The Molchanov-Vainberg Laplacian

It is well known that the Green function of the standard discrete Laplacian on ,

exhibits a pathological behavior in dimension . In particular, the estimate

fails for . This fact complicates the study of the scattering theory of discrete Schrödinger operators. Molchanov and Vainberg suggested the following alternative to the standard discrete Laplacian,

and conjectured that the estimate

holds for all . In this paper we prove this conjecture.

     

Surfactant‐Free Spinning of Composite Carbon Nanotube Fibers

Summary: Fibers and yarns are promising forms to use and control the spatial orientation of carbon nanotubes in macroscopic materials. Various approaches have been proposed in the last few years to achieve fibers with a fraction of carbon nanotubes. Among them, coagulation spinning in aqueous media has proven to be a simple and capable method of leading to super‐tough materials. However, all water‐based processes described so far have made use of surfactant‐stabilized carbon nanotubes. In the present work, a method is shown to spin fibers from surfactant‐free nanotube solutions while preserving an all water‐based process. The resultant fibers exhibit mechanical and electrical properties that compare well with those of previously reported fibers spun with surfactants. The fibers exhibit a significant toughness and a high electrical conductivity.

Scanning electron micrograph of the fiber, showing the surface texture.     

Inferring Post-Necking Strain Hardening Behavior of Sheets by a Combination of Continuous Bending Under Tension Testing and Finite Element Modeling

Experimental Mechanics - This paper presents a combined experimental and simulation approach to identify post-necking hardening behavior of ductile sheet metal. The method is based on matching a...     

Assessment of ease of excavation of surface mines

An empirical ground classification system for surface mines is presented. It is designed to provide a means for determining the ease of excavation, diggability, by mechanical excavators. The background and the methodology for determining this excavation index is introduced. This index, which is suitable for rock characterization relies on the point load index of the rock, its block size as defined by the presence of discontinuities. The system is also flexible to account for the influence of weathering as well as the relative ground structure which may assist or hinder the excavation process. The economic consequences of selecting mining excavation equipment are also addressed. The Excavation Index was applied with success to 49 case studies (Hadjigergiou, J. Studies of machine ground interaction in surface mines. Ph.D. thesis, McGill University, 1993, p. 214).     

Multiscale electrochemistry of hydrogels embedding conductive nanotubes

The local functionalities of biocompatible objects can be characterized under conditions similar to the operating ones, using scanning electrochemical microscopy (SECM). In the case of alginate beads entrapping carbon nanotubes (CNTs), SECM allows evidencing of the local conductivity, organization, and communication between the CNTs. It shows that the CNT network is active enough to allow long range charge evacuation, enabling the use of alginate/CNT beads as soft 3D electrodes. Direct connection or local interrogation by a microelectrode allows visualization of their communication as a network and eventually the study of them individually at the nanoscale.     

Untersuchung des Harns

Ohne Zusammenfassung     

Charge-transfer complex study by chemical force spectroscopy: a dynamic force spectroscopic approach

Charge-transfer interaction, as a reversible and rapid phenomenon, was evidenced by force microscopy. Pull-off forces were measured between a tip grafted with a trinitrofluorenone derivative and a surface functionalized with an electron-rich aromatic anthracene compound in a dodecane environment. The effect of the sweep time on the measured interaction forces is described, together with an extensive study of a competitive influence of free aromatic molecules in dodecane diluted solutions. These forces depend on the nature of the competitor and its concentration as well as on the velocity of tip/sample separation.     

Optimized carbon nanotube fiber microelectrodes as potential analytical tools

The preparation and interesting electrochemical properties of carbon nanotube (CNT) fiber microelectrodes are reported. By combining the advantages of CNT with those of fiber electrodes, this type of microelectrode differs from CNT-modified or CNT-containing composite electrodes, because they are made solely of CNT without other components, for example additives or binders. The performance of these electrodes has been characterized with regard to, among others, the electrocatalytic oxidation of analytes via dehydrogenase-mediated reactions. In this context the reversible regeneration of the coenzyme NAD(+) using a mediator is a key step in the development of new amperometric sensor devices and we have successfully immobilized mediator molecules that are very efficient for this purpose on the surface of the CNT fiber electrode. The microelectrodes thus obtained have been compared with classic carbon microelectrodes and have promising behavior in biosensing applications, especially after specific pretreatments such as CNT alignment inside the fiber or expansion of the specific surface by chemically induced swelling.