15,898 research outputs found
Relativistic Quantum Scattering of High Energy Fermions in the Presence of Phase Transition
We study the high energy behaviour of fermions hitting a general wall caused
by a first-order phase transition. The wall profile is introduced through a
general analytic function. The reflection coefficient is computed in the high
energy limit and expressed in terms of the poles of the wall profile function.
It is shown that the leading singularity gives the high energy behaviour.Comment: 10 page
Mathisson's helical motions demystified
The motion of spinning test particles in general relativity is described by
Mathisson-Papapetrou-Dixon equations, which are undetermined up to a spin
supplementary condition, the latter being today still an open question. The
Mathisson-Pirani (MP) condition is known to lead to rather mysterious helical
motions which have been deemed unphysical, and for this reason discarded. We
show that these assessments are unfounded and originate from a subtle (but
crucial) misconception. We discuss the kinematical explanation of the helical
motions, and dynamically interpret them through the concept of hidden momentum,
which has an electromagnetic analogue. We also show that, contrary to previous
claims, the frequency of the helical motions coincides exactly with the
zitterbewegung frequency of the Dirac equation for the electron.Comment: To appear in the Proceedings of the Spanish Relativity Meeting 2011
(ERE2011), "Towards new paradigms", Madrid 29 August - 2 September 201
Comment on 'A generalized Helmholtz theorem for time-varying vector fields by A. M. Davis, [Am. J. Phys. 74, 72-76 (2006)]'
In a recent paper Davis formulated a generalized Helmholtz theorem for a
time-varying vector field in terms of the Lorenz gauge retarded potentials. The
purposes of this comment are to point out that Davis's generalization of the
theorem is a version of the extension of the Helmholtz theorem formulated some
years ago by McQuistan and also by Jefimenko and more recently by the present
author and to show that Davis's expression for the time-dependent vector field
is also valid for potentials in gauges other than the Lorenz gau
Chaos in a Switched-Capacitor Circuit
We report chaotic phenomena observed from a simple nonlinear switched-capacitor circuit. The experimentally measured bifurcation tree diagram reveals a period-doubling route to chaos. This circuit is described by a first-order discrete equation which can be transformed into the logistic map whose chaotic dynamics is well known.National Science Foundation ECS-8542885Comisión Interministerial de Ciencia y Tecnología 0245/81Office of Naval Research under Contract NOOO14-76-C-057
Duality and the Equivalence Principle of Quantum Mechanics
Following a suggestion by Vafa, we present a quantum-mechanical model for
S-duality symmetries observed in the quantum theories of fields, strings and
branes. Our formalism may be understood as the topological limit of Berezin's
metric quantisation of the upper half-plane H, in that the metric dependence
has been removed. Being metric-free, our prescription makes no use of global
quantum numbers. Quantum numbers arise only locally, after the choice of a
local vacuum to expand around. Our approach may be regarded as a manifestly non
perturbative formulation of quantum mechanics, in that we take no classical
phase space and no Poisson brackets as a starting point. The reparametrisation
invariance of H under SL(2,R) induces a natural SL(2,R) action on the quantum
mechanical operators that implements S-duality. We also link our approach with
the equivalence principle of quantum mechanics recently formulated by Faraggi
and Matone.Comment: 14 pages, JHEP styl
Pragmatic approach to the little hierarchy problem: the case for Dark Matter and neutrino physics
We show that the addition of real scalars (gauge singlets) to the Standard
Model can both ameliorate the little hierarchy problem and provide realistic
Dark Matter candidates. To this end, the coupling of the new scalars to the
standard Higgs boson must be relatively strong and their mass should be in the
1-3 TeV range, while the lowest cutoff of the (unspecified) UV completion must
be >~ 5 TeV, depending on the Higgs boson mass and the number of singlets
present. The existence of the singlets also leads to realistic and surprisingly
reach neutrino physics. The resulting light neutrino mass spectrum and mixing
angles are consistent with the constraints from the neutrino oscillations.Comment: discussion of multi singlet case adde
GRASS UTILIZATION IN GROWING FINISHING BÍSARO PIGS (85-107 KG). PERFORMANCE AND CARCASS COMPOSITION
The use of different quantities of vegetables, forages or fresh grass as fodder for growing-finishing pigs is an important factor of the northern Portugal traditional system. The increasing development of swine production in outdoor systems, extensive and organic production, turns to upcoming natural diets, in which grass performs a significant part. With regard to this, some investigation has been made concerning the use of fibre-rich feed ingredients in pig nutrition. Metabolic effects of its ingestion are analysed concerning different sights (economical, social, environmental and physiological ones).
The aim of this work was to study the effects of grass utilization in the diets on performances of finishing Bísaro pigs. A total of 22 pigs (16 castrated males and 6 females) was housed outdoor and fed ad libitum (37 – 85 kg live weight) with a growing diet and then transferred to an indoor system (with free access to an outdoor area) for 49 days, according to 3 different treatments: 100% concentrate (C), 75% concentrate + ad libitum grass (CE75), 50% concentrate + ad libitum grass (CE50). The grass was supplied and its intake registered on a daily basis. Every 14 days, the pigs were weighted and their back fat (P2 in vivo) measured. After slaughter (average weight of 107 kg LW), yield and ½ left carcass characteristics were controlled. During the outdoor growing phase, the ADG was 513 g/day. During the indoor finishing phase, the increase grass intake was proportional to the reduction of concentrate in the diet. The ADG (g) and the fat deposition (P2 cm) were significantly different (P<0,05) in the 3 treatments (ADG: C=641, CE75=467, CE50=356 and: C=11,4, CE75=+9,5, CE50=+6,2). The empty body weight (kg) was also proportional to the intake of concentrate (C=116,2; CE75=107,7; CE50=102,2). Comparatively to the weight of the body parts, pigs that had higher intake of grass and lower of concentrate showed a higher % of shoulder (P<0,05; C=20,4, CE75=21,7, CE50=22,2) and the pH45min of CE carcasses was significantly higher (P<0,05). As a conclusion, concentrate substitution for grass showed a slower growing rate, thinner carcasses and a high technological quality.
Neverthelles variability (CV %) of the productive parameters at the end of this study were higher in the treatments that included grass: live weight (C= 10,5%; C75=10,7%; C50=14,3%), finishing ADG (C=24%; C75=37%, C50=42%), and final fat (C=37%; C75=32%, C50=52%). These values suggest that the utilization of fibrous feeds in growing-finishing swine may be one of the possible explanations of the more heterogeneous products and carcasses found in the traditional or extensive systems, common users of fibrous feeds in the carcass finishing phase
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