Estimation of Hydrochemical Unsaturated Soil Parameters Using a Multivariational Objective Analysis

Transport in Porous Media - Numerical experiment involving both moisture and solute transport predictions is performed to estimate the hydrochemical characteristics of unsaturated porous soil. The...     

Nickel-mediated hydrogenolysis of C-O bonds of aryl ethers: what is the source of the hydrogen?

Mechanistic studies of the hydrogenolysis of aryl ethers by nickel were undertaken with (diphosphine)aryl methyl ethers. A Ni(0) complex containing Ni-arene interactions adjacent to the aryl-O bond was isolated. Heating led to aryl-O bond activation and generation of a nickel aryl methoxide complex. Formal β-H elimination from this species produced a nickel aryl hydride which can undergo reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). The reported complexes map out a plausible mechanism of aryl ether hydrogenolysis catalyzed by nickel. Investigations of a previously reported catalytic system using isotopically labeled substrates are consistent with the mechanism proposed in the stoichiometric system, involving β-H elimination from a nickel alkoxide rather than cleavage of the Ni-O bond by H(2).     

The application of high throughput siRNA screening technology to study host-pathogen interactions

Recent advances in high throughput screening technologies have accelerated the identification and characterization of potential factors involved in host-virus interactions, facilitating early detection and diagnosis of diseases, as well as providing promising drug targets. The last decade has seen a plethora of successful examples of high throughput screening approaches, especially siRNA screening. With support from protein interaction studies, mRNA expression profiling, and bioinformatics, siRNA screening has also been successfully utilized to identify host factors required for a number of viruses including HIV, West Nile virus and H1N1 virus. Such studies have raised the awareness of virologists, and have opened a new chapter of global analysis of host-pathogen interactions. However, to play a more defining role in prognostics, diagnostics and therapeutics for virus diseases, acknowledged drawbacks, including false positives and negatives, inherent in this technology, must be successfully addressed.     

Pp IX Silica Nanoparticles Demonstrate Differential Interactions with In Vitro Tumor Cell Lines and In Vivo Mouse Models of Human Cancers

Protoporphyrin IX (Pp IX) silica nanoparticles, developed for effective use in photodynamic therapy (PDT), were explored in in vitro and in vivo models with the ambition to improve knowledge on the role of biological factors in the photodamage. Pp IX silica nanoparticles are found efficient at temperature with extreme metabolic downregulation, which suggest a high proportion of passive internalization. For the first time, clearance of silica nanoparticles on tumor cells is established. Cell viability assessment in six tumor cell lines is reported. In all tumor types, Pp IX silica nanoparticles are more efficient than free Pp IX. A strong fluorescence signal of reactive oxygen species generation colocalized with Pp IX silica nanoparticles, correlates with 100% of cell death. In vivo studies performed in HCT 116, A549 and glioblastoma multiforme tumors-bearing mice show tumor uptake of Pp IX silica nanoparticles with better tumor accumulation than the control alone, highlighting a high selectivity for tumor tissues. As observed in in vitro tests, tumor cell type is likely a major determinant but tumor microenvironment could more influence this differential time accumulation dynamic. The present results strongly suggest that Pp IX silica nanoparticles may be involved in new alternative local applications of PDT.     

Concise Total Syntheses of Amphidinolides C and F

The marine natural products amphidinolide C ( 1 ) and F ( 4 ) differ in their side chains but share a common macrolide core with a signature 1,4‐diketone substructure. This particular motif inspired a synthesis plan predicating a late‐stage formation of this non‐consonant (“umpoled”) pattern by a platinum‐catalyzed transannular hydroalkoxylation of a cycloalkyne precursor. This key intermediate was assembled from three building blocks ( 29 , 41 and 47 (or 65 )) by Yamaguchi esterification, Stille cross‐coupling and a macrocyclization by ring‐closing alkyne metathesis (RCAM). This approach illustrates the exquisite alkynophilicity of the catalysts chosen for the RCAM and alkyne hydroalkoxylation steps, which activate triple bonds with remarkable ease but left up to five other π‐systems in the respective substrates intact. Interestingly, the inverse chemoselectivity pattern was exploited for the preparation of the tetrahydrofuran building blocks 47 and 65 carrying the different side chains of the two target macrolides. These fragments derive from a common aldehyde precursor 46 formed by an exquisitely alkene‐selective cobalt‐catalyzed oxidative cyclization of the diunsaturated alcohol 44 , which left an adjacent acetylene group untouched. The northern sector 29 was prepared by a two‐directional Marshall propargylation strategy, whereas the highly adorned acid subunit 41 derives from D ‐glutamic acid by an intramolecular oxa‐Michael addition and a proline‐mediated hydroxyacetone aldol reaction as the key steps; the necessary Me₃Sn‐group on the terminus of 41 for use in the Stille coupling was installed via enol triflate 39 , which was obtained by selective deprotonation/triflation of the ketone site of the precursor 38 without competing enolization of the ester also present in this particular substrate.     

A curved ultrasonic actuator optimized for spherical motors: Design and experiments

Multi-degree-of-freedom angular actuators are commonly used in numerous mechatronic areas such as omnidirectional robots, robot articulations or inertially stabilized platforms. The conventional method to design these devices consists in placing multiple actuators in parallel or series using gimbals which are bulky and difficult to miniaturize. Motors using a spherical rotor are interesting for miniature multidegree-of-freedom actuators. In this paper, a new actuator is proposed. It is based on a curved piezoelectric element which has its inner contact surface adapted to the diameter of the rotor. This adaptation allows to build spherical motors with a fully constrained rotor and without a need for additional guiding system. The work presents a design methodology based on modal finite element analysis. A methodology for mode selection is proposed and a sensitivity analysis of the final geometry to uncertainties and added masses is discussed. Finally, experimental results that validate the actuator concept on a single degree-of-freedom ultrasonic motor set-up are presented.     

Fast and accurate point-based method for time-harmonic maxwell problems involving thin layer materials

We present a high-order hybrid boundary-finite elements method well-suited for solving time-harmonic electromagnetic scattering problems. Actually, this method is specially devoted to perfect electric conductors coated with a thin layer material. On such class of problems this method is shown to be fast and accurate. The fast feature is due to the joint use of finite elements of anisotropic order fitting the layer thickness, and of a point-based boundary element method on the skin. The accuracy is ensured, first by a discretization scheme satisfying the H_curl–H_div conformity required by the integro-differential equation and, secondly, by an adaptive technique of integration based on the detection of some local potential trouble on the geometry such as sharp edges or high dilatation of the elements. This algorithm does not need further information from the user and does not deteriorate the computation time. Numerical examples confirm the efficiency of this approach.     

Universality of Correlations of Levels¶with Discrete Statistics

We study the statistics of a system of N random levels with integer values, in the presence of a logarithmic repulsive potential of Dyson type. This problem arises in sums over representations (Young tableaux) of GL(N) in various matrix problems and in the study of statistics of partitions for the permutation group. The model is generalized to include an external source and its correlators are found in closed form for any N. We reproduce the density of levels in the large N and double scaling limits and the universal correlation functions in Dyson's short-distance scaling limit. We also study the statistics of small levels. Received: 26 October 1999 / Accepted: 7 July 2000