Inelastic current-voltage characteristics of atomic and molecular junctions

We report first-principles calculations of the inelastic current-voltage (I-V) characteristics of a gold point contact and a molecular junction in the nonresonant regime. Discontinuities in the I-V curves appear in correspondence to the normal modes of the structures. Due to the quasi-one-dimensional nature of these systems, specific modes with large longitudinal component dominate the inelastic I-V curves. In the case of the gold point contact, our results are in good agreement with recent experimental data. For the molecular junction, we find that the inelastic I-V curves are quite sensitive to the structure of the contact between the molecule and the electrodes thus providing a powerful tool to extract the bonding geometry in molecular wires.Comment: 4 pages, 3 figure

Antikinetoplastid SAR study in 3-nitroimidazopyridine series: identification of a novel non-genotoxic and potent anti-T. b. brucei hit-compound with improved pharmacokinetic properties

To study the antikinetoplastid 3-nitroimidazo[1,2-a]pyridine pharmacophore, a structure-activity relationship study was conducted through the synthesis of 26 original derivatives and their in vitro evaluation on both Leishmania spp and Trypanosoma brucei brucei. This SAR study showed that the antitrypanosomal pharmacophore was less restrictive than the antileishmanial one and highlighted positions 2, 6 and 8 of the imidazopyridine ring as key modulation points. None of the synthesized compounds allowed improvement in antileishmanial activity, compared to previous hit molecules in the series. Nevertheless, compound 8, the best antitrypanosomal molecule in this series (EC50 = 17 nM, SI = 2650 & E° = -0.6 V), was not only more active than all reference drugs and previous hit molecules in the series but also displayed improved aqueous solubility and better in vitro pharmacokinetic characteristics: good microsomal stability (T1/2 > 40 min), moderate albumin binding (77%) and moderate permeability across the blood brain barrier according to a PAMPA assay. Moreover, both micronucleus and comet assays showed that nitroaromatic molecule 8 was not genotoxic in vitro. It was evidenced that bioactivation of molecule 8 was operated by T. b. brucei type 1 nitroreductase, in the same manner as fexinidazole. Finally, a mouse pharmacokinetic study showed that 8 displayed good systemic exposure after both single and repeated oral administrations at 100 mg/kg (NOAEL) and satisfying plasmatic half-life (T1/2 = 7.7 h). Thus, molecule 8 appears as a good candidate for initiating a hit to lead drug discovery program

The effects of aging of scientists on their publication and citation patterns

The average age at which U.S. researchers get their first grant from NIH has increased from 34.3 in 1970, to 41.7 in 2004. These data raise the crucial question of the effects of aging on the scientific creativity and productivity of researchers. Those who worry about the aging of scientists usually believe that the younger they are the more creative and productive they will be. Using a large population of 13,680 university professors in Quebec, we show that, while scientific productivity rises sharply between 28 and 40, it increases at a slower pace between 41 and 50 and stabilizes afterward until retirement for the most active researchers. The average scientific impact per paper decreases linearly until 50-55 years old, but the average number of papers in highly cited journals and among highly cited papers rises continuously until retirement. Our results clearly show for the first time the natural history of the scientific productivity of scientists over their entire career and bring to light the fact that researchers over 55 still contribute significantly to the scientific community by producing high impact papers.Comment: 12 pages, 4 figure

Noonops.

48 pages : illustrations (some color) ; 26 cm. Part of the oonopid PBI project. Cf. acknowledgments.A new genus, Noonops, is established to contain 23 species of soft-bodied, New World oonopine spiders that differ from those of Oonops Templeton and similar genera in having the male palpal bulb fused to the cymbium, and from those of Wanops Chamberlin and Ivie and Oonopoides Bryant in having shorter legs. Six specific names are transferred from Oonops to Noonops: O. floridanus (Chamberlin and Ivie) from Florida and Georgia (chosen as the type species), O. gertschi Chickering from the Bahama Islands (which is placed as a junior synonym of N. floridanus), O. furtivus Gertsch from Texas and Tamaulipas, O. sonora Gertsch and Davis from Arizona, California, Sonora, Baja California, and Baja California Sur, O. puebla Gertsch and Davis from Puebla, and O. chilapensis Chamberlin and Ivie from Guerrero. Males of N. sonora and females of N. furtivus are described for the first time; 18 new species are described: N. ocotillo, N. mortero, N. joshua, N. skinner, N. coachella, and N. californicus from Arizona and southern California and N. willisi, N. mesa, N. naci, N. tarantula, N. miraflores, N. culiacan, N. taxquillo, N. chapul, N. beattyi, N. iviei, N. tonila, and N. minutus from Mexico

The NASA STI Program Office ... in Profile

Many new materials are being produced for aerospace applications with the objective of maximizing certain ideal properties without sacrificing others. Polymer composites in various forms and configurations are being developed in an effort to provide lighter weight construction and better thermal and electrical properties and still maintain adequate strength and stability. To this end, thin film polymer nanocomposites, synthesized for the purpose of influencing electrical conductivity using metal oxide particles as filler without incurring losses in mechanical properties, were examined to determine elastic modulus and degree of dispersion of particles. The effects of various metal oxides on these properties will be discussed

Rate-Distortion Analysis for Vector Quantization Based on a Variable Block-Size Classification Model

Vector quantization (VQ) based on a fixed block-size classification (FBSC) model, which is known as classified VQ (CVQ), offers a useful solution for the edge degradation problem of conventional image VQ. In our previous work, we have developed a VQ technique based on a variable block-size classification (VBSC) model, in which an image is segmented into blocks of various size, and each segmented region is encoded at a different rate according to its level of detail. The low-detail regions of the image consist of variable size blocks and are encoded at very low bitrates with little perceptual degradation. High-detail regions, which are isolated into the smallest blocks, are classified into various edges of which each is separately encoded. In this paper, a rate-distortion function (RDF), R(D), is presented for a VBSC model. We obtain a theoretical R(D) bound on the performance of VQ based on a VBSC model. It is theoretically proved that the R(D) bound of the VBSC model is lower than th..