3,410 research outputs found
Three-quark exchange operators, crossing matrices and Fierz transformations in SU(2) and SU(3)
We give explicit expressions for the three-quark exchange operators, crossing
matrices and Fierz transforms for the SU(2) and SU(3) groups. We identify the
invariant terms in these operators and express them in terms of Casimir
operators.Comment: 8 pages, RevTex, to appear in Jour. Math. Phy
Cubic Casimir operator of SU(3) and confinement in the nonrelativistic quark model
Only two-body [] confining potentials have
been considered, thus far, in the quark model without gluons, which by
construction can only depend on the quadratic Casimir operator of the colour
SU(3) group. A three-quark potential that depends on the cubic Casimir operator
is added to the quark model. This results in improved properties of
colour non-singlet states, which can now be arranged to have (arbitrarily)
higher energy than the singlet, and the "colour dissolution/anticonfinement"
problem of the model is avoided.Comment: 10 pages, 2 tables, RevTex, to appear in Phys. Lett.
Geometric factors in the Bohr--Rosenfeld analysis of the measurability of the electromagnetic field
The Geometric factors in the field commutators and spring constants of the
measurement devices in the famous analysis of the measurability of the
electromagnetic field by Bohr and Rosenfeld are calculated using a
Fourier--Bessel method for the evaluation of folding integrals, which enables
one to obtain the general geometric factors as a Fourier--Bessel series. When
the space region over which the factors are defined are spherical, the
Fourier--Bessel series terms are given by elementary functions, and using the
standard Fourier-integral method of calculating folding integrals, the
geometric factors can be evaluated in terms of manageable closed-form
expressions.Comment: 21 pages, REVTe
Rat muscle opacity decrease due to the osmosis of a simple mixture
It is known that the fibrous structure of muscle causes light scattering. This phenomenon occurs due to the refractive index discontinuities located between muscle fibers and interstitial fluid. To study the possibility of reducing light scattering inside muscle, we consider its spectral transmittance evolution during an immersion treatment with an optical clearing solution containing ethanol, glycerol, and distilled water. Our methodology consists of registering spectral transmittance of muscle samples while immersed in that solution. With the spectral data collected, we represent the transmittance evolution for some wavelengths during the treatment applied. Additionally, we study the variations that the treatment has caused on the samples regarding tissue refractive index and mass. By analyzing microscopic photographs of tissue cross section, we can also verify changes in the internal arrangement of muscle fibers caused by the immersion treatment. Due to a mathematical model that we develop, we can explain the variations observed in the studied parameters and estimate the amount of optical clearing agent that has diffused into the tissue samples during the immersion treatment. At the end of the study, we observe and explain the improvement in tissue spectral transmittance, which is approximately 65% after 20 min
Optical characterization of muscle
Optical characterization and internal structure of biological tissues is highly important for biomedical optics. In particular for optical clearing processes, such information is of vital importance to understand the mechanisms involved through the variation of the refractive indices of tissue components. The skeletal muscle presents a fibrous structure with an internal arrangement of muscle fiber cords surrounded by interstitial fluid that is responsible for strong light scattering. To determine the refractive index of muscle components we have used a simple method of measuring tissue mass and refractive index during dehydration. After performing measurements for natural and ten dehydration states of the muscle samples, we have determined the dependence between the refractive index of the muscle and its water content. Also, we have joined our measurements with some values reported in literature to perform some calculations that have permitted to determine the refractive index of the dried muscle fibers and their corresponding volume percentage inside the natural muscle.info:eu-repo/semantics/publishedVersio
Areias de Vale de Santarém. Estratigrafia e Palinologia
The palynologic study of several boreholes for lignite prospection at the "Vale de Santarém sands" is presented.
Height spores and 18 pollen forms have been identified. The quantitative and qualitative results are shown in table 2. Four
palynologic associations (A - D) corresponding to climatic changes have been characterized. Correlations are established with the plant associations of Rio Maior Basin.
Correlation between the boreholes allow a better understanding of the small, Vale de Santarém basin infilling
Reoxygenation of asphyxiated newborn piglets: administration of 100% oxygen causes significantly higher apoptosis in cortical neurons, as compared to 21%.
Low Concentrations of Bisphenol A Induce Mouse Spermatogonial Cell Proliferation by G Protein–Coupled Receptor 30 and Estrogen Receptor-α
Background: Bisphenol A (BPA) is one of the most prevalent chemicals in daily-use materials; therefore, human exposure to BPA is ubiquitous. The estrogenicity of BPA is generally mediated by nuclear estrogen receptors (ERs). However, low concentrations of BPA stimulate seminoma cell proliferation by an uncertain mechanism that does not involve activation of ERs
Classical Many-particle Clusters in Two Dimensions
We report on a study of a classical, finite system of confined particles in
two dimensions with a two-body repulsive interaction. We first develop a simple
analytical method to obtain equilibrium configurations and energies for few
particles. When the confinement is harmonic, we prove that the first transition
from a single shell occurs when the number of particles changes from five to
six. The shell structure in the case of an arbitrary number of particles is
shown to be independent of the strength of the interaction but dependent only
on its functional form. It is also independent of the magnetic field strength
when included. We further study the effect of the functional form of the
confinement potential on the shell structure. Finally we report some
interesting results when a three-body interaction is included, albeit in a
particular model.Comment: Minor corrections, a few references added. To appear in J. Phys:
Condensed Matte
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