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121.
Stefano Catani 《Zeitschrift fur Physik C Particles and Fields》1997,75(4):665-678
I present a theoretical discussion of the uncertainties related to the QCD analysis of the proton structure function F 2(x,Q 2) at small x. The role played by the ‘unphysical’ gluon density is pointed out. It is shown how the study of more observables can reduce the theoretical uncertainty and, in particular, an alternative method of analysis, based on the introduction of physical anomalous dimensions, is suggested. 相似文献
122.
We consider the task of resolving accurately the nth eigenpair of a generalized eigenproblem rooted in some elliptic partial differential equation (PDE), using an adaptive finite element method (FEM). Conventional adaptive FEM algorithms call a generalized eigensolver after each mesh refinement step. This is not practical in our situation since the generalized eigensolver needs to calculate n eigenpairs after each mesh refinement step, it can switch the order of eigenpairs, and for repeated eigenvalues it can return an arbitrary linear combination of eigenfunctions from the corresponding eigenspace. In order to circumvent these problems, we propose a novel adaptive algorithm that only calls a generalized eigensolver once at the beginning of the computation, and then employs an iterative method to pursue a selected eigenvalue–eigenfunction pair on a sequence of locally refined meshes. Both Picard’s and Newton’s variants of the iterative method are presented. The underlying partial differential equation (PDE) is discretized with higher-order finite elements (hp-FEM) but the algorithm also works for standard low-order FEM. The method is described and accompanied with theoretical analysis and numerical examples. Instructions on how to reproduce the results are provided. 相似文献
123.
József Fritz Carlangelo Liverani Stefano Olla 《Communications in Mathematical Physics》1997,189(2):481-496
The set of stationary measures of an infinite Hamiltonian system with noise is investigated. The model consists of particles
moving in with bounded velocities and subject to a noise that does not violate the classical laws of conservation, see [OVY]. Following
[LO] we assume that the noise has also a finite radius of interaction, and prove that translation invariant stationary states
of finite specific entropy are reversible with respect to the stochastic component of the evolution. Therefore the results
of [LO] imply that such invariant measures are superpositions of Gibbs states.
Received: 26 September 1996 / Accepted: 3 January 1997 相似文献
124.
Stefano De Leo Waldyr A. Rodrigues Jayme Vaz 《International Journal of Theoretical Physics》1998,37(9):2415-2431
Complex geometry represents a fundamentalingredient in the formulation of the Dirac equation bythe Clifford algebra. The choice of appropriate complexgeometries is strictly related to the geometricinterpretation of the complex imaginary unit
. We discuss two possibilities which appearin the multivector algebra approach: the123 and 21 complexgeometries. Our formalism provides a set of rules which allows an immediate translation between thecomplex standard Dirac theory and its version withingeometric algebra. The problem concerning a doublegeometric interpretation for the complex imaginary unit
is also discussed. 相似文献
125.
The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical dark energy results as byproduct of quantum entanglement. 相似文献
126.
Stefano Vannucci 《Annals of Operations Research》2002,109(1-4):99-127
Stability properties of several governance structures are studied by means of their effectivity functions. It is shown that (strong) stability of a governance structure is mainly determined by the collegial nature of the underlying assembly's decision rule. 相似文献
127.
In this paper we study the relationship between Constraint Programming (CP) and Shortest Path (SP) problems. In particular, we show that classical, multicriteria, partially ordered, and modality-based SP problems can be naturally modeled and solved within the Soft Constraint Logic Programming (SCLP) framework, where logic programming is coupled with soft constraints. In this way we provide this large class of SP problems with a high-level and declarative linguistic support whose semantics takes care of both finding the cost of the shortest path(s) and also of actually finding the path(s). On the other hand, some efficient algorithms for certain classes of SP problems can be exploited to provide some classes of SCLP programs with an efficient way to compute their semantics. 相似文献
128.
Egidio Di Gialleonardo Francesco Braghin Stefano Bruni 《Journal of sound and vibration》2012,331(19):4246-4258
This paper investigates the effect of different models for track flexibility on the simulation of railway vehicle running dynamics on tangent and curved track. To this end, a multi-body model of the rail vehicle is defined including track flexibility effects on three levels of detail: a perfectly rigid pair of rails, a sectional track model and a three-dimensional finite element track model. The influence of the track model on the calculation of the nonlinear critical speed is pointed out and it is shown that neglecting the effect of track flexibility results in an overestimation of the critical speed by more than 10%. Vehicle response to stochastic excitation from track irregularity is also investigated, analysing the effect of track flexibility models on the vertical and lateral wheel–rail contact forces. Finally, the effect of the track model on the calculation of dynamic forces produced by wheel out-of-roundness is analysed, showing that peak dynamic loads are very sensitive to the track model used in the simulation. 相似文献
129.
We apply the semigroup setting of Desch and Miller to a class of stochastic integral equations of Volterra type with completely
monotone kernels with a multiplicative noise term; the corresponding equation is an infinite dimensional stochastic equation
with unbounded diffusion operator that we solve with the semigroup approach of Da Prato and Zabczyk. As a motivation of our
results, we study an optimal control problem when the control enters the system together with the noise.
相似文献
130.
Online weighted flow time and deadline scheduling 总被引:1,自引:0,他引:1
Luca Becchetti Stefano Leonardi Alberto Marchetti-Spaccamela Kirk Pruhs 《Journal of Discrete Algorithms》2006,4(3):339
In this paper we study some aspects of weighted flow time. We first show that the online algorithm Highest Density First is an O(1)-speed O(1)-approximation algorithm for P|ri,pmtn|∑wiFi. We then consider a related Deadline Scheduling Problem that involves minimizing the weight of the jobs unfinished by some unknown deadline D on a uniprocessor. We show that any c-competitive online algorithm for weighted flow time must also be c-competitive for deadline scheduling. We then give an O(1)-competitive algorithm for deadline scheduling. 相似文献