379 research outputs found
Tests of isospin symmetry breaking at meson factories
In a model of isospin symmetry breaking we obtain the () amplitude and the isospin and
relative phase at the resonance in aproximate agreement
with experiment. The model predicts \Gamma(\phi \rightarrow \omega \pi^{0})
\approx 4 \cdot 10^{-4} \;\mbox{MeV}. We have also obtained \Gamma (\phi
\rightarrow \eta' \gamma)=5.2 \cdot 10^{-4} \;\mbox{MeV}. Measuring this
partial width would strongly constrain - mixing. The branching
ratios of the isospin violating decays
and are predicted to be and , respectively, leading to and .Comment: 11 pages 2 Figures ( not included available on request ), Latex,
Karlsruhe TTP42-9
Strange vector currents and the OZI-rule
We investigate the role of correlated exchange in the extraction of
matrix elements of the strange vector current in the proton. We show that a
realistic isoscalar spectral function including this effect leads to sizeably
reduced strange vector form factors based on the dispersion--theoretical
analysis of the nucleons' electromagnetic form factors.Comment: 8 pp, plain LaTeX, uses epsf, 3 figure
Nucleon form factors: From the space-like to the time-like region
I discuss how dispersion relations can be used to analyse the nucleon
electromagnetic form factors, with particular emphasis on the constraints from
unitarity and pQCD. Results for nucleon radii, vector-meson couplings, the
onset of pQCD and bounds on the strangeness form factors are presented. The em
form factors in the time-like region reveal some interesting physics which is
not yet understood in full detail. The need for a better data basis at low,
intermediate and large momentum transfer and also in the time-like region is
stressed.Comment: 11 pp, LaTeX, uses epsf and espcrc1.sty, 6 figures, invited talk,
DAPHCE 96, Frascati, November 1996, to appear in the proceedings (Nucl. Phys.
A
Postfeminist Media Cultures
This entry provides an overview of postfeminism, which has become central in the last two decades not only within feminist cultural discourse but also within neoliberal discourses and popular culture. The dominant attempts to conceptualize postfeminism often bring to the surface approaches that are complex and contradictory in nature. For instance, postfeminism is viewed as a theoretical framework, as a sensibility, as an expansion of feminist theory, or as a rejection of it. The discussion of postfeminism against the backdrop of media productions further highlights its implications for women and gender representation. A look at quintessential postfeminist texts shows, for instance, that postfeminism essentially problematizes contemporary constructions of gender as it simultaneously evokes and rejects basic feminist tenets
Chiral Symmetry and the Nucleon's Vector Strangeness Form Factors
The nucleon's strange-quark vector current form factors are studied from the
perspective of chiral symmetry. It is argued that chiral perturbation theory
cannot yield a prediction for the strangeness radius and magnetic moment.
Arrival at definite predictions requires the introduction of additional,
model-dependent assumptions which go beyond the framework of chiral
perturbation theory. A variety of such model predictions is surveyed, and the
credibility of each is evaluated. The most plausible prediction appears in a
model where the unknown chiral counterterms are identified with -channel
vector meson exchange amplitudes. The corresponding prediction for the mean
square Dirac strangeness radius is fm, which
would be observable in up-coming semileptonic determinations of the nucleon's
strangeness form factors.Comment: LaTex 31 pages, four figures available from authors
Dispersion-Theoretical Analysis of the Nucleon Electromagnetic Formfactors
Dispersion relations allow for a coherent description of the nucleon
electromagnetic form factors measured over a large range of momentum transfer,
GeV. Including constraints from unitarity and
perturbative QCD, we present a novel parametrisation of the absorptive parts of
the various isoscalar and isovector nucleon form factors. Using the current
world data, we obtain results for the electromagnetic form factors, nucleon
radii and meson couplings. We stress the importance of measurements at large
momentum transfer to test the predictions of perturbative QCD.Comment: 33 pp, RevTEX or plain LaTeX, 7 figures (in ffig.uu
The influence of anesthetics, neurotransmitters and antibiotics on the relaxation processes in lipid membranes
In the proximity of melting transitions of artificial and biological
membranes fluctuations in enthalpy, area, volume and concentration are
enhanced. This results in domain formation, changes of the elastic constants,
changes in permeability and slowing down of relaxation processes. In this study
we used pressure perturbation calorimetry to investigate the relaxation time
scale after a jump into the melting transition regime of artificial lipid
membranes. This time corresponds to the characteristic rate of domain growth.
The studies were performed on single-component large unilamellar and
multilamellar vesicle systems with and without the addition of small molecules
such as general anesthetics, neurotransmitters and antibiotics. These drugs
interact with membranes and affect melting points and profiles. In all systems
we found that heat capacity and relaxation times are related to each other in a
simple manner. The maximum relaxation time depends on the cooperativity of the
heat capacity profile and decreases with a broadening of the transition. For
this reason the influence of a drug on the time scale of domain formation
processes can be understood on the basis of their influence on the heat
capacity profile. This allows estimations of the time scale of domain formation
processes in biological membranes.Comment: 12 pages, 6 figure
Robust Association Tests Under Different Genetic Models, Allowing for Binary or Quantitative Traits and Covariates
The association of genetic variants with outcomes is usually assessed under an additive model, for example by the trend test. However, misspecification of the genetic model will lead to a reduction in power. More robust tests for association might therefore be preferred. A useful approach is to consider the maximum of the three test statistics under additive, dominant and recessive models (MAX3). The p-value however has to be adjusted to maintain the type I error rate. Previous studies and software on robust association tests have focused on binary traits without covariates. In this study we developed an analytic approach to robust association tests using MAX3, allowing for quantitative or binary traits as well as covariates. The p-values from our theoretical calculations match very well with those from a bootstrap resampling procedure. The methodology is implemented in the R package RobustSNP which is able to handle both small-scale studies and GWAS. The package and documentation are available at http://sites.google.com/site/honcheongso/software/robustsnp
Domain formation in DODABâcholesterol mixed systems monitored via nile red anisotropy
The effect of the cholesterol (Ch) on liposomes composed of the cationic lipid dioctadecyldimethylammonium bromide (DODAB) was assessed by studying both the steady-state and time-resolved fluorescence anisotropy of the dye Nile Red. The information obtained combined with analysis of the steady-state emission and luorescence lifetime of Nile Red (NR) for different cholesterol concentrations (5â50%) elucidated the presence of âcondensed complexesâ and cholesterol-rich domains in these mixed systems. The steady-state fluorescence spectra were decomposed into the sum of two lognormal emissions, emanating from two different states, and the effect of temperature on the anisotropy decay of Nile Red for different cholesterol concentrations was observed. At room temperature, the time-resolved anisotropy decays are indicative of NR being relatively immobile (manifest by a high râ value). At higher temperature, rotational times ca. 1 ns were obtained throughout and a trend in increasing hindrance was seen with increase of Ch content
- âŠ