106 research outputs found
Dynamical meson-baryon resonances with chiral Lagrangians
The s-wave meson-baryon interaction is studied using the lowest-order chiral
Lagrangian in a unitary coupled-channels Bethe-Salpeter equation. In the
strangeness sector the low-energy dynamics leads to the
dynamical generation of the as a state, along with
a good description of the scattering observables. At higher energies,
the is also found to be generated dynamically as a
quasibound state for the first time. For strangeness S=0, it is the
resonance that emerges from the coupled-channels equations,
leading to a satisfactory description of meson-baryon scattering observables in
the energy region around the . We speculate on the possible
dynamical generation of resonances within the chiral sector as
or quasibound states.Comment: 8 pages, 5 figures, Talk given at NSTAR2001, Workshop on the Physics
of Excited Nucleons, Mainz (Germany), March 7-10, to be published in World
Scientifi
High Statistics Analysis using Anisotropic Clover Lattices: (I) Single Hadron Correlation Functions
We present the results of high-statistics calculations of correlation
functions generated with single-baryon interpolating operators on an ensemble
of dynamical anisotropic gauge-field configurations generated by the Hadron
Spectrum Collaboration using a tadpole-improved clover fermion action and
Symanzik-improved gauge action. A total of 292,500 sets of measurements are
made using 1194 gauge configurations of size 20^3 x 128 with an anisotropy
parameter \xi= b_s/b_t = 3.5, a spatial lattice spacing of b_s=0.1227\pm 0.0008
fm, and pion mass of m_\pi ~ 390 MeV. Ground state baryon masses are extracted
with fully quantified uncertainties that are at or below the ~0.2%-level in
lattice units. The lowest-lying negative-parity states are also extracted
albeit with a somewhat lower level of precision. In the case of the nucleon,
this negative-parity state is above the N\pi threshold and, therefore, the
isospin-1/2 \pi N s-wave scattering phase-shift can be extracted using
Luescher's method. The disconnected contributions to this process are included
indirectly in the gauge-field configurations and do not require additional
calculations. The signal-to-noise ratio in the various correlation functions is
explored and is found to degrade exponentially faster than naive expectations
on many time-slices. This is due to backward propagating states arising from
the anti-periodic boundary conditions imposed on the quark-propagators in the
time-direction. We explore how best to distribute computational resources
between configuration generation and propagator measurements in order to
optimize the extraction of single baryon observables
Octet baryon magnetic moments from lattice QCD: Approaching experiment from a three-flavor symmetric point
Lattice QCD calculations with background magnetic fields are used to determine the magnetic moments of the octet baryons. Computations are performed at the physical value of the strange quark mass, and two values of the light quark mass, one corresponding to the SU(3)(F)-symmetric point, where the pion mass is m(pi) similar to 800 MeV, and the other corresponding to a pion mass of m(pi) similar to 450 MeV. The moments are found to exhibit only mild pion-mass dependence when expressed in terms of appropriately chosen magneton units-the natural baryon magneton. A curious pattern is revealed among the anomalous baryon magnetic moments which is linked to the constituent quark model, however, careful scrutiny exposes additional features. Relations expected to hold in the large-N-c limit of QCD are studied; and, in one case, a clear preference for the quark model over the large-Nc prediction is found. The magnetically coupled Lambda-Sigma(0) system is treated in detail at the SU(3)(F) point, with the lattice QCD results comparing favorably with predictions based on SU(3)(F) symmetry. This analysis enables the first extraction of the isovector transition magnetic polarizability. The possibility that large magnetic fields stabilize strange matter is explored, but such a scenario is found to be unlikely
Genomic characterization of a novel group A lamb rotavirus isolated in Zaragoza, Spain
An ovine rotavirus (OVR) strain, 762, was isolated from a 30-day-old lamb affected with severe gastroenteritis, in Zaragoza, Spain, and the VP4, VP7, VP6, NSP4, and NSP5/NSP6 genes were subsequently characterized molecularly. Strain OVR762 was classified as a P[14] rotavirus, as the VP4 and VP8* trypsin-cleavage product of the VP4 protein revealed the highest amino acid (aa) identity (94% and 97%, respectively) with that of the P11[14] human rotavirus (HRV) strain PA169, isolated in Italy. Analysis of the VP7 gene product revealed that OVR762 possessed G8 serotype specificity, a type common in ruminants, with the highest degree of aa identity(95–98%) shared with serotype G8 HRV, bovine rotavirus, and guanaco (Lama guanicoe) rotavirus strains. Moreover, strain OVR762 displayed a bovine-like NSP4 (genotype E2) and NSP5/NSP6 (genotype H3), and a VP6 genotype I2, as well as a long electropherotype pattern. This is the first report of a lamb rotavirus with P[14] and G8 specificities, providing additional evidence for the wide genetic and antigenic diversity of group A rotaviruses
Combination of niacin extended-release and simvastatin results in a less atherogenic lipid profile than atorvastatin monotherapy
Age-related changes in eye lens biomechanics, morphology, refractive index and transparency
Life-long eye lens function requires an appropriate gradient refractive index, biomechanical integrity and transparency. We conducted an extensive study of wild-type mouse lenses 1-30 months of age to define common age-related changes. Biomechanical testing and morphometrics revealed an increase in lens volume and stiffness with age. Lens capsule thickness and peripheral fiber cell widths increased between 2 to 4 months of age but not further, and thus, cannot account for significant age-dependent increases in lens stiffness after 4 months. In lenses from mice older than 12 months, we routinely observed cataracts due to changes in cell structure, with anterior cataracts due to incomplete suture closure and a cortical ring cataract corresponding to a zone of compaction in cortical lens fiber cells. Refractive index measurements showed a rapid growth in peak refractive index between 1 to 6 months of age, and the area of highest refractive index is correlated with increases in lens nucleus size with age. These data provide a comprehensive overview of age-related changes in murine lenses, including lens size, stiffness, nuclear fraction, refractive index, transparency, capsule thickness and cell structure. Our results suggest similarities between murine and primate lenses and provide a baseline for future lens aging studies
Dibaryons with Strangeness: their Weak Nonleptonic Decay using SU(3) Symmetry and how to find them in Relativistic Heavy-Ion Collisions
Weak SU(3) symmetry is successfully applied to the weak hadronic decay
amplitudes of octet hyperons. Weak nonmesonic and mesonic decays of various
dibaryons with strangeness, their dominant decay modes, and lifetimes are
calculated. Production estimates for BNL's Relativistic Heavy-Ion Collider are
presented employing wave function coalescence. Signals for detecting strange
dibaryon states in heavy-ion collisions and revealing information about the
unknown hyperon-hyperon interactions are outlined.Comment: 4 pages, 2 figures, uses RevTeX, discussion about the model of the
weak decay and experimental signals extended, references update
Genomic hallmarks and therapeutic implications of G0 cell cycle arrest in cancer
BACKGROUND: Therapy resistance in cancer is often driven by a subpopulation of cells that are temporarily arrested in a non-proliferative G0 state, which is difficult to capture and whose mutational drivers remain largely unknown. RESULTS: We develop methodology to robustly identify this state from transcriptomic signals and characterise its prevalence and genomic constraints in solid primary tumours. We show that G0 arrest preferentially emerges in the context of more stable, less mutated genomes which maintain TP53 integrity and lack the hallmarks of DNA damage repair deficiency, while presenting increased APOBEC mutagenesis. We employ machine learning to uncover novel genomic dependencies of this process and validate the role of the centrosomal gene CEP89 as a modulator of proliferation and G0 arrest capacity. Lastly, we demonstrate that G0 arrest underlies unfavourable responses to various therapies exploiting cell cycle, kinase signalling and epigenetic mechanisms in single-cell data. CONCLUSIONS: We propose a G0 arrest transcriptional signature that is linked with therapeutic resistance and can be used to further study and clinically track this state
- …