618 research outputs found
Epoxy/ graphene nanocomposites – processing and properties: a review
Graphene has recently attracted significant academic and industrial interest because of its excellent performance in mechanical, electrical and thermal applications. Graphene can significantly improve physical properties of epoxy at extremely small loading when incorporated appropriately. Herein, the structure, preparation and properties of epoxy/graphene nanocomposites are reviewed in general, along with detailed examples drawn from the key scientific literature. The modification of graphene and the utilization of these materials in the fabrication of nanocomposites with different processing methods have been explored. This review has been focused on the processing methods and mechanical, electrical, thermal, and fire retardant properties of the nanocomposites. The synergic effects of graphene and other fillers in epoxy matrix have been summarised as well
A Semantic Hierarchy for Erasure Policies
We consider the problem of logical data erasure, contrasting with physical
erasure in the same way that end-to-end information flow control contrasts with
access control. We present a semantic hierarchy for erasure policies, using a
possibilistic knowledge-based semantics to define policy satisfaction such that
there is an intuitively clear upper bound on what information an erasure policy
permits to be retained. Our hierarchy allows a rich class of erasure policies
to be expressed, taking account of the power of the attacker, how much
information may be retained, and under what conditions it may be retained.
While our main aim is to specify erasure policies, the semantic framework
allows quite general information-flow policies to be formulated for a variety
of semantic notions of secrecy.Comment: 18 pages, ICISS 201
Tracking Data-Flow with Open Closure Types
Type systems hide data that is captured by function closures in function
types. In most cases this is a beneficial design that favors simplicity and
compositionality. However, some applications require explicit information about
the data that is captured in closures. This paper introduces open closure
types, that is, function types that are decorated with type contexts. They are
used to track data-flow from the environment into the function closure. A
simply-typed lambda calculus is used to study the properties of the type theory
of open closure types. A distinctive feature of this type theory is that an
open closure type of a function can vary in different type contexts. To present
an application of the type theory, it is shown that a type derivation
establishes a simple non-interference property in the sense of information-flow
theory. A publicly available prototype implementation of the system can be used
to experiment with type derivations for example programs.Comment: Logic for Programming Artificial Intelligence and Reasoning (2013
A stochastic fractal model of the universe related to the fractional Laplacian
A new stochastic fractal model based on a fractional Laplace equation is developed. Exact representation for the spectral and correlation functions under random boundary excitation are obtained. Randomized spectral expansion is constructed for simulation of the solution of the fractional Laplace equation. We present calculations for 2D and 3D spaces for a series of fractional parameters showing a strong memory effect: the decay of correlations is several order of magnitudes less compared to the conventional Laplace equation model
Expansion of random boundary excitations for elliptic PDEs
In this paper we deal with elliptic boundary value problems with random boundary conditions.
Solutions to these problems are inhomogeneous random fields which can be represented as series expansions involving a complete set
of deterministic functions with corresponding random coefficients.
We construct the Karhunen-Lo\`eve (K-L) series expansion which is based on the eigen-decomposition
of the covariance operator.
It can be applied to simulate both homogeneous and inhomogeneous random fields.
We study the correlation structure of solutions to some classical elliptic equations
in respond to random excitations of functions prescribed on the boundary.
We analyze the stochastic solutions for Dirichlet and Neumann boundary conditions
to Laplace equation,
biharmonic equation, and to the Lam\'e system of elasticity equations.
Explicit formulae for the correlation tensors of the generalized solutions
are obtained when
the boundary function is a white noise, or a homogeneous random field on a circle, a sphere,
and a half-space.
These exact results may serve as an excellent benchmark for
developing numerical methods, e.g., Monte Carlo simulations,
stochastic volume and boundary element methods
Stokes flows under random boundary velocity excitations
A viscous Stokes flow over a disc under random fluctuations of the
velocity on the boundary is studied.
We give exact Karhunen-Lo\`eve (K-L) expansions for the velocity components,
pressure, stress, and vorticity, and the series representations for
the corresponding correlation tensors.
Both the white noise fluctuations, and general homogeneous
random excitations of the velocities prescribed on the boundary are studied.
We analyze the decay of correlation functions in angular and radial
directions, both for exterior and interior Stokes problems.
Numerical experiments show the fast convergence of the K-L expansions.
The results indicate that ignoring the boundary
condition uncertainty dramatically underestimates the variance of
the velocity and pressure in the interior/exterior of the domain
Expansion of random boundary excitations for elliptic PDEs
In this paper we deal with elliptic boundary value problems with random
boundary conditions. Solutions to these problems are inhomogeneous random
fields which can be represented as series expansions involving a complete set
of deterministic functions with corresponding random coefficients. We
construct the Karhunen-Loève (K-L) series expansion which is based on the
eigen-decomposition of the covariance operator. It can be applied to simulate
both homogeneous and inhomogeneous random fields. We study the correlation
structure of solutions to some classical elliptic equations in respond to
random excitations of functions prescribed on the boundary. We analyze the
stochastic solutions for Dirichlet and Neumann boundary conditions to Laplace
equation, biharmonic equation, and to the Lamé system of elasticity
equations. Explicit formulae for the correlation tensors of the generalized
solutions are obtained when the boundary function is a white noise, or a
homogeneous random field on a circle, a sphere, and a half-space. These exact
results may serve as an excellent benchmark for developing numerical methods,
e.g., Monte Carlo simulations, stochastic volume and boundary element
methods
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Termination-insensitive noninterference leaks more than just a bit
Current tools for analysing information flow in programs build upon ideas going back to Denning's work from the 70's. These systems enforce an imperfect notion of information flow which has become known as termination-insensitive noninterference. Under this version of noninterference, information leaks are permitted if they are transmitted purely by the program's termination behaviour (i.e., whether it terminates or not). This imperfection is the price to pay for having a security condition which is relatively liberal (e.g. allowing while-loops whose termination may depend on the value of a secret) and easy to check. But what is the price exactly? We argue that, in the presence of output, the price is higher than the “one bit” often claimed informally in the literature, and effectively such programs can leak all of their secrets. In this paper we develop a definition of termination-insensitive noninterference suitable for reasoning about programs with outputs. We show that the definition generalises “batch-job” style definitions from the literature and that it is indeed satisfied by a Denning-style program analysis with output. Although more than a bit of information can be leaked by programs satisfying this condition, we show that the best an attacker can do is a brute-force attack, which means that the attacker cannot reliably (in a technical sense) learn the secret in polynomial time in the size of the secret. If we further assume that secrets are uniformly distributed, we show that the advantage the attacker gains when guessing the secret after observing a polynomial amount of output is negligible in the size of the secret
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