347 research outputs found
Analysing and attacking the 4-way handshake of IEEE 802.11i standard
The IEEE 802.11i standard has been designed to enhance security in wireless networks. In the 4-way handshake the supplicant and the authenticator use the pairwise master key (PMK) to derive a fresh pairwise transient key (PTK). The PMK is not used directly for security while assuming the supplicant and authenticator have the same PMK before running 4-way handshake. In this paper, the 4-way handshake phase has been analysed using Isabelle tool to identify a new Denial-of-Service (DoS) attack. The attack prevents the authenticator from receiving message 4 after the supplicant sends it out. This attack forces the authenticator to re-send the message 3 until time out and subsequently to de-authenticate supplicant. This paper has proposed improvements to the 4-way handshake to avoid the Denial-of-Service attack
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Prediction of jet engine parameters for control design using genetic programming
The simulation of a jet engine behavior is widely used in many different aspects of the engine development and maintenance. Achieving high quality jet engine control systems requires the iterative use of these simulations to virtually test the performance of the engine avoiding any possible damage on the real engine. Jet engine simulations involve the use of mathematical models which are complex and may not always be available. This paper introduces an approach based on Genetic Programming (GP) to model different parameters of a small engine for control design such as the Exhaust Gas Temperature (EGT). The GP approach has no knowledge of the characteristics of the engine. Instead, the model is found by the evolution of models based on past measurements of parameters such as the pump voltage. Once the model is obtained, it is used to predict the behaviour of the jet engine one step ahead. The proposed approach is successfully applied for the simulation of a Behotec j66 jet engine and the results are presented
Transform Ranking: a New Method of Fitness Scaling in Genetic Algorithms
The first systematic evaluation of the effects of six existing forms of fitness scaling in genetic algorithms is presented alongside a new method called transform ranking. Each method has been applied to stochastic universal sampling (SUS) over a fixed number of generations. The test functions chosen were the two-dimensional Schwefel and Griewank functions. The quality of the solution was improved by applying sigma scaling, linear rank scaling, nonlinear rank scaling, probabilistic nonlinear rank scaling, and transform ranking. However, this benefit was always at a computational cost. Generic linear scaling and Boltzmann scaling were each of benefit in one fitness landscape but not the other. A new fitness scaling function, transform ranking, progresses from linear to nonlinear rank scaling during the evolution process according to a transform schedule. This new form of fitness scaling was found to be one of the two methods offering the greatest improvements in the quality of search. It provided the best improvement in the quality of search for the Griewank function, and was second only to probabilistic nonlinear rank scaling for the Schwefel function. Tournament selection, by comparison, was always the computationally cheapest option but did not necessarily find the best solutions
Means, Intent, Lethality, Behaviors, and Psychiatric Diagnosis in Latina Adolescent Suicide Attempters
This article describes the means, intent, lethality, behavioral profiles, and psychiatric diagnoses of adolescent Latina suicide attempters. From a large, mixed-method project studying the sociocultural processes of Latina suicide attempts, we selected 76 participants for this report. In addition to quantitative research data, medical records were available for all 76 participants, as was qualitative data from in-depth interviews for 34 of them. Using the qualitative and quantitative research data, we explored intent and behavioral profiles of the suicidal adolescents. Medical records provided additional information about the means the adolescents used in their attempts, and about their psychiatric diagnoses. The lethality of suicide attempts was coded using the Lethality of Suicide Attempt Rating Scale (LSARS) and the Lethality of Suicide Attempt Rating ScaleâUpdated (LSARS-II). Findings showed that Latina adolescent suicide attempts are low in lethality. Consistent with the literature, most adolescents reported that they attempted by using means available in their homes (cutting and overdosing with medications were the predominant methods). Interesting discrepancies emerged when comparing adolescentsâ self-reported behavioral profiles with cliniciansâ psychiatric diagnoses. This report has implications for diagnosis and treatment approaches for both inpatient and outpatient service providers
Universality Classes for Interface Growth with Quenched Disorder
We present numerical evidence that there are two distinct universality
classes characterizing driven interface roughening in the presence of quenched
disorder. The evidence is based on the behavior of , the coefficient
of the nonlinear term in the growth equation. Specifically, for three of the
models studied, at the depinning transition, while
for the two other models, .Comment: 11 pages and 3 figures (upon request), REVTeX 3.0, (submitted to PRL
Singularities and Avalanches in Interface Growth with Quenched Disorder
A simple model for an interface moving in a disordered medium is presented.
The model exhibits a transition between the two universality classes of
interface growth phenomena. Using this model, it is shown that the application
of constraints to the local slopes of the interface produces avalanches of
growth, that become relevant in the vicinity of the depinning transition. The
study of these avalanches reveals a singular behavior that explains a recently
observed singularity in the equation of motion of the interface.Comment: 4 pages. REVTEX. 4 figs available on request from [email protected]
Delocalization Transition of a Rough Adsorption-Reaction Interface
We introduce a new kinetic interface model suitable for simulating
adsorption-reaction processes which take place preferentially at surface
defects such as steps and vacancies. As the average interface velocity is taken
to zero, the self- affine interface with Kardar-Parisi-Zhang like scaling
behaviour undergoes a delocalization transition with critical exponents that
fall into a novel universality class. As the critical point is approached, the
interface becomes a multi-valued, multiply connected self-similar fractal set.
The scaling behaviour and critical exponents of the relevant correlation
functions are determined from Monte Carlo simulations and scaling arguments.Comment: 4 pages with 6 figures, new comment
Structural and magnetic deconvolution of FePt/FeOx-nanoparticles using x-ray magnetic circular dichroism
Recently, magnetite nanoparticles have attracted much attention, due to their technological potential based on different optic, magnetic and catalytic sections. In particular, the magnetic properties of hybrid nanocrystals can be tailored by the combination of complementary magnetic materials like for example magnetite and FePt. In order to analyse the related magnetic and structural properties of the resulting bi-component systems, we present x-ray absorption and x-ray magnetic circular dichroism studies at the Fe L2,3 edges simultaneously performed in total electron yield and transmission mode, done at room and low temperatures. This provides in particular the separation of volume- and surface-related properties. The investigated system was made up of FePt/FeOx hybrid nanocrystals, which could be uniquely tuned in size and volume ratios. These measurements have been combined with magnetometry and high-resolution transmission electron microscopy studies. The separation between surface and bulk has been done by a deconvolution of the absorption spectra in terms of a linear superposition of reference spectra. With this universally applicable technique we are able to experimentally determine that the outer FeOx shell fraction at the surface has a strongly reduced magnetization and is of maghemite character, while the inner part is more magnetite like. So the technique shown here can be used to characterize nanoparticular systems and determine their structural and magnetic properties
Scaling properties of driven interfaces in disordered media
We perform a systematic study of several models that have been proposed for
the purpose of understanding the motion of driven interfaces in disordered
media. We identify two distinct universality classes: (i) One of these,
referred to as directed percolation depinning (DPD), can be described by a
Langevin equation similar to the Kardar-Parisi-Zhang equation, but with
quenched disorder. (ii) The other, referred to as quenched Edwards-Wilkinson
(QEW), can be described by a Langevin equation similar to the Edwards-Wilkinson
equation but with quenched disorder. We find that for the DPD universality
class the coefficient of the nonlinear term diverges at the depinning
transition, while for the QEW universality class either or
as the depinning transition is approached. The identification
of the two universality classes allows us to better understand many of the
results previously obtained experimentally and numerically. However, we find
that some results cannot be understood in terms of the exponents obtained for
the two universality classes {\it at\/} the depinning transition. In order to
understand these remaining disagreements, we investigate the scaling properties
of models in each of the two universality classes {\it above\/} the depinning
transition. For the DPD universality class, we find for the roughness exponent
for the pinned phase, and
for the moving phase. For the growth exponent, we find for the pinned phase, and for the moving phase.
Furthermore, we find an anomalous scaling of the prefactor of the width on the
driving force. A new exponent , characterizing the
scaling of this prefactor, is shown to relate the values of the roughnessComment: Latex manuscript, Revtex 3.0, 15 pages, and 15 figures also available
via anonymous ftp from ftp://jhilad.bu.edu/pub/abms/ (128.197.42.52
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