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101.
Stefan Müller-Stach 《K-Theory》1995,9(4):395-406
LetX be a smooth projective variety over an algebraically closed fieldk. We repeat Bloch's construction of aG
m
-biextension (torseur)E over CH
hom
p
(X)×CH
hom
q
(X) forp+q=dim(X)+1. First we show that in characteristic zeroE comes via pullback from the Poincaré biextension over the corresponding product of intermediate Jacobians which has been conjectured by Bloch and Murre. Then the relations betweenE and various equivalence relations for algebraic cycles are studied. In particular we reprove Murre's theorem stating that Griffiths' conjecture holds for codimension 2 cycles, i.e. every 2-codimensional cycle which is algebraically and incidence equivalent to zero has torsion Abel-Jacobi invariant. 相似文献
102.
We make a high-precision Monte Carlo study of two- and three-dimensional self-avoiding walks (SAWs) of length up to 80,000 steps, using the pivot algorithm and the Karp-Luby algorithm. We study the critical exponentsv and 2
4 – as well as several universal amplitude ratios; in particular, we make an extremely sensitive test of the hyperscaling relationdv = 2
4 –. In two dimensions, we confirm the predicted exponentv=3/4 and the hyperscaling relation; we estimate the universal ratios <R
g
2
>/<R
e
2
>=0.14026±0.00007, <R
m
2
>/<R
e
2
>=0.43961±0.00034, and *=0.66296±0.00043 (68% confidence limits). In three dimensions, we estimatev=0.5877±0.0006 with a correctionto-scaling exponent
1=0.56±0.03 (subjective 68% confidence limits). This value forv agrees excellently with the field-theoretic renormalization-group prediction, but there is some discrepancy for
1. Earlier Monte Carlo estimates ofv, which were 0.592, are now seen to be biased by corrections to scaling. We estimate the universal ratios <R
g
2
>/<R
e
2
>=0.1599±0.0002 and *=0.2471±0.0003; since *>0, hyperscaling holds. The approach to * is from above, contrary to the prediction of the two-parameter renormalization-group theory. We critically reexamine this theory, and explain where the error lies. In an appendix, we prove rigorously (modulo some standard scaling assumptions) the hyperscaling relationdv = 2
4 – for two-dimensional SAWs. 相似文献
103.
The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family 总被引:2,自引:0,他引:2
Dankmar Böhning Ekkehart Dietz Rainer Schaub Peter Schlattmann Bruce G. Lindsay 《Annals of the Institute of Statistical Mathematics》1994,46(2):373-388
We here consider testing the hypothesis ofhomogeneity against the alternative of a two-component mixture of densities. The paper focuses on the asymptotic null distribution of 2 log
n
, where
n
is the likelihood ratio statistic. The main result, obtained by simulation, is that its limiting distribution appears pivotal (in the sense of constant percentiles over the unknown parameter), but model specific (differs if the model is changed from Poisson to normal, say), and is not at all well approximated by the conventional
(2)
2
-distribution obtained by counting parameters. In Section 3, the binomial with sample size parameter 2 is considered. Via a simple geometric characterization the case for which the likelihood ratio is 1 can easily be identified and the corresponding probability is found. Closed form expressions for the likelihood ratio
n
are possible and the asymptotic distribution of 2 log
n
is shown to be the mixture giving equal weights to the one point distribution with all its mass equal to zero and the 2-distribution with 1 degree of freedom. A similar result is reached in Section 4 for the Poisson with a small parameter value (0.1), although the geometric characterization is different. In Section 5 we consider the Poisson case in full generality. There is still a positive asymptotic probability that the likelihood ratio is 1. The upper precentiles of the null distribution of 2 log
n
are found by simulation for various populations and shown to be nearly independent of the population parameter, and approximately equal to the (1–2)100 percentiles of
(1)
2
. In Sections 6 and 7, we close with a study of two continuous densities, theexponential and thenormal with known variance. In these models the asymptotic distribution of 2 log
n
is pivotal. Selected (1–) 100 percentiles are presented and shown to differ between the two models. 相似文献
104.
Joe Zhu 《Annals of Operations Research》1996,66(5):311-335
This article employs new data envelopment analysis/assurance region (DEA/AR) methods to evaluate the efficiency of the 35 textile factories of the Nanjing Textiles Corporation (NTC), Nanjing, China. The returns to scale (RTS) of these factories were studied without assuming that the optimal DEA solutions were unique. All DMUs are identified with pointsE (Extreme Efficient),E (Efficient but not an extreme point) andF (Frontier but not efficient). We then further identify the nonfrontier DMUs with pointsNE, NE andNF according to whether they are projected onto a point inE, E, orF en route to evaluating their performances. All of the inefficient factories were in classNF and had unique optimal primal-dual solution pairs. Consequently, the solution pairs satisfy the strong complementary slackness condition (SCSC). Application of cone-ratio (CR) ARs reduced significantly the number of factories in classE, and showed that some AR-efficient factories were more flexible in adopting the mixture of central planning and market economies that China currently is trying to use. Also, linked-cone (LC) ARs were applied to measure maximum and minimum profit ratios. The SCSC multiplier space approach was utilized to analyze the sensitivity of the efficiency results to potential errors in the data with and without ARs. The results in this article suggest that collective units had a better performance than state-owned units in the two consecutive years analyzed.This paper was written while the author was at the School of Economics and Management, Southeast University, Nanjing 210018, P.R. China. 相似文献
105.
Detlev W. Hoffmann 《Transactions of the American Mathematical Society》1996,348(8):3267-3281
Let and be anisotropic quadratic forms over a field of characteristic not . Their function fields and are said to be equivalent (over ) if and are isotropic. We consider the case where and is divisible by an -fold Pfister form. We determine those forms for which becomes isotropic over if , and provide partial results for . These results imply that if and are equivalent and , then is similar to over . This together with already known results yields that if is of height and degree or , and if , then and are equivalent iff and are isomorphic over .
106.
S. Abboudy A. E. Hamed M. E. Kassem L. I. Abou-El-Nasr 《Journal of Thermal Analysis and Calorimetry》1993,39(3):301-308
The influence of stoichiometric ratio on the phase transition of sodium potassium sulphate (NaxK1–x)2SO4 crystals is investigated in the temperature range 300–500 K. The stoichiometric ratiox is chosen to bex=0.2, 0.3, 0.4, 0.8 and 0.9. The study has been carried out by using differential scanning calorimetry, DSC technique. The value of the specific heat,C
p, at the transition temperature,T
c
, increases asx is increased up tox=0.4 and then decreases for higher values ofx. The change in the specific heat, C
p, is following a relation of the form C
p C
p (T–T
c
/T
c
)– with = 0.12 which is in a fair agreement with the 3d Ising model. Insertion of Cu2+ ions into the lattice of (NaxK1–x)2SO4 crystals leads to a multiple peak in the temperature dependence ofC
p. The results are discussed from thermodynamical point of view.We would like to thank Prof. E. F. El-Wahidy, Prof. of Solid State Physics and Head of Physics Department, Faculty of Science, Alexandria University, for his interest and support of this work. 相似文献
107.
108.
A set of seven bituminous coal chars has been characterised by IR spectroscopy (FTIR), thermogravimetry (TG) and elemental analysis. FTIR study provided suitable information to establish differences between coal samples according to their chemical compositions. The reactivity of these samples was also studied and correlated with the coal parameters of mean vitrinite reflectance, fuel ratio and H/C ratio. The data suggest that reactivity as determined can be correlated with the mean vitrinite reflectance, fuel ratio and H/C ratio (0.90). The order of reactivity of samples were; Amasra (S1) (R m= 0.65)>Azdavay (S4) (R m=0.99)»Armutcuk (S2) (R m=0.81)»Acenta (S3) (R m=0.92)>Ac2l2k (S6) (R m=1.11) Cay (S5) (R m=1.03)>Sogutozu (S7) (R m=2.14). 相似文献
109.
Summary A modified Wald statistic for testing simple hypothesis against fixed as well as local alternatives is proposed. The asymptotic
expansions of the distributions of the proposed statistic as well as the Wald and Rao statistics under both the null and alternative
hypotheses are obtained. The powers of these statistics are compared and its is shown that for special structures of parameters
some statistics have same power in the sence of order
. The results obtained are applied for testing the hypothesis about the covariance matrix of the multivariate normal distribution
and it is shown that none of the tests based on the above statistics is uniformly superior.
Research supported by the National Science Foundation Grant MCS 830149. 相似文献
110.