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111.
The title compound was obtained in crystalline form suitable for X-ray structure determination. It forms crystals in the monoclinic space group P21/c with two centrosymmetric molecules in a unit cell of dimensions, a = 10.888(1) Å, b = 10.182(2) Å, c = 17.929(4) Å, β = 104.33(1)°. The central Mo2Cl2(O2C)2P2 core has effectively C2h-symmetry with the following principal dimensions: MoMo = 2.091(1) Å, MoCl = 2.405 Å, MoP = 2.566(2) Å, MoO(av.) = 2.103[4] Å, MoMoP = 104.38(7)°, and MoMoCl = 116.23(8)°.  相似文献   
112.
113.
Davidon [1] provides a variable metric algorithm for minimization calculations that achieves quadratic termination without any line searches by a method that uses positive definite second derivative approximations. We give a new and elementary proof of these termination properties. It shows the great freedom allowed by the algorithm in the choice of search directions and it explains the effect of a restart procedure.  相似文献   
114.
The invariant cross sections for π0 meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of 7 GeVc and 8 GeVc, respectively. These measurements are compared with π0 production in pp collisions at the same values of s/nucleon, and the variation of the nuclear A-dependence with pT is determined.  相似文献   
115.
An unusual form of the maximum entropy problem is considered, that includes simple bound constraints on the Fourier coefficients of the required image, as well as nonnegativity conditions on the image intensities. The algorithm avoids mixing these constraints by introducing a parameter into the objective function that is adjusted by an outer iteration. For each parameter value an inner iteration solves a large optimization calculation, whose constraints are just the simple bounds, by a combination of the conjugate gradient procedure and an active set method. An important feature is the ability to make many changes to the active set at once. The outer iteration includes a test for inconsistency of all the given constraints. The algorithm is described, a proof of convergence is given, and there are some second-hand remarks on numerical results.  相似文献   
116.
The intermediate and forward gamma detectors of EHS are used to reconstructπ°'s produced by 360 GeV/cpp interactions in the Rapid Cycling Bubble Chamber (RCBC). Using thepp forwardbackward symmetry, the inclusiveπ° production cross section is obtainedσ π°=(132±11) mb. The averageπ° multiplicity is determined as a function of the charged particle multiplicity. The (1?x) dependence is given for differentp T regions.  相似文献   
117.
Time-resolved spectroscopy measurements on tetracene doped fluorene provide a crucial test for models proposed to explain the observed time dependent energy transfer rates in similar doped organic crystals. The results verify the importance of activator induced host traps.  相似文献   
118.
Laser-excited, time-resolved spectroscopy techniques were used to investigate host-sensitized energy transfer in bismuth germanate crystals doped with erbium. The transfer characteristics at room temperature are consistent with a thermally-activated migration process. The transfer rate decreases exponentially as temperature is lowered and reaches a minimum near 75 K. An increase in the transfer rate is observed as temperature is lowered further and the transfer characteristics become consistent with a single step dipole-dipole interaction process. This low temperature behavior is correlated with the observations in undoped bismuth germanate at these temperatures of a significant shift to lower energy of the fluorescence peak position and a significant increase in the fluorescence lifetime. A trapped exciton model is proposed to explain these results.  相似文献   
119.
Phonon dispersion curves along the c-axis in GaSe derived from inelastic neutron scattering experiments are presented. A model for the rigid layer and conjugate modes is used to obtain the interlayer interaction which is shown to be of short range. A discussion of the identification of polytypes in GaSe in also given.  相似文献   
120.
Many trust region algorithms for unconstrained minimization have excellent global convergence properties if their second derivative approximations are not too large [2]. We consider how large these approximations have to be, if they prevent convergence when the objective function is bounded below and continuously differentiable. Thus we obtain a useful convergence result in the case when there is a bound on the second derivative approximations that depends linearly on the iteration number.  相似文献   
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