940 research outputs found
Kaon Weak Decays in Chiral Theories
The ten nonleptonic weak decays , , , , , are predicted for a
chiral pole model based on the linear sigma model theory which automatically
satisfies the partial conservation of axial current (PCAC) hypothesis. These
predictions, agreeing with data to the 5% level and containing no or at most
one free parameter, are compared with the results of chiral perturbation theory
(ChPT). The latter ChPT approach to one-loop level is known to contain at least
four free parameters and then predicts a rate
which is 60% shy of the experimental value. This suggests that ChPT is an
unsatisfactory approach towards predicting kaon weak decays.Comment: 12 pages, 8 eps figure
Family support and cardiac rehabilitation: A comparative study of the experiences of South Asian and White-European patients and their carer's living in the United Kingdom
Background: Effective lifestyle modification facilitated by cardiac rehabilitation is known to reduce the occurrence of adverse coronary events and mortality. South Asians have poorer outcomes after a myocardial infarction than the general UK population, but little is known about their experiences of family support, cardiac rehabilitation and lifestyle change. Aims: To explore the nature of family support available to a sample of South Asian and White-European cardiac patients and to highlight similarities and differences between these groups with regard to cardiac rehabilitation and lifestyle modification. Methods: Using a qualitative approach, semi-structured interviews (in 1 of 6 languages) were conducted by researchers with; 45 South Asian patients and 37 carers and 20 White-European patients and 17 carers. Interviews were conducted in a home setting, up to eighteen months after discharge from hospital following myocardial infarction, coronary artery bypass surgery or unstable angina. Results: The main themes that emerged related to the provision of advice and information, family support and burden, dietary change and exercise regimes. Conclusions: Several cultural and ethnic differences were identified between patients and their families alongside similarities, irrespective of ethnicity. These may represent generic characteristics of recovery after a cardiac event. Health professionals should develop a cultural repertoire to engage with diversity and difference. Not every difficulty a person encounters as they try to access appropriate service delivery can be attributed to ethnic background. By improving services generally, support for South Asian populations can be improved. The challenge is to know when ethnicity makes a difference and mediates a person's relationship with service support and when it does not. (C) 2007 European Society of Cardiology. Published by Elsevier B.V. All rights reserved
Polynomial Cointegration among Stationary Processes with Long Memory
n this paper we consider polynomial cointegrating relationships among
stationary processes with long range dependence. We express the regression
functions in terms of Hermite polynomials and we consider a form of spectral
regression around frequency zero. For these estimates, we establish consistency
by means of a more general result on continuously averaged estimates of the
spectral density matrix at frequency zeroComment: 25 pages, 7 figures. Submitted in August 200
Consistently computing the K -> pi long distance weak transition
First we extract the long-distance (LD) weak matrix element from certain data
and give compatible theoretical estimates. We also link this LD scale to the
single-quark-line (SQL) transition scale and then test the latter SQL scale
against the decuplet weak decay amplitude ratio. Finally, we study LD decay.
All of these experimental and theoretical values are in good agreement. We
deduce an average value from eleven experimental determinations compared to the
theoretical SQL values average.Comment: 19 pages, 9 figures minor change to the Conclusions and abstract
sectio
CP Violation and Enhancement for , Weak Decays
Data indicate that transitions account for 4.5-4.7% of both CP
conserving and CP violating decays, as well as CP conserving
radiative processes. Observed
branching ratios are shown to scale near or . The
- mixing angle and the semileptonic weak-rate asymmetry
are reviewed, and theory is shown to be consistent with data. Also, dominance is studied in the context of the chiral
constituent quark model, displaying again excellent agreement with data.
Finally, indirect and direct kaon CP violation are successfully described in
the framework of photon-mediated loop graphs. This suggests that kaon CPV can
be understood via second-order weak transitions, radiatively corrected.Comment: Plain LaTeX, 12 pages, 4 EPS figures. PACS numbers: 11.30.Er,
12.15.Lk, 13.20.Eb, 13.40.Ks. Version 2: 14 pages, improved presentation,
introductory and concluding remarks as well as references added; accepted for
publication in Mod. Phys. Lett. A (2004
Changes in growing season duration and productivity of northern vegetation inferred from long-term remote sensing data
Monitoring and understanding climate-induced changes in the boreal and arctic vegetation is critical to aid in prognosticating their future. Weused a 33 year (1982-2014) long record of satellite observations to robustly assess changes in metrics of growing season (onset: SOS, end: EOS and length: LOS) and seasonal total gross primary productivity. Particular attention was paid to evaluating the accuracy of these metrics by comparing them to multiple independent direct and indirect growing season and productivity measures. These comparisons reveal that the derived metrics capture the spatio-temporal variations and trends with acceptable significance level (generally p < 0.05). We find that LOS has lengthened by 2.60 d dec(-1) (p < 0.05) due to an earlier onset of SOS (-1.61 d dec(-1), p < 0.05) and a delayed EOS (0.67 d dec(-1), p < 0.1) at the circumpolar scale over the past three decades. Relatively greater rates of changes in growing season were observed in Eurasia (EA) and in boreal regions than in North America (NA) and the arctic regions. However, this tendency of earlier SOS and delayed EOS was prominent only during the earlier part of the data record (1982-1999). During the later part (2000-2014), this tendency was reversed, i.e. delayed SOS and earlier EOS. As for seasonal total productivity, we find that 42.0% of northern vegetation shows a statistically significant (p < 0.1) greening trend over the last three decades. This greening translates to a 20.9% gain in productivity since 1982. In contrast, only 2.5% of northern vegetation shows browning, or a 1.2% loss of productivity. These trends in productivity were continuous through the period of record, unlike changes in growing season metrics. Similarly, we find relatively greater increasing rates of productivity in EA and in arctic regions than in NA and the boreal regions. These results highlight spatially and temporally varying vegetation dynamics and are reflective of biome-specific responses of northern vegetation during last three decades
On the upstream mobility scheme for two-phase flow in porous media
When neglecting capillarity, two-phase incompressible flow in porous media is
modelled as a scalar nonlinear hyperbolic conservation law. A change in the
rock type results in a change of the flux function. Discretizing in
one-dimensional with a finite volume method, we investigate two numerical
fluxes, an extension of the Godunov flux and the upstream mobility flux, the
latter being widely used in hydrogeology and petroleum engineering. Then, in
the case of a changing rock type, one can give examples when the upstream
mobility flux does not give the right answer.Comment: A preprint to be published in Computational Geoscience
Remarks on the f_0(400-1200) scalar meson as the dynamically generated chiral partner of the pion
The quark-level linear sigma model is revisited, in particular concerning the
identification of the f_0(400-1200) (or \sigma(600)) scalar meson as the chiral
partner of the pion. We demonstrate the predictive power of the linear sigma
model through the pi-pi and pi-N s-wave scattering lengths, as well as several
electromagnetic, weak, and strong decays of pseudoscalar and vector mesons. The
ease with which the data for these observables are reproduced in the linear
sigma model lends credit to the necessity to include the sigma as a fundamental
q\bar{q} degree of freedom, to be contrasted with approaches like chiral
perturbation theory or the confining NJL model of Shakin and Wang.Comment: 15 pages, plain LaTeX, 3 EPS figure
A theory of -dissipative solvers for scalar conservation laws with discontinuous flux
We propose a general framework for the study of contractive semigroups
of solutions to conservation laws with discontinuous flux. Developing the ideas
of a number of preceding works we claim that the whole admissibility issue is
reduced to the selection of a family of "elementary solutions", which are
certain piecewise constant stationary weak solutions. We refer to such a family
as a "germ". It is well known that (CL) admits many different contractive
semigroups, some of which reflects different physical applications. We revisit
a number of the existing admissibility (or entropy) conditions and identify the
germs that underly these conditions. We devote specific attention to the
anishing viscosity" germ, which is a way to express the "-condition" of
Diehl. For any given germ, we formulate "germ-based" admissibility conditions
in the form of a trace condition on the flux discontinuity line (in the
spirit of Vol'pert) and in the form of a family of global entropy inequalities
(following Kruzhkov and Carrillo). We characterize those germs that lead to the
-contraction property for the associated admissible solutions. Our
approach offers a streamlined and unifying perspective on many of the known
entropy conditions, making it possible to recover earlier uniqueness results
under weaker conditions than before, and to provide new results for other less
studied problems. Several strategies for proving the existence of admissible
solutions are discussed, and existence results are given for fluxes satisfying
some additional conditions. These are based on convergence results either for
the vanishing viscosity method (with standard viscosity or with specific
viscosities "adapted" to the choice of a germ), or for specific germ-adapted
finite volume schemes
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