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

Simplified Langevin approach to the Peyrard-Bishop-Dauxois model of DNA

A simple Langevin approach is used to study stationary properties of the Peyrard-Bishop-Dauxois model for DNA, allowing known properties to be recovered in an easy way. Results are shown for the denaturation transition in homogeneous samples, for which some implications, so far overlooked, of an analogy with equilibrium wetting transitions are highlighted. This analogy implies that the order-parameter, asymptotically, exhibits a second order transition even if it may be very abrupt for non-zero values of the stiffness parameter. Not surprisingly, we also find that for heterogeneous DNA, within this model the largest bubbles in the pre-melting stage appear in adenine-thymine rich regions, while we suggest the possibility of some sort of not strictly local effects owing to the merging of bubbles.Comment: 4 pages, 2 figure

Topics in coarsening phenomena

These lecture notes give a very short introduction to coarsening phenomena and summarize some recent results in the field. They focus on three aspects: the super-universality hypothesis, the geometry of growing structures, and coarsening in the spiral kinetically constrained model.Comment: Lecture notes. Fundamental Problems in Statistical Physics XII, Leuven, Aug 30 - Sept 12, 200

Mean-field analysis of the q-voter model on networks

We present a detailed investigation of the behavior of the nonlinear q-voter model for opinion dynamics. At the mean-field level we derive analytically, for any value of the number q of agents involved in the elementary update, the phase diagram, the exit probability and the consensus time at the transition point. The mean-field formalism is extended to the case that the interaction pattern is given by generic heterogeneous networks. We finally discuss the case of random regular networks and compare analytical results with simulations.Comment: 20 pages, 10 figure

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

Nonequilibrium wetting

When a nonequilibrium growing interface in the presence of a wall is considered a nonequilibrium wetting transition may take place. This transition can be studied trough Langevin equations or discrete growth models. In the first case, the Kardar-Parisi-Zhang equation, which defines a very robust universality class for nonequilibrium moving interfaces, with a soft-wall potential is considered. While in the second, microscopic models, in the corresponding universality class, with evaporation and deposition of particles in the presence of hard-wall are studied. Equilibrium wetting is related to a particular case of the problem, it corresponds to the Edwards-Wilkinson equation with a potential in the continuum approach or to the fulfillment of detailed balance in the microscopic models. In this review we present the analytical and numerical methods used to investigate the problem and the very rich behavior that is observed with them.Comment: Review, 36 pages, 16 figure

The rise in narghile (shisha, hookah) waterpipe tobacco smoking: A qualitative study of perceptions of smokers and non smokers

<p>Abstract</p> <p>Background</p> <p>The prevalence of waterpipe tobacco smoking (WTS) in the Middle East region and worldwide is increasing. There is evidence to indicate both short term and long term health effects of WTS, resulting in the issuance of an advisory note by the World Health Organization.</p> <p>Methods</p> <p>This research aimed at gaining an in-depth understanding of the factors contributing to the rise in WTS in Lebanon. Qualitative focus groups (25) and in-depth interviews (9) were conducted with adults in Lebanon in 2007. Participants were recruited to represent diversity in smoking status, gender, age groups and urban/rural residence. The interviews and focus groups were thematically analyzed, and recurrent themes noted and summarized.</p> <p>Results</p> <p>The main themes identified were availability, affordability, innovation, influence of media, lack of a policy framework, and the sensory characteristics evoked from WTS. Men and women, smokers and non-smokers, and younger and older participants differed in their emphases on the above themes. These themes, though specific to waterpipe, are similar to themes manipulated by the cigarette industry, and eventually controlled through tobacco control policies.</p> <p>Conclusions</p> <p>Understanding reasons behind the rise in waterpipe tobacco use is important if appropriate prevention, cessation, and policy interventions are to be formulated. Strict adherence to the FCTC is warranted, with careful and vigilant attention that all tobacco products are covered by laws in both high as well as middle to lower income countries.</p

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

Women’s health and well-being in low-income formal and informal neighbourhoods on the eve of the armed conflict in Aleppo

Objectives To explore how married women living in low-income formal and informal neighbourhoods in Aleppo, Syria, perceived the effects of neighbourhood on their health and well-being, and the relevance of these findings to future urban rebuilding policies post-conflict. Methods Semi-structured interviews were undertaken with eighteen married women living in informal or socioeconomically disadvantaged formal neighbourhoods in Aleppo in 2011, a year before the armed conflict caused massive destruction in all these neighbourhoods. Results Our findings suggest that the experience of neighbourhood social characteristics is even more critical to women’s sense of well-being than environmental conditions and physical infrastructure. Most prominent was the positive influence of social support on well-being. Conclusions The significance of this study lies, first, in its timing, before the widespread destruction of both formal and informal neighbourhoods in Aleppo and, second, and in its indication of the views of women who lived in marginalised communities on what neighbourhood characteristics mattered to them. Further research post-conflict needs to explore how decisions on urban rebuilding are made and their likely influence on health and well-being

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