1,249 research outputs found
Interactive Password Schemes
Only the abstract is available for this technical report.Usual password schemes suffer from the flaw that they are easy to steal. An attacker who has correctly observed a login session (by peeping, wiretapping and/or by launching a "man-in-the-middle" attack, etc.) can easily impersonate the corresponding user.
Available protection techniques require computations on hundreds digit integers that are so complex that they require special software and/or hardware.
This project tries to combine the simplicity of the conventional password schemes with a protection technique that results in a different password being typed each session, but only requires simple computation performed in the user's head
Fission modes of mercury isotopes
Background: Recent experiments on beta-delayed fission in the mercury-lead
region and the discovery of asym- metric fission in 180 Hg [1] have stimulated
theoretical interest in the mechanism of fission in heavy nuclei. Purpose: We
study fission modes and fusion valleys in 180 Hg and 198 Hg to reveal the role
of shell effects in pre-scission region and explain the experimentally observed
fragment mass asymmetry and its variation with A. Methods: We use the
self-consistent nuclear density functional theory employing Skyrme and Gogny
energy density functionals. Results: The potential energy surfaces in
multi-dimensional space of collective coordinates, including elongation,
triaxiality, reflection-asymmetry, and necking, are calculated for 180 Hg and
198 Hg. The asymmetric fission valleys - well separated from fusion valleys
associated with nearly spherical fragments - are found in in both cases. The
density distributions at scission configurations are studied and related to the
experimentally observed mass splits. Conclusions: The energy density
functionals SkM\ast and D1S give a very consistent description of the fission
process in 180 Hg and 198 Hg. We predict a transition from asymmetric fission
in 180 Hg towards more symmetric distribution of fission fragments in 198 Hg.
For 180 Hg, both models yield 100 Ru/80 Kr as the most probable split. For 198
Hg, the most likely split is 108 Ru/90 Kr in HFB-D1S and 110 Ru/88 Kr in
HFB-SkM\ast.Comment: 6 pages, 5 figures, to be published in Physical Review
Frequency Domain Simulations of Charge-Density-Wave Strains: Comparison with Electro-Optic Measurements
We have studied changes in charge-density-wave strain under application of
square-wave currents of variable amplitude and frequency by numerically solving
the phase-slip augmented diffusion model introduced by Adelman et al (Phys.
Rev. B 53, 1833 (1996)). The frequency dependence of the strain, at each
position and amplitude, was fit to a modified harmonic oscillator expression,
and the position and current dependence of the fitting parameters determined.
In particular, the delay time (1/resonant frequency) vanishes adjacent to the
contact and grows with distance from the contact, and both the delay time and
relaxation time decrease rapidly with increasing current (and phase-slip rate),
as experimentally observed in the electro-optic response of blue bronze. We
have also found that pinning the phase at the contacts causes more rapid
changes in strain between the contacts than allowing the phase to flow outside
the contacts.Comment: 12 pages, 4 figures, submitted to Phys. Rev.
Application of Hybrid Fillers for Improving the Through-Plane Heat Transport in Graphite Nanoplatelet-Based Thermal Interface Layers.
The in-plane alignment of graphite nanoplatelets (GNPs) in thin thermal interface material (TIM) layers suppresses the though-plane heat transport thus limiting the performance of GNPs in the geometry normally required for thermal management applications. Here we report a disruption of the GNP in-plane alignment by addition of spherical microparticles. The degree of GNP alignment was monitored by measurement of the anisotropy of electrical conductivity which is extremely sensitive to the orientation of high aspect ratio filler particles. Scanning Electron Microscopy images of TIM layer cross-sections confirmed the suppression of the in-plane alignment. The hybrid filler formulations reported herein resulted in a synergistic enhancement of the through-plane thermal conductivity of GNP/Al2O3 and GNP/Al filled TIM layers confirming that the control of GNP alignment is an important parameter in the development of highly efficient GNP and graphene-based TIMs
The contrasting fission potential-energy structure of actinides and mercury isotopes
Fission-fragment mass distributions are asymmetric in fission of typical
actinide nuclei for nucleon number in the range
and proton number in the range . For somewhat
lighter systems it has been observed that fission mass distributions are
usually symmetric. However, a recent experiment showed that fission of
Hg following electron capture on Tl is asymmetric. We calculate
potential-energy surfaces for a typical actinide nucleus and for 12 even
isotopes in the range Hg--Hg, to investigate the similarities
and differences of actinide compared to mercury potential surfaces and to what
extent fission-fragment properties, in particular shell structure, relate to
the structure of the static potential-energy surfaces. Potential-energy
surfaces are calculated in the macroscopic-microscopic approach as functions of
fiveshape coordinates for more than five million shapes. The structure of the
surfaces are investigated by use of an immersion technique. We determine
properties of minima, saddle points, valleys, and ridges between valleys in the
5D shape-coordinate space. Along the mercury isotope chain the barrier heights
and the ridge heights and persistence with elongation vary significantly and
show no obvious connection to possible fragment shell structure, in contrast to
the actinide region, where there is a deep asymmetric valley extending from the
saddle point to scission. The mechanism of asymmetric fission must be very
different in the lighter proton-rich mercury isotopes compared to the actinide
region and is apparently unrelated to fragment shell structure. Isotopes
lighter than Hg have the saddle point blocked from a deep symmetric
valley by a significant ridge. The ridge vanishes for the heavier Hg isotopes,
for which we would expect a qualitatively different asymmetry of the fragments.Comment: 8 pages, 9 figure
Group Key Manager on a Smart Card
Only the abstract is available for this technical report.Group communication is as an important functionality, which needs to be supported by various communication technologies. Applications of group communication include IP (or application-level) multicast, wireless and/or ad-hoc networks, broadcast, conference calling, pay-per-view, and even such seemingly unrelated to networks areas as copy protection. For many, if not all, of these applications, security and trust play an important role. Securing group communication typically requires confidentiality and authentication, which typically rely on secret keys. Thus key management issues must be addressed.
This paper describes an implementation of one approach to dynamic group key management, which is based on Logical Key Hierarchy or Subset-Cover approach [1,2].
Our approach achieves a dramatic reduction of the storage requirements for the Group Key Manager, and in particular allows all the secret key data to be stored on a smart-card. It also allows a number of subsequent improvements
Effect of physical and chemical doping on optical spectra of SWNT's
We discuss the use of far-infrared spectroscopy in the characterization of doped and
functionalized nanotube derivatives
Band Electronic Structure of One- and Two-Dimensional Pentacene Molecular Crystals
We report EHT calculations of the band electronic structure of substituted pentacene derivatives and the polymorphs of the parent compound. The results show that there are wide disparities among the bandwidths and electronic dimensionalities of these compounds. The parent pentacene polymorphs are 2-dimensional in their band electronic structure with moderate dispersions; the bandwidths in the 14.1 Ă… d-spacing polymorph are noticeably larger than for the 14.5 Ă… d-spacing polymorph, reported by Campbell. Whereas the parent pentacene polymorphs adopt the well-known herringbone packing, the new, substituted pentacenes are noticeably different in their solid state structures and this is reflected in the band electronic structures. TMS adopts a highly 1-dimensional structure that leads to a large bandwidth along the stacking direction; TIPS also adopts a stacked structure, but because the molecules are laterally interleaved in the fashion of bricks in a wall, this compound is strongly 2-dimensional.
Mass distributions for induced fission of different Hg isotopes
With the improved scission-point model the mass distributions are calculated
for induced fission of different Hg isotopes with the masses 180-196. The
drastic change in the shape of the mass distribution from asymmetric to
symmetric is revealed with increasing mass number of the fissioning Hg isotope,
and the reactions are proposed to verify this prediction experimentally. The
asymmetric mass distribution of fission fragments observed in the recent
experiment on the fission of 180Hg is explained. The calculated mass
distribution and mean total kinetic energy of fission fragments are in a good
agreement with the available experimental data
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