Modal quantum theory

We present a discrete model theory similar in structure to ordinary quantum mechanics, but based on a finite field instead of complex amplitudes. The interpretation of this theory involves only the "modal" concepts of possibility and necessity rather than quantitative probability measures. Despite its simplicity, our model theory includes entangled states and has versions of both Bell's theorem and the no cloning theorem.Comment: Presented at the 7th Workshop on Quantum Physics and Logic, Oxford University (29-30 May 2010). Revised 1 Aug 2011 in response to referee comment

Effects of resonant single-particle states on pairing correlations

Effects of resonant single-particle (s.p.) states on the pairing correlations are investigated by an exact treatment of the pairing Hamiltonian on the Gamow shell model basis. We introduce the s.p. states with complex energies into the Richardson equations. The solution shows the property that the resonant s.p. states with large widths are less occupied. The importance of many-body correlations between bound and resonant prticle pairs is shown.Comment: 4 pages, 3 figures, to be published in Phys. Rev.

Stabilizer notation for Spekkens' toy theory

Spekkens has introduced a toy theory [Phys. Rev. A, 75, 032110 (2007)] in order to argue for an epistemic view of quantum states. I describe a notation for the theory (excluding certain joint measurements) which makes its similarities and differences with the quantum mechanics of stabilizer states clear. Given an application of the qubit stabilizer formalism, it is often entirely straightforward to construct an analogous application of the notation to the toy theory. This assists calculations within the toy theory, for example of the number of possible states and transformations, and enables superpositions to be defined for composite systems.Comment: 7+4 pages, 5 tables. v2: Clarifications added and typos fixed in response to referee comment

Cosmic String Cusps with Small-Scale Structure: Their Forms and Gravitational Waveforms

We present a method for the introduction of small-scale structure into strings constructed from products of rotation matrices. We use this method to illustrate a range of possibilities for the shape of cusps that depends on the properties of the small-scale structure. We further argue that the presence of structure at cusps under most circumstances leads to the formation of loops at the size of the smallest scales. On the other hand we show that the gravitational waveform of a cusp remains generally unchanged; the primary effect of small-scale structure is to smooth out the sharp waveform emitted in the direction of cusp motion.Comment: RevTeX, 8 pages. Replaced with version accepted for publication by PR

Targeted free energy perturbation

A generalization of the free energy perturbation identity is derived, and a computational strategy based on this result is presented. A simple example illustrates the efficiency gains that can be achieved with this method.Comment: 8 pages + 1 color figur

Recovery of Fertilizer Nitrogen Under Field Conditions Using Nitrogen-15

An experiment was conducted under field conditions to study the movement and recovery of N15-enriched nitrogen fertilizer added to soil in the forms of NaNO2 and (NH4)2SO4. The plots consisted of the soil mass inside cylinders 30 or 60 cm in diameter, which were pressed into the soil to a depth of 45-60 cm. These plots were either seeded to sudangrass (sorghum sudanense) or left uncropped. The plant tops, roots, and the soil, by 15-cm layers, were analyzed for total N and excess N15 content. Recovery of added N15 from the 32 plots ranged between 96.3 and 101.8%, and averaged 99.0%. There was no significant difference in recovery of the fertilizer N due to the percent of excess N15 in the fertilizer, size of plot, exposure to natural rainfall, cropping, N source, or the time of application of the fertilizer. Wide variation in recovery of excess N15 occurred with core sampling and it was found necessary to remove, weigh, mix and subsample the entire soil mass from within the rims. The small amounts of unrecovered N were probably due to procedural errors in the field and laboratory, and leaching and root growth beyond the sampling zone. There was no indication of any N loss in the gaseous form. The fate of applied fertilizer N was followed under field conditions using N15-enriched nitrogen fertilizer applied to the soil in situ enclosed by large steel cylinders. Total recovery of the fertilizer N from these experiments after 8 weeks ranged from 88 to 96%, but dropped as low as 77% after 10 months. Recovery of the fertilizer N was greater from an ammonium source than from nitrate. Better recovery of fertilizer was obtained when the plots were cropped to sudangrass rather than left fallow. Doubling the rate of application of the fertilizer N from 336 to 672 kg/ha did not affect percent of total recovery. The 4 to 12% of fertilizer N unrecovered after 8 weeks appears to be due to a loss in the gaseous form, since special precautions were taken to restrict leaching and to eliminate errors in sampling and analysis

Perceptions and experiences of appetite awareness training among African-American women who binge eat

Introduction: Binge eating may contribute to the prevalence of obesity in African-American women. Yet, there has been scant intervention research on the treatment of binge eating in this population. We tested the feasibility of an appetite awareness training (AAT) intervention in a sample of African-American women with binge and overeating behaviors. Participants who completed AAT were recruited to participate in focus groups to elicit information about their perceptions and experiences with this intervention to inform the design of future interventions to treat binge eating and obesity in African-American women. Methods: African-American women, aged 18–70 years, who had completed an 8-week randomized AAT intervention, were invited to attend a focus group discussion. Session content was recorded and transcribed. Data were analyzed by use of open coding. Themes were identified that described their perceptions and experiences of participating in the intervention. Results: Seventeen women participated in three focus group discussions. Pertinent themes identified included: paying attention to internal cues of hunger and satiety, influence of culture on eating patterns, breaking patterns of disordered eating, and perceptions about weight. Overall, participants were satisfied with their experience of AAT, and reported they found it valuable to learn about listening to biological signals of hunger and satiety and to learn specific strategies to reduce maladaptive eating patterns. Conclusion: AAT was acceptable and provided helpful eating behavior instruction to African-American women with reported binge and overeating behaviors. Future research should examine the potential of AAT to improve weight management in this underserved population. Level of evidence: Level V, qualitative descriptive study

Peripheral brain-derived neurotrophic factor contributes to chronic osteoarthritis joint pain

Brain-derived neurotrophic factor (BDNF) and the high-affinity receptor tropomyosin receptor kinase B (TrkB) have important roles in neuronal survival and in spinal sensitization mechanisms associated with chronic pain. Recent clinical evidence also supports a peripheral role of BDNF in osteoarthritis (OA), with synovial expression of TrkB associated with higher OA pain. The aim of this study was to use clinical samples and animal models to explore the potential contribution of knee joint BDNF/TrkB signalling to chronic OA pain. Brain-derived neurotrophic factor and TrkB mRNA and protein were present in knee synovia from OA patients (16 women, 14 men, median age 67 years [interquartile range: 61-73]). There was a significant positive correlation between mRNA expression of NTRK2 (TrkB) and the proinflammatory chemokine fractalkine in the OA synovia. Using the surgical medial meniscal transection (MNX) model and the chemical monosodium iodoacetate (MIA) model of OA pain in male rats, the effects of peripheral BDNF injection, vs sequestering endogenous BDNF with TrkB-Fc chimera, on established pain behaviour were determined. Intra-articular injection of BDNF augmented established OA pain behaviour in MIA rats, but had no effect in controls. Intra-articular injection of the TrkB-Fc chimera acutely reversed pain behaviour to a similar extent in both models of OA pain (weight-bearing asymmetry MIA: -11 ± 4%, MNX: -12 ± 4%), compared to vehicle treatment. Our data suggesting a contribution of peripheral knee joint BDNF/TrkB signalling in the maintenance of chronic OA joint pain support further investigation of the therapeutic potential of this target

Revisiting consistency conditions for quantum states of systems on closed timelike curves: an epistemic perspective

There has been considerable recent interest in the consequences of closed timelike curves (CTCs) for the dynamics of quantum mechanical systems. A vast majority of research into this area makes use of the dynamical equations developed by Deutsch, which were developed from a consistency condition that assumes that mixed quantum states uniquely describe the physical state of a system. We criticise this choice of consistency condition from an epistemic perspective, i.e., a perspective in which the quantum state represents a state of knowledge about a system. We demonstrate that directly applying Deutsch's condition when mixed states are treated as representing an observer's knowledge of a system can conceal time travel paradoxes from the observer, rather than resolving them. To shed further light on the appropriate dynamics for quantum systems traversing CTCs, we make use of a toy epistemic theory with a strictly classical ontology due to Spekkens and show that, in contrast to the results of Deutsch, many of the traditional paradoxical effects of time travel are present.Comment: 10 pages, 6 figures, comments welcome; v2 added references and clarified some points; v3 published versio