3,691 research outputs found
Checking Interaction-Based Declassification Policies for Android Using Symbolic Execution
Mobile apps can access a wide variety of secure information, such as contacts
and location. However, current mobile platforms include only coarse access
control mechanisms to protect such data. In this paper, we introduce
interaction-based declassification policies, in which the user's interactions
with the app constrain the release of sensitive information. Our policies are
defined extensionally, so as to be independent of the app's implementation,
based on sequences of security-relevant events that occur in app runs. Policies
use LTL formulae to precisely specify which secret inputs, read at which times,
may be released. We formalize a semantic security condition, interaction-based
noninterference, to define our policies precisely. Finally, we describe a
prototype tool that uses symbolic execution to check interaction-based
declassification policies for Android, and we show that it enforces policies
correctly on a set of apps.Comment: This research was supported in part by NSF grants CNS-1064997 and
1421373, AFOSR grants FA9550-12-1-0334 and FA9550-14-1-0334, a partnership
between UMIACS and the Laboratory for Telecommunication Sciences, and the
National Security Agenc
Randomized Extended Kaczmarz for Solving Least-Squares
We present a randomized iterative algorithm that exponentially converges in
expectation to the minimum Euclidean norm least squares solution of a given
linear system of equations. The expected number of arithmetic operations
required to obtain an estimate of given accuracy is proportional to the square
condition number of the system multiplied by the number of non-zeros entries of
the input matrix. The proposed algorithm is an extension of the randomized
Kaczmarz method that was analyzed by Strohmer and Vershynin.Comment: 19 Pages, 5 figures; code is available at
https://github.com/zouzias/RE
The application of reliability methods in the design of stiffened FRP composite panels for marine vessels
The use of composite laminate materials has increased rapidly in recent years due to their excellent strength to weight ratio and resistance to corrosion. In the construction of marine vessels, stiffened plates are the most commonly used structural elements, forming the deck, bottom hull, side shells and bulkheads. This paper presents the use of a stochastic approach to the design of stiffened marine composite panels as part of a current research programme into developing stochastic methods for composite ship structures, accounting for variations in material properties, geometric indices and processing techniques, from the component level to the full system level. An analytical model for the solution of a stiffened isotropic plate using a grillage analogy is extended by the use of equivalent elastic properties for composite modelling. This methodology is applied in a reliability analysis of an isotropic (steel) stiffened plate before the final application for a reliability analysis for a FRP composite stiffened plate
Synergistic Gravity and the Role of Resonances in GRS-Inspired Braneworlds
We consider 5D braneworld models of quasi-localized gravity in which 4D
gravity is reproduced at intermediate scales while the extra dimension opens up
at both the very short and the very long distances, where the geometry is flat.
Our main interest is the interplay between the zero mode of these models,
whenever a normalizable zero mode exists, and the effects of zero energy
graviton resonant modes coming from the contributions of massive KK modes. We
first consider a compactified version of the GRS model and find that
quasi-localized gravity is characterized by a scale for which both the
resonance and the zero mode have significant contribution to 4D gravity. Above
this scale, gravity is primarily mediated by the zero mode, while the resonance
gives only minor corrections. Next, we consider an asymmetric version of the
standard non-compact GRS model, characterized by different cosmological
constants on each AdS side. We show that a resonance is present but the
asymmetry, through the form of the localizing potential, can weaken it,
resulting in a shorter lifetime and, thus, in a shorter distance scale for 4D
gravity. As a third model exhibiting quasi-localization, we consider a version
of the GRS model in which the central positive tension brane has been replaced
by a configuration of a scalar field propagating in the bulk.Comment: 18 pages, 3 figures, added 1 figure, revised version as published in
Class. Quant. Gra
Rational solutions of the discrete time Toda lattice and the alternate discrete Painleve II equation
The Yablonskii-Vorob'ev polynomials , which are defined by a second
order bilinear differential-difference equation, provide rational solutions of
the Toda lattice. They are also polynomial tau-functions for the rational
solutions of the second Painlev\'{e} equation (). Here we define
two-variable polynomials on a lattice with spacing , by
considering rational solutions of the discrete time Toda lattice as introduced
by Suris. These polynomials are shown to have many properties that are
analogous to those of the Yablonskii-Vorob'ev polynomials, to which they reduce
when . They also provide rational solutions for a particular
discretisation of , namely the so called {\it alternate discrete}
, and this connection leads to an expression in terms of the Umemura
polynomials for the third Painlev\'{e} equation (). It is shown that
B\"{a}cklund transformation for the alternate discrete Painlev\'{e} equation is
a symplectic map, and the shift in time is also symplectic. Finally we present
a Lax pair for the alternate discrete , which recovers Jimbo and Miwa's
Lax pair for in the continuum limit .Comment: 23 pages, IOP style. Title changed, and connection with Umemura
polynomials adde
Sigurðar saga fóts (The Saga of Sigurðr Foot): A Translation
This is the first English translation of the short Icelandic romance Sigurðar saga fóts, with an introduction presenting the evidence for its dating and immediate literary context. Like most Icelandic romances, Sigurðar saga is a bridal-quest story; the support of a foster-brother is key to the hero winning the bride; and the foster-brothers start out as opponents before recognising their mutual excellence and swearing foster-brotherhood. Uniquely, however, the men who become foster-brothers begin by competing for the same bride (Signý): the eponymous Sigurðr fótr wins Signý only because Ásmundr gives her to him in exchange for foster-brotherhood. Ásmundr’s decision can be read as demonstrating with unusual starkness the superior importance in much Icelandic romance of homosocial relationships over heterosexual ones, giving the saga a certain paradigmatic status. Translating the saga in an open-access forum and reconstructing its literary context will, we hope, encourage further analyses
Sigurðar saga fóts (The Saga of Sigurðr Foot): A Translation
This is the first English translation of the short Icelandic romance Sigurðar saga fóts, with an introduction presenting the evidence for its dating and immediate literary context. Like most Icelandic romances, Sigurðar saga is a bridal-quest story; the support of a foster-brother is key to the hero winning the bride; and the foster-brothers start out as opponents before recognising their mutual excellence and swearing foster-brotherhood. Uniquely, however, the men who become foster-brothers begin by competing for the same bride (Signý): the eponymous Sigurðr fótr wins Signý only because Ásmundr gives her to him in exchange for foster-brotherhood. Ásmundr’s decision can be read as demonstrating with unusual starkness the superior importance in much Icelandic romance of homosocial relationships over heterosexual ones, giving the saga a certain paradigmatic status. Translating the saga in an open-access forum and reconstructing its literary context will, we hope, encourage further analyses
Dynamics of a lattice Universe
We find a solution to Einstein field equations for a regular toroidal lattice
of size L with equal masses M at the centre of each cell; this solution is
exact at order M/L. Such a solution is convenient to study the dynamics of an
assembly of galaxy-like objects. We find that the solution is expanding (or
contracting) in exactly the same way as the solution of a
Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average
density as our model. This points towards the absence of backreaction in a
Universe filled with an infinite number of objects, and this validates the
fluid approximation, as far as dynamics is concerned, and at the level of
approximation considered in this work.Comment: 14 pages. No figure. Accepted version for Classical and Quantum
Gravit
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