4,475 research outputs found
Conduction bands and invariant energy gaps in alkali bromides
Electronic structure calculations of the alkali bromides LiBr, NaBr, KBr, RbBr and CsBr are reported. It is shown that the conduction band has primarily bromine character. The size of the band gaps of bromides and alkali halides in general is reinterpreted
Reversed spin polarization at the Co(001)-HfO2(001) interface
Ab initio electronic-structure calculations on the Co(001)-HfO2(001) interface are reported. The spin polarization of conduction electrons is positive at the interface, i.e., it is reversed with respect to the spin polarization in bulk Co. The electronic structure is very sensitive to the interface structure; without atomic relaxations the reversed spin polarization is not found. The possible relation with spin-polarized tunneling and magnetoresistance is discussed
Black Holes and Calogero Models
We argue that the large limit of the -particle
superconformal Calogero model provides a microscopic description of the extreme
Reissner-Nordstr{\"o}m black hole in the near-horizon limit.Comment: Revtex 5pp. Revision includes improved discussion of entropy and
includes an additional referenc
Anomalous behavior of the semiconducting gap in WO3 from first-principles calculations
Several crystal structures of tungsten trioxide have been studied with a first-principles pseudopotential method. The electronic band gap increases significantly with the distortion of the octahedra that are the building blocks of the various crystal structures. Moreover, the tilting of the octahedra in the more complex structures leads to a strong increase of the gap upon compression
Does a surface attached globule phase exist ?
A long flexible neutral polymer chain immersed in a poor solvent and
interacting with an impenetrable attractive surface exhibits a phase known as
surface attached globule ({\bf SAG}) in addition to other adsorbed and desorbed
phases. In the thermodynamic limit, the {\bf SAG} phase has the same free
energy per monomer as the globular phase, and the transition between them is a
surface transition. We have investigated the phase diagrams of such a chain in
both two- and three- dimensions and calculated the distribution of monomers in
different domains of the phase diagram.Comment: 7 pages, 7 postscript figure
Evaluation of Labeling Strategies for Rotating Maps
We consider the following problem of labeling points in a dynamic map that
allows rotation. We are given a set of points in the plane labeled by a set of
mutually disjoint labels, where each label is an axis-aligned rectangle
attached with one corner to its respective point. We require that each label
remains horizontally aligned during the map rotation and our goal is to find a
set of mutually non-overlapping active labels for every rotation angle so that the number of active labels over a full map rotation of
2 is maximized. We discuss and experimentally evaluate several labeling
models that define additional consistency constraints on label activities in
order to reduce flickering effects during monotone map rotation. We introduce
three heuristic algorithms and compare them experimentally to an existing
approximation algorithm and exact solutions obtained from an integer linear
program. Our results show that on the one hand low flickering can be achieved
at the expense of only a small reduction in the objective value, and that on
the other hand the proposed heuristics achieve a high labeling quality
significantly faster than the other methods.Comment: 16 pages, extended version of a SEA 2014 pape
Blood clearance and tissue distribution of PEGylated and non-PEGylated gold nanorods after intravenous administration in rats\ud
Aims: To develop and determine the safety of gold nanorods, whose aspect ratios can be tuned to obtain plasmon peaks between 650 and 850 nm, as contrast enhancing agents for diagnostic and therapeutic applications. Materials & methods: In this study we compared the blood clearance and tissue distribution of cetyl trimethyl ammonium bromide (CTAB)-capped and polyethylene glycol (PEG)-coated gold nanorods after intravenous injection in the tail vein of rats. The gold content in blood and various organs was measured quantitatively with inductively coupled plasma mass spectrometry. Results & discussion: The CTAB-capped gold nanorods were almost immediately (<15 min) cleared from the blood circulation whereas the PEGylation of gold nanorods resulted in a prolonged blood circulation with a half-life time of 19 h and more wide spread tissue distribution. While for the CTAB-capped gold nanorods the tissue distribution was limited to liver, spleen and lung, the PEGylated gold nanorods also distributed to kidney, heart, thymus, brain and testes. PEGylation of the gold nanorods resulted in the spleen being the organ with the highest exposure, whereas for the non-PEGylated CTAB-capped gold nanorods the liver was the organ with the highest exposure, per gram of organ. Conclusion: The PEGylation of gold nanorods resulted in a prolongation of the blood clearance and the highest organ exposure in the spleen. In view of the time frame (up to 48 h) of the observed presence in blood circulation, PEGylated gold nanorods can be considered to be promising candidates for therapeutic and diagnostic imaging purpose
Pellicle ultrastructure demonstrates that Moyeria is a fossil euglenid
An earlier proposal of euglenid affinity for the acritarch Moyeria was based primarily on the pattern of bi-helical striate ornamentation as seen in scanning electron microscopy and light microscopy. Examination of specimens using transmission electron microscopy reveals that the ‘striae’ are actually integral components of the microfossil wall itself, corresponding to the pellicle strips of some euglenid species today. A Silurian specimen from Scotland preserves an articulated wall composed of thickened arches and thinner U-shaped interconnecting segments paralleling that seen in some modern photosynthetic euglenids. A second specimen from the Moyeria holotype section (Silurian of New York State) shows fused articulation, again compatible with some extant euglenids. This evidence is sufficient to transfer Moyeria out of the Incertae sedis group, Acritarcha, and into the Euglenida. This proposal helps establish the morphological basis for the recognition of euglenid microfossils and ultimately provides evidence of a lengthy fossil record of the eukaryotic supergroup Excavata
Non-Abelian Einstein-Born-Infeld Black Holes
We construct regular and black hole solutions in SU(2) Einstein-Born-Infeld
theory. These solutions have many features in common with the corresponding
SU(2) Einstein-Yang-Mills solutions. In particular, sequences of neutral
non-abelian solutions tend to magnetically charged limiting solutions, related
to embedded abelian solutions. Thermodynamic properties of the black hole
solutions are addressed.Comment: LaTeX, 14 pages, 6 postscript figures; typos corrected in reference
Membrane tension and manifest IIB S-duality
A manifestly S-dual, and `12 dimensional', IIB superstring action with an
Sl(2;\bR) doublet of `Born-Infeld' fields is presented. The M-theory origin
of the 12th dimension is the M-2-brane tension, which can be regarded as the
flux of a 3-form worldvolume field strength. The latter is required by the fact
that the M-2-brane can have a boundary on an M-5-brane.Comment: 10 pp. Phyzxx. Typos corrected. Some points clarified. Some refs.
added (Yesterday's revised version wasn't
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