Continued evaluation of potential for geologic storage of carbon dioxide in the southeastern United States

Southern States Energy Board Duke Energy Santee Cooper Power Southern CompanyBureau of Economic Geolog

Stress response function of a two-dimensional ordered packing of frictional beads

We study the stress profile of an ordered two-dimensional packing of beads in response to the application of a vertical overload localized at its top surface. Disorder is introduced through the Coulombic friction between the grains which gives some indeterminacy and allows the choice of one constrained random number per grain in the calculation of the contact forces. The so-called `multi-agent' technique we use, lets us deal with systems as large as $1000\times1000$ grains. We show that the average response profile has a double peaked structure. At large depth $z$, the position of these peaks grows with $cz$, while their widths scales like $\sqrt{Dz}$. $c$ and $D$ are analogous to `propagation' and `diffusion' coefficients. Their values depend on that of the friction coefficient $\mu$. At small $\mu$, we get $c_0-c \propto \mu$ and $D \propto \mu^\beta$, with $\beta \sim 2.5$, which means that the peaks get closer and wider as the disorder gets larger. This behavior is qualitatively what was predicted in a model where a stochastic relation between the stress components is assumed.Comment: 7 pages, 7 figures, accepted version to Europhys. Let

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

Innovative in silico approaches to address avian flu using grid technology

The recent years have seen the emergence of diseases which have spread very quickly all around the world either through human travels like SARS or animal migration like avian flu. Among the biggest challenges raised by infectious emerging diseases, one is related to the constant mutation of the viruses which turns them into continuously moving targets for drug and vaccine discovery. Another challenge is related to the early detection and surveillance of the diseases as new cases can appear just anywhere due to the globalization of exchanges and the circulation of people and animals around the earth, as recently demonstrated by the avian flu epidemics. For 3 years now, a collaboration of teams in Europe and Asia has been exploring some innovative in silico approaches to better tackle avian flu taking advantage of the very large computing resources available on international grid infrastructures. Grids were used to study the impact of mutations on the effectiveness of existing drugs against H5N1 and to find potentially new leads active on mutated strains. Grids allow also the integration of distributed data in a completely secured way. The paper presents how we are currently exploring how to integrate the existing data sources towards a global surveillance network for molecular epidemiology.Comment: 7 pages, submitted to Infectious Disorders - Drug Target

Diversification of EPR signatures in site directed spin labeling using a beta-phosphorylated nitroxide

Site Directed Spin Labeling (SDSL) combined with EPR spectroscopy is a very powerful approach to investigate structural transitions in proteins in particular flexible or even disordered ones. Conventional spin labels are based on nitroxide derivatives leading to classical 3-line spectra whose spectral shapes are indicative of the environment of the labels and thus constitute good reporters of structural modifications. However, the similarity of these spectral shapes precludes probing two regions of a protein or two partner proteins simultaneously. To overcome the limitation due to the weak diversity of nitroxide label EPR spectral shapes, we designed a new spin label based on a β-phosphorylated nitroxide giving 6-line spectra. This paper describes the synthesis of this new spin label, its grafting at four different positions of a model disordered protein able to undergo an induced α-helical folding and its characterization by EPR spectroscopy. For comparative purposes, a classical nitroxide has been grafted at the same positions of the model protein. The ability of the new label to report on structural transitions was evaluated by analyzing the spectral shape modifications induced either by the presence of a secondary structure stabilizer (trifluoroethanol) or by the presence of a partner protein. Taken together the results demonstrate that the new phosphorylated label gives a very distinguishable signature which is able to report from subtle to larger structural transitions, as efficiently as the classical spin label. As a complementary approach, molecular dynamics (MD) calculations were performed to gain further insights into the binding process between the labeled NTAIL and PXD. MD calculations revealed that the new label does not disturb the interaction between the two partner proteins and reinforced the conclusion on its ability to probe different local environments in a protein. Taken together this study represents an important step forward in the extension of the panoply of SDSL-EPR approaches. This journal is © 2014 the Owner Societies

An oil pipeline design problem

Copyright @ 2003 INFORMSWe consider a given set of offshore platforms and onshore wells producing known (or estimated) amounts of oil to be connected to a port. Connections may take place directly between platforms, well sites, and the port, or may go through connection points at given locations. The configuration of the network and sizes of pipes used must be chosen to minimize construction costs. This problem is expressed as a mixed-integer program, and solved both heuristically by Tabu Search and Variable Neighborhood Search methods and exactly by a branch-and-bound method. Two new types of valid inequalities are introduced. Tests are made with data from the South Gabon oil field and randomly generated problems.The work of the first author was supported by NSERC grant #OGP205041. The work of the second author was supported by FCAR (Fonds pour la Formation des Chercheurs et l’Aide à la Recherche) grant #95-ER-1048, and NSERC grant #GP0105574