Carbon Nanotubes for Space Photovoltaic Applications

Carbon nanotubes (CNTs) can be envisioned as an individual graphene sheet rolled into a seamless cylinder (single-walled, SWNT), or concentric sheets as in the case of a multi-walled carbon nanotube (MWNT) (1). The role-up vector will determine the hexagonal arrangement and "chirality" of the graphene sheet, which will establish the nanotube to be metallic or semiconducting. The optoelectronic properties will depend directly on this chiral angle and the diameter of the SWNT, with semiconductor types exhibiting a band gap energy (2). Characteristic of MWNTs are the concentric graphene layers spaced 0.34 nm apart, with diameters from 10-200 nm and lengths up to hundreds of microns (2). In the case of SWNTs, the diameters range from 0.4 - 2 nm and lengths have been reported up to 1.5 cm (3). SWNTs have the distinguishable property of "bundling" together due to van der Waal's attractions to form "ropes." A comparison of these different structural types is shown in Figure 1. The use of SWNTS in space photovoltaic (PV) applications is attractive for a variety of reasons. Carbon nanotubes as a class of materials exhibit unprecedented optical, electrical, mechanical properties, with the added benefit of being nanoscale in size which fosters ideal interaction in nanomaterial-based devices like polymeric solar cells. The optical bandgap of semiconducting SWNTs can be varied from approx. 0.4 - 1.5 eV, with this property being inversely proportional to the nanotube diameter. Recent work at GE Global Research has shown where a single nanotube device can behave as an "ideal" pn diode (5). The SWNT was bridged over a SiO2 channel between Mo contacts and exhibited an ideality factor of 1, based on a fit of the current-voltage data using the diode equation. The measured PV efficiency under a 0.8 eV monochromatic illumination showed a power conversion efficiency of 0.2 %. However, the projected efficiency of these junctions is estimated to be > 5 %, especially when one considers the enhanced absorption (from nanotubes whose bandgap is tailored to illumination) and electromagnetic coupling in a network of nanotubes

Synthesis, Characterisation, and Preliminary In Vitro Studies of Vanadium(IV) Complexes with a Schiff Base and Thiosemicarbazones as Mixed Ligands

[VO(sal‐L‐tryp)(H2O)] (1, sal‐L‐tryp = N‐salicylidene‐L‐tryptophanate) was used as a precursor to produce the new complexes [VO(sal‐L‐tryp)(MeATSC)]·1.5C2H5OH [2, MeATSC = 9‐Anthraldehyde‐N(4)‐methylthiosemicarbazone], [VO(sal‐L‐tryp)(N‐ethhymethohcarbthio)]·H2O [3, N‐ethhymethohcarbthio = (E)‐N‐ethyl‐2‐(4‐hydroxy‐3‐methoxybenzylidene)hydrazinecarbothioamide] and [VO(sal‐L‐tryp)(acetylethTSC)]·C2H5OH {4, acetylethTSC = (E)‐N‐ethyl‐2‐[1‐(thiazol‐2‐yl)ethylidene]hydrazinecarbothioamide} by reaction with the respective thiosemicarbazone. The chemical and structural properties of these ligands and complexes were characterised by elemental analysis, ESI‐MS, FTIR, UV/Vis, ESR and 1H and 13C NMR spectroscopy and X‐ray crystallography. Dimethyl sulfoxide (DMSO) and [D6]DMSO solutions of 1–4 were oxidised in air to produce vanadium(V) species, which were verified by ESI‐MS and 51V NMR spectroscopy. The anticancer properties of 2–4 were examined with three colon cancer cell lines, HTC‐116, Caco‐2 and HT‐29, and noncancerous colonic myofibroblasts, CCD18‐Co. Compounds 2–3 exhibited less inhibitory effects in the CCD‐18Co cells, which indicates a possible cytotoxic selectivity towards colon cancer cells. In general, compounds that exhibit antiproliferative activity to cancer cells but do not affect noncancerous cells may have a potential in chemotherapy

Vocal imitations and the identification of sound events

International audienceIt is commonly observed that a speaker vocally imitates a sound that she or he intends to communicate to an interlocutor. We report on an experiment that examined the assumption that vocal imitations can e ffectively communicate a referent sound, and that they do so by conveying the features necessary for the identifi cation of the referent sound event. Subjects were required to sort a set of vocal imitations of everyday sounds. The resulting clusters corresponded in most of the cases to the categories of the referent sound events, indicating that the imitations enabled the listeners to recover what was imitated. Furthermore, a binary decision tree analysis showed that a few characteristic acoustic features predicted the clusters. These features also predicted the classi fication of the referent sounds, but did not generalize to the categorization of other sounds. This showed that, for the speaker, vocally imitating a sound consists of conveying the acoustic features important for recognition, within the constraints of human vocal production. As such vocal imitations prove to be a phenomenon potentially useful to study sound identifi cation

Main Group Metal Halide Complexes with Sterically Hindered Thioureas XIV. A Reinvestigation of Coordination Sensitive Modes in the Solid State Vibrational Spectrum of 1,3-Dimethyl-2(3H)-imidazolethione and Related Compounds

The assignment of the C-S stretch in the IR spectrum for 1,3-dimethyl-2(3H)-imidazolethione (dmit) reported in an earlier paper was restudied in light of new compds. reported and an x-ray structure of 1,3-dimethyl-2-(S-methylthio)-2(3H)-imidazoylium iodide (tmii). Conflicting literature values and assignments were also studied. For dmit, the C-S stretch was found in the 1170-1180 cm-1 region, and 3 of the 4 thioamide peaks reported by other researchers as coordination sensitive modes for thiourea-type compds. did not have significant C-S contribution based on the compds. studied . Crystallog. data for tmii: C6H11N2SI, M = 207.04, space group P21/n, Z = 4, λ(Mo Kα) = 0.71073 Å, μ(Mo Kα) = 3.13 mm-1, dc = 1.699 g/cm3, Do = 1.66 g/cm3, a 7.846(2), b 11.754(2), c 12.578(2) Å, β 95.51(2)°, R = 0.034, Rw = 0.042. Addnl., a new sterically hindered thiourea, 1-Me-3-(2-propenyl)-2(3H)-imidazolethione (mpit), and a new complex, ZnCl2(mpit)2, are reported and characterized