49 research outputs found
On baryon resonances and chiral symmetry
We study J^P=(3/2)^- baryon resonances as generated by chiral coupled-channel
dynamics. Parameter free results are obtained in terms of the Weinberg-Tomozawa
term predicting the leading s-wave interaction strength of Goldstone bosons
with baryon-decuplet states. In the 'heavy' SU(3) limit with m_\pi = m_K \sim
500 MeV the resonances turn into bound states forming a decuplet and octet
representation of the SU(3) group. Using physical masses the mass splitting are
remarkably close to the empirical pattern.Comment: revised version: includes two additional references, gives improved
discussions and eliminted some misprint
Logistic regression for simulating damage occurrence on a fruit grading line
Many factors influence the incidence of mechanical damage in fruit handled on a grading line. This makes it difficult to address damage estimation from an analytical point of view. During fruit transfer from one element of a grading line to another, damage occurs as a combined effect of machinery roughness and the intrinsic susceptibility of fruit. This paper describes a method to estimate bruise probability by means of logistic regression, using data yielded by specific laboratory tests. Model accuracy was measured via the statistical significance of its parameters and its classification ability. The prediction model was then linked to a simulation model through which impacts and load levels, similar to those of real grading lines, could be generated. The simulation output sample size was determined to yield reliable estimations. The process makes it possible to derive a suitable line design and the type of fruit that should be handled to maintain bruise levels within European Union (EU) Standards. A real example with peaches was carried out with the aid of the software implementation SIMLINÂź, developed by the authors and registered by Madrid Technical University. This kind of tool has been demanded by inter-professional associations and grading lines designers in recent year
Quark mass dependence of s-wave baryon resonances
We study the quark mass dependence of J(P) = 1/2(-) s-wave baryon resonances. Parameter free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with m(pi) = M-K similar or equal to 500 MeV the resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. A contrasted result is obtained in the 'light' SU(3) limit with m(pi) = m(K) similar or equal to 140 MeV for which no resonances exist. Using physical quark masses our analysis suggests to assign to the S = -2 resonances Xi(1690) and Xi(1620) the quantum numbers J(P) = 1/2(-)
Changes in cannabinoid receptor binding and mRNA levels in several brain regions of aged rats
AbstractWe have recently found that cannabinoid receptor binding and gene expression markedly decreased in extrapyramidal structures of aged rats. The present study was designed to analyze the possible existence of similar aging-induced changes in cannabinoid receptor binding and gene expression in brain regions other than extrapyramidal areas, but that also contain a significant population of cannabinoid receptors, such as the cerebellum, hippocampal structures, limbic and hypothalamic nuclei, the cerebral cortex and others. To this end, we analyzed cannabinoid receptor binding, using autoradiography, and cannabinoid receptor mRNA levels, using in situ hybridization, in slide-mounted brain sections obtained from young (3 month old) and aged (>2 year old) rats. Results were as follows. In the cerebellum, aged rats exhibited a marked decrease in cannabinoid receptor binding in the molecular layer (â33.3%), although accompanied by no changes in mRNA levels in the granular layer. In the cerebral cortex, a small, although statistically significant, decrease in binding was found in the deep layer (VI) (â18.3%) of aged rats, whereas no changes were found in the superficial layer (I). As in the case of the cerebellum, mRNA levels did not change in the cerebral cortex layers (IIâIII and VâVI). The different regions of the Ammonâs horn of the hippocampus exhibited similar cannabinoid receptor binding levels in aged and young rats. Interestingly, mRNA levels decreased in aged rats to a small, but statistically significant, extent (CA1: â26.1%; CA2: â21.6%; CA3: â14.4%). This was also seen in another hippocampal structure, the dentate gyrus (â14.6%), although in this region binding levels increased in aged rats (+28.4%). Two hypothalamic structures, the arcuate nucleus and the ventromedial hypothalamic nucleus, exhibited decreased cannabinoid receptor binding in aged rats (â31.1% and â30.3%, respectively), but this was not seen in the medial preoptic area. This was accompanied by no changes in mRNA levels in the ventromedial hypothalamic nucleus. In the limbic structures, aged rats exhibited similar binding levels to young rats. This was seen in the nucleus accumbens, septum nuclei and basolateral amygdaloid nucleus. However, mRNA levels slightly decreased in the basolateral amygdaloid nucleus (â13.4%), whereas they were not altered in the septum nuclei. Finally, other brain structures, such as the central gray substance and the brainstem, exhibited similar binding levels in aged and young rats. However, it is important to note that mRNA levels increased significantly (+211.2%) in the brainstem of aged rats, an area where the levels of binding and mRNA were very low in young rats. This marked increase may be related to an increase in the presence of glial elements in this region, as revealed by the increase in the immunoreactivity for glial fibrillary acidic protein observed in the brainstem of aged rats as compared to young animals. In summary, senescence was associated with changes in cannabinoid receptors in the cerebellum, the cerebral cortex, limbic and hypothalamic structures, the hippocampus and other brain regions. However, the changes observed (i) were not as marked and relevant as those early reported in extrapyramidal areas, and (ii) exhibited regional differences that might be attributed to the different roles played by these receptors in each region. Of particular relevance by their magnitude were the aging-induced decrease in binding found in the cerebellum and the hypothalamus, and the increase in mRNA levels observed in the brainstem. The latter might be related to an increase in the presence of glial cells which might contain cannabinoid receptor mRNA
On meson resonances and chiral symmetry
We study meson resonances with quantum numbers J^P=1^+ in terms of the chiral
SU(3) Lagrangian. At leading order a parameter-free prediction is obtained for
the scattering of Goldstone bosons off vector mesons with J^P=1^- once we
insist on approximate crossing symmetry of the unitarized scattering amplitude.
A resonance spectrum arises that is remarkably close to the empirical pattern.
In particular, we find that the strangeness-zero resonances h_1(1380), f_(1285)
and b_1(1235) are formed due to strong K \bar K_\mu and \bar K K_\mu channels.
This leads to large coupling constants of those resonances to the latter
states.Comment: 29 pages, 6 figures, more detailed discussions are give
Antikaon production in A+A collisions at SIS energies within an off-shell G-matrix approach
The production and propagation of antikaons -- described by dynamical
spectral functions as evaluated from a coupled channel
-matrix approach -- is studied for nucleus-nucleus collisions at SIS
energies in comparison to the conventional quasi-particle limit and the
available experimental data using off-shell transport theory. We find that the
spectra for and at 1.8 AGeV
remain underestimated in the -matrix approach as in the on-shell
quasi-particle approximation whereas the preliminary spectra for at
1.5 AGeV are well described in both limits. This also holds
approximately for the rapidity distributions in semi-central collisions
of at 1.93 AGeV. However, in all limits considered there is no
convincing description of all spectra simultaneously. Our off-shell transport
calculations, furthermore, demonstrate that the strongest in-medium effects
should be found for low antikaon momenta in the center-of-mass frame, since the
deceleration of the antikaons in the attractive Coulomb and nuclear potentials
and the propagation to the on-shell mass induces a net shift and squeezing of
the spectra to the low momentum regime.Comment: 44 pages, including 18 eps figures, to be published in Nucl. Phys.
bound states in nuclei
The energies and widths of bound states of the meson in different
nuclei are obtained using the results for its selfenergy in a nuclear medium,
which is evaluated in a selfconsistent manner using techniques of unitarized
chiral perturbation theory. We find bound states in all studied nuclei (from
on) and the half widths obtained are larger than the separation of
the levels, what makes the experimental observation of peaks unlikely. We have
paid a special attention to the region of nuclei where only the state
appears and the binding energies are of the order of magnitude of the half
width, which would magnify the chances that some broad peak could be observed.
This is found in the region of with a binding energy around 12.6
MeV and half width of 16.7 MeV. In heavy nuclei like there are
many bound states which would be difficult to disentangle and the deepest state
has a binding energy about 21 MeV and half width around 16 MeV. Such an
overlapping accumulation of states could be seen as an extension of the
continuum of strength into the bound region in production
experiments.Comment: 9 pages, Latex, 2 Figure
Light scattering from self-affine fractal silver surfaces with nanoscale cutoff: Far-field and near-field calculations
We study the light scattered from randomly rough, one-dimensional self-affine
fractal silver surfaces with nanoscale lower cutoff, illuminated by s- or
p-polarized Gaussian beams a few microns wide. By means of rigorous numerical
calculations based on the Green theorem integral equation formulation, we
obtain both the far- and near-field scattered intensities. The influence of
diminishing the fractal lower scale cutoff (from below a hundred, down to a few
nanometers) is analyzed in the case of both single realizations and ensemble
average magnitudes. For s polarization, variations are small in the far field,
being only significant in the higher spatial frequency components of evanescent
character in the near field. In the case of p polarization, however, the
nanoscale cutoff has remarkable effects stemming from the roughness-induced
excitation of surface-plasmon polaritons. In the far field, the effect is
noticed both in the speckle pattern variation and in the decrease of the total
reflected energy upon ensemble averaging, due to increased absorption. In the
near field, more efficient excitation of localized optical modes is achieved
with smaller cutoff, which in turn leads to huge surface electric field
enhancements.Comment: REVTeX 4, 10 page
Recent advances in liquid and gas chromatography methodology for extending coverage of the metabolome
The metabolome is the complete complement of metabolites (small organic biomolecules). In order to comprehensively understand the effect of stimuli on a biological system, it is important to detect as many of the metabolites within that system as possible. This review briefly describes some new advances in liquid and gas chromatography to improve coverage of the metabolome, including the serial combination of two columns in tandem, column switching and different variations of two-dimensional chromatography. Supercritical fluid chromatography could provide complimentary data to liquid and gas chromatography. Although there have been many recent advancements in the field of metabolomics, it is evident that a combination, rather than a single method, is required to approach full coverage of the metabolome