Aharonov-Bohm Radiation

A solenoid oscillating in vacuum will pair produce charged particles due to the Aharonov-Bohm (AB) interaction. We calculate the radiation pattern and power emitted for charged scalar particles. We extend the solenoid analysis to cosmic strings, and find enhanced radiation from cusps and kinks on loops. We argue by analogy with the electromagnetic AB interaction that cosmic strings should emit photons due to the gravitational AB interaction of fields in the conical spacetime of a cosmic string. We calculate the emission from a kink and find that it is of similar order as emission from a cusp, but kinks are vastly more numerous than cusps and may provide a more interesting observational signature.Comment: Accepted for publication in Phys Rev

A Nearly Scale Invariant Spectrum of Gravitational Radiation from Global Phase Transitions

Using a large N sigma model approximation we explicitly calculate the power spectrum of gravitational waves arising from a global phase transition in the early universe and we confirm that it is scale invariant, implying an observation of such a spectrum may not be a unique feature of inflation. Moreover, the predicted amplitude can be over 3 orders of magnitude larger than the naive dimensional estimate, implying that even a transition that occurs after inflation may dominate in Cosmic Microwave Background polarization or other gravity wave signals.Comment: 4 pages, PRL published versio

A New Class of non-Hermitian Quantum Hamiltonians with PT Symmetry

In a remarkable development Bender and coworkers have shown that it is possible to formulate quantum mechanics consistently even if the Hamiltonian and other observables are not Hermitian. Their formulation, dubbed PT quantum mechanics, replaces hermiticity by another set of requirements, notably that the Hamiltonian should be invariant under the discrete symmetry PT, where P denotes parity and T denotes time reversal. All prior work has focused on the case that time reversal is even (T^2 = 1). We generalize the formalism to the case of odd time reversal (T^2 = -1). We discover an analogue of Kramer's theorem for PT quantum mechanics, present a prototypical example of a PT quantum system with odd time reversal, and discuss potential applications of the formalism. Odd time reversal symmetry applies to fermionic systems including quarks and leptons and a plethora of models in nuclear, atomic and condensed matter physics. PT quantum mechanics makes it possible to enlarge the set of possible Hamiltonians that physicists could deploy to describe fundamental physics beyond the standard model or for the effective description of condensed matter phenomena.Comment: Replaced submitted version with accepted version; to appear in Phys Rev

Jet evolution, flux ratios and light-travel time effects

Studies of the knotty jets in both quasars and microquasars frequently make use of the ratio of the intensities of corresponding knots on opposite sides of the nucleus in order to infer the product of the intrinsic jet speed (beta) and the cosine of the inclination angle of the jet-axis (cos{theta}), via the formalism I_{a}/I_{r} = ((1+beta cos{theta})/(1-beta cos{theta}))^{3+alpha}, where alpha relates the intensity I_{nu} as a function of frequency nu as I_{nu} propto nu^{-alpha}. Where beta cos{theta} is determined independently, the intensity ratio of a given pair of jet to counter-jet knots is over-predicted by the above formalism compared with the intensity ratio actually measured from radio images. As an example in the case of Cygnus X-3 the original formalism predicts an intensity ratio of about 185, whereas the observed intensity ratio at one single epoch is about 3. Mirabel and Rodriguez (1999) have refined the original formalism, and suggested measuring the intensity ratio of knots when they are at equal angular separations from the nucleus. This method is only applicable where there is sufficient time-sampling with sufficient physical resolution to interpolate the intensities of the knots at equal distances from the nucleus, and can therefore be difficult to apply to microquasars and is impossible to apply to quasars. Accounting for both the light-travel time between the knots and the simple evolution of the knots themselves reconciles this over-prediction and renders the original formalism obsolete.Comment: 5 pages, no figures, to be published in ApJ Letter

Evaluating Participatory Modeling: Developing a Framework for Cross-case Analysis

Participatory modeling is increasingly recognised as an effective way to assist collective decision-making processes in the domain of natural resource management. This paper introduces a framework for evaluating projects that have adopted a participatory modeling approach. This framework – known as the ‘Protocol of Canberra’ – was developed through a collaboration between French and Australian researchers engaged in participatory modeling and evaluation research. The framework seeks to assess the extent to which different participatory modeling practices reinforce or divert from the theoretical assumptions they are built upon. The paper discusses the application of the framework in three case-studies, two from Australia and one from the Pacific island of the Republic of Kiribati. The paper concludes with some comments for future use of the framework in a range of participatory modeling contexts, including fostering consideration of why and how different methodological approaches are used to achieve project aims and to build a collective vision amongst diverse stakeholders.participation, modeling, evaluation, complex systems science

Integrating Best Evidence into Practice: Outcomes of a Community-Based 12-week Exercise and Education Intervention in Women with Cancer

Objective Cancer-related fatigue is the most commonly reported side effect of cancer treatment, affecting 70-100% of patients and current literature suggests exercise is an important component of managing this side effect. The specific objective of this project was to evaluate the effectiveness of a 12-week evidence-based cancer exercise and education intervention on outcomes of fatigue, pain, depression, sleep disturbance and quality of life for women with cancer; the intervention was delivered by an interprofessional team in a medically-based wellness center. Methods The team was led by a physical therapist and included medical and radiation oncologists, general surgeons, nurses and cancer survivors, who developed the structure, content and format of this 12-week community-based intervention. The intervention consisted of group exercise sessions and education. Women with any type of cancer were eligible to enroll regardless of whether or not they were on active cancer treatment. Women were not eligible to enroll if they had any contraindication to exercise. Groups of no more than 15, completed hour-long supervised group exercise sessions twice weekly that were led by a physical therapist or exercise specialist. These sessions included resistance training, aerobic, flexibility, balance, aquatic or yoga exercises. The weekly education sessions included topics such as nutrition, sleep disturbance, depression, coping, lymphedema, exercise habits, healing arts, women’s health, spirituality, and stress management. This intervention was offered at no cost to participants, with funding provided by the hospital foundation. Participants reported their pre- and post-intervention perceptions of fatigue, pain, depression, sleep disturbance and quality of life on a 0 -10 point Likert scale (0 = none, 10 = worst). We used the related-sample Wilcoxon Signed Rank test to compare pre- and post- intervention scores and independent sample Mann-Whitney U test to compare change scores between those on and off treatment. Results Approximately 80% (n=139) of the women having a mean age of 53.6 years (SD=11.8; range 23-87) completed the 12-week intervention. Upon completion, we found significant decreases in the perceptions of self-reported fatigue (-5.5, p\u3c.001), pain (-0.5, p=.017), depression (-1.0, p\u3c.001), sleep disturbance (-0.5, p\u3c.001), and quality of life (-1.4, p\u3c.001). However, a subgroup analysis revealed that the impact of the intervention varied according to treatment status. Specifically, perceptions of fatigue decreased significantly for the 49 women who were on treatment (-1.4 vs. -0.03 p=.007) as compared to the 90 women who had completed treatment. Women on active treatment reported significantly higher levels of fatigue at the start of the intervention than did the women who had completed treatment (6.4 vs. 5.0, p\u3c.0001). Our findings indicate that implementation of an evidence-based exercise and education intervention in a medically-based wellness center is effective in improving self-reported outcomes for women with cancer. The most significant impact of the intervention appeared to be in decreasing fatigue for women on active cancer treatment

Good Catch! Using Interdisciplinary Teams and Team Reflexivity to Improve Patient Safety

Interdisciplinary teams play an important role implementing innovations that facilitate the quality and safety of patient care. This article examined the role of reflexivity in team innovation implementation and its association with an objective patient safety outcome, inpatient fall rates (a fall is an unintended downward displacement of a patient’s body to the ground or other object). In this study, we implemented, supported, and evaluated interdisciplinary teams intended to decrease fall risk in 16 small rural hospitals. These hospitals were part of a collaborative that sought to increase knowledge and facilitate reflexivity about fall event reporting and fall risk reduction structures and processes. We assessed team reflexivity at the start and at the end of the 2-year intervention and innovation implementation at the end of the intervention. The 16 hospitals reported objective fall event data and patient days throughout the project, which we used to calculate comparative rates for assisted, unassisted, and injurious falls. The results suggest that teams benefited from the intervention, increasing reflexivity from the start of the project to the end, which was related to innovation implementation and decreases in fall rates. Theoretical and practical applications of the results are discussed

Group and Organizational Safety Norms Set the Stage for Good Post-Fall Huddles

We explored group and organizational safety norms as antecedents to meeting leader behaviors and achievement of desired outcomes in a special after-action review case—a post-fall huddle. A longitudinal survey design was used to investigate the relationship between organizational/group safety norms, huddle leader behavior, and huddle meeting effectiveness. The sample included health care workers in critical access hospitals (N = 206) who completed a baseline safety norm assessment and an assessment of post-fall huddle experiences 3 to 6 months later. Findings indicate that organizational and group safety norms relate to perceived huddle meeting effectiveness through appropriate huddle leader behavior in a partial mediated framework. In contrast to previous research showing after-action reviews predicting group and organizational safety norms, the longitudinal study presented here suggests that group and organizational safety norms set the stage for the enactment of post-fall huddles in an effective manner