Towards a quantum approach to cell membrane electrodynamics

The ultimate active constituents of the living medium, membranes, ions and molecules, are at the level of the nanometer. Their interactions thus require a quantum processing. The characteristic Action A, linked to the "quantum objects" : ions, radicals, water molecule... of the living medium, has an average value of A ~= 14.10-34 J.s or A ~= 2 h . It is thus strictly impossible to formulate a realistic "classical " theory of membrane electrodynamics. The transfer of the sodium ion - among others - could be then ensured under the action of a Tunnel effect, (with Hartman?s mechanism) specific to the channel and the ion transferred.Comment: 7 page

Grid Added Value to Address Malaria

Through this paper, we call for a distributed, internet-based collaboration to address one of the worst plagues of our present world, malaria. The spirit is a non-proprietary peer-production of information-embedding goods. And we propose to use the grid technology to enable such a world wide "open source" like collaboration. The first step towards this vision has been achieved during the summer on the EGEE grid infrastructure where 46 million ligands were docked for a total amount of 80 CPU years in 6 weeks in the quest for new drugs.Comment: 7 pages, 1 figure, 6th IEEE International Symposium on Cluster Computing and the Grid, Singapore, 16-19 may 2006, to appear in the proceeding

A perspective on the Healthgrid initiative

This paper presents a perspective on the Healthgrid initiative which involves European projects deploying pioneering applications of grid technology in the health sector. In the last couple of years, several grid projects have been funded on health related issues at national and European levels. A crucial issue is to maximize their cross fertilization in the context of an environment where data of medical interest can be stored and made easily available to the different actors in healthcare, physicians, healthcare centres and administrations, and of course the citizens. The Healthgrid initiative, represented by the Healthgrid association (http://www.healthgrid.org), was initiated to bring the necessary long term continuity, to reinforce and promote awareness of the possibilities and advantages linked to the deployment of GRID technologies in health. Technologies to address the specific requirements for medical applications are under development. Results from the DataGrid and other projects are given as examples of early applications.Comment: 6 pages, 1 figure. Accepted by the Second International Workshop on Biomedical Computations on the Grid, at the 4th IEEE/ACM International Symposium on Cluster Computing and the Grid (CCGrid 2004). Chicago USA, April 200

A quantitative assessment of the ecological value of sycamore maple habitats in the French Alps

La naturalité est un critère important pour l'évaluation de mesures conservatoires des écosystèmes. Au niveau local, une telle évaluation doit être basée sur des indicateurs objectifs et quantifiables sur le terrain. Dans cette étude, nous avons utilisé une méthode multicritères basée sur la différence entre Valeur Naturelle (NV) et Valeur Conservatoire (CV) pour quantifier la valeur écologique des érablaies de versant à érable sycomore (Acer pseudoplatanus L.) par comparaison avec les peuplements mixtes de hêtraie-sapinière-pessière avoisinants. En effet, les naturalistes ainsi que l'Union Européenne considèrent que les érablaies de versant ont une valeur de conservation et de naturalité élevée. Nos résultats montrent que les valeurs naturelle et de conservation sont significativement plus élevées pour l'érablaie que pour la forêt mixte avoisinante et que cette évaluation ne dépend pas de facteurs abiotiques tels que l'altitude ou l'exposition. En fait, la naturalité de structure et de composition des érablaies de versant sont plus fortes que celles des forêts mixtes et permettent de différencier les deux habitats en termes de valeur écologique. Les gestionnaires peuvent facilement utiliser cette méthode pour évaluer la valeur écologique de petits habitats en zone de montagne, ce qui permet d'établir des orientations sylvicoles pour une gestion conservatoire et proche de la nature. / Naturalness is an important criterion in nature conservation assessment. At the stand-level, such assessment must be based on objective and quantifiable indicators measurable in the field. In this study, we used a multi-criterion method based on the difference between a Natural Value(NV) and a Conservation Value (CV) to quantify the ecological value of sycamore maple patches compared to the surrounding mixed forests. Indeed, sycamore habitats are considered of high natural and conservation value both by naturalists and by European institutions. Our results showed that the natural and conservation values were significantly higher for the sycamore forests than for the surrounding mixed forests and that this assessment did not depend on abiotic factors such as elevation or aspect. Actually, naturalness of structure and composition in the sycamore habitats was higher than for mixed forests and allowed us to differentiate between the two habitats. Managers could easily use this method in order to assess the ecological value of small habitats in mountainous regions and to provide guidelines for close-to-nature and conservation-related silviculture.FORET DE MONTAGNE;ECOLOGIE FORESTIERE;EVALUATION;PROTECTION DE LA NATURE;ACER PSEUDOPLATANUS;METHODOLOGIE;HABITAT;VALEUR ECOLOGIQUE;NATURALITE;ALPES FRANCAISES;CHARTREUSE MASSIF;ACER PSEUDOPLATANUS;CHARTREUSE;INDICATORS;NATURALNESS;ECOLOGICAL VALUE

Monte Carlo tomographic reconstruction in SPECT impact of bootstrapping and number of generated events

In Single Photon Emission Computed Tomography (SPECT), 3D images usually reconstructed by performing a set of bidimensional (2D) analytical or iterative reconstructions can also be reconstructed using an iterative reconstruction algorithm involving a 3D projector. Accurate Monte Carlo (MC) simulations modeling all the physical effects that affect the imaging process can be used to estimate this projector. However, the accuracy of the projector is affected by the stochastic nature of MC simulations. In this paper, we study the accuracy of the reconstructed images with respect to the number of simulated histories used to estimate the MC projector. Furthermore, we study the impact of applying the bootstrapping technique when estimating the projectorComment: 15 pages, 9 figures, 2 table

Generating Gowdy cosmological models

Using the analogy with stationary axisymmetric solutions, we present a method to generate new analytic cosmological solutions of Einstein's equation belonging to the class of $T^3$ Gowdy cosmological models. We show that the solutions can be generated from their data at the initial singularity and present the formal general solution for arbitrary initial data. We exemplify the method by constructing the Kantowski-Sachs cosmological model and a generalization of it that corresponds to an unpolarized $T^3$ Gowdy model.Comment: Latex, 15 pages, no figure

Validation of the GATE Monte Carlo simulation platform for modelling a CsI(Tl) scintillation camera dedicated to small animal imaging

Monte Carlo simulations are increasingly used in scintigraphic imaging to model imaging systems and to develop and assess tomographic reconstruction algorithms and correction methods for improved image quantitation. GATE (GEANT 4 Application for Tomographic Emission) is a new Monte Carlo simulation platform based on GEANT4 dedicated to nuclear imaging applications. This paper describes the GATE simulation of a prototype of scintillation camera dedicated to small animal imaging and consisting of a CsI(Tl) crystal array coupled to a position sensitive photomultiplier tube. The relevance of GATE to model the camera prototype was assessed by comparing simulated 99mTc point spread functions, energy spectra, sensitivities, scatter fractions and image of a capillary phantom with the corresponding experimental measurements. Results showed an excellent agreement between simulated and experimental data: experimental spatial resolutions were predicted with an error less than 100 mu m. The difference between experimental and simulated system sensitivities for different source-to-collimator distances was within 2%. Simulated and experimental scatter fractions in a [98-182 keV] energy window differed by less than 2% for sources located in water. Simulated and experimental energy spectra agreed very well between 40 and 180 keV. These results demonstrate the ability and flexibility of GATE for simulating original detector designs. The main weakness of GATE concerns the long computation time it requires: this issue is currently under investigation by the GEANT4 and the GATE collaboration

Palaeoecology of the Cenomanian amber forest of Sarthe (western France)

Cretaceous ambers have been discovered in France since the beginning of the 18th century. The best known are those from south-western France which are Late Albian-Early Cenomanian in age, but there are other important amber deposits in other regions. Here, we summarise the data on one of these other Cretaceous amber regions, the Sarthe Department. These deposits have been mentioned in the literature since the end of the 18th century, but they have remained relatively unknown. The material, that has been studied during the 1970's and 1980's, yielded a well-diversified arthropod fauna (72 arthropod specimens, including arachnids, cockroaches, bugs, beetles, flies, wasps...) dated to late Early-Middle Cenomanian. In the last decade, 4 types of bacteria, a possible testate amoeba and fungal remains were also found. A re-examination of the historical collections of the Sarthe amber, housed in the "Musée Vert" (Le Mans, France), allows to estimate the geographical extent of the amber deposits in the Sarthe Department. The study of the microfossils of these samples provides new data on their palaeoenvironment

Effect of noise and modeling errors on the reliability of fully 3D Monte Carlo reconstruction in SPECT

We recently demonstrated the value of reconstructing SPECT data with fully 3D Monte Carlo reconstruction (F3DMC), in terms of spatial resolution and quantification. This was shown on a small cubic phantom (64 projections 10 x 10) in some idealistic configurations. The goals of the present study were to assess the effect of noise and modeling errors on the reliability of F3DMC, to propose and evaluate strategies for reducing the noise in the projector, and to demonstrate the feasibility of F3DMC for a dataset with realistic dimensions. A small cubic phantom and a realistic Jaszczak phantom dataset were considered. Projections and projectors for both phantoms were calculated using the Monte Carlo simulation code GATE. Projectors with different statistics were considered and two methods for reducing noise in the projector were investigated: one based on principal component analysis (PCA) and the other consisting in setting small probability values to zero. Energy and spatial shifts in projection sampling with respect to projector sampling were also introduced to test F3DMC in realistic conditions. Experiments with the cubic phantom showed the importance of using simulations with high statistics for calculating the projector, and the value of filtering the projector using a PCA approach. F3DMC was shown to be robust with respect to energy shift and small spatial sampling off-set between the projector and the projections. Images of the Jaszczak phantom were successfully reconstructed and also showed promising results in terms of spatial resolution recovery and quantitative accuracy in small structures. It is concluded that the promising results of F3DMC hold on realistic data set

The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis

The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise around conjunction when the radio waves emitted by pulsar A are absorbed as they propagate through the magnetosphere of its companion pulsar B. These eclipses offer a unique opportunity to probe directly the magnetospheric structure and the plasma properties of pulsar B. We have performed a comprehensive analysis of the eclipse phenomenology using multi-frequency radio observations obtained with the Green Bank Telescope. We have characterized the periodic flux modulations previously discovered at 820 MHz by McLaughlin et al., and investigated the radio frequency dependence of the duration and depth of the eclipses. Based on their weak radio frequency evolution, we conclude that the plasma in pulsar B's magnetosphere requires a large multiplicity factor (~ 10^5). We also found that, as expected, flux modulations are present at all radio frequencies in which eclipses can be detected. Their complex behavior is consistent with the confinement of the absorbing plasma in the dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such a geometric connection explains that the observed periodicity is harmonically related to pulsar B's spin frequency. We observe that the eclipses require a sharp transition region beyond which the plasma density drops off abruptly. Such a region defines a plasmasphere which would be well inside the magnetospheric boundary of an undisturbed pulsar. It is also two times smaller than the expected standoff radius calculated using the balance of the wind pressure from pulsar A and the nominally estimated magnetic pressure of pulsar B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres