Forces on Dust Grains Exposed to Anisotropic Interstellar Radiation Fields

Grains exposed to anisotropic radiation fields are subjected to forces due to the asymmetric photon-stimulated ejection of particles. These forces act in addition to the ``radiation pressure'' due to absorption and scattering. Here we model the forces due to photoelectron emission and the photodesorption of adatoms. The ``photoelectric'' force depends on the ambient conditions relevant to grain charging. We find that it is comparable to the radiation pressure when the grain potential is relatively low and the radiation spectrum is relatively hard. The calculation of the ``photodesorption'' force is highly uncertain, since the surface physics and chemsitry of grain materials are poorly understood at present. For our simple yet plausible model, the photodesorption force dominates the radiation pressure for grains with size >~0.1 micron exposed to starlight from OB stars. We find that the anisotropy of the interstellar radiation field is ~10% in the visible and ultraviolet. We estimate size-dependent drift speeds for grains in the cold and warm neutral media and find that micron-sized grains could potentially be moved across a diffuse cloud during its lifetime.Comment: LaTeX(41 pages, 19 figures), submitted to Ap

Role of bulk and surface phonons in the decay of metal surface states

We present a comprehensive theoretical investigation of the electron-phonon contribution to the lifetime broadening of the surface states on Cu(111) and Ag(111), in comparison with high-resolution photoemission results. The calculations, including electron and phonon states of the bulk and the surface, resolve the relative importance of the Rayleigh mode, being dominant for the lifetime at small hole binding energies. Including the electron-electron interaction, the theoretical results are in excellent agreement with the measured binding energy and temperature dependent lifetime broadening.Comment: 4 pages, 3 figure

Model study of adsorbed metallic quantum dots: Na on Cu(111)

We model electronic properties of the second monolayer Na adatom islands (quantum dots) on the Cu(111) surface covered homogeneously by the first Na monolayer. An axially-symmetric three-dimensional jellium model, taking into account the effects due to the first Na monolayer and the Cu substrate, has been developed. The electronic structure is solved within the local-density approximation of the density-functional theory using a real-space multigrid method. The model enables the study of systems consisting of thousands of Na-atoms. The results for the local density of states are compared with differential conductance ($dI/dV$) spectra and constant current topographs from Scanning Tunneling Microscopy.Comment: 10 pages, 8 figures. For better quality figures, download http://www.fyslab.hut.fi/~tto/cylart1.pd

Neutron reflection study of the adsorption of the phosphate surfactant NaDEHP onto alumina from water.

The adsorption of a phosphorus analogue of the surfactant AOT, sodium bis(2-ethylhexyl) phosphate (NaDEHP), at the water/alumina interface is described. The material is found to adsorb as an essentially water-free bilayer from neutron reflection measurements. This is similar to the behavior of AOT under comparable conditions, although AOT forms a thicker, more hydrated layer. The NaDEHP shows rather little variation with added salt, but a small thickening of the layer on increasing the pH, in contrast to the behavior of AOT.We thank BP plc and EPSRC for financial support for this work as well as the ISIS and ILL staff and scientists for the allocation of beam time and technical assistance with NR measurements. We also appreciate Chris Sporikou at Department of Chemistry, University of Cambridge, for help with the surfactant synthesis.This is the final version of the article. It first appeared at http://dx.doi.org/10.1021/la504837

Theory of inelastic lifetimes of surface-state electrons and holes at metal surfaces

After the early suggestion by John Pendry to probe unoccupied bands at surfaces through the time reversal of the photoemission process, the inverse-photoemission technique yielded the first conclusive experimental evidence for the existence of image-potential bound states at metal surfaces and has led over the last two decades to an active area of research in condensed-matter and surface physics. Here we describe the current status of the many-body theory of inelastic lifetimes of these image-potential states and also the Shockley surface states that exist near the Fermi level in the projected bulk band gap of simple and noble metals. New calculations of the self-energy and lifetime of surface states on Au surfaces are presented as well, by using the $GW\Gamma$ approximation of many-body theory.Comment: 17 pages, 7 figures, to appear in J Phys-Condens Ma

Incidence and trends of low back pain hospitalisation during military service – An analysis of 387,070 Finnish young males

<p>Abstract</p> <p>Background</p> <p>There is evidence that low back pain (LBP) during young adulthood and military service predicts LBP later in life. The purpose of this study was to investigate the incidence and trends of LBP hospitalisation among Finnish military conscripts.</p> <p>Methods</p> <p>All male conscripts performing their compulsory military service during 1990–2002 were included in the study population. Altogether 387,070 military conscripts were followed throughout their six-to-twelve-month service period. Data on LBP hospitalisations were obtained from the National Hospital Discharge Register.</p> <p>Results</p> <p>Altogether 7,240 LBP hospitalisations were identified among 5,061 (1.3%) male conscripts during the study period. The event-based incidence of LBP hospitalisation was 27.0 (95% confidence interval (CI): 25.7–28.2). In most cases, the diagnosis was unspecified LBP (<it>n </it>= 5,141, 71%) followed by lumbar disc disorders (<it>n </it>= 2,069, 29%). Hospitalisation incidence due to unspecified LBP was 19.1 per 1,000 person-years (95% CI: 18.3 to 20.4), and 7.8 per 1,000 person-years (95% CI: 6.7 to 8.3) due to lumbar disc disorders. The incidence of unspecified LBP remained unaltered, while hospitalisation due to lumbar disc disorders declined from 1993 onwards.</p> <p>Conclusion</p> <p>Although conscripts accepted into military training pass physician-performed examinations as healthy, young adults, LBP hospitalisation causes significant morbidity during military service.</p

The formation of defect Complexes in a ZnO grain boundary

The microscopic properties a ZnO grain boundary containing extrinsic point defects are studied using a density functional computational approach. The results show that the grain boundary acts as a sink for native defects, such as the zinc vacancy and the oxygen interstitial, and also for bismuth substitutional impurities. The defects tend to accumulate at under-coordinated sites in the boundary core and prefer to form small clusters. In particular the segregation of Bi promotes the formation of the other native defects by lowering their formation energies in the boundary. Individually, the native defects and the Bi impurity do not produce deep interface states in the band gap which are electrically active. However, when the defects cluster to form a Bi zn -V zn -O i complex, new gap states are created of acceptor type. It is suggested that these new states are caused by defect interactions which compensate one another resulting in the depletion of an occupied impurity state and new bond formation. The results are discussed in terms of the Schottky barrier model commonly used to describe the electrical characteristics of ZnO varistors

Interaction of Moringa oleifera seed protein with a mineral surface and the influence of surfactants

The paper describes the adsorption of purified protein from seeds of Moringa olelfera to a sapphire interface and the effects of addition of the anionic surfactant sodium dodecylsulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). Neutron reflection was used to determine the structure and composition of interfacial layers adsorbed at the solid/solution interface. The maximum surface excess of protein was found to be about 5.3 mg m(-2). The protein does not desorb from the solid/liquid interface when rinsed with water. Addition of SDS increases the reflectivity indicating co-adsorption. It was observed that CTAB is able to remove the protein from the interface. The distinct differences to the behavior observed previously for the protein at the silica/water interface are identified. The adsorption of the protein to alumina in addition to other surfaces has shown why it is an effective flocculating agent for the range of impurities found in water supplies. The ability to tailor different surface layers in combination with various surfactants also offers the potential for adsorbed protein to be used in separation technologies