694 research outputs found
Ab initio correlation approach to a ferric wheel-like molecular cluster
We present an ab initio study of electronic correlation effects in a
molecular cluster derived from the hexanuclear ferric wheel
[LiFe6(OCH3)12-(dbm)6]PF6. The electronic and magnetic properties of this
cluster have been studied with all-electron Hartree-Fock, full-potential
density functional calculations and multi-reference second-order perturbation
theory. For different levels of correlation, a detailed study of the impact of
the electronic correlation on the exchange parameter was feasible. As the main
result, we found that the influence of the bridge oxygen atoms on the exchange
parameter is less intense than the influence of the apical ligand groups, which
is due to the geometry of the cluster. With respect to the cluster model
approach, the experimental value of the exchange parameter was affirmed.Comment: to be published in EPJ
Correlated ab-initio calculations for ground-state properties of II-VI semiconductors
Correlated ab-initio ground-state calculations, using relativistic
energy-consistent pseudopotentials, are performed for six II-VI semiconductors.
Valence () correlations are evaluated using the coupled cluster approach
with single and double excitations. An incremental scheme is applied based on
correlation contributions of localized bond orbitals and of pairs and triples
of such bonds. In view of the high polarity of the bonds in II-VI compounds, we
examine both, ionic and covalent embedding schemes for the calculation of
individual bond increments. Also, a partitioning of the correlation energy
according to local ionic increments is tested. Core-valence ()
correlation effects are taken into account via a core-polarization potential.
Combining the results at the correlated level with corresponding Hartree-Fock
data we recover about 94% of the experimental cohesive energies; lattice
constants are accurate to \sim 1%; bulk moduli are on average 10% too large
compared with experiment.Comment: 10 pages, twocolumn, RevTex, 3 figures, accepted Phys. Rev.
CO adsorption on neutral iridium clusters
The adsorption of carbon monoxide on neutral iridium clusters in the size
range of n = 3 to 21 atoms is investigated with infrared multiple photon
dissociation spectroscopy. For each cluster size only a single v(CO) band is
present with frequencies in the range between 1962 cm-1 (n = 8) and 1985 cm-1
(n = 18) which can be attributed to an atop binding geometry. This behaviour is
compared to the CO binding geometries on clusters of other group 9 and 10
transition metals as well as to that on extended surfaces. The preference of Ir
for atop binding is rationalized by relativistic effects on the electronic
structure of the later 5d metals
Magnetism, FeS colloids, and Origins of Life
A number of features of living systems: reversible interactions and weak
bonds underlying motor-dynamics; gel-sol transitions; cellular connected
fractal organization; asymmetry in interactions and organization; quantum
coherent phenomena; to name some, can have a natural accounting via
interactions, which we therefore seek to incorporate by expanding the horizons
of `chemistry-only' approaches to the origins of life. It is suggested that the
magnetic 'face' of the minerals from the inorganic world, recognized to have
played a pivotal role in initiating Life, may throw light on some of these
issues. A magnetic environment in the form of rocks in the Hadean Ocean could
have enabled the accretion and therefore an ordered confinement of
super-paramagnetic colloids within a structured phase. A moderate H-field can
help magnetic nano-particles to not only overcome thermal fluctuations but also
harness them. Such controlled dynamics brings in the possibility of accessing
quantum effects, which together with frustrations in magnetic ordering and
hysteresis (a natural mechanism for a primitive memory) could throw light on
the birth of biological information which, as Abel argues, requires a
combination of order and complexity. This scenario gains strength from
observations of scale-free framboidal forms of the greigite mineral, with a
magnetic basis of assembly. And greigite's metabolic potential plays a key role
in the mound scenario of Russell and coworkers-an expansion of which is
suggested for including magnetism.Comment: 42 pages, 5 figures, to be published in A.R. Memorial volume, Ed
Krishnaswami Alladi, Springer 201
Evidence for the η_b(1S) Meson in Radiative Υ(2S) Decay
We have performed a search for the η_b(1S) meson in the radiative decay of the Υ(2S) resonance using a sample of 91.6 × 10^6 Υ(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E_γ = 609.3^(+4.6)_(-4.5)(stat)±1.9(syst) MeV, corresponding to an η_b(1S) mass of 9394.2^(+4.8)_(-4.9)(stat) ± 2.0(syst) MeV/c^2. The branching fraction for the decay Υ(2S) → γη_b(1S) is determined to be [3.9 ± 1.1(stat)^(+1.1)_(-0.9)(syst)] × 10^(-4). We find the ratio of branching fractions B[Υ(2S) → γη_b(1S)]/B[Υ(3S) → γη_b(1S)]= 0.82 ± 0.24(stat)^(+0.20)_(-0.19)(syst)
Quantitative Treatment of Decoherence
We outline different approaches to define and quantify decoherence. We argue
that a measure based on a properly defined norm of deviation of the density
matrix is appropriate for quantifying decoherence in quantum registers. For a
semiconductor double quantum dot qubit, evaluation of this measure is reviewed.
For a general class of decoherence processes, including those occurring in
semiconductor qubits, we argue that this measure is additive: It scales
linearly with the number of qubits.Comment: Revised version, 26 pages, in LaTeX, 3 EPS figure
In Vitro and In Vivo Antagonism of a G Protein-Coupled Receptor (S1P3) with a Novel Blocking Monoclonal Antibody
Background: S1P 3 is a lipid-activated G protein-couple receptor (GPCR) that has been implicated in the pathological processes of a number of diseases, including sepsis and cancer. Currently, there are no available high-affinity, subtypeselective drug compounds that can block activation of S1P3. We have developed a monoclonal antibody (7H9) that specifically recognizes S1P3 and acts as a functional antagonist. Methodology/Principal Findings: Specific binding of 7H9 was demonstrated by immunocytochemistry using cells that over-express individual members of the S1P receptor family. We show, in vitro, that 7H9 can inhibit the activation of S1P3mediated cellular processes, including arrestin translocation, receptor internalization, adenylate cyclase inhibiton, and calcium mobilization. We also demonstrate that 7H9 blocks activation of S1P3 in vivo, 1) by preventing lethality due to systemic inflammation, and 2) by altering the progression of breast tumor xenografts. Conclusions/Significance: We have developed the first-reported monoclonal antibody that selectively recognizes a lipidactivated GPCR and blocks functional activity. In addition to serving as a lead drug compound for the treatment of sepsi
Observation and study of baryonic B decays: B -> D(*) p pbar, D(*) p pbar pi, and D(*) p pbar pi pi
We present a study of ten B-meson decays to a D(*), a proton-antiproton pair,
and a system of up to two pions using BaBar's data set of 455x10^6 BBbar pairs.
Four of the modes (B0bar -> D0 p anti-p, B0bar -> D*0 p anti-p, B0bar -> D+ p
anti-p pi-, B0bar -> D*+ p anti-p pi-) are studied with improved statistics
compared to previous measurements; six of the modes (B- -> D0 p anti-p pi-, B-
-> D*0 p anti-p pi-, B0bar -> D0 p anti-p pi- pi+, B0bar -> D*0 p anti-p pi-
pi+, B- -> D+ p anti-p pi- pi-, B- -> D*+ p anti-p pi- pi-) are first
observations. The branching fractions for 3- and 5-body decays are suppressed
compared to 4-body decays. Kinematic distributions for 3-body decays show
non-overlapping threshold enhancements in m(p anti-p) and m(D(*)0 p) in the
Dalitz plots. For 4-body decays, m(p pi-) mass projections show a narrow peak
with mass and full width of (1497.4 +- 3.0 +- 0.9) MeV/c2, and (47 +- 12 +- 4)
MeV/c2, respectively, where the first (second) errors are statistical
(systematic). For 5-body decays, mass projections are similar to phase space
expectations. All results are preliminary.Comment: 28 pages, 90 postscript figures, submitted to LP0
A randomised, controlled, two-Centre open-label study in healthy Japanese subjects to evaluate the effect on biomarkers of exposure of switching from a conventional cigarette to a tobacco heating product
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