193 research outputs found
Electron-phonon induced spin relaxation in InAs quantum dots
We have calculated spin relaxation rates in parabolic quantum dots due to the
phonon modulation of the spin-orbit interaction in presence of an external
magnetic field. Both, deformation potential and piezoelectric electron-phonon
coupling mechanisms are included within the Pavlov-Firsov spin-phonon
Hamiltonian. Our results have demonstrated that, in narrow gap materials, the
electron-phonon deformation potential and piezoelectric coupling give
comparable contributions as spin relaxation processes. For large dots, the
deformation potential interaction becomes dominant. This behavior is not
observed in wide or intermediate gap semiconductors, where the piezoelectric
coupling, in general, governs the spin relaxation processes. We also have
demonstrated that spin relaxation rates are particularly sensitive to the
Land\'e -factor.Comment: 4 pages, 2 figures, to be appear in Physica E: Proceedings of the 11
International Conference on Narrow Gap Semiconductor
Revisiting loss-specific training of filter-based MRFs for image restoration
It is now well known that Markov random fields (MRFs) are particularly
effective for modeling image priors in low-level vision. Recent years have seen
the emergence of two main approaches for learning the parameters in MRFs: (1)
probabilistic learning using sampling-based algorithms and (2) loss-specific
training based on MAP estimate. After investigating existing training
approaches, it turns out that the performance of the loss-specific training has
been significantly underestimated in existing work. In this paper, we revisit
this approach and use techniques from bi-level optimization to solve it. We
show that we can get a substantial gain in the final performance by solving the
lower-level problem in the bi-level framework with high accuracy using our
newly proposed algorithm. As a result, our trained model is on par with highly
specialized image denoising algorithms and clearly outperforms
probabilistically trained MRF models. Our findings suggest that for the
loss-specific training scheme, solving the lower-level problem with higher
accuracy is beneficial. Our trained model comes along with the additional
advantage, that inference is extremely efficient. Our GPU-based implementation
takes less than 1s to produce state-of-the-art performance.Comment: 10 pages, 2 figures, appear at 35th German Conference, GCPR 2013,
Saarbr\"ucken, Germany, September 3-6, 2013. Proceeding
Phase Diagram of Bosonic Atoms in Two-Color Superlattices
We investigate the zero temperature phase diagram of a gas of bosonic atoms
in one- and two-color standing-wave lattices in the framework of the
Bose-Hubbard model. We first introduce some relevant physical quantities;
superfluid fraction, condensate fraction, quasimomentum distribution, and
matter-wave interference pattern. We then discuss the relationships between
them on the formal level and show that the superfluid fraction, which is the
relevant order parameter for the superfluid to Mott-insulator transition,
cannot be probed directly via the matter wave interference patterns. The formal
considerations are supported by exact numerical solutions of the Bose-Hubbard
model for uniform one-dimensional systems. We then map out the phase diagram of
bosons in non-uniform lattices. The emphasis is on optical two-color
superlattices which exhibit a sinusoidal modulation of the well depth and can
be easily realized experimentally. From the study of the superfluid fraction,
the energy gap, and other quantities we identify new zero-temperature phases,
including a localized and a quasi Bose-glass phase, and discuss prospects for
their experimental observation.Comment: 18 pages, 17 figures, using REVTEX
Modern topics in theoretical nuclear physics
Over the past five years there have been profound advances in nuclear physics
based on effective field theory and the renormalization group. In this brief,
we summarize these advances and discuss how they impact our understanding of
nuclear systems and experiments that seek to unravel their unknowns. We discuss
future opportunities and focus on modern topics in low-energy nuclear physics,
with special attention to the strong connections to many-body atomic and
condensed matter physics, as well as to astrophysics. This makes it an exciting
era for nuclear physics.Comment: 8 pages, 1 figure, prepared for the Nuclear Physics Town Hall Meeting
at TRIUMF, Sept. 9-10, 2005, comments welcome, references adde
DNA repair modulates the vulnerability of the developing brain to alkylating agents
Neurons of the developing brain are especially vulnerable to environmental agents that damage DNA (i.e., genotoxicants), but the mechanism is poorly understood. The focus of the present study is to demonstrate that DNA damage plays a key role in disrupting neurodevelopment. To examine this hypothesis, we compared the cytotoxic and DNA damaging properties of the methylating agents methylazoxymethanol (MAM) and dimethyl sulfate (DMS) and the mono- and bifunctional alkylating agents chloroethylamine (CEA) and nitrogen mustard (HN2), in granule cell neurons derived from the cerebellum of neonatal wild type mice and three transgenic DNA repair strains. Wild type cerebellar neurons were significantly more sensitive to the alkylating agents DMS and HN2 than neuronal cultures treated with MAM or the half-mustard CEA. Parallel studies with neuronal cultures from mice deficient in alkylguanine DNA glycosylase (Aag[superscript −/−]) or O6-methylguanine methyltransferase (Mgmt[superscript −/−]), revealed significant differences in the sensitivity of neurons to all four genotoxicants. Mgmt−/− neurons were more sensitive to MAM and HN2 than the other genotoxicants and wild type neurons treated with either alkylating agent. In contrast, Aag[superscript −/−] neurons were for the most part significantly less sensitive than wild type or Mgmt[superscript −/−] neurons to MAM and HN2. Aag[superscript −/−] neurons were also significantly less sensitive than wild type neurons treated with either DMS or CEA. Granule cell development and motor function were also more severely disturbed by MAM and HN2 in Mgmt[superscript −/−] mice than in comparably treated wild type mice. In contrast, cerebellar development and motor function were well preserved in MAM-treated Aag[superscript −/−] or MGMT-overexpressing (Mgmt[superscript Tg+]) mice, even as compared with wild type mice suggesting that AAG protein increases MAM toxicity, whereas MGMT protein decreases toxicity. Surprisingly, neuronal development and motor function were severely disturbed in Mgmt[superscript Tg+] mice treated with HN2. Collectively, these in vitro and in vivo studies demonstrate that the type of DNA lesion and the efficiency of DNA repair are two important factors that determine the vulnerability of the developing brain to long-term injury by a genotoxicant.United States. Army Medical Research and Materiel Command (Contract/Grant/Intergovernmental Project Order DAMD 17-98-1-8625)United States. National Institutes of Health (grants CA075576)United States. National Institutes of Health (RO1 C63193)United States. National Institutes of Health (P30 CA043703
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Sex-dependent diversity in ventral tegmental dopaminergic neurons and developmental programing: a molecular, cellular and behavioral analysis
The knowledge that diverse populations of dopaminergic neurons within the ventral tegmental area (VTA) can be distinguished in terms of their molecular, electrophysiological and functional properties, as well as their differential projections to cortical and subcortical regions has significance for key brain functions, such as the regulation of motivation, working memory and sensorimotor control. Almost without exception, this understanding has evolved from landmark studies performed in the male sex. However, converging evidence from both clinical and pre-clinical studies illustrates that the structure and functioning of the VTA dopaminergic systems are intrinsically different in males and females. This may be driven by sex differences in the hormonal environment during adulthood ('activational' effects) and development (perinatal and/or pubertal 'organizational' effects), as well as genetic factors, especially the SRY gene on the Y chromosome in males, which is expressed in a sub-population of adult midbrain dopaminergic neurons. Stress and stress hormones, especially glucocorticoids, are important factors which interact with the VTA dopaminergic systems in order to achieve behavioral adaptation and enable the individual to cope with environmental change. Here, also, there is male/female diversity not only during adulthood, but also in early life when neurobiological programing by stress or glucocorticoid exposure differentially impacts dopaminergic developmental trajectories in male and female brains. This may have enduring consequences for individual resilience or susceptibility to pathophysiological change induced by stressors in later life, with potential translational significance for sex bias commonly found in disorders involving dysfunction of the mesocorticolimbic dopaminergic systems. These findings highlight the urgent need for a better understanding of the sexual dimorphism in the VTA if we are to improve strategies for the prevention and treatment of debilitating conditions which differentially affect men and women in their prevalence and nature, including schizophrenia, attention/deficit hyperactivity disorder, autism spectrum disorders, anxiety, depression and addiction
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