3,352 research outputs found
Particle-in-cell simulations of collisionless magnetic reconnection with a non-uniform guide field
Results are presented of a first study of collisionless magnetic reconnection starting from a recently found exact nonlinear force-free Vlasov–Maxwell equilibrium. The initial state has a Harris sheet magnetic field profile in one direction and a non-uniform guide field in a second direction, resulting in a spatially constant magnetic field strength as well as a constant initial plasma density and plasma pressure. It is found that the reconnection process initially resembles guide field reconnection, but that a gradual transition to anti-parallel reconnection happens as the system evolves. The time evolution of a number of plasma parameters is investigated, and the results are compared with simulations starting from a Harris sheet equilibrium and a Harris sheet plus constant guide field equilibrium
Features and flaws of a contact interaction treatment of the kaon
Elastic and semileptonic transition form factors for the kaon and pion are
calculated using the leading-order in a global-symmetry-preserving truncation
of the Dyson-Schwinger equations and a momentum-independent form for the
associated kernels in the gap and Bethe-Salpeter equations. The computed form
factors are compared both with those obtained using the same truncation but an
interaction that preserves the one-loop renormalisation-group behaviour of QCD
and with data. The comparisons show that: in connection with observables
revealed by probes with |Q^2|<~ M^2, where M~0.4GeV is an infrared value of the
dressed-quark mass, results obtained using a symmetry-preserving regularisation
of the contact-interaction are not realistically distinguishable from those
produced by more sophisticated kernels; and available data on kaon form factors
do not extend into the domain whereupon one could distinguish between the
interactions. The situation is different if one includes the domain Q^2>M^2.
Thereupon, a fully consistent treatment of the contact interaction produces
form factors that are typically harder than those obtained with QCD
renormalisation-group-improved kernels. Amongst other things also described are
a Ward identity for the inhomogeneous scalar vertex, similarity between the
charge distribution of a dressed-u-quark in the K^+ and that of the
dressed-u-quark in the pi^+, and reflections upon the point whereat one might
begin to see perturbative behaviour in the pion form factor. Interpolations of
the form factors are provided, which should assist in working to chart the
interaction between light-quarks by explicating the impact on hadron properties
of differing assumptions about the behaviour of the Bethe-Salpeter kernel.Comment: 17 pages, 9 figures, 4 table
Can we evaluate population screening strategies in UK general practice? A pilot randomised controlled trial comparing postal and opportunistic screening for genital chlamydial infection
STUDY OBJECTIVE: To assess whether opportunistic and postal screening strategies for Chlamydia trachomatis can be compared with usual care in a randomised trial in general practice
DESIGN: Feasibility study for a randomised controlled trial.
SETTING: Three West of Scotland general medical practices: one rural, one urban/deprived and one urban/affluent.
PARTICIPANTS: 600 women aged 16-30 years, 200 from each of three participating practices selected at random from a sample of West of Scotland practices that had expressed interest in the study. The women could opt out of the study. Those who did not were randomly assigned to one of three groups: postal screening, opportunistic screening or usual care.
MAIN RESULTS: 38% (85/221) of the approached practices expressed interest in the study. Data were collected successfully from the 3 participating practices, although intensive support was required. There were considerable workload implications for staff, both in relation to implementing the screening strategies and managing the research process.
124 of the 600 women opted out of the study. During the four-month study period, 55% (81/146) of the control group attended their practice but none was offered screening. 59% (80/136) women in the opportunistic group attended their practice of whom 55% (44/80) were offered screening. Of those, 64% (28/44) accepted, representing 21% of the opportunistic group. 48% (59/124) of the postal group returned samples.
CONCLUSION: A randomised controlled trial comparing postal and opportunistic screening for chlamydial infection in general practice is feasible, though resource intensive. There may be problems with generalising from screening trials in which patients may opt out from the offer of screening
Optimizing treatment outcomes in adolescents with eating disorders: The potential role of cognitive behavioral therapy
Objective
While family‐based treatment (FBT) is the leading psychological therapy for adolescents with eating disorders, it is not universally effective or suitable. This study considered the effectiveness of cognitive‐behavioral therapy for eating disorders (CBT‐ED) in adolescent cases where FBT was not fully effective or where it was not applicable to the individual case.
Method
A transdiagnostic case series of 54 adolescents with eating disorders (52% with anorexia nervosa; 31% with atypical anorexia nervosa) were offered CBT‐ED following previous treatment using FBT or following FBT being judged inappropriate. Pre‐post outcomes were assessed using standardized measures of eating attitudes and clinical impairment, and weight change was measured for the patients with anorexia nervosa.
Results
The rate of attrition was similar to that found in other CBT‐ED studies (38.9% of patients who started CBT‐ED; 59.3% of those offered CBT‐ED). The patients showed positive outcomes on all measures, regardless of whether they had previously been treated with FBT. Effect sizes were moderate to large. Severity and duration of the eating disorder were unrelated to outcomes.
Discussion
CBT‐ED merits consideration as a second‐line approach for adolescents with eating disorders when FBT has not been effective or could not be applied. There is no evidence that previous failure to benefit from FBT impairs outcome from subsequent CBT‐ED, and severity and duration of the eating disorder did not influence outcome. Treatment matching for adolescents with eating disorders might consider the role of previous treatment outcomes and family availability in determining optimum treatment strategies for individuals
The Energy Spectrum of Primary Cosmic Ray Electrons in Clusters of Galaxies and Inverse Compton Emission
Models for the evolution of the integrated energy spectrum of primary cosmic
ray electrons in clusters of galaxies have been calculated, including the
effects of losses due to inverse Compton (IC), synchrotron, and bremsstrahlung
emission, and Coulomb losses to the intracluster medium (ICM). The combined
time scale for these losses reaches a maximum of ~3e9 yr for electrons with a
Lorentz factor ~300. Only clusters in which there has been a substantial
injection of relativistic electrons since z <~ 1 will have any significant
population of primary cosmic ray electrons at present. In typical models, there
is a broad peak in the electron energy distribution extending to gamma~300, and
a steep drop in the electron population beyond this. In clusters with current
particle injection, there is a power-law tail of higher energy electrons with
an abundance determined by the current rate of injection. A significant
population of electrons with gamma~300, associated with the peak in the
particle loss time, is a generic feature of the models. The IC and synchrotron
emission from these models was calculated. In the models, EUV and soft X-ray
emission are nearly ubiquitous. This emission is produced by electrons with
gamma~300. The spectra are predicted to drop rapidly in going from the EUV to
the X-ray band. The IC emission also extends down the UV, optical, and IR bands
with a fairly flat spectrum. Hard X-ray (HXR) and diffuse radio emission due to
high energy electrons (gamma~10e4) is present only in clusters which have
current particle acceleration. Assuming that the electrons are accelerated in
ICM shocks, one would only expect diffuse HXR/radio emission in clusters which
are currently undergoing a large merger.Comment: Accepted for publication in the Astrophysical Journal, with minor
revisons to wording for clarity and one additional reference. 19 pages with
16 embedded Postscript figures in emulateapj.sty. Abbreviated abstract belo
Exercise motivation: a cross-sectional analysis examining its relationships with frequency, intensity, and duration of exercise
BACKGROUND: It is important to engage in regular physical activity in order to maintain a healthy lifestyle however a large portion of the population is insufficiently active. Understanding how different types of motivation contribute to exercise behavior is an important first step in identifying ways to increase exercise among individuals. The current study employs self-determination theory as a framework from which to examine how motivation contributes to various characteristics of exercise behavior.
METHODS: Regular exercisers (N = 1079; n = 468 males; n = 612 females) completed inventories which assessed the frequency, intensity, and duration with which they exercise, as well as the Behavioral Regulation in Exercise Questionnaire including four additional items assessing integrated regulation.
RESULTS: Bivariate correlations revealed that all three behavioral indices (frequency, intensity, and duration of exercise) were more highly correlated with more autonomous than controlling regulations. Regression analyses revealed that integrated and identified regulations predicted exercise frequency for males and females. Integrated regulation was found to be the only predictor of exercise duration across both genders. Finally, introjected regulation predicted exercise intensity for females only.
CONCLUSIONS: These findings suggest that exercise regulations that vary in their degree of internalization can differentially predict characteristics of exercise behavior. Furthermore, in the motivational profile of a regular exerciser, integrated regulation appears to be an important determinant of exercise behavior. These results highlight the importance of assessing integrated regulation in exercise settings where the goal of understanding motivated behavior has important health implications
A topologically unique alternating {Co III 3 Gd III 3 } magnetocaloric ring
The adiabatic temperature change of the star-shaped {CoIII3GdIII3} magnetocaloric ring is enhanced via topological control over the assembly process, by using a pre-formed {CoII(H6L)} building block that undergoes oxidation to CoIII, successfully separating the GdIII ions
Commentary on rainbow-ladder truncation for excited states and exotics
Ground-state, radially-excited and exotic scalar-, vector- and
flavoured-pseudoscalar-mesons are studied in rainbow-ladder truncation using an
interaction kernel that is consonant with modern DSE- and lattice-QCD results.
The inability of this truncation to provide realistic predictions for the
masses of excited- and exotic-states is confirmed and explained. On the other
hand, its application does provide information that is potentially useful in
proceeding beyond this leading-order truncation, e.g.: assisting with
development of projection techniques that ease the computation of excited state
properties; placing qualitative constraints on the long-range behaviour of the
interaction kernel; and highlighting and illustrating some features of hadron
observables that do not depend on details of the dynamics.Comment: 10 pages, 6 figures, 2 table
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