Finite-Size Scaling Studies of Reaction-Diffusion Systems Part III: Numerical Methods

The scaling exponent and scaling function for the 1D single species coagulation model $(A+A\rightarrow A)$ are shown to be universal, i.e. they are not influenced by the value of the coagulation rate. They are independent of the initial conditions as well. Two different numerical methods are used to compute the scaling properties: Monte Carlo simulations and extrapolations of exact finite lattice data. These methods are tested in a case where analytical results are available. It is shown that Monte Carlo simulations can be used to compute even the correction terms. To obtain reliable results from finite-size extrapolations exact numerical data for lattices up to ten sites are sufficient.Comment: 19 pages, LaTeX, 5 figures uuencoded, BONN HE-94-0

Slipping friction of an optically and magnetically manipulated microsphere rolling at a glass-water interface

The motion of submerged magnetic microspheres rolling at a glass-water interface has been studied using magnetic rotation and optical tweezers combined with bright-field microscopy particle tracking techniques. Individual microspheres of varying surface roughness were magnetically rotated both in and out of an optical trap to induce rolling, along either plain glass cover slides or glass cover slides functionalized with polyethylene glycol. It has been observed that the manipulated microspheres exhibited nonlinear dynamic rolling-while-slipping motion characterized by two motional regimes: At low rotational frequencies, the speed of microspheres free-rolling along the surface increased proportionately with magnetic rotation rate; however, a further increase in the rotation frequency beyond a certain threshold revealed a sharp transition to a motion in which the microspheres slipped with respect to the external magnetic field resulting in decreased rolling speeds. The effects of surface-microsphere interactions on the position of this threshold frequency are posed and investigated. Similar experiments with microspheres rolling while slipping in an optical trap showed congruent results.Comment: submitted to Journal of Applied Physics, 11 figure

Mentalizing the body: spatial and social cognition in anosognosia for hemiplegia

Following right-hemisphere damage, a specific disorder of motor awareness can occur called anosognosia for hemiplegia, i.e. the denial of motor deficits contralateral to a brain lesion. The study of anosognosia can offer unique insights into the neurocognitive basis of awareness. Typically, however, awareness is assessed as a first person judgement and the ability of patients to think about their bodies in more ‘objective’ (third person) terms is not directly assessed. This may be important as right-hemisphere spatial abilities may underlie our ability to take third person perspectives. This possibility was assessed for the first time in the present study. We investigated third person perspective taking using both visuospatial and verbal tasks in right-hemisphere stroke patients with anosognosia ( n = 15) and without anosognosia ( n = 15), as well as neurologically healthy control subjects ( n = 15). The anosognosic group performed worse than both control groups when having to perform the tasks from a third versus a first person perspective. Individual analysis further revealed a classical dissociation between most anosognosic patients and control subjects in mental (but not visuospatial) third person perspective taking abilities. Finally, the severity of unawareness in anosognosia patients was correlated to greater impairments in such third person, mental perspective taking abilities (but not visuospatial perspective taking). In voxel-based lesion mapping we also identified the lesion sites linked with such deficits, including some brain areas previously associated with inhibition, perspective taking and mentalizing, such as the inferior and middle frontal gyri, as well as the supramarginal and superior temporal gyri. These results suggest that neurocognitive deficits in mental perspective taking may contribute to anosognosia and provide novel insights regarding the relation between self-awareness and social cognition

Diffusion-Limited Coalescence with Finite Reaction Rates in One Dimension

We study the diffusion-limited process $A+A\to A$ in one dimension, with finite reaction rates. We develop an approximation scheme based on the method of Inter-Particle Distribution Functions (IPDF), which was formerly used for the exact solution of the same process with infinite reaction rate. The approximation becomes exact in the very early time regime (or the reaction-controlled limit) and in the long time (diffusion-controlled) asymptotic limit. For the intermediate time regime, we obtain a simple interpolative behavior between these two limits. We also study the coalescence process (with finite reaction rates) with the back reaction $A\to A+A$, and in the presence of particle input. In each of these cases the system reaches a non-trivial steady state with a finite concentration of particles. Theoretical predictions for the concentration time dependence and for the IPDF are compared to computer simulations. P. A. C. S. Numbers: 82.20.Mj 02.50.+s 05.40.+j 05.70.LnComment: 13 pages (and 4 figures), plain TeX, SISSA-94-0

A formacao do neonatologista e os paradigmas implicados na relacao com os pais dos bebes na Unidade de Terapia Intensiva Neonatal

Objective:To analyze and to interpret the psychological repercussions generated by the presence of parents in the Neonatal Intensive Care Unit for residents in Neonatology.Methods:Study based on the psychoanalytic theory, involving a methodological interface with qualitative surveys in Health Sciences. Twenty resident physicians in Neonatology, from five public institutions of São Paulo state, responded to a single semi-structured interview. Based on several readings of the material, achieving the core of emergent meanings that would be significant to the object of the survey, six categories were elected for analysis and interpretation: parents' staying at the Neonatal Intensive Care Unit and its effects on the neonatologists' professional practice; communication of the diagnosis and what parents should know; impasses between parents and doctors when the diagnosis is being communicated; doctor's identification with parents; communication of the child's death and their participation in the interview.Results:The interpretation of the categories provided an understanding of the psychic mechanisms mobilized in doctors in their relationships with the children's parents, showing that the residents experience anguish and suffering when they provide medical care and during their training process, and also that they lack psychological support to handle these feelings.Conclusions:There is a need of intervention in neonatologists training and education, which may favor the elaboration of daily experiences in the Unit, providing a less anguishing and defensive way out for young doctors, especially in their relationship with patients and parents.Objetivo:Analizar e interpretar las repercusiones psicológicas suscitadas en el médico neonatologista en formación debido a la entrada y a la permanencia de los padres en la Unidad de Terapia Intensiva Neonatal. Métodos:Estudio sustentado en la teoría psicoanalítica, manteniéndose una interlocución metodológica con la investigación cualitativa en salud. Veinte residentes en Neonatología, de cinco instituciones públicas de la provincia de São Paulo (Brasil), participaron de una entrevista semiestructurada individual. A partir de innúmeras lecturas del material, objetivando los núcleos de sentido emergentes, significativos para el objeto de investigación, se eligieron categorías para análisis e interpretación: permanencia de los padres en la Unidad de Terapia Intensiva Neonatal y su repercusión en la actuación del neonatologista; comunicación del diagnóstico y qué los padres deben saber; impases entre los médicos y los padres de los bebés en la comunicación del diagnóstico; situaciones de identificación con los padres; comunicación de la muerte y participación en la entrevista. Resultados:La interpretación de las categorías propició la comprensión de los mecanismos psíquicos movilizados en los médicos en la relación con los padres de los bebés y expuso la angustia y el sufrimiento suscitados en los residentes en la atención asistencial y en el proceso de formación, para los que están desprovistos de anclajes psíquicos.Conclusiones:A partir del contenido que se explicitó en el análisis de las entrevistas, se verificó la necesidad de una propuesta de intervención en la formación de esos profesionales que favorezca la elaboración de las experiencias vividas en el cotidiano de la Unidad, a fin de propiciar una salida menos angustiante y defensiva para el médico, incluso en la relación con el paciente y con los padres.Objetivo:Analisar e interpretar as repercussões psicológicas suscitadas no médico neonatologista em formação devido à entrada e à permanência dos pais na Unidade de Terapia Intensiva Neonatal.Métodos:Estudo sustentado na teoria psicanalítica, mantendo-se uma interlocução metodológica com a pesquisa qualitativa em saúde. Vinte residentes de Neonatologia, de cinco instituições públicas do estado de São Paulo, participaram de uma entrevista semiestruturada individual. A partir de inúmeras leituras do material, objetivando-se os núcleos de sentido emergentes, significativos para o objeto de pesquisa, elegeram-se seis categorias para análise e interpretação: permanência dos pais na Unidade de Terapia Intensiva Neonatal e sua repercussão na atuação do neonatologista; comunicação do diagnóstico e o que os pais devem saber; impasses entre os médicos e os pais dos bebês na comunicação do diagnóstico; situações de identificação com os pais; comunicação da morte e participação na entrevista.Resultados:A interpretação das categorias propiciou a compreensão dos mecanismos psíquicos mobilizados nos médicos na relação com os pais dos bebês e expôs a angústia e o sofrimento suscitados nos residentes no atendimento assistencial e no processo de formação, para os quais estão desprovidos de ancoragens psíquicas.Conclusões:A partir do conteúdo que se explicitou na análise das entrevistas, verificou-se a necessidade de uma proposta de intervenção na formação desses profissionais que favoreça a elaboração das experiências vividas no cotidiano da Unidade, a fim de propiciar uma saída menos angustiante e defensiva para o médico, inclusive na relação com o paciente e com os pais.Universidade Federal de São Paulo (UNIFESP), Escola Paulista de Medicina (EPM)Universidade Federal de Minas GeraisUNIFESP, EPMSciEL

Triplet exciton percolation and superexchange: Naphthalene C10H8–C10D8

The phosphorescence of betamethylnaphthalene doped into a naphthalene−h8/naphthalene−d8 mixed crystal has been measured. The results demonstrate that (1) dynamical exciton percolation does occur (i.e., a transition from an exciton insulator to an exciton conductor), that (2) it is very useful for the investigation of energy transfer in molecular aggregates, and that (3) it is a critical test of our current knowledge of exciton exchange and superexchange. (AIP)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70872/2/JCPSA6-62-1-292-1.pd

Circadian Timing of Food Intake Contributes to Weight Gain

Studies of body weight regulation have focused almost entirely on caloric intake and energy expenditure. However, a number of recent studies in animals linking energy regulation and the circadian clock at the molecular, physiological, and behavioral levels raise the possibility that the timing of food intake itself may play a significant role in weight gain. The present study focused on the role of the circadian phase of food consumption in weight gain. We provide evidence that nocturnal mice fed a high‐fat diet only during the 12‐h light phase gain significantly more weight than mice fed only during the 12‐h dark phase. A better understanding of the role of the circadian system for weight gain could have important implications for developing new therapeutic strategies for combating the obesity epidemic facing the human population today

Concentration for One and Two Species One-Dimensional Reaction-Diffusion Systems

We look for similarity transformations which yield mappings between different one-dimensional reaction-diffusion processes. In this way results obtained for special systems can be generalized to equivalent reaction-diffusion models. The coagulation (A + A -> A) or the annihilation (A + A -> 0) models can be mapped onto systems in which both processes are allowed. With the help of the coagulation-decoagulation model results for some death-decoagulation and annihilation-creation systems are given. We also find a reaction-diffusion system which is equivalent to the two species annihilation model (A + B ->0). Besides we present numerical results of Monte Carlo simulations. An accurate description of the effects of the reaction rates on the concentration in one-species diffusion-annihilation model is made. The asymptotic behavior of the concentration in the two species annihilation system (A + B -> 0) with symmetric initial conditions is studied.Comment: 20 pages latex, uuencoded figures at the en