71 research outputs found
Optimal control of open quantum systems: Cooperative effects of driving and dissipation
No full textWe investigate the optimal control of open quantum systems, in particular, the mutual influence of driving and dissipation. A stochastic approach to open-system control is developed, using a generalized version of Krotov's iterative algorithm, with no need for Markovian or rotating-wave approximations. The application to a harmonic degree of freedom reveals cooperative effects of driving and dissipation that a standard Markovian treatment cannot capture. Remarkably, control can modify the open-system dynamics to the point where the entropy change turns negative, thus achieving cooling of translational motion without any reliance on internal degrees of freedom. © 2011 American Physical Society
SELECTIVE EMOTION PROCESSING IN THE VISUAL BRAIN: THE NEAR ABSENCE OF HABITUATION
No full textRecent studies support the hypothesis that emotional stimuli draw attentional
resources. Specifically, emotional images elicit augmented negative amplitudes over
occipito-temporal regions (early posterior negativity, EPN) around 150 ms after
stimulus onset, most apparent between 200 and 300 ms. Accordingly, it was
explored in this study whether the selective processing of emotional cues is an
obligatory phenomenon that does not habituate. Pleasant, neutral, and unpleasant
pictures were presented for 330 ms without perceivable interstimulus interval. The
picture set was repeated 90 times amounting to a total of 3600 picture
presentations. The EEG was collected continuously with a 129 dense sensor array
during passive picture viewing. Replicating previous results, emotional contents
were associated with significantly augmented EPN amplitudes over temporooccipital
sites. Of most interest, emotional modulation was similarly expressed for
the first and last block of picture presentation. The present findings demonstrate the
near absence of habituation of the selective attention devoted to emotionally
significant stimuli during perceptual processing. These findings contrast with the
rapid habituation that can be observed for autonomic indices of emotional
processing. Accordingly, it appears that habituation changes the networks that
regulate the organization of the emotional response output, but that those networks
responsible for the detection of emotional significant stimuli in environment are not
altered by habituation, and might therefore be an obligatory response
Comments on the authors’ reply to the critical appraisal concerning “Wearable cardioverter defibrillators for the prevention of sudden cardiac arrest: a health technology assessment and patient focus group study”
No full textJohannes Sperzel,1 Ingo Staudacher,2 Olaf Goeing,3 Martin Stockburger,4 Thorsten Meyer,5 Ana Sofia Oliveira Gonçalves,6 Hanna Sydow,6 Tonio Schoenfelder,6 Volker Amelung6 1Department of Cardiology, Hospital Kerckhoff Klinik GmbH, Bad Nauheim, Germany; 2Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany; 3Department of Cardiology, Sana-Hospital Lichtenberg, Berlin, Germany; 4Medical Department I, Havelland Kliniken GmbH, Nauen, Germany; 5Department of Public Health, Universität Bielefeld, Bielefeld, Germany; 6inav – privates Institut für angewandte Versorgungsforschung GmbH, Berlin, GermanySince the authors’ reply to our critical appraisal did not properly address the points we raised, we still see need for further clarification. The wearable cardioverter defibrillator (WCD) is not an adequate substitute for an implantable cardioverter defibrillator (ICD). The authors state that both can be compared immediately post-myocardial infarction (MI). According to the current guidelines, primary prevention of sudden cardiac death with the ICD within 40 days after MI is generally not indicated.1 Therefore, we disagree with the authors’ proposal of conducting such a trial. In this context, the authors mentioned the VEST trial, which compares a WCD population and one receiving medical treatment. There is explicitly no comparison to an ICD population.View the original paper by Sperzel and colleagues
Critical appraisal concerning “Wearable cardioverter defibrillators for the prevention of sudden cardiac arrest: a health technology assessment and patient focus group study”
No full textJohannes Sperzel,1 Ingo Staudacher,2 Olaf Goeing,3 Martin Stockburger,4 Thorsten Meyer,5 Ana Sofia Oliveira Gonçalves,6 Hanna Sydow,6 Tonio Schoenfelder,6 Volker Eric Amelung6 1Department of Cardiology, Hospital Kerckhoff Klinik GmbH, Bad Nauheim, Germany; 2Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany; 3Department of Cardiology, Sana-Hospital Lichtenberg, Berlin, Germany; 4Medical Department I, Havelland Kliniken GmbH, Nauen, Germany; 5Department of Public Health, Universität Bielefeld, Bielefeld, Germany; 6Institute for Applied Health Services Research, inav – privates Institut für angewandte Versorgungsforschung GmbH, Berlin, GermanyWe read with great interest the article “Wearable cardioverter defibrillators for the prevention of sudden cardiac arrest: a health technology assessment and patient focus group study” by Ettinger et al. The authors conclude that wearable cardioverter defibrillators (WCDs) seem to be fairly safe in the short-to-medium term, but the quality of the available evidence is low. They also state that – according to their study inclusion criteria – they were not able to identify studies to assess the clinical effectiveness of the WCD. Given the importance of WCD for its target population and considering our clinical expertise, we see a particular need to clarify some points of this article.Author's ReplySabine Ettinger,1 Michal Stanak,1 Piotr Szymański,2 Claudia Wild,1 Romana Tandara Haček,3 Darija Erčević,3 Renata Grenković,3 Mirjana Huić31Ludwig Boltzmann Institute for Health Technology Assessment, Vienna, Austria; 2Institute of Cardiology, Warsaw, Poland; 3Department for Development, Research and Health Technology Assessment, Agency for Quality and Accreditation in Health Care and Social Welfare, Zagreb, CroatiaWe read the letter to the editor with regard to our published paper on “Wearable cardioverter defibrillators for the prevention of sudden cardiac arrest: a health technology assessment and patient focus group study” and gladly take the opportunity to appropriately address and clarify the issues that were raised. View the original paper by Ettinger and colleagues. 
Environment-Mediated Long-Ranged Correlations in Many-Body System
No full textQuantum states in complex aggregates are unavoidably affected by environmental effects, which typically cannot be accurately modeled by simple Markovian processes. As system sizes scale up, nonperturbative simulation become thus unavoidable but they are extremely challenging due to the intimate interplay of intrinsic many-body interaction and time-retarded feedback from environmental degrees of freedom. In this work, we utilize the recently developed Quantum Dissipation with Minimally Extended State Space (QD-MESS) approach to address reservoir induced long-ranged temporal correlations in finite size Ising-type spin chains. For thermal reservoirs with ohmic and subohmic spectral density we simulate the quantum time evolution from finite to zero temperature. The competition between thermal fluctuations, quantum fluctuations, and anti-/ferromagnetic interactions reveal a rich pattern of dynamical phases including dissipative induced phase transitions and spatiotemporal correlations.27 pages, 8 figure
Currents and fluctuations of quantum heat transport in harmonic chains
No full textAbstract
Heat transport in open quantum systems is particularly susceptible to the modeling of system–reservoir interactions. It thus requires us to consistently treat the coupling between a quantum system and its environment. While perturbative approaches are successfully used in fields like quantum optics and quantum information, they reveal deficiencies—typically in the context of thermodynamics, when it is essential to respect additional criteria such as fluctuation-dissipation theorems. We use a non-perturbative approach for quantum dissipative dynamics based on a stochastic Liouville–von Neumann equation to provide a very general and extremely efficient formalism for heat currents and their correlations in open harmonic chains. Specific results are derived not only for first- but also for second-order moments, which requires us to account for both real and imaginary parts of bath–bath correlation functions. Spatiotemporal patterns are compared with weak coupling calculations. The regime of stronger system–reservoir couplings gives rise to an intimate interplay between reservoir fluctuations and heat transfer far from equilibrium
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