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991.
We develop a notion of an n-fold monoidal category and show that it corresponds in a precise way to the notion of an n-fold loop space. Specifically, the group completion of the nerve of such a category is an n-fold loop space, and free n-fold monoidal categories give rise to a finite simplicial operad of the same homotopy type as the classical little cubes operad used to parametrize the higher H-space structure of an n-fold loop space. We also show directly that this operad has the same homotopy type as the n-th Smith filtration of the Barratt-Eccles operad and the n-th filtration of Berger's complete graph operad. Moreover, this operad contains an equivalent preoperad which gives rise to Milgram's small model for when n=2 and is very closely related to Milgram's model of for n>2. 相似文献
992.
A. Pautrat A. Daignere C. Goupil Ch. Simon B. Andrzejewski A.I. Rykov S. Tajima 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):279-284
We report complex impedance measurements in an untwinned YBaCuO crystal. Our broad frequency range covers both the quasi static
response and the resistive response of the vortex lattice. It allow us to characterize the irreversibility line without the
need of any frequency dependent pinning parameters. We confirm the validity of the two modes model of vortex dynamic, and
extract both the surface critical current and the flux flow resistivity around the first order transition Tm. This latter is identified by the abrupt loss of pinning and by an unexpected step of (T) at Tm.
Received 22 November 2002 / Received in final form 17 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: alain.pautrat@ismra.fr
RID="b"
ID="b"UMR 6508 associée au CNRS 相似文献
993.
We consider quadratic diophantine equations of the shape
for a polynomial Q(X1, ..., Xs) Z[X1, ..., Xs] of degree 2.Let H be an upper bound for the absolute values of the coefficientsof Q, and assume that the homogeneous quadratic part of Q isnon-singular. We prove, for all s 3, the existence of a polynomialbound s(H) with the following property: if equation (1) hasa solution x Zs at all, then it has one satisfying
For s = 3 and s = 4 no polynomial bounds s(H) were previouslyknown, and for s 5 we have been able to improve existing boundsquite significantly. 2000 Mathematics Subject Classification11D09, 11E20, 11H06, 11P55. 相似文献
994.
Yeh Lam 《应用数学学报(英文版)》2003,19(3):405-416
Geometric process (GP) was introduced by Lam[4,5], it is defined as a stochastic process {Xn, n = 1, 2,…} for which there exists a real number a > 0, such that {an-1 Xn, n = 1,2, …} forms a renewal process (RP). In this paper, we study some limit theorems in GP. We first derive the Wald equation for GP and then obtain the limit theorems of the age, residual life and the total life at t for a GP. A general limit theorem for Sn with a > 1 is also studied. Furthermore, we make a comparison between GP and RP, including the comparison of their limit distributions of the age, residual life and the total life at t. 相似文献
995.
Ralph Kummetz 《Applied Categorical Structures》2003,11(1):3-25
This paper investigates function spaces of structures consisting of a partially ordered set together with some directed family of projections.More precisely, given a fixed directed index set (I,), we consider triples (D,,(p
i
)
iI
) with (D,) a poset and (p
i
)
iI
a monotone net of projections of D. We call them (I,)-pop's (posets with projections). Our main purpose is to study structure preserving maps between (I,)-pop's. Such homomorphisms respect both order and projections.Any (I,)-pop is known to induce a uniformity and thus a topology. The set of all homomorphisms between two (I,)-pop's turns out to form an (I,)-pop itself. We show that its uniformity is the uniformity of uniform convergence. This enables us to prove that properties such as completeness and compactness transfer to function pop's.Concerning categorical properties of (I,)-pop's, we will see that we are in a lucky situation from a computer scientist's point of view: we obtain Cartesian closed categories. Moreover, by a D
-construction we get (I,)-pop's that are isomorphic to their own exponent. This yields new models for the untyped -calculus. 相似文献
996.
The main theme of this paper is that almost fixed point properties of discrete structures and fixed point properties of (topological) spaces are interdeducible via a suitable category which contains both graphs and spaces as objects. To carry out the program, we have to consider (almost) fixed points of multifunctions, and for this we need a preliminary discussion of power structures for graphs and simplicial complexes. Specific applications developed are: a digital convexity (discrete) version of Kakutani's fixed point theorem for convex-valued multifunctions; and fixed point properties of dendrites in terms of those of finite discrete trees. 相似文献
997.
Martin Juráš 《Acta Appl Math》2001,66(1):25-39
On the equation manifold of the 2nth-order scalar ordinary differential equation, n3,
we construct a contact two-form such that d0mod, if and only if Equation (1) admits a nondegenerate Lagrangian of order n. We show that the space of all nondegenerate Lagrangians for (1) is at most one-dimensional. The necessary and sufficient conditions for sixth-order and eighth-order scalar ordinary differential equation to admit a variational multiplier are found in terms of vanishing of a certain set of functions. The exact relationship between the Lie algebra of the classical infinitesimal contact symmetries of a variational Equation (1) and its the Lie subalgebra of infinitesimal divergence symmetries is established. 相似文献
998.
V. Kroha P. Bém V. Burjan J. Novák Š. Piskoř E. Šimečková J. Vincour A. Azhari C.A. Gagliardi A.M. Mukhamedzhanov X. Tang L. Trache R.E. Tribble F. Carstoiu 《Czechoslovak Journal of Physics》2001,51(5):471-489
The indirect method of determining astrophysical nuclear reaction rates is discussed. The overall normalization of the astrophysical S-factor for such reactions may be determined from one quantity, the asymptotic normalization coefficient of the overlap function of the bound state wave functions for the initial and final channels. These coefficients can be found also from peripheral transfer reactions whose amplitudes are determined by the same overlap function as the amplitudes of the corresponding astrophysical radiative capture processes. The experimental test of this approach and the last results of S17 measurements are presented. 相似文献
999.
We have obtained theoretically an expression for the nuclear free precession signal in an inhomogeneously broadened spin system with a complex structure of the NMR spectrum. It is shown that in this case in the nuclear precession signal there appear maxima the moments of whose formation depend on the detuning of the pulse carrier frequency from the central frequencies of the NMR lines, their widths, and the Rabi frequency. The theoretical results are in good agreement with the experimental data on the observation of proton free precession in toluene. We have constructed a physical model explaining the appearance of maxima in the free precession signal of the spin system. 相似文献
1000.
Thomas B Paasch S Steuernagel S Eichele K 《Solid state nuclear magnetic resonance》2001,20(3-4):108-117
In 31P MAS NMR spectra of chlorocyclophosphazenes, characteristic splittings have been observed for PCl or PCl2 groups. At different applied magnetic fields, the fine structure and total width of the patterns change in a characteristic way, demonstrating that the splittings are due to indirect spin–spin and residual dipolar interactions with the chlorine nuclei directly bonded to phosphorus. For trans-nongeminal N3P3Cl3(NMe2)3 and N3P3Cl6 as examples, the spectra have been analyzed to obtain information on chlorine nuclear quadrupole coupling constants and 35,37Cl, 31P indirect spin–spin coupling constants. Neglect of these interactions may result in misinterpretations of the multiplicity in 31P MAS spectra of chlorophosphazenes. 相似文献