99 research outputs found
Critical wetting of a class of nonequilibrium interfaces: A mean-field picture
A self-consistent mean-field method is used to study critical wetting
transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang
(KPZ) interfaces in the presence of a bounding substrate. In the case of
positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary,
interfaces corresponding to negative nonlinearities lead to three different
regimes of critical behavior for the surface order-parameter: (i) a trivial
Gaussian regime, (ii) a weak-fluctuation regime with a trivially located
critical point and nontrivial exponents, and (iii) a highly non-trivial
strong-fluctuation regime, for which we provide a full solution by finding the
zeros of parabolic-cylinder functions. These analytical results are also
verified by solving numerically the self-consistent equation in each case.
Analogies with and differences from equilibrium critical wetting as well as
nonequilibrium complete wetting are also discussed.Comment: 11 pages, 2 figure
Anisotropic model of kinetic roughening:he strong-coupling regime
We study the strong coupling (SC) limit of the anisotropic Kardar-Parisi-Zhang (KPZ) model. A systematic mapping of the continuum model to its lattice equivalent shows that in the SC limit, anisotropic perturbations destroy all spatial correlations but retain a temporal scaling which shows a remarkable crossover along one of the two spatial directions, the choice of direction depending on the relative strength of anisotropicity. The results agree with exact numerics and are expected to settle the long-standing SC problem of a KPZ model in the infinite range limit. © 2007 The American Physical Society
Classification d'expressions vocales passives versus actives
Six expressions sont gĂ©nĂ©ralement considĂ©rĂ©es pour caractĂ©riser les Ă©tats Ă©motifs humains : Sourire, Surprise, ColĂšre, Tristesse, dĂ©goĂ»t et Neutre. DiffĂ©rentes mesures peuvent ĂȘtre extraites Ă partir du signal de parole pour caractĂ©riser ces expressions, Ă savoir la frĂ©quence fondamentale, l'Ă©nergie, le SPI (rapport des Ă©nergies des HF et des BF dans le signal) et le dĂ©bit de parole. Une classification automatique des cinq expressions basĂ©es sur ces caractĂ©ristiques prĂ©sente des conflits entre la ColĂšre, la Surprise et le Sourire d'une part et le Neutre et la Tristesse d'autre part. Ce conflit entre classes d'expressions est Ă©galement retrouvĂ© chez le classifieur humain. Nous proposons donc de dĂ©finir deux classes d'expressions: Active regroupant le Sourire, la Surprise et la ColĂšre et Passive regroupant le Neutre et la Tristesse. Une telle classification est Ă©galement plus rĂ©aliste et plus appropriĂ©e pour l'intĂ©gration d'information de parole dans un systĂšme de classification multimodale combinant la parole et la vidĂ©o, ce qui est Ă long terme le but de notre travail. Dans ce papier, diffĂ©rentes mĂ©thodes de classification sont testĂ©es: un classifieur BayĂ©sien, une Analyse Discriminante LinĂ©aire (ADL), le classifieur au K plus proches vosins(KNN) et un classifieur Ă Machine Ă Vecteur de Support (SVM) avec une fonction de base gaussienne. Pour les deux classes considĂ©rĂ©es, les meilleurs taux de classification sont obtenus avec le classificateur SVM avec un taux de reconnaissance de 89.74% pour l'Ă©tat Actif et de 86.54 % pour l'Ă©tat Passif
âWaterpipe Is Like a Wifeâ: Qualitative Assessment of Perspectives on Waterpipe Smoking Dependence
Background: Waterpipe (WP) smoking has become a global public health problem in recent decades and growing evidence indicates that it can cause nicotine dependence. Most evidence on WP dependence to date has been derived from survey- or laboratory based studies. This study employed qualitative methods to explore WP usersâ perceptions of dependence in Aleppo, Syria.Methods: A total of 15 focus groups were conducted with 64 adult WP smokers (51 males and 13 females) using a semi-structured interview. All focus group discussions were audiotaped, transcribed, and coded using directed content analysis. Findings: Several WP dependence features were consistent with those commonly reported by cigarette smokers. These included positively reinforced features, such as smokingâs association with social gatherings and cultural connectedness, and negatively reinforced features including relief of withdrawal symptoms, stress, and boredom. Although interest in quitting was low, many users perceived quitting WP to be difficult and an indicator of loss of control over smoking, a common marker of dependence. Several observed dependence features were specific to WP, including transitioning from social smoking to smoking alone, and adapting oneâs behavior to the considerable effort normally required to engage in WP smoking despite inconvenience or cost, and often atthe expense of other reinforcers such as social interaction.Conclusion: The general and specific features of WP dependence need to be considered in developing instruments to measure WP dependence, in clinical assessment of WP dependence, and in developing cessation programs
Absorbing state phase transitions with a non-accessible vacuum
We analyze from the renormalization group perspective a universality class of
reaction-diffusion systems with absorbing states. It describes models where the
vacuum state is not accessible, as the set of reactions together
with creation processes of the form with . This class
includes the (exactly solvable in one-dimension) {\it reversible} model as a particular example, as well as many other {\it
non-reversible} reactions, proving that reversibility is not the main feature
of this class as previously thought. By using field theoretical techniques we
show that the critical point appears at zero creation-rate (in accordance with
exact results), and it is controlled by the well known pair-coagulation
renormalization group fixed point, with non-trivial exactly computable critical
exponents in any dimension. Finally, we report on Monte-Carlo simulations,
confirming all field theoretical predictions in one and two dimensions for
various reversible and non-reversible models.Comment: 6 pages. 3 Figures. Final version as published in J.Stat.Mec
Critical wetting of a class of nonequilibrium interfaces: A computer simulation study
Critical wetting transitions under nonequilibrium conditions are studied
numerically and analytically by means of an interface-displacement model
defined by a Kardar-Parisi-Zhang equation, plus some extra terms representing a
limiting, short-ranged attractive wall. Its critical behavior is characterized
in detail by providing a set of exponents for both the average height and the
surface order-parameter in one dimension. The emerging picture is qualitatively
and quantitatively different from recently reported mean-field predictions for
the same problem. Evidence is shown that the presence of the attractive wall
induces an anomalous scaling of the interface local slopes.Comment: 7 pages, 8 figure
Applications of Field-Theoretic Renormalization Group Methods to Reaction-Diffusion Problems
We review the application of field-theoretic renormalization group (RG)
methods to the study of fluctuations in reaction-diffusion problems. We first
investigate the physical origin of universality in these systems, before
comparing RG methods to other available analytic techniques, including exact
solutions and Smoluchowski-type approximations. Starting from the microscopic
reaction-diffusion master equation, we then pedagogically detail the mapping to
a field theory for the single-species reaction k A -> l A (l < k). We employ
this particularly simple but non-trivial system to introduce the
field-theoretic RG tools, including the diagrammatic perturbation expansion,
renormalization, and Callan-Symanzik RG flow equation. We demonstrate how these
techniques permit the calculation of universal quantities such as density decay
exponents and amplitudes via perturbative eps = d_c - d expansions with respect
to the upper critical dimension d_c. With these basics established, we then
provide an overview of more sophisticated applications to multiple species
reactions, disorder effects, L'evy flights, persistence problems, and the
influence of spatial boundaries. We also analyze field-theoretic approaches to
nonequilibrium phase transitions separating active from absorbing states. We
focus particularly on the generic directed percolation universality class, as
well as on the most prominent exception to this class: even-offspring branching
and annihilating random walks. Finally, we summarize the state of the field and
present our perspective on outstanding problems for the future.Comment: 10 figures include
Childhood solid tumours in relation to population mixing around the time of birth
In a retrospective cohort study of 673 787 live births in the Northern Region of England, 1975 - 1994, we investigated whether a higher level of population mixing around birth was a risk factor for solid tumours, by diagnostic group (Hodgkin's disease, brain and spinal tumours, neuroblastoma, other solid tumours), diagnosed during 1975-2001 under age 15 years. Logistic regression was used to relate risk to population mixing, based on (i) all movers and (ii) incomers from outside the region. Both ward and county district level analyses were performed. There was a decreased risk of brain and spinal tumours with increasing population mixing based on incomers from outside the region (OR for trend across three categories = 0.79, 95% CI: 0.66-0.95, P = 0.01 in the ward level analysis). Although this may be because of chance, it is consistent with a role of exposure to infection and immunological response in the aetiology of these tumours. For other tumour groups, there was no consistent evidence of an association between risk and population mixing
Identifying related cancer types based on their incidence among people with multiple cancers
BACKGROUND: There are several reasons that someone might be diagnosed with more than one primary cancer. The aim of this analysis was to determine combinations of cancer types that occur more often than expected. The expected values in previous analyses are based on age-and-gender-adjusted risks in the population. However, if cancer in people with multiple primaries is somehow different than cancer in people with a single primary, then the expected numbers should not be based on all diagnoses in the population. METHODS: In people with two or more cancer types, the probability that a specific type is diagnosed was determined as the number of diagnoses for that cancer type divided by the total number of cancer diagnoses. If two types of cancer occur independently of one another, then the probability that someone will develop both cancers by chance is the product of the individual probabilities for each type. The expected number of people with both cancers is the number of people at risk multiplied by the separate probabilities for each cancer. We performed the analysis on records of cancer diagnoses in British Columbia, Canada between 1970 and 2004. RESULTS: There were 28,159 people with records of multiple primary cancers between 1970 and 2004, including 1,492 people with between three and seven diagnoses. Among both men and women, the combinations of esophageal cancer with melanoma, and kidney cancer with oral cancer, are observed more than twice as often as expected. CONCLUSION: Our analysis suggests there are several pairs of primary cancers that might be related by a shared etiological factor. We think that our method is more appropriate than others when multiple diagnoses of primary cancer are unlikely to be the result of therapeutic or diagnostic procedures
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