3,447 research outputs found
Worker Profiling and Due Process
Abstract for a piece in the 1995 Unemployment Compensation: Continuity and Change symposium presented by the Advisory Council on Unemployment Compensation and the University of Michigan Journal of Law Reform
Unbiased sampling of globular lattice proteins in three dimensions
We present a Monte Carlo method that allows efficient and unbiased sampling
of Hamiltonian walks on a cubic lattice. Such walks are self-avoiding and visit
each lattice site exactly once. They are often used as simple models of
globular proteins, upon adding suitable local interactions. Our algorithm can
easily be equipped with such interactions, but we study here mainly the
flexible homopolymer case where each conformation is generated with uniform
probability. We argue that the algorithm is ergodic and has dynamical exponent
z=0. We then use it to study polymers of size up to 64^3 = 262144 monomers.
Results are presented for the effective interaction between end points, and the
interaction with the boundaries of the system
Monte Carlo simulations of the HP model (the "Ising model" of protein folding)
Using Wang-Landau sampling with suitable Monte Carlo trial moves (pull moves
and bond-rebridging moves combined) we have determined the density of states
and thermodynamic properties for a short sequence of the HP protein model. For
free chains these proteins are known to first undergo a collapse "transition"
to a globule state followed by a second "transition" into a native state. When
placed in the proximity of an attractive surface, there is a competition
between surface adsorption and folding that leads to an intriguing sequence of
"transitions". These transitions depend upon the relative interaction strengths
and are largely inaccessible to "standard" Monte Carlo methods.Comment: 6 pages, 6 figures. Article in press. To be published in Computer
Physics Communications (2011
A lattice model of hydrophobic interactions
Hydrogen bonding is modeled in terms of virtual exchange of protons between
water molecules. A simple lattice model is analyzed, using ideas and techniques
from the theory of correlated electrons in metals. Reasonable parameters
reproduce observed magnitudes and temperature dependence of the hydrophobic
interaction between substitutional impurities and water within this lattice.Comment: 7 pages, 3 figures. To appear in Europhysics Letter
Analytical description of finite size effects for RNA secondary structures
The ensemble of RNA secondary structures of uniform sequences is studied
analytically. We calculate the partition function for very long sequences and
discuss how the cross-over length, beyond which asymptotic scaling laws apply,
depends on thermodynamic parameters. For realistic choices of parameters this
length can be much longer than natural RNA molecules. This has to be taken into
account when applying asymptotic theory to interpret experiments or numerical
results.Comment: 10 pages, 13 figures, published in Phys. Rev.
Markov processes follow from the principle of Maximum Caliber
Markov models are widely used to describe processes of stochastic dynamics.
Here, we show that Markov models are a natural consequence of the dynamical
principle of Maximum Caliber. First, we show that when there are different
possible dynamical trajectories in a time-homogeneous process, then the only
type of process that maximizes the path entropy, for any given singlet
statistics, is a sequence of identical, independently distributed (i.i.d.)
random variables, which is the simplest Markov process. If the data is in the
form of sequentially pairwise statistics, then maximizing the caliber dictates
that the process is Markovian with a uniform initial distribution. Furthermore,
if an initial non-uniform dynamical distribution is known, or multiple
trajectories are conditioned on an initial state, then the Markov process is
still the only one that maximizes the caliber. Second, given a model, MaxCal
can be used to compute the parameters of that model. We show that this
procedure is equivalent to the maximum-likelihood method of inference in the
theory of statistics.Comment: 4 page
Analysing the Security of Google's implementation of OpenID Connect
Many millions of users routinely use their Google accounts to log in to
relying party (RP) websites supporting the Google OpenID Connect service.
OpenID Connect, a newly standardised single-sign-on protocol, builds an
identity layer on top of the OAuth 2.0 protocol, which has itself been widely
adopted to support identity management services. It adds identity management
functionality to the OAuth 2.0 system and allows an RP to obtain assurances
regarding the authenticity of an end user. A number of authors have analysed
the security of the OAuth 2.0 protocol, but whether OpenID Connect is secure in
practice remains an open question. We report on a large-scale practical study
of Google's implementation of OpenID Connect, involving forensic examination of
103 RP websites which support its use for sign-in. Our study reveals serious
vulnerabilities of a number of types, all of which allow an attacker to log in
to an RP website as a victim user. Further examination suggests that these
vulnerabilities are caused by a combination of Google's design of its OpenID
Connect service and RP developers making design decisions which sacrifice
security for simplicity of implementation. We also give practical
recommendations for both RPs and OPs to help improve the security of real world
OpenID Connect systems
Heteropolymer Sequence Design and Preferential Solvation of Hydrophilic Monomers: One More Application of Random Energy Model
In this paper, we study the role of surface of the globule and the role of
interactions with the solvent for designed sequence heteropolymers using random
energy model (REM). We investigate the ground state energy and surface monomer
composition distribution. By comparing the freezing transition in random and
designed sequence heteropolymers, we discuss the effects of design. Based on
our results, we are able to show under which conditions solvation effect
improves the quality of sequence design. Finally, we study sequence space
entropy and discuss the number of available sequences as a function of imposed
requirements for the design quality
Security Issues in OAuth 2.0 SSO Implementations
Abstract. Many Chinese websites (relying parties) use OAuth 2.0 as the basis of a single sign-on service to ease password management for users. Many sites support five or more different OAuth 2.0 identity providers, giving users choice in their trust point. However, although OAuth 2.0 has been widely implemented (particularly in China), little attention has been paid to security in practice. In this paper we report on a detailed study of OAuth 2.0 implementation security for ten major identity providers and 60 relying parties, all based in China. This study reveals two critical vulnerabilities present in many implementations, both allowing an attacker to control a victim user’s accounts at a relying party without knowing the user’s account name or password. We provide sim-ple, practical recommendations for identity providers and relying parties to enable them to mitigate these vulnerabilities. The vulnerabilities have been reported to the parties concerned.
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