614 research outputs found
Dissipative Dynamics with Trapping in Dimers
The trapping of excitations in systems coupled to an environment allows to
study the quantum to classical crossover by different means. We show how to
combine the phenomenological description by a non-hermitian Liouville-von
Neumann Equation (LvNE) approach with the numerically exact path integral
Monte-Carlo (PIMC) method, and exemplify our results for a system of two
coupled two-level systems. By varying the strength of the coupling to the
environment we are able to estimate the parameter range in which the LvNE
approach yields satisfactory results. Moreover, by matching the PIMC results
with the LvNE calculations we have a powerful tool to extrapolate the
numerically exact PIMC method to long times.Comment: 5 pages, 2 figure
Hardware-aware block size tailoring on adaptive spacetree grids for shallow water waves.
Spacetrees are a popular formalism to describe dynamically adaptive Cartesian grids. Though they directly yield an
adaptive spatial discretisation, i.e. a mesh, it is often more efficient to augment them by regular Cartesian blocks embedded into the spacetree leaves. This facilitates stencil kernels working efficiently on homogeneous data chunks. The choice of a proper block size, however, is delicate. While large block sizes foster simple loop parallelism, vectorisation, and lead to branch-free compute kernels, they bring along disadvantages. Large blocks restrict the granularity of adaptivity and hence increase the memory footprint and lower the numerical-accuracy-per-byte efficiency. Large block sizes also reduce the block-level concurrency that can be used for dynamic load balancing. In the present paper, we therefore propose a spacetree-block coupling that can dynamically tailor
the block size to the compute characteristics. For that purpose, we allow different block sizes per spacetree node. Groups of blocks of the same size are identied automatically
throughout the simulation iterations, and a predictor function triggers the replacement of these blocks by one huge, regularly rened block. This predictor can pick up hardware characteristics while the dynamic adaptivity of the fine grid mesh is not constrained. We study such characteristics with a state-of-the-art shallow water solver and examine proper block size choices on AMD Bulldozer and Intel Sandy Bridge processors
Polaron Physics in Optical Lattices
We investigate the effects of a nearly uniform Bose-Einstein condensate (BEC)
on the properties of immersed trapped impurity atoms. Using a weak-coupling
expansion in the BEC-impurity interaction strength, we derive a model
describing polarons, i.e., impurities dressed by a coherent state of Bogoliubov
phonons, and apply it to ultracold bosonic atoms in an optical lattice. We show
that, with increasing BEC temperature, the transport properties of the
impurities change from coherent to diffusive. Furthermore, stable polaron
clusters are formed via a phonon-mediated off-site attraction.Comment: 4 pages, 4 figure
Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates
In many molecular systems one encounters the situation where electronic
excitations couple to a quasi-continuum of phonon modes. That continuum may be
highly structured e.g. due to some weakly damped high frequency modes. To
handle such a situation, an approach combining the non-Markovian quantum state
diffusion (NMQSD) description of open quantum systems with an efficient but
abstract approximation was recently applied to calculate energy transfer and
absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL
103 (2009) 058301]. To explore the validity of the used approximation for such
complicated systems, in the present work we compare the calculated
(approximative) absorption spectra with exact results. These are obtained from
the method of pseudomodes, which we show to be capable of determining the exact
spectra for small aggregates and a few pseudomodes. It turns out that in the
cases considered, the results of the two approaches mostly agree quite well.
The advantages and disadvantages of the two approaches are discussed
TCT-858 Transapical Aortic Valve Replacement With The JenaValve: Less Pravalvular Leackage And Higher Transvalvular Gradient
Influence of Complex Exciton-Phonon Coupling on Optical Absorption and Energy Transfer of Quantum Aggregates
We present a theory that efficiently describes the quantum dynamics of an
electronic excitation that is coupled to a continuous, highly structured phonon
environment. Based on a stochastic approach to non-Markovian open quantum
systems, we develop a dynamical framework that allows us to handle realistic
systems where a fully quantum treatment is desired yet the usual approximation
schemes fail. The capability of the method is demonstrated by calculating
spectra and energy transfer dynamics of mesoscopic molecular aggregates,
elucidating the transition from fully coherent to incoherent transfer
Hardware-aware block size tailoring on adaptive spacetree grids for shallow water waves
Spacetrees are a popular formalism to describe dynamically adaptive Cartesian grids. Though they directly yield an adaptive spatial discretisation, i.e. a mesh, it is often more efficient to augment them by regular Cartesian blocks embedded into the spacetree leaves. This facilitates stencil kernels working efficiently on homogeneous data chunks. The choice of a proper block size, however, is delicate. While large block sizes foster simple loop parallelism, vectorisation, and lead to branch-free compute kernels, they bring along disadvantages. Large blocks restrict the granularity of adaptivity and hence increase the memory footprint and lower the numerical-accuracy-per-byte efficiency. Large block sizes also reduce the block-level concurrency that can be used for dynamic load balancing. In the present paper, we therefore propose a spacetree-block coupling that can dynamically tailor the block size to the compute characteristics. For that purpose, we allow different block sizes per spacetree node. Groups of blocks of the same size are identied automatically throughout the simulation iterations, and a predictor function triggers the replacement of these blocks by one huge, regularly rened block. This predictor can pick up hardware characteristics while the dynamic adaptivity of the fine grid mesh is not constrained. We study such characteristics with a state-of-the-art shallow water solver and examine proper block size choices on AMD Bulldozer and Intel Sandy Bridge processors
a prospective cohort study
Background The effects of target temperature management (TTM) on the heart
aren’t thoroughly studied yet. Several studies showed the prolongation of
various ECG parameters including Tpeak-Tend-time under TTM. Our study’s goal
is to evaluate the acute and long-term outcome of these prolongations. Methods
In this study we included patients with successful resuscitation after cardiac
arrest who were admitted to the Charité Virchow Klinikum Berlin or the Heart
and Vascular Centre of the Ruhr University Bochum between February 2006 and
July 2013 (Berlin) or May 2014 to November 2015 (Bochum). For analysis, one
ECG during TTM was recorded after reaching the target temperature (33–34 °C)
or in the first 6 h of TTM. If possible, another ECG was taken after TTM. The
patients were being followed until February 2016. Primary endpoint was
ventricular arrhythmia during TTM, secondary endpoints were death and
hospitalization due to cardiovascular diseases during follow-up. Results One
hundred fifty-eight patients were successfully resuscitated in the study
period of which 95 patients had usable data (e.g. ECGs without artifacts).
During TTM significant changes for different parameters of ventricular de- and
repolarization were noted: QRS (103.2 ± 23.7 vs. 95.3 ± 18.1; p = 0.003),QT
(405.8 ± 76.4 vs. 373.8 ± 75.0; p = 0.01), QTc (474.9 ± 59.7 vs. 431.0 ± 56.8;
p < 0.001), JT (302.8 ± 69.4 vs. 278.5 ± 75.2; p = 0.043), JTc (354.3 ± 60.2
vs. 318.7 ± 59.1; p = 0.001). 13.7% of the patients had ventricular
arrhythmias during TTM, however these patients showed no difference regarding
their ECG parameters in comparison to those were no ventricular arrhythmias
occurred. We were able to follow 69 Patients over an average period of 35 ± 31
months. The 14 (21.5%) patients who died during the follow-up had significant
prolongations of the TpTe-time in the ECGs without TTM (103.9 ± 47.2 vs. 75.8
± 28.6; p = 0.023). Conclusion Our results show a significant prolongation of
ventricular repolarization during TH. However, there was no significant
difference between the ECG parameters of those who developed a ventricular
arrhythmia and those who did not. The temporary prolongation of the
repolarization during TTM seems to be less important for the prognosis of the
patient. Whereas the prolongation of the repolarization in the basal ECG is
associated with a higher mortality in our study
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Electronic properties of wurtzite GaAs: A correlated structural, optical, and theoretical analysis of the same polytypic GaAs nanowire
III-V compound semiconductor nanowires are generally characterized by the
coexistence of zincblende and wurtzite structures. So far, this polytypism has
impeded the determination of the electronic properties of the metastable
wurtzite phase of GaAs, which thus remain highly controversial. In an effort to
obtain new insights into this topic, we cross-correlate nanoscale spectral imaging
by near-field scanning optical microscopy with a transmission electron microscopy
analysis of the very same polytypic GaAs nanowire dispersed onto a Si wafer.
Thus, spatially resolved photoluminescence spectra could be unambiguously
assigned to nanowire segments whose structure is known with lattice-resolved
accuracy. An emission energy of 1.528 eV was observed from extended zincblende
segments, revealing that the dispersed nanowire was under uniaxial strain
presumably due to interaction with its supporting substrate. These crucial
information and the emission energy obtained for extended pure wurtzite
segments were used to perform envelope function calculations of zincblende
quantum disks in a wurtzite matrix as well as the inverse structure. In these
calculations, we varied the fundamental bandgap, the electron mass, and the
band offset between zincblende and wurtzite GaAs. From this multi-parameter
comparison with the experimental data, we deduced that the bandgap between
the Γ8 conduction and A valence band ranges from 1.532 to 1.539 eV in strain-free
wurtzite GaAs, and estimated values of 1.507 to 1.514 eV for the Γ7–A bandgap.
Address correspondenc
Stochastic differential equations for non-linear hydrodynamics
We formulate the stochastic differential equations for non-linear
hydrodynamic fluctuations. The equations incorporate the random forces through
a random stress tensor and random heat flux as in the Landau and Lifshitz
theory. However, the equations are non-linear and the random forces are
non-Gaussian. We provide explicit expressions for these random quantities in
terms of the well-defined increments of the Wienner process.Comment: 11 pages, submitted to Phys. Rev.
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