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961.
G. A. Ayçik 《Journal of Radioanalytical and Nuclear Chemistry》1992,157(1):115-123
To perform quantitative analysis of Ge(Li) spectra, not only energy calibration but also efficiency calibration procedures are done. Although the use of standard sample volume, mass, density and geometry is preferable, this optimum is not always possible. So to achieve an optimization is the main objective of the work reported here. Efficiencies have to be determined as a function of energy, density, thickness, mass of sample, intensity, and source-to-detector distance. 相似文献
962.
963.
We study the 2D motion of independent point particles colliding with a periodic array of circular obstacles. The interaction between the particles and the obstacles is described by a total accommodation reflection law. Assuming that the array of scatterers has finite horizon, the density of particles is approximated by the solution of a diffusion equation in the long-time and large-scale regime. The proof relies on a multiscale asymptotics and gives the order of approximation. 相似文献
964.
Y.K. Yoḡurtçu A.J. Miller G.A. Saunders 《Journal of Physics and Chemistry of Solids》1981,42(1):49-56
The six third order elastic constants of GaP have been obtained from measurements of the effect of hydrostatic and uniaxial pressures on ultrasonic wave velocities. The valence force field model has been used to obtain the bond-bending and stretching force constants. Confirmatory evidence is added to the hypotheses that zinc blende structure crystals undergo the densification transition under pressure when (1) a modified Born stability criterion that equals about 0.2 is reached at the phase transition pressure Pt, and (2) the ratio of the second order bond-bending βt to bond-stretching αt, force constants is about 0.1. These findings suggest that a macroscopic shear takes place at the transition 相似文献
965.
966.
967.
2,3-Bis (bromomethyl)-1,3 butadiene 1 was found to be a good reagent for C-dialkylation by phase transfer reaction. Adducts of 1 with propiolic acid are versatile precursors of 2H-isoindoles and of 2,3-dithianaphtelenes. 相似文献
968.
2-Phenyl-1,3,2-dioxaphosphorinane rearranges at 250°C to afford 2-phenyl-2-oxo-l,2-oxaphospholane which is, in turn, converted into the 2-thio derivative by P4S10. This cyclic thiophosphinate reacts with nickelocene and allyl iodide to yield (L = 2-phenyl-1,2-oxaphospholane) by reduction—complexation. The same scheme is successfully applied to the 1-oxa-2-phosphacyclohepta-4,6-diene nucleus. Thus, the PIV=S reduction—complexation process works with POC compounds. This is not the case with PSC compounds (for example, with dithiophosphinates). Some chemistry of 2-phenyl-l,3,2-dithiaphosphorinane is also described: Arbuzov reaction with PhCH2Br, thermal rearrangement and complexation with nickelocene and allyl iodide. 相似文献
969.
The vacuum uv emission of the 15N22+ ion has been recorded for the first time. Rotational analysis of two bands, analogous to those already observed in the case of the natural isotope, confirm their assignment to the D1Σu+-X1Σg+ (0, 0) and (1, 1) bands. More precise data are also obtained for the 3Σg? state which perturbs ground state vibrational levels. 相似文献
970.
François Robert 《Linear algebra and its applications》1978,19(3):237-250
The eigenelements of a Boolean matrix are defined. A “normal form” is given, which allows one to characterize those Boolean matrices the (Boolean) spectral radius of which is 0 or 1. Then the following results are proved: a Boolean Perron-Frobenius theorem, a “Truncated” Boolean Stein-Rosenberg theorem, and a Boolean Stein-Rosenberg theorem, which are the exact Boolean analoques of the usual corresponding theorems concerning real nonnegative matrices. Applications of these results are given elsewhere. 相似文献