Fast vibrational calculation of anharmonic OH-stretch frequencies for two low-energy noradrenaline conformers

We introduce a new reduced-coupling technique to accelerate direct calculations of a selected number of vibrational frequencies in large molecular systems. Our method combines the advantages of the single-to-all correlation-corrected vibrational self-consistent field (STA-CC-VSCF) approach [D. M. Benoit, J. Chem. Phys. 125, 244110 (2006)] with those of the fast-CC-VSCF technique [D. M. Benoit, J. Chem. Phys. 120, 562 (2004)] and allows the ab initio calculation of only the relevant parts of the required potential energy surface (PES). We demonstrate, using a set of five aliphatic alcohol molecules, that the new fast-STA-CC-VSCF method is accurate and leads to very substantial time gains for the computations of the PES. We then use the fast-STA-CC-VSCF method to accelerate the computation of the OH-stretch and NH-stretch frequencies of the two lowest-energy conformers of noradrenaline, namely, AG1a and GG1a. Our new approach enables us to run the calculation 89 times faster than the standard CC-VSCF technique and makes it possible to use a high-level MP2/TZP description of the PES. We demonstrate that the influence of the strong mode-mode couplings is crucial for a realistic description of the particular OH-stretch vibrational signature of each conformer. Finally, of the two possible low-energy conformers, we identify AG1a as the one most likely to have been observed in the experiments of Snoek [Mol. Phys. 101, 1239 (2003)]

Vibrational signature of a single water molecule adsorbed on Pt(111): toward a reliable anharmonic description

In this study, we present a thorough benchmarking of our direct anharmonic vibrational variation-perturbation approach for adsorbed molecules on surfaces. We then use our method to describe the vibrational structure of a water molecule adsorbed on a Pt(111) surface and compare our results with the available experimental data. By using an explicitly correlated hybrid method to describe the molecule-surface interaction, we improve on the initial periodic PBE/DZP potential energy landscape and obtain vibrational frequencies that are of near-experimental accuracy. We introduce an implementation of anharmonic z-polarized IR intensity calculation and explain the absence of antisymmetric O-H stretch in the experimental data for the adsorbed water molecule, while the symmetric O-H stretch is predicted to be visible

Measuring cell adhesion forces with the atomic force microscope at the molecular level

In the past 25 years many techniques have been developed to characterize cell adhesion and to quantify adhesion forces. Atomic force microscopy (AFM) has been used to measure forces in the pico-newton range, an experimental technique known as force spectroscopy. We modified such an AFM to measure adhesion forces between live cells or between cells and surfaces. This strategy required functionalizing the surface of the sensors for immobilizing the cell. We used Dictyostelium discoideum cells which respond to starvation by surface expression of the adhesion molecule csA and consequent aggregation to measure the adhesion force of a single csA-csA bond. Relevant experimental parameters include the duration of contact between the interacting surfaces, the force against which this contact is maintained, the number and specificity of interacting adhesion molecules and the constituents of the medium in which the interaction occurs. This technology also permits the measurement of the viscoelastic properties of single cells or cell layers. Copyright (C) 2002 S, Karger AG, Basel

The nature and role of the gold-krypton interactions in small neutral gold clusters

© 2015 American Chemical Society. We investigate the nature and role of krypton embedding in small neutral gold clusters. For some of these clusters, we observe a particular site-dependent character of the Kr binding that does not completely follow the criterion of binding at low-coordinated sites, widely accepted for interaction of a noble gas with closed-shell metal systems such as metal surfaces. We aim at understanding the effect of low dimensionality and open-shell electronic structure of the odd-numbered clusters on the noble gas-metal cluster interaction. First, we investigate the role of attractive and repulsive forces, and the frontier molecular orbitals. Second, we investigate the Au-Kr interaction in terms of reactivity and bonding character. We use a reactivity index derived from Fukui formalism, and criteria provided by the electron localization function (ELF), in order to classify the type of bonding. We carry out this study on the minimum energy structures of neutral gold clusters, as obtained using pseudo potential plane-wave density functional theory (DFT). A model is proposed that includes the effect of attractive electrostatic, van der Waals and repulsive forces, together with effects originating from orbital overlap. This satisfactorily explains minimum configurations of the noble gas-gold cluster systems, the site preference of the noble gas atoms, and changes in electronic properties

Cereal Supplies in Rural Families of the Senegalese Groundnut Basin. Who is Responsible for Meeting Family Food Needs?

In the traditional operation of production-consumption groups in rural areas of Senegal, the group chief, or Borom njël, has a social duty to make sure family food needs are met. His ability to do this is supported by certain social rules governing these groups, and by a favourable environment. However, various changes have now adversely affected the environment. These changes prompted us to assess the Borom njël's current ability to go on playing his social rule as a food provider. From data collected in two villages of the Senegalese Groundnut Basin, using multivariate analysis, we identified three production-consumption group profiles according to how the Borom njël ensured main cereal supplies: (i°) market purchase with migrants' remittances; (ii°) home production and (iii°) market purchase with own resources. The ability of the Borom njël to ensure cereal supplies differed according to the profile. We used a multivariate logit model to study the determinants affecting the Borom njël's ability to ensure cereal supplies for the production-consumption group. We found that physical assets and wage labour employment increased this ability. We also found that agricultural income, including livestock, was positively correlated to the likelihood of the Borom njël successfully ensuring cereal supplies, particularly those depending heavily on own production. Additional income earned by the Borom njël from non-agricultural activity had the same positive effect, particularly when ensuring cereals provision through market purchase. We end with some thoughts on the increasing reliance of Borom njëls on migrants' remittances to ensure that family cereal needs are met. ...French Abstract : Dans le passé, le fonctionnement traditionnel des populations rurales du Bassin arachidier Sénégalais regroupées au sein de groupes de production-consommation, reposait sur un système de droits et obligations gouvernant l'allocation des ressources en terre, en travail et en nourriture entre les différents membres de groupes familiaux. Ainsi, le chef du groupe familial de production-consommation, encore appelé Borom njël en wolof, avait l'obligation de satisfaire les besoins alimentaires des autres membres essentiellement, grâce à sa production agricole. En contrepartie ceux-ci travaillaient sur ses parcelles alors que chaque adulte dépendant avait un droit de culture sur une parcelle d'arachide dont il gardait les revenus. Vu tous les changements qui ont affecté le contexte socio-économique de ces populations rurales, il est devenu plus difficile pour les Borom njël d'honorer leurs obligations. Et, nous nous sommes plus particulièrement intéressés à la capacité du Borom njël à assurer l'approvisionnement en céréales et satisfaire les besoins alimentaires des différents membres. A partir de données collectées dans deux villages du Bassin Arachidier, nous avons procédé à une analyse multivariée qui nous a permis d'identifier trois profils de groupes de production-consommation, suivant que les besoins alimentaires sont principalement assurés avec: i°) les achats sur le marché grâce aux transferts d'argent des migrants ; ii°) la production agricole du Borom njël permettant ainsi l'autoconsommation ; iii°) les achats sur le marché grâce aux revenus du Borom njël. Ensuite, nous avons utilisé un modèle de logit multivarié pour étudier les déterminants qui affectent la capacité du Borom njël à assurer l'approvisionnement en céréales du groupe de production-consommation. Les résultats montrent que la possession d'actifs physiques ainsi que l'emploi de salariés agricoles augmentent cette capacité à assurer l'approvisionnement en céréales. En outre, le revenu agricole -y compris celui de l'élevage- est positivement corrélé à la probabilité du Borom njël à assurer l'approvisionnement en céréales, particulièrement pour ceux qui dépendent de leurs propres productions agricoles. Quant aux revenus non agricoles obtenus grâce à la diversification locale, ils augmentent aussi cette probabilité, mais uniquement à l'intérieur des groupes où l'approvisionnement en céréales est assuré grâce aux achats sur le marché avec les revenus du Borom njël.CEREAL SUPPLIES; CONSUMPTION-PRODUCTION GROUPS; MULTINOMIAL LOGIT; GROUNDNUT BASIN; SENEGAL

Minority-carrier dynamics in semiconductors probed by two-photon microscopy

Two-photon time-resolved photoluminescence has been recently applied to various semiconductor devices to determine carrier lifetime and surface recombination velocities. So far the theoretical modeling activity has been mainly limited to the commonly used one-photon counterpart of the technique. Here we provide the analytical solution to a 3D diffusion equation that describes two-photon microscopy in the low-injection regime. We focus on a system with a single buried interface with enhanced recombination, and analyze how transport, bulk and surface recombinations influence photoluminescence decays. We find that bulk measurements are dominated by diffusion at short times and by bulk recombination at long times. Surface recombination modifies bulk signals when the optical spot is less than a diffusion length away from the probed interface. In addition, the resolution is increased as the spot size is reduced, which however makes the signal more sensitive to diffusion.Comment: 4 pages, 4 figures, IEEE PVSC 2016 proceeding pape