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The stability limits of nonaxisymmetric liquid bridges between equal in diameter, coaxial disks have been determined experimentally. Experiments have been performed by working with very small size liquid bridges. The experimental setup allows any orientation of the liquid bridge axis with respect to the local gravity vector acceleration. By appropriately orienting the liquid bridge axis, the influence on the stability limits of both the lateral and the axial component of the acceleration acting on the liquid bridge has been investigated.

This paper describes a study of the occurrence, levels and temporal evolution of PAHs in a bay characterized by persistent chronic impacts. A total of 40 samples, 20 of sediment and 20 of water, were taken at each of five different stations, in four sampling campaigns. Analyses of pollutants have been made using GC-MS. Results indicate that in a coastal environment subjected to chronic pollution by pyrolytic PAHs, episodes of petrogenic pollution, like oil-spills, can be identified by the combination of different source ratios. Results also indicate that, in the study area, PAHs are transported from superficial water to sediment. This conclusion is based on the degree of coincidence found in the presence/absence of individual PAHs in both compartments and in their petrogenic/pyrolytic nature, the positive sedimentation rate in the study area, together with the performance of the analyses of unfiltered water and the distribution of sources of PAHs found.

Bifurcation diagrams of nonaxisymmetric liquid bridges subject to a lateral gravitational force and to both lateral and axial gravitational forces are found by solving the Young–Laplace equation for the interface by a finite difference method. The potential energy of the equilibrium shapes is also calculated. The results obtained show that the slenderness of the bridge determines whether the breaking of the liquid bridge subject to a lateral gravitational force leads to equal or unequal drops. The stability limits calculated are compared with the ones obtained using asymptotic techniques around the cylinder, the agreement being extremely good for a wide range of the parameters.

The minimum volume stability limit of axisymmetric liquid bridges has been obtained in the past for zero Bond number, no solid body rotation and equal disks. When gravity, rotation or different disk diameters are considered, only a few numerical results are available and the singular case of small values of these parameters have been only partly considered. An analytical study using the Lyapunov-Schmidt method considering small values of gravity, disk diameter ratio and rotation rate is presented and the variation of the stability limit determined.

Errors in the Although early studies dealing with the stability of liquid bridges were published long time ago, these studies were mainly concerned with the stability of axisymmetric liquid bridges between parallel, coaxial, equal-in-diameter solid disks, with regard to axisymmetric perturbations. Results including effects such as solid rotation of the liquid column, supporting disks of different diameters and an axial acceleration acting parallel to the liquid column can be found in several works published in the early eighties, although most of these analysis were restricted to liquid bridge configurations having a volume of liquid equal or close enough to that of a cylinder of the same radius. Leaving apart some asymptotic studies, the analysis of non-axisymmetric effects on the stability of liquid bridges (lateral acceleration, eccentricity of the supporting disks) and other not so-classical effects (electric field) has been initiated much more recently, the results concerning these aspect of liquid bridge stability being yet scarce.

Recientes modelos neurobiológicos conciben la adicción como una transición del control de la conducta a lo largo del eje que va de la impulsividad a la compulsividad. La naturaleza dinámica de esta transición hace difícil detectar la posición de los adictos en este continuo, pero una de las aproximaciones mejor validadas es la caracterización de su estado mediante índices neuropsicológicos de impulsividad (o desinhibición) y compulsividad (o perseverancia). En esta investigación se pretende estimar la posición relativa de cada uno de los individuos en un grupo de pacientes dependientes de cocaína (PDC) en el eje impulsividadcompulsividad —en función de su rendimiento en índices de inhibición y perseverancia— y asociar su estatus neuropsicológico (impulsivo vs. compulsivo) con medidas de impulsividad-rasgo y severidad de exposición a la sustancia. 42 PDC y 65 controles sanos fueron evaluados mediante el cuestionario UPPS-P (para evaluar impulsividad), las pruebas Stroop y Go/No Go (para evaluar inhibición de respuesta) y los test de aplicación de estrategias y aprendizaje de inversión (para evaluar perseverancia). El 45% de los PDC fueron clasificados como compulsivos. Este subgrupo presentaba puntuaciones significativamente más altas que el subgrupo impulsivo en los rasgos de falta de premeditación y falta de perseverancia. Un porcentaje sustancial de PDC presenta características neuropsicológicas compatibles con un patrón de compulsividad. No se corroboró la idea de que los pacientes clasificados como compulsivos mostraran mayores niveles de severidad de la exposición a la cocaína; sin embargo, sí tienden a emitir respuestas poco meditadas y a desistir de tareas dirigidas a objetivos a largo plazo, tal y como muestran las pruebas de autoiforme de personalidad impulsiva. A recent theoretical approach describes addiction as a dynamic behaviou ral change process on the impulsivity-compulsivity axis. However, on the basis of current evidence, it is still difficult to establish a selective association between the course of addiction and individual transition along this axis. The aim of this study is to categorize each of the individuals in a sample of cocaine-dependent patients (CDI) as mainly impulsive or mainly compulsive, on the basis of their performance in neuropsychological inhibition and perseveration tests, and to test the association between the assigned category and their scores in trait impulsivity, and severity of cocaine addiction (measured by means of self-report assessment tools). A total of 42 CDI and 65 healthy control individuals (HCI) were assessed using the UPPS-P Scale (to explore trait impulsivity), the Stroop and Go/No Go (to assess response inhibition), and Revised-Strategy Application and Probabilistic Reversal tests (to assess response perseveration). Forty-five per cent of the CDIs were classified as compulsive, and this subgroup scored significantly higher than the impulsive group on the UPPS-P dimensions of lack of perseverance and lack of premeditation. A substantial proportion of CDIs can be classified as compulsive. No differences between compulsive and impulsive CDIs were found with regard to severity of exposure to cocaine; however, patients classified as compulsive by means of neuropsychological tasks are less perseverative in the pursuit of long-term objectives and more prone to make under-meditated decisions, as shown by trait impulsivity assessment questionnaires. La investigación descrita en este trabajo ha sido financiada por un proyecto del Ministerio de Educación a través del Plan Nacional FPU (referencia AP 2005-1411) para la primera autora, un proyecto del Ministerio de Ciencia e Innovación (MICINN), a través de la Dirección General de Investigación y Gestión del Plan Nacional de I+D+i (referencia PSI2009-13133) para el segundo autor, por el proyecto P07.HUM 03089 a través de la Junta de Andalucía (referencia SEJ 2006-8278) y por el proyecto COPERNICO a través del Plan Nacional sobre Drogas (2009) para el último autor.

The dynamics of a noncylindrical, axisymmetric, marginally unstable liquid bridge between two equal disks is analyzed in the inviscid limit. The resulting model allows for the weakly nonlinear description of both the (first stage of) breakage for unstable configurations and the (slow) dynamics for stable configurations. The analysis is made for both slender and short liquid brides. In the former range, the dynamics breaks reflection symmetry on the midplane between the supporting disks and can be described by a standard Duffing equation, while for short bridges reflection symmetry is preserved and the equation is still Duffing-like but exhibiting a quadratic nonlinearity. The asymptotic results compare well with existing experiments.

The stability of axisymmetric liquid bridges spanning two equal-diameter solid disks subjected to an axial gravity field of arbitrary intensity is analyzed for all possible liquid volumes. The boundary of the stability region for axisymmetric shapes (considering both axisymmetric and nonaxisymmetric perturbations) have been calculated. It is found that, for sufficiently small Bond numbers, three different unstable modes can appear. If the volume of liquid is decreased from that of an initially stable axisymmetric configuration the bridge either develops an axisymmetric instability (breaking in two drops as already known) or detaches its interface from the disk edges (if the length is smaller than a critical value depending on contact angle), whereas if the volume is increased the unstable mode consists of a nonaxisymmetric deformation. This kind of nonaxisymmetric deformation can also appear by decreasing the volume if the Bond number is large enough. A comparison with other previous partial theoretical analyses is presented, as well as with available experimental results.

A general one-dimensional model is considered that describes the dynamics of slender, axisymmetric, noncylindrical liquid bridges between two equal disks. Such model depends on two adjustable parameters and includes as particular cases the standard Lee and Cosserat models. For slender liquid bridges, the model provides sufficiently accurate results and involves much easier and faster calculations than the full three-dimensional model. In particular, viscous effects are easily accounted for. The one-dimensional model is used to derive a simple weakly nonlinear description of the dynamics near the instability limit. Small perturbations of marginal instability conditions are also considered that account for volume perturbations, nonequality of the supporting disks, and axial gravity. The analysis shows that the dynamics breaks the reflection symmetry on the midplane between the supporting disks. The weakly nonlinear evolution of the amplitude of the perturbation is given by a Duffing equation, whose coefficients are calculated in terms of the slenderness as a part of the analysis and exhibit a weak dependence on the adjustable parameters of the one-dimensional model. The amplitude equation is used to make quantitative predictions of both the (first stage of) breakage for unstable configurations and the (slow) dynamics for stable configurations.

This paper deals with the influence of axial microgravity on the stability limits of axisymmetric, cylindrical liquid columns held by capillary forces between two circular, concentric, solid disks. A fair number of experiments have been performed and both the maximum and the minimum volume of liquid that a capillary liquid bridge can withstand have been obtained as a function of the geometry of the liquid bridge and of the value of the axial microgravity acting on it. Experimental results are compared with published theoretical predictions made by other investigators and discrepancies between those results criticized.

This paper deals with the dynamics of isothermal, axisymmetric, cylindrical liquid columns held by capillary forces between two circular, concentric, solid disks; in particular, it deals with the dynamic response of the bridge to an excitation consisting of a small change in the value of the microgravity level. The problem has been solved by using a linearized one‐dimensional Cosserat model, which includes viscosity effects, and with the axial velocity considered as constant in each section of the liquid bridge. The analysis has been performed by using the Laplace transform, and the time variation of both the axial velocity field and the liquid bridge interface have been obtained.

The bifurcation to unstable equilibrium shapes in the neighborhood of the minimum volume stability limit of liquid bridges has been described by using the Lyapunov–Schmidt technique. Prior to the bifurcation analysis, the stability limits of axisymmetric liquid bridges (both that of maximum and that of minimum volume) have been analytically calculated when the liquid bridge supports are two circular, coaxial disks. The interface shapes have been parametrically described and the parameters corresponding to the marginally stable shapes have been determined in terms of elliptic variables. Bifurcation equations have been obtained analytically describing the behavior near the critical points previously calculated and the effect of small axisymmetric imperfections has been considered. The considered imperfections are inequality in the diameter of the supporting disks, small body forces due to an axial gravity, and liquid bridge rotation as a solid body.

High precision computations of the minimum volume and the corresponding shape of axisymmetric liquid bridges at rest, anchored to unequal and coaxial discs, are presented. The tables and graphs provide a standard for comparison of linearized and other approximate models, as well an aid in detecting very small departures in shape due to weak (for instance, electrostatic) forces. Relevance to crystal growth by the floating zone technique in the absence of gravity is elucidated.

The analytical solution for the different shapes that a bidimensional liquid bridge in a gravity field may adopt is reviewed, criticizing the well-known limit of Heywang. The work is shown in the context of a wider-scope program to model the fluid-mechanical behaviour of molten bridges in the floating zone and related techniques of crystal growth, which has blossomed with the advent of microgravity platforms.

The stability of long liquid bridges under non-axisymmetric disturbances like a microgravitational force acting perpendicular to the liquid bridge axis or a non-coaxiality of the disks is analyzed through an asymptotic method based on bifurcation techniques. Results obtained indicate that such non-axisymmetric effects are of higher order than those produced by axisymmetric perturbations.

Este estudio pretende explorar la relacion entre impulsividad y consecuencias negativas percibidas del consumo de alcohol y del uso de Internet. Especificamente si las dimensiones de impulsividad – urgencia positiva y negativa, falta de premeditacion, falta de perseverancia y busqueda de sensaciones – estan asociadas a (1) la aparicion de las primeras consecuencias negativas, y a (2) la transicion entre un malestar indicativo de un posible problema y otro indicativo de un muy probable problema, en el consumo de alcohol y uso de Internet. Para ello, 709 universitarios de primer ano fueron evaluados mediante cuestionarios de impulsividad (UPPS–P) y consecuencias negativas percibidas de conductas adictivas (Multicage CAD–4). Utilizando analisis de regresion logistica se comprobo que, en el caso del alcohol, la urgencia positiva y la falta de premeditacion distinguian entre participantes con puntuacion Multicage 0 (ningun problema) y 1 (aparicion inicial de consecuencias negativas), mientras que la urgencia negativa lo hacia entre puntuaciones 2 y 3/4 (transicion entre un posible y un muy probable problema clinico). Respecto al uso de Internet, ninguna dimension resulto predictiva de la aparicion de las primeras consecuencias negativas, y la urgencia positiva marco la transicion hacia un muy probable problema clinico. La urgencia negativa aparece pues como un indicador de patologizacion del consumo de alcohol. Por su parte, el uso en niveles subclinicos parece relacionarse con la impulsividad elicitada por emociones positivas. Para Internet no se observo este patron, lo que puede indicar diferencias en la etiologia del uso abusivo de Internet respecto al consumo de sustancias.

La corteza prefrontal ventromedial (VMPFC) ha sido implicada en la toma de decisiones emocionales debido a su posible participación en el aprendizaje de inversión afectivo, la propensión al riesgo y la impulsividad. Su especial entramado de conexiones con otras áreas de la corteza y con estructuras subcorticales como la amígdala justifican que pueda tener un papel de interfase entre cognición y emoción, y desempeñar una función fundamental en la regulación y el control del comportamiento. En este trabajo revisamos estudios realizados con la tarea de apuestas de Iowa, tareas de aprendizaje de inversión afectivo, tareas de apuestas con diferente varianza para medir la propensión al riesgo y tareas que introducen demora temporal de la recompensa para evaluar la impulsividad. Los datos obtenidos en esos trabajos con pacientes lesionados en la VMPFC o en otras áreas prefrontales y controles no lesionados, y datos conductuales y de actividad cerebral pueden interpretarse mejor si asumimos que la VMPFC está encargada de representar la expectativa de refuerzo. La representación de un reforzador esperado incluye la demora del reforzador, y la varianza de su magnitud.

In spite of the fact that shoot selection is a crucial ingredient of performance in basketball, the judgment and decision making processes involved in it have been largely neglected. In the present work, we explore individuals' strategies to assess the adequateness of shooting (in a simulation laboratory task) in situations varying in the degree of physical defensive pressure, rebound, defensive balance and shooting distance. Our results showed that the four target dimensions have an impact on participants' judgments. More importantly, training influences the degree to which one of the non-obvious dimensions (defensive balance) is taken into account by participants in order to make their judgments. These results stress the necessity to develop measures of shot selection decisional quality beyond scoring rates.

Uno de los aspectos del aprendizaje causal menos estudiado es el papel que las emociones juegan en dicho aprendizaje. El principal objetivo de esta investigación fue estudiar el impacto que ejercen las emociones sobre una tarea de detección de relaciones causales de carácter afectivo neutral. La inducción de emociones negativas hizo que los participantes subestimaran la relación causal entre los sucesos presentados tanto cuando ésta era de tipo generativo (Experimento 1) contingencia positiva como cuando era de tipo preventivo (Experimento 2) contingencia negativa . Sin embargo, los participantes recordaban adecuadamente la frecuencia de ocurrencia de cada tipo de ensayo, y sus respuestas de predicción ensayo-a-ensayo no se vieron afectadas por la inducción de emociones. Estos datos parecen apoyar a las teorías que propugnan la existencia de procesos añadidos al mecanismo de cómputo de ocurrencias en la apreciación de relaciones causales entre sucesos, como serían los procesos de integración de la información derivada de las creencias causales previas.

BACKGROUND: The negative consequences of energy dense foods are well known, yet people increasingly make unhealthy food choices leading to obesity (i.e., risky decisions). The aims of this study were: [1] to compare performance in decision-making tasks under risk and under ambiguity between individuals with obesity, overweight and normal weight; [2] to examine the associations between body mass index (BMI) and decision-making, and the degree to which these associations are modulated by reward sensitivity. METHODS: Seventy-nine adults were recruited and classified in three groups according to their BMI: obesity, overweight and normal-weight. Groups were similar in terms of age, education and socio-economic status, and were screened for comorbid medical and mental health conditions. Decision-making under risk was measured via the Wheel of Fortune Task (WoFT) and decision-making under ambiguity via the Iowa Gambling Task (IGT). Reward sensitivity was indicated by the Sensitivity to Punishment and Sensitivity to Reward Questionnaire (SPSRQ). RESULTS: Individuals with obesity made riskier choices in the WoFT, specifically in choices with an expected value close to zero and in the propensity to risk index. No differences were found in IGT performance or SPSRQ scores. BMI was associated with risk-taking (WoFT performance), independently of reward sensitivity. CONCLUSIONS: Obesity is linked to a propensity to make risky decisions in experimental conditions analogous to everyday food choices. Language: en