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排序方式: 共有54条查询结果,搜索用时 15 毫秒
1.
H. Weisen F. Hofmann M. J. Dutch J. -M. Moret J. B. Lister A. Pochelon R. A. Pitts M. Anton R. Behn S. Bernel F. Bühlmann R. Chavan B. P. Duval D. Fasel A. Favre S. Franke A. Heym Ch. Hollenstein P. Isoz B. Joye X. Llobet B. Marletaz Ph. Marmillod Y. Martin Ch. Nieswand P. J. Paris A. Perez Z. A. Pietrzyk O. Sauter W. Van Toledo G. Tonetti M. Q. Tran F. Troyon D. J. Ward 《Czechoslovak Journal of Physics》1995,45(12):1095-1110
During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B
tor1.46T,I
p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors (
tor
aB/I
p) up to two and densities up to 2.25×1020m–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×1020m–3 have been obtained in elongated D-shaped plasmas with 360 kAI
P600 kA.Presented at 17th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique. 相似文献
2.
Alain Joye 《Journal of statistical physics》1994,75(5-6):929-952
The spectrum of the Floquet operator associated with time-periodic perturbations of discrete Hamiltonians is considered. If the gap between successive eigenvalues
j
of the unperturbed Hamiltonian grows as
j
-
j-1
j
and the multiplicity of
j
grows asj
with >0 asj tends to infinity, then the corresponding Floquet operator possesses no absolutely continuous spectrum provided the perturbation is smooth enough. 相似文献
3.
George A. Hagedorn Alain Joye 《Journal of Mathematical Analysis and Applications》2002,267(1):235-246
We present an elementary proof that the quantum adiabatic approximation is correct up to exponentially small errors for Hamiltonians that depend analytically on the time variable. Our proof uses optimal truncation of a straightforward asymptotic expansion. We estimate the terms of the expansion with standard Cauchy estimates. 相似文献
4.
We consider a quantum system in contact with a heat bath consisting in an infinite chain of identical sub-systems at thermal
equilibrium at inverse temperature β. The time evolution is discrete and such that over each time step of duration τ, the
reference system is coupled to one new element of the chain only, by means of an interaction of strength λ. We consider three
asymptotic regimes of the parameters λ and τ for which the effective evolution of observables on the small system becomes
continuous over suitable macroscopic time scales T and whose generator can be computed: the weak coupling limit regime λ → 0, τ = 1, the regime τ → 0, λ2τ → 0 and the critical case λ2τ = 1, τ → 0. The first two regimes are perturbative in nature and the effective generators they determine is such that a
non-trivial invariant sub-algebra of observables naturally emerges. The third asymptotic regime goes beyond the perturbative
regime and provides an effective dynamics governed by a general Lindblad generator naturally constructed from the interaction
Hamiltonian. Conversely, this result shows that one can attach to any Lindblad generator a repeated quantum interactions model
whose asymptotic effective evolution is generated by this Lindblad operator. 相似文献
5.
Olivier Bourget James S. Howland Alain Joye 《Communications in Mathematical Physics》2003,234(2):191-227
This paper is devoted to the spectral properties of a class of unitary operators with a matrix representation displaying
a band structure. Such band matrices appear as monodromy operators in the study of certain quantum dynamical systems. These
doubly infinite matrices essentially depend on an infinite sequence of phases which govern their spectral properties. We prove
the spectrum is purely singular for random phases and purely absolutely continuous in case they provide the doubly infinite
matrix with a periodic structure in the diagonal direction. We also study some properties of the singular spectrum of such
matrices considered as infinite in one direction only.
Received: 29 April 2002 / Accepted: 7 August 2002 Published online: 20 January 2003
Communicated by B. Simon 相似文献
6.
Jongsung Kim Jaechul Sung Ermaliza Razali Raphael C.-W. Phan Marc Joye 《Designs, Codes and Cryptography》2011,60(1):15-35
The theory of designing block ciphers is mature, having seen significant progress since the early 1990s for over two decades,
especially during the AES development effort. Nevertheless, interesting directions exist, in particular in the study of the
provable security of block ciphers along similar veins as public-key primitives, i.e. the notion of pseudorandomness (PRP)
and indistinguishability (IND). Furthermore, recent cryptanalytic progress has shown that block ciphers well designed against
known cryptanalysis techniques including related-key attacks (RKA) may turn out to be less secure against RKA than expected.
The notion of provable security of block ciphers against RKA was initiated by Bellare and Kohno, and subsequently treated
by Lucks. Concrete block cipher constructions were proposed therein with provable security guarantees. In this paper, we are
interested in the security notions for RKA-secure block ciphers. In the first part of the paper, we show that secure tweakable
permutation families in the sense of strong pseudorandom permutation (SPRP) can be transformed into secure permutation families
in the sense of SPRP against some classes of RKA (SPRP–RKA). This fact allows us to construct a secure SPRP–RKA cipher which
is faster than the Bellare–Kohno PRP–RKA cipher. We also show that function families of a certain form secure in the sense
of a pseudorandom function (PRF) can be transformed into secure permutation families in the sense of PRP against some classes
of RKA (PRP–RKA). We can exploit it to get various constructions secure against some classes of RKA from known MAC algorithms.
Furthermore, we discuss how the key recovery (KR) security of the Bellare–Kohno PRP–RKA, the Lucks PRP–RKA and our SPRP–RKA
ciphers relates to existing types of attacks on block ciphers like meet-in-the-middle and slide attacks. In the second part
of the paper, we define other security notions for RKA-secure block ciphers, namely in the sense of indistinguishability (IND) and non-malleability, and show the relations between these security notions. In particular, we show that secure tweakable permutation families
in the sense of IND (resp. non-malleability) can be transformed into RKA-secure permutation families in the sense of IND (resp.
non-malleability). 相似文献
7.
8.
Letters in Mathematical Physics - We consider the dynamical properties of Quantum Walks defined on the d-dimensional cubic lattice, or the homogeneous tree of coordination number 2d, with... 相似文献
9.
This paper establishes dynamical localization properties of certain families of unitary random operators on the d-dimensional lattice in various regimes. These operators are generalizations of one-dimensional physical models of quantum
transport and draw their name from the analogy with the discrete Anderson model of solid state physics. They consist in a
product of a deterministic unitary operator and a random unitary operator. The deterministic operator has a band structure,
is absolutely continuous and plays the role of the discrete Laplacian. The random operator is diagonal with elements given
by i.i.d. random phases distributed according to some absolutely continuous measure and plays the role of the random potential.
In dimension one, these operators belong to the family of CMV-matrices in the theory of orthogonal polynomials on the unit
circle. We implement the method of Aizenman-Molchanov to prove exponential decay of the fractional moments of the Green function
for the unitary Anderson model in the following three regimes: In any dimension, throughout the spectrum at large disorder
and near the band edges at arbitrary disorder and, in dimension one, throughout the spectrum at arbitrary disorder. We also
prove that exponential decay of fractional moments of the Green function implies dynamical localization, which in turn implies
spectral localization. These results complete the analogy with the self-adjoint case where dynamical localization is known
to be true in the same three regimes. 相似文献
10.
We consider the discrete time unitary dynamics given by a quantum walk on ${\mathbb {Z}^d}$ performed by a particle with internal degree of freedom, called coin state, according to the following iterated rule: a unitary update of the coin state takes place, followed by a shift on the lattice, conditioned on the coin state of the particle. We study the large time behavior of the quantum mechanical probability distribution of the position observable in ${\mathbb {Z}^d}$ for random updates of the coin states of the following form. The random sequences of unitary updates are given by a site-dependent function of a Markov chain in time, with the following properties: on each site, they share the same stationary Markovian distribution and, for each fixed time, they form a deterministic periodic pattern on the lattice. We prove a Feynman–Kac formula to express the characteristic function of the averaged distribution over the randomness at time n in terms of the nth power of an operator M. By analyzing the spectrum of M, we show that this distribution possesses a drift proportional to the time and its centered counterpart displays a diffusive behavior with a diffusion matrix we compute. Moderate and large deviation principles are also proven to hold for the averaged distribution and the limit of the suitably rescaled corresponding characteristic function is shown to satisfy a diffusion equation. An example of random updates for which the analysis of the distribution can be performed without averaging is worked out. The random distribution displays a deterministic drift proportional to time and its centered counterpart gives rise to a random diffusion matrix, the law of which we compute. We complete the picture by presenting an uncorrelated example. 相似文献