4,084 research outputs found
Nonequilibrium electron spin polarization in a double quantum dot. Lande mechanism
In moderately strong magnetic fields, the difference in Lande g-factors in
each of the dots of a coupled double quantum dot device may induce oscillations
between singlet and triplet states of the entangled electron pair and lead to a
nonequilibrium electron spin polarization. We will show that this polarization
may partially survive the rapid inhomogeneous decoherence due to random nuclear
magnetic fields.Comment: New version contains figures. New title better reflects the content
of the pape
Electron-vibration coupling constants in positively charged fullerene
Recent experiments have shown that C60 can be positively field-doped. In that
state, fullerene exhibits a higher resistivity and a higher superconducting
temperature than the corresponding negatively doped state. A strong
intramolecular hole-phonon coupling, connected with the Jahn-Teller effect of
the isolated positive ion, is expected to be important for both properties, but
the actual coupling strengths are so far unknown. Based on density functional
calculations, we determine the linear couplings of the two a_g, six g_g, and
eight h_g vibrational modes to the H_u HOMO level of the C60 molecule. The
couplings predict a D_5 distortion, and an H_u vibronic ground state for C60^+.
They are also used to generate the dimensionless coupling constant
which controls the superconductivity and the phonon contribution to the
electrical resistivity in the crystalline phase. We find that is 1.4
times larger in positively-charged C60 than in the negatively-doped case. These
results are discussed in the context of the available transport data and
superconducting temperatures. The role of higher orbital degeneracy in
superconductivity is also addressed.Comment: 22 pages - 3 figures. This revision includes few punctuation
corrections from proofreadin
Re-Annotator: Annotation Pipeline for Microarray Probe Sequences.
Microarray technologies are established approaches for high throughput gene expression, methylation and genotyping analysis. An accurate mapping of the array probes is essential to generate reliable biological findings. However, manufacturers of the microarray platforms typically provide incomplete and outdated annotation tables, which often rely on older genome and transcriptome versions that differ substantially from up-to-date sequence databases. Here, we present the Re-Annotator, a re-annotation pipeline for microarray probe sequences. It is primarily designed for gene expression microarrays but can also be adapted to other types of microarrays. The Re-Annotator uses a custom-built mRNA reference database to identify the positions of gene expression array probe sequences. We applied Re-Annotator to the Illumina Human-HT12 v4 microarray platform and found that about one quarter (25%) of the probes differed from the manufacturer's annotation. In further computational experiments on experimental gene expression data, we compared Re-Annotator to another probe re-annotation tool, ReMOAT, and found that Re-Annotator provided an improved re-annotation of microarray probes. A thorough re-annotation of probe information is crucial to any microarray analysis. The Re-Annotator pipeline is freely available at http://sourceforge.net/projects/reannotator along with re-annotated files for Illumina microarrays HumanHT-12 v3/v4 and MouseRef-8 v2
Towards Supergravity Duals of Chiral Symmetry Breaking in Sasaki-Einstein Cascading Quiver Theories
We construct a first order deformation of the complex structure of the cone
over Sasaki-Einstein spaces Y^{p,q} and check supersymmetry explicitly. This
space is a central element in the holographic dual of chiral symmetry breaking
for a large class of cascading quiver theories. We discuss a solution
describing a stack of N D3 branes and M fractional D3 branes at the tip of the
deformed spaces.Comment: 28 pages, no figures. v2: typos, references and a note adde
Group projector generalization of dirac-heisenberg model
The general form of the operators commuting with the ground representation
(appearing in many physical problems within single particle approximation) of
the group is found. With help of the modified group projector technique, this
result is applied to the system of identical particles with spin independent
interaction, to derive the Dirac-Heisenberg hamiltonian and its effective space
for arbitrary orbital occupation numbers and arbitrary spin. This gives
transparent insight into the physical contents of this hamiltonian, showing
that formal generalizations with spin greater than 1/2 involve nontrivial
additional physical assumptions.Comment: 10 page
Density Functional Theory for the Photoionization Dynamics of Uracil
Photoionization dynamics of the RNA base Uracil is studied in the framework
of Density Functional Theory (DFT). The photoionization calculations take
advantage of a newly developed parallel version of a multicentric approach to
the calculation of the electronic continuum spectrum which uses a set of
B-spline radial basis functions and a Kohn-Sham density functional hamiltonian.
Both valence and core ionizations are considered. Scattering resonances in
selected single-particle ionization channels are classified by the symmetry of
the resonant state and the peak energy position in the photoelectron kinetic
energy scale; the present results highlight once more the site specificity of
core ionization processes. We further suggest that the resonant structures
previously characterized in low-energy electron collision experiments are
partly shifted below threshold by the photoionization processes. A critical
evaluation of the theoretical results providing a guide for future experimental
work on similar biosystems
Neutrino Physics and Nuclear Axial Two-Body Interactions
We consider the counter-term describing isoscalar axial two-body currents in
the nucleon-nucleon interaction, L1A, in the effective field theory approach.
We determine this quantity using the solar neutrino data. We investigate the
variation of L1A when different sets of data are used.Comment: 8 pages with 4 figures. To be published in the Proceedings of the
Conference "Blueprints For The Nucleus: From First Principles to Collective
Motion" held at Feza Gursey Institute, Istanbul, Turkey; May 17 -22, 200
Spin Polaron Effective Magnetic Model for La_{0.5}Ca_{0.5}MnO_3
The conventional paradigm of charge order for La_{1-x}Ca_xMnO_3 for x=0.5 has
been challenged recently by a Zener polaron picture emerging from experiments
and theoretical calculations. The effective low energy Hamiltonian for the
magnetic degrees of freedom has been found to be a cubic Heisenberg model, with
ferromagnetic nearest neighbor and frustrating antiferromagnetic next nearest
neighbor interactions in the planes, and antiferromagnetic interaction between
planes. With linear spin wave theory and diagonalization of small clusters up
to 27 sites we find that the behavior of the model interpolates between the A
and CE-type magnetic structures when a frustrating intraplanar interaction is
tuned. The values of the interactions calculated by ab initio methods indicate
a possible non-bipartite picture of polaron ordering differing from the
conventional one.Comment: 21 pages and 8 figures (included), Late
- …