Quantum Brownian motion of multipartite systems and their entanglement dynamics

We solve the model of N quantum Brownian oscillators linearly coupled to an environment of quantum oscillators at finite temperature, with no extra assumptions about the structure of the system-environment coupling. Using a compact phase-space formalism, we give a rather quick and direct derivation of the master equation and its solutions for general spectral functions and arbitrary temperatures. Since our framework is intrinsically nonperturbative, we are able to analyze the entanglement dynamics of two oscillators coupled to a common scalar field in previously unexplored regimes, such as off resonance and strong coupling.Comment: 10 pages, 6 figure

Nonequilibrium Dynamics of Charged Particles in an Electromagnetic Field: Causal and Stable Dynamics from 1/c Expansion of QED

We derive from a microscopic Hamiltonian a set of stochastic equations of motion for a system of spinless charged particles in an electromagnetic (EM) field based on a consistent application of a dimensionful 1/c expansion of quantum electrodynamics (QED). All relativistic corrections up to order 1/c^3 are captured by the dynamics, which includes electrostatic interactions (Coulomb), magnetostatic backreaction (Biot-Savart), dissipative backreaction (Abraham-Lorentz) and quantum field fluctuations at zero and finite temperatures. With self-consistent backreaction of the EM field included we show that this approach yields causal and runaway-free equations of motion, provides new insights into charged particle backreaction, and naturally leads to equations consistent with the (classical) Darwin Hamiltonian and has quantum operator ordering consistent with the Breit Hamiltonian. To order 1/c^3 the approach leads to a nonstandard mass renormalization which is associated with magnetostatic self-interactions, and no cutoff is required to prevent runaways. Our new results also show that the pathologies of the standard Abraham-Lorentz equations can be seen as a consequence of applying an inconsistent (i.e. incomplete, mixed-order) expansion in 1/c, if, from the start, the analysis is viewed as generating a low-energy effective theory rather than an exact solution. Finally, we show that the 1/c expansion within a Hamiltonian framework yields well-behaved noise and dissipation, in addition to the multiple-particle interactions.Comment: 17 pages, 2 figure

Non-Markovian Dynamics and Entanglement of Two-level Atoms in a Common Field

We derive the stochastic equations and consider the non-Markovian dynamics of a system of multiple two-level atoms in a common quantum field. We make only the dipole approximation for the atoms and assume weak atom-field interactions. From these assumptions we use a combination of non-secular open- and closed-system perturbation theory, and we abstain from any additional approximation schemes. These more accurate solutions are necessary to explore several regimes: in particular, near-resonance dynamics and low-temperature behavior. In detuned atomic systems, small variations in the system energy levels engender timescales which, in general, cannot be safely ignored, as would be the case in the rotating-wave approximation (RWA). More problematic are the second-order solutions, which, as has been recently pointed out, cannot be accurately calculated using any second-order perturbative master equation, whether RWA, Born-Markov, Redfield, etc.. This latter problem, which applies to all perturbative open-system master equations, has a profound effect upon calculation of entanglement at low temperatures. We find that even at zero temperature all initial states will undergo finite-time disentanglement (sometimes termed "sudden death"), in contrast to previous work. We also use our solution, without invoking RWA, to characterize the necessary conditions for Dickie subradiance at finite temperature. We find that the subradiant states fall into two categories at finite temperature: one that is temperature independent and one that acquires temperature dependence. With the RWA there is no temperature dependence in any case.Comment: 17 pages, 13 figures, v2 updated references, v3 clarified results and corrected renormalization, v4 further clarified results and new Fig. 8-1

Adherence to medication in children and adolescents with asthma: methods for monitoring and intervention

Introduction: Poor adherence in children with asthma is a major cause of asthma attacks and poor control, leads to large health-care costs, and has been identified as a factor in asthma deaths. However, it is difficult to detect and frequently overlooked leading to inappropriate escalation of asthma treatment. There is a need for cost effective ways to monitor adherence in order to intervene to change this modifiable behavior. Areas covered: Several measurement tools have been developed to assess adherence in adults and children with asthma. The current methods for measuring adherence, both subjective and objective, have several flaws and even the current gold standard, electronic monitoring devices (EMDs), has limitations. This review will outline and critique the adherence monitoring tools and highlight ways in which they have been used for the purpose of intervention. Expert commentary: Although advances have been made in adherence monitoring, we still have some way to go in creating the ideal monitoring tool. There are no validated tailored self-monitoring questionnaires for children with asthma and most objective measures, such as prescription refill rate and weighing canisters, overestimate adherence. Current EMDs, although useful, need improved accuracy to ensure that both actuation and inhalation are measured, and the devices need to be affordable for use in routine health-care practice

Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 2: Advanced energy conversion systems. Part 3: Direct energy conversion cycles

For abstract, see N76-23680

Initial state preparation with dynamically generated system-environment correlations

The dependence of the dynamics of open quantum systems upon initial correlations between the system and environment is an utterly important yet poorly understood subject. For technical convenience most prior studies assume factorizable initial states where the system and its environments are uncorrelated, but these conditions are not very realistic and give rise to peculiar behaviors. One distinct feature is the rapid build up or a sudden jolt of physical quantities immediately after the system is brought in contact with its environments. The ultimate cause of this is an initial imbalance between system-environment correlations and coupling. In this note we demonstrate explicitly how to avoid these unphysical behaviors by proper adjustments of correlations and/or the coupling, for setups of both theoretical and experimental interest. We provide simple analytical results in terms of quantities that appear in linear (as opposed to affine) master equations derived for factorized initial states.Comment: 6 pages, 2 figure

The Rotating-Wave Approximation: Consistency and Applicability from an Open Quantum System Analysis

We provide an in-depth and thorough treatment of the validity of the rotating-wave approximation (RWA) in an open quantum system. We find that when it is introduced after tracing out the environment, all timescales of the open system are correctly reproduced, but the details of the quantum state may not be. The RWA made before the trace is more problematic: it results in incorrect values for environmentally-induced shifts to system frequencies, and the resulting theory has no Markovian limit. We point out that great care must be taken when coupling two open systems together under the RWA. Though the RWA can yield a master equation of Lindblad form similar to what one might get in the Markovian limit with white noise, the master equation for the two coupled systems is not a simple combination of the master equation for each system, as is possible in the Markovian limit. Such a naive combination yields inaccurate dynamics. To obtain the correct master equation for the composite system a proper consideration of the non-Markovian dynamics is required.Comment: 17 pages, 0 figures

Photograph-based diagnosis of burns in patients with dark-skin types: The importance of case and assessor characteristics

AbstractAimThis study assessed whether photographs of burns on patients with dark-skin types could be used for accurate diagnosing and if the accuracy was affected by physicians’ clinical background or case characteristics.Method21 South-African cases (Fitzpatrick grades 4–6) of varying complexity were photographed using a camera phone and uploaded on a web-survey. Respondents were asked to assess wound depth (3 categories) and size (in percentage). A sample of 24 burn surgeons and emergency physicians was recruited in South-Africa, USA and Sweden. Measurements of accuracy (using percentage agreement with bedside diagnosis), inter- (n=24), and intra-rater (n=6) reliability (using percentage agreement and kappa) were computed for all cases aggregated and by case characteristic.ResultsOverall diagnostic accuracy was 67.5% and 66.0% for burn size and depth, respectively. It was comparable between burn surgeons and emergency physicians and between countries of practice. However, the standard deviations were smaller, showing higher similarities in diagnoses for burn surgeons and South-African clinicians compared to emergency physicians and clinicians from other countries. Case characteristics (child/adult, simple/complex wound, partial/full thickness) affected the results for burn size but not for depth. Inter- and intra-rater reliability for burn depth was 55% and 77%.ConclusionSize and depth of burns on patients with dark-skin types could be assessed at least as well using photographs as at bedside with 67.5% and 66.0% average accuracy rates. Case characteristics significantly affected the accuracy for burn size, but medical specialty and country of practice seldom did in a statistically significant manner

Indigenous wellbeing in Australia: Evidence from HILDA

This study explores the subjective wellbeing of Indigenous Australians. We focus on mean levels of self-reported life satisfaction, inequality in life satisfaction within the Indigenous and non-Indigenous Australian populations, and the prevalence and severity of dissatisfaction with one’s life. Evidence on differences in the determinants of life satisfaction between Indigenous and non-Indigenous Australians is provided. Results indicate that Indigenous life satisfaction peaked in 2003 and has since declined. We also find that inequality in life satisfaction is greater for Indigenous than non-Indigenous Australians. Despite a downward trend in the level of dissatisfaction for non-Indigenous Australians, dissatisfaction among Indigenous Australians has remained relatively unchanged