Análise volumétrica de cerebelo e tronco cerebral de pacientes com doença de Machado Joseph

Machado-Joseph disease, or spinocerebellar ataxia type 3(MJD/SCA3), is the most frequent late onset spinocerebellar ataxia and results from a CAG repeat expansion in the ataxin-3 gene. Previous studies have found correlation between atrophy of cerebellum and brainstem with age and CAG repeats, although no such correlation has been found with disease duration and clinical manifestations. In this study we test the hypothesis that atrophy of cerebellum and brainstem in MJD/SCA3 is related to clinical severity, disease duration and CAG repeat length as well as to other variables such as age and ICARS (International Cooperative Ataxia Rating Scale). Whole brain high resolution MRI and volumetric measurement with cranial volume normalization were obtained from 15 MJD/SCA3 patients and 15 normal, age and sex-matchedcontrols. We applied ICARS and compared the score with volumes and CAG number, disease duration and age. We found significant correlation of both brain stem and cerebellar atrophy with CAG repeat length, age, disease duration and degree of disability. The Spearman rank correlation was stronger with volumetric reduction of the cerebellum than with brain stem. Our data allow us to conclude that volumetric analysis might reveal progressive degeneration after disease onset, which in turn is linked to both age and number of CAG repeat expansions in SCA 3.Doença de Machado-Joseph, ou ataxia espinocerebelar tipo 3 (MJD/SCA3) é ataxia espinocerebelar de início tardio mais frequente e resulta de uma expansão da repetição CAG no gene da ataxina-3. Estudos precedentes encontraram correlação entre a atrofia do cerebelo e do tronco cerebral com a idade e número de expansões CAG. Tais correlações não foram encontradas em relação ao tempo de doença ou manifestações clínicas. Neste estudo testamos a hipótese de que a atrofia do cerebelo e do tronco encefálico em MJD/SCA3 está relacionada à gravidade clínica, duração da doença e número de repetições CAG, bem como com outras variáveis como a idade e a ICARS (escala cooperativa internacional de avaliação de ataxias). Foram realizados estudos de imagem pela ressonância magnética de alta resolução e volumetria com normalização de volume craniano de 15 pacientes portadores de MJD/SCA3 e 15 controles pareados por idade e sexo. Nós aplicamos a ICARS e correlacionamos com o escore de volumes e número de CAG, duração da doença e idade. Encontramos correlação significativa entre atrofia de tronco cerebral e cerebelo com duração da doença, repetição CAG, idade e grau de acometimento da doença. O índice de correlação de Spearman foi maior em relação à atrofia de cerebelo do que à atrofia de tronco. Nossos dados permitem concluir que a análise volumétrica pode revelar degeneração progressiva após o início da doença que, por sua vez, está ligada à idade e número de expansões CAG em SCA 3.(FAEPA) Faculdade de Medicina de Ribeirão Preto - Fundação de Amparo ao Ensino e Pesquisa do Hospital das ClínicasFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

A Study of Two-Temperature Non-Equilibrium Ising Models: Critical Behavior and Universality

We study a class of 2D non-equilibrium Ising models based on competing dynamics induced by contact with heat-baths at two different temperatures. We make a comparative study of the non-equilibrium versions of Metropolis, heat bath/Glauber and Swendsen-Wang dynamics and focus on their critical behavior in order to understand their universality classes. We present strong evidence that some of these dynamics have the same critical exponents and belong to the same universality class as the equilibrium 2D Ising model. We show that the bond version of the Swendsen-Wang update algorithm can be mapped into an equilibrium model at an effective temperature.Comment: 12 pages of LaTeX plus 18 pages of postscript figures in a uuencoded file (608k

The Ultrasensitivity of Living Polymers

Synthetic and biological living polymers are self-assembling chains whose chain length distributions (CLDs) are dynamic. We show these dynamics are ultrasensitive: even a small perturbation (e.g. temperature jump) non-linearly distorts the CLD, eliminating or massively augmenting short chains. The origin is fast relaxation of mass variables (mean chain length, monomer concentration) which perturbs CLD shape variables before these can relax via slow chain growth rate fluctuations. Viscosity relaxation predictions agree with experiments on the best-studied synthetic system, alpha-methylstyrene.Comment: 4 pages, submitted to Phys. Rev. Let

The shape and erosion of pebbles

The shapes of flat pebbles may be characterized in terms of the statistical distribution of curvatures measured along their contours. We illustrate this new method for clay pebbles eroded in a controlled laboratory apparatus, and also for naturally-occurring rip-up clasts formed and eroded in the Mont St.-Michel bay. We find that the curvature distribution allows finer discrimination than traditional measures of aspect ratios. Furthermore, it connects to the microscopic action of erosion processes that are typically faster at protruding regions of high curvature. We discuss in detail how the curvature may be reliable deduced from digital photographs.Comment: 10 pages, 11 figure

Magnetic field tuning of antiferromagnetic Yb3_{3}Pt4_{4}

We present measurements of the specific heat, magnetization, magnetocaloric effect and magnetic neutron diffraction carried out on single crystals of antiferromagnetic Yb$_{3}$Pt$_{4}$, where highly localized Yb moments order at $T_{\rm N}=2.4$ K in zero field. The antiferromagnetic order was suppressed to $T_{\rm N}\rightarrow 0$ by applying a field of 1.85 T in the $ab$ plane. Magnetocaloric effect measurements show that the antiferromagnetic phase transition is always continuous for $T_{\rm N}>0$, although a pronounced step in the magnetization is observed at the critical field in both neutron diffraction and magnetization measurements. These steps sharpen with decreasing temperature, but the related divergences in the magnetic susceptibility are cut off at the lowest temperatures, where the phase line itself becomes vertical in the field-temperature plane. As $T_{\rm N}\rightarrow0$, the antiferromagnetic transition is increasingly influenced by a quantum critical endpoint, where $T_{\rm N}$ ultimately vanishes in a first order phase transition.Comment: 9 pages, 6 figure