Noise and dynamics of self-organized critical phenomena

Different microscopic models exhibiting self-organized criticality are studied numerically and analytically. Numerical simulations are performed to compute critical exponents, mainly the dynamical exponent, and to check universality classes. We find that various models lead to the same exponent, but this universality class is sensitive to disorder. From the dynamic microscopic rules we obtain continuum equations with different sources of noise, which we call internal and external. Different correlations of the noise give rise to different critical behavior. A model for external noise is proposed that makes the upper critical dimensionality equal to 4 and leads to the possible existence of a phase transition above d=4. Limitations of the approach of these models by a simple nonlinear equation are discussed.

Self-organized evolution in a socio-economic environment

We propose a general scenario to analyze technological changes in socio-economic environments. We illustrate the ideas with a model that incorporating the main trends is simple enough to extract analytical results and, at the same time, sufficiently complex to display a rich dynamic behavior. Our study shows that there exists a macroscopic observable that is maximized in a regime where the system is critical, in the sense that the distribution of events follow power laws. Computer simulations show that, in addition, the system always self-organizes to achieve the optimal performance in the stationary state.

Self-dynamic structure factor of dense liquids: Theory and simulation

The self-intermediate dynamic structure factor Fs(k,t) of liquid lithium near the melting temperature is calculated by molecular dynamics. The results are compared with the predictions of several theoretical approaches, paying special attention to the Lovesey model and the Wahnstrm and Sjgren mode-coupling theory. To this end the results for the Fs(k,t) second memory function predicted by both models are compared with the ones calculated from the simulations.

Self and cross-velocity correlation functions and diffusion coefficients in liquids: a molecular dynamics study of binary mixtures of soft spheres

Molecular dynamics simulation is applied to the study of the diffusion properties in binary liquid mixtures made up of soft-sphere particles with different sizes and masses. Self- and distinct velocity correlation functions and related diffusion coefficients have been calculated. Special attention has been paid to the dynamic cross correlations which have been computed through recently introduced relative mean molecular velocity correlation functions which are independent on the reference frame. The differences between the distinct velocity correlations and diffusion coefficients in different reference frames (mass-fixed, number-fixed, and solvent-fixed) are discussed.

Dynamical properties of the Zhang model of self-organized criticality

Critical exponents of the infinitely slowly driven Zhang model of self-organized criticality are computed for d=2 and 3, with particular emphasis devoted to the various roughening exponents. Besides confirming recent estimates of some exponents, new quantities are monitored, and their critical exponents computed. Among other results, it is shown that the three-dimensional exponents do not coincide with the Bak-Tang-Wiesenfeld [Phys. Rev. Lett. 59, 381 (1987); Phys. Rev. A 38, 364 (1988)] (Abelian) model, and that the dynamical exponent as computed from the correlation length and from the roughness of the energy profile do not necessarily coincide, as is usually implicitly assumed. An explanation for this is provided. The possibility of comparing these results with those obtained from renormalization group arguments is also briefly addressed.

Self-organizing propagation patterns from dynamic self-assembly in monolayers

Propagation of localized orientational waves, as imaged by Brewster angle microscopy, is induced by low intensity linearly polarized light inside axisymmetric smectic-C confined domains in a photosensitive molecular thin film at the air/water interface (Langmuir monolayer). Results from numerical simulations of a model that couples photoreorientational effects and long-range elastic forces are presented. Differences are stressed between our scenario and the paradigmatic wave phenomena in excitable chemical media.

Self-organizing propagation patterns from dynamic self-assembly in monolayers

Propagation of localized orientational waves, as imaged by Brewster angle microscopy, is induced by low intensity linearly polarized light inside axisymmetric smectic-C confined domains in a photosensitive molecular thin film at the air/water interface (Langmuir monolayer). Results from numerical simulations of a model that couples photoreorientational effects and long-range elastic forces are presented. Differences are stressed between our scenario and the paradigmatic wave phenomena in excitable chemical media.

Willigness to pay for long-term care coverage: the role of private information and self-insurance

Both public and private insurance for long-term care is undeveloped in some European countries such as in Spain and empirical evidence is still limited. This paper aims at exmining the determinants of the demand for Long Term Care (LTC) coverage in Spain using contingent valuation techniques. Our findings indicate that only one-fifth of the population is willing to pay to assure coverage decisions are significantly affected by private information asymmetry and housing tenure in giving rise to self-insurance reduces the probability of insurance being hypothetically purchased.

Self construction, cognitive conflicts and polarization in bulimia nervosa

This study explores the cognitive structures, understood as construct systems, of patients suffering from bulimia nervosa (BN). Previous studies investigated the construct systems of disordered eaters suggesting that they had a higher distance between their construction of the self and the «ideal self», and also more rigidity. In addition to these aspects, this study explored the presence of implicative dilemmas (ID). Thirty two women who met criteria for BN and were treated in a specialized center were compared to a non clinical group composed by 32 women matched by age. All participants were assessed using Repertory Grid Technique (RGT). In BN patients it was more common (71.9%) to find IDs than in controls (18.8%). They also showed higher polarization and higher self-ideal discrepancies (even more for those with a long history of BN). The measures provided by the RGT can be useful for the assessment of self-construction and cognitive conflicts in BN patients and to appreciate their role in this disorder. In addition, this technique could be helpful for clinicians to explore the patient"s constructs system, and specially to identify IDs that could be maintaining the symptoms or hindering change in order to focus on them to facilitate improvement.

Self reported physical activity, public health, and perceived environment: results from a comparative European study

The focus of physical activity promotion is moving from methods for increasing health enhancing physical activity on the individual level to higher level strategies including environmental and policy approaches. Scientific inquiry, traditionally related to individual-based strategies, requires adaptation and refinement when environmental and policy changes become more relevant. The objective of this study is to investigate the significance for behaviour and health of community-based environments that encourage physical activity. DESIGN AND SETTING The article presents data and results from a cross sectional comparative survey of the general population in six European countries (Belgium, Finland, Germany (East and West), Netherlands, Spain, Switzerland). Specifically, the relation between perceived community-based opportunities for physical activity, self reported physical activity, and self rated health status is investigated. PARTICIPANTS Representative samples of general populations (adults 18 years or older). Overall response rate: 53.5%. Sample sizes realised: Belgium: n=389; Finland: n=400; Germany (East): n = 913; Germany (West): n=489; Netherlands: n=366; Spain: n=380; Switzerland: n=406. MAIN RESULTS Analyses show that best opportunities are reported by people who are lightly to moderately physically active. People's self rated health is moderately, but significantly associated with both perceived opportunities, and physical activity itself. These predictors interact in that especially for women, the health impact of physical activity is more pronounced in case of good opportunities. CONCLUSIONS The paper shows the potential of opportunities within residential and community environments with regard to physical activity, both for behaviour and health. Opportunities may enable the population, especially women, to develop an active lifestyle, and thus improve their health. Future studies with objective indicators for physical activity related environments should test the findings that are based on perceptions.

Bond strength of orthodontic brackets using different light and self-curing cements

The purpose of the study was to evaluate the shear bond strength of stainless steel orthodontic brackets directly bonded to extracted human premolar teeth. Fifty teeth were randomly divided into ¿ve groups: (1) System One (chemically cured composite resin), (2) Light Bond (light-cured composite resin), (3) Vivaglass Cem (self-curing glass ionomer cement), (4) Fuji Ortho LC (light-cured glass ionomer cement) used after 37% orthophosphoric acid¿etching of enamel (5) Fuji Ortho LC without orthophosphoric acid¿etching. The brackets were placed on the buccal and lingual surfaces of each tooth, and the specimens were stored in distilled water (24 hours) at 378C and thermocycled. Teeth were mounted on acrylic block frames, and brackets were debonded using an Instron machine. Shear bond strength values at fracture (Nw)were recorded. ANOVA and Student-Newman-Keuls multiple comparison tests were performed (P , .05). Bonding failure site was recorded by stereomicroscope and analyzed by Chi-square test, selected specimens of each group were observed by scanning electron microscope. System One attained the highest bond strength. Light Bond and Fuji Ortho LC, when using an acid-etching technique, obtained bond strengths that were within the range of estimated bond strength values for successful clinical bonding. Fuji Ortho LC and Vivaglass Cem left an almost clean enamel surface after debracketing.

Self-Construction, Cognitive Conflicts, and Disordered Eating Attitudes in Young Women

The aim of this study is to identify cognitive variables that predict disordered eating attitudes in a nonclinical sample composed of 50 female university students. Repertory grid technique was used to assess cognitive features of self-construing and cognitive conflicts. Drive for Thinness and Body Dissatisfaction scales from the Eating Disorder Inventory 2 were used as dependent variables, as previous studies suggested that high scores on these scales are associated with the risk of developing or aggravating eating syndromes. Results suggest that drive for thinness can be associated with cognitive conflicts, whereas body dissatisfaction may be higher for those who construct themselves as inadequate and similar to others. In addition, both dependent variables were predicted by being younger and having a higher body mass index.

Photonic characteristics of Langmuir-Blodgett self-assembled monolayers of colloidal silica particles

Monodispersed colloidal crystals based on silica sub-micrometric particles were synthesized using the Stöber-Fink-Bohn process. The control of nucleation and coalescence result in improved characteristics such as high sphericity and very low size dispersion. The resulting silica particles show characteristics suitable for self-assembling across large areas of closely-packed 2D crystal monolayers by an accurate Langmuir-Blodgett deposition process on glass, fused silica and silicon substrates. Due to their special optical properties, colloidal films have potential applications in fields including photonics, electronics, electro-optics, medicine (detectors and sensors), membrane filters and surface devices. The deposited monolayers of silica particles were characterized by means of FESEM, AFM and optical transmittance measurements in order to analyze their specific properties and characteristics. We propose a theoretical calculation for the photonic band gaps in 2D systems using an extrapolation of the photonic behavior of the crystal from 3D to 2D. In this work we show that the methodology used and the conditions in self-assembly processes are decisive for producing high-quality two-dimensional colloidal crystals by the Langmuir-Blodgett technique.

Self-organization mechanisms for the formation on nearshore crescentic and transverse sand bars

The formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow-water equations and on a simpli ed sediment transport parameterization. By assuming normally approaching waves and a saturated surf zone, rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed. Two types of bedforms appear: one is a crescentic bar pattern centred around the breakpoint and the other, herein modelled for the rst time, is a transverse bar pattern. The feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations. Basically, the waves stir up the sediment and keep it in suspension with a certain cross-shore distribution of depth-averaged concentration. Then, a current flowing with (against) the gradient of sediment concentration produces erosion (deposition). It is shown that inside the surf zone, these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms. Numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro-morphodynamic input conditions to which of the patterns develops. It is suggested that crescentic bar growth would be favoured by high-energy conditions and ne sediment while transverse bars would grow for milder waves and coarser sediment. In intermediate conditions mixed patterns may occur.

Norbert Elias : una proposta d’intellectual portrait vint anys després de la seva mort

L’estiu de 1990 moria a Amsterdam un dels sociòlegs més preeminents del segle XX, l’alemany Norbert Elias. La seva vida i la seva obra, profundament imbricades, són un reflex de la complexitat, de les llums i les ombres del segle passat. Amb aquesta proposta de retrat intel·lectual pretenem per una banda commemorar l’efemèride dels 20 anys de la mort d’un sociòleg poc reconegut i poc emprat. I d’altra banda, oferir una introducció a un personatge i una obra que, per la seva magnitud i originalitat, mereixen estar entre les més rellevants de la sociologia. Com a fil conductor de l’article proposem una combinació de llocs físics i simbòlics que van marcar la seva trajectòria.