Optimal stopping with irregular reward functions

We consider optimal stopping problems with finite horizon for one-dimensional diffusions. We assume that the reward function is bounded and Borel-measurable, and we prove that the value function is continuous and can be characterized as the unique solution of a variational inequality in the sense of distributions.     

A measurable-group-theoretic solution to von Neumann’s problem

We give a positive answer, in the measurable-group-theory context, to von Neumann’s problem of knowing whether a non-amenable countable discrete group contains a non-cyclic free subgroup. We also get an embedding result of the free-group von Neumann factor into restricted wreath product factors. D. Gaboriau’s research was supported by CNRS. R. Lyons’ research was supported partially by NSF grant DMS-0705518 and Microsoft Research.     

Minimal arithmetic thickness connecting discrete planes

While connected arithmetic discrete lines are entirely characterized, only partial results exist for the more general case of arithmetic discrete hyperplanes. In the present paper, we focus on the three-dimensional case, that is on arithmetic discrete planes. Thanks to arithmetic reductions on a vector , we provide algorithms either to determine whether a given arithmetic discrete plane with as normal vector is connected, or to compute the minimal thickness for which an arithmetic discrete plane with normal vector is connected.     

Electrochemistry of immobilized redox enzymes: kinetic characteristics of NADH oxidation catalysis at diaphorase monolayers affinity immobilized on electrodes

In the class of NADH:acceptor oxidoreductases, the diaphorase from Bacillus stearothermophilusis a particularly promising enzyme for sensing NADH, and indirectly a great number of analytes, when coupled with a NAD-dependent dehydrogenase as well as for the design of mono- and multienzyme affinity sensors. The design and rational optimization of such systems require devising immobilization procedures that prevent dramatic losses of the enzymatic activity and a full kinetic characterization of the immobilized enzyme system. Two immobilization procedures are described, which involve recognition of the biotinylated diaphorase by a monolayer of neutravidin adsorbed on the electrode surface either directly or through the intermediacy of a monolayer of biotinylated rabbit immunoglobulin. Thorough kinetic characterization of the two systems is derived from cyclic voltammetric responses. A precise estimate of the enzyme coverages is obtained after comparing the enzyme kinetics of the immobilized and the homogeneous system.     

Orientation of native cellulose in an electric field

Native cellulose has been oriented in an ac electric field at both the macroscopic and colloidal level. Ramie fiber fragments suspended in chloroform have been shown to point along the field. Cellulose microcrystal suspensions in cyclohexane have also been allowed to evaporate in an electric field and have exhibited a high degree of orientation when further examined by TEM and electron diffraction. Similarly, cellulose whisker suspensions showed increasing birefringence with increasing field strength and displayed interference Newton colors that saturated at around 2000 V cm(-)(1). A high degree of order of this suspension was also obtained by evaluating the induced birefringence with color charts.     

An EPR, ENDOR and EIE study of gamma-irradiated poly (lactide-co-glycolide) polymers

Gamma radiation of poly (lactide-co-glycolide) raw polymers and processed microspheres under vacuum and at 77 K results in the formation of a series of free radicals. The resulting powder electron paramagnetic resonance (EPR) spectrum contains a distribution of several different radicals, depending on the annealing temperature, and is therefore difficult to interpret. By utilising the selectivity of the electron nuclear DOuble resonance (ENDOR) and associated ENDOR induced EPR (EIE) techniques, a more direct approach for the deconvolution of the EPR spectrum can be achieved. Using this approach, the radiolytically induced CH3 *CHC(O)R- chain scission radical was identified at 120 K by simulation of the EIE spectrum. At elevated temperatures (250 K), this radical decays considerably and the more stable radicals -O*CHC(O)-, CH3 *C(OR)C(O)- and CH3 *C(OH)C(O)- predominate. This work demonstrates the utility of the EIE approach to supplement and aid the interpretation of powder EPR spectra of radicals in a polymer matrix.     

Laser-driven shock experiments on precompressed water: Implications for "icy" giant planets

Laser-driven shock compression of samples precompressed to 1 GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor<-->electronic conductor transition in water, and is found at pressures above approximately 130 GPa for single-shocked samples precompressed to 1 GPa. Our results indicate that conductivity in the deep interior of "icy" giant planets is greater than realized previously because of an additional contribution from electrons.     

A novel design approach for the epitaxial layer for 4H-SiC and 6H-SiC power bipolar devices

The paper evaluates the optimal design of the low-doped base region inside power diodes and other bipolar devices. It is demonstrated theoretically that a low-doped base region of P⁺N⁻N⁺ diodes can provide a high breakdown voltage and an optimal on-resistance . A simple, accurate and CPU timesaving approach is presented to extract an optimal value for the base region width, W_B, and its doping concentration, N_D. The paper details an analytical relation between W_B and N_D, and gives a method for quantifying the trade-off between their values for a given breakdown voltage and for obtaining the minimal on-resistance. Analytical results are confronted with experimental results for 4H-SiC- and 6H-SiC-based diodes.     

Use of ram extruder as a combined rheo-tribometer to study the behaviour of high yield stress fluids at low strain rate

We propose in this work to provide an efficient and simple extruder device able to evaluate the rheological and tribological behaviour of high yield stress fluids, such as extrudible materials. An extruder able to measure simultaneously both the friction force acting on the extruder wall and the total extrusion force is developed. Based on previous studies, an efficient and accurate method of data analysis is then proposed and applied in order to obtain both a flow curve and a tribological law. Experimental tests are performed on soft modelling clay, kaolin paste and cement-based materials. Results are compared to conventional rheometry measurements. This comparison helps to evaluate the accuracy of the proposed experimental device and procedure.