Learning and policy search in stochastic dynamical systems with Bayesian neural networks

We present an algorithm for policy search in stochastic dynamical systems using model-based reinforcement learning. The system dynamics are described with Bayesian neural networks (BNNs) that include stochastic input variables. These input variables allow us to capture complex statistical patterns in the transition dynamics (e.g. multi-modality and heteroskedasticity), which are usually missed by alternative modeling approaches. After learning the dynamics, our BNNs are then fed into an algorithm that performs random roll-outs and uses stochastic optimization for policy learning. We train our BNNs by minimizing a-divergences with a = 0.5, which usually produces better results than other techniques such as variational Bayes. We illustrate the performance of our method by solving a challenging problem where model-based approaches usually fail and by obtaining promising results in real-world scenarios including the control of a gas turbine and an industrial benchmark

Familial ATTR amyloidosis: microalbuminuria as a predictor of symptomatic disease and clinical nephropathy

Familial ATTR amyloidosis: microalbuminuria as a predictor of symptomatic disease and clinical nephropathy. Lobato L, Beirão I, Silva M, Bravo F, Silvestre F, Guimarães S, Sousa A, Noël LH, Sequeiros J. SourceDepartment of Nephrology and Centro de Estudos de Paramiloidose, Hospital Geral de Santo António and Institute for Molecular and Cell Biology, Porto, Portugal. [email protected] Abstract BACKGROUND: Portuguese type familial amyloid polyneuropathy (FAP) is a neuropathic amyloidosis caused by a mutant transthyretin (TTR). Varying degrees of renal involvement have been reported. Our aim was to assess the value of microalbuminuria (MA) for predicting clinical neurological disease and overt nephropathy in TTR-related amyloidosis. METHODS: All subjects had the TTR Val30Met mutation, and were recruited between 1993 and 1999. We have prospectively evaluated 22 asymptomatic gene carriers (7 male, 15 female; mean age 41.6+/-9.6 years) and 32 patients with neuropathy (14 male, 18 female; 36.8+/-8.8 years, on average, 33.0+/-9.3 years at the onset of neuropathy). We measured urinary albumin excretion every year, if asymptomatic, or every 6 months if already affected. Kidney biopsies were performed in patients with normal urinary albumin excretion, MA, and overt nephropathy, respectively. RESULTS: In asymptomatic carriers, persistent MA was detected in eight (36%) subjects. The presence of MA in asymptomatic gene carriers, compared with those having normal urinary albumin excretion, conferred a 4.8-fold risk of developing neuropathy, usually within the subsequent 3 years. Once neurological signs appeared, nephropathy, manifested as MA, progressed to overt nephropathy in one-half of subjects. In patients with neuropathy, 24 (75%) had MA during follow-up: evolution towards clinical renal disease occurred in 14 (58%) and renal failure occurred in five (21%), always after a course of MA. Proteinuria or renal failure without prior persistent MA were never observed in the present patient cohort. Histopathological evaluation did not reveal glomerular lesions other than amyloid deposits to explain abnormal urinary albumin excretion. The amount of mesangial and vascular-pole amyloid deposits was correlated with the degree of albuminuria. CONCLUSIONS: Microalbuminuria represents the first stage of clinical TTR amyloid nephropathy and is premonitory of neuropathy. Its presence identifies a subgroup of patients who are more prone to develop overt nephropathy. Screening of MA may be important to assess disease onset and to recommend liver transplantation in individuals at risk

Epidemiologia do vírus da língua azul em rebanhos bovinos.

A Língua Azul é uma doença re-emergente que causa aborto em vacas, queda do desempenho reprodutivo, perda de condição corporal e redução na produção e leite. A ocorrência dessa doença está relacionada à presença de vetores transmissores. No Brasil, apesar da existência de poucos estudos sobre a ocorrência dos vetores dessa doença, levantamentos sorológicos indicam a circulação do vírus da Língua Azul em rebanhos bovinos, inclusive no Pantanal.bitstream/CPAP/55963/1/DOC85.pdfFormato Eletrônic

Development and operation of a pixel segmented liquid-filled linear array for radiotherapy quality assurance

A liquid isooctane (C$_{8}$H$_{18}$) filled ionization linear array for radiotherapy quality assurance has been designed, built and tested. The detector consists of 128 pixels, each of them with an area of 1.7 mm $\times$ 1.7 mm and a gap of 0.5 mm. The small pixel size makes the detector ideal for high gradient beam profiles like those present in Intensity Modulated Radiation Therapy (IMRT) and radiosurgery. As read-out electronics we use the X-Ray Data Acquisition System (XDAS) with the Xchip developed by the CCLRC. Studies concerning the collection efficiency dependence on the polarization voltage and on the dose rate have been made in order to optimize the device operation. In the first tests we have studied dose rate and energy dependences, and signal reproducibility. Dose rate dependence was found lower than 2.5 % up to 5 Gy min$^{-1}$, and energy dependence lower than 2.1 % up to 20 cm depth in solid water. Output factors and penumbras for several rectangular fields have been measured with the linear array and were compared with the results obtained with a 0.125 cm$^{3}$ air ionization chamber and radiographic film, respectively. Finally, we have acquired profiles for an IMRT field and for a virtual wedge. These profiles have also been compared with radiographic film measurements. All the comparisons show a good correspondence. Signal reproducibility was within a 2% during the test period (around three months). The device has proved its capability to verify on-line therapy beams with good spatial resolution and signal to noise ratio.Comment: 16 pages, 12 figures Submitted to Phys. Med. Bio

Variables motivacionales predictoras de las barreras para la práctica de ejercicio físico en adolescentes

En el presente trabajo se realizó una predicción de las barreras para la práctica de ejercicio físico en 356 adolescentes, con edades comprendidas entre los 11 y los 17 años (M = 13,56; DT = 1,39), empleando como marco teórico el modelo jerárquico de la motivación de Vallerand, para ello, a través de cuestionarios se midió: la percepción del clima motivacional que implica a la tarea de los padres, la creencia incremental de habilidad, la necesidad de competencia, la motivación intrínseca y las barreras para la práctica de ejercicio físico. El modelo de ecuaciones estructurales mostró que la percepción del clima motivacional que implica a la tarea de los padres predecía positivamente la creencia incremental, ésta a su vez, predecía de forma positiva la necesidad de competencia, dicho mediador predijo positivamente la motivación intrínseca, y por último, la motivación más autodeterminada predecía de forma negativa las barreras para la práctica de ejercicio físico. De los hallazgos de este trabajo destacar la relevancia de fomentar la necesidad psicológica básica de competencia para reducir el número de barreras percibidas por los sujetos a la hora de realizar ejercicio físico, y en consecuencia evitar el abandono de la práctica físico-deportiva de los adolescentes