341 research outputs found
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Californium-252: a remarkable versatile radioisotope
A product of the nuclear age, Californium-252 ({sup 252}Cf) has found many applications in medicine, scientific research, industry, and nuclear science education. Californium-252 is unique as a neutron source in that it provides a highly concentrated flux and extremely reliable neutron spectrum from a very small assembly. During the past 40 years, {sup 252}Cf has been applied with great success to cancer therapy, neutron radiography of objects ranging from flowers to entire aircraft, startup sources for nuclear reactors, fission activation for quality analysis of all commercial nuclear fuel, and many other beneficial uses, some of which are now ready for further growth. Californium-252 is produced in the High Flux Isotope Reactor (HFIR) and processed in the Radiochemical Engineering Development Center (REDC), both of which are located at the Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee. The REDC/HFIR facility is virtually the sole supplier of {sup 252}Cf in the western world and is the major supplier worldwide. Extensive exploitation of this product was made possible through the {sup 252}Cf Market Evaluation Program, sponsored by the United States Department of Energy (DOE) [then the Atomic Energy Commission (AEC) and later the Energy Research and Development Administration (ERDA)]. This program included training series, demonstration centers, seminars, and a liberal loan policy for fabricated sources. The Market Evaluation Program was instituted, in part, to determine if large-quantity production capability was required at the Savannah River Laboratory (SRL). Because of the nature of the product and the means by which it is produced, {sup 252}Cf can be produced only in government-owned facilities. It is evident at this time that the Oak Ridge research facility can meet present and projected near-term requirements. The production, shipment, and sales history of {sup 252}Cf from ORNL is summarized herein
Strings between branes
D-brane configurations containing fundamental strings are constructed as
classical solutions of Yang-Mills theory. The fundamental strings in these
systems stretch between D-branes. In the case of D1-branes, this construction
gives smooth (classical) resolutions of string junctions and string networks.
Using a non-abelian Yang-Mills analysis of the string current, the string
charge density is computed and is shown to have support in the region between
the D-brane world-volumes. The 't Hooft-Polyakov monopole is analyzed using
similar methods, and is shown to contain D-strings whose flux has support off
the D-brane world-volume defined by the Higgs scalar field, when this field is
interpreted in terms of a transverse dimension. The constructions presented
here are used to give a qualitative picture of tachyon condensation in the
Yang-Mills limit, where fundamental strings and lower-dimensional D-branes
arise in a volume of space-time where brane-antibrane annihilation has
occurred.Comment: 35 pages, 16 eps figures, JHEP style; v2: a comment adde
Experimental study on critical heat flux under rolling condition
Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.This paper presents defining characteristics of the critical heat flux (CHF) for the boiling of R-134a in vertical tube operation under rolling motion in marine reactor. It is important to predict CHF of marine reactor having the rolling motion in order to increase the safety of the reactor. MArine Reactor Moving Simulator (MARMS) tests are conducted to measure the critical heat flux using R-134a flowing upward in a uniformly heated vertical tube under rolling motion. MARMS was rotated by motor and mechanical power transmission gear. The CHF tests were performed in a 9.5 mm I.D. test section with heated length of 1m. Mass fluxs range from 285 to 1300 kg/m2s, inlet subcoolings from 3 to 38oC and outlet pressures from 1.3 to 2.4 bar. Amplitudes of rolling range from 15 to 45 degrees and periods from 6 to 12 sec. To convert the test conditions of CHF test using R-134a in water, Katto's fluid-to- fluid modeling was used in present investigation. A CHF correlation is presented which accounts for the effects of pressure, mass flux, inlet subcooling and rolling angle over all conditions tested. Unlike existing transient CHF experiments, CHF ratio of certain mass flux and pressure are different in rolling motion. For the mass fluxes below 500 kg/m2s at 13, 16 (region of relative low mass flux), CHF ratio was decreased but was increased above that mass flux (region of relative high mass flux) bar. Moreover, CHF tend to enhance in entire mass flux at 24 bar.dc201
Chiral radiative corrections and D_s(2317)/D(2308) mass puzzle
We show that one loop chiral corrections for heavy-light mesons in potential
model can explain the small mass of D_s(2317) as well as the small mass gap
between D_s(2317) and D(2308).Comment: To appear in EPJC. A figure and references addede
Extensions of AdS_5 x S^5 and the Plane-wave Superalgebras and Their Realization in the Tiny Graviton Matrix Theory
In this paper we consider all consistent extensions of the AdS_5 x S^5
superalgebra, psu(2,2|4), to incorporate brane charges by introducing both
bosonic and fermionic (non)central extensions. We study the Inonu-Wigner
contraction of the extended psu(2,2|4) under the Penrose limit to obtain the
most general consistent extension of the plane-wave superalgebra and compare
these extensions with the possible BPS (flat or spherical) brane configurations
in the plane-wave background. We give an explicit realization of some of these
extensions in terms of the Tiny Graviton Matrix Theory (TGMT)[hep-th/0406214]
which is the 0+1 dimensional gauge theory conjectured to describe the DLCQ of
strings on the AdS_5 x S^5 and/or the plane-wave background.Comment: 27 pages, LaTe
Strong decays and with light-cone QCD sum rules
In this article, we calculate the strong coupling constants and with the light-cone QCD sum rules. Then we
take into account the small transition matrix according to
Dashen's theorem, and obtain the small decay widths for the isospin violation
processes and . We can search the strange-bottomed mesons and
in the invariant and mass distributions
respectively.Comment: 15 pages, 2 figures, revised versio
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Three-month-olds, but not newborns, prefer own-race faces
Adults are sensitive to the physical differences that define ethnic groups. However, the age at which we become sensitive to ethnic
differences is currently unclear. Our study aimed to clarify this by testing newborns and young infants for sensitivity to ethnicity
using a visual preference (VP) paradigm. While newborn infants demonstrated no spontaneous preference for faces from either
their own- or other-ethnic groups, 3-month-old infants demonstrated a significant preference for faces from their own-ethnic
group. These results suggest that preferential selectivity based on ethnic differences is not present in the first days of life, but is
learned within the first 3 months of life. The findings imply that adultsâ perceptions of ethnic differences are learned and derived
from differences in exposure to own- versus other-race faces during early developmen
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High density genetic mapping identifies new susceptibility loci for rheumatoid arthritis
Summary Using the Immunochip custom single nucleotide polymorphism (SNP) array, designed for dense genotyping of 186 genome wide association study (GWAS) confirmed loci we analysed 11,475 rheumatoid arthritis cases of European ancestry and 15,870 controls for 129,464 markers. The data were combined in meta-analysis with GWAS data from additional independent cases (n=2,363) and controls (n=17,872). We identified fourteen novel loci; nine were associated with rheumatoid arthritis overall and 5 specifically in anti-citrillunated peptide antibody positive disease, bringing the number of confirmed European ancestry rheumatoid arthritis loci to 46. We refined the peak of association to a single gene for 19 loci, identified secondary independent effects at six loci and association to low frequency variants (minor allele frequency <0.05) at 4 loci. Bioinformatic analysis of the data generated strong hypotheses for the causal SNP at seven loci. This study illustrates the advantages of dense SNP mapping analysis to inform subsequent functional investigations
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