pi-Conjugation and conformation in a semiconducting polymer: small angle x-ray scattering study

Small angle X-ray scattering (SAXS) in poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) solution has shown the important role of pi-electron conjugation in controlling the chain conformation and assembly. By increasing the extent of conjugation from 30 to 100 %, the persistence length (l_p) increases from 20 to 66 Angstrom. Moreover, a pronounced second peak in the pair distribution function has been observed in fully conjugated chain, at larger length scales. This feature indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. Xylene enhances the rigidity of PPV backbone to yield extended structures, while tetrahydrofuran solvates the side groups to form compact coils in which the l_p is much shorter.Comment: accepted (J. Phy. Cond. Mat.

Distinguishing the Littlest Higgs model with T-parity from supersymmetry at the LHC using trileptons

We analyse hadronically quiet trilepton signatures in the T-parity conserving Littlest Higgs model and in R-parity conserving supersymmetry at the Large Hadron Collider. We identify the regions of the parameter space where such signals can reveal the presence of these new physics models above the Standard Model background and distinguish them from each other, even in a situation when the mass spectrum of the Littlest Higgs model resembles the supersymmetric pattern.Comment: 14 pages, 4 figures, Latex; v2: a few comments and references added, typos corrected, conclusions unchanged, version to be published in Physics Letters

Correlated conformation and charge transport in multiwall carbon nanotube - conducting polymer nanocomposites

The strikingly different charge transport behaviors in nanocomposites of multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylene dioxythiophene - polystyrene sulfonic acid (PEDOT-PSS) at low temperatures are explained by probing their conformational properties using small angle X-ray scattering (SAXS). The SAXS studies indicate assembly of elongated PEDOT-PSS globules on the walls of nanotubes, coating them partially thereby limiting the interaction between the nanotubes in the polymer matrix. This results in a charge transport governed mainly by small polarons in the conducting polymer despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge carriers following 1D-VRH is evident which also gives rise to a positive magnetoresistance (MR) with an enhanced localization length (~ 5 nm) due to the presence of MWNTs. However, at T < 4 K, the observation of an unconventional positive temperature coefficient of resistivity (TCR) is attributed to small polaron tunnelling. The exceptionally large negative MR observed in this temperature regime is conjectured to be due to the presence of quasi-1D MWNTs that can aid in lowering the tunnelling barrier across the nanotube - polymer boundary resulting in large delocalization.Comment: Accepted J. Phys.: Condens. Matte

Aquaculture governance: five engagement arenas for sustainability transformation

A greater focus on governance is needed to facilitate effective and substantive progress toward sustainability transformations in the aquaculture sector. Concerted governance efforts can help move the sector beyond fragmented technical questions associated with intensification and expansion, social and environmental impacts, and toward system-based approaches that address interconnected sustainability issues. Through a review and expert-elicitation process, we identify five engagement arenas to advance a governance agenda for aquaculture sustainability transformation: (1) setting sustainability transformation goals, (2) cross-sectoral linkages, (3) land–water–sea connectivity, (4) knowledge and innovation, and (5) value chains. We then outline the roles different actors and modes of governance can play in fostering sustainability transformations, and discuss action items for researchers, practitioners, and policymakers to operationalize activities within their engagement arenas

Approximate evaluation of cumulative distribution function of central sampling distributions: A review

Cumulative distribution functions of some sampling distributions do not have closed form representation. Hence an approximate formula can be of immense use. In this paper, we review the development of literature of approximations to cumulative distribution function of some popular central sampling distributions

Modified conformation and physical properties in conducting polymers due to varying conjugation and solvent interactions

Small angle X-ray scattering (SAXS) studies of poly2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with varying conjugation, and polyethylene dioxythiophene complexed with polystyrene sulfonate (PEDOT-PSS) in different solvents have shown the importance of the role of pi-electron conjugation and solvent-chain interactions in controlling the chain conformation and assembly. In MEH-PPV, by increasing the extent of conjugation from 30 to 100%, the persistence length (l(p)) increases from 20 to 66 angstrom. Moreover, a pronounced second peak in the pair distribution function has been observed in the fully conjugated chain, at larger length scales. This feature indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. In the case of PEDOT-PSS, the chains undergo solvent induced expansion and enhanced chain organization. The clusters formed by chains are better correlated in dimethyl sulfoxide (DMSO) solution than water, as observed in the scattered intensity profiles. The values of radius of gyration and the exponent (water: 2.6, DMSO: 2.31) of power-law decay, obtained from the unified scattering function (Beaucage) analysis, give evidence for chain expansion from compact (in water) to an extended coil in DMSO solutions, which is consistent with the Kratky plot analysis. The mechanism of this transition and the increase in dc conductivity of PEDOT-PSS in DMSO solution are discussed. The onset frequency for the increase in ac conduction, as well as its temperature dependence, probes the extent of the connectivity in the PEDOT-PSS system. The enhanced charge transport in PEDOT-PSS in DMSO is attributed to the extended chain conformation, as observed in the SAXS results

Lovastatin induces apoptosis by inhibiting mitotic and post-mitotic events in cultured mesangial cells

AbstractLovastatin, an inhibitor of protein prenylation, was reported to inhibit DNA synthesis and induce apoptosis in cultured cells. This report describes the morphological consequences of lovastatin treatment. Lovastatin (50 μM) induced mesangial cell rounding and disassembly of actin stress fibers within 24 to 48 h. After 48 to 72 h of lovastatin treatment, the cells detached from the substratum and underwent apoptotic cell death as evidenced by condensed nuclear chromatin, nuclear fragmentation, cell blebbing and decrease in cell size. Time lapse cinematography revealed that lovastatin caused cell rounding by either inhibiting cytokinesis or cell spreading following cytokinesis. Lovastatin-induced cell rounding, detachment, and apoptosis were dependent upon cell proliferation. These effects were prevented by serum deprivation to inhibit cell proliferation or by plating cells at densities which resulted in contact inhibition of cell growth. Lovastatin-induced mesangial cell rounding and apoptosis were also prevented by the inclusion of the isoprenoids all-trans-farnesol or all-trans-geranylgeraniol in the incubation medium. These results indicate that the effects of lovastatin were mediated by inhibition of protein isoprenylation because exogenous all-trans-geranylgeraniol can be used only in protein prenylation. The small GTP-binding protein RhoA, which may be important for cell spreading and cytokinesis, accumulated in the cytosol following treatment with lovastatin, suggestive of its inactivation. This effect was also prevented by the inclusion of either farnesol or geranylgeraniol in the incubation medium. Thus, lovastatin-induced apoptosis in mesangial cells occurs by interfering with prenylation dependent mitotic and post-mitotic events