143 research outputs found
SU(3) Symmetry Breaking and Octet Baryon Polarizabilities
Static polarizabilities of the low--lying baryons are studied within
the collective coordinate approach to the three flavor generalization of the
Skyrme model; in particular, magnetic polarizabilities are considered.
Predicted polarizabilities, which result from different treatments of the
strange degrees of freedom in this model, are critically compared. Their
deviations from the flavor symmetric formulations are discussed.Comment: 11 pages, LaTeX, 4 tables, no figures, final version to be published
in Phys. Lett.
Boehler (Jean-Michel) et Lerch (Dominique), Moissons d’histoire (XVe-XIXe siècles). Jean Vogt : un demi-siècle de recherches sur l’histoire de la campagne alsacienne (1952-2005)
Ces Moissons d’histoire que Jean-Michel Boehler et Dominique Lerch consacrent à l’œuvre de Jean Vogt viennent combler un grand vide. Quel est l’historien alsacien ou l’amateur d’histoire de l’Alsace qui ne connaît pas le nom de cet historien-géographe, auteur d’une invraisemblable quantité d’articles parus dans les diverses revues éditées par les sociétés d’histoire de l’Alsace ? Comme ils le précisent en sous-titre, les deux auteurs entendent saluer l’immense travail de recherche conduit ave..
The Strangeness Radius and Magnetic Moment of the Nucleon Revisited
We update Jaffe's estimate of the strange isoscalar radius and magnetic
moment of the nucleon. We make use of a recent dispersion--theoretical fit to
the nucleon electromagnetic form factors and an improved description of
symmetry breaking in the vector nonet. We find ~n.m.
and ~fm. The strange formfactor follows
a dipole with a cut--off mass of 1.46~GeV, . These numbers should be considered as upper limits on the
strange vector current matrix--elements in the nucleon.Comment: 8 pp, LaTeX, uses epsf, 1 figure in separate fil
On the strange vector form factors of the nucleon in the NJL soliton model
Within the Nambu--Jona--Lasinio model strange degrees of freedom are
incorporated into the soliton picture using the collective approach of Yabu and
Ando. The form factors of the nucleon associated with the nonet vector current
are extracted. The numerical results provide limits for the strange magnetic
moment: . For the strange magnetic form factor of the
nucleon the valence quark and vacuum contributions add coherently while there
are significant cancellations for the strange electric form factor.Comment: 9 pages, one figure, postscript file submitted as uuencoded
compressed fil
Polarized Structure Functions in the Valence Quark and Resonance Regions and the GDH Sum
I present in this paper the neutron spin physics program in Hall A at
Jefferson Laboratory using a polarized helium-3 target. The program encompasses
several completed experiments, in which, valuable spin observables (spin
dependent structure functions) were measured in order to learn about how the
nucleon spin arises from the behavior of the constituents. These experiments
also offer a ground for testing our understanding of the strong regime of
quantum chromodynamics (QCD) the theory of strong interactions through the
determination of moments of these structure functions.Comment: 9 pages, 2 Postscript figures, XVth International Conference on
Particles and Nuclei (PANIC02), Osaka, Japan, 30 September-4 October 200
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Utility of 2013 American College of Cardiology/American Heart Association Cholesterol Guidelines in HIV-Infected Adults With Carotid Atherosclerosis.
BackgroundAlthough HIV is associated with increased atherosclerotic cardiovascular disease (CVD) risk, it is unknown whether guidelines can identify HIV-infected adults who may benefit from statins. We compared the 2013 American College of Cardiology/American Heart Association and 2004 Adult Treatment Panel III recommendations in HIV-infected adults and evaluated associations with carotid artery intima-media thickness and plaque.Methods and resultsCarotid artery intima-media thickness was measured at baseline and 3 years later in 352 HIV-infected adults without clinical atherosclerotic CVD and not on statins. Plaque was defined as IMT >1.5 mm in any segment. At baseline, the median age was 43 (interquartile range, 39-49), 85% were men, 74% were on antiretroviral medication, and 50% had plaque. The American College of Cardiology/American Heart Association guidelines were more likely to recommend statins compared with the Adult Treatment Panel III guidelines, both overall (26% versus 14%; P<0.001), in those with plaque (32% versus 17%; P=0.0002), and in those without plaque (16% versus 7%; P=0.025). In multivariable analysis, older age, higher low-density lipoprotein cholesterol, pack per year of smoking, and history of opportunistic infection were associated with baseline plaque. Baseline IMT (hazard ratio, 1.18 per 10% increment; 95% confidence interval, 1.05-1.33; P=0.005) and plaque (hazard ratio, 2.06; 95% confidence interval, 1.02-4.08; P=0.037) were each associated with all-cause mortality, independent of traditional CVD risk factors.ConclusionsAlthough the American College of Cardiology/American Heart Association guidelines recommended statins to a greater number of HIV-infected adults compared with the Adult Treatment Panel III guidelines, both failed to recommend therapy in the majority of HIV-affected adults with carotid plaque. Baseline carotid atherosclerosis but not atherosclerotic CVD risk scores was an independent predictor of mortality. HIV-specific guidelines that include detection of subclinical atherosclerosis may help to identify HIV-infected adults who are at increased atherosclerotic CVD risk and may be considered for statins
Strange results from chiral soliton models
The standard collective quantization treatment of the strangeness content of
the nucleon in chiral soliton models such as the Skyrmion is shown to be
inconsistent with the semi-classical expansion on which the treatment is based.
The strangeness content vanishes at leading order in the semi-classical
expansion. Collective quantization correctly describes some contributions to
the strangeness content at the first nonvanishing order in the expansion, but
neglects others at the same order--namely, those associated with continuum
modes. Moreover, there are fundamental difficulties in computing at a constant
order in the expansion due to the non-renormalizable nature of chiral soliton
models. Moreover, there are fundamental difficulties in computing at a constant
order in the expansion due to the non-renormalizable nature of chiral soliton
models and the absence of any viable power counting scheme. We show that the
continuum mode contribution to the strangeness diverges, and as a result the
computation of the strangeness content at leading non-vanishing order is not a
well-posed mathematical problem in these models.Comment: Reference added. Some change of emphasis in the discussion of the
role of power counting. 5 page
HIV and Hepatitis C-Coinfected Patients Have Lower Low-Density Lipoprotein Cholesterol Despite Higher Proprotein Convertase Subtilisin Kexin 9 (PCSK9): An Apparent "PCSK9-Lipid Paradox".
BackgroundProprotein convertase subtilisin kexin 9 (PCSK9) inhibitors reduce low-density lipoprotein cholesterol (LDL-C) and improve outcomes in the general population. HIV-infected individuals are at increased risk for cardiovascular events and have high rates of dyslipidemia and hepatitis C virus (HCV) coinfection, making PCSK9 inhibition a potentially attractive therapy.Methods and resultsWe studied 567 participants from a clinic-based cohort to compare PCSK9 levels in patients with HIV/HCV coinfection (n=110) with those with HIV infection alone (n=385) and with uninfected controls (n=72). The mean age was 49 years, and the median LDL-C level was 100 mg/dL (IQR 77-124 mg/dL); 21% were taking statins. The 3 groups had similar rates of traditional risk factors. Total cholesterol, LDL-C, and high-density lipoprotein cholesterol levels were lower in coinfected patients compared with controls (P<0.001). PCSK9 was 21% higher in HIV/HCV-coinfected patients versus controls (95% CI 9-34%, P<0.001) and 11% higher in coinfected individuals versus those with HIV infection alone (95% CI 3-20%, P=0.008). After adjustment for cardiovascular risk factors, HIV/HCV coinfection remained significantly associated with 20% higher PCSK9 levels versus controls (95% CI 8-33%, P=0.001). Interleukin-6 levels increased in a stepwise fashion from controls (lowest) to HIV-infected to HIV/HCV-coinfected individuals (highest) and correlated with PCSK9 (r=0.11, P=0.018).ConclusionsDespite having lower LDL-C, circulating PCSK9 levels were increased in patients coinfected with HIV and HCV in parallel with elevations in the inflammatory, proatherogenic cytokine interleukin-6. Clinical trials should be conducted to determine the efficacy of targeted PCSK9 inhibition in the setting of HIV/HCV coinfection
Percolation and Schramm-Loewner evolution in the 2D random-field Ising model
The presence of random fields is well known to destroy ferromagnetic order in
Ising systems in two dimensions. When the system is placed in a sufficiently
strong external field, however, the size of clusters of like spins diverges.
There is evidence that this percolation transition is in the universality class
of standard site percolation. It has been claimed that, for small disorder, a
similar percolation phenomenon also occurs in zero external field. Using exact
algorithms, we study ground states of large samples and find little evidence
for a transition at zero external field. Nevertheless, for sufficiently small
random field strengths, there is an extended region of the phase diagram, where
finite samples are indistinguishable from a critical percolating system. In
this regime we examine ground-state domain walls, finding strong evidence that
they are conformally invariant and satisfy Schramm-Loewner evolution
() with parameter . These results add support to the
hope that at least some aspects of systems with quenched disorder might be
ultimately studied with the techniques of SLE and conformal field theory
Baryons as non-topological chiral solitons
The present review gives a survey of recent developments and applications of
the Nambu--Jona-Lasinio model with and quark flavors for the
structure of baryons. The model is an effective chiral quark theory which
incorporates the SU(N)SU(N)U(1) approximate
symmetry of Quantum chromodynamics. The approach describes the spontaneous
chiral symmetry breaking and dynamical quark mass generation. Mesons appear as
quark-antiquark excitations and baryons arise as non-topological solitons with
three valence quarks and a polarized Dirac sea. For the evaluation of the
baryon properties the present review concentrates on the non-linear
Nambu--Jona-Lasinio model with quark and Goldstone degrees of freedom which is
identical to the Chiral quark soliton model obtained from the instanton liquid
model of the QCD vacuum. In this non-linear model, a wide variety of
observables of baryons of the octet and decuplet is considered. These include,
in particular, electromagnetic, axial, pseudoscalar and pion nucleon form
factors and the related static properties like magnetic moments, radii and
coupling constants of the nucleon as well as the mass splittings and
electromagnetic form factors of hyperons. Predictions are given for the strange
form factors, the scalar form factor and the tensor charge of the nucleon.Comment: 104 pages, 27 figures as uuencoded and compressed postscript files ,
hardcopy available upon request; Prog.Part.Nucl.Phys. 37 (1996) (in print
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