Hydrogen Compounds of Group-IV Nanosheets

The structural and electronic properties of the hydrides of silicene and germanene have been studied using ab initio calculations. The trend for the M-H (M=C, Si, Ge) bond lengths, and corresponding bond energies, is consistent with the atomic size trend, and comparable to those of MH_4 hydrides. Band structures were also obtained for the buckled configuration, which is the stable form for both silicene and germanene. Upon hydrogenation, both silicane (indirect gap) and germanane (direct gap) are semiconducting.Comment: 9 pages, 7 figure

Development and validation of a semi-quantitative food frequency questionnaire for young school-aged children

The objective of the present study was to examine the validity for estimating energy and macronutrients intake of a newly developed picture aid, semi quantitative FFQ for Greek children and preadolescents. The two methods were found to agree in terms of mean energy intake according to the Bland and Altman method, although a trend in overestimating energy intake was found as the intake increased. Additionally, results of the Wilcoxon signed rank test revealed the similarity of the distribution in energy intake as estimated from the FFQ and the 3DD [median (IQR): 2038 (1264 - 2651) kcals for the FFQ vs. 1902 (1583 - 2324) kcals for the 3DD, p=0.33] (Table 1). Concerning macronutrients intake, according to the Bland and Altman method, although the mean difference was different than zero (all p’s <0.05), the agreement was considered adequate as the mean difference for each nutrient (with the exception of poly-unsaturated fatty acids) was < 1SD of the same nutrient intake as estimated from the reference method

Magnetic-field effects on transport in carbon nanotube junctions

Here we address a theoretical study on the behaviour of electronic states of heterojunctions and quantum dots based on carbon nanotubes under magnetic fields. Emphasis is put on the analysis of the local density of states, the conductance, and on the characteristic curves of current versus voltage. The heterostructures are modeled by joining zigzag tubes through single pentagon-heptagon pair defects, and described within a simple tight binding calculation. The conductance is calculated using the Landauer formula in the Green functions formalism. The used theoretical approach incorporates the atomic details of the topological defects by performing an energy relaxation via Monte Carlo calculation. The effect of a magnetic field on the conductance gap of the system is investigated and compared to those of isolated constituent tubes. It is found that the conductance gap of the studied CNHs exhibits oscillations as a function of the magnetic flux. However, unlike the pristine tubes case, they are not Aharonov-Bohm periodic oscillations

Localized and Delocalized Charge Transport in Single-Wall Carbon-Nanotube Mats

We measured the complex dielectric constant in mats of single-wall carbon-nanotubes between 2.7 K and 300 K up to 0.5 THz. The data are well understood in a Drude approach with a negligible temperature dependence of the plasma frequency (omega_p) and scattering time (tau) with an additional contribution of localized charges. The dielectric properties resemble those of the best ''metallic'' polypyrroles and polyanilines. The absence of metallic islands makes the mats a relevant piece in the puzzle of the interpretation of tau and omega_p in these polymers.Comment: 4 pages including 4 figure

Negative differential resistance in nanotube devices

Carbon nanotube junctions are predicted to exhibit negative differential resistance, with very high peak-to-valley current ratios even at room temperature. We treat both nanotube p-n junctions and undoped metal-nanotube-metal junctions, calculating quantum transport through the self-consistent potential within a tight-binding approximation. The undoped junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Multi-soliton energy transport in anharmonic lattices

We demonstrate the existence of dynamically stable multihump solitary waves in polaron-type models describing interaction of envelope and lattice excitations. In comparison with the earlier theory of multihump optical solitons [see Phys. Rev. Lett. {\bf 83}, 296 (1999)], our analysis reveals a novel physical mechanism for the formation of stable multihump solitary waves in nonintegrable multi-component nonlinear models.Comment: 4 pages, 4 figure