893 research outputs found
Relativistic Ring-Diagram Nuclear Matter Calculations
A relativistic extension of the particle-particle hole-hole ring-diagram
many-body formalism is developed by using the Dirac equation for
single-particle motion in the medium. Applying this new formalism, calculations
are performed for nuclear matter. The results show that the saturation density
is improved and the equation of state becomes softer as compared to
corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A
potential, nuclear matter is predicted to saturate at an energy per nucleon of
--15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm, in
excellent agreement with empirical information. The compression modulus is 152
MeV at the saturation point.Comment: 23 pages text (LaTex) and 2 figures (paper, will be faxed upon
request), UI-NTH-92-0
Influence of season of birth, sex and paternal line on growth performance and carcass traits in pigs
Participants in the pig production industry focus on feed and feed additives to improve growth performance and meat quality of pigs. Consequently, the Rural Development Administration of the Republic of Korea produced a new paternal line to improve economic traits in pigs. However, there is an absence of information on pig traits with regard to season and sex, and a comparison between the new paternal line and past paternal lines. Therefore, the authors conducted this study to investigate the influence of season of birth, sex and paternal line on growth performance and carcass traits in pigs. A total of 2888 piglets ((Landrace Ă Yorkshire) Ă Darby Duroc (DD) or Chookjin Duroc (CD)) with an average age of three weeks were tested for 22 weeks during the four season of the year (spring 608 piglets, summer 404 piglets, autumn 576 piglets and winter 1300 piglets). The bodyweights (BW) of individual pig were recorded, and feed consumption was recorded at weeks 2, 12 and 22, to determine growth performance. At reaching market weight, backfat thickness was determined at the last rib area. Meat was graded according to the criteria of the slaughterhouse. There were no significant differences in growth performance and carcass traits between sexes. The CD line crossbred pig had a significant higher BW at 16 weeks, and higher carcass trait values at 22 weeks than the DD line. During weeks 8 to 16 the CD line crossbred pigs showed a tendency of an increased average daily gain (ADG) and gain : feed (G : F) ratio compared with the DD line. Furthermore, pigs born in spring had significant lower ADG, average daily feed intake (ADFI) and carcass trait values than born in the other seasons. In conclusion, the new paternal line (Chookjin Duroc) improved growth performance and carcass traits compare with the DD line.Keywords: sex, growth, terminal sire, meat quality, backfat thicknes
Electromagnetic Interference in Measurements of Radial Stress During Split Hopkinson Pressure Bar Experiments
Split Hopkinson pressure bar experiments on soils are often carried out using a rigid steel confining ring to provide plane strain conditions, and measurements of the circumferential strain in the ring can be used to infer the radial stress on the surface of the specimen. Previous experiments have shown evidence of irregular electromagnetic interference in measurements of radial stress, which obscures the signals and impedes analysis. The development of robust constitutive models for soils in blast and impact events relies on the accurate characterisation of this behaviour, and so it is necessary to isolate and remove the source of interference. This paper uses an induction coil to identify the source of the anomalous signals, which are found to be due to induced currents in the gauge lead wires from the movement of magnetised pressure bars (martensitic stainless steel, 440C). Comparative experiments on sand and rubber specimens are used to show that the deforming soil specimen does not make a significant contribution to this activity, and recommendations are made on reducing electromagnetic interference to provide reliable radial stress measurements
Equation of state and magnetic susceptibility of spin polarized isospin asymmetric nuclear matter
Properties of spin polarized isospin asymmetric nuclear matter are studied
within the framework of the Brueckner--Hartree--Fock formalism. The
single-particle potentials of neutrons and protons with spin up and down are
determined for several values of the neutron and proton spin polarizations and
the asymmetry parameter. It is found an almost linear and symmetric variation
of the single-particle potentials as increasing these parameters. An analytic
parametrization of the total energy per particle as a function of the asymmetry
and spin polarizations is constructed. This parametrization is employed to
compute the magnetic susceptibility of nuclear matter for several values of the
asymmetry from neutron to symmetric matter. The results show no indication of a
ferromagnetic transition at any density for any asymmetry of nuclear matter.Comment: 23 pages, 8 figures, 2 tables (submitted to Phys. Rev. C
Solidification of Al alloys under electromagnetic pulses and characterization of the 3D microstructures under synchrotron x-ray tomography
A novel programmable electromagnetic pulse device was developed and used to study the solidification of Al-15 pct Cu and Al-35 pct Cu alloys. The pulsed magnetic fluxes and Lorentz forces generated inside the solidifying melts were simulated using finite element methods, and their effects on the solidification microstructures were characterized using electron microscopy and synchrotron X-ray tomography. Using a discharging voltage of 120 V, a pulsed magnetic field with the peak Lorentz force of ~1.6 N was generated inside the solidifying Al-Cu melts which were showed sufficiently enough to disrupt the growth of the primary Al dendrites and the Al2Cu intermetallic phases. The microstructures exhibit a strong correlation to the characteristics of the applied pulse, forming a periodical pattern that resonates the frequency of the applied electromagnetic field
Effect of Grain Boundary Character Distribution on the Impact Toughness of 410NiMo Weld Metal
Grain boundary character distributions in 410NiMo weld metal were studied in the as-welded, first-stage, and second-stage postweld heat treatment (PWHT) conditions, and these were correlated with the Charpy-V impact toughness values of the material. The high impact toughness values in the weld metal in the as-welded and first-stage PWHT conditions compared to that in the second-stage condition are attributed to the higher fraction of low-energy I pound boundaries. A higher volume fraction of retained austenite and coarser martensite after second-stage PWHT accompanied by the formation of the ideal cube component in the 2-hour heat-treated specimen led to a reduction in the toughness value. A subsequent increase in the PWHT duration at 873 K (600 A degrees C) enhanced the formation of {111}aOE (c) 112 >, which impedes the adverse effect of the cubic component, resulting in an increase in the impact toughness. In addition to this, grain refinement during 4-hour PWHT in the second stage also increased the toughness of the weld metal
The Proton Spin and Flavor Structure in the Chiral Quark Model
After a pedagogical review of the simple constituent quark model and deep
inelastic sum rules, we describe how a quark sea as produced by the emission of
internal Goldstone bosons by the valence quarks can account for the observed
features of proton spin and flavor structures. Some issues concerning the
strange quark content of the nucleon are also discussed.Comment: 59 pages with table of contents, Lecture delivered at the Schladming
Winter School (March 1997), to be published by Springer-Verlag under the
title "Computing Particle Properties" (eds. C. B. Lang and H. Gausterer
Quark Imaging in the Proton Via Quantum Phase-Space Distributions
We develop the concept of quantum phase-space (Wigner) distributions for
quarks and gluons in the proton. To appreciate their physical content, we
analyze the contraints from special relativity on the interpretation of elastic
form factors, and examine the physics of the Feynman parton distributions in
the proton's rest frame. We relate the quark Wigner functions to the
transverse-momentum dependent parton distributions and generalized parton
distributions, emphasizing the physical role of the skewness parameter. We show
that the Wigner functions allow to visualize quantum quarks and gluons using
the language of the classical phase space. We present two examples of the quark
Wigner distributions and point out some model-independent features.Comment: 20 pages with 3 fiture
Relic Neutrino Absorption Spectroscopy
Resonant annihilation of extremely high-energy cosmic neutrinos on big-bang
relic anti-neutrinos (and vice versa) into Z-bosons leads to sizable absorption
dips in the neutrino flux to be observed at Earth. The high-energy edges of
these dips are fixed, via the resonance energies, by the neutrino masses alone.
Their depths are determined by the cosmic neutrino background density, by the
cosmological parameters determining the expansion rate of the universe, and by
the large redshift history of the cosmic neutrino sources. We investigate the
possibility of determining the existence of the cosmic neutrino background
within the next decade from a measurement of these absorption dips in the
neutrino flux. As a by-product, we study the prospects to infer the absolute
neutrino mass scale. We find that, with the presently planned neutrino
detectors (ANITA, Auger, EUSO, OWL, RICE, and SalSA) operating in the relevant
energy regime above 10^{21} eV, relic neutrino absorption spectroscopy becomes
a realistic possibility. It requires, however, the existence of extremely
powerful neutrino sources, which should be opaque to nucleons and high-energy
photons to evade present constraints. Furthermore, the neutrino mass spectrum
must be quasi-degenerate to optimize the dip, which implies m_{nu} >~ 0.1 eV
for the lightest neutrino. With a second generation of neutrino detectors,
these demanding requirements can be relaxed considerably.Comment: 19 pages, 26 figures, REVTeX
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