154 research outputs found
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
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 () 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
Regional Nerve Block of the Temporomandibular Joint Capsule: A Technique for Clinical Research and Differential Diagnosis
In previous studies in which regional anesthesia of the temporomandibular joint capsule was used to examine the role of the joint in mandibular movement and distinguish it from muscle control, the anesthetic techniques used have not been satisfactorily described. The accuracy of the injeetion technique described in this paper was determined by dissection and radiographic examination of fixed and fresh specimens. Using this technique, trial patient studies were made using an anesthetic solution to which a radiopaque medium was added. Radiographic examination of the patients affirmed the location of the injected material, while clinical assessment determined its functional effectiveness. Using the described technique, anesthetic solution was accurately and reproducibly introduced posteriorly and laterally to the temporomandibular joint to achieve anesthesia of the joint.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67376/2/10.1177_00220345800590110101.pd
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
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 approximation of many-body theory.Comment: 17 pages, 7 figures, to appear in J Phys-Condens Ma
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
- …