Sensitivity enhancement of a flexible MEMS strain sensor by a field effect transistor in an all organic approach

We report a low-cost piezoresistive nanocomposite based organic micro electro mechanical system (MEMS) strain sensor that has been combined to an organic field effect transistor (OFET) with the objective of amplifying the sensitivity of the sensor. When the MEMS cantilever is strained by a mechanical deflection, the resulting variation of resistivity influences the gate voltage (V_GS) of the OFET and, hence, changes the drain current (I_DS) of the transistor. The present combination allows an enhancement of sensitivity to strain by a factor 3.7, compared to the direct detection of resistance changes of the nanocomposite. As a consequence, a low limit of detection of 24 ppm has been estimated in terms of strain transduction efficiency. Furthermore, the organic microsystem exhibits a short response time and operates reversibly with an excellent robustness.     

Hydrogen sensor based on a graphene – palladium nanocomposite

A composite material was prepared from graphene and palladium nanoparticles (PdNP) by layer-by-layer deposition on gold electrodes. The material was characterized by absorption spectroscopy, scanning electron microscopy, Raman spectroscopy and surface plasmon resonance. Cyclic voltammetry demonstrated the presence of electrocatalytic centers in the palladium decorated graphene. This material can serve as a sensor material for hydrogen at levels from 0.5 to 1% in synthetic air. Pure graphene is poorly sensitive to hydrogen, but incorporation of PdNPs increases its sensitivity by more than an order of magnitude. The effects of hydrogen, nitrogen dioxide and humidity were studied. Sensor regeneration is accelerated in humid air. The sensitivity of the nanocomposite depends on the number of bilayers of graphene–PdNPs.     

Photographic Emulsion Grains with Cores: Part I. Evidence for the Presence of Cores*

Neutral iodobromide emulsions made by the addition of silver nitrate to alkali halides in gelatin may, under certain conditions, contain a proportion of grains with cores of iodobromide phases. The maximum iodide contents (i) of these cores are related to the precipitation temperature (T) by the empirical equation i= 34.5+0.165(T–25). Grains containing such cores show very regular print-out distribution.     

Synthesis and characterization of cytidine derivatives that inhibit the kinase IspE of the non-mevalonate pathway for isoprenoid biosynthesis

The enzymes of the non-mevalonate pathway for isoprenoid biosynthesis are attractive targets for the development of novel drugs against malaria and tuberculosis. This pathway is used exclusively by the corresponding pathogens, but not by humans. A series of water-soluble, cytidine-based inhibitors that were originally designed for the fourth enzyme in the pathway, IspD, were shown to inhibit the subsequent enzyme, the kinase IspE (from Escherichia coli). The binding mode of the inhibitors was verified by co-crystal structure analysis, using Aquifex aeolicus IspE. The crystal structures represent the first reported example of a co-crystal structure of IspE with a synthetic ligand and confirmed that ligand binding affinity originates mainly from the interactions of the nucleobase moiety in the cytidine binding pocket of the enzyme. In contrast, the appended benzimidazole moieties of the ligands adopt various orientations in the active site and establish only poor intermolecular contacts with the protein. Defined binding sites for sulfate ions and glycerol molecules, components in the crystallization buffer, near the well-conserved ATP-binding Gly-rich loop of IspE were observed. The crystal structures of A. aeolicus IspE nicely complement the one from E. coli IspE for use in structure-based design, namely by providing invaluable structural information for the design of inhibitors targeting IspE from Mycobacterium tuberculosis and Plasmodium falciparum. Similar to the enzymes from these pathogens, A. aeolicus IspE directs the OH group of a tyrosine residue into a pocket in the active site. In the E. coli enzyme, on the other hand, this pocket is lined by phenylalanine and has a more pronounced hydrophobic character.     

Meissner Effect, Spin Meissner Effect and Charge Expulsion in Superconductors

The Meissner effect and the Spin Meissner effect are the spontaneous generation of charge and spin current respectively near the surface of a metal, making a transition to the superconducting state. The Meissner effect is well known but, I argue, not explained by the conventional theory; the Spin Meissner effect has yet to be detected. I propose that both effects take place in all superconductors, the first one in the presence of an applied magnetostatic field, the second one even in the absence of applied external fields. Both effects can be understood under the assumption that electrons expand their orbits and thereby lower their quantum kinetic energy in the transition to superconductivity. Associated with this process, the metal expels negative charge from the interior to the surface and an electric field is generated in the interior. The resulting charge current can be understood as arising from the magnetic Lorenz force on radially outgoing electrons, and the resulting spin current can be understood as arising from a spin Hall effect originating in the Rashba-like coupling of the electron magnetic moment to the internal electric field. The associated electrodynamics is qualitatively different from London electrodynamics, yet can be described by a small modification of the conventional London equations. The stability of the superconducting state and its macroscopic phase coherence hinge on the fact that the orbital angular momentum of the carriers of the spin current is found to be exactly ?/2, indicating a topological origin. The simplicity and universality of our theory argue for its validity, and the occurrence of superconductivity in many classes of materials can be understood within our theory.     

Polysomnographic screening of infants at risk for SIDS

The authors present a Sudden Infant Death Syndrome prevention program. The study analyses the data of 92 children having participated in the complex prevention program, including polysomnography, between May 1997 and February 1998. The role of polysomnography and its use as a clinical method is described through the statistical analysis of the results of the study.     

Large-scale system testing of a power system dynamic equivalencingprogram

This paper presents the results of applying the EPRI Dynamic Equivalencing Program to a large-scale system test case of the New York Power Pool. The effects of coherent generator selection, network reduction, generator aggregation, and generator modeling on the accuracy of the reduced models are investigated     

Surface ionization on tungsten in a varying ambient atmosphere

Experiments show that under suitable conditions the introduction of oxygen can raise the surface ionization current emitted by a heated tungsten wire by several orders of magnitude. The ions in this case are alkali ions originating from alkali silicates normally present as additives in tungsten. From the simultaneous observation, in a varying ambient atmosphere, of both the positive ion current produced by surface ionization and of the electron current due to thermionic emission, it is concluded that the large observed increase in positive ion current is not primarily a consequence of an increase in the work function of tungsten, but is mainly due to a reduction in the residence time of the ions on the ionizing surface. This appears to be caused by alkali ions being preferentially replaced as an adsorbate on tungsten by the impinging oxygen molecules. The observations suggest that the increased ion production does not occur on the outer wire surface, but at inter-phase boundaries within the wire.