501 research outputs found
Identification of excitons, trions and biexcitons in single-layer WS2
Single-layer WS is a direct-gap semiconductor showing strong excitonic
photoluminescence features in the visible spectral range. Here, we present
temperature-dependent photoluminescence measurements on mechanically exfoliated
single-layer WS, revealing the existence of neutral and charged excitons at
low temperatures as well as at room temperature. By applying a gate voltage, we
can electrically control the ratio of excitons and trions and assert a residual
n-type doping of our samples. At high excitation densities and low
temperatures, an additional peak at energies below the trion dominates the
photoluminescence, which we identify as biexciton emission.Comment: 6 pages, 5 figure
Economic Effects of VAT Reform in Germany
In the tax policy debate, differentiation of value-added taxes is often justified by distributional concerns. Our quantitative analysis for Germany indicates that such concerns are misplaced. We find that the abolition of VAT differentiation has only negligible redistributive effects. Instead, reduced VAT are found to act as industry-specific subsidies. Whereas the overall welfare effects of pure VAT reforms are very small, a revenue-neutral introduction of a harmonised VAT combined with reductions in the marginal income tax rates or social security contributions turns out to produce substantial welfare gains for all households
Economic effects of VAT reforms in Germany
In the tax policy debate, differentiation of value-added taxes is often justified
by distributional concerns. Our quantitative analysis for Germany indicates
that such concerns are misplaced. We find that the abolition of VAT differentiation
has only negligible redistributive effects. Instead, reduced VAT are
found to act as industry-specific subsidies. Whereas the overall welfare effects
of pure VAT reforms are very small, a revenue-neutral introduction of a harmonised
VAT combined with reductions in the marginal income tax rates or
social security contributions turns out to yield substantial welfare gains for
all households
Serotonin and neuroplasticity - Links between molecular, functional and structural pathophysiology in depression
Serotonin modulates neuroplasticity, especially during early life, and dysfunctions in both systems likewise contribute to pathophysiology of depression. Recent findings demonstrate that serotonin reuptake inhibitors trigger reactivation of juvenile-like neuroplasticity. How these findings translate to clinical antidepressant treatment in major depressive disorder remains unclear. With this review, we link preclinical with clinical work on serotonin and neuroplasticity to bring two pathophysiologic models in clinical depression closer together. Dysfunctional developmental plasticity impacts on later-life cognitive and emotional functions, changes of synaptic serotonin levels and receptor levels are coupled with altered synaptic plasticity and neurogenesis. Structural magnetic resonance imaging in patients reveals disease-state-specific reductions of gray matter, a marker of neuroplasticity, and reversibility upon selective serotonin reuptake inhibitor treatment. Translational evidence from magnetic resonance imaging in animals support that reduced densities and sizes of neurons and reduced hippocampal volumes in depressive patients could be attributable to changes of serotonergic neuroplasticity. Since ketamine, physical exercise or learning enhance neuroplasticity, combinatory paradigms with selective serotonin reuptake inhibitors could enhance clinical treatment of depression. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe
Influence of Heat Transfer and Material Temperature on Combustion Instabilities in a Swirl Burner
The current work focuses on the large eddy simulation (LES) of combustion instability in a laboratory-scale swirl burner. Air and fuel are injected at ambient conditions. Heat conduction from the combustion chamber to the plenums results in a preheating of the air and fuel flows above ambient conditions. The paper compares two computations: In the first computation, the temperature of the injected reactants is 300 K (equivalent to the experiment) and the combustor walls are treated as adiabatic. The frequency of the unstable mode ( 635 Hz) deviates significantly from the measured frequency ( 750 Hz). In the second computation, the preheating effect observed in the experiment and the heat losses at the combustion chamber walls are taken into account. The frequency ( 725 Hz) of the unstable mode agrees well with the experiment. These results illustrate the impor- tance of accounting for heat transfer/losses when applying LES for the prediction of com- bustion instabilities. Uncertainties caused by unsuitable modeling strategies when using computational fluid dynamics for the prediction of combustion instabilities can lead to an improper design of passive control methods (such as Helmholtz resonators) as these are often only effective in a limited frequency range
Indistinguishability of identical bosons from a quantum information theory perspective
Using tools from quantum information theory, we present a general theory of
indistinguishability of identical bosons in experiments consisting of passive
linear optics followed by particle number detection. Our results do neither
rely on additional assumptions on the input state of the interferometer, such
as, for instance, a fixed mode occupation, nor on any assumption on the degrees
of freedom that potentially make the particles distinguishable. We identify the
expectation value of the projector onto the -particle symmetric subspace as
an operationally meaningful measure of indistinguishability, and derive tight
lower bounds on it that can be efficiently measured in experiments. Moreover,
we present a consistent definition of perfect distinguishability and
characterize the corresponding set of states. In particular, we show that these
states are diagonal in the computational basis up to a permutationally
invariant unitary. Moreover, we find that convex combinations of states that
describe partially distinguishable and perfectly indistinguishable particles
can lead to perfect distinguishability, which itself is not preserved under
convex combinations
Cemented vs screw-retained zirconia-based single implant reconstructions: A 3-year prospective randomized controlled clinical trial
OBJECTIVES
The objective of the present randomized clinical trial was to test whether or not the use of screw-retained all ceramic implant-borne reconstructions results in clinical, technical, and biologic outcomes similar to those obtained with cemented all ceramic reconstructions. The hypothesis was that there is no difference in clinical, technical, and biological parameters between the two types of retention.
MATERIALS AND METHODS
Forty-four patients randomly received 20 cemented reconstruction (CR) and 24 screw-retained (SR) all ceramic single crowns on two-piece dental implants with nonmatching implant-abutment junctions. All patients were recalled after crown insertion, at 6 months, 1 year, as well as at 3 years. At these visits, biological and radiographic evaluations were performed. Technical outcomes were assessed using modified USPHS (United States Public Health Service) criteria. Data were statistically analyzed with Wilcoxon-Mann-Whitney, Wilcoxon and Fisher exact tests.
RESULTS
During 3 years of follow-up, eight patients (18.2%) lost the reconstruction due to technical (6 patients, 13.6%, 2 CR and 4 SR group) or biological complications (2 patients, 4.5%, only CR group). Thirty-two subjects with 18 SR and 14 CR reconstructions attended the FU-3Y, whereas four patients (9.1%, 2 SR, 2 CR) were not available (drop-outs). Biological, technical, and radiographic outcomes did not differ significantly between the groups (P > 0.05). One implant (2.3%) was lost in the CR group. One more cemented crown (2.3%) had to be removed because of peri-implant disease. Six patients (13.6%) lost the reconstructions due to a fracture of the zirconia abutment (4 SR, 2 CR). The mean marginal bone level at 3 years was -0.4 mm (-0.5; -0.3) in group SR and - 0.4 mm (-0.6; -0.3) group CR (P = 0.864).
CONCLUSIONS
At 3 years, CR and SR exhibited similar survival technical, biological and radiographic outcomes. The rate of technical complications was high in both groups
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