1,343 research outputs found
Efficient Conditional Proxy Re-encryption with Chosen-Ciphertext Security
Recently, a variant of proxy re-encryption, named conditional proxy re-encryption (C-PRE), has been introduced. Compared with traditional proxy re-encryption, C-PRE enables the delegator to implement fine-grained delegation of decryption rights, and thus is more useful in many applications. In this paper, based on a careful observation on the existing definitions and security notions for C-PRE, we reformalize more rigorous definition and security notions for C-PRE. We further propose a more efficient C-PRE scheme, and prove its chosenciphertext security under the decisional bilinear Diffie-Hellman (DBDH) assumption in the random oracle model. In addition, we point out that a recent C-PRE scheme fails to achieve the chosen-ciphertext security
Effects of Al doping on the structural and electronic properties of Mg(1-x)Al(x)B2
We have studied the structural and electronic properties of Mg(1-x)Al(x)B2
within the Virtual Crystal Approximation (VCA) by means of first-principles
total-energy calculations. Results for the lattice parameters, the electronic
band structure, and the Fermi surface as a function of Al doping for 0<x<0.6
are presented. The ab initio VCA calculations are in excellent agreement with
the experimentally observed change in the lattice parameters of Al doped MgB2.
The calculations show that the Fermi surface associated with holes a the boron
planes collapses gradually with aluminum doping and vanishes for x=0.56. In
addition, an abrupt topological change in the sigma-band Fermi surface was
found for x=0.3. The calculated hole density correlates closely with existing
experimental data for Tc(x), indicating that the observed loss of
superconductivity in Mg(1-x)Al(x)B2 is a result of hole bands filling.Comment: 4 pages (revtex) and 4 figures (postscript
Cancellation of Global Anomalies in Spontaneously Broken Gauge Theories
We discuss the generalization to global gauge anomalies of the familiar
procedure for the cancellation of local gauge anomalies in effective theories
of spontaneously broken symmetries. We illustrate this mechanism in a recently
proposed six-dimensional extension of the standard model.Comment: 5 pages; v2: version to appear in Phys. Rev.
Comparison of some Reduced Representation Approximations
In the field of numerical approximation, specialists considering highly
complex problems have recently proposed various ways to simplify their
underlying problems. In this field, depending on the problem they were tackling
and the community that are at work, different approaches have been developed
with some success and have even gained some maturity, the applications can now
be applied to information analysis or for numerical simulation of PDE's. At
this point, a crossed analysis and effort for understanding the similarities
and the differences between these approaches that found their starting points
in different backgrounds is of interest. It is the purpose of this paper to
contribute to this effort by comparing some constructive reduced
representations of complex functions. We present here in full details the
Adaptive Cross Approximation (ACA) and the Empirical Interpolation Method (EIM)
together with other approaches that enter in the same category
Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance
We theoretically study the influence of the noise strength on the excitation
of the Brillouin propagation modes in a dissipative optical lattice. We show
that the excitation has a resonant behavior for a specific amount of noise
corresponding to the precise synchronization of the Hamiltonian motion on the
optical potential surfaces and the dissipative effects associated with optical
pumping in the lattice. This corresponds to the phenomenon of stochastic
resonance. Our results are obtained by numerical simulations and correspond to
the analysis of microscopic quantities (atomic spatial distributions) as well
as macroscopic quantities (enhancement of spatial diffusion and pump-probe
spectra). We also present a simple analytical model in excellent agreement with
the simulations
Interface ferromagnetism and orbital reconstruction in BiFeO3- La0.7Sr0.3MnO3 heterostructures
We report the formation of a novel ferromagnetic state in the antiferromagnet
BiFeO3 at the interface with La0.7Sr0.3MnO3. Using x-ray magnetic circular
dichroism at Mn and Fe L2,3-edges, we discovered that the development of this
ferromagnetic spin structure is strongly associated with the onset of a
significant exchange bias. Our results demonstrate that the magnetic state is
directly related with an electronic orbital reconstruction at the interface,
which is supported by the linearly polarized x-ray absorption measurement at
oxygen K-edge.Comment: 17 pages, 4 figures, PRL in pres
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