Single-particle vs. pair superfluidity in a bilayer system of dipolar bosons

We consider the ground state of a bilayer system of dipolar bosons, where dipoles are oriented by an external field in the direction perpendicular to the parallel planes. Quantum Monte Carlo methods are used to calculate the ground-state energy, the one-body and two-body density matrix, and the superfluid response as a function of the separation between layers. We find that by decreasing the interlayer distance for fixed value of the strength of the dipolar interaction, the system undergoes a quantum phase transition from a single-particle to a pair superfluid. The single-particle superfluid is characterized by a finite value of both the atomic condensate and the super-counterfluid density. The pair superfluid phase is found to be stable against formation of many-body cluster states and features a gap in the spectrum of elementary excitations.Comment: 4 figure

Phonon transport effects in one-dimensional width-modulated graphene nanoribbons

We investigate the thermal conductance of one-dimensional periodic width-modulated graphene nanoribbons using lattice dynamics for the phonon spectrum and the Landauer formalism for phonon transport. We conduct a full investigation considering all relevant geometrical features, i.e., the various lengths and widths of the narrow and wide regions that form the channel. In all cases that we examine, we find that width-modulation suppresses the thermal conductance at values even up to ∼70% below those of the corresponding uniform narrow nanoribbon. We show that this can be explained by the fact that the phonon spectrum of the width-modulated channels acquires less dispersive bands with lower group velocities and several narrow bandgaps, which reduce the phonon transmission function significantly. The largest degradation in thermal conductance is determined by the geometry of the narrow regions. The geometry of the wider regions also influences thermal conductance, although modestly. Our results add to the ongoing efforts in understanding the details of phonon transport at the nanoscale, and our conclusions are generic and could also apply to other one-dimensional channel materials

Antimicrobial susceptibility testing in biofilm-growing bacteria

AbstractBiofilms are organized bacterial communities embedded in an extracellular polymeric matrix attached to living or abiotic surfaces. The development of biofilms is currently recognized as one of the most relevant drivers of persistent infections. Among them, chronic respiratory infection by Pseudomonas aeruginosa in cystic fibrosis patients is probably the most intensively studied. The lack of correlation between conventional susceptibility test results and therapeutic success in chronic infections is probably a consequence of the use of planktonically growing instead of biofilm-growing bacteria. Therefore, several in vitro models to evaluate antimicrobial activity on biofilms have been implemented over the last decade. Microtitre plate-based assays, the Calgary device, substratum suspending reactors and the flow cell system are some of the most used in vitro biofilm models for susceptibility studies. Likewise, new pharmacodynamic parameters, including minimal biofilm inhibitory concentration, minimal biofilm-eradication concentration, biofilm bactericidal concentration, and biofilm-prevention concentration, have been defined in recent years to quantify antibiotic activity in biofilms. Using these parameters, several studies have shown very significant quantitative and qualitative differences for the effects of most antibiotics when acting on planktonic or biofilm bacteria. Nevertheless, standardization of the procedures, parameters and breakpoints, by official agencies, is needed before they are implemented in clinical microbiology laboratories for routine susceptibility testing. Research efforts should also be directed to obtaining a deeper understanding of biofilm resistance mechanisms, the evaluation of optimal pharmacokinetic/pharmacodynamic models for biofilm growth, and correlation with clinical outcome

Microscopic description of anisotropic low-density dipolar Bose gases in two dimensions

A microscopic description of the zero energy two-body ground state and many-body static properties of anisotropic homogeneous gases of bosonic dipoles in two dimensions at low densities is presented and discussed. By changing the polarization angle with respect to the plane, we study the impact of the anisotropy, present in the dipole--dipole interaction, on the energy per particle, comparing the results with mean field predictions. We restrict the analysis to the regime where the interaction is always repulsive, although the strength of the repulsion depends on the orientation with respect to the polarization field. We present a series expansion of the solution of the zero energy two-body problem which allows us to find the scattering length of the interaction and to build a suitable Jastrow factor that we use as a trial wave function for both a variational and diffusion Monte Carlo simulation of the infinite system. We find that the anisotropy has an almost negligible impact on the ground state properties of the many-body system in the universal regime where the scattering length governs the physics of the system. We also show that scaling in the gas parameter persists in the dipolar case up to values where other isotropic interactions with the same scattering length yield different predictions.Comment: 9 figures, 1 tabl

Hidden dimers and the matrix maps: Fibonacci chains re-visited

The existence of cycles of the matrix maps in Fibonacci class of lattices is well established. We show that such cycles are intimately connected with the presence of interesting positional correlations among the constituent `atoms' in a one dimensional quasiperiodic lattice. We particularly address the transfer model of the classic golden mean Fibonacci chain where a six cycle of the full matrix map exists at the centre of the spectrum [Kohmoto et al, Phys. Rev. B 35, 1020 (1987)], and for which no simple physical picture has so far been provided, to the best of our knowledge. In addition, we show that our prescription leads to a determination of other energy values for a mixed model of the Fibonacci chain, for which the full matrix map may have similar cyclic behaviour. Apart from the standard transfer-model of a golden mean Fibonacci chain, we address a variant of it and the silver mean lattice, where the existence of four cycles of the matrix map is already known to exist. The underlying positional correlations for all such cases are discussed in details.Comment: 14 pages, 2 figures. Submitted to Physical Review

FIBONACCI SUPERLATTICES OF NARROW-GAP III-V SEMICONDUCTORS

We report theoretical electronic structure of Fibonacci superlattices of narrow-gap III-V semiconductors. Electron dynamics is accurately described within the envelope-function approximation in a two-band model. Quasiperiodicity is introduced by considering two different III-V semiconductor layers and arranging them according to the Fibonacci series along the growth direction. The resulting energy spectrum is then found by solving exactly the corresponding effective-mass (Dirac-like) wave equation using tranfer-matrix techniques. We find that a self-similar electronic spectrum can be seen in the band structure. Electronic transport properties of samples are also studied and related to the degree of spatial localization of electronic envelope-functions via Landauer resistance and Lyapunov coefficient. As a working example, we consider type II InAs/GaSb superlattices and discuss in detail our results in this system.Comment: REVTeX 3.0, 16 pages, 8 figures available upon request. To appear in Semiconductor Science and Technolog

Obésité, facteurs socio-démographiques et indicateurs de santé chez les personnes âgées à Marseille

L’objectif de cette étude est triple : (1) déterminer si les facteurs socio-démographiques que sont l’âge, le niveau d’éducation et le statut marital ont le même impact sur l’obésité chez les femmes et chez les hommes, âgés de 60 ans et plus ; (2) évaluer les associations entre d’une part l’obésité et, d’autre part, l’auto-évaluation de la santé, les incapacités physiques et l’estime de soi ; (3) tester le rôle médiateur potentiel des maladies cardio-vasculaires et du diabète sur la relation entre obésité et auto-évaluation de la santé. Pour cela, 400 personnes âgées de 60 à 92 ans, vivant à Marseille, ont été interrogées. Ces rencontres individuelles comprenaient une prise de mesures anthropométriques et un entretien dirigé à l’aide d’un questionnaire (durée moyenne : 1h30). La prévalence de l’obésité dans notre échantillon de population est de 17 %, taux comparable à l’ensemble de la population française du même âge. Nos analyses ont permis de montrer que les corrélats de l’obésité sont fort différents entre les femmes et les hommes âgés. Chez les hommes, seul le statut marital est significativement associé à l’obésité alors que chez les femmes, l’âge, le niveau d’éducation, l’auto-évaluation de la santé et les incapacités physiques sont associés à l’obésité. Enfin, nous avons montré que la relation entre obésité et auto-évaluation de la santé (observée chez les femmes) est une association indirecte « médiée » par les maladies cardio-vasculaires.The purpose of this study is threefold: (1) to determine whether the socio-demographic factors of age, level of education and marital status have the same impact on obesity in women and in men aged 60 years and above; (2) to evaluate the associations between obesity on the one hand and self-rated health, physical incapacities and self-esteem on the other; (3) to test the mediatory potential of cardio-vascular diseases and diabetes on the relationship between obesity and self-rated health. For this, 400 persons aged from 60 to 92 years, living in Marseille, were questioned. These individual encounters included anthropometric measurement, and an interview carried out with the aid of a questionnaire (average duration: 1h30). The prevalence of obesity in our population sample is 17%, a rate comparable to the whole of this age group in the French population. Our analyses show that the correlates of obesity are very different between older women and men. For the men, only marital status is significantly associated with obesity while for the women, age, education level, self-rated health and physical incapacities are associated with obesity. Finally we have shown that the relation between obesity and self-rated health (for the women) is an indirect association affected by cardio-vascular diseases

Relations entre l’estime de soi et l’état de santé « objectif » des aînés

Malgré de nombreuses études portant sur l’évolution de l’estime de soi au cours de la vie, les relations entre estime de soi, vieillissement et santé restent en partie inexplorées, particulièrement dans la population française. L’objectif de cette étude est double : (1) évaluer les relations entre l’estime de soi et les variables sociodémographiques chez les aînés, notamment l’âge et (2) si, comme nous le supposons, l’avancée en âge est associée à une baisse d’estime de soi : tester le rôle de médiateur des maladies chroniques et des incapacités physiques sur la relation entre estime de soi et avancée en âge. Pour cela, 400 personnes âgées de 60 à 92 ans, aux états de santé fort différents, ont été interviewées individuellement à Marseille (durée moyenne : 1 h 30). Dans cet échantillon, l’âge, le lieu de résidence et la catégorie socioprofessionnelle sont associés à l’estime de soi. Si les maladies chroniques n’ont pas d’effet sur l’estime de soi, les incapacités physiques y sont fortement associées. Nos analyses ont permis de montrer que la relation entre estime de soi négative et avancée en âge n’est pas directe, mais « médiée » par les incapacités physiques. Par ailleurs, et sans cette fois dichotomiser l’estime de soi, une analyse en pistes causales nous a permis de montrer que les incapacités physiques et l’institutionnalisation jouent des rôles de médiateurs entre l’âge et l’estime de soi, considérée cette fois comme variable continue. Ces résultats sont discutés par le biais des activités sociales, mais également à travers les relations de pouvoir inhérentes à la survenue de la dépendance.In spite of several studies on self-esteem covering the human life-span, the relation between self-esteem, aging and health remains incompletely explored, particularly in the French population. The objective of this study is twofold: (1) to assess the relation between self-esteem and socio-demographic factors, notably age, among older French adults, and (2) if, as is presumed, advancing age is associated with lower self-esteem, to test the mediating effect of chronic diseases and physical incapacities on the relation between age and negative self-esteem. For this, 400 older adults living in Marseille, aged from 60 to 92, were individually interviewed (average duration: 1 h 30). In this sample, age, place of residence and educational level were associated with self-esteem. Physical incapacities were also associated with self-esteem, but chronic diseases were not. Our analyses showed that the relationship between advancing age and negative self-esteem is not direct, but mediated by physical incapacities. On the other hand, and without dichotomizing self-esteem, analysis of cause indicates that the relation between age and self-esteem (entered in the model as a continuous variable) was mediated by physical incapacities and institutionalization. These results are discussed through the social activities theory, and through power relationships inherent in dependency

Base de dados geográficos do "Corredor de Nacala", Moçambique.

The demand for agricultural products has been increasing in all countries in the last decades. Together with the decrease in natural resources and the possible impacts to agriculture caused by climatic changes, this aspect has aroused concerns in terms of the development of new global agricultural frontiers. In this context, some regions in Africa have been drawing attention from the world due to their edaphoclimatic conditions, which are favorable for agricultural development. The vision of a modern and dynamic agriculture must be based on the capacity of applying appropriate knowledge and technologies to the environment, as well as to the country´s economic and social situation. Such condition demands the installment of an efficient agricultural innovation system composed by a technical and operational structure which is able to support the agricultural industry along all its stages. Thus, this article aims at presenting some contributions to the formatting of a geographic database of natural resources for the Nacala Corridor, Mozambique. Geotechnology instruments were used for planning, generating and maintaining the accomplished database's data and information. This database will subsidize the integrated management of the region's geographic space from spatial information about landscape, soil, climate, land use, and land cover, thus subsidizing the management of the natural resources and of Mozambique's agricultural sustainability as well