2,405 research outputs found
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
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
Active Shooter Preparedness Among Dental Hygiene Students
Purpose: Active shooter incidents (ASIs) occurring in dental hygiene academic settings present unique challenges and research examining institutional preparation of dental hygiene students for such incidents is lacking. The purpose of this pilot project was to examine the perceived preparedness, confidence, and awareness of dental hygiene students regarding ASIs. Methods: A validated 24-item electronic survey was distributed to dental hygiene students (n=68) at one institution to measure their preparedness, confidence, and awareness regarding ASIs. Descriptive statistics and Pearson correlations were used for data analysis. Results: Fifty-seven dental hygiene students completed the survey for a response rate of 84%. Many participants felt slightly prepared (n=26, 45.6%) or not prepared (n=15, 26.3%) to respond to an ASI in the classroom. Most were slightly confident (n=26, 45.6%) or not confident (n=16, 26.3%) in helping to control the classroom during an ASI. Over half (n=32, 56.1%) were not certain if their institution provided active shooter trainings and were not certain if drills occurred (n=25,43.8%). Perceived preparedness was positively correlated with confidence in helping to control an ASI in the classroom (r(56)=.616, p=.000). Positive correlations were also identified with perceived preparedness to respond in a lab or clinic with the assumption that ASIs are taken seriously at their institution (r(56)=.375, p=.004). Conclusion: A general lack of preparedness and confidence for responding to ASIs may exist among dental hygiene students along with a lack of awareness regarding trainings and drills. Educational institutions should implement best practices for preparing dental hygiene students for ASIs
The Heider balance - a continuous approach
The Heider balance (HB) is investigated in a fully connected graph of
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
Divergent transcriptional responses to low temperature among populations of alpine and lowland species of New Zealand stick insects (Micrarchus).
In widespread and genetically structured populations, temperature variation may lead to among-population differentiation of thermal biology. The New Zealand stick insect genus Micrarchus contains four species that inhabit different thermal environments, two of which are geographically widespread. RNA-Seq and quantitative PCR were used to investigate the transcriptional responses to cold shock among lowland and alpine species to identify cold-responsive transcripts that differ between the species and to determine whether there is intraspecific geographical variation in gene expression. We also used mitochondrial DNA, nuclear 28S ribosomal DNA and transcriptome-wide SNPs to determine phylogeographic structure and the potential for differences in genetic backgrounds to contribute to variation in gene expression. RNA-Seq identified 2160 unigenes that were differentially expressed as a result of low-temperature exposure across three populations from two species (M. hystriculeus and M. nov. sp. 2), with a majority (68% ± 20%) being population specific. This extensive geographical variation is consistent across years and is likely a result of background genetic differences among populations caused by genetic drift and possibly local adaptation. Responses to cold shock shared among alpine M. nov. sp. 2 populations included the enrichment of cuticular structure-associated transcripts, suggesting that cuticle modification may have accompanied colonization of low-temperature alpine environments and the development of a more cold-hardy phenotype
Dynamics of Social Balance on Networks
We study the evolution of social networks that contain both friendly and
unfriendly pairwise links between individual nodes. The network is endowed with
dynamics in which the sense of a link in an imbalanced triad--a triangular loop
with 1 or 3 unfriendly links--is reversed to make the triad balanced. With this
dynamics, an infinite network undergoes a dynamic phase transition from a
steady state to "paradise"--all links are friendly--as the propensity p for
friendly links in an update event passes through 1/2. A finite network always
falls into a socially-balanced absorbing state where no imbalanced triads
remain. If the additional constraint that the number of imbalanced triads in
the network does not increase in an update is imposed, then the network quickly
reaches a balanced final state.Comment: 10 pages, 7 figures, 2-column revtex4 forma
Identification of cold-responsive genes in a New Zealand alpine stick insect using RNA-Seq.
The endemic New Zealand alpine stick insect Micrarchus nov. sp. 2 regularly experiences sub-zero temperatures in the wild. 454-based RNA-Seq was used to generate a de novo transcriptome and differentiate between treatments to investigate the genetic basis of cold tolerance. Non cold-treated individuals were compared to those exposed to 0°C for 1 h followed by a 1 h recovery period at 20°C. We aligned 607,410 Roche 454 reads, generating a transcriptome of 5235 contigs. Differential expression analysis ranked candidate cold responsive genes for qPCR validation by P-value. The top nine up-regulated candidates, together with eight a priori targets identified from previous studies, had their relative expression quantified using qPCR. Three candidate cold responsive genes from the RNA-Seq data were verified as significantly up-regulated, annotated as: prolyl 4-hydroxylase subunit alpha-1 (P4HA1), staphylococcal nuclease domain-containing protein 1 (snd1) and cuticular protein analogous to peritrophins 3-D2 (Cpap3-d2). All three are novel candidate genes, illustrating the varied response to low temperature across insects
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