141 research outputs found
Ising spin models of partially connected neural networks
SIGLEAvailable from British Library Document Supply Centre- DSC:D86394 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Comparison of CâC bond hydrogenation in C-4 unsaturated nitriles over Pt/alumina
The hydrogenation of allyl cyanide (but-1-ene-4-nitrile, AC), trans- and cis-crotononitrile (E- and Z-but-2-ene nitrile, TCN and CCN), and methacrylonitrile (2-cyano-1-propene, MCN) were studied, both singly and competitively, over a Pt/alumina catalyst in the liquid phase. Each unsaturated nitrile only underwent CâC bond hydrogenation: no evidence was found for the formation of the saturated or unsaturated amine. The nonconjugated allyl cyanide was found to be the most reactive unsaturated nitrile. Activation energies for the hydrogenation of the CâC bond in AC and MCN were determined giving values of 64 ± 7 kJ molâ1 for AC and 37 ± 4 kJ molâ1 for MCN. The reaction was zero order for both nitriles. Competitive hydrogenations revealed that not only does allyl cyanide react preferentially over the other isomers but also it inhibits the hydrogenation of the other isomers. When all four nitriles were simultaneously hydrogenated, inhibition effects were easily seen suggesting that in terms of strength of bonding to the surface an order of AC > CCN > TCN ⌠MN can be generated
Gender differences in the relationship between self-esteem and aggression in young people leaving care
Young people in care are known to have high levels of aggressive behaviors and high levels of self-esteem, and these difficulties continue into adult life. Previous research has suggested that there is a relationship between self-esteem and aggression, although the nature of this relationship is unclear and possible differences due to gender have rarely been explored. Therefore, the relationships between different forms of self-esteem (global self-esteem, social rank, social fit, and attractiveness) and aggression were investigated in a sample of young care-leavers. For men, high levels of social rank and high levels of attractiveness were predictive of aggression, whereas for women low levels of perceived social inclusion and low levels of attractiveness were predictive of aggression. These findings suggest that there are significant gender differences in the relationship between self-esteem and aggression in care-leavers and that using domain-specific measures of self-esteem provides a richer understanding of these relationships. They also suggest that a more targeted approach to intervention is needed
Effects of d-electrons in pseudopotential screened-exchange density functional calculations
We report a theoretical study on the role of shallow d states in the screened-exchange local density approximation (sX-LDA) band structure of binary semiconductor systems.We found that inaccurate pseudo-wavefunctions can lead to 1) an overestimation of the screened-exchange interaction betweenthe localized d states and the delocalized higher energy s and p states and 2) an underestimation of the screened-exchange interaction between the d states. The resulting sX-LDA band structures have substantially smaller band gaps compared with experiments. We correct the pseudo-wavefunctions of d states by including the semicore s and p states of the same shell in the valence states. The correction of pseudo-wavefunctions yields band gaps and d state binding energies in good agreement with experiments and the full potential linearized augmented plane wave sX-LDA calculations. Compared with the quasi-particle GW method, our sX-LDA results shows not only similar quality on the band gaps but also much better d state binding energies. Combined with its capability of ground state structure calculation, the sX-LDA is expected to be a valuable theoretical tool for the II-VI and III-V (especially the III-N) bulk semiconductors and nanostructure studies
Carbon superatom thin films
Assembling clusters on surfaces has emerged as a novel way to grow thin films
with targeted properties. In particular, it has been proposed from experimental
findings that fullerenes deposited on surfaces could give rise to thin films
retaining the bonding properties of the incident clusters. However the
microscopic structure of such films is still unclear. By performing quantum
molecular dynamics simulations, we show that C_28 fullerenes can be deposited
on a surface to form a thin film of nearly defect free molecules, which act as
carbon superatoms. Our findings help clarify the structure of disordered small
fullerene films and also support the recently proposed hyperdiamond model for
solid C_28.Comment: 13 pages, RevTeX, 2 figures available as black and white PostScript
files; color PostScript and/or gif files available upon reques
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Effects of d-electrons in pseudopotential screened-exchange density functional calculations
We report a theoretical study on the role of shallow d states in the screened-exchange local density approximation (sX-LDA) band structure of binary semiconductor systems. We found that the inaccurate pseudo-wavefunctions can lead to (1) an overestimation of the screened-exchange interaction between the localized d states and the delocalized higher energy s and p states and (2) an underestimation of the screened-exchange interaction between the d states. The resulting sX-LDA band structures have substantially smaller band gaps compared with experiments. We correct the pseudo-wavefunctions of d states by including the semicore s and p states of the same shell in the valence states. The correction of pseudo-wavefunctions yields band gaps and the d state binding energy with good agreements with experiments and the full potential linearized augmented planewave (FLAPW) calculations. Compared with the quasi-particle GW method, our sX-LDA results shows not only similar quality on the band gaps but also much better d state binding energy. Combined with its capability of ground state structure calculation, the sX-LDA is expected to be a valuable theoretical tool for the II-VI and III-V (especially the III-N) bulk semiconductors and nanostructure studies
A Comparison of Delayed Self-Heterodyne Interference Measurement of Laser Linewidth Using Mach-Zehnder and Michelson Interferometers
Linewidth measurements of a distributed feedback (DFB) fibre laser are made using delayed self heterodyne interferometry (DHSI) with both Mach-Zehnder and Michelson interferometer configurations. Voigt fitting is used to extract and compare the Lorentzian and Gaussian linewidths and associated sources of noise. The respective measurements are wL (MZI) = (1.6 ± 0.2) kHz and wL (MI) = (1.4 ± 0.1) kHz. The Michelson with Faraday rotator mirrors gives a slightly narrower linewidth with significantly reduced error. This is explained by the unscrambling of polarisation drift using the Faraday rotator mirrors, confirmed by comparing with non-rotating standard gold coated fibre end mirrors
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