Role of quantum nuclei and local fields in the x-ray absorption spectra of water and ice

We calculate the x-ray absorption spectra of liquid water at ambient conditions and of hexagonal ice close to melting, using a static GW approach that includes approximately local field effects. Quantum dynamics of the nuclei is taken into account by averaging the absorption cross section over molecular configurations generated by path integral simulations. We find that inclusion of quantum disorder is essential to bring the calculated spectra in close agreement with experiment. In particular, the intensity of the pre-edge feature, a spectral signature of broken and distorted hydrogen bonds, is accurately reproduced, in water and ice, only when quantum nuclei are considered. The effect of the local fields is less important but non negligible, particularly in ice

DECISION SUPPORT SYSTEMS: ISSUES AND PERSPECTIVES

Information Systems Working Papers Serie

Estudo comparativo de dois métodos de arraste principal do desbaste de Pinus taeda L.

Desempenho e custos na operação de arraste principal de dois tratores agrícolas com implementos diferentes foram submetidos a uma análise crítica, em uma plantação de Pinus taeda, com nove anos de idade e desbastada de forma sistemática e seletiva. A pesquisa foi instalada na Fazenda Monte Alegre, município de Telêmaco Borba, PR. Foram testados tratores do tipo MF 265 e os seguintes implementos de arraste: a) barra com fendas para engatar correntes, de segurar feixes de fustes, e b) pinça hidráulica traseira e lâmina hidráulica na frente. Sob as mesmas condições de distância e volume arrastado, os rendimentos foram similares, porém apresentaram grandes diferenças, quando baseados em volumes médios da carga. O trator com barra e correntes apresentou um volume médio de 0,8 m3 por ciclo e, numa distância média de 200 m, um rendimento de 6,85 m3/h, a um custo de Cr$60,80/m3. O trator com pinça hidráulica e lâmina dianteira, sob as mesmas condições de arraste, porém com um volume médio por ciclo de 0,5 m3, atingiu um rendimento de 5,39 m3/h, a um custo de Cr$ 82,10/m3. Sob as condições testadas, convém utilizar o trator com barra quando houver disponibilidade de mão-de-obra, pois arrasta maior volume de madeira por unidade de tempo a um custo mais baixo e com um grau de mecanização menor, portanto menos susceptível a falhas mecânicas. A exigência de maior tempo de oficina, com consertos e manutenção, em função da necessidade do equipamento, reduz a produção média anual em 35%, aproximadamente, no caso do trator com pinça. Detectaram-se, em ambos os métodos, grandes possibilidades de racionalização e, por conseguinte, de redução dos custos de arraste entre 24 e 27%

A Workflow-centric Study of Organizational Knowledge Distribution

Organizations require mechanisms to efficiently distribute knowledge such as news releases, seminar announcements, and memos. While the machinery for information storage, manipulation. and retrieval exists, research dealing directly with knowledge distribution in an organizational context is scarce. In this paper, we address this need by first examining the pros and cons of the conventional "mailing lists" approach and then proposing new workflow mechanisms that improve the efficiency and effectiveness of knowledge distribution. The main contributions of this study include: (I) a workflow perspective on organizational knowledge distribution. (2) workflow analysis of two new knowledge distribution methods based on dynamic mailing lists and profile matching, respectively, and (3) a new way of matching knowledge supply and demand that extends existing information filtering algorithms.Information Systems Working Papers Serie

X-Ray Detection of Transient Magnetic Moments Induced by a Spin Current in Cu

We have used a MHz lock-in x-ray spectro-microscopy technique to directly detect changes of magnetic moments in Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x-rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of $3\times 10^{-5}$ $\mu_\mathrm{B}$ on Cu atoms within the bulk of the 28 nm thick Cu film due to spin-accumulation. The moment value is compared to predictions by Mott's two current model. We also observe that the hybridization induced existing magnetic moments on Cu interface atoms are transiently increased by about 10% or $4\times 10^{-3}$ $\mu_\mathrm{B}$. This reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow

Observation of Magnetic Edge State and Dangling Bond State on Nanographene in Activated Carbon Fibers

The electronic structure of nanographene in pristine and fluorinated activated carbon fibers (ACFs) have been investigated with near-edge x-ray absorption fine structure (NEXAFS) and compared with magnetic properties we reported on previously. In pristine ACFs in which magnetic properties are governed by non-bonding edge states of the \pi-electron, a pre-peak assigned to the edge state was observed below the conduction electron {\pi}* peak close to the Fermi level in NEXAFS. Via the fluorination of the ACFs, an extra peak, which was assigned to the \sigma-dangling bond state, was observed between the pre-peak of the edge state and the {\pi}* peak in the NEXAFS profile. The intensities of the extra peak correlate closely with the spin concentration created upon fluorination. The combination of the NEXAFS and magnetic measurement results confirms the coexistence of the magnetic edge states of \pi-electrons and dangling bond states of \sigma-electrons on fluorinated nanographene sheets.Comment: 4 figures, to appear in Phys. Rev.