Infinite-dimensional representations of the rotation group and Dirac's monopole problem

Within the context of infinite-dimensional representations of the rotation group the Dirac monopole problem is studied in details. Irreducible infinite-dimensional representations, being realized in the indefinite metric Hilbert space, are given by linear unbounded operators in infinite-dimensional topological spaces, supplied with a weak topology and associated weak convergence. We argue that an arbitrary magnetic charge is allowed, and the Dirac quantization condition can be replaced by a generalized quantization rule yielding a new quantum number, the so-called topological spin, which is related to the weight of the Dirac string.Comment: JHEP style. Extended version of hep-th/0403146. Revised version, title and some notations are changed. References and Appendix B are adde

Gross output and livestock sales modelling in Spanish extensive farms using PLSR

The aim of this paper is to model some production variables in extensive livestock farms located in the dehesa ecosystem. We intend to use not only purely economic variables in the construction of the model, but also structural variables in order to identify the characteristics of the farms that have the higher influence. Another objective is to be able to predict these variables at the farm level, using structural variables that are easy to measure. The data used in this work were obtained from a questionnaire survey to the holders/managers of a sample of 69 dehesa farms in Extremadura (SW Spain). The statistical methodology used for the construction of the model was Partial Least Square Regression (PLSR). It can be concluded that the variables relative to farm intensification, to labour and especially to Iberian pig breeding, are those that take part mainly in the model.dehesa, livestock farming systems, partial least square regression, gross output, Crop Production/Industries, Livestock Production/Industries, Research Methods/ Statistical Methods,

Numerical model of the inhomogeneous scattering by the human lens

We present in this work a numerical model for characterizing the scattering properties of the human lens. After analyzing the scattering properties of two main scattering particles actually described in the literature through FEM (finite element method) simulations, we have modified a Monte Carlo''s bulk scattering algorithm for computing ray scattering in non-sequential ray tracing. We have implemented this ray scattering algorithm in a layered model of the human lens in order to calculate the scattering properties of the whole lens. We have tested our algorithm by simulating the classic experiment carried out by Van der Berg et al for measuring "in vitro" the angular distribution of forward scattered light by the human lens. The results show the ability of our model to simulate accurately the scattering properties of the human lens. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Hysteretic behavior of methionine adenosyltransferase III. Methionine switches between two conformations of the enzyme with different specific activity

Methionine adenosyltransferase III (MATIII) catalyzes S-adenosylmethionine (AdoMet) synthesis and, as part of its reaction mechanism, it also hydrolyzes tripolyphosphate. Tripolyphosphatase activity was linear over time and had a slightly sigmoidal behavior with an affinity in the low micromolar range. On the contrary, AdoMet synthetase activity showed a lag phase that was independent of protein concentration but decreased at increasing substrate concentrations. Tripolyphosphatase activity, which appeared to be slower than AdoMet synthesis, was stimulated by preincubation with ATP and methionine so that it matched AdoMet synthetase activity. This stimulation process, which is probably the origin of the lag phase, represents the slow transition between two conformations of the enzyme that could be distinguished by their different tripolyphosphatase activity and sensitivity to S-nitrosylation. Tripolyphosphatase activity appeared to be the rate-determining reaction in AdoMet synthesis and the one inhibited by S-nitrosylation. The methionine concentration necessary to obtain half-maximal stimulation was in the range of physiological methionine fluctuations. Moreover, stimulation of MAT activity by methionine was demonstrated in vivo. We propose that the hysteretic behavior of MATIII, in which methionine induces the transition to a higher specific activity conformation, can be considered as an adaptation to the specific functional requirements of the liver

High strength stainless steel 14301 for prestressed concrete structures protection

High Strength Stainless Steels (HSSS) are being developed with the aim to improve corrosion resistance of prestressed concrete structures in aggressive environments. In the present paper focus is given to mechanical and corrosion performance of a HSSS type 14301. The ability of passivation in alkaline media and the risk of local corrosion (pitting) in presence of chlorides, has been determined. Besides, the response of the stainless steel submitted to mechanical strains similar to those in service is considered with respect to the risk of corrosion, Stress Corrosion Cracking (SCC) and Hydrogen Embrittlement (HE). The cold-drawn HSSS 14301 shows higher tolerance to chloride ion than conventional prestressing steel. The local corrosion becomes significant for chloride contents above 0.75 M. The applied load moves pitting corrosion initiation at lower concentrations of chlorides. The pitting enhances risk for SCC developing, although the steel is more resistance to HE in comparison with conventional presstressing ste

Measurement method of optical properties of ex vivo biological tissues of rats in the near-infrared range

An optical fiber-based supercontinuum setup and a custom-made spectrophotometer that can measure spectra from 1100 to 2300 nm, are used to describe attenuation properties from different ex vivo rat tissues. Our method is able to differentiate between scattering and absorption coefficients in biological tissues. Theoretical assumptions combined with experimental measurements demonstrate that, in this infrared range, tissue attenuation and absorption can be accurately measured, and scattering can be described as the difference between both magnitudes. Attenuation, absorption, and scattering spectral coefficients of heart, brain, spleen, retina, and kidney are given by applying these theoretical and experimental methods. Light through these tissues is affected by high scattering, resulting in multiple absorption events, and longer wavelengths should be used to obtain lower attenuation values. It can be observed that the absorption coefficient has a similar behavior in the samples under study, with two main zones of absorption due to the water absorption bands at 1450 and 1950 nm, and with different absolute absorption values depending on the constituents of each tissue. The scattering coefficient can be determined, showing slight differences between retina and brain samples, and among heart, spleen and kidney tissues

Formation of the seed black holes: a role of quark nuggets?

Strange quark nuggets (SQNs) could be the relics of the cosmological QCD phase transition, and they could very likely be the candidate of cold quark matter if survived the cooling of the later Universe, although the formation and evolution of these SQNs depend on the physical state of the hot QGP (quark-gluon plasma) phase and the state of cold quark matter. We reconsider the possibility of SQNs as cold dark matter, and find that the formation of black holes in primordial halos could be significantly different from the standard scenario. In a primordial halo, the collision between gas and SQNs could be frequent enough, and thus the viscosity acting on each SQN would decrease its angular momentum and make it to sink into the center of the halo, as well as heat the gas. The SQNs with baryon numbers less than $10^{35}$ could assemble in the center of the halo before the formation of primordial stars. A black hole could form by merger of these SQNs, and then its mass could quickly become about $10^3\ M_\odot$ or higher, by accreting the surrounding SQNs or gas. The black holes formed in this way could be the seeds for the supermassive black holes at redshift as high as $z\sim 6$.Comment: 15 page

Folding of dimeric methionine adenosyltransferase III: identification of two folding intermediates

Methionine adenosyl transferase (MAT) is an essential enzyme that synthesizes AdoMet. The liver-specific MAT isoform, MAT III, is a homodimer of a 43.7-kDa subunit that organizes in three nonsequential alpha-beta domains. Although MAT III structure has been recently resolved, little is known about its folding mechanism. Equilibrium unfolding and refolding of MAT III, and the monomeric mutant R265H, have been monitored using different physical parameters. Tryptophanyl fluorescence showed a three-state folding mechanism. The first unfolding step was a folding/association process as indicated by its dependence on protein concentration. The monomeric folding intermediate produced was the predominant species between 1.5 and 3 m urea. It had a relatively compact conformation with tryptophan residues and hydrophobic surfaces occluded from the solvent, although its N-terminal region may be very unstructured. The second unfolding step monitored the denaturation of the intermediate. Refolding of the intermediate showed first order kinetics, indicating the presence of a kinetic intermediate within the folding/association transition. Its presence was confirmed by measuring the 1,8-anilinonaphtalene-8-sulfonic acid binding in the presence of tripolyphosphate. We propose that the folding rate-limiting step is the formation of an intermediate, probably a structured monomer with exposed hydrophobic surfaces, that rapidly associates to form dimeric MAT III

Variability in population traits of a sentinel iberian fish in a highly modified mediterranean-type river

Human pressures on water resources have been suggested as a driver of biological traits that induce changes in native fish populations. This study highlighted the interplay between environmental stress factors, mostly related to flow regulation, and the longitudinal river gradient in biological traits such as the growth, size structure and somatic condition of a sentinel fish, Luciobarbus sclateri. We found an increase in size-related metrics and somatic condition at population levels associated with downstream reaches, although fragmentation and habitat alteration, flow regime alteration and the abundance of non-native fish were also significantly involved in their variability. Age-related parameters and growth were only explained by flow regime alterations and the abundance of non-native fish species. The high plasticity observed in L. sclateri population traits suggests that this is a key factor in the species adaptability to resist in a strongly altered Mediterranean river basin. However, the interplay of multiple stressors plays an important role in fish population dynamics and could induce complex responses that may be essential for long-term monitoring in sentinel species