868 research outputs found
Space Symmetries and Quantum Behavior of Finite Energy Configurations in SU(2)-Gauge Theory
The quantum properties of localized finite energy solutions to classical
Euler-Lagrange equations are investigated using the method of collective
coordinates. The perturbation theory in terms of inverse powers of the coupling
constant is constructed, taking into account the conservation laws of
momentum and angular momentum (invariance of the action with respect to the
group of motion M(3) of 3-dimensional Euclidean space) rigorously in every
order of perturbation theory.Comment: LaTex, 17 pages typos correcte
The WKB Approximation without Divergences
In this paper, the WKB approximation to the scattering problem is developed
without the divergences which usually appear at the classical turning points. A
detailed procedure of complexification is shown to generate results identical
to the usual WKB prescription but without the cumbersome connection formulas.Comment: 13 pages, TeX file, to appear in Int. J. Theor. Phy
Evaluation of perceived persuasiveness constructs by combining user tests and expert assessments
To develop effective behaviour change support systems, persuasive technology can be used. The persuasive systems design model offers a framework to identify and operationalize such elements. In this pilot study, we evaluate the questionnaire developed to measure perceived persuasiveness of information technology. We analyzed verbatim user-test transcripts, and performed expert-assessments of the Nurse Antibiotic Information App (NAIA). These data were compared to questionnaire results on this app. Expert-assessment identified task support, perceived persuasiveness, unobtrusiveness, credibility, perceived effort and perceived effectiveness (as defined in the Persuasive Systems Design model) as being present within the NAIA. These constructs also scored satisfactory in the questionnaire. User-test transcripts are in line with questionnaire results. Given the consistent results in this pilot study, our approach seems promising for evaluating the questionnaire and will be applied to other settings and websites/application
Sulphate measurement in organic-rich solutions: Carbonate fusion pretreatment to remove organic interferences
Sulphate measurement using a barium sulphate turbidimetric method in solutions with high concentrations of organic material is shown to be problematic. The organics give background colour, which introduces a positive error to the measured absorption, and inhibit the barium sulphate precipitate, which results in a negative error. A carbonate fusion pretreatment of the sample results in the removal of the organic matter and associated interferences. With this pretreatment, excellent sulphate recoveries were obtained (100%). Rigorous testing of the method shows that reproducible and accurate results are obtainable
Educational aspirations in inner city schools
The research aimed to assess the nature and level of pupils’ educational aspirations and to elucidate the factors that influence these aspirations. A sample of five inner city comprehensive secondary schools were selected by their Local Authority because of poor pupil attendance, below average examination results and low rates of continuing in full-time education after the age of 16. Schools were all ethnically mixed and co-educational. Over 800 pupils aged 12-14 completed a questionnaire assessing pupils’ experience of home, school and their peers. A sub-sample of 48 pupils selected by teachers to reflect ethnicity and ability levels in individual schools also participated in detailed focus group interviews. There were no significant differences in aspirations by gender or year group, but differences between ethnic groups were marked. Black African, Asian Other and Pakistani groups had significantly higher educational aspirations than the White British group, who had the lowest aspirations. The results suggest the high aspirations of Black African, Asian Other and Pakistani pupils are mediated through strong academic self-concept, positive peer support, a commitment to schooling and high educational aspirations in the home. They also suggest that low educational aspirations may have different mediating influences in different ethnic groups. The low aspirations of White British pupils seem to relate most strongly to poor academic self-concept and low educational aspirations in the home, while for Black Caribbean pupils disaffection, negative peers and low commitment to schooling appear more relevant. Interviews with pupils corroborated the above findings and further illuminated the factors students described as important in their educational aspirations. The results are discussed in relation to theories of aspiration which stress its nature as a cultural capacity
The X-ray Emissions from the M87 Jet: Diagnostics and Physical Interpretation
We reanalyze the deep Chandra observations of the M87 jet, first examined by
Wilson & Yang (2002). By employing an analysis chain that includes image
deconvolution, knots HST-1 and I are fully separated from adjacent emission. We
find slight but significant variations in the spectral shape, with values of
ranging from . We use VLA radio observations, as well
as HST imaging and polarimetry data, to examine the jet's broad-band spectrum
and inquire as to the nature of particle acceleration in the jet. As shown in
previous papers, a simple continuous injection model for synchrotron-emitting
knots, in which both the filling factor, , of regions within which
particles are accelerated and the energy spectrum of the injected particles are
constant, cannot account for the X-ray flux or spectrum. Instead, we propose
that is a function of position and energy and find that in the inner
jet, , and
in knots A and B, , where is the emitted photon energy and and is the
emitting electron energy. In this model, the index of the injected electron
energy spectrum () is at all locations in
the jet, as predicted by models of cosmic ray acceleration by ultrarelativistic
shocks. There is a strong correlation between the peaks of X-ray emission and
minima of optical percentage polarization, i.e., regions where the jet magnetic
field is not ordered. We suggest that the X-ray peaks coincide with shock waves
which accelerate the X-ray emitting electrons and cause changes in the
direction of the magnetic field; the polarization is thus small because of beam
averaging.Comment: Accepted for publication in ApJ; 21 pages, 9 figures, 2 tables;
abstract shortened for astro-ph; Figures 1, 7 and 8 at reduced resolutio
Lower treatment intensity and poorer survival in metastatic colorectal cancer patients who live alone
BACKGROUND: Socioeconomic status (SES) and social support influences cancer survival. If SES and social support affects cancer treatment has not been thoroughly explored. METHODS: A cohort consisting of all patients who were initially diagnosed with or who developed metastatic colorectal cancer (mCRC, n=781) in three Scandinavian university hospitals from October 2003 to August 2006 was set up. Clinical and socioeconomic data were registered prospectively. RESULTS: Patients living alone more often had synchronous metastases at presentation and were less often treated with combination chemotherapy than those cohabitating (HR 0.19, 95% CI 0.04–0.85, P=0.03). Surgical removal of metastases was less common in patients living alone (HR 0.29, 95% CI 0.10–0.86, P=0.02) but more common among university-educated patients (HR 2.22, 95% CI 1.10–4.49, P=0.02). Smoking, being married and having children did not influence treatment or survival. Median survival was 7.7 months in patients living alone and 11.7 months in patients living with someone (P<0.001). Living alone remained a prognostic factor for survival after correction for age and comorbidity. CONCLUSION: Patients living alone received less combination chemotherapy and less secondary surgery. Living alone is a strong independent risk factor for poor survival in mCRC
Noise storm continua: power estimates for electron acceleration
We use a generic stochastic acceleration formalism to examine the power
() input to nonthermal electrons that cause
noise storm continuum emission. The analytical approach includes the derivation
of the Green's function for a general second-order Fermi process, and its
application to obtain the particular solution for the nonthermal electron
distribution resulting from the acceleration of a Maxwellian source in the
corona. We compare with the power observed in noise
storm radiation. Using typical values for the various parameters, we find that
, yielding an efficiency
estimate in the range 10^{-10} \lsim \eta
\lsim 10^{-6} for this nonthermal acceleration/radiation process. These
results reflect the efficiency of the overall process, starting from electron
acceleration and culminating in the observed noise storm emission.Comment: Accepted for publication in Solar Physic
Stochastic Cellular Automata Model for Stock Market Dynamics
In the present work we introduce a stochastic cellular automata model in
order to simulate the dynamics of the stock market. A direct percolation method
is used to create a hierarchy of clusters of active traders on a two
dimensional grid. Active traders are characterised by the decision to buy,
(+1), or sell, (-1), a stock at a certain discrete time step. The remaining
cells are inactive,(0). The trading dynamics is then determined by the
stochastic interaction between traders belonging to the same cluster. Most of
the stylized aspects of the financial market time series are reproduced by the
model.Comment: 17 pages and 7 figure
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