468 research outputs found
Re II and Other Exotic Spectra in HD 65949
Powerful astronomical spectra reveal an urgent need for additional work on
atomic lines, levels, and oscillator strengths. The star HD 65949 provides some
excellent examples of species rarely identified in stellar spectra. For
example, the Re II spectrum is well developed, with 17 lines between 3731 and
4904 [A], attributed wholly or partially to Re II. Classifications and
oscillator strengths are lacking for a number of these lines. The spectrum of
Os II is well identified. Of 14 lines attributed wholly or partially to Os II,
only one has an entry in the VALD database. We find strong evidence that Te II
is present. There are NO Te II lines in the VALD database. Ru II is clearly
present, but oscillator strengths for lines in the visual are lacking. There is
excellent to marginal evidence for a number of less commonly identified
species, including Kr II, Nb II, Sb II, Xe II, Pr III, Ho III, Au II, and Pt II
(probably Pt-198), to be present in the spectrum of HD 65949. The line Hg II at
3984 [A] is of outstanding strength, and all three lines of Multiplet 1 of Hg I
are present, even though the surface temperature of HD 65949 is relatively
high. Finally, we present the case of an unidentified, 24 [mA], line at 3859.63
[A], which could be the same feature seen in magnetic CP stars. It is typically
blended with a putative U II line used in cosmochronology.Comment: ASOS9 Poster (Lund, Sweden, August 2007), to be published in Journal
of Physics: Conference Series (JPCS), 6 pages 1 figur
An evaluation of 14C age relationships between co-occurring foraminifera, alkenones, and total organic carbon in continental margin sediments
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA1016, doi:10.1029/2004PA001103.Radiocarbon age relationships between co-occurring planktic foraminifera, alkenones and
total organic carbon in sediments from the continental margins of Southern Chile, Northwest
Africa and the South China Sea were compared with published results from the Namibian
margin. Age relationships between the sediment components are site-specific and relatively
constant over time. Similar to the Namibian slope, where alkenones have been reported to be
1000 to 4500 years older than co-occurring foraminifera, alkenones were significantly (~1000
yrs) older than co-occurring foraminifera in the Chilean margin sediments. In contrast,
alkenones and foraminifera were of similar age (within 2σ error or better) in the NW African
and South China Sea sediments. Total-organic-matter and alkenone ages were similar off
Namibia (age difference TOC-alkenones: 200-700 years), Chile (100-450 years), and NW
Africa (360-770 years), suggesting minor contributions of pre-aged terrigenous material. In
the South China Sea total organic carbon is significantly (2000-3000 yrs) older due to greater
inputs of pre-aged terrigenous material.
Age offsets between alkenones and planktic foraminifera are attributed to lateral advection
of organic matter. Physical characteristics of the depositional setting, such as sea-floor
morphology, shelf width, and sediment composition, may control the age of co-occurring
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sediment components. In particular, offsets between alkenones and foraminifera appear to be
greatest in deposition centers in morphologic depressions. Aging of organic matter is
promoted by transport. Age offsets are correlated with organic richness, suggesting that
formation of organic aggregate is a key process.GM and MK acknowledge financial support from the WHOI postdoctoral scholarship program. This work was funded by NSF grant OCE-0327405
Optical emission spectroscopy of metal-halide lamps: Radially resolved atomic state distribution functions of Dy and Hg
Absolute line intensity measurements are performed on a metal-halide lamp. Several transitions of atomic and ionic Dy and atomic Hg are measured at different radial positions from which we obtain absolute atomic and ionic Dy intensity profiles. From these profiles we construct the radially resolved atomic state distribution function (ASDF) of the atomic and ionic Dy and the atomic Hg. From these ASDFs several quantities are determined as functions of radial position, such as the (excitation) temperature, the ion ratio Hg^+/Dy^+, the electron density, the ground state, and the totaldensity of Dy atoms and ions. Moreover, these ASDFs give us insight about the departure from equilibrium. The measurements show a hollow density profile for the atoms and the ionization of atoms in the center. In the outer parts of the lamp molecules dominate
Quantum transport through a DNA wire in a dissipative environment
Electronic transport through DNA wires in the presence of a strong
dissipative environment is investigated. We show that new bath-induced
electronic states are formed within the bandgap. These states show up in the
linear conductance spectrum as a temperature dependent background and lead to a
crossover from tunneling to thermal activated behavior with increasing
temperature. Depending on the strength of the electron-bath coupling, the
conductance at the Fermi level can show a weak exponential or even an algebraic
length dependence. Our results suggest a new environmental-induced transport
mechanism. This might be relevant for the understanding of molecular conduction
experiments in liquid solution, like those recently performed on poly(GC)
oligomers in a water buffer (B. Xu et al., Nano Lett 4, 1105 (2004)).Comment: 5 pages, 3 figure
Ab-initio study of model guanine assemblies: The role of pi-pi coupling and band transport
Several assemblies of guanine molecules are investigated by means of
first-principle calculations. Such structures include stacked and
hydrogen-bonded dimers, as well as vertical columns and planar ribbons,
respectively, obtained by periodically replicating the dimers. Our results are
in good agreement with experimental data for isolated molecules, isolated
dimers, and periodic ribbons. For stacked dimers and columns, the stability is
affected by the relative charge distribution of the pi orbitals in adjacent
guanine molecules. pi-pi coupling in some stacked columns induces dispersive
energy bands, while no dispersion is identified in the planar ribbons along the
connections of hydrogen bonds. The implications for different materials
comprised of guanine aggregates are discussed. The bandstructure of dispersive
configurations may justify a contribution of band transport (Bloch type) in the
conduction mechanism of deoxyguanosine fibres, while in DNA-like configurations
band transport should be negligible.Comment: 21 pages, 6 figures, 3 tables, to be published in Phys. Rev.
Designing organometallic compounds for catalysis and therapy
Bioorganometallic chemistry is a rapidly developing area of research. In recent years organometallic compounds have provided a rich platform for the design of effective catalysts, e.g. for olefin metathesis and transfer hydrogenation. Electronic and steric effects are used to control both the thermodynamics and kinetics of ligand substitution and redox reactions of metal ions, especially Ru II. Can similar features be incorporated into the design of targeted organometallic drugs? Such complexes offer potential for novel mechanisms of drug action through incorporation of outer-sphere recognition of targets and controlled activation features based on ligand substitution as well as metal- and ligand-based redox processes. We focus here on η 6-arene, η 5-cyclopentadienyl sandwich and half-sandwich complexes of Fe II, Ru II, Os II and Ir III with promising activity towards cancer, malaria, and other conditions. © 2012 The Royal Society of Chemistry
GSK3β inhibition blocks melanoma cell/host interactions by downregulating N-cadherin expression and decreasing FAK phosphorylation.
This study addresses the role of glycogen synthase kinase (GSK)-3β signaling in the tumorigenic behavior of melanoma. Immunohistochemical staining revealed GSK3β to be focally expressed in the invasive portions of 12 and 33% of primary and metastatic melanomas, respectively. GSK3 inhibitors and small interfering RNA (siRNA) knockdown of GSK3β were found to inhibit the motile behavior of melanoma cells in scratch wound, three-dimensional collagen-implanted spheroid, and modified Boyden chamber assays. Functionally, inhibition of GSK3β signaling was found to suppress N-cadherin expression at the messenger RNA and protein levels, and was associated with decreased expression of the transcription factor Slug. Pharmacological and genetic ablation of GSK3β signaling inhibited the adhesion of melanoma cells to both endothelial cells and fibroblasts and prevented transendothelial migration, an effect rescued by the forced overexpression of N-cadherin. A further role for GSK3β signaling in invasion was suggested by the ability of GSK3β inhibitors and siRNA knockdown to block phosphorylation of focal adhesion kinase (FAK) and increase the size of focal adhesions. In summary, we have, to our knowledge, demonstrated a previously unreported role for GSK3β in modulating the motile and invasive behavior of melanoma cells through N-cadherin and FAK. These studies suggest the potential therapeutic utility of inhibiting GSK3β in defined subsets of melanoma
HD 65949: Rosetta Stone or Red Herring
HD 65949 is a late B star with exceptionally strong Hg II at 3984[A], but it
is not a typical HgMn star. The Re II spectrum is of extraordinary strength.
Abundances, or upper limits are derived here for 58 elements based on a model
with Teff = 13100K, and log(g) = 4.0. Even-Z elements through nickel show minor
deviations from solar abundances. Anomalies among the odd-Z elements through
copper are mostly small. Beyond the iron peak, a huge scatter is found. The
abundance pattern of the heaviest elements resembles the N=126 r-process peak
of solar material, though not in detail. We find a significant correlation of
the abundance excesses with second ionization potentials for elements with Z >
30. This indicates the relevance of photospheric or near-photospheric
processes. We explore a model with mass accretion of exotic material followed
by the more commonly accepted differentiation by diffusion. That model leads to
a number of predictions which challenge future work.
Likely primary and secondary masses are near 3.3 and 1.6 M(solar), with a
separation of ca. 0.25 AU. New atomic structure calculations are presented in
two appendices.Comment: Accepted by MNRAS: 16 pages, 5 figure
Green function techniques in the treatment of quantum transport at the molecular scale
The theoretical investigation of charge (and spin) transport at nanometer
length scales requires the use of advanced and powerful techniques able to deal
with the dynamical properties of the relevant physical systems, to explicitly
include out-of-equilibrium situations typical for electrical/heat transport as
well as to take into account interaction effects in a systematic way.
Equilibrium Green function techniques and their extension to non-equilibrium
situations via the Keldysh formalism build one of the pillars of current
state-of-the-art approaches to quantum transport which have been implemented in
both model Hamiltonian formulations and first-principle methodologies. We offer
a tutorial overview of the applications of Green functions to deal with some
fundamental aspects of charge transport at the nanoscale, mainly focusing on
applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references,
submitted to Springer series "Lecture Notes in Physics
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