Comment on "Quantum back-reaction through the Bohmian particle"

In this Comment I point out some limitations of the proposal of Prezhdo and Brooksby for coupling quantum and classical degrees of freedom (Phys.Rev.Lett.86(2001)3215) if it is pushed too far.Comment: 1 page, REVTEX, no figure

Effects of forage supplements on milk production and chemical properties, in vivo digestibility, rumen fermentation and N excretion in dairy cows offered red clover silage and corn silage or dry ground corn

peer-reviewedThis study concerned the effects of partial substitution of clover silage with high starch forages on milk production and chemical composition, in vivo digestibility, rumen fermentation pattern and nitrogen excretion of dairy cows. Sixteen dairy cows were separated into two groups and were assigned to treatments in a two-period crossover design. Two forage supplements were used: corn silage (CS) and dry ground corn (DG). All animals received 4.5 kg of concentrate dry matter per day. Results showed no significant difference between the forage supplements for milk production, while significant differences (P<0.01) were observed for milk fat, milk protein and nitrogen utilisation efficiency (42 v. 4.0 g/kg, 3.5 v. 3.3 g/kg and 222 v. 188 g/kg, respectively, for DG and CS). Faecal N excretion did not differ between forage supplements, but urinary N excretion was higher for CS (P<0.05). No significant differences were observed between treatments for rumen fluid pH or for rumen fluid concentrations of ammonium nitrogen or of acetic, propionic or butyric acids. Dry matter intake and the in vivo digestibility of dry matter, organic matter, acid detergent fibre and neutral detergent fibre were all higher for CS compared with DG.The authors are grateful to the Environmental Office of the Cantabrian Government for funding the project 05-640.02-2174

Bounds on the mass and abundance of dark compact objects and black holes in dwarf spheroidal galaxy halos

We establish new dynamical constraints on the mass and abundance of compact objects in the halo of dwarf spheroidal galaxies. In order to preserve kinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMi dSph) against gravitational scattering, we place upper limits on the density of compact objects as a function of their assumed mass. The mass of the dark matter constituents cannot be larger than 1000 solar masses at a halo density in UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenario in which dark halo cores are formed by two-body relaxation processes. Our bounds on the fraction of dark matter in compact objects with masses >3000 solar masses improve those based on dynamical arguments in the Galactic halo. In particular, objects with masses $\sim 10^{5}$ solar masses can comprise no more than a halo mass fraction $\sim 0.01$. Better determinations of the velocity dispersion of old overdense regions in dSphs may result in more stringent constraints on the mass of halo objects. For illustration, if the preliminary value of 0.5 km/s for the secondary peak of UMi is confirmed, compact objects with masses above $\sim 100$ solar masses could be excluded from comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter

Electromagnetic structure and weak decay of pseudoscalar mesons in a light-front QCD-inspired model

We study the scaling of the $^3S_1-^1S_0$ meson mass splitting and the pseudoscalar weak decay constants with the mass of the meson, as seen in the available experimental data. We use an effective light-front QCD-inspired dynamical model regulated at short-distances to describe the valence component of the pseudoscalar mesons. The experimentally known values of the mass splittings, decay constants (from global lattice-QCD averages) and the pion charge form factor up to 4 [GeV/c]$^2$ are reasonably described by the modelComment: 27 Pages, 7 eps figures,use revtex

The quark-antiquark potential at finite temperature and the dimension two gluon condensate

A recently proposed phenomenological model, which includes non perturbative effects from dimension two gluon condensates, is applied to analyze the available lattice data for the heavy quark free energy in the deconfined phase of quenched QCD. For large $q\bar{q}$ separations we recover previous results for the Polyakov loop, exhibiting unequivocal condensate contributions. For the $q\bar{q}$ potential at finite temperature and finite separation we find that a good overall description of the lattice data can be achieved once the condensate is properly accounted for. In addition, the model predicts a duality between the zero temperature potential as a function of the $q\bar{q}$ separation, on the one hand, and the quark selfenergy as a function of the temperature, on the other, which turns out to be satisfied to a high degree by the lattice data.Comment: 9 pages, 5 figure

Weak decay constant of pseudscalar meson in a QCD-inspired model

We show that a linear scaling between the weak decay constants of pseudoscalar and the vector mesons masses is supported by the available experimental data. The decay constant scale as $f_m/f_{pi}=M_V/M_{\rho}$ (f_m is decay constant and M_V vector meson ground state mass). This simple form is justified within a renormalized light-front QCD-inpired model for quark-antiquark bound states.Comment: 4 pages, use revtex style. To appear "Brazilian Journal of Physics (2003)

Cosmological Effects of Nonlinear Electrodynamics

It will be shown that a given realization of nonlinear electrodynamics, used as source of Einstein's equations, generates a cosmological model with interesting features, namely a phase of current cosmic acceleration, and the absence of an initial singularity, thus pointing to a way to solve two important problems in cosmology

Two new species of Hydnum with ovoid basidiospores: H. ovoideisporum and H. vesterholtii

Two new species of Hydnum, characterized by slender Hydnum rufescens-like basidiomes and ovoid to broadly ellipsoid basidiospores, are described from the Iberian Peninsula based on morphological and ITS molecular data. Hydnum ovoideisporum is distinguished by pilei with deep orange tones and strong preference for calcareous soil. It is widespread in the Iberian-Mediterranean area. Hydnum vesterholtii is characterized by its ocher to light ocher pileus, and nearly all the collections were made in the Pyrenees. Both ovoid-spored species are monophyletic well supported groups in the maximum parsimony and Bayesian ITS phylogenies, while the remainder of the samples assigned to H. rufescens s.l. and having globose basidiospores split into six well supported clades. The need to typify the name Hydnum rufescens is discussed, and a provisional key is given for the European taxa of Hydnum.Peer Reviewe

Entropy, diffusivity and the energy landscape of a water-like fluid

Molecular dynamics simulations and instantaneous normal mode (INM) analysis of a fluid with core-softened pair interactions and water-like liquid-state anomalies are performed to obtain an understanding of the relationship between thermodynamics, transport properties and the poten- tial energy landscape. Rosenfeld-scaling of diffusivities with the thermodynamic excess and pair correlation entropy is demonstrated for this model. The INM spectra are shown to carry infor- mation about the dynamical consequences of the interplay between length scales characteristic of anomalous fluids, such as bimodality of the real and imaginary branches of the frequency distribu- tion. The INM spectral information is used to partition the liquid entropy into two contributions associated with the real and imaginary frequency modes; only the entropy contribution from the imaginary branch captures the non-monotonic behaviour of the excess entropy and diffusivity in the anomalous regime of the fluid