134 research outputs found
Evaluation des sites internet. Construction d'indicateurs à partir des réseaux de sitations
National audienceL'Internet est de nos jours une nouvelle source d'information incontournable. Par contre, qui n'a pas Ă©tĂ© dĂ©jĂ confrontĂ© au phĂ©nomĂšne de sur-information lors de la recherche sur un moteur ou de dĂ©sorientation lors de la navigation sur Internet. Ces problĂšmes sont persistants sur le rĂ©seau Internet, du fait mĂȘme de sa construction, et sont Ă l'origine de pertes de temps considĂ©rables. Comment dans ce foisonnement de donnĂ©es juger l'importance des pages Internet et des sites les contenant ? Comment rationaliser la gestion de ces ressources et amĂ©liorer la performance de leur exploitation ? La communication abordera dans un premier temps l'ensemble des diffĂ©rentes approches actuellement dĂ©veloppĂ©es pour aider l'utilisateur Ă mieux gĂ©rer l'information prĂ©sentes sur Internet. Ces techniques ont principalement pour principe l'Ă©valuation de pages ou des sites Internet. Nous Ă©voquerons les rĂ©flexions qui actuellement ont cours pour l'Ă©valuation des ressources Internet [1]. Nous verrons que les principaux critĂšres proposĂ©s font bien souvent appel Ă une Ă©valuation purement intellectuelle. MalgrĂ© tout, il parait indispensable de concevoir des outils de traitement automatique pour l'aide Ă l'Ă©valuation de ces nouvelles ressources. Nous passerons rapidement en revue les diffĂ©rentes techniques d'Ă©valuation actuellement disponible en essayant de les classer par catĂ©gorie : - analyse du contenu lexical des pages Web : classement par pertinence (moteurs de recherche ou robots tels que DigOut4U, Search'97) ; simple classement (Search'97, Nomino) ; agrĂ©gation statistique suivie d'une cartographie soit parcellaire (Sampler) soit intĂ©grale (WebSom, Neuronav+, SemioMap, Umap, TKS, TĂ©tralogie) - analyse du contenu multimĂ©dia des pages Web [2] - analyse de la dimension hypertextuelle des pages Web : analyse de l'espace des relations entre pages [3]; analyse du phĂ©nomĂšne de rĂ©fĂ©rencement entre sites, la " sitation " [4] Nous positionnerons alors notre approche, l'analyse des rĂ©seaux de " sitations ", par rapport Ă ces techniques. Une description de l'ensemble des indicateurs et cartographie rĂ©seaux mise au point sera exposĂ©e
Audit d'un serveur Internet et approche réseau
National audienceUn certain nombre de logiciels, connus sous le nom d'analyseurs de .Log proposent un ensemble d'indicateurs statistiques d'usage d'un site web. Cette Ă©tude a pour objectif de renouveler l'approche traditionnelle des analyseurs de .Log en utilisant l'analyse en terme de rĂ©seau. Cette nouvelle dĂ©marche est prĂ©sentĂ©e en s'appuyant sur l'exemple de l'audit du serveur du CRRM rĂ©alisĂ© en DĂ©cembre 1996 Ă partir de 2869 connexions. Dans un premier temps, nous positionnerons la mĂ©thode rĂ©seau par rapport aux mĂ©thodes existantes. Dans un second temps, nous dĂ©velopperons un bref aperçu de la richesse des analyses qui peuvent ĂȘtre conduites par cette mĂ©thode
Treating bibliometric indicators with caution: their dependence on the source database
International audienceNowadays, with computer-supported analysis of databases, constructing bibliometric or scientometric indicators may be considered easy. The problem is more to verify the accuracy of the global analysis, including the sampling of data. The global coherence of an analysis depends on the adequacy of all the steps. Using on-line databases, an experiment was designed to demonstrate this. Keeping the same protocol for data collection, the same indicators are used over the various samples . The results from three separate databases are profoundly different.Aujourd'hui, avec l'analyse automatique des bases de donnĂ©es, la construction d'indicateurs bibliomĂ©triques ou scientomĂ©triques est facilitĂ©e. Le problĂšme est plus de vĂ©rifier l'exactitude de l'analyse globale, y compris l'Ă©chantillonnage des donnĂ©es. La cohĂ©rence globale de l'analyse dĂ©pend de la pertinence de tous les maillons de la chaĂźne. En utilisant des bases de donnĂ©es en ligne, une expĂ©rience a Ă©tĂ© conduite : les mĂȘmes indicateurs ont Ă©tĂ© utilisĂ©s sur diffĂ©rents Ă©chantillons. Les rĂ©sultats obtenus sont profondĂ©ment diffĂ©rentes
Traitement de l'information : analyse de données classiques versus analyse de réseau. Un cas d'application : la bibliométrie
National audienceLâanalyse en terme de rĂ©seau a fait lâobjet dâun certain nombre de recherches, dans le domaine des sciences humaines et sociales. Les principaux rĂ©sultats sont prĂ©sentĂ©s dans lâouvrage de Wasserman (1994).L'objet de ce travail est de porter Ă la connaissance de la communautĂ© acadĂ©mique une pratique originale de traitement de l'information qui utilise un graphe appelĂ© rĂ©seau pour reprĂ©senter une information complexe de façon synthĂ©tique. Cette technique est d'abord positionnĂ©e par rapport aux analyses de donnĂ©es classiques et fait ensuite l'objet d'une application dans le cas particulier du traitement des donnĂ©es bibliomĂ©triques
Analyse de commentaires libres par la technique des réseaux de segments
International audienceLes techniques dâanalyse du contenu dâun corpus de textes sont multiples. Le traitement exposĂ© ici est basĂ© sur une approche hybride intĂ©grant lâanalyse de rĂ©seaux, employĂ©e en sciences sociales ou en bibliomĂ©trie, et la technique de segmentation utilisĂ©e en analyse statistique textuelle.Lâapplication de cette mĂ©thode dans le cadre dâĂ©tude dâanalyse sensorielle est prĂ©sentĂ©e. Ces Ă©tudes ont pour objet lâinterprĂ©tation dâun corpus de commentaires libres proposĂ©s par des consommateurs soumis Ă des tests de produits agro-alimentaires. Ces commentaires Ă©tant saisis sous formes de textes Ă©lectroniques, la mise en Ćuvre dâoutils informatiques spĂ©cifiques a permis lâanalyse de rĂ©seaux des segments prĂ©sents dans ces commentaires. La premiĂšre phase du traitement de ces commentaires est leur postcodage : correction orthographique ; rĂ©duction du vocabulaire par lemmatisation et synonymie ; marquage des termes ou locutions selon leur appartenance Ă des classes (arĂŽme/odeur, hĂ©donique, perception, saveur, texture, aspect, intensitĂ© des sensations) ; dĂ©coupage du texte en segments. La seconde phase passe par le dĂ©nombrement des segments et de leurs associations, construction dâun tableau exprimant ces donnĂ©es. La derniĂšre phase du traitement est la reprĂ©sentation de ce tableau sous la forme dâun rĂ©seau. Lâoutil informatique qui gĂ©nĂšre ce rĂ©seau permet le renvoi vers les commentaires contenant les noeuds du rĂ©seau ainsi quâune navigation hypertexte
Water-exchange MRI detects subtle blood-brain barrier breakdown in Alzheimer's disease rats
Blood-brain barrier (BBB) breakdown has been hypothesized to play a key role in the onset and progression of Alzheimer's disease (AD). However, the question of whether AD itself contributes to loss of BBB integrity is still uncertain, as many in-vivo studies have failed to detect signs of AD-related BBB breakdown. We hypothesize AD-related BBB damage is subtle, and that these negative results arise from a lack of measurement sensitivity. With the aim of developing a more sensitive measure of BBB breakdown, we have designed a novel MRI scanning protocol to quantify the trans-BBB exchange of endogenous water. Using this method, we detect increased BBB water permeability in a rat model of AD that is associated with reduced expression of the tight junction protein occludin. BBB permeability to MRI contrast agent, assessed using dynamic contrast-enhanced (DCE)-MRI, did not differ between transgenic and wild-type animals and was uncorrelated with occludin expression. Our data supports the occurrence of AD-related BBB breakdown, and indicates that such BBB pathology is subtle and may be undetectable using existing âtracer leakageâ methods. Our validated water-exchange MRI method provides a new powerful tool with which to study BBB damage in-vivo
Alzheimer's disease pathology is associated with earlier alterations to bloodâbrain barrier water permeability compared with healthy ageing in TgF344âAD rats
From Wiley via Jisc Publications RouterHistory: received 2020-11-05, rev-recd 2021-02-06, accepted 2021-02-26, pub-electronic 2021-03-15, pub-print 2021-07Article version: VoRPublication status: PublishedFunder: Biotechnology and Biological Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000268; Grant(s): BB/F011350Funder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/M005909/1Funder: European Unionâs Seventh Framework Programme; Grant(s): FP7/2007â2013, HEALTHâF2â2011â278850, HEALTHâF2â2011â278850The effects of Alzheimer's disease (AD) and ageing on bloodâbrain barrier (BBB) breakdown are investigated in TgF344âAD and wildâtype rats aged 13, 18 and 21 months. Permeability surface area products of the BBB to water (PSw) and gadoliniumâbased contrast agent (PSg) were measured in grey matter using multiflip angle multiecho dynamic contrastâenhanced MRI. At 13 months of age, there was no significant difference in PSw between TgF344âAD and wildâtypes (p = 0.82). Between 13 and 18 months, PSw increased in TgF344âAD rats (p = 0.027), but not in wildâtypes (p = 0.99), leading to significantly higher PSw in TgF344âAD rats at 18 months, as previously reported (p = 0.012). Between 18 and 21 months, PSw values increased in wildâtypes (p = 0.050), but not in TgF344âAD rats (p = 0.50). These results indicate that BBB water permeability is affected by both AD pathology and ageing, but that changes occur earlier in the presence of AD pathology. There were no significant genotype or ageing effects on PSg (p > 0.05). In conclusion, we detected increases in BBB water permeability with age in TgF344âAD and wildâtype rats, and found that changes occurred at an earlier age in rats with AD pathology
Filter exchange imaging with crusher gradient modelling detects increased bloodâbrain barrier water permeability in response to mild lung infection
Bloodâbrain barrier (BBB) dysfunction occurs in many brain diseases, and there is increasing evidence to suggest that it is an early process in dementia which may be exacerbated by peripheral infection. Filter-exchange imaging (FEXI) is an MRI technique for measuring trans-membrane water exchange. FEXI data is typically analysed using the apparent exchange rate (AXR) model, yielding estimates of the AXR. Crusher gradients are commonly used to remove unwanted coherence pathways arising from longitudinal storage pulses during the mixing period. We first demonstrate that when using thin slices, as is needed for imaging the rodent brain, crusher gradients result in underestimation of the AXR. To address this, we propose an extended crusher-compensated exchange rate (CCXR) model to account for diffusion-weighting introduced by the crusher gradients, which is able to recover ground truth values of BBB water exchange (kin) in simulated data. When applied to the rat brain, kin estimates obtained using the CCXR model were 3.10 sâ1 and 3.49 sâ1 compared to AXR estimates of 1.24 sâ1 and 0.49 sâ1 for slice thicknesses of 4.0 mm and 2.5 mm respectively. We then validated our approach using a clinically relevant Streptococcus pneumoniae lung infection. We observed a significant 70â±â10% increase in BBB water exchange in rats during active infection (kinâ=â3.78â±â0.42 sâ1) compared to before infection (kinâ=â2.72â±â0.30 sâ1; pâ=â0.02). The BBB water exchange rate during infection was associated with higher levels of plasma von Willebrand factor (VWF), a marker of acute vascular inflammation. We also observed 42% higher expression of perivascular aquaporin-4 (AQP4) in infected animals compared to non-infected controls, while levels of tight junction proteins remain consistent between groups. In summary, we propose a modelling approach for FEXI data which removes the bias in estimated water-exchange rates associated with the use of crusher gradients. Using this approach, we demonstrate the impact of peripheral infection on BBB water exchange, which appears to be mediated by endothelial dysfunction and associated with an increase in perivascular AQP4
Evaluation of \u3csup\u3e18\u3c/sup\u3eF-IAM6067 as a sigma-1 receptor PET tracer for neurodegeneration in vivo in rodents and in human tissue
© The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/). See http://ivyspring.com/terms for full terms and conditions. The sigma 1 receptor (S1R) is widely expressed in the CNS and is mainly located on the endoplasmic reticulum. The S1R is involved in the regulation of many neurotransmission systems and, indirectly, in neurodegenerative diseases. The S1R may therefore represent an interesting neuronal biomarker in neurodegenerative diseases such as Parkinson\u27s (PD) or Alzheimer\u27s diseases (AD). Here we present the characterisation of the S1R-specific 18F-labelled tracer 18F-IAM6067 in two animal models and in human brain tissue. Methods: Wistar rats were used for PET-CT imaging (60 min dynamic acquisition) and metabolite analysis (1, 2, 5, 10, 20, 60 min post-injection). To verify in vivo selectivity, haloperidol, BD1047 (S1R ligand), CM398 (S2R ligand) and SB206553 (5HT2B/C antagonist) were administrated for pre-saturation studies. Excitotoxic lesions induced by intra-striatal injection of AMPA were also imaged by 18F-IAM6067 PET-CT to test the sensitivity of the methods in a well-established model of neuronal loss. Tracer brain uptake was also verified by autoradiography in rats and in a mouse model of PD (intrastriatal 6-hydroxydopamine (6-OHDA) unilateral lesion). Finally, human cortical binding was investigated by autoradiography in three groups of subjects (control subjects with Braak â€2, and AD patients, Braak \u3e2 & â€4 and Braak \u3e4 stages). Results: We demonstrate that despite rapid peripheral metabolism of 18F-IAM6067, radiolabelled metabolites were hardly detected in brain samples. Brain uptake of 18F-IAM6067 showed differences in S1R anatomical distribution, namely from high to low uptake: pons-raphe, thalamus medio-dorsal, substantia nigra, hypothalamus, cerebellum, cortical areas and striatum. Pre-saturation studies showed 79-90% blockade of the binding in all areas of the brain indicated above except with the 5HT2B/C antagonist SB206553 and S2R ligand CM398 which induced no significant blockade, indicating good specificity of 18F-IAM6067 for S1Rs. No difference between ipsi- and contralateral sides of the brain in the mouse model of PD was detected. AMPA lesion induced a significant 69% decrease in 18F-IAM6067 uptake in the globus pallidus matching the neuronal loss as measured by NeuN, but only a trend to decrease (-16%) in the caudate putamen despite a significant 91% decrease in neuronal count. Moreover, no difference in the human cortical binding was shown between AD groups and controls. Conclusion: This work shows that 18F-IAM6067 is a specific and selective S1R radiotracer. The absence or small changes in S1R detected here in animal models and human tissue warrants further investigations and suggests that S1R might not be the anticipated ideal biomarker for neuronal loss in neurodegenerative diseases such as AD and PD
- âŠ