Tunable band structure effects on ballistic transport in graphene nanoribbons

Graphene nanoribbons (GNR) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of the applied fields on its own preserves the even symmetry Ek=E−k of the subband dispersion. When applied together, they reverse the dispersion parity to be odd and gives Ee,k=−Eh,−k and mix the electron and hole subbands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range.     

Growth and dc conductivity studies of tripotassium sodium dichromate single crystal

DC electrical conductivity studies were carried out along the three crystallographic axes for tripotassium sodium dichromate (K₃Na(CrO₄)₂ or KNCr). Earlier studies of phase transition in this crystal show successive phase transitions at 239 K and 853 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303–430 K along the crystallographic axes. An anomaly in conductivity was obtained around 326 K along both the axes. This may be attributed as due to a newly observed phase transition in the crystal. DSC taken for the sample also shows exothermic peak supporting the occurrence of newly observed phase transition.     

Microfluidic cell arrays for metabolic monitoring of stimulated cardiomyocytes

An array of PDMS microchambers was aligned to an array of sensor electrodes and stimulating microelectrodes, which was used for the electrochemical monitoring of the metabolic activity of single isolated adult ventricular myocytes inside the chamber array, stimulated within a transient electric field. The effect of the accumulation of metabolic byproducts in the limited extracellular volume of the picolitre chambers was demonstrated by measuring single muscle cell contraction optically, while concomitant changes in intracellular calcium transients and pH were recorded independently using fluorescent indicator dyes. Both the amplitude of the cell shortening and the magnitude of the intracellular calcium transients decreased over time and both nearly ceased after 20 min of continuous stimulation in the limited extracellullar volume. The intracellular pH decreased gradually during 20 min of continuous stimulation after which a dramatic pH drop was observed, indicating the breakdown of the intracellular buffering capacity. After continuous stimulation, intracellular lactate was released into the microchamber through cell electroporation and was detected electrochemically at a lactate microbiosensor, within the chamber. A mitochondrial uncoupler was used to mimic ischaemia and thus to enhance the cellular content of lactate. Under these circumstances, intracellular lactate concentrations were found to have risen to ～15 mM. This array system has the potential of simultaneous electrochemical and optical monitoring of extracellular and intracellular metabolites from single beating heart cells at a controlled metabolic state.     

Block polymers of isocyanates and vinyl monomers by homogeneous anionic polymerization

The “living” polymer method was used to prepare block polymers of vinyl monomers and isocyanates at low temperatures in toluene–tetrahydrofuran mixtures. Vinyl monomers and diisocyanates, which have one hindered isocyanate group, as in 2,4-toluene diisocyanate, form block polymers which contain pendant reactive isocyanate groups. These block polymers can be crosslinked with water, diols, diamines, etc. The polymerization is apparently limited to block polymer formation, since the polyisocyanate anion is incapable of initiating the polymerization of common vinyl monomers.     

Assessing the effects of homosexuals and bisexuals on the intrinsic dynamics of HIV/AIDS in heterosexual settings

A deterministic compartmental sex-structured HIV/AIDS model for assessing the effects of homosexuals and bisexuals on the intrinsic dynamics of the disease in heterosexual settings in which homosexuality and bisexuality issues have remained taboo is presented. The epidemic threshold and equilibria for the model are determined and stabilities are investigated. Comprehensive qualitative analysis of the model including invariance of solutions and permanence are carried out. The epidemic threshold known as the basic reproductive number suggests that heterosexuality, homosexuality, and bisexuality influence the growth of the epidemic in HIV/AIDS affected populations and the partial reproductive number (homosexuality induced or heterosexuality and bisexuality induced) with the larger value influences the overall dynamics of the epidemic in a setting. Numerical simulations of the model show that as long as one of the partial reproductive numbers is greater than unity, the disease will exist in the population. We conclude from the study that homosexuality and bisexuality enlarge the epidemic in a heterosexual setting. The theoretical study highlights the need to carry out substantial research to map homosexuals and bisexuals as it has remained unclear as to what extent this group has contributed to the epidemic in heterosexual settings especially in southern Africa, which has remained the epidemiological locus of the epidemic.     

Crystallographic effects in low energy ion scattering due to local ion-atom neutralisation

New experiments on 1 keV ₄He⁺ ion scattering from Ni {100} and Ni {100} (√2 × √2)R45°?O surfaces show azimuthal anisotropies attributable to variations in ion neutralisation probability for different ion trajectories relative to the position of the surface atoms. These effects are shown to be compatible with a simple localised ion-atom neutralisation mechanism. The results indicate that local neutralization is an important process in substrate shadowing in low energy ion scattering studies of adsorbate structures.     

Hyperfine interactions in the microwave spectrum of 2-propen-1-Imine (vinylimine)

A high resolution study of the microwave spectrum of 2-propen-1-imine has yielded values for ¹⁴N hyperfine coupling constants for both the trans-syn and trans-anti isomers. In the latter case, evidence was found for magnetic spin-rotation interaction. Rotational and centrifugal distortion constants of improved accuracy have been derived in the course of the analysis.     

Observations on the chemistry of the iodoxy group

In the presence of an appropriate catalyst, iodoxy-arenes act as oxidants towards a variety of diverse functional groups     

Conformational analysis of alkyl aryl ethers and alkyl aryl sulphides by photoelectron spectroscopy

Photoelectron spectroscopy shows that in t-butoxybenzenes, but not in methoxy-, ethoxy- or isopropoxybenzenes, there is a loss of p-π orbital overlap. A similar effect is observed in 2,6-dimethylalkoxybenzenes. In alkyl aryl sulphides two conformers predominate, the one with maximum p-π overlap and the other with reduced overlap. The importance of the less conjugated conformer increases monotonously through the series hydrogen, methyl, ethyl, isopropyl and t-butyl in alkyl phenyl sulphides.