4,677 research outputs found
Conformation dependence of charge transfer and level alignment in nitrobenzene junctions with pyridyl anchor groups
The alignment of molecular levels with the Fermi energy in single molecule
junctions is a crucial factor in determining their conductance or the
observability of quantum interference effects. In the present study which is
based on density functional theory calculations, we explore the zero-bias
charge transfer and level alignment for nitro-bipyridyl-phenyl adsorbed between
two gold surfaces which we find to vary significantly with the molecular
conformation. The net charge transfer is the result of two opposing effects,
namely Pauli repulsion at the interface between the molecule and the leads, and
the electron accepting nature of the NO group, where only the latter which
we analyze in terms of the electronegativity of the isolated molecules depends
on the two intra-molecular torsion angles. We provide evidence that the
conformation dependence of the alignment of molecular levels and peaks in the
transmission function can indeed be understood in terms of charge transfer for
this system, and that other properties such as molecular dipoles do not play a
significant role. Our study is relevant for device design in molecular
electronics where nitrobenzene appears as a component in proposals for
rectification, quantum interference or chemical gating.Comment: 10 pages, 6 figure
The shape of the baryon in a covariant spectator quark model
Using a covariant spectator quark model that describes the recent lattice QCD
data for the electromagnetic form factors and all available
experimental data on transitions, we analyze the charge
and magnetic dipole distributions of the baryon and discuss its shape.
We conclude that the quadrupole moment of the is a good indicator of
the deformation and that the charge distribution has an oblate
shape. We also calculate transverse moments and find that they do not lead to
unambiguous conclusions about the underlying shape.Comment: Extended introduction, references added, other small modifications.
To appear in Phys. Rev. D. 14 pages, 8 figure
Simultaneous reconstruction of evolutionary history and epidemiological dynamics from viral sequences with the birth-death SIR model
The evolution of RNA viruses such as HIV, Hepatitis C and Influenza virus
occurs so rapidly that the viruses' genomes contain information on past
ecological dynamics. Hence, we develop a phylodynamic method that enables the
joint estimation of epidemiological parameters and phylogenetic history. Based
on a compartmental susceptible-infected-removed (SIR) model, this method
provides separate information on incidence and prevalence of infections.
Detailed information on the interaction of host population dynamics and
evolutionary history can inform decisions on how to contain or entirely avoid
disease outbreaks.
We apply our Birth-Death SIR method (BDSIR) to two viral data sets. First,
five human immunodeficiency virus type 1 clusters sampled in the United Kingdom
between 1999 and 2003 are analyzed. The estimated basic reproduction ratios
range from 1.9 to 3.2 among the clusters. All clusters show a decline in the
growth rate of the local epidemic in the middle or end of the 90's.
The analysis of a hepatitis C virus (HCV) genotype 2c data set shows that the
local epidemic in the C\'ordoban city Cruz del Eje originated around 1906
(median), coinciding with an immigration wave from Europe to central Argentina
that dates from 1880--1920. The estimated time of epidemic peak is around 1970.Comment: Journal link:
http://rsif.royalsocietypublishing.org/content/11/94/20131106.ful
Microwave Heating of Water, Ice and Saline Solution: Molecular Dynamics Study
In order to study the heating process of water by the microwaves of 2.5-20GHz
frequencies, we have performed molecular dynamics simulations by adopting a
non-polarized water model that have fixed point charges on rigid-body
molecules. All runs are started from the equilibrated states derived from the
I ice with given density and temperature. In the presence of microwaves,
the molecules of liquid water exhibit rotational motion whose average phase is
delayed from the microwave electric field. Microwave energy is transferred to
the kinetic and inter-molecular energies of water, where one third of the
absorbed microwave energy is stored as the latter energy. The water in ice
phase is scarcely heated by microwaves because of the tight hydrogen-bonded
network of water molecules. Addition of small amount of salt to pure water
substantially increases the heating rate because of the weakening by defects in
the water network due to sloshing large-size negative ions.Comment: 21 pages, 13 figure
Meson-Meson Interactions and Resonances in the 't Hooft Model
We studied meson-meson interactions using the 't Hooft model, which
represents QCD in 1+1 dimensions and assumes a large number of colors ().
The dominant interactions in this large limit are generated by quark
exchange. Our results show that QCD in 1+1 dimensions allows the realization of
a constituent-type quark model for the mesons, and generates a scalar
``''-like meson-meson resonance, whose effective coupling and mass are
determined by the underlying QCD dynamics. These results suggest an
interpretation of the lightest scalar mesons as systems.Comment: 19 pages, 8 figures, accepted for publication in PR
Plasma N-Terminal Pro-Brain Natriuretic Peptide as Prognostic Marker in Fatal Cardial Decompensation with Sunitinib Malate Therapy
A 74-year-old man with metastatic renal cell carcinoma and a history of cardiac failure was treated with sunitinib malate. MUGA echocardiography could not detect a relevant change in the ejection fraction although the clinical situation of the patient worsened dramatically. The only parameter to hint at the deteriorated cardiac function was plasma N-terminal pro-brain natriuretic peptide (BNP). Finally, the patient died after only one cycle of sunitinib treatment. We propose to prospectively include BNP for the early detection of cardiovascular decompensation in high-risk patients. Future studies concerning the relevance of BNP in drug-related cardiotoxicity are urgently needed. Copyright (C) 2010 S. Karger AG, Base
Data Protection: International Trends and the Austrian Example
Ensuring personal privacy in today's computerized-information society seems to be a common goal among the member states of the OECD. In this paper an attempt is made to summarize the discussions at the political and law-making level, both nationally and internationally within the framework of the OECD member countries.
From the concrete outcome of these discussions, i.e., the data protection acts adopted and yet in force, the Austrian situation has been chosen as example
Quantum interference effects in electron transport through nitrobenzene with pyridil anchor groups
We present density functional theory (DFT) based non-equilibrium Green's
function (NEGF) calculations for the conductance through a nitrobenzene
molecule, which is anchored by pyridil-groups to Au electrodes. This work is
building up on earlier theoretical studies where quantum interference effects
(QIE) have been identified both in qualitative tight binding and in DFT
descriptions for the same molecule with different chemical connections to the
leads. The novelty in the current contribution is two-fold: i) The
pyridil-anchors guarantee for the conductance to be determined by rather narrow
peaks situated closely to the Fermi energy which is relevant because it might
maximize the impact of quantum interferences on the I/V behaviour. In a scan of
eight different junction setups, where the connection sites of aromatic rings,
their torsion angle with respect to each other and the surface structure have
been varied, QIE was found to dominate the conductance for only one planar
geometry. For finite torsion angles between aromatic rings the effect moves to
higher energies and would therefore only be accessible for experimental
observation in a gated junction. ii) A detailed comparison between simple
topological models and DFT results for the investigated systems aims at
assessing the usefulness of such models as analysis tools for a better
understanding of the physics of QIE and its structure dependence
Metastable States in High Order Short-Range Spin Glasses
The mean number of metastable states in higher order short-range spin
glasses is estimated analytically using a variational method introduced by
Tanaka and Edwards for very large coordination numbers. For lattices with small
connectivities, numerical simulations do not show any significant dependence on
the relative positions of the interacting spins on the lattice, indicating thus
that these systems can be described by a few macroscopic parameters. As an
extremely anisotropic model we consider the low autocorrelated binary spin
model and we show through numerical simulations that its landscape has an
exceptionally large number of local optima
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