmussen A.V.Ramayya C.Goodin A.V.Daniel N.J.Stone 朱胜江 J.K.Hwang 刘少华 C.J.Beyer 李科 H.L.Crowell D.Almehed S.Frauendorf A.Covello V.Dimitrov 张敬业 车兴来 姜卓 D.Fong A.Gelberg I.Stefanescu A.Gargano E.F.Jones P.M.Gore I.Y.Lee G.M.Ter-Akopian M.A.Stoyer R.Donangelo 马文超 J.D.Cole J.Kormicki 张学谦 S.C.Wu J.Gilat T.N.Ginter S.J.Asztalos 《原子核物理评论》2010,27(4):363-389
使用Gammasphere多探测器系统对252Cf裂变源瞬发γ射线进行γ-γ-γ和γ-γ(θ)符合测量,A~100(Z~40,N56)丰中子核区关于形状过渡、形状共存和形状突变的深入研究获得了新的进展。奇-Z核的系统研究揭示了从Z=39(Y)同位素的轴对称大四极形变到Z=43(Tc),44(Ru)和45(Rh)同位素中具有中等四极形变之大三轴形变的过渡。Nb(Z=41)同位素具有过渡核的特征。根据邻近同位素和同中素带交叉信息的系统性及推转壳模型(CSM)计算,Tc和Rh偶-N同位素中观察到的带交叉产生于一对h11/2中子的转动顺排。首次观察到100Nb(Z=41,N=59)的高自旋能级纲图和形变态,从而证实了100Nb中的形状共存,并确认,在Nb同位素链上,基态形状突变发生于N=58(球形)到N=59(大形变);而在Sr(Z=38),Y(Z=39)和Zr(Z=40)各同位素链上,基态形状突变均发生于N=59(球形)到N=60(大形变)。100Nb具有大形变基态,同现有理论预言相矛盾,其大形变的基态及转动带所具有的很大的和不规则的转动惯量具有重要的理论意义。对奇-质子Cs(Z=55)和La(Z=57)丰中子同位素八极激发的详细研究,发现了141,143,144Cs同位素链上电二极矩D0随中子数增加而减小的急剧变化,此前在145,147La中观察到的电二极矩D0的较缓和的减小似乎亦很陡地下延至148La。在Cs和La同位素中观察到的电二极矩D0的急剧下降很可能同偶-质子核146Ba和224Ra中观察到的电二极矩D0的急剧下降相类似,后者已获反射非对称平均场壳修正理论的成功解释。实验证明,141Cs具有很大电二极矩D0。141Cs和142Xe中观测到的很大的电二极矩D0和仅在141Cs中观察到的电二极矩D0的simplex量子数相关性需要进一步的理论研究。根据转动频率比值ω-(I)/ω+(I)的检定,同Xe同位素一样,认定Cs同位素中包括号143Cs的八极激发为八极振动,而在La同位素中存在八极形变。 相似文献
10.
Tensile tests with simultaneous full-field strain and temperature measurements at the nominal strain rates of 0.01, 0.1, 1, 200 and 3000 s?1 are presented. Three different testing methods with specimens of the same thin and flat gage-section geometry are utilized. The full-field deformation is measured on one side of the specimen, using the DIC technique with low and high speed visible cameras, and the full-field temperature is measured on the opposite side using an IR camera. Austenitic stainless steel is used as the test material. The results show that a similar deformation pattern evolves at all strain rates with an initial uniform deformation up to the strain of 0.25–0.35, followed by necking with localized deformation with a maximum strain of 0.7–0.95. The strain rate in the necking regions can exceed three times the nominal strain rate. The duration of the tests vary from 57 s at the lowest strain rate to 197 μs at the highest strain rate. The results show temperature rise at all strain rates. The temperature rise increases with strain rate as the test duration shortens and there is less time for the heat to dissipate. At a strain rate of 0.01 s?1 the temperature rise is small (up to 48 °C) but noticeable. At a strain rate of 0.1 the temperature rises up to 140 °C and at a strain rate of 1 s?1 up to 260 °C. The temperature increase in the tests at strain rates of 200 s?1 and 3000 s?1 is nearly the same with the maximum temperature reaching 375 °C. 相似文献