186 research outputs found
When human life begins
The moment attributed to the beginning of human life is debated not only in religious and political communities, but within the scientific community as well. Particular attention is given to this issue as advances in science make it possible to manipulate the embryo and fetus at early stages of development. This study explores these issues as they are revealed in the literature. In particular, examination of the stages of human development associated with this issue and the correlation between these stages and their influence on ethical concerns in current scientific technologies such as abortion, cloning, and embryonic stem cell experimentation
B Production Asymmetries in Perturbative QCD
This paper explores a new mechanism for B production in which a b quark
combines with a light parton from the hard-scattering process before
hadronizing into the B hadron. This recombination mechanism can be calculated
within perturbative QCD up to a few nonperturbative constants. Though
suppressed at large transverse momentum by a factor Lambda_QCD m_b/p_t^2
relative to b quark fragmentation production, it can be important at large
rapidities. A signature for this heavy-quark recombination mechanism in
proton-antiproton colliders is the presence of rapidity asymmetries in B cross
sections. Given reasonable assumptions about the size of nonperturbative
parameters entering the calculation, we find that the asymmetries are only
significant for rapidities larger than those currently probed by collider
experiments.Comment: 17 pages, LaTeX, 4 ps figures, tightenlines, sections added, final
version accepted for publication in Phys. Rev.
Parton Distributions in the Valon Model
The parton distribution functions determined by CTEQ at low are used as
inputs to test the validity of the valon model. The valon distributions in a
nucleon are first found to be nearly independent. The parton distribution
in a valon are shown to be consistent with being universal, independent of the
valon type. The momentum fractions of the partons in the valon add up
separately to one. These properties affirm the validity of the valon model. The
various distributions are parameterized for convenient application of the
model.Comment: 9 pages + 9 figures in ep
Comparison of Nuclear Suppression Effects on Meson Production at High p_T and p_L
The medium effect on the pion distribution at high in collisions
is compared to that of the pion distribution at high in collisions.
Both the suppression of the spectra and the energy losses of the measured pions
are studied. Although the medium effect on is larger than on , the
difference is found surprisingly to be not as big as one would naively expect.Comment: 8 RevTex pages with 5 figure
Scaling Distributions of Quarks, Mesons and Proton for all , Energy and Centrality
We present the evidences for the existence of a universal scaling behavior of
the production of at all transverse momenta in heavy-ion collisions at
all centralities and all collision energies. The corresponding scaling behavior
of the quarks is then derived just before the quarks recombine with antiquarks
to form the pions. The degradation effect of the dense medium on the quark
is derived from the scaling distribution. In the recombination model it
is then possible to calculate the distributions of the produced proton
and kaon, which are scaling also. Experimentally verifiable predictions are
made. Implications of the existence of the scaling behavior are discussed.Comment: 10 pages in RevTeX, including 14 figures in eps file
The asymmetry of the proton in a Pion Cloud Model approach
We study the asymmetry of the proton in a model approach
in which hadronic fluctuations of the nucleon are generated through gluon
splitting and recombination mechanisms. Within this framework, it is shown that
the
asymmetry of the proton is consistently described by including only
nucleon fluctuations to and bound states. Predictions
of the model closely agree with the recent experimental data of the E866/NuSea
Collaboration.Comment: Final version. To appear in Phys. Rev.
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 shape of the <i>T</i><sub>z</sub> = +1 nucleus <sup>94</sup>Pd and the role of proton-neutron interactions on the structure of its excited states
Reduced transition probabilities have been extracted between excited, yrast states in the N = Z + 2 nucleus 94Pd. The transitions of interest were observed following decays of the IÏ = 14+ , Ex = 2129-keV isomeric state, which was populated following the projectile fragmentation of a 124Xe primary beam at the GSI Helmholtzzentrum fĂŒr Schwerionenforschung accelerator facility as part of FAIR Phase-0. Experimental information regarding the reduced E2 transition strengths for the decays of the yrast 8+ and 6+ states was determined following isomer-delayed EÎł1 â EÎł2 â âłT2,1 coincidence method, using the LaBr3(Ce)-based FATIMA fast-timing coincidence gamma-ray array, which allowed direct determination of lifetimes of states in 94Pd using the Generalized Centroid Difference (GCD) method. The experimental value for the half-life of the yrast 8+ state of 755(106) ps results in a reduced transition probability of B(E2:8+ â6+ ) = 205+34 â25 e2fm4 , which enables a precise verification of shell-model calculations for this unique system, lying directly between the N = Z line and the N = 50 neutron shell closure. The determined B(E2) value provides an insight into the purity of (g9/2)n configurations in competition with admixtures from excitations between the (lower) N = 3 pf and (higher) N = 4 gds orbitals for the first time. The results indicate weak collectivity expected for near-zero quadrupole deformation and an increasing importance of the T = 0 proton-neutron interaction at N = 48
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