Dielectric resonances of ordered passive arrays

The electrical and optical properties of ordered passive arrays, constituted of inductive and capacitive components, are usually deduced from Kirchhoff's rules. Under the assumption of periodic boundary conditions, comparable results may be obtained via an approach employing transfer matrices. In particular, resonances in the dielectric spectrum are demonstrated to occur if all eigenvalues of the transfer matrix of the entire array are unity. The latter condition, which is shown to be equivalent to the habitual definition of a resonance in impedance for an array between electrodes, allows for a convenient and accurate determination of the resonance frequencies, and may thus be used as a tool for the design of materials with a specific dielectric response. For the opposite case of linear arrays in a large network, where periodic boundary condition do not apply, several asymptotic properties are derived. Throughout the article, the derived analytic results are compared to numerical models, based on either Exact Numerical Renormalisation or the spectral method.Comment: 12 pages, 12 figure

Dielectric resonances in disordered media

Binary disordered systems are usually obtained by mixing two ingredients in variable proportions: conductor and insulator, or conductor and super-conductor. and are naturally modeled by regular bi-dimensional or tri-dimensional lattices, on which sites or bonds are chosen randomly with given probabilities. In this article, we calculate the impedance of the composite by two independent methods: the so-called spectral method, which diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact Numerical Renormalization method (ENR). These methods are applied to mixtures of resistors and capacitors (R-C systems), simulating e.g. ionic conductor-insulator systems, and to composites consituted of resistive inductances and capacitors (LR-C systems), representing metal inclusions in a dielectric bulk. The frequency dependent impedances of the latter composites present very intricate structures in the vicinity of the percolation threshold. We analyse the LR-C behavior of compounds formed by the inclusion of small conducting clusters (``$n$-legged animals'') in a dielectric medium. We investigate in particular their absorption spectra who present a pattern of sharp lines at very specific frequencies of the incident electromagnetic field, the goal being to identify the signature of each animal. This enables us to make suggestions of how to build compounds with specific absorption or transmission properties in a given frequency domain.Comment: 10 pages, 6 figures, LaTeX document class EP

On-road traffic emissions of polycyclic aromatic hydrocarbons and their oxy- and nitro- derivative compounds measured in a road tunnel environment

AbstractVehicular emissions are a key source of polycyclic aromatic compounds (PACs), including polycyclic aromatic hydrocarbons (PAHs) and their oxygenated (OPAH) and nitrated (NPAH) derivatives, in the urban environment. Road tunnels are a useful environment for the characterisation of on-road vehicular emissions, providing a realistic traffic fleet and a lack of direct sunlight, chemical reactivity and non-traffic sources. In the present investigation the concentrations of selected PAHs, OPAHs and NPAHs have been measured in the Parc des Princes Tunnel in Paris (PdPT, France), and at the Queensway Road Tunnel and an urban background site in Birmingham (QT, U.K). A higher proportion of semi-volatile (3–4 ring) PAH, OPAH and NPAH compounds are associated with the particulate phase compared with samples from the ambient environment. A large (~85%) decline in total PAH concentrations is observed between 1992 and 2012 measurements in QT. This is attributed primarily to the introduction of catalytic converters in the U.K as well as increasingly stringent EU vehicle emissions legislation. In contrast, NPAH concentrations measured in 2012 are similar to those measured in 1996. This observation, in addition to an increased proportion of (Phe+Flt+Pyr) in the observed PAH burden in the tunnel, is attributed to the increased number of diesel passenger vehicles in the U.K during this period. Except for OPAHs, comparable PAH and NPAH concentrations are observed in both investigated tunnels (QT and PdP). Significant differences are shown for specific substances between PAC chemical profiles in relation with the national traffic fleet differences (33% diesel passenger cars in U.K. vs 69% in France and up to 80% taking into account all vehicle categories). The dominating and sole contribution of 1-Nitropyrene observed in the PdPT NPAH profile strengthens the promising use of this compound as a diesel exhaust marker for PM source apportionment studies

Rôle de la sphingosine 1-phosphate dans les interactions mélanome-stroma

Le mélanome métastatique demeure un cancer au sombre pronostic, et aucune des thérapies conventionnelles n'a pu apporter de bénéfice sur la survie globale. Malgré les nombreux progrès réalisés dans la compréhension de la biologie et la génétique du mélanome, peu de traitements efficaces sont actuellement disponibles. De plus en plus de preuves renforcent la notion que le microenvironnement tumoral jouerait un rôle clé dans la progression de ces tumeurs. Les cellules cancéreuses intéragissent de façon dynamique et bidirectionnelle avec le stroma à travers des échanges moléculaires modulant le phénotype tumoral. L'objectif de ces travaux de thèse a été de définir le rôle de la sphingosine 1-phosphate (S1P) dans les interactions mélanome-stroma. La signalisation "inside-out" de la S1P lui permet d'agir à la fois sur les cellules tumorales et sur les cellules stromales et souligne l'intérêt de ce métabolite bioactif pour la thérapie ciblée des mélanomes de stade avancé. L'analyse de l'expression des enzymes du métabolisme de la S1P dans des lignées cellulaires de mélanome humain a mis en évidence des altérations en faveur de l'accumulation de S1P dans les cellules malignes en comparaison avec des mélanocytes sains. Cette observation a été confirmée in situ dans des tissus tumoraux issus de patients atteints de mélanome. La prolifération et la migration des cellules de mélanome ne sont pas affectées par des modifications d'expression des enzymes du métabolisme de la S1P, mais peuvent être modulées par l'addition de S1P exogène. Ainsi, des fibroblastes dermiques qui sécrètent de la S1P influencent la migration des cellules de mélanome en co-culture. De plus, l'incubation de ces fibroblastes avec du milieu conditionné issu de cellules de mélanome induit l'expression de protéines impliquées dans la différenciation myofibroblastique ainsi que celle de la sphingosine kinase 1 (SK1) par les fibroblastes. Des expériences de tumorigenèse in vivo ont permis de montrer que la croissance tumorale locale et les métastases étaient augmentées de façon plus efficace par la co-injection de fibroblastes cutanés sauvages par rapport à des fibroblastes issus de souris Sphk1-/-. Enfin, tandis que la diminution des taux de S1P plasmatique chez les souris Sphk1-/- est associée à une inhibition de la croissance et de la dissémination des cellules de mélanome, cette dernière est à l'inverse potentialisée chez les souris Sphk2-/- qui présentent des taux de S1P plasmatique élevés. L'ensemble de nos résultats démontre l'implication de la S1P dans les interactions entre le mélanome et son microenvironnement, soulignant l'intérêt de cibler ce sphingolipide bioactif en thérapeutique.Metastatic melanoma remains an aggressive malignancy conferring a very poor prognosis, and conventional therapies have not demonstrated an overall survival benefit. While significant progress in the understanding of the biology and genetics of melanoma has been made, few effective treatments are currently available. Increasing evidence supports the notion that the adjacent microenvironment plays a key role in the progression of these tumors. Malignant cells actively interact with stroma in a bidirectional manner through molecular signals that modulate tumor phenotype. This thesis aimed at defining the role of sphingosine-1-phosphate (S1P) in melanoma-stroma interactions. The "inside-out" signaling of S1P allowing an action on both tumor and stroma cells makes this bioactive sphingolipid metabolite of particular interest for targeted therapy of advanced melanoma. Expression analysis of S1P-metabolizing enzymes on human melanoma cell lines showed a dysregulation in favor of S1P accumulation in malignant cells as compared to normal melanocytes. This observation was confirmed in situ in tumor tissues obtained from patients with melanoma. Neither the proliferation nor migration of cultured melanoma cells were affected by changes of S1P-metabolizing enzymes expression but were modulated by exogen S1P. Thereby, secretion of S1P by dermal fibroblasts impacted on melanoma cells migration in co-culture. Moreover, incubation of those fibroblasts with conditioned medium from melanoma cells induced the expression of myofibroblastic differentiation markers and sphingosine kinase 1 (SK1) by fibroblasts. In vivo tumorigenesis experiments showed that local tumor growth and metastases were enhanced more efficiently by co-injection of wild-type skin fibroblasts than by fibroblasts from Sphk1-/- mice. Finally, reduced S1P levels in the plasma of Sphk1-/- mice prevented melanoma growth and dissemination while metastases were potentiated in Sphk2-/- mice displaying high plasmatic S1P levels. Altogether, our findings demonstrate the implication of S1P in the interactions between melanoma and its microenvironment, pointing out the relevance of targeting this bioactive sphingolipid in therapy

Polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs and oxygenated PAHs in ambient air of the Marseilles area (South of France) : concentrations and sources

International audienceAmbient measurements (gas + particle phases) of 15 polycyclic aromatic hydrocarbons (PAHs), 17 nitrated PAHs (NPAHs) and 9 oxygenated PAHs (OPAHs) were carried out during July 2004 on three different sites (urban, sub-urban and rural) in the region of Marseilles (South of France). Atmospheric concentrations of these classes of polyaromatics are great of interest because of their high potential mutagenicity and carcinogenicity. OPAH concentrations were of the same order of magnitude as those of PAHs while NPAH concentrations were one to two orders lower. 9-Fluorenone and 9,10-anthraquinone were the most abundant OPAHs, accounting for about 60% and 20% of the total OPAH concentration. Respectively 1-and 2-nitronaphthalene were the most abundant NPAHs and were accounting for about 30-50% and 15-30% of the total NPAH concentration. NPAHs and OPAHs concentration levels were consistent with the characteristics of the sampling sites. Study of source specific ratios (2-nitrofluoranthene/1-nitropyrene) clearly showed those primary NPAH sources influence the urban and sub-urban sites whereas production of secondary NPAHs by gas phase reactions was prevalent at the rural site. The study of NPAH and OPAH sources suggested that gasoline engines were an important source of such compounds Whereas the dominant source of 1-nitropyrene, 2-nitrofluorene, 6-nitrochrysene and benz[a]anthracene-7,12-dione seems to be diesel vehicles. Finally, 9,10-anthraquinone presents a double origin: primary diesel emission and photochemical processes. Formation of 9,10-anthraquinone from anthracene ozonation was shown at the rural site. Further investigations will be necessary in order to discriminate when (before or during the sampling) the OPAHs are formed

Sampling precautions for the measurement of nitrated polycyclic aromatic hydrocarbons in ambient air

International audienceBecause of the toxicity of polycyclic aromatic hydrocarbons (PAHs) and of their oxidation products, such as nitrated and oxygenated PAHs (NPAHs and OPAHs), the determination of their concentrations is of great interest in terms of atmospheric pollution control. Then, normalisation of sampling procedures appears essential. In this context, this paper presents a comparison of particulate PAH, OPAH and NPAH concentrations determined with two different samplers (cascade impactor and conventional high volume sampler) installed in parallel during several field sampling campaigns carried out under different environmental conditions. For winter and summer periods, the PAH and OPAH concentrations determined with both sampling systems were considered as equivalent. In the summer period, NPAH concentrations quantified with both sampling devices were similar whereas in the winter period, the conventional high volume sampler underestimated their concentrations by a factor of 3-4. This underestimation was observed in the same proportion for all the 17 quantified NPAHs. Analytical error, NPAH formation during the sampling and NPAH degradation by reaction with gaseous oxidants associated to sampling methodology were unable to explain such differences between both samplers used in parallel. A probable hypothesis is that the heating of the PM10 head of the high volume sampler in the winter period generates an increase of the internal sampler temperature that could intensify the chemical degradation of the NPAHs inducing the underestimation of their concentrations in the atmosphere. Further investigations will be necessary to confirm the importance of the temperature on the chemical degradation of these compounds and to understand the different behaviour of PAHs and OPAHs. Consequently, we suggest using oxidant scrubber to prevent chemical degradation of PAHs and derivatives during their sampling. Moreover, we advise against the heating of the sampling head which could induce an increase of these reactions of degradation especially for NPAHs

Caractérisation de la sûreté de fonctionnement des systèmes d'exploitation en présence de pilotes défaillants

Les pilotes de périphériques composent désormais une part essentielle des systèmes d’exploitation. Plusieurs études montrent qu’ils sont fréquemment à l’origine des dysfonctionnements des systèmes opératoires. Dans ce mémoire, nous présentons une méthode pour l’évaluation de la robustesse des noyaux face aux comportements anormaux des pilotes de périphériques. Pour cela, après avoir analysé et précisé les caractéristiques des échanges entre les pilotes et le noyau (DPI - Driver Programming Interface), nous proposons une technique originale d’injection de fautes basée sur la corruption des paramètres des fonctions manipulées au niveau de cette interface. Nous définissons différentes approches pour l’analyse et l’interprétation des résultats observés pour obtenir des mesures objectives de sûreté de fonctionnement. Ces mesures permettent la prise en compte de différents points de vue afin de répondre aux besoins réels de l’utilisateur. Enfin, nous illustrons et validons l’applicabilité de cette méthode par sa mise en oeuvre dans le cadre d’un environnement expérimental sous Linux. La méthode proposée contribue à la caractérisation de la sûreté de fonctionnement des noyaux vis-à-vis des défaillances des pilotes du système. L’impact des résultats est double : a) permettre au développeur de tels logiciels d’identifier les faiblesses potentielles affectant la sûreté de fonctionnement du système, b) aider un intégrateur dans le choix du composant le mieux adapté à ses besoins