3,496 research outputs found
Ultrafast pump-probe dynamics in ZnSe-based semiconductor quantum-wells
Pump-probe experiments are used as a controllable way to investigate the
properties of photoexcited semiconductors, in particular, the absorption
saturation. We present an experiment-theory comparison for ZnSe quantum wells,
investigating the energy renormalization and bleaching of the excitonic
resonances. Experiments were performed with spin-selective excitation and
above-bandgap pumping. The model, based on the semiconductor Bloch equations in
the screened Hartree-Fock approximation, takes various scattering processes
into account phenomenologically. Comparing numerical results with available
experimental data, we explain the experimental results and find that the
electron spin-flip occurs on a time scale of 30 ps.Comment: 10 pages, 9 figures. Key words: nonlinear and ultrafast optics,
modeling of femtosecond pump-probe experiments, electron spin-flip tim
Polarons in semiconductor quantum-dots and their role in the quantum kinetics of carrier relaxation
While time-dependent perturbation theory shows inefficient carrier-phonon
scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic
description of carrier-phonon interaction predicts fast carrier capture and
relaxation. The considered processes do not fulfill energy conservation in
terms of free-carrier energies because polar coupling of localized quantum-dot
states strongly modifies this picture.Comment: 6 pages, 6 figures, accepted for publication in Phys.Rev.
Intraocular pressure fluctuations in professional brass and woodwind musicians during common playing conditions.
BACKGROUND: We investigated the effects on intraocular pressure (IOP) and blood pressure (BP) of playing brass and woodwind instruments by monitoring IOP and BP in a representative group of professional musicians under a variety of common playing conditions. METHODS: IOP and BP measurements were recorded from 37 brass and 15 woodwind instrument players, before and after playing tones of low, middle and high frequency. We also measured IOP and BP before and during playing common exercises of 10 minutes duration, as well as after playing a sustained high-pitched tone, to test for changes in IOP under conditions of maximum effort. RESULTS: Playing tones on brass and woodwind instruments causes a temporary elevation in IOP and BP, depending on the tone frequency: brass instrument players showed a significant elevation after playing high and middle frequency tones (p < 0.0001) whereas woodwind instrument players showed a significant increase only for high frequencies (e.g., oboe, 17 ± 2.9 mm Hg to 21 ± 4.4 mm Hg; p = 0.017). Playing a typical exercise of 10 minutes temporarily increased IOP in both groups of musicians. Finally, playing a sustained tone of high pitch caused a significant elevation in IOP in brass instrument players only (16.6 ± 3.5 mm Hg to 23.3 ± 8.9 mm Hg; p < 0.0001). CONCLUSIONS: The temporary and sometimes dramatic elevations and fluctuations in IOP observed in this study, coupled with daily exposure to instrument play, puts professional wind instrument players at increased risk of developing glaucoma. Consequently, these musicians should be monitored for signs of glaucoma, especially those with co-existing risk factors
Real-Time Noninvasive Analysis of Biocatalytic PET Degradation
The Earth has entered the Anthropocene, which is branded by ubiquitous and devastating environmental pollution from plastics such as polyethylene terephthalate (PET). Ecofriendly and at the same time economical solutions for plastic recycling and reuse are being sought more urgently now than ever. With the possibility to recover its building blocks, the hydrolysis of PET waste by its selective biodegradation with polyester hydrolases is an appealing solution. We demonstrate how changing the dielectric properties of PET films can be used to evaluate the performance of polyester hydrolases. For this purpose, a PET film separates two reaction chambers in an impedimetric setup to quantify the film thickness- and surface area-dependent change in capacitance caused by the enzyme. The derived degradation rates determined for the polyester hydrolases PHL7 and LCC were similar to those obtained by gravimetric and vertical scanning interferometry measurements. Compared to optical methods, this technique is also insensitive to changes in the solution composition. AFM and FEM simulations further supported that impedance spectroscopy is a powerful tool for the detailed analysis of the enzymatic hydrolysis process of PET films. The developed monitoring system enabled both high-temporal resolution and parallel processing suitable for the analysis of the enzymatic degradability of polyester films and the properties of the biocatalysts.Version 2.0 is updated to include an acknowledgement of funding from the ENZYCLE projec
Transfer ionization and its sensitivity to the ground-state wave function
We present kinematically complete theoretical calculations and experiments
for transfer ionization in HHe collisions at 630 keV/u. Experiment and
theory are compared on the most detailed level of fully differential cross
sections in the momentum space. This allows us to unambiguously identify
contributions from the shake-off and two-step-2 mechanisms of the reaction. It
is shown that the simultaneous electron transfer and ionization is highly
sensitive to the quality of a trial initial-state wave function
Supercurrent in Nodal Superconductors
In recent years, a number of nodal superconductors have been identified;
d-wave superconductors in high T_c cuprates, CeCoIn, and
\kappa-(ET)_2Cu(NCS)_2, 2D f-wave superconductor in Sr_2RuO_4 and hybrid
s+g-wave superconductor in YNi_2B_2C. In this work we conduct a theoretical
study of nodal superconductors in the presence of supercurrent. For simplicity,
we limit ourselves to d-wave and 2D f-wave superconductors. We compute the
quasiparticle density of states and the temperature dependence of the depairing
critical current in nodal superconductors, both of which are accessible
experimentally.Comment: revtex4, 6 pages, 7 figures; fixed typos, updated references, trimmed
introductio
Resolving the dynamical mass of a z~1.3 QSO host galaxy using SINFONI and Laser Guide Star assisted Adaptive Optics
Recent studies of the tight scaling relations between the masses of
supermassive black holes and their host galaxies have suggested that in the
past black holes constituted a larger fraction of their host galaxies' mass.
However, these arguments are limited by selection effects and difficulties in
determining robust host galaxy masses at high redshifts. Here we report the
first results of a new, complementary diagnostic route: we directly determine a
dynamical host galaxy mass for the z=1.3 luminous quasar J090543.56+043347.3
through high-spatial-resolution (0.47", 4kpc FWHM) observations of the host
galaxy gas kinematics over 30x40 kpc using ESO/VLT/SINFONI with LGS/AO.
Combining our result of M_dyn = 2.05+1.68_0.74 x 10^11 M_sun (within a radius
5.25 +- 1.05 kpc) with M_BH,MgII = 9.02 \pm 1.43 x 10^8 M_sun, M_BH,Halpha =
2.83 +1.93-1.13 x 10^8 M_sun, we find that the ratio of black hole mass to host
galaxy dynamical mass for J090543.56+043347.3 matches the present-day relation
for M_BH vs. M_Bulge,Dyn, well within the IR scatter, deviating at most a
factor of two from the mean. J090543.56+043347.3 displays clear signs of an
ongoing tidal interaction and of spatially extended star formation at a rate of
50-100 M_sun/yr, above the cosmic average for a galaxy of this mass and
redshift. We argue that its subsequent evolution may move J090543.56+043347.3
even closer to the z=0 relation for M_BH vs. M_Bulge,Dyn. Our results support
the picture where any substantive evolution in these relations must occur prior
to z~1.3. Having demonstrated the power of this modelling approach we are
currently analyzing similar data on seven further objects to better constrain
such evolution.Comment: Accepted for publication in ApJ, 14 pages, 10 Figure
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