1,232 research outputs found
AC-Conductance through an Interacting Quantum Dot
We investigate the linear ac-conductance for tunneling through an arbitrary
interacting quantum dot in the presence of a finite dc-bias. In analogy to the
well-known Meir-Wingreen formula for the dc case, we are able to derive a
general formula for the ac-conductance. It can be expressed entirely in terms
of local correlations on the quantum dot, in the form of a Keldysh block
diagram with four external legs. We illustrate the use of this formula as a
starting point for diagrammatic calculations by considering the ac-conductance
of the noninteracting resonant level model and deriving the result for the
lowest order of electron-phonon coupling. We show how known results are
recovered in the appropriate limits.Comment: 4+ pages, 4 figure
Proposal for a Precision Measurement of |Vub|
A new method for a precision measurement of the CKM matrix element |Vub| is
discussed, which combines good theoretical control with high efficiency and a
powerful discrimination against charm background. The resulting combined
theoretical uncertainty on |Vub| is estimated to be 10%.Comment: 4 pages, 2 figures, RevTe
Collective dynamics in optomechanical arrays
The emerging field of optomechanics seeks to explore the interaction between
nanomechanics and light. Recently, the exciting concept of optomechanical
crystals has been introduced, where defects in photonic crystal structures are
used to generate both localized optical and mechanical modes that interact with
each other. Here we start exploring the collective dynamics of arrays
consisting of many coupled optomechanical cells. We show that such
"optomechanical arrays" can display synchronization and that they can be
described by a modified Kuramoto model that allows to explain and predict most
of the features that will be observable in future experiments.Comment: 6 pages, 5 figure
Cost and benefit analysis of quality requirements in competitive software product management: a case study on the QUPER model
In market-driven product development, it is important that the software product is released to the market at the right time, and offers higher quality than the competitors. In release planning, the allocation of development effort in investments into product enhancements, functions are competing with quality requirements for limited resources. In addition, it is important to find the right balance between competing quality requirements. In this paper, we present an industrial evaluation of the benefit and cost views in the QUality PERformance (QUPER) model. The results indicate that the model is relevant in the release planning process, and that the combination of the benefit and cost views provides a clear picture of the current market situation
The Effect of the Sparticle Mass Spectrum on the Conversion of B-L to B
In the context of many leptogenesis and baryogenesis scenarios, B-L (baryon
minus the lepton number) is converted into B (baryon number) by
non-perturbative B+L violating operators in the SU(2)_L sector. We correct a
common misconversion of B-L to B in the literature in the context of
supersymmetry. More specifically, kinematic effects associated with the
sparticle masses can be generically important (typically a factor of 2/3
correction in mSUGRA scenarios), and in some cases, it may even flip the sign
between B-L and B. We give explicit formulae for converting B-L to B for
temperatures approaching the electroweak phase transition temperature from
above. Enhancements of B are also possible, leading to a mild relaxation of the
reheating temperature bounds coming from gravitino constraints.Comment: 17 page
Pou5f3, SoxB1, and Nanog Remodel Chromatin on High Nucleosome Affinity Regions at Zygotic Genome Activation
The zebrafish embryo is transcriptionally mostly quiescent during the first 10 cell cycles, until the main wave of zygotic genome activation (ZGA) occurs, accompanied by fast chromatin remodeling. At ZGA, homologs of the mammalian stem cell transcription factors (TFs) Pou5f3, Nanog, and Sox19b bind to thousands of developmental enhancers to initiate transcription. So far, how these TFs influence chromatin dynamics at ZGA has remained unresolved. To address this question, we analyzed nucleosome positions in wild-type and maternal-zygotic (MZ) mutants for pou5f3 and nanog by MNase-seq. We show that Nanog, Sox19b, and Pou5f3 bind to the high nucleosome affinity regions (HNARs). HNARs are spanning over 600 bp, featuring high in vivo and predicted in vitro nucleosome occupancy and high predicted propeller twist DNA shape value. We suggest a two-step nucleosome destabilization-depletion model, in which the same intrinsic DNA properties of HNAR promote both high nucleosome occupancy and differential binding of TFs. In the first step, already before ZGA, Pou5f3 and Nanog destabilize nucleosomes at HNAR centers genome-wide. In the second step, post-ZGA, Nanog, Pou5f3, and SoxB1 maintain open chromatin state on the subset of HNARs, acting synergistically. Nanog binds to the HNAR center, whereas the Pou5f3 stabilizes the flanks. The HNAR model will provide a useful tool for genome regulatory studies in a variety of biological systems
QGP collective effects and jet transport
We present numerical simulations of the SU(2) Boltzmann-Vlasov equation
including both hard elastic particle collisions and soft interactions mediated
by classical Yang-Mills fields. We provide an estimate of the coupling of jets
to a hot isotropic plasma, which is independent of infrared cutoffs. In
addition, we investigate jet propagation in anisotropic plasmas, as created in
heavy-ion collisions. The broadening of jets is found to be stronger along the
beam line than in azimuth due to the creation of field configurations with
B_t>E_t and E_z>B_z via plasma instabilities.Comment: 4 pages, 5 figures. Presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008),
Jaipur, India, 4-10 Feb 200
Hypothesis and theory : a pathophysiological concept of stroke-induced acute phase response and increased intestinal permeability leading to secondary brain damage
Gut integrity impairment leading to increased intestinal permeability (IP) is hypothesized to be a trigger of critically illness. Approximately 15–20% of human ischemic stroke (IS) victims require intensive care, including patients with impaired level of consciousness or a high risk for developing life-threatening cerebral edema. Local and systemic inflammatory reactions are a major component of the IS pathophysiology and can significantly aggravate brain tissue damage. Intracerebral inflammatory processes following IS have been well studied. Until now, less is known about systemic inflammatory responses and IS consequences apart from a frequently observed post-IS immunosuppression. Here, we provide a hypothesis of a crosstalk between systemic acute phase response (APR), IP and potential secondary brain damage during acute and subacute IS stages supported by preliminary experimental data. Alterations of the acute phase proteins (APPs) C-reactive protein and lipopolysaccharide-binding protein and serum level changes of antibodies directed against Escherichia coli-cell extract antigen (IgA-, IgM-, and IgG-anti-E. coli) were investigated at 1, 2, and 7 days following IS in ten male sheep. We found an increase of both APPs as well as a decrease of all anti-E. coli antibodies within 48 h following IS. This may indicate an early systemic APR and increased IP, and underlines the importance of the increasingly recognized gut-brain axis and of intestinal antigen release for systemic immune responses in acute and subacute stroke stages
Memory effects in radiative jet energy loss
In heavy-ion collisions the created quark-gluon plasma forms a quickly
evolving background, leading to a time dependent radiative behavior of high
momentum partons traversing the medium. We use the Schwinger Keldysh formalism
to describe the jet evolution as a non-equilibrium process including the
Landau-Pomeranschuk-Migdal effect. Concentrating on photon emission, a
comparison of our results to a quasistatic calculation shows good agreement,
leading to the conclusion that the radiative behavior follows the changes in
the medium almost instantaneously
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