1,018 research outputs found
Exactly Solvable Balanced Tenable Urns with Random Entries via the Analytic Methodology
This paper develops an analytic theory for the study of some Polya urns with
random rules. The idea is to extend the isomorphism theorem in Flajolet et al.
(2006), which connects deterministic balanced urns to a differential system for
the generating function. The methodology is based upon adaptation of operators
and use of a weighted probability generating function. Systems of differential
equations are developed, and when they can be solved, they lead to
characterization of the exact distributions underlying the urn evolution. We
give a few illustrative examples.Comment: 23rd International Meeting on Probabilistic, Combinatorial, and
Asymptotic Methods for the Analysis of Algorithms (AofA'12), Montreal :
Canada (2012
La présence des petits bùtiments en ruine dans les Alpes-de-Haute-Provence
De nombreux petits bĂątiments en ruine (bergeries, fermes, habitationsâŠ) Ă©maillent le territoire des Alpes du Sud. Leur prĂ©sence nâest pas neutreet sâexplique par lâimportante dĂ©prise connue par la rĂ©gion durant le 19Ăšmeet le 20ĂšmesiĂšcle. Cette Ă©tude sâattache Ă souligner le rĂŽle de ces ruines dans le paysage de quelques vallĂ©es des Alpes-de-Haute-Provence. A notre sens, celles-ci reprĂ©sentent Ă proprement parler le lieu de lâentre-deux, Ă la fois entre lâhomme et la nature, entre le passĂ© et le prĂ©sent, entre ce qui est productif et ce qui ne lâest pas. Pour les habitants de la rĂ©gion par ailleurs, ces espaces de marges interrogent et marquent, comme des signes du passĂ© et dâun territoire alors organisĂ© diffĂ©remment.Many small ruined building (sheepfolds, farms, housesâŠ) are visible in Southern French Alpsâ landscape. Their presence is not neutral. It may be explained by the important rural exodus that struck the area during the 19th and 20th centuries. This study focuses on the role of these ruins in the landscape of several valleys in the Alpes-de-Haute-Provence. From our point of view, it might be described as the place of the in-between, between human and nature, between past and present, between what is productive and what is lost. It participates in the creation of a space of the in-between. Cartographical analysis and field work showed how this ruins are distributed in the area and proved that they are considered as important signs for the inhabitants of the region, some consider it as interesting landmarks, on the contrary,others would rather not see it here
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Combination of mesoscale and synoptic mechanisms for triggering an isolated thunderstorm: Observational case study of CSIP IOP 1
Copyright @ 2007 AMSAn isolated thunderstorm formed in the southern United Kingdom on 15 June 2005 and moved through the area where a large number of observational instruments were deployed as part of the Convective Storm Initiation Project. Earlier, a convergence line had formed downstream of Devon in the southwest of the United Kingdom in a southwesterly airflow, along which a series of light showers had formed. The depth of these showers was limited by a capping inversion, or lid, at around 2.5 km. The deep thunderstorm convection developed from one of these showers when the convection broke through the lid and ascended up to the next inversion, associated with a tropopause fold at around 6 km. A series of clear-air reflectivity RHIs are used to map the height of the capping inversion and its lifting resulting from the ascent along the convergence line. The origins of the lid are tracked back to some descent from the midtroposphere along dry adiabats. The strength of the lid was weaker along a northwest-to-southeast-oriented region located behind an overrunning upper cold front. The transition from shallow to deep convection occurred where this region with a weaker lid intersected the region with a raised lid, oriented southwest to northeast, downstream of Devon. A very high resolution forecast model that is being developed by the Met Office predicted the isolated thunderstorm successfully. This success depended on the accurate representation of the following two scales: the synoptic-scale and the surface-forced mesoscale convergence line. The interaction between these scales localized the convection sufficiently in space and time for the initiation and subsequent development to be highly predictable despite the relatively poor representation in the model of processes at the cloud scale.This work was funded from the Natural Environment Research Council and the Met Office National Meteorology Programme
Micro et nanoparticules pour des applications biotechnologiques : fabrication de nanoparticules par copolymĂšre dibloc pour lâimagerie mĂ©dicale ; destruction de cellules cancĂ©reuses par vibrations magnĂ©to-mĂ©caniques de microparticules magnĂ©tiques
Magnetic nanoparticles are now used in a wide range of applications such as diagnostic, therapeutics or more recently theranostics. The numerous and diverse fabrication processes allow the fabrication of a wide range of nanoparticles in terms of size, shape, material and magnetic properties. An ideal fabrication process would allow the simple and cheap fabrication of a great quantity of monodisperse nanoparticles. In this objective, the first part of this work will be focused on a new and original fabrication process based on the combination of a âtop-downâ and âbottom-upâ approach. The idea relies on the special auto organization properties of a diblock copolymer: one of the two phases has the ability to self organize into vertical cylinders in the matrix of the other polymer, provided that the annealing conditions are favourable. The selective etching of the cylinders leads to a mask of holes in a polymer matrix. Then, the deposit of a magnetic material and the etching of the polymer matrix leads to the formation of a hexagonal network of nanoparticles attached to the substrate. If the substrate is composed of a sacrificial layer, the nanoparticles can be released in a solution. The structural and magnetic properties of theses nanoparticles fabricated via a PS-PMMA template will be studied. Their characterization will show that the process is still to be optimized but allows already to obtain monodisperse superparamagnetic nanoparticles.A second part focuses on another biomedical applications of magnetic particles: the cancer treatment. A new technique, which is an alternative to the existing methods such as hyperthermia or drug delivery, was first proposed by the Argonne National Laboratory (2010) and taken over at Spintec (2011). The idea is to reactivate the apoptosis (programmed cell death) of cancer cells via the magneto mechanical vibrations of magnetic microparticles attached to their membranes. It was proved that weak external magnetic fields (30mT at 20Hz) applied on permalloy disks in a vortex configuration lead to a significant increase of the apoptotic rate of cancer cells. In the objective of making this method possible for clinical applications, biocompatible magnetite microparticles were fabricated via the same fabrication process than the permalloy disks (optic lithography). Their structural and magnetic properties are compared, as well as their behavior in a suspension and their lethal effect on cancer cells via the application of an external magnetic field. For now, the permalloy microdisks provide better results than the magnetite particles. Some parameters of the experimental set up have to be optimized for the magnetite particles, such as the amplitude of the applied magnetic field. However, the first effects observed with the magnetite particles are quite promising.Les nanoparticules magnĂ©tiques sont de nos jours largement exploitĂ©es dans le domaine de la recherche pour le biomĂ©dical, pour des applications aussi variĂ©es que le diagnostic, la thĂ©rapeutique ou plus rĂ©cemment la thĂ©ranostique. Les nombreuses mĂ©thodes de fabrication mises au point Ă ce jour permettent lâobtention dâune large gamme de nanoparticules en termes de taille, forme, matĂ©riaux et donc propriĂ©tĂ©s magnĂ©tiques. Le procĂ©dĂ© de fabrication idĂ©al est celui qui permet la fabrication simple, peu coĂ»teuse et Ă grande Ă©chelle de nanoparticules parfaitement monodisperses. En ce sens, le premier volet de la thĂšse sera consacrĂ© Ă lâĂ©tude dâun nouveau procĂ©dĂ© de fabrication basĂ© sur la combinaison dâune approche « top-down » et « bottom-up », qui permet dâobtenir des nanoparticules de dispersion en taille trĂšs Ă©troite. LâidĂ©e est dâexploiter les propriĂ©tĂ©s dâauto-organisation dâun copolymĂšre dibloc, dont lâune des deux phases peut sâorganiser en cylindres verticaux dans la matrice de lâautre phase sous certaines conditions. La gravure sĂ©lective des cylindres mĂšne Ă lâobtention dâun masque de trous dans une matrice de polymĂšre. On peut ensuite dĂ©poser le matĂ©riau magnĂ©tique, puis graver la matrice de polymĂšre pour rĂ©vĂ©ler les nanoparticules attachĂ©es au substrat. Si ce procĂ©dĂ© est menĂ© sur une couche sacrificielle, les particules peuvent ĂȘtre consĂ©cutivement mises en suspension. Les caractĂ©ristiques structurales et magnĂ©tiques de ces particules obtenues par auto-organisation du copolymĂšre PS-PMMA seront Ă©tudiĂ©es, montrant que bien que ce procĂ©dĂ© de fabrication soit encore Ă amĂ©liorer, il prĂ©sente des avantages non nĂ©gligeables en Ă©tant versatile, simple Ă mettre en Ćuvre et en permettant lâobtention de nanoparticules monodisperses et superparamagnĂ©tiques.Dans une seconde partie, un autre domaine biomĂ©dical sera abordĂ© : le traitement du cancer. Une mĂ©thode nouvelle et alternative aux techniques dâhyperthermie ou de dĂ©livrance ciblĂ©e de mĂ©dicaments avait Ă©tĂ© initiĂ©e par lâArgonne National Laboratory en 2010 et reprise Ă Spintec en 2011 : lâidĂ©e est de rĂ©activer lâapoptose (ou mort programmĂ©e) de cellules cancĂ©reuses par vibrations magnĂ©to-mĂ©caniques de microparticules magnĂ©tiques attachĂ©es Ă leur membrane. Il avait Ă©tĂ© dĂ©montrĂ© quâavec des champs extĂ©rieurs aussi faibles que 30mT Ă 20Hz, des disques de permalloy en configuration magnĂ©tique vortex induisent lâapoptose de façon significative. Dans ce contexte et dans lâoptique de pouvoir utiliser cette mĂ©thode pour des tests cliniques, des microparticules de magnĂ©tite, matĂ©riau biocompatible, ont Ă©tĂ© fabriquĂ©es par lithographie optique via le mĂȘme procĂ©dĂ© que les disques de permalloy. Leurs propriĂ©tĂ©s structurales, magnĂ©tiques et leur comportement en suspension sont comparĂ©s, ainsi que leurs effets sur les cellules in vitro via lâapplication dâun champ magnĂ©tique extĂ©rieur. A ce jour, les particules de permalloy sont supĂ©rieures en termes dâefficacitĂ© sur le dĂ©clenchement de lâapoptose des cellules cancĂ©reuses. Certains paramĂštres du protocole tels que lâamplitude du champ doivent ĂȘtre optimisĂ©s pour les particules de magnĂ©tite, bien que les premiers effets observĂ©s soient encourageants pour la suite
Micro et nanoparticules pour des applications biotechnologiques : fabrication de nanoparticules par copolymĂšre dibloc pour lâimagerie mĂ©dicale ; destruction de cellules cancĂ©reuses par vibrations magnĂ©to-mĂ©caniques de microparticules magnĂ©tiques
Magnetic nanoparticles are now used in a wide range of applications such as diagnostic, therapeutics or more recently theranostics. The numerous and diverse fabrication processes allow the fabrication of a wide range of nanoparticles in terms of size, shape, material and magnetic properties. An ideal fabrication process would allow the simple and cheap fabrication of a great quantity of monodisperse nanoparticles. In this objective, the first part of this work will be focused on a new and original fabrication process based on the combination of a âtop-downâ and âbottom-upâ approach. The idea relies on the special auto organization properties of a diblock copolymer: one of the two phases has the ability to self organize into vertical cylinders in the matrix of the other polymer, provided that the annealing conditions are favourable. The selective etching of the cylinders leads to a mask of holes in a polymer matrix. Then, the deposit of a magnetic material and the etching of the polymer matrix leads to the formation of a hexagonal network of nanoparticles attached to the substrate. If the substrate is composed of a sacrificial layer, the nanoparticles can be released in a solution. The structural and magnetic properties of theses nanoparticles fabricated via a PS-PMMA template will be studied. Their characterization will show that the process is still to be optimized but allows already to obtain monodisperse superparamagnetic nanoparticles.A second part focuses on another biomedical applications of magnetic particles: the cancer treatment. A new technique, which is an alternative to the existing methods such as hyperthermia or drug delivery, was first proposed by the Argonne National Laboratory (2010) and taken over at Spintec (2011). The idea is to reactivate the apoptosis (programmed cell death) of cancer cells via the magneto mechanical vibrations of magnetic microparticles attached to their membranes. It was proved that weak external magnetic fields (30mT at 20Hz) applied on permalloy disks in a vortex configuration lead to a significant increase of the apoptotic rate of cancer cells. In the objective of making this method possible for clinical applications, biocompatible magnetite microparticles were fabricated via the same fabrication process than the permalloy disks (optic lithography). Their structural and magnetic properties are compared, as well as their behavior in a suspension and their lethal effect on cancer cells via the application of an external magnetic field. For now, the permalloy microdisks provide better results than the magnetite particles. Some parameters of the experimental set up have to be optimized for the magnetite particles, such as the amplitude of the applied magnetic field. However, the first effects observed with the magnetite particles are quite promising.Les nanoparticules magnĂ©tiques sont de nos jours largement exploitĂ©es dans le domaine de la recherche pour le biomĂ©dical, pour des applications aussi variĂ©es que le diagnostic, la thĂ©rapeutique ou plus rĂ©cemment la thĂ©ranostique. Les nombreuses mĂ©thodes de fabrication mises au point Ă ce jour permettent lâobtention dâune large gamme de nanoparticules en termes de taille, forme, matĂ©riaux et donc propriĂ©tĂ©s magnĂ©tiques. Le procĂ©dĂ© de fabrication idĂ©al est celui qui permet la fabrication simple, peu coĂ»teuse et Ă grande Ă©chelle de nanoparticules parfaitement monodisperses. En ce sens, le premier volet de la thĂšse sera consacrĂ© Ă lâĂ©tude dâun nouveau procĂ©dĂ© de fabrication basĂ© sur la combinaison dâune approche « top-down » et « bottom-up », qui permet dâobtenir des nanoparticules de dispersion en taille trĂšs Ă©troite. LâidĂ©e est dâexploiter les propriĂ©tĂ©s dâauto-organisation dâun copolymĂšre dibloc, dont lâune des deux phases peut sâorganiser en cylindres verticaux dans la matrice de lâautre phase sous certaines conditions. La gravure sĂ©lective des cylindres mĂšne Ă lâobtention dâun masque de trous dans une matrice de polymĂšre. On peut ensuite dĂ©poser le matĂ©riau magnĂ©tique, puis graver la matrice de polymĂšre pour rĂ©vĂ©ler les nanoparticules attachĂ©es au substrat. Si ce procĂ©dĂ© est menĂ© sur une couche sacrificielle, les particules peuvent ĂȘtre consĂ©cutivement mises en suspension. Les caractĂ©ristiques structurales et magnĂ©tiques de ces particules obtenues par auto-organisation du copolymĂšre PS-PMMA seront Ă©tudiĂ©es, montrant que bien que ce procĂ©dĂ© de fabrication soit encore Ă amĂ©liorer, il prĂ©sente des avantages non nĂ©gligeables en Ă©tant versatile, simple Ă mettre en Ćuvre et en permettant lâobtention de nanoparticules monodisperses et superparamagnĂ©tiques.Dans une seconde partie, un autre domaine biomĂ©dical sera abordĂ© : le traitement du cancer. Une mĂ©thode nouvelle et alternative aux techniques dâhyperthermie ou de dĂ©livrance ciblĂ©e de mĂ©dicaments avait Ă©tĂ© initiĂ©e par lâArgonne National Laboratory en 2010 et reprise Ă Spintec en 2011 : lâidĂ©e est de rĂ©activer lâapoptose (ou mort programmĂ©e) de cellules cancĂ©reuses par vibrations magnĂ©to-mĂ©caniques de microparticules magnĂ©tiques attachĂ©es Ă leur membrane. Il avait Ă©tĂ© dĂ©montrĂ© quâavec des champs extĂ©rieurs aussi faibles que 30mT Ă 20Hz, des disques de permalloy en configuration magnĂ©tique vortex induisent lâapoptose de façon significative. Dans ce contexte et dans lâoptique de pouvoir utiliser cette mĂ©thode pour des tests cliniques, des microparticules de magnĂ©tite, matĂ©riau biocompatible, ont Ă©tĂ© fabriquĂ©es par lithographie optique via le mĂȘme procĂ©dĂ© que les disques de permalloy. Leurs propriĂ©tĂ©s structurales, magnĂ©tiques et leur comportement en suspension sont comparĂ©s, ainsi que leurs effets sur les cellules in vitro via lâapplication dâun champ magnĂ©tique extĂ©rieur. A ce jour, les particules de permalloy sont supĂ©rieures en termes dâefficacitĂ© sur le dĂ©clenchement de lâapoptose des cellules cancĂ©reuses. Certains paramĂštres du protocole tels que lâamplitude du champ doivent ĂȘtre optimisĂ©s pour les particules de magnĂ©tite, bien que les premiers effets observĂ©s soient encourageants pour la suite
Toward a New UV Index Diagnostic in the Met Office's Forecast Model
This is the final version. Available on open access from AGU via the DOI in this recordThe United Kingdom sporadically experiences low ozone events in the spring which can increase UV to harmful levels and is particularly dangerous as sunburn is not expected by the public at this time of year. This study investigates the benefits to the UV Index diagnostic produced by the UM at the Met Office of including either, or both of, a more highly resolved spectrum, and forecasted ozone profiles from the ECMWF CAMS database. Two new configurations of the spectral parameters governing the radiative transfer calculation over the UV region are formulated using the correlatedâk method to give surface fluxes that are within 0.1 UV Index of an accurate reference scheme. Clearâsky comparisons of modeled fluxes with groundâbased spectral observations at two UK sites (Reading and Chilton) between 2011 and 2015 show that when raw CAMS ozone profiles are included noontime UV indices are always overestimated, by up to 3 UV indices at a low ozone event and up to 1.5 on a clear summer day, suggesting CAMS ozone concentrations are too low. The new spectral parameterizations reduce UV Index biases, apart from when combined with ozone profiles that are significantly underestimated. When the same biases are examined spectrally across the UV region some low biases on low ozone days are found to be the result of compensating errors in different parts of the spectrum. Aerosols are postulated to be an additional source of error if their actual concentrations are higher than those modeled.Department for Environment Food & Rural Affairs (DEFRA
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Modulation of precipitation by conditional symmetric instability release
Although many theoretical and observational studies have investigated the mechanism of conditional symmetric instability (CSI) release and associated it with mesoscale atmospheric phenomena such as frontal precipitation bands, cloud heads in rapidly developing extratropical cyclones and sting jets, its climatology and contribution to precipitation have not been extensively documented. The aim of this paper is to quantify the contribution of CSI release, yielding slantwise convection, to climatological precipitation accumulations for the North Atlantic and western Europe. Case studies reveal that CSI release could be common along cold fronts of mature extratropical cyclones and the North Atlantic storm track is found to be a region with large CSI according to two independent CSI metrics. Correlations of CSI with accumulated precipitation are also large in this region and CSI release is inferred to be occurring about 20% of the total time over depths of over 1km. We conclude that the inability of current global weather forecast and climate prediction models to represent CSI release (due to insufficient resolution yet lack of subgrid parametrization schemes) may lead to errors in precipitation distributions, particularly in the region of the North Atlantic storm track
Exactly Solvable Balanced Tenable Urns with Random Entries via the Analytic Methodology
This paper develops an analytic theory for the study of some PĂłlya urns with random rules. The idea is to extend the isomorphism theorem in Flajolet et al. (2006), which connects deterministic balanced urns to a differential system for the generating function. The methodology is based upon adaptation of operators and use of a weighted probability generating function. Systems of differential equations are developed, and when they can be solved, they lead to characterization of the exact distributions underlying the urn evolution. We give a few illustrative examples
Impact of an improved shortwave radiation scheme in the MAECHAM5 General Circulation Model
International audienceIn order to improve the representation of ozone absorption in the stratosphere of the MAECHAM5 general circulation model, the spectral resolution of the shortwave radiation parameterization used in the model has been increased from 4 to 6 bands. Two 20-years simulations with the general circulation model have been performed, one with the standard and the other with the newly introduced parameterization respectively, to evaluate the temperature and dynamical changes arising from the two different representations of the shortwave radiative transfer. In the simulation with the increased spectral resolution in the radiation parameterization, a significant warming of almost the entire model domain is reported. At the summer stratopause the temperature increase is about 6 K and alleviates the cold bias present in the model when the standard radiation scheme is used. These general circulation model results are consistent both with previous validation of the radiation scheme and with the offline clear-sky comparison performed in the current work with a discrete ordinate 4 stream scattering line by line radiative transfer model. The offline validation shows a substantial reduction of the daily averaged shortwave heating rate bias (1?2 K/day cooling) that occurs for the standard radiation parameterization in the upper stratosphere, present under a range of atmospheric conditions. Therefore, the 6 band shortwave radiation parameterization is considered to be better suited for the representation of the ozone absorption in the stratosphere than the 4 band parameterization. Concerning the dynamical response in the general circulation model, it is found that the reported warming at the summer stratopause induces stronger zonal mean zonal winds in the middle atmosphere. These stronger zonal mean zonal winds thereafter appear to produce a dynamical feedback that results in a dynamical warming (cooling) of the polar winter (summer) mesosphere, caused by an increased downward (upward) circulation in the winter (summer) hemisphere. In addition, the comparison of the two simulations performed with the general circulation model shows that the increase in the spectral resolution of the shortwave radiation and the associated changes in the cloud optical properties result in a warming (0.5?1 K) and moistening (3%?12%) of the upper tropical troposphere. By comparing these modeled differences with previous works, it appears that the reported changes in the solar radiation scheme contribute to improve the model mean temperature also in the troposphere
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