14,186 research outputs found
On explaining the F-region seasonal anomaly in terms of composition changes in the lower atmosphere
Seasonal anomaly of F-region explained in terms of composition changes in lower atmospher
Mitigating Branch-Shadowing Attacks on Intel SGX using Control Flow Randomization
Intel Software Guard Extensions (SGX) is a promising hardware-based
technology for protecting sensitive computations from potentially compromised
system software. However, recent research has shown that SGX is vulnerable to
branch-shadowing -- a side channel attack that leaks the fine-grained (branch
granularity) control flow of an enclave (SGX protected code), potentially
revealing sensitive data to the attacker. The previously-proposed defense
mechanism, called Zigzagger, attempted to hide the control flow, but has been
shown to be ineffective if the attacker can single-step through the enclave
using the recent SGX-Step framework.
Taking into account these stronger attacker capabilities, we propose a new
defense against branch-shadowing, based on control flow randomization. Our
scheme is inspired by Zigzagger, but provides quantifiable security guarantees
with respect to a tunable security parameter. Specifically, we eliminate
conditional branches and hide the targets of unconditional branches using a
combination of compile-time modifications and run-time code randomization.
We evaluated the performance of our approach by measuring the run-time
overhead of ten benchmark programs of SGX-Nbench in SGX environment
Emergent Critical Phase and Ricci Flow in a 2D Frustrated Heisenberg Model
We introduce a two-dimensional frustrated Heisenberg antiferromagnet on
interpenetrating honeycomb and triangular lattices. Classically the two
sublattices decouple, and "order from disorder" drives them into a coplanar
state. Applying Friedan's geometric approach to nonlinear sigma models, we show
that the scaling of the spin-stiffnesses corresponds to the Ricci flow of a 4D
metric tensor. At low temperatures, the relative phase between the spins on the
two sublattices is described by a six-state clock model with an emergent
critical phase.Comment: 4+ pages, 2 figure
Structural, Magnetic and Magneto-caloric studies of Ni50Mn30Sn20Shape Memory Alloy
We have synthesized a nominal composition of Ni50Mn30Sn20 alloy using arc
melting technique. Rietveld refinement confirms the austenite L21 structure in
Fm-3m space group. Electrical resistivity has been found to clearly exhibiting
two different phenomena viz. a magnetic transition from paramagnetic to
ferromagnetic and a structural transition from austenite to martensitic phase.
Thermo-magnetization measurements M(T) confirms ferromagnetic transition
temperature TC at 222 K and martensitic transition starting at 127 K(MS).
Magnetization measurement M(H) at 10 K confirms the ferromagnetic state.
Frequency dependence of ac susceptibility \c{hi}' at low temperature suggests
spin glass behavior in the system. The isothermal magnetic entropy change
values have been found to be 1.14 J/Kg.K, 2.69 J/Kg.K and 3.9 J/Kg.K, with
refrigeration capacities of 19.6 J/kg, 37.8 J/kg and 54.6 J/kg for the field
change of 1, 2 and 3 Tesla respectively at 227 K.Comment: 16 pages text + Figs. Ni50Mn30Sn20 alloy: reasonable refrigeration
capacity tunable to Room
Synchrotron aging and the radio spectrum of SN 1993J
We combine the GMRT low frequency radio observations of SN 1993J with the VLA
high frequency radio data to get a near simultaneous spectrum around day 3200
since explosion. The low frequency measurements of the supernova determine the
turnover frequency and flux scale of the composite spectrum and help reveal a
steepening in the spectral index, , in the optically
thin part of the spectrum. This is the first observational evidence of a break
in the radio spectrum of a young supernova. We associate this break with the
phenomenon of synchrotron aging of radiating electrons. From the break in the
spectrum we calculate the magnetic field in the shocked region independent of
the equipartition assumption between energy density of relativistic particles
and magnetic energy density. We determine the ratio of these two energy
densities and find that this ratio is in the range: . We also predict the nature of the evolution of the synchrotron break
frequency with time, with competing effects due to diffusive Fermi acceleration
and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ
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