Density-functional-based predictions of Raman and IR spectra for small Si clusters

We have used a density-functional-based approach to study the response of silicon clusters to applied electric fields. For the dynamical response, we have calculated the Raman activities and infrared (IR) intensities for all of the vibrational modes of several clusters (SiN with N=3-8, 10, 13, 20, and 21) using the local density approximation (LDA). For the smaller clusters (N=3-8) our results are in good agreement with previous quantum-chemical calculations and experimental measurements, establishing that LDA-based IR and Raman data can be used in conjunction with measured spectra to determine the structure of clusters observed in experiment. To illustrate the potential of the method for larger clusters, we present calculated IR and Raman data for two low-energy isomers of Si10 and for the lowest-energy structure of Si13 found to date. For the static response, we compare our calculated polarizabilities for N=10, 13, 20, and 21 to recent experimental measurements. The calculated results are in rough agreement with experiment, but show less variation with cluster size than the measurements. Taken together, our results show that LDA calculations can offer a powerful means for establishing the structures of experimentally fabricated clusters and nanoscale systems

Theory for transport through a single magnetic molecule: Endohedral N@C60

We consider transport through a single N@C60 molecule, weakly coupled to metallic leads. Employing a density-matrix formalism we derive rate equations for the occupation probabilities of many-particle states of the molecule. We calculate the current-voltage characteristics and the differential conductance for N@C60 in a break junction. Our results reveal Coulomb-blockade behavior as well as a fine structure of the Coulomb-blockade peaks due to the exchange coupling of the C60 spin to the spin of the encapsulated nitrogen atom.Comment: 5 pages, 4 figures, v2: version as publishe

Negative differential resistance in molecular junctions: The effect of the electrodes electronic structure

We have carried out calculations of electron transport through a metal-molecule-metal junction with metal nanoclusters taking the part of electrodes. We show that negative differential resistance peaks could appear in the current-voltage curves. The peaks arise due to narrow features in the electron density of states of the metal clusters. The proposed analysis is based on the ab initio computations of the relevant wave functions and energies within the framework of the density functional theory using NRLMOL software package.Comment: 4 pages, 2 figures, added text

Effects of Caffeinated and Non-Caffeinated Gum on Premotor, Motor, and Overall Reaction Time

Chewing gum and caffeine when used independently and concurrently increase neural activity ultimately improving reaction time but less is known about how caffeinated gum influences distinct phases of the reaction time response. Physically active college females (n=14) completed a 60-second reaction time test on a visuomotor board under the following counterbalanced conditions: 1) Baseline, 2) Non-caffeinated gum, 3) Caffeinated gum (300 mg caffeine). Point of application #1: Chewing gum improved premotor reaction time compared to baseline, but caffeine did not provide additional benefit. Point of application #2: Neither non-caffeinated nor caffeinated gum improved motor reaction times from baseline. Point of application #3: Chewing gum improved overall reaction time compared to baseline, but caffeine did not provide additional benefit. Keywords: Chewing, Visuomotor, Visual processin

Discovering and verifying DNA polymorphisms in a mung bean [V. radiata (L.) R. Wilczek] collection by EcoTILLING and sequencing

<p>Abstract</p> <p>Background</p> <p><it>Vigna radiata</it>, which is classified in the family Fabaceae, is an important economic crop and a dietary staple in many developing countries. The species <it>radiata </it>can be further subdivided into varieties of which the variety <it>sublobata </it>is currently acknowledged as the putative progenitor of <it>radiata</it>. EcoTILLING was employed to identify single nucleotide polymorphisms (SNPs) and small insertions/deletions (INDELS) in a collection of <it>Vigna radiata </it>accessions.</p> <p>Findings</p> <p>A total of 157 DNA polymorphisms in the collection were produced from ten primer sets when using <it>V. radiata </it>var. <it>sublobata </it>as the reference. The majority of polymorphisms detected were found in putative introns. The banding patterns varied from simple to complex as the number of DNA polymorphisms between two pooled samples increased. Numerous SNPs and INDELS ranging from 4–24 and 1–6, respectively, were detected in all fragments when pooling <it>V. radiata </it>var. <it>sublobata </it>with <it>V. radiata </it>var. <it>radiata</it>. On the other hand, when accessions of <it>V. radiata </it>var. <it>radiata </it>were mixed together and digested with CEL I relatively few SNPs and no INDELS were detected.</p> <p>Conclusion</p> <p>EcoTILLING was utilized to identify polymorphisms in a collection of mung bean, which previously showed limited molecular genetic diversity and limited morphological diversity in the flowers and pod descriptors. Overall, EcoTILLING proved to be a powerful genetic analysis tool providing the rapid identification of naturally occurring variation.</p

Non-Compositional Term Dependence for Information Retrieval

Modelling term dependence in IR aims to identify co-occurring terms that are too heavily dependent on each other to be treated as a bag of words, and to adapt the indexing and ranking accordingly. Dependent terms are predominantly identified using lexical frequency statistics, assuming that (a) if terms co-occur often enough in some corpus, they are semantically dependent; (b) the more often they co-occur, the more semantically dependent they are. This assumption is not always correct: the frequency of co-occurring terms can be separate from the strength of their semantic dependence. E.g. "red tape" might be overall less frequent than "tape measure" in some corpus, but this does not mean that "red"+"tape" are less dependent than "tape"+"measure". This is especially the case for non-compositional phrases, i.e. phrases whose meaning cannot be composed from the individual meanings of their terms (such as the phrase "red tape" meaning bureaucracy). Motivated by this lack of distinction between the frequency and strength of term dependence in IR, we present a principled approach for handling term dependence in queries, using both lexical frequency and semantic evidence. We focus on non-compositional phrases, extending a recent unsupervised model for their detection [21] to IR. Our approach, integrated into ranking using Markov Random Fields [31], yields effectiveness gains over competitive TREC baselines, showing that there is still room for improvement in the very well-studied area of term dependence in IR

Quasi one dimensional 4^4He inside carbon nanotubes

We report results of diffusion Monte Carlo calculations for both $^4$He absorbed in a narrow single walled carbon nanotube (R = 3.42 \AA) and strictly one dimensional $^4$He. Inside the tube, the binding energy of liquid $^4$He is approximately three times larger than on planar graphite. At low linear densities, $^4$He in a nanotube is an experimental realization of a one-dimensional quantum fluid. However, when the density increases the structural and energetic properties of both systems differ. At high density, a quasi-continuous liquid-solid phase transition is observed in both cases.Comment: 11 pages, 3ps figures, to appear in Phys. Rev. B (RC

A critical assessment of the Self-Interaction Corrected Local Density Functional method and its algorithmic implementation

We calculate the electronic structure of several atoms and small molecules by direct minimization of the Self-Interaction Corrected Local Density Approximation (SIC-LDA) functional. To do this we first derive an expression for the gradient of this functional under the constraint that the orbitals be orthogonal and show that previously given expressions do not correctly incorporate this constraint. In our atomic calculations the SIC-LDA yields total energies, ionization energies and charge densities that are superior to results obtained with the Local Density Approximation (LDA). However, for molecules SIC-LDA gives bond lengths and reaction energies that are inferior to those obtained from LDA. The nonlocal BLYP functional, which we include as a representative GGA functional, outperforms both LDA and SIC-LDA for all ground state properties we considered.Comment: 14 pages, 5 figure