Electroactive cytochromeP450BM3 cast polyion films on graphite electrodes

Films of electrochemically active cytochrome P450BM3 were constructed on graphite electrodes using alternate assembly with polyethyleneimin(PEI). The original layer-by-layer adsorption method was slightly modified here to form so-called “cast polyion” films. The cast polyion films were elaborated by immobilizing two successive layers of PEI and protein in very large excess with respect to a monolayer, without any intermediate washing step. Following the immobilization steps by SEM showed that uniform films of a few micrometers were deposited on the graphite surface. The electrochemically activity of the immobilized cytP450 was tested with regard to the reduction of oxygen and the one-electron reduction of the heme. Cyclic voltammetry indicated surface concentration of electrochemically active cytP450 around 0.6 nmol/cm2, which corresponded to 5% of the total amount of protein that was consumed by the immobilisation process. Adapting the procedure to a graphite felt electrode with the view of scaling up porous electrodes for large scale synthesis increased the concentration to 0.9 nmol/cm2. Cast polyion films may represent a simple technique to immobilize high amount of electrochemically active protein, keeping the advantage of the electrostatic interactions of the regular layer-by-layer method

Setting-up rules to characterize microsegregation

Characterization of chemical heterogeneities such as microsegregation resulting from solidification of metallic alloys is most often performed by EDS or WDS microanalysis with spot measurements located at corners of a regular grid. Rather than attempting a theoretical treatment of the statistics of such analyses, the quality of the procedure has been investigated by implementing “measurement” grids on numerical images that mimic solidification structures. Microstructures either with no geometrical constraints (uniform distribution of the solid nuclei) or with limited constraints that give some periodicity have been investigated. Systematic analysis of the effect of the location and size of the “measurement” grid enlightens the procedures which should be followed to minimize bias

Simple design of cast myoglobin/polyethyleneimine modified electrodes

Negatively charged myoglobin (at pH values above its isoelectric point) was immobilized with the positively charged polyion polyethyleneimine (PEI) on pyrolytic graphite electrodes. A modified form of the common layer-by-layer technique was proposed, which consisted in forming non-ordered cast polyion films. The modified Mb electrodes obtained by both techniques were compared by cyclic voltammetry. The cast polyion technique gave less reproducible results but enable the immobilization of higher percentages of the total quantity of protein required to prepare the electrodes. The electrochemical properties of the negatively charged myoglobin were determined, and its capability to catalyze the electrochemical reduction of oxygen and the dechlorination of trichloroacetic acid was demonstrated. The mechanisms are discussed, and the modified pathway that has been proposed to take into account the influence of pH in the Mb-catalyzed reduction of oxygen was confirmed here

Resampling technique applied to the characterization of microsegregation

Characterization of short-range chemical heterogeneities in metallic materials, such as the so-called microsegregation resulting from solidification, is most often performed using EDS or WDS spot measurements. The most usual way is to perform countings on points located along a regular grid. Due to experimental limitation, the grid step is generally of the same order of magnitude than the characteristic distance(s) of the chemical heterogeneities under investigation. In such a case, the measurements can not be assumed to be independent one from each other, and the resulting interferences (correlations) preclude application of simple statistics to the solute distribution obtained. In the present work, this is clearly shown by using a resampling technique applied to "chemical" images obtained by phase field modelling

Modeling the Worldwide Spread of Pandemic Influenza: Baseline Case and Containment Interventions

We present a study of the worldwide spread of a pandemic influenza and its possible containment at a global level taking into account all available information on air travel. We studied a metapopulation stochastic epidemic model on a global scale that considers airline travel flow data among urban areas. We provided a temporal and spatial evolution of the pandemic with a sensitivity analysis of different levels of infectiousness of the virus and initial outbreak conditions (both geographical and seasonal). For each spreading scenario we provided the timeline and the geographical impact of the pandemic in 3,100 urban areas, located in 220 different countries. We compared the baseline cases with different containment strategies, including travel restrictions and the therapeutic use of antiviral (AV) drugs. We show that the inclusion of air transportation is crucial in the assessment of the occurrence probability of global outbreaks. The large-scale therapeutic usage of AV drugs in all hit countries would be able to mitigate a pandemic effect with a reproductive rate as high as 1.9 during the first year; with AV supply use sufficient to treat approximately 2% to 6% of the population, in conjunction with efficient case detection and timely drug distribution. For highly contagious viruses (i.e., a reproductive rate as high as 2.3), even the unrealistic use of supplies corresponding to the treatment of approximately 20% of the population leaves 30%-50% of the population infected. In the case of limited AV supplies and pandemics with a reproductive rate as high as 1.9, we demonstrate that the more cooperative the strategy, the more effective are the containment results in all regions of the world, including those countries that made part of their resources available for global use.Comment: 16 page

PLTL Partitioned Model Checking for Reactive Systems under Fairness Assumptions

We are interested in verifying dynamic properties of finite state reactive systems under fairness assumptions by model checking. The systems we want to verify are specified through a top-down refinement process. In order to deal with the state explosion problem, we have proposed in previous works to partition the reachability graph, and to perform the verification on each part separately. Moreover, we have defined a class, called Bmod, of dynamic properties that are verifiable by parts, whatever the partition. We decide if a property P belongs to Bmod by looking at the form of the Buchi automaton that accepts the negation of P. However, when a property P belongs to Bmod, the property f => P, where f is a fairness assumption, does not necessarily belong to Bmod. In this paper, we propose to use the refinement process in order to build the parts on which the verification has to be performed. We then show that with such a partition, if a property P is verifiable by parts and if f is the expression of the fairness assumptions on a system, then the property f => P is still verifiable by parts. This approach is illustrated by its application to the chip card protocol T=1 using the B engineering design language

Syntactic Abstraction of B Models to Generate Tests

In a model-based testing approach as well as for the verification of properties, B models provide an interesting solution. However, for industrial applications, the size of their state space often makes them hard to handle. To reduce the amount of states, an abstraction function can be used, often combining state variable elimination and domain abstractions of the remaining variables. This paper complements previous results, based on domain abstraction for test generation, by adding a preliminary syntactic abstraction phase, based on variable elimination. We define a syntactic transformation that suppresses some variables from a B event model, in addition to a method that chooses relevant variables according to a test purpose. We propose two methods to compute an abstraction A of an initial model M. The first one computes A as a simulation of M, and the second one computes A as a bisimulation of M. The abstraction process produces a finite state system. We apply this abstraction computation to a Model Based Testing process.Comment: Tests and Proofs 2010, Malaga : Spain (2010

Vibration induced phase noise in Mach-Zehnder atom interferometers

The high inertial sensitivity of atom interferometers has been used to build accelerometers and gyrometers but this sensitivity makes these interferometers very sensitive to the laboratory seismic noise. This seismic noise induces a phase noise which is large enough to reduce the fringe visibility in many cases. We develop here a model calculation of this phase noise in the case of Mach-Zehnder atom interferometers and we apply this model to our thermal lithium interferometer. We are thus able to explain the observed dependence of the fringe visibility with the diffraction order. The dynamical model developed in the present paper should be very useful to further reduce this phase noise in atom interferometers and this reduction should open the way to improved interferometers