On model checking data-independent systems with arrays without reset

A system is data-independent with respect to a data type X iff the operations it can perform on values of type X are restricted to just equality testing. The system may also store, input and output values of type X. We study model checking of systems which are data-independent with respect to two distinct type variables X and Y, and may in addition use arrays with indices from X and values from Y . Our main interest is the following parameterised model-checking problem: whether a given program satisfies a given temporal-logic formula for all non-empty nite instances of X and Y . Initially, we consider instead the abstraction where X and Y are infinite and where partial functions with finite domains are used to model arrays. Using a translation to data-independent systems without arrays, we show that the u-calculus model-checking problem is decidable for these systems. From this result, we can deduce properties of all systems with finite instances of X and Y . We show that there is a procedure for the above parameterised model-checking problem of the universal fragment of the u-calculus, such that it always terminates but may give false negatives. We also deduce that the parameterised model-checking problem of the universal disjunction-free fragment of the u-calculus is decidable. Practical motivations for model checking data-independent systems with arrays include verification of memory and cache systems, where X is the type of memory addresses, and Y the type of storable values. As an example we verify a fault-tolerant memory interface over a set of unreliable memories.Comment: Appeared in Theory and Practice of Logic Programming, vol. 4, no. 5&6, 200

An approximation scheme for an Eikonal Equation with discontinuous coefficient

We consider the stationary Hamilton-Jacobi equation where the dynamics can vanish at some points, the cost function is strictly positive and is allowed to be discontinuous. More precisely, we consider special class of discontinuities for which the notion of viscosity solution is well-suited. We propose a semi-Lagrangian scheme for the numerical approximation of the viscosity solution in the sense of Ishii and we study its properties. We also prove an a-priori error estimate for the scheme in an integral norm. The last section contains some applications to control and image processing problems

Degradation and breakdown characteristics of thin MgO dielectric layers

MgO has been suggested as a possible high-k dielectric for future complementary metal-oxide semiconductor processes. In this work, the time dependent dielectric breakdown (TDDB) characteristics of 20 nm MgO films are discussed. Stress induced leakage current measurements indicate that the low measured Weibull slopes of the TDDB distributions for both n-type and p-type devices cannot be attributed to a lower trap generation rate than for SiO2. This suggests that much fewer defects are required to trigger breakdown in MgO under voltage stress than is the case for SiO2 or other metal-oxide dielectrics. This in turn explains the progressive nature of the breakdown in these films which is observed both in this work and elsewhere. The reason fewer defects are required is attributed to the morphology of the films

Social Balance on Networks: The Dynamics of Friendship and Enmity

How do social networks evolve when both friendly and unfriendly relations exist? Here we propose a simple dynamics for social networks in which the sense of a relationship can change so as to eliminate imbalanced triads--relationship triangles that contains 1 or 3 unfriendly links. In this dynamics, a friendly link changes to unfriendly or vice versa in an imbalanced triad to make the triad balanced. Such networks undergo a dynamic phase transition from a steady state to "utopia"--all friendly links--as the amount of network friendliness is changed. Basic features of the long-time dynamics and the phase transition are discussed.Comment: 16 pages, 11 figures, paper based on an invited talk at Dyonet06, Dynamics on Complex Networks and Applications, Dresden, Germany, Feburary 200

First Results from SPARO: Evidence for Large-Scale Toroidal Magnetic Fields in the Galactic Center

We have observed the linear polarization of 450 micron continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends ~ 170 pc along the Galactic plane and ~ 30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence for poloidal fields in the Galactic center, and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are basically consistent with the model.Comment: 11 pages, 2 figures, 1 table, submitted to ApJ Let

The Heider balance - a continuous approach

The Heider balance (HB) is investigated in a fully connected graph of $N$ nodes. The links are described by a real symmetric array r(i,j), i,j=1,...,N. In a social group, nodes represent group members and links represent relations between them, positive (friendly) or negative (hostile). At the balanced state, r(i,j)r(j,k)r(k,i)>0 for all the triads (i,j,k). As follows from the structure theorem of Cartwright and Harary, at this state the group is divided into two subgroups, with friendly internal relations and hostile relations between the subgroups. Here the system dynamics is proposed to be determined by a set of differential equations. The form of equations guarantees that once HB is reached, it persists. Also, for N=3 the dynamics reproduces properly the tendency of the system to the balanced state. The equations are solved numerically. Initially, r(i,j) are random numbers distributed around zero with a symmetric uniform distribution of unit width. Calculations up to N=500 show that HB is always reached. Time to get the balanced state varies with the system size N as N^{-1/2}. The spectrum of relations, initially narrow, gets very wide near HB. This means that the relations are strongly polarized. In our calculations, the relations are limited to a given range around zero. With this limitation, our results can be helpful in an interpretation of somestatistical data.Comment: 9 pages, 4 figures. Int. J. Mod. Phys. C (2005), in prin

Postmortem Dental Records Identification by Dental Hygiene Students: A Pilot Study

Purpose: Dental hygienists have the potential for filling critical roles in multidisciplinary victim identification teams. The purpose of this pilot study was to evaluate the accuracy of dental hygiene students utilizing dental charting, bitewings, and skull dentitions for the purpose of making identification matches. Methods: Thirty senior dental hygiene students (n=30) independently viewed an asynchronous online multimedia-based presentation on the procedures used for collecting and recording forensic dental evidence. Following the presentation participants attempted to chart and match three bitewing radiograph sets to three human skull dentitions by correlating matches/exclusions. Immediately following the activity, each student completed a questionnaire rating the difficulty of the exercise, as well as their confidence, and willingness to volunteer as a forensics team member. Descriptive statistics were used to analyze the data. Results: Of the total sample 36.7% (n=11) reported having prior experiences with dental radiography; while the majority (63.33%, n=19) reported no prior experience. Participants\u27 accuracy scores for dental charting ranged from 91.23% (SD=9.42) to 99.06% (SD=3.60), with no statistically significant difference based on prior experience (p\u3e0.05). The average interrater reliability was 86% (p\u3c0.0001), indicating a high level of agreement with charting skulls and radiographs. No statistically significant differences were found for charting time, perceived difficulty, or level of confidence when comparing experience among the participants (p\u3e0.05). Conclusions: Regardless of previous experience, dental hygiene students were able to match postmortem dentitions and radiographs with good interrater reliability and did not differ statistically for charting time, perceived difficulty, or confidence. Results suggest dental hygienists can work as effective victim identification team members when educational programs are implemented