4,800 research outputs found
A renormalization group approach to time dependent transport through correlated quantum dots
We introduce a real time version of the functional renormalization group
which allows to study correlation effects on nonequilibrium transport through
quantum dots. Our method is equally capable to address (i) the relaxation out
of a nonequilibrium initial state into a (potentially) steady state driven by a
bias voltage and (ii) the dynamics governed by an explicitly time-dependent
Hamiltonian. All time regimes from transient to asymptotic can be tackled; the
only approximation is the consistent truncation of the flow equations at a
given order. As an application we investigate the relaxation dynamics of the
interacting resonant level model which describes a fermionic quantum dot
dominated by charge fluctuations. Moreover, we study decoherence and relaxation
phenomena within the ohmic spin-boson model by mapping the latter to the
interacting resonant level model
Prenatal diagnosis of isovaleric acidaemia by enzyme and metabolite assay in the first and second trimesters
Isovaleric acidaemia (IVA) is caused by a deficiency of isovaleryl CoA dehydrogenase. The diagnosis can be established biochemically by the demonstration of increased levels of isovalerylglycine (IVG) and 3-hydroxyisovaleric acid in urine and by the deficiency of incorporation of radiolabel from [14C]isovaleric acid in macromolecules in cultured fibroblasts. This paper reports a consecutive series of 24 prenatal diagnoses in pregnancies at high risk, using both methods-metabolite and indirect enzyme assay. Affected fetuses were diagnosed in four pregnancies: three in the second trimester and one recent case in the first trimester. The latter represents the first reported case of a first-trimester diagnosis of IVA by direct analysis of chorionic villi. We also report the first demonstration of strongly accumulated IVG in the amniotic fluid in the 12th week of an affected pregnancy
Charge transport through single molecules, quantum dots, and quantum wires
We review recent progresses in the theoretical description of correlation and
quantum fluctuation phenomena in charge transport through single molecules,
quantum dots, and quantum wires. A variety of physical phenomena is addressed,
relating to co-tunneling, pair-tunneling, adiabatic quantum pumping, charge and
spin fluctuations, and inhomogeneous Luttinger liquids. We review theoretical
many-body methods to treat correlation effects, quantum fluctuations,
nonequilibrium physics, and the time evolution into the stationary state of
complex nanoelectronic systems.Comment: 48 pages, 14 figures, Topical Review for Nanotechnolog
Nonequilibrium functional RG with frequency dependent vertex function: A study of the single impurity Anderson model
We investigate nonequilibrium properties of the single impurity Anderson
model by means of the functional renormalization group (fRG) within Keldysh
formalism. We present how the level broadening Gamma/2 can be used as flow
parameter for the fRG. This choice preserves important aspects of the Fermi
liquid behaviour that the model exhibits in case of particle-hole symmetry. An
approximation scheme for the Keldysh fRG is developed which accounts for the
frequency dependence of the two-particle vertex in a way similar but not
equivalent to a recently published approximation to the equilibrium Matsubara
fRG. Our method turns out to be a flexible tool for the study of weak to
intermediate on-site interactions U <= 3 Gamma. In equilibrium we find
excellent agreement with NRG results for the linear conductance at finite gate
voltage, magnetic field, and temperature. In nonequilibrium, our results for
the current agree well with TD-DMRG. For the nonlinear conductance as function
of the bias voltage, we propose reliable results at finite magnetic field and
finite temperature. Furthermore, we demonstrate the exponentially small scale
of the Kondo temperature to appear in the second order derivative of the
self-energy. We show that the approximation is, however, not able to reproduce
the scaling of the effective mass at large interactions.Comment: [v2] - minor changes throughout the text; added new Fig. 3; corrected
pert.-theory data in Figs. 10, 11; published versio
Gluon-induced W-boson pair production at the LHC
Pair production of W bosons constitutes an important background to Higgs
boson and new physics searches at the Large Hadron Collider LHC. We have
calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons,
including intermediate light and heavy quarks and allowing for arbitrary
invariant masses of the W bosons. While formally of next-to-next-to-leading
order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at
the LHC and by experimental Higgs search cuts, and increases the
next-to-leading order WW background estimate for Higgs searches by about 30%.
We have extended our previous calculation to include the contribution from the
intermediate top-bottom massive quark loop and the Higgs signal process. We
provide updated results for cross sections and differential distributions and
study the interference between the different gluon scattering contributions. We
describe important analytical and numerical aspects of our calculation and
present the public GG2WW event generator.Comment: 20 pages, 4 figure
Entrained Flow Gasification Part 1 : Gasification of Glycol in an Atmospheric-pressure Experimental Rig
Three coordinated papers are presented concerning entrained flow gasification of a liquid fuel under atmospheric conditions. The work is based on a detailed mapping of process parameters inside the entrained flow gasifier and at the gasifier outlet. In this paper the experimental setup and the experimental data are reported. Mono ethylene glycol (MEG) is used as a well-defined surrogate fuel for biogenic oils. The overall performance of the reactor is evaluated by measuring the gas-phase composition at the reactor outlet; radial profiles of gas-phase composition (CO₂, CO, H₂, CH₄, hydrocarbons) and temperature at 300 and 680 mm distances from the burner are measured to describe the mixing and reaction pattern in the gasifier. Global and local species balances are used to derive data that are not accessible by measurement. Characteristic parameters, i.e. stoichiometry, carbon conversion and water gas shift temperature, are derived to assess consistency of the measured data. Droplet size distribution and droplet velocity at the burner nozzle are reported based on atomization test rig experiments and direct measurements in the burner near field under gasification conditions. The experiments show a free jet with a strong outer recirculation zone as core gasification pattern. The measured species concentrations and temperatures provide an insight into both the mixing and the reactions in the burner near field. The water gas shift equilibrium is reached for a temperature of 1495 K upstream of the gasifier outlet. Hydrocarbons are not completely converted due to the low temperatures near the gasifier outlet. The research work has been conducted within the research cooperation of the Helmholtz Virtual Institute HVIGasTech
Prospects for the Search for a Standard Model Higgs Boson in ATLAS using Vector Boson Fusion
The potential for the discovery of a Standard Model Higgs boson in the mass
range m_H < 2 m_Z in the vector boson fusion mode has been studied for the
ATLAS experiment at the LHC. The characteristic signatures of additional jets
in the forward regions of the detector and of low jet activity in the central
region allow for an efficient background rejection. Analyses for the H -> WW
and H -> tau tau decay modes have been performed using a realistic simulation
of the expected detector performance. The results obtained demonstrate the
large discovery potential in the H -> WW decay channel and the sensitivity to
Higgs boson decays into tau-pairs in the low-mass region around 120 GeV.Comment: 20 pages, 13 ps figures, uses EPJ style fil
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