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51.
We present a novel semi-parametric model for two-sample survival data, and an estimation method with a simple, closed-form solution. We study analytically the asymptotics of the estimators, and conduct a small simulation study. 相似文献
52.
We present a method for constructing families of isospectral systems, using linear representations of finite groups. We focus
on quantum graphs, for which we give a complete treatment. However, the method presented can be applied to other systems such
as manifolds and two-dimensional drums. This is demonstrated by reproducing some known isospectral drums, and new examples
are obtained as well. In particular, Sunada’s method (Ann. Math. 121, 169–186, 1985) is a special case of the one presented. 相似文献
53.
Non-classical negations may fail to be contradictory-forming operators in more than one way, and they often fail also to respect fundamental meta-logical properties such as the replacement property. Such drawbacks are witnessed by intricate semantics and proof systems, whose philosophical interpretations and computational properties are found wanting. In this paper we investigate congruential non-classical negations that live inside very natural systems of normal modal logics over complete distributive lattices; these logics are further enriched by adjustment connectives that may be used for handling reasoning under uncertainty caused by inconsistency or undeterminedness. Using such straightforward semantics, we study the classes of frames characterized by seriality, reflexivity, functionality, symmetry, transitivity, and some combinations thereof, and discuss what they reveal about sub-classical properties of negation. To the logics thereby characterized we apply a general mechanism that allows one to endow them with analytic ordinary sequent systems, most of which are even cut-free. We also investigate the exact circumstances that allow for classical negation to be explicitly defined inside our logics. 相似文献
54.
Mayuko Ori 《Tetrahedron》2005,61(8):2075-2104
An efficient methodology for the synthesis of 2,2,3-trisubstituted tetrahydroquinolines has been developed, which involves the triphenylphosphine-CCl4-mediated stereospecific rearrangement of α,α-disubstituted indoline-2-methanols 15 to 2,2,3-trisubstituted tetrahydroquinolines 26. The rearrangement precursors 15 are readily prepared by the diastereoselective Grignard addition to 2-acylindolines 13. The total syntheses of (+)-benzastatin E (1) and natural virantmycin (2a) were accomplished utilizing this methodology. This rearrangement reaction might afford some chemical precedent for the biogenetic pathway of the benzastatin family. 相似文献
55.
Electronic relaxation dynamics of water cluster anions 总被引:1,自引:0,他引:1
Bragg AE Verlet JR Kammrath A Cheshnovsky O Neumark DM 《Journal of the American Chemical Society》2005,127(43):15283-15295
The electronic relaxation dynamics of water cluster anions, (H(2)O)(n)(-), have been studied with time-resolved photoelectron imaging. In this investigation, the excess electron was excited through the p<--s transition with an ultrafast laser pulse, with subsequent electronic evolution monitored by photodetachment. All excited-state lifetimes exhibit a significant isotope effect (tau(D)2(O)/tau(H)2(O) approximately 2). Additionally, marked dynamical differences are found for two classes of water cluster anions, isomers I and II, previously assigned as clusters with internally solvated and surface-bound electrons, respectively. Isomer I clusters with n > or = 25 decay exclusively by internal conversion, with relaxation times that extrapolate linearly with 1/n toward an internal conversion lifetime of 50 fs in bulk water. Smaller isomer I clusters (13 < or = n < or = 25) decay through a combination of excited-state autodetachment and internal conversion. The relaxation of isomer II clusters shows no significant size dependence over the range of n = 60-100, with autodetachment an important decay channel following excitation of these clusters. Photoelectron angular distributions (PADs) were measured for isomer I and isomer II clusters. The large differences in dynamical trends, relaxation mechanisms, and PADs between large isomer I and isomer II clusters are consistent with their assignment to very different electron binding motifs. 相似文献
56.
T. Passerat de Silans B. Farias M. Oriá M. Chevrollier 《Applied physics. B, Lasers and optics》2006,82(3):367-371
We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a
realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to
a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the
atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms
into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is
calculated, considering the adatoms’ interaction with the crystal phonons.
PACS 34.50.Dy; 68.43.-h; 68.35.Ja; 32.80.Pj 相似文献
57.
Ezra Einy Ori Haimanko Ram Orzach Aner Sela 《International Journal of Game Theory》2002,30(3):405-419
In a general model of common-value second-price auctions with differential information, we show equivalence between the following
characteristics of a bidder: (i) having a dominant strategy; (ii) possessing superior information; (iii) being immune from
winner's curse. When a dominant strategy exists, it is given by the conditional expectation of the common value with respect
to bidder's information field; if the dominant strategy is used, other bidders cannot make a profit.
Final version November 2001 相似文献
58.
Feintuch A Alexandrowicz G Tashma T Boasson Y Grayevsky A Kaplan N 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,142(2):382-385
Three-dimensional pulsed ESR imaging was performed on a (FA)(2)PF(6) crystal using a three-dimensional Fourier imaging sequence. The best resolution achieved was of 20 microm(3). Comparison with images obtained using the filtered back-projection method shows the superiority of this method under the given conditions. 相似文献
59.
Alexandrowicz G Tashma T Feintuch A Grayevsky A Dormann E Kaplan N 《Physical review letters》2000,84(13):2973-2976
Novel implementation of the Fourier imaging technique on conduction electron spins in the one-dimensional organic conductors (FA)2PF6 (FA: fluoranthene) is reported. Two-dimensional spatial imaging of resolution 30 &mgr;m(2) is combined with the pulsed-gradient spin-echo technique, to derive maps revealing the local properties of the electron spin density and mobility. The maps generally show pronounced inhomogeneity of both density and mobility on the scale of approximately 30-300 &mgr;m. Highly mobile regions were identified to exist, and the mobility in these was quantitatively evaluated by a basic theoretical model of restricted diffusion. 相似文献
60.
We present a practical method for calculating the local gravitational self-force (often called "radiation-reaction force") for a pointlike particle orbiting a Schwarzschild black hole. This is an implementation of the method of mode-sum regularization, in which one first calculates the (finite) contribution to the force due to each individual multipole mode of the perturbation, and then applies a certain regularization procedure to the mode sum. Here we give the values of all the "regularization parameters" required for implementing this regularization procedure, for any geodesic orbit in Schwarzschild spacetime. 相似文献