820 research outputs found
Measurement induced quantum-classical transition
A model of an electrical point contact coupled to a mechanical system
(oscillator) is studied to simulate the dephasing effect of measurement on a
quantum system. The problem is solved at zero temperature under conditions of
strong non-equilibrium in the measurement apparatus. For linear coupling
between the oscillator and tunneling electrons, it is found that the oscillator
dynamics becomes damped, with the effective temperature determined by the
voltage drop across the junction. It is demonstrated that both the quantum
heating and the quantum damping of the oscillator manifest themselves in the
current-voltage characteristic of the point contact.Comment: in RevTex, 1 figure, corrected notatio
Induction of leaf senescence in Arabidopsis thaliana by long days through a light-dosage effect
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74662/1/j.1399-3054.1996.tb00463.x.pd
Quantum theory of electromechanical noise and momentum transfer statistics
A quantum mechanical theory is developed for the statistics of momentum
transferred to the lattice by conduction electrons. Results for the
electromechanical noise power in the semiclassical diffusive transport regime
agree with a recent theory based on the Boltzmann-Langevin equation. All
moments of the transferred momentum are calculated for a single-channel
conductor with a localized scatterer, and compared with the known statistics of
transmitted charge.Comment: 10 pages, 2 figure
Tunneling through a multigrain system: deducing the sample topology from the nonlinear conductance
We study a current transport through a system of a few grains connected with
tunneling links. The exact solution is given for an arbitrarily connected
double-grain system with a shared gate in the framework of the orthodox model.
The obtained result is generalized for multigrain systems with strongly
different tunneling resistances. We analyse the large-scale nonlinear
conductance and demonstrate how the sample topology can be unambiguously
deduced from the spectroscopy pattern (differential conductance versus
gate-bias plot). We present experimental data for a multigrain sample and
reconstruct the sample topology. A simple selection rule is formulated to
distinguish samples with spectral patterns free from spurious disturbance
caused by recharging of some grains nearby. As an example, we demonstrate
experimental data with additional peaks in the spectroscopy pattern, which can
not be attributed to coupling to additional grains. The described approach can
be used to judge the sample topology when it is not guaranteed by fabrication
and direct imaging is not possible.Comment: 13 pages (including 8 figures
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction across a tunneling junction out of equilibrium
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic
- spin impurities across a tunneling junction is studied when the system
is driven out of equilibrium through biasing the junction. The nonequilibrium
situation is handled with the Keldysh time-loop perturbation formalism in
conjunction with appropriate coupling methods for tunneling systems due to
Caroli and Feuchtwang. We find that the presence of a nonequilibrium bias
across the junction leads to an interference of several fundamental
oscillations, such that in this tunneling geometry, it is possible to tune the
interaction between ferromagnetic and antiferromagnetic coupling at a fixed
impurity configuration, simply by changing the bias across the junction.
Furthermore, it is shown that the range of the RKKY interaction is altered out
of equilibrium, such that in particular the interaction energy between two
slabs of spins scales extensively with the thickness of the slabs in the
presence of an applied bias.Comment: 38 pages revtex preprint; 5 postscript figures; submitted to Phys.
Rev.
Performance of ab initio and density functional methods for conformational equilibria of CnH2n+2 alkane isomers (n=2-8)
Conformational energies of n-butane, n-pentane, and n-hexane have been
calculated at the CCSD(T) level and at or near the basis set limit.
Post-CCSD(T) contribution were considered and found to be unimportant. The data
thus obtained were used to assess the performance of a variety of density
functional methods. Double-hybrid functionals like B2GP-PLYP and B2K-PLYP,
especially with a small Grimme-type empirical dispersion correction, are
capable of rendering conformational energies of CCSD(T) quality. These were
then used as a `secondary standard' for a larger sample of alkanes, including
isopentane and the branched hexanes as well as key isomers of heptane and
octane. Popular DFT functionals like B3LYP, B3PW91, BLYP, PBE, and PBE0 tend to
overestimate conformer energies without dispersion correction, while the M06
family severely underestimates GG interaction energies. Grimme-type dispersion
corrections for these overcorrect and lead to qualitatively wrong conformer
orderings. All of these functionals also exhibit deficiencies in the conformer
geometries, particularly the backbone torsion angles. The PW6B95 and, to a
lesser extent, BMK functionals are relatively free of these deficiencies.
Performance of these methods is further investigated to derive conformer
ensemble corrections to the enthalpy function, , and the Gibbs
energy function, , of these alkanes. While
is only moderately sensitive to the level of theory, exhibits more pronounced sensitivity. Once again, double hybrids
acquit themselves very well.Comment: J. Phys. Chem. A, revised [Walter Thiel festschrift
Mini Black Holes in the first year of the LHC
The experimental signatures of TeV-mass black hole (BH) formation in heavy
ion collisions at the LHC is examined. We find that the black hole production
results in a complete disappearance of all very high ({} GeV)
back-to-back correlated di-jets of total mass {}TeV. We show
that the subsequent Hawking-decay produces multiple hard mono-jets and discuss
their detection. We study the possibility of cold black hole remnant (BHR)
formation of mass and the experimental distinguishability of
scenarios with BHRs and those with complete black hole decay. Due to the rather
moderate luminosity in the first year of LHC running the least chance for the
observation of BHs or BHRs at this early stage will be by ionizing tracks in
the ALICE TPC. Finally we point out that stable BHRs would be interesting
candidates for energy production by conversion of mass to Hawking radiation.Comment: 10 pages, 2 figure
Dicke Effect in the Tunnel Current through two Double Quantum Dots
We calculate the stationary current through two double quantum dots which are
interacting via a common phonon environment. Numerical and analytical solutions
of a master equation in the stationary limit show that the current can be
increased as well as decreased due to a dissipation mediated interaction. This
effect is closely related to collective, spontaneous emission of phonons (Dicke
super- and subradiance effect), and the generation of a `cross-coherence' with
entanglement of charges in singlet or triplet states between the dots.
Furthermore, we discuss an inelastic `current switch' mechanism by which one
double dot controls the current of the other.Comment: 12 pages, 6 figures, to appear in Phys. Rev.
Functional Contribution of Elevated Circulating and Hepatic Non-Classical CD14+CD16+ Monocytes to Inflammation and Human Liver Fibrosis
BACKGROUND: Monocyte-derived macrophages critically perpetuate inflammatory responses after liver injury as a prerequisite for organ fibrosis. Experimental murine models identified an essential role for the CCR2-dependent infiltration of classical Gr1/Ly6C(+) monocytes in hepatic fibrosis. Moreover, the monocyte-related chemokine receptors CCR1 and CCR5 were recently recognized as important fibrosis modulators in mice. In humans, monocytes consist of classical CD14(+)CD16(-) and non-classical CD14(+)CD16(+) cells. We aimed at investigating the relevance of monocyte subpopulations for human liver fibrosis, and hypothesized that 'non-classical' monocytes critically exert inflammatory as well as profibrogenic functions in patients during liver disease progression. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed circulating monocyte subsets from freshly drawn blood samples of 226 patients with chronic liver disease (CLD) and 184 healthy controls by FACS analysis. Circulating monocytes were significantly expanded in CLD-patients compared to controls with a marked increase of the non-classical CD14(+)CD16(+) subset that showed an activated phenotype in patients and correlated with proinflammatory cytokines and clinical progression. Correspondingly, CD14(+)CD16(+) macrophages massively accumulated in fibrotic/cirrhotic livers, as evidenced by immunofluorescence and FACS. Ligands of monocyte-related chemokine receptors CCR2, CCR1 and CCR5 were expressed at higher levels in fibrotic and cirrhotic livers, while CCL3 and CCL4 were also systemically elevated in CLD-patients. Isolated monocyte/macrophage subpopulations were functionally characterized regarding cytokine/chemokine expression and interactions with primary human hepatic stellate cells (HSC) in vitro. CD14(+)CD16(+) monocytes released abundant proinflammatory cytokines. Furthermore, CD14(+)CD16(+), but not CD14(+)CD16(-) monocytes could directly activate collagen-producing HSC. CONCLUSIONS/SIGNIFICANCE: Our data demonstrate the expansion of CD14(+)CD16(+) monocytes in the circulation and liver of CLD-patients upon disease progression and suggest their functional contribution to the perpetuation of intrahepatic inflammation and profibrogenic HSC activation in liver cirrhosis. The modulation of monocyte-subset recruitment into the liver via chemokines/chemokine receptors and their subsequent differentiation may represent promising approaches for therapeutic interventions in human liver fibrosis
Global hybrids from the semiclassical atom theory satisfying the local density linear response
We propose global hybrid approximations of the exchange-correlation (XC)
energy functional which reproduce well the modified fourth-order gradient
expansion of the exchange energy in the semiclassical limit of many-electron
neutral atoms and recover the full local density approximation (LDA) linear
response. These XC functionals represent the hybrid versions of the APBE
functional [Phys. Rev. Lett. 106, 186406, (2011)] yet employing an additional
correlation functional which uses the localization concept of the correlation
energy density to improve the compatibility with the Hartree-Fock exchange as
well as the coupling-constant-resolved XC potential energy. Broad energetical
and structural testings, including thermochemistry and geometry, transition
metal complexes, non-covalent interactions, gold clusters and small
gold-molecule interfaces, as well as an analysis of the hybrid parameters, show
that our construction is quite robust. In particular, our testing shows that
the resulting hybrid, including 20\% of Hartree-Fock exchange and named hAPBE,
performs remarkably well for a broad palette of systems and properties, being
generally better than popular hybrids (PBE0 and B3LYP). Semi-empirical
dispersion corrections are also provided.Comment: 12 pages, 4 figure
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