1,078 research outputs found
The Nucleon ``Tensor Charges'' and the Skyrme Model
The lowest moment of the twist-two, chiral-odd parton distribution
of the nucleon can be related to the so-called ``tensor charges'' of the
nucleon. We consider the tensor charges in the Skyrme model, and find that in
the large-, SU(3)-symmetric limit, the model predicts that the octet
isosinglet tensor charge, , is of order with respect to the
octet isovector tensor charge, . The predicted ratio is then 1/3,
in the large- limit. These predictions coincide with the Skyrme model
predictions for the octet charges, and . (The
prediction for the axial charges differs from the commonly quoted
prediction of 5/9, which is based on an inconsistent treatment of the
large- limit.) The model also predicts that the singlet tensor charge,
, is of order with respect to .Comment: 9 single-spaced pages, no figures, MIT-CTP-212
High angular resolution mm- and submm-observations of dense molecular gas in M82
Researchers observed CO(7-6), CO(3-2), HCN(3-2) and HCO+(3-2) line emission toward the starburst nucleus of M82 and have obtained an upper limit to H13CN(3-2). These are the first observations of the CO(7-6), HCN(3-2) and HCO+(3-2) lines in any extragalactic source. Researchers took the CO(7-6) spectrum in January 1988 at the Infrared Telescope Facility (IRTF) with the Max Planck Institute for Extraterrestrial Physics/Univ. of California, Berkeley 800 GHz Heterodyne Receiver. In March 1989 researchers used the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope to observe the CO(3-2) line with the new MPE 350 GHz Superconductor Insulator Superconductor (SIS) receiver and the HCN(3-2) and HCO+(3-2) lines with the (IRAM) 230 GHz SIS receiver (beam 12" FWHM, Blundell et al. 1988). The observational parameters are summarized
Photochemical and microbial alteration of dissolved organic matter in temperate headwater streams associated with different land use
Photochemical and microbial transformations of DOM were evaluated in headwater streams draining forested and human-modified lands (pasture, cropland, and urban development) by laboratory incubations. Changes in DOC concentrations, DOC isotopic signatures, and DOM fluorescence properties were measured to assess the amounts, sources, ages, and properties of reactive and refractory DOM under the influence of photochemistry and/or bacteria. DOC in streams draining forest-dominated watersheds was more photoreactive than in streams draining mostly human-modified watersheds, possibly due to greater contributions of terrestrial plant-derived DOC and lower amounts of prior light exposure in forested streams. Overall, the percentage of photoreactive DOC in stream waters was best predicted by the relative content of terrestrial fluorophores. The bioreactivity of DOC was similar in forested and human-modified streams, but variations were correlated with temperature and may be further controlled by the diagenetic status of organic matter. Alterations to DOC isotopes and DOM fluorescence properties during photochemical and microbial incubations were similar between forested and human-modified streams and included (1) negligible effects of microbial alteration on DOC isotopes and DOM fluorescence properties, (2) selective removal of C-13-depleted and C-14-enriched DOC under the combined influence of photochemical and microbial processes, and (3) photochemical alteration of DOM resulting in a preferential loss of terrestrial humic fluorescence components relative to microbial fluorescence components. This study provides a unique comparison of DOC reactivity in a regional group of streams draining forested and human-modified watersheds and indicates the importance of land use on the photoreactivity of DOC exported from upstream watersheds
Current Problems in Securities Regulation
This comment analyzes four areas of central significance to adequate protection for the investor: (1) qualifications of those in the securities industry who deal with the public; (2) dissemination of corporate publicity; (3) dissemination of investment advice; and (4) selling practices in the securities industry. The findings and recommendations of the Special Study are given special attention insofar as they bear upon the problems covered. In certain areas, however, recent developments in court and Commission decisions have brought about changes equally as significant as the findings and recommendations of the Special Study. Thus each section covers the background and recent developments in the designated area, as well as the Special Study itself
An estimate of \Omega_m without priors
Using mean relative peculiar velocity measurements for pairs of galaxies, we
estimate the cosmological density parameter and the amplitude of
density fluctuations . Our results suggest that our statistic is a
robust and reproducible measure of the mean pairwise velocity and thereby the
parameter. We get and . These estimates do not depend on prior assumptions on
the adiabaticity of the initial density fluctuations, the ionization history,
or the values of other cosmological parameters.Comment: 12 pages, 4 figures, slight changes to reflect published versio
Ariel - Volume 6 Number 4
Editors
Mark Dembert
J.D. Kanofsky
Frank Chervenak
John Lammie
Curt Cummings
Entertainment
Robert Breckenridge
Joe Conti
Gary Kaskey
Photographer
Larry Glazerman
Overseas Editor
Mike Sinason
Humorist
Jim McCann
Staff
Ken Jaffe
Bob Sklaroff
Halley Faust
Jim Burk
Ariel - Volume 6 Number 4 (Alternate Version)
Editors
Mark Dembert
J.D. Kanofsky
Frank Chervenak
John Lammie
Curt Cummings
Entertainment
Robert Breckenridge
Joe Conti
Gary Kaskey
Photographer
Larry Glazerman
Overseas Editor
Mike Sinason
Humorist
Jim McCann
Staff
Kenn Jaffe
Bob Sklaroff
Halley Faust
Jim Burke
Jay Amsterdam
Morton A. Klein
Nancy Redfer
Effect of off-center ion substitution in morphotropic lead zirconate titanate
This research was supported by the DOD Grant No. FA9550–16-1–0295. S.P.P. gratefully acknowledges the financial assistance from IFN-NSF under the Grant No. EPS-1002410.A detailed study of the effect of off-center donor ion (Sc3+) substitution on structural, microstructural, optical, dielectric, electrical and ferroelectric properties of morphotropic lead zirconate titanate electroceramics with the stoichiometric formula Pb0.85Sc0.10Zr0.53Ti0.47O3 (PSZT), synthesized using a high-energy solid-state reaction technique, was carried out. Powder x-ray diffractometry was used to identify the stabilized tetragonal phase (space group P4mm) with considerably reduced tetragonal strain, c/a = 1.005. An analysis of the thermal dependence of the Raman results indicated a smooth order-disorder displacive (ferroelectric-paraelectric) phase transition as revealed by the observed disappearance of the soft modes A1 (1TO) and A1 (2TO) above 460 K. The dielectric response of Pt/PSZT/Pt metal-ferroelectric-metal (MFM) capacitors was probed over a wide range of thermal excursions (85-600 K) and ac signal frequencies (102-106 Hz). Thermally activated dynamic and static conduction processes indicate hopping conduction mechanism (Eact ≤ 0.015 eV) and the formation of small polarons caused by the electron and/or hole-lattice (phonon) interaction (Eact ≥ 0.1 eV) at low (100−300 K) and high temperatures (300−600 K), respectively. The reduction in remnant polarization obtained is in good agreement with the largely reduced tetragonal strain observed in this sample, ( Pr ∝√(c/a-1) ). DC current conduction is dominated by Poole-Frenkel mechanism that assumes a Coulombic attraction between de-trapped electrons and positively charged stationary defects in the polycrystalline matrix.PostprintPeer reviewe
Tetraquarks in a chiral constituent quark model
We analyze the possibility of heavy-light tetraquark bound states by means of
a chiral constituent quark model. The study is done in a variational approach.
Special attention is paid to the contribution given by the different terms of
the interacting potential and also to the role played by the different color
channels. We find a stable state for both and
configurations. Possible decay modes of these structures are
analyzed.Comment: 13 pages, no figures. Accepted for publication in European Journal of
Physics
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