Confluent Thalamic Hyperintensities in CADASIL

Background: CADASIL is responsible for diffuse hyperintensities in the white matter on FLAIR images. These lesions are often associated with focal lesions in the basal ganglia such as lacunar infarctions. The prevalence and significance of diffuse or confluent thalamic hyperintensities (CTH) remain unknown. Methods: The frequency of hyperintensities on FLAIR images in the thalamus was assessed in 147 CADASIL patients, and signal abnormalities on both FLAIR and T(1)-weighted images were categorized as focal/punctuate or diffuse/confluent by the same reader. The areas of increased diffusion were also analyzed on apparent diffusion coefficient maps. The association of CTH with vascular risk factors, the main clinical manifestations of the disease and MRI markers (brain parenchymal fraction, volume of white matter hyperintensities, volume of lacunar infarcts and number of microbleeds) was analyzed with generalized linear regression models. Results: CTH were detected in 12% of the CADASIL subjects in association with hypointensities on T(1)-weighted images. CTH corresponded to areas of increased diffusion apparent diffusion coefficient maps. CTH were found significantly associated with age and independently related to the volume of white matter hyperintensities but not to that of lacunar infarctions or to cerebral atrophy after adjustment for age and sex. No significant association was found between CTH and global cognitive performances. Conclusion: CTH are observed on FLAIR images in a sizeable proportion of CADASIL patients. They are mainly related to the extent of white matter hyperintensities and do not correlate with cognitive decline. Demyelination and/or loss of glial cells appear to be the most plausible cause of these confluent signal changes in the thalamus. Copyright (C) 2010 S. Karger AG, Base

Carotid Atherosclerotic Markers in CADASIL

Purpose: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a cerebral small vessel disease caused by mutations of the NOTCH3 gene. Marked variations in disease severity have raised the hypothesis that non-genetic factors may modulate the expressivity of the phenotype. The aim of the current study was to evaluate whether atherosclerosis, assessed by carotid duplex ultrasonography, is associated with variations in the clinical and MRI phenotype of CADASIL. Methods: Data from 144 consecutive patients enrolled in an ongoing prospective cohort study were collected. Degree of disability was assessed by the modified Rankin Scale, that of cognitive impairment by the Mattis Dementia Rating Scale (MDRS). The total volume of the brain, of lacunar lesions and of white matter hyperintensities, the number of cerebral microhemorrhages, and parameters derived from histograms of apparent diffusion coefficient were measured on cerebral MRI. Atherosclerosis was evaluated by B-mode ultrasonography of carotid arteries. Both the carotid intima-media thickness cIMT) and the presence of carotid plaques or stenosis were recorded. Results: Higher cIMT was found to be independently associated with lower MDRS scores when this score was less than the quartile limit (p = 0.02). Only a trend for a positive association was detected between cIMT and the Rankin score (p = 0.06). There was no significant association between carotid markers and the occurrence of stroke or MRI parameters except for diffusion data. The mean and peak values of MRI diffusion histograms were found positively associated with the presence of plaques (p < 0.01). Conclusion: The results suggest that the severity of atherosclerosis may relate to cognitive decline in CADASIL and that this effect is possibly related to the degree of microstructural cerebral tissue lesions. Longitudinal studies are needed to confirm these results. Copyright (C) 2010 S. Karger AG, Base

Intermittency study of global solar radiation on Reunion Island using Hilbert-Huang transform

The characterization of the solar radiation variability is a fundamental step before prediction and is crucial to transform an intermittent source of energy into a stable one. As solar irradiance result from a nonlinear and non-stationary process, we use a multifractal approach based on the Hilbert-Huang Transform (HHT) consisting of an empirical mode decomposition (EMD) followed by a spectral analysis. In this paper, we will briefly introduce the HHT data analysis method. Such a recent adaptive data analysis method has been applied to Reunion Island global solar radiation time series of measurements with a sampling rate of 1/60 Hz over six years. Through the EMD, daily global solar radiation data were decomposed into several intrinsic mode functions (IMF). For each IMF, we estimate the amplitude, instantaneous frequency and Hilbert spectrum for the original data. From the comparison of Hilbert Spectrum and Fourier Spectrum, we find the calculated solar radiation power spectrum follows a power law behavior close to the Kolmogorov law. The method described in this paper provides an amplitude frequency representation of the global solar radiation sequences resulting in a probability density function and a scaling coefficient. The multifractal approach allows to extract parameters connected to the multifractal properties of the global solar radiation.fb201

Dilated perivascular spaces in small-vessel disease: A study in CADASIL

BACKGROUND AND AIM Dilated perivascular spaces (dPVS) have previously been associated with aging and hypertension-related cerebral microangiopathy. However, their risk factors, radiological features and clinical relevance have been poorly evaluated in CADASIL (cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy), a unique model to investigate the pathophysiology of ischemic small-vessel disease. The purpose of this study was to investigate these different aspects in a large cohort of patients with this disorder. METHODS Demographic and MRI data of 344 patients from a prospective cohort study were analyzed. The severity of dPVS was evaluated separately in the anterior temporal lobes, subinsular areas, basal ganglia and white matter, using validated semiquantitative scales. Logistic and multiple linear regression models were used to determine the risk factors associated with the severity of dPVS in these different regions and their relationships with cognition, disability and the MRI markers of the disease (white matter hyperintensities (WMH) lacunar infarcts, microbleeds and brain parenchymal fraction (BPF)). RESULTS The severity of dPVS was found to increase with age regardless of cerebral area (p\textless0.001). In contrast with dPVS in other locations, the severity of dPVS in the temporal lobes or subinsular areas was also found strongly and specifically related to the extent of WMH (p\textless0.001). Conversely, no significant association was detected with lacunar volume, number of microbleeds or BPF. A high degree of dPVS in the white matter was associated with lower cognitive performances independently of age and other MRI markers of the disease including BPF (p≤0.04). CONCLUSIONS In CADASIL, the progression of the hereditary microangiopathy with aging may promote the dilation of perivascular spaces throughout the whole brain but with variable extent according to cerebral location. In temporal lobes and subinsular areas, dPVS are common MRI features and may share a similar pathogenesis with the extension of WMH during the course of the disease. dPVS may also participate in the development of cognitive decline in this model of small-vessel disease, and their large number in white matter may alert clinicians to a higher risk of cognitive decline in CADASIL

ADC Histograms from Routine DWI for Longitudinal Studies in Cerebral Small Vessel Disease: A Field Study in CADASIL.

Diffusion tensor imaging (DTI) histogram metrics are correlated with clinical parameters in cerebral small vessel diseases (cSVD). Whether ADC histogram parameters derived from simple diffusion weighted imaging (DWI) can provide relevant markers for long term studies of cSVD remains unknown. CADASIL patients were evaluated by DWI and DTI in a large cohort study overa6-year period. ADC histogram parameters were compared to those derived from mean diffusivity (MD) histograms in 280 patients using intra-class correlation and Bland-Altman plots. Impact of image corrections applied to ADC maps was assessed and a mixed effect model was used for analyzing the effects of scanner upgrades. The results showed that ADC histogram parameters are strongly correlated to MD histogram parameters and that image corrections have only limited influence on these results. Unexpectedly, scanner upgrades were found to have major effects on diffusion measures with DWI or DTI that can be even larger than those related to patients' characteristics. These data support that ADC histograms from daily used DWI can provide relevant parameters for assessing cSVD, but the variability related to scanner upgrades as regularly performed in clinical centers should be determined precisely for longitudinal and multicentric studies using diffusion MRI in cSVD

Modèles de connaissance de la cristallisation de troisième jet en sucrerie de cannes (expérimentations et simulations)

Cette étude concerne la modélisation d un procédé de cristallisation de troisième jet, dite cristallisation C, en sucrerie de cannes. De par la complexité des phénomènes physico-chimiques mis en jeu lors d une cristallisation industrielle, il est nécessaire de développer plusieurs approches de modélisation. Cette multiplicité de modèles permet de comparer ainsi les diverses approches proposées. Nous avons pour cela axé notre étude sur la modélisation des diverses cinétiques des phénomènes physiques qui interviennent lors d une cristallisation C, par le biais de plusieurs modèles mathématiques. En effet, nous avons considéré trois types de cinétiques pouvant exister au sein de la solution : les cinétiques de nucléation, de croissance et d agglomération. Nous avons aussi mis en place plusieurs stratégies de modélisation dites hybrides , qui sont en fait les combinaisons de réseaux de neurones et de modèles de connaissances. Les phases d apprentissage des réseaux de neurones sont basées sur des mesures, et la modélisation globale du procédé de cristallisation combine cette approche systémique aux différents modèles de connaissance choisis. Ces diverses approches utilisées n occultent pas les démarches classiques de modélisation en génie de la cristallisation. De ce fait, si nous souhaitons contrôler le procédé, plusieurs modèles mathématiques s articulant autour de différents bilans de population sont proposés. Ce travail est original, d une part, car il décrit la cristallisation de troisième jet, et d autre part, du fait que les divers modèles de cinétiques soient identifiés avec des données industrielles. En effet, il faut souligner qu il n existe quasiment pas de travaux relatifs à la cristallisation C, donc peu de références bibliographiques sur cette cristallisation de bas produit en milieu industriel sucrier.This study deals with modeling the boiling third crystallization process, boiling C crystallization in cane sugar mill. Due to the complexity of physicochemical phenomena involved in the industrial boiling crystallization, it is necessary to develop several modelling approaches. By this way, the variability of these models leads to compare the various modeling suggested. We have focused our research on modeling various kinetics of physical phenomena contributing to the boiling C crystallization, through mathematical models. We have considered three kinetics that exist in solution: the nucleation rate, the growth rate and the agglomeration rate. We are proposing several boiling modeling, called hybrid modeling strategies , which are the combinations of neural networks and the prior knowledge.The neural networks training is based on some industrial data, and the boiling C crystallization process modelling associates this systemic model to the prior knowledge. The various approaches presented do not exclude the classical modelling in boiling crystallization. For this reason, if we want to supervise the boiling crystallization process, several mathematical models are suggested through the population balances.This study is original, on one hand, by describing the boiling C crystallization, and on the other hand, by the identification of several modeling with industrial data. It is necessary to underline that there is a lack of literature data regarding the boiling C crystallization, and thus there are only few bibliographical references on the boiling C crystallization in cane sugar mill.SAINT DENIS/REUNION-Droit Lettre (974112101) / SudocSudocFranceReunionFRR

Cristallisation C en sucrerie de canne (modélisation de la pureté de la liqueur mère et étude de l'ensemencement)

SAINT DENIS/REUNION-Droit Lettre (974112101) / SudocSudocFranceReunionFRR

Impact of decomposition and kriging models on the solar irradiance downscaling accuracy in regions with complex topography

International audienceMany small island states are planning to invest heavily in solar photovoltaics in an attempt to curb their overreliance on fossil fuels for electricity generation. In order to efficiently exploit the abundant solar energy resource, these islands need reliable solar irradiance data. However, the orographic effects arising from their volcanic origins often result in strong variability and uncertainty in the solar resource. In this context, satellite-based models present an effective alternative to ground-based measurements. Different downscaling approaches have been applied that compensate for the large spatial resolution of satellite images and the terrain-related effects that they disregard. Nevertheless, the accuracy of these methods is influenced by the solar radiation decomposition model used. Moreover, the variogram model used in the kriging process to characterize the spatial dependence of the solar radiation has a significant effect on the results. In this study, we compare the performances of seven radiation decomposition models for the anisotropy analysis and seven variogram models for the spatial interpolation of the solar irradiance. A dense network of ground measurements at 43 stations is used to evaluate the accuracy of the different models. Results reveal that the Yao radiation model coupled with the Matern variogram provide the best results

Impact of the temperature on calendar aging of an open cathode fuel cell stack

International audienceThis paper deals with calendar aging of a proton exchange membrane open-cathode fuel cell. Calendar aging is already developed for energy sources as supercapacitor and batteries but the literature is very poor for fuel cell stacks. However, this kind of test is necessary to determine the actual lifetime of the system without running it and to define the aging impact of the storage of such a system. One possible outcome for fuel cells is to provide electricity in remote areas without connection to the grid. This issue becomes even more challenging under hard environmental conditions, especially in areas with possible negative ambient temperatures. Experimental research on the degradation of open cathode fuel cells under these tricky conditions is needed to investigate the impact of resting states on the fuel cell lifetime and to evaluate the impact of the sub-zero temperatures on the performance losses

Modelling and simulation of a complete system of energy transmission

International audienceThis article presents an equivalent circuit approach used for the modelling of a system consisting of an antenna and a RF/DC rectifying circuit (rectenna) at 2.45 GHz. The measurements and simulations steps used for parameter extraction and model validation are presented. The major interest in this approach is the ability to study a complete system of energy transmission in a single simulator environment. This method is illustrated in the case of a microwave transmission without any modulation, that is to say the derived model can be easily integrated. The results obtained using this simple example show a relatively good agreement with the experiment and can form the basis for further developments of more complex system