Hamiltonian Composite Dynamics Can Almost Always Lead To Negative Reduced Dynamics

Complete positivity is a ubiquitous assumption in the study of quantum systems interacting with the environment, despite repeated efforts to point out that the assumption is not empirically justified. It will be shown that Hamiltonian evolution of a quantum system and its environment can be negative (i.e.\ not completely positive) in the energy basis, by showing that such evolution is {\it almost always} negative for given initial conditions. Ignoring or "correcting" experimental data that is not completely positive may cause the loss of important information regarding system-environment correlations and coupling. A relationship between the negativity of an evolution and the eigenvalues of the Hamiltonian will be shown, and experimental verification of negative reduced dynamics will be proposed.Comment: 7 pages, 2 figures; Added a discussion of discord and proposed experimental observations of negativit

Quantum Channel Negativity as a Measure of System-Bath Coupling and Correlation

Complete positivity is a ubiquitous assumption in the study of quantum systems interacting with the environment, but the lack of complete positivity of a quantum evolution (called the "negativity") can be used as a measure of the system-bath coupling and correlation. The negativity can be computed from the Choi representation of a channel, is always defined and bounded, and can be used to understand environmentally induced noise in a quantum system.Comment: 11 pages, 9 figures; added acknowledgement

Could light harvesting complexes exhibit non-classical effects at room temperature?

Mounting experimental and theoretical evidence suggests that coherent quantum effects play a role in the efficient transfer of an excitation from a chlorosome antenna to a reaction center in the Fenna-Matthews-Olson protein complex. However, it is conceivable that a satisfying alternate interpretation of the results is possible in terms of a classical theory. To address this possibility, we consider a class of classical theories satisfying the minimal postulates of macrorealism and frame Leggett-Garg-type tests that could rule them out. Our numerical simulations indicate that even in the presence of decoherence, several tests could exhibit the required violations of the Leggett-Garg inequality. Remarkably, some violations persist even at room temperature for our decoherence model.Comment: 10 pages, 4 figures, 2 tables, submitted to the Proceedings of the Royal Society

Predictors of painkiller dependence among people with pain in the general population

Aims: Self-medication with painkillers is widespread and increasing, and evidence about influences on painkiller dependence is needed to inform efforts to prevent and treat problem painkiller use. Design: Online questionnaire survey. Participants: People in the general population who had pain and used painkillers in the last month (n=112). Measurements: Pain frequency and intensity, use of over-the-counter and prescription painkillers, risk of substance abuse (SOAPP scale), depression, anxiety, stress, alexithymia, pain catastrophizing, pain anxiety, pain self-efficacy, pain acceptance, mindfulness, self-compassion, and painkiller dependence (Leeds Dependence Questionnaire). Findings: In multiple regression, the independent predictors of painkiller dependence were prescription painkiller use (ß 0.21), SOAPP score (ß 0.31), and pain acceptance (ß -0.29). Prescription painkiller use mediated the influence of pain intensity. Alexithymia, anxiety and pain acceptance all moderated the influence of pain. Conclusions: The people most at risk of developing painkiller dependence are those who use prescription painkillers more frequently, who have a prior history of substance-related problems more generally, and who are less accepting of pain. Based on these findings, a preliminary model is presented with three types of influence on the development of painkiller dependence: a) pain leading to painkiller use, b) risk factors for substance-related problems irrespective of pain, and c) psychological factors related to pain. The model could guide further research among the general population and high risk groups, and acceptance-based interventions could be adapted and evaluated as methods to prevent and treat painkiller dependence.The Leonardo Da Vinci Lifelong Learning Programme funded Joana Duarte’s graduate research placement at the University of Derb

An assessment of the relative influence of pain coping, negative thoughts about pain, and pain acceptance on health-related quality of life among people with hemophilia

Many people with hemophilia are affected by chronic arthritic joint pain as well as acute bleeding pain. In this cross-sectional study, 209 men with hemophilia A or B completed the Hemophilia Pain Coping Questionnaire (HPCQ), the Chronic Pain Acceptance Questionnaire (CPAQ), and the RAND 36-item Health Survey (SF-36), a measure of health-related quality of life. Multiple regression was used to test the influence of active pain coping, passive adherence coping, and negative thoughts about pain (HPCQ scales), and activity engagement and pain willingness (CPAQ scales), on physical and mental components of quality of life (SF-36 PCS and MCS scales), taking account of age, hemophilia severity, use of clotting factor, and pain intensity. Pain intensity was the main influence on physical quality of life and negative thoughts was the main influence on mental quality of life. Activity engagement and pain willingness had small but significant influences on physical and mental quality of life. Pain willingness also moderated and partly mediated the influence of pain intensity on physical quality of life, and activity engagement and pain willingness mediated the influence of negative thoughts on mental quality of life. Negative thoughts moderated and partly mediated the influence of pain intensity on mental quality of life. There was no evidence that active pain coping influenced quality of life. The findings suggest that quality of life in hemophilia could potentially be improved by interventions to increase pain acceptance and reduce negative thoughts about pain, especially among those with less severe pain.Haemophilia Society UK; Institute for Health Policy and Research, London Metropolitan University

Advanced Solar-propelled Cargo Spacecraft for Mars Missions

Three concepts for an unmanned, solar powered, cargo spacecraft for Mars support missions were investigated. These spacecraft are designed to carry a 50,000 kg payload from a low Earth orbit to a low Mars orbit. Each design uses a distinctly different propulsion system: A Solar Radiation Absorption (SRA) system, a Solar-Pumped Laser (SPL) system and a solar powered magnetoplasmadynamic (MPD) arc system. The SRA directly converts solar energy to thermal energy in the propellant through a novel process. In the SPL system, a pair of solar-pumped, multi-megawatt, CO2 lasers in sunsynchronous Earth orbit converts solar energy to laser energy. The MPD system used indium phosphide solar cells to convert sunlight to electricity, which powers the propulsion system. Various orbital transfer options are examined for these concepts. In the SRA system, the mother ship transfers the payload into a very high Earth orbit and a small auxiliary propulsion system boosts the payload into a Hohmann transfer to Mars. The SPL spacecraft and the SPL powered spacecraft return to Earth for subsequent missions. The MPD propelled spacecraft, however, remains at Mars as an orbiting space station. A patched conic approximation was used to determine a heliocentric interplanetary transfer orbit for the MPD propelled spacecraft. All three solar-powered spacecraft use an aerobrake procedure to place the payload into a low Mars parking orbit. The payload delivery times range from 160 days to 873 days (2.39 years)