Molecular hydrogen diffusion in nanostructured amorphous silicon thin films

We study hydrogen stability and its evolution during thermal annealing in nanostructured amorphous silicon thin films. From the simultaneous measurement of heat and hydrogen desorption, we obtain the experimental evidence of molecular diffusion in these materials. In addition, we introduce a simple diffusion model which shows good agreement with the experimental data

Effect of drift on segregation in two-component diffusion-limited aggregation

An effect of drift is investigated on the segregation pattern in diffusion-limited aggregation (DLA) with two components (A and B species). The sticking probability PAB (=PBA) between the different species is introduced into the DLA model with drift, where the sticking probability PAA (=PBB) between the same species equals 1. By using computer simulation it is found that the drift has an important effect on not only the morphology but also the segregation pattern. Under the drift and the small sticking probability, a characteristic pattern appears where elongated clusters of A species and of B species are periodically dispersed. The period decreases with increasing drift. The periodic structure of the deposits is characterized by an autocorrelation function. The shape of the cluster consisting of only A species (or B species) shows a vertically elongated filamentlike structure. Each cluster becomes vertically longer with decreasing sticking probability PAB. The segregation pattern is distinctly different from that with no drift and a small sticking probability PAA. The effect of the concentration on the segregation pattern is also shown.

Characterizing the connectome in schizophrenia with diffusion spectrum imaging.

Schizophrenia is a complex psychiatric disorder characterized by disabling symptoms and cognitive deficit. Recent neuroimaging findings suggest that large parts of the brain are affected by the disease, and that the capacity of functional integration between brain areas is decreased. In this study we questioned (i) which brain areas underlie the loss of network integration properties observed in the pathology, (ii) what is the topological role of the affected regions within the overall brain network and how this topological status might be altered in patients, and (iii) how white matter properties of tracts connecting affected regions may be disrupted. We acquired diffusion spectrum imaging (a technique sensitive to fiber crossing and slow diffusion compartment) data from 16 schizophrenia patients and 15 healthy controls, and investigated their weighted brain networks. The global connectivity analysis confirmed that patients present disrupted integration and segregation properties. The nodal analysis allowed identifying a distributed set of brain nodes affected in the pathology, including hubs and peripheral areas. To characterize the topological role of this affected core, we investigated the brain network shortest paths layout, and quantified the network damage after targeted attack toward the affected core. The centrality of the affected core was compromised in patients. Moreover the connectivity strength within the affected core, quantified with generalized fractional anisotropy and apparent diffusion coefficient, was altered in patients. Taken together, these findings suggest that the structural alterations and topological decentralization of the affected core might be major mechanisms underlying the schizophrenia dysconnectivity disorder. Hum Brain Mapp, 36:354-366, 2015. © 2014 Wiley Periodicals, Inc.

Interobserver and intraobserver variability of apparent diffusion coefficient measurements in treated malignant hepatic lesions: measurements in the whole lesion versus in the area with the most restricted diffusion

Purpose: The increase of apparent diffusion coefficient (ADC) in treated hepatic malignancies compared to pre-therapeutic values has been interpreted as treatment success; however, the variability of ADC measurements remains unknown. Furthermore, ADC has been usually measured in the whole lesion, while measurements should be probably centered on the area with the most restricted diffusion (MRDA) as it represents potential tumoral residue. Our objective was to compare the inter/intraobserver variability of ADC measurements in the whole lesion and in MRDA. Material and methods: Forty patients previously treated with chemoembolization or radiofrequency were evaluated (20 on 1.5T and 20 on 3.0T). After consensual agreement on the best ADC image, two readers measured the ADC values using separate regions of interest that included the whole lesion and the whole MRDA without exceeding their borders. The same measurements were repeated two weeks later. Spearman test and the Bland-Altman method were used. Results: Interobserver correlation in ADC measurements in the whole lesion and MRDA was as follows: 0.962 and 0.884. Intraobserver correlation was, respectively, 0.992 and 0.979. Interobserver limits of variability (mm2/sec*10-3) were between -0.25/+0.28 in the whole lesion and between -0.51/+0.46 in MRDA. Intraobserver limits of variability were, respectively: -0.25/+0.24 and -0.43/+0.47. Conclusion: We observed a good inter/intraobserver correlation in ADC measurements. Nevertheless, a limited variability does exist, and it should be considered when interpreting ADC values of hepatic malignancies.

Estimation of a maximum Lu diffusion rate in a natural eclogite garnet

Lutetium zoning in garnet within eclogites from the Zermatt-Saas Fee zone, Western Alps, reveal sharp, exponentially decreasing central peaks. They can be used to constrain maximum Lu volume diffusion in garnets. A prograde garnet growth temperature interval of 450-600 A degrees C has been estimated based on pseudosection calculations and garnet-clinopyroxene thermometry. The maximum pre-exponential diffusion coefficient which fits the measured central peak is in the order of D-0= 5.7*10(-6) m(2)/s, taking an estimated activation energy of 270 kJ/mol based on diffusion experiments for other rare earth elements in garnet. This corresponds to a maximum diffusion rate of D (600 A degrees C) = 4.0*10(-22) m(2)/s. The diffusion estimate of Lu can be used to estimate the minimum closure temperature, T-c, for Sm-Nd and Lu-Hf age data that have been obtained in eclogites of the Western Alps, postulating, based on a literature review, that D (Hf) < D (Nd) < D (Sm) a parts per thousand currency sign D (Lu). T-c calculations, using the Dodson equation, yielded minimum closure temperatures of about 630 A degrees C, assuming a rapid initial exhumation rate of 50A degrees/m.y., and an average crystal size of garnets (r = 1 mm). This suggests that Sm/Nd and Lu/Hf isochron age differences in eclogites from the Western Alps, where peak temperatures did rarely exceed 600 A degrees C must be interpreted in terms of prograde metamorphism.

Understanding diffusion MR imaging techniques: from scalar diffusion-weighted imaging to diffusion tensor imaging and beyond.

The complex structural organization of the white matter of the brain can be depicted in vivo in great detail with advanced diffusion magnetic resonance (MR) imaging schemes. Diffusion MR imaging techniques are increasingly varied, from the simplest and most commonly used technique-the mapping of apparent diffusion coefficient values-to the more complex, such as diffusion tensor imaging, q-ball imaging, diffusion spectrum imaging, and tractography. The type of structural information obtained differs according to the technique used. To fully understand how diffusion MR imaging works, it is helpful to be familiar with the physical principles of water diffusion in the brain and the conceptual basis of each imaging technique. Knowledge of the technique-specific requirements with regard to hardware and acquisition time, as well as the advantages, limitations, and potential interpretation pitfalls of each technique, is especially useful.

Microstructural evolution of primary crystallization in diffusion-controlled grain growth

A model has been developed for evaluating grain size distributions in primary crystallizations where the grain growth is diffusion controlled. The body of the model is grounded in a recently presented mean-field integration of the nucleation and growth kinetic equations, modified conveniently in order to take into account a radius-dependent growth rate, as occurs in diffusion-controlled growth. The classical diffusion theory is considered, and a modification of this is proposed to take into account interference of the diffusion profiles between neighbor grains. The potentiality of the mean-field model to give detailed information on the grain size distribution and transformed volume fraction for transformations driven by nucleation and either interface- or diffusion-controlled growth processes is demonstrated. The model is evaluated for the primary crystallization of an amorphous alloy, giving an excellent agreement with experimental data. Grain size distributions are computed, and their properties are discussed.

MOLECULAR MECHANISMS OF A ROOT SYSTEM TO SOIL ADAPTATION

Contrairement aux animaux, les plantes sont des organismes sessiles qui ne possèdent pas de mécanismes de fuite quand les conditions environnementales ne sont plus optimales. Les plantes sont physiquement ancrées à l'endroit où elles ont germées et aux conditions environnementales qui parfois peuvent être extrêmes. Les possibilités d'acclimatation de différentes espèces, parfois même de groupes de plantes au sein d'une même espèce, peuvent varier mais repose sur une adaptation génétique de la plante. L'adaptation est un long processus qui repose sur l'apparition spontanée de mutations génétiques, leur mise à l'épreuve face aux conditions environnementales, et dans le cas où la mutation a un impact positif sur la survie dans cet habitat particulier, elle sera maintenue dans une population donnée de plantes. De telles populations, appelées écotypes, sont le matériel de départ pour la découverte de gènes qui induisent un bénéfice pour la plante dans un environnement donné. La plante la plus étudiée en biologie moléculaire est Arabidopsis thaliana, l'arabette des prés. Dans une étude précédente, les racines d'écotypes naturels d'Arabidopsis ont été comparées et un écotype, Uk-1, avait le système racinaire le plus particulier. Cet écotype possède des racines beaucoup plus courtes et plus ramifiées que tous les autres écotypes. Des analyses plus poussées ont montré qu'une seule mutation dans un gène était la cause de ce phénotype, le gène BREVIS RADIX (BRX), mot latin signifiant 'racine courte'. Bien que l'on connaisse le gène BRX, on connaît finalement peu de choses sur son importance adaptative. Dans cette étude, nous avons montré que la mutation dans le gène BRX rend la plante plus résistante aux sols acides. Dans l'optique de mieux comprendre cette valeur adaptative du mutant brx, nous avons analysé dans quels tissus le gène BRX jouait un rôle important. Nous avons pu mettre en évidence que BRX est important pour le développement du protophloème. Le protophloème est un élément du système vasculaire de la plante. En général, les plantes supérieures possèdent deux systèmes de transport à longue distance. L'un d'eux, appelé xylème, transporte l'eau et les nutriments absorbés du sol par les racines vers les feuilles. Les feuilles sont le siège du processus de photosynthèse au cours duquel sont produits des sucres qui devront être distribués partout dans les autres parties de la plante. Le tissu cellulaire chargé de livrer les produits de la photosynthèse, ainsi que les régulateurs de croissance, est le phloème. Ce dernier regroupe le métaphloème et le protophloème. Le protophloème est essentiel pour la livraison des sucres synthétisés ainsi que des signaux de croissance aux pointes des racines, centres organogéniques responsables de la production de nouvelles cellules durant la phase de croissance de la racine. La structure du protophloème peut être décrite comme des tubes continus, vides et résistants, faits de cellules spécialisées qui permettent un transport efficace et rapide. Nous avons montré que dans les mutants brx ces canaux de transports sont discontinus car certaines cellules n'ont pas terminé leur cycle de différenciation. Ces cellules obstruent le conduit ce qui fait que les sucres et les signaux de croissance, comme l'auxine, ne peuvent plus être transportés aux méristèmes. En conséquence, la prolifération de l'activité des méristèmes est compromise, ce qui explique les racines courtes. Au lieu d'être délivré aux méristèmes, l'auxine se concentre en amont des méristèmes où cela provoque l'apparition de nouvelles racines branchées et, très probablement, l'activation des pompes à protons. Sur des sols acides, la concentration en ion H+ est très élevée. Ces ions entrent dans les cellules de la racine par diffusion et perturbent notablement la croissance des racines et de la plante en général. Si les cellules de la racine possédaient des pompes à protons hyperactives, elles seraient capable d'évacuer le surplus d'ions H+ en dehors de la cellule, ce qui leur assurerait de meilleures chances de survie sur sols acides. De fait, le mutant brx est capable d'acidifier le milieu de culture dans lequel il est cultivé plus efficacement que la plante sauvage. Ce mutant est également capable de donner plus de progéniture sur ce type de milieu de croissance que les plantes sauvages. Finalement, nous avons trouvé d'autres mutants brx en milieu naturel poussant sur sols acides, ce qui suggère fortement que la mutation du gène BRX est une des causes de l'adaptation aux sols acides. -- Plants as sessile organisms have developed different mechanisms to cope with the complex environmental conditions in which they live. Adaptation is the process through which traits evolve by natural selection to functionally improve in a given environmental context. An adaptation to the environment is characterized by the genetic changes in the entire populations that have been fixed by natural selection over many generations. BREVIS RADIX (BRX) gene was found through natural Arabidopsis accessions screen and was characterized as a root growth regulator since loss-of-function mutants exhibit arrested post-embryonic primary root growth in addition to a more branched root system. Although brx loss-of-function causes a complete alteration in root architecture, BRX activity is only required in the root vasculature, in particular in protophloem cell file. Protophloem is a part of the phloem transport network and is responsible for delivery of photo-assimilates and growth regulators, coming from the shoot through mature phloem component - metaphloem, to the all plant primary meristems. In order to perform its function, protophloem is the first cell file to differentiate within the root meristem. During this process, protophloem cells undergo a partial programmed cell death, during which they build a thicker cell wall, degrade nucleus and tonoplast while plasma membrane stays functional. Interestingly, protophloem cells enter elongation process only after differentiation into sieve elements is completed. Here we show that brx mutants fail to differentiate protophloem cell file properly, a phenotype that can be distinguished by a presence of a "gap" cells, non-differentiated cells between two flanking differentiated cells. Discontinuity of protophloem differentiation in brx mutants is considered to be a consequence of local hyperactivity of CLAVATA3/EMBRYO SURROUNDING REGION 45 (CLE45) - BARELY ANY MERISTEM 3 (BAM3) signaling module. Interestingly, a CLE45 activity, most probably at the level of receptor binding, can be modulated by apoplastic pH. Altogether, our results imply that the activity of proton pumps, expressed in non-differentiated cells of protophloem, must be maintained under certain threshold, otherwise CLE45-BAM3 signaling pathway will be stimulated and in turn protophloem will not differentiate. Based on vacuolar morphology, a premature cell wall acidification in brx mutants stochastically prevents the protophloem differentiation. Only after protophloem differentiates, proton pumps can be activated in order to acidify apoplast and to support enucleated protophloem multifold elongation driven by surrounding cells growth. Finally, the protophloem differentiation failure would result in an auxin "traffic jam" in the upper parts of the root, created from the phloem-transported auxin that cannot be efficiently delivered to the meristem. Physiologically, auxin "leakage" from the plant vasculature network could have various consequences, since auxin is involved in the regulation of almost every aspect of plant growth and development. Thus, given that auxin stimulates lateral roots initiation and growth, this scenario explains more branched brx root system. Nevertheless, auxin is considered to activate plasma membrane proton pumps. Along with this, it has been shown that brx mutants acidify media much more than the wild type plants do, a trait that was proposed as an adaptive feature of naturally occurring brx null alleles in Arabidopsis populations found on acidic soils. Additionally, in our study we found that most of accessions originally collected from acidic sampling sites exhibit hypersensitivity to CLE45 treatment. This implies that adaptation of plants to acidic soil involves a positive selection pressure against upstream negative regulators of CLE45-BAM3 signaling, such as BRX. Perspective analysis of these accessions would provide more profound understanding of molecular mechanisms underlying plant adaptation to acidic soils. All these results are suggesting that targeting of the factors that affect protophloem differentiation is a good strategy of natural selection to change the root architecture and to develop an adaptation to a certain environment. -- Les plantes comme organismes sessiles ont développé différents mécanismes pour s'adapter aux conditions environnementales complexes dans lesquelles elles vivent. L'adaptation est le processus par lequel des traits vont évoluer via la sélection naturelle vers une amélioration fonctionnelle dans un contexte environnemental donné. Une adaptation à l'environnement est caractérisée par des changements génétiques dans des populations entières qui ont été fixés par la sélection naturelle sur plusieurs générations. Le gène BREVIS RADIX (BRX) a été identifié dans le crible d'une collection d'accessions naturelles d'Arabidopsis et a été caractérisé comme un régulateur de la croissance racinaire étant donné que le mutant perte-de-fonction montre une croissance racinaire primaire arrêtée au stade post-embryonnaire et présente de plus un système racinaire plus ramifié que la plante sauvage. Bien que le mutant perte-de-fonction brx cause une altération complète de l'architecture racinaire, l'activité de BRX n'est requise que dans la vascularisation racinaire, en particulier au niveau du protophloème. Le protophloème est un composant du réseau de transport du phloème et est responsable du transit des dérivés de la photosynthèse ainsi que des régulateurs de croissances, venant de la partie aérienne par le phloème mature (métaphloème) vers tous les méristèmes primaires de la plante. Pour pouvoir réaliser sa fonction, le protophloème est la première file de cellules à se différencier à l'intérieur du méristème de la racine. Pendant ce processus, les cellules du protophloème subissent une mort cellulaire programmée partielle durant laquelle elles épaississent leur paroi cellulaire, dégradent le noyau et le tonoplaste tandis que la membrane plasmique demeure fonctionnelle. De manière intéressante, les cellules du protophloème entament le processus d'allongement seulement après que la différenciation en tubes criblés soit complète. Ce travail montre que le mutant brx est incapable de mener à bien la différenciation de la file de cellules du protophloème, phénotype qui peut être visualisé par la présence de cellules 'trous', de cellules non différenciées entourées de deux cellules différenciées. La discontinuité de la différenciation du phloème dans le mutant brx est considérée comme la conséquence de l'hyperactivité localisée du module de signalisation CLA VA TA3/EMBRYO SURROUNDING REGION 45 (CLE45) - BARELY ANY MERISTEM 3 (BAM3). De manière intéressante, l'activité de CLE45, très probablement au niveau de la liaison avec le récepteur, peut être modulé par le pH apoplastique. Pris ensemble, nos résultats impliquent que l'activité des pompes à protons, actives dans les cellules non différenciées du protophloème, doit être maintenue en dessous d'un certain seuil autrement la cascade de signalisation CLE45-BAM3 serait stimulée, en conséquence de quoi le protophloème ne pourrait se différencier. D'après la morphologie vacuolaire, une acidification prématurée de la paroi cellulaire dans le mutant brx empêche la différenciation du protophloème de manière stochastique. Une fois que le protophloème se différencie, les pompes à protons peuvent alors être activées afin d'acidifier l'apoplaste et ainsi faciliter l'allongement des cellules énuclées du protophloème, entraînées par la croissance des cellules environnantes. Finalement, la différenciation défectueuse du protophloème produit une accumulation d'auxine dans la partie supérieure de la racine car le phloème ne peut plus acheminer efficacement l'auxine au méristème. Physiologiquement, la 'fuite' d'auxine à partir du réseau vasculaire de la plante peut avoir des conséquences variées puisque l'auxine est impliquée dans la régulation de la majorité des aspects de la croissance et développement de la plante. Etant donné que l'auxine stimule l'initiation et développement des racines latérales, ce scénario pourrait expliquer le système racinaire plus ramifié du mutant brx. En plus, l'auxine est considérée comme un activateur des pompes à protons. Par ailleurs, nous avons montré que les mutants brx ont la capacité d'acidifier le milieu plus efficacement que les plantes sauvages, une caractéristique des populations sauvages <¥Arabidopsis poussant sur des sols acides et contenant les allèles délétés brx. De plus, dans nos résultats nous avons mis en évidence que la plupart des accessions collectées originellement sur des sites acidophiles montre une hypersensibilité au traitement par CLE45. Ceci implique que l'adaptation des plantes aux sols acides repose sur la pression de sélection positive à rencontre des régulateurs négatifs de CLE45- BAM3, situés en amont de la cascade, tel le produit du gène BRX. Les analyses de ces accessions pourraient aboutir à une meilleure compréhension des mécanismes moléculaires responsables de l'adaptation des plantes aux sols acides. Tous nos résultats suggèrent que le ciblage des facteurs affectant la différenciation du protophloème serait une stratégie gagnante dans la sélection naturelle pour changer l'architecture de la racine et ainsi s'adapter efficacement à un nouvel environnement.

Diffusion of influenza during the winter of 1889-90 in Switzerland

The influenza of the winter of 1889-90 was one of the first epidemics to spread all over the world. At the time, several people hypothesized that the railway was one of the main vectors of diffusion of this influenza. This hypothesis was defended in Switzerland especially by Schmid, Chief of the Swiss Office of Health, who collected an impressive body of material about the spread of the epidemic in that country. These data on influenza combined with data about the structure of the railway are used in this paper in order to test the hypothesis of a mixed diffusion process, first between communes interconnected by the railway, and secondly, between those communes and neighbouring communes. An event history analysis model taking into account diffusion effects is proposed and estimated. Results show that the hypothesis is supported if the railway network in Switzerland is not taken as a whole but if a distinction between railway companies is made.

L'agrégation toxique des protéines: une forme de "delinquance moléculaire" activement combattue dans la cellule par les chaperones moléculaires et les protéases [The toxic aggregation of proteins: a kind of "molecular delinquency" actively fought in the cell by molecular chaperones and proteases]

Under various stresses, mutation-sensitised proteins may spontaneously convert into inactive, aggregation-prone structures, which may be cytotoxic and infectious. In the cell, this new kind of "molecular criminality" is actively fought against by a network of molecular chaperones that can specifically identify, isolate and unfold damaged (delinquent) proteins and favour their subsequent native refolding. Irreversibly damaged molecules unable to natively refold are preferentially "executed" and recycled by proteases. Failing that, they are "imprisoned" within compact amyloids, or "evicted" from the cell. Thus, striking parallels, although of questionable ethical value, exist between protein and human criminality, and between the cellular and social responses to these different types of criminality. Fundamental differences also exist. Whereas programmed death (apoptosis) is the preferred solution chosen by aged and aggregation-stressed cells, collective suicide is seldom an option chosen by lawless human societies. More significantly, there is no clear cellular equivalent for the role of the family and the education system, which are so essential to the proper shaping of functional individuals in the society, and give rise to humanism, that favours crime prevention, reeducation and reinsertion programs over capital punishment. To the cardiologist and transplantation surgeon, the interest of molecular chaperones, in particular of Hsp70, Hsp90 and Hsp27, lays in their ability to inhibit the signalling pathway of programmed cell death. Their induction before and during ischemia, by various treatments and drugs could significantly reduce damages from the post ischemic reperfusion of organs.

Crossed ataxia: a case report and a diffusion tensor imaging tractography study.

Background and Purpose-Ever since the seminal description of ataxic hemiparesis contralateral to a pontine lesion by Miller-Fisher, the question of why contralesional crossing pontocerebellar fibers do not more frequently produce ipsilesional hemiataxia was raised. The few cases of "quadrataxic hemiparesis" or bilateral leg ataxia remain exceptions.Summary of Case-We report an even more unusual variant, namely "crossed ataxia" of the contralesional arm and the ipsilesional leg subsequent to an anteromedial pontine ischemic stroke.Conclusions-MRI diffusion tensor imaging tractography shows that caudal contralesional crossing pontocerebellar fibers (those for the leg) travel trough the lesion, whereas more rostral fibers (those for the arm) are spared. (Stroke. 2011; 42:e571-e573.)

Diffusion in stationary flow from mesoscopic nonequilibrium thermodynamics

We analyze the diffusion of a Brownian particle in a fluid under stationary flow. By using the scheme of nonequilibrium thermodynamics in phase space, we obtain the Fokker-Planck equation that is compared with others derived from the kinetic theory and projector operator techniques. This equation exhibits violation of the fluctuation-dissipation theorem. By implementing the hydrodynamic regime described by the first moments of the nonequilibrium distribution, we find relaxation equations for the diffusion current and pressure tensor, allowing us to arrive at a complete description of the system in the inertial and diffusion regimes. The simplicity and generality of the method we propose makes it applicable to more complex situations, often encountered in problems of soft-condensed matter, in which not only one but more degrees of freedom are coupled to a nonequilibrium bath.

Biased diffusion in confined media: Test of the Fick-Jacobs approximation and validity criteria

We study biased, diffusive transport of Brownian particles through narrow, spatially periodic structures in which the motion is constrained in lateral directions. The problem is analyzed under the perspective of the Fick-Jacobs equation, which accounts for the effect of the lateral confinement by introducing an entropic barrier in a one-dimensional diffusion. The validity of this approximation, based on the assumption of an instantaneous equilibration of the particle distribution in the cross section of the structure, is analyzed by comparing the different time scales that characterize the problem. A validity criterion is established in terms of the shape of the structure and of the applied force. It is analytically corroborated and verified by numerical simulations that the critical value of the force up to which this description holds true scales as the square of the periodicity of the structure. The criterion can be visualized by means of a diagram representing the regions where the Fick-Jacobs description becomes inaccurate in terms of the scaled force versus the periodicity of the structure.