48,156 research outputs found
Note on lattice regularization and equal-time correlators for parton distribution functions
We show that a recent interesting idea to circumvent the difficulties with
the continuation of parton distribution functions to the Euclidean region, that
consists in looking at equal time correlators between proton states of infinite
momentum, encounters some problems related to the power divergent mixing
pattern of DIS operators, when implemented within the lattice regularization.Comment: 15 pages, no figures, Physical Review D (2017
Hilbert Functions of Filtered Modules
In this presentation we shall deal with some aspects of the theory of Hilbert
functions of modules over local rings, and we intend to guide the reader along
one of the possible routes through the last three decades of progress in this
area of dynamic mathematical activity. Motivated by the ever increasing
interest in this field, our goal is to gather together many new developments of
this theory into one place, and to present them using a unifying approach which
gives self-contained and easier proofs. In this text we shall discuss many
results by different authors, following essentially the direction typified by
the pioneering work of J. Sally. Our personal view of the subject is most
visibly expressed by the presentation of Chapters 1 and 2 in which we discuss
the use of the superficial elements and related devices. Basic techniques will
be stressed with the aim of reproving recent results by using a more elementary
approach. Over the past few years several papers have appeared which extend
classical results on the theory of Hilbert functions to the case of filtered
modules. The extension of the theory to the case of general filtrations on a
module has one more important motivation. Namely, we have interesting
applications to the study of graded algebras which are not associated to a
filtration, in particular the Fiber cone and the Sally-module. We show here
that each of these algebras fits into certain short exact sequences, together
with algebras associated to filtrations. Hence one can study the Hilbert
function and the depth of these algebras with the aid of the know-how we got in
the case of a filtration.Comment: 127 pages, revised version. Comments and remarks are welcom
Quantum Cloning by Cellular Automata
We introduce a quantum cellular automaton that achieves approximate
phase-covariant cloning of qubits. The automaton is optimized for 1-to-2N
economical cloning. The use of the automaton for cloning allows us to exploit
different foliations for improving the performance with given resources.Comment: 4 pages, 6 figures, 1 table, published versio
Lateral conduction effects on heat-transfer data obtained with the phase-change paint technique
A computerized tool, CAPE, (Conduction Analysis Program using Eigenvalues) has been developed to account for lateral heat conduction in wind tunnel models in the data reduction of the phase-change paint technique. The tool also accounts for the effects of finite thickness (thin wings) and surface curvature. A special reduction procedure using just one time of melt is also possible on leading edges. A novel iterative numerical scheme was used, with discretized spatial coordinates but analytic integration in time, to solve the inverse conduction problem involved in the data reduction. A yes-no chart is provided which tells the test engineer when various corrections are large enough so that CAPE should be used. The accuracy of the phase-change paint technique in the presence of finite thickness and lateral conduction is also investigated
Linear and nonlinear evolution of current-carrying highly magnetized jets
We investigate the linear and nonlinear evolution of current-carrying jets in
a periodic configuration by means of high resolution three-dimensional
numerical simulations. The jets under consideration are strongly magnetized
with a variable pitch profile and initially in equilibrium under the action of
a force-free magnetic field. The growth of current-driven (CDI) and
Kelvin-Helmholtz (KHI) instabilities is quantified using three selected cases
corresponding to static, Alfvenic and super-Alfvenic jets.
During the early stages, we observe large-scale helical deformations of the
jet corresponding to the growth of the initially excited CDI mode. A direct
comparison between our simulation results and the analytical growth rates
obtained from linear theory reveals good agreement on condition that
high-resolution and accurate discretization algorithms are employed.
After the initial linear phase, the jet structure is significantly altered
and, while slowly-moving jets show increasing helical deformations, larger
velocity shear are violently disrupted on a few Alfven crossing time leaving a
turbulent flow structure. Overall, kinetic and magnetic energies are quickly
dissipated into heat and during the saturated regime the jet momentum is
redistributed on a larger surface area with most of the jet mass travelling at
smaller velocities. The effectiveness of this process is regulated by the onset
of KHI instabilities taking place at the jet/ambient interface and can be held
responsible for vigorous jet braking and entrainment.Comment: 14 pages, 11 figure
Experimental reconstruction of photon statistics without photon counting
Experimental reconstructions of photon number distributions of both
continuous-wave and pulsed light beams are reported. Our scheme is based on
on/off avalanche photodetection assisted by maximum-likelihood estimation and
does not involve photon counting. Reconstructions of the distribution for both
semiclassical and quantum states of light are reported for single-mode as well
as for multimode beams.Comment: Revised version: in press on PRL. 4 pages, 4 fig
On lattice chiral gauge theories
The Smit-Swift-Aoki formulation of a lattice chiral gauge theory is presented. In this formulation the Wilson and other non invariant terms in the action are made gauge invariant by the coupling with a nonlinear auxilary scalar field, omega. It is shown that omega decouples from the physical states only if appropriate parameters are tuned so as to satisfy a set of BRST identities. In addition, explicit ghost fields are necessary to ensure decoupling. These theories can give rise to the correct continuum limit. Similar considerations apply to schemes with mirror fermions. Simpler cases with a global chiral symmetry are discussed and it is shown that the theory becomes free at decoupling. Recent numerical simulations agree with those considerations
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