Environmental and genetic variation of the effective radiative properties of the coat of Holstein cows under tropical conditions

Morphological characteristics, coat effective radiative properties, and the percentage of white colour were measured in the coats of 973 Holstein cows, and estimates of the genetic parameters were obtained for these traits, except morphological characteristics. The results showed that white coats are more dense with long, thin hairs, while the black coats are less dense with short, thick hairs. Effective transmissivity is greater in the less-dense coats with short, thin hairs, independently of coat colour. Effective reflectivity depends more on the variation in the radiative properties of the coat and skin surface rather than on the morphological characteristics of the coat. Effective absorptivity is greater in black and dense coats with long, thick hairs, than in the white and less-dense coat with short, thin hairs. All heritability estimates were of low magnitude, except for the percentage of white coat colour.

Static potential in scalar QED(3) with non-minimal coupling

Here we compute the static potential in scalar QED(3) at leading order in 1/Nf. We show that the addition of a non-minimal coupling of Pauli-type (is an element of(mu nu alpha)j(mu)partial derivative(nu)A(alpha)), although it breaks parity, it does not change the analytic structure of the photon propagator and consequently the static potential remains logarithmic ( confining) at large distances. The non-minimal coupling modifies the potential, however, at small charge separations giving rise to a repulsive force of short range between opposite sign charges, which is relevant for the existence of bound states. This effect is in agreement with a previous calculation based on Moller scattering, but differently from such calculation we show here that the repulsion appears independently of the presence of a tree level Chern-Simons term which rather affects the large distance behaviour of the potential turning it into a constant.

THE GREEN-FUNCTION IN THE BLOCH-NORDSIECK MODEL FOR QED(3)

The electron Green's function is obtained in the Bloch-Nordsieck approximation of three-dimensional QED. Dimensional regularization is used in the intermediate stages of calculation.

Durango apatite fission-track dating using length-based age corrections and neutron fluence measurements by natural thorium thin films and natural U-doped glasses calibrated through natural uranium thin films

In this work, we present an approach for neutron fluence measurements based on natural thorium thin films and natural uranium-doped glasses calibrated through natural uranium thin films to be used for dating with the Fission-Track Method (FTM). This neutron dosimetry approach allows the employment of FTM even when dating is carried out using low neutron themalization facilities. Besides, it makes possible the determination of the Th/U ratio of the mineral to be dated. Durango apatite which is often employed in FTM as an age standard was analyzed. This apatite presented a fairly high Th/U ratio, 29.9 +/- 1.7. Th fissions were 18%, 12% and 10% of the total for irradiations where thermal to fast neutron flux ratios were 2.4, 4.4 and 5,2, respectively. These results show that Th fission must be considered for this apatite, when not well-thermalized irradiation facilities are used. The ratio between spontaneous and induced track length, L(S)/L(1), close to 0.89, indicates a certain amount of rejuvenation of the age of Durango apatite. Therefore, its apparent age should be corrected, the application of a technique based on track-length measurements produced a corrected age of 29.7 +/- 1.1 Ma, consistent with the independent reference age of this apatite (31.4 +/- 0.5 Ma). This result represents a support for viability of the neutron dosimetry approach studied in this work for FTM.(C) 2002 Elsevier B.V. B.V. All rights reserved.

THE VACUUM ENERGY OF QED WITH 4-FERMION INTERACTION

We consider quantum electrodynamics in the quenched approximation including a four-fermion interaction with coupling constant g. The effective potential at stationary points is computed as a function of the coupling constants alpha and g and an ultraviolet cutoff LAMBDA, showing a minimum of energy in the (alpha, g) plane for alpha = alpha(c) = pi/3 and g = infinity. When we go to the continuum limit (LAMBDA --> infinity), keeping finite the dynamical mass, the minimum of energy moves to (alpha = 0, g = 1), which correspond to a point where the theory is trivial.

Remarks on infrared dynamics in QED(3)

In this work we study how the infrared sector of the interaction Hamiltonian can affect the construction of the S-matrix operator of QED in (2+1) dimensions.

CAUSAL APPROACH TO (2+1)-DIMENSIONAL QED

It is shown that the causal approach to (2 + 1)-dimensional quantum electrodynamics yields a well-defined perturbative theory. In particular, and in contrast to renormalized perturbative quantum field theory, it is free of any ambiguities and ascribes a nonzero value to the dynamically generated, nonperturbative photon mass. (C) 1994 Academic Press, Inc.

VACUUM POLARIZATION TENSOR IN 3-DIMENSIONAL QUANTUM ELECTRODYNAMICS

We evaluate the one-loop vacuum polarization tensor for three-dimensional quantum electrodynamics (QED), using an analytic regularization technique, implemented in a gauge-invariant way. We show thus that a gauge boson mass is generated at this level of radiative correction to the photon propagator. We also point out in our conclusions that the generalization for the non Abelian case is straightforward.

Radiative properties of the skin and haircoat of cattle and other animals

Radiative properties (reflectance rho, transmittance tau, and absorptance alpha) were determined for wavelengths from 300 to 850 nm in the haircoat and the skin of water buffalo, deer (Pantanal deer, Blastocerus dichotomus), and cattle of the Holstein, Simmental, Canchim, Brangus, and Nelore breeds. The results showed that white hairs have higher rho (0.60 to 0.67) than the other coat colors, but the gray coats (mixed white and dark hair) of the Nelore cattle presented higher rho than that of the white coats of the European breeds at wavelengths lower than 600 nm. The light gray colored skin of the Canchim cattle had higher rho (0. 66) than the non-pigmented skin of Holstein (0.53). Red skins presented rho values higher than those of dark gray and black skins. Buffalo skin (dark gray) presented an average rho of 0.23+/-0.02 and alpha of 0.77+/-0.02. The red haircoat of the deer presented rho lower (0.37) than that of cattle of the same color (0.58). However, there was little difference between deer and cattle with respect to reflectance and absorptance of the skin. As for the spectral transmittance of the skin, it was very low and about the same for both species, until 600 nm. In the range 600 to 850 nm, the tau values for cattle rose to 0. 17, while those for deer increased only to 0.12.

Virial coefficients from (2+1)-dimensional QED effective actions at finite temperature and density

From spinor and scalar (2 + 1)-dimensional QED effective actions at finite temperature and density in a constant magnetic field background, we calculate the corresponding virial coefficients for particles in the lowest Landau level. These coefficients depend on a parameter theta related to the time-component of the gauge field, which plays an essential role for large gauge invariance. The variation of the parameter theta might lead to an interpolation between fermionic and bosonic virial coefficients, although these coefficients are singular for theta = pi/2.

Luminescence and non-radiative processes in lanthanide squarate hydrates

The luminescence properties of solid hydrated lanthanide squarates (Ln2(C4O4)3(H2O) x; x = 8 or 13;Ln3+ = Gd, La, Eu, Tb, Pr) are reported for temperatures down to 4.2K. The luminescence of the squarate group is observed for the Gd3+ and La3+ compounds at low temperatures (below 150K). The Pr3+ compound does not show any emission at all, not even at 4.2K. This is ascribed to the quenching of the Pr3+ emission by multiphonon relaxation and/or concentration quenching. The quantum efficiencies of the 5D0 emission of Eu3+ and of the 5D4 emission of Tb3+ in these squarate complexes are strikingly different. Whereas the Tb3+ emission shows a temperature independent quantum efficiency of 50% upon ligand excitation, the Eu3+ emission is strongly quenched, showing a temperature dependent quantum efficiency of 0.8% at 4.2K upon ligand excitation. This quenching is ascribed to the low energy position of the charge-transfer state of Eu3+ in these compounds.

Effective action for QED in 2+1 dimensions at finite temperature

Both the parity-breaking and parity-invariant parts of the effective action for the gauge field in QED 3 with massive fermions at finite temperature are obtained exactly. This is feasible because we use a particular configuration of the background gauge field, namely a constant magnetic field and a time-dependent time component of the background gauge field. Our results allow us to compute exactly physically interesting quantities such as the induced charge density and fermion condensate whose dependence on the temperature, fermion mass and gauge field is discussed. ©1999 The American Physical Society.

Chiral corrections in hadron spectroscopy

We show that the implementation of chiral symmetry in recent studies of the hadron spectrum in the context of the constituent quark model is inconsistent with chiral perturbation theory. In particular, we show that the leading nonanalytic (LNA) contributions to the hadron masses are incorrect in such approaches. The failure to implement the correct chiral behaviour of QCD results in incorrect systematics for the corrections to the masses. © 1999 Published by Elsevier Science B.V. All rights reserved.