461 research outputs found
Two-dimensional spatial power spectra of photospheric velocity fluctuations
Two-dimensional spatial autocorrelation functions and power spectral density distributions were obtained from high-resolution velocity spectroheliograms. Although the autocorrelation functions indicate the existence of velocity cells of size roughly 2500 to 3500 km, the power spectra fail to reveal them because the cells are not strictly spatially periodic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43736/1/11207_2004_Article_BF00162429.pd
Higher spin quaternion waves in the Klein-Gordon theory
Electromagnetic interactions are discussed in the context of the Klein-Gordon
fermion equation. The Mott scattering amplitude is derived in leading order
perturbation theory and the result of the Dirac theory is reproduced except for
an overall factor of sixteen. The discrepancy is not resolved as the study
points into another direction. The vertex structures involved in the scattering
calculations indicate the relevance of a modified Klein-Gordon equation, which
takes into account the number of polarization states of the considered quantum
field. In this equation the d'Alembertian is acting on quaternion-like plane
waves, which can be generalized to representations of arbitrary spin. The
method provides the same relation between mass and spin that has been found
previously by Majorana, Gelfand, and Yaglom in infinite spin theories
Ferromagnetic Semiconductors: Moving Beyond (Ga,Mn)As
The recent development of MBE techniques for growth of III-V ferromagnetic
semiconductors has created materials with exceptional promise in spintronics,
i.e. electronics that exploit carrier spin polarization. Among the most
carefully studied of these materials is (Ga,Mn)As, in which meticulous
optimization of growth techniques has led to reproducible materials properties
and ferromagnetic transition temperatures well above 150 K. We review progress
in the understanding of this particular material and efforts to address
ferromagnetic semiconductors as a class. We then discuss proposals for how
these materials might find applications in spintronics. Finally, we propose
criteria that can be used to judge the potential utility of newly discovered
ferromagnetic semiconductors, and we suggest guidelines that may be helpful in
shaping the search for the ideal material.Comment: 37 pages, 4 figure
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Observation of Excess J/Ï Yield at Very Low Transverse Momenta in Au+Au Collisions at sqrt[s_{NN}]=200ââGeV and U+U Collisions at sqrt[s_{NN}]=193ââGeV.
We report on the first measurements of J/Ï production at very low transverse momentum (p_{T}<0.2ââGeV/c) in hadronic Au+Au collisions at sqrt[s_{NN}]=200ââGeV and U+U collisions at sqrt[s_{NN}]=193ââGeV. Remarkably, the inferred nuclear modification factor of J/Ï at midrapidity in Au+Au (U+U) collisions reaches about 24 (52) for p_{T}<0.05ââGeV/c in the 60%-80% collision centrality class. This noteworthy enhancement cannot be explained by hadronic production accompanied by cold and hot medium effects. In addition, the dN/dt distribution of J/Ï for the very low p_{T} range is presented for the first time. The distribution is consistent with that expected from the Au nucleus and shows a hint of interference. Comparison of the measurements to theoretical calculations of coherent production shows that the excess yield can be described reasonably well and reveals a partial disruption of coherent production in semicentral collisions, perhaps due to the violent hadronic interactions. Incorporating theoretical calculations, the results strongly suggest that the dramatic enhancement of J/Ï yield observed at extremely low p_{T} originates from coherent photon-nucleus interactions. In particular, coherently produced J/Ï's in violent hadronic collisions may provide a novel probe of the quark-gluon plasma
Plasma Electronics
Contains research objectives and reports on ten research projects.National Science Foundation (Grant GK-57)United States Atomic Energy Commission under Contract AT(30-1)-322
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Measurements of the transverse-momentum-dependent cross sections of J /Ï production at mid-rapidity in proton+proton collisions at s =510 and 500 GeV with the STAR detector
We present measurements of the differential cross sections of inclusive J/Ï meson production as a function of transverse momentum (pTJ/Ï) using the ÎŒ+ÎŒ- and e+e- decay channels in proton+proton collisions at center-of-mass energies of 510 and 500 GeV, respectively, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The measurement from the ÎŒ+ÎŒ- channel is for
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Measurement of inclusive J/Ï suppression in Au+Au collisions at sNN=200 GeV through the dimuon channel at STAR
J/Ï suppression has long been considered a sensitive signature of the formation of the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. In this letter, we present the first measurement of inclusive J/Ï production at mid-rapidity through the dimuon decay channel in Au+Au collisions at sNN=200 GeV with the STAR experiment. These measurements became possible after the installation of the Muon Telescope Detector was completed in 2014. The J/Ï yields are measured in a wide transverse momentum (pT) range of 0.15 GeV/c to 12 GeV/c from central to peripheral collisions. They extend the kinematic reach of previous measurements at RHIC with improved precision. In the 0-10% most central collisions, the J/Ï yield is suppressed by a factor of approximately 3 for pT>5 GeV/c relative to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The J/Ï nuclear modification factor displays little dependence on pT in all centrality bins. Model calculations can qualitatively describe the data, providing further evidence for the color-screening effect experienced by J/Ï mesons in the QGP
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Charge-dependent pair correlations relative to a third particle in pâŻ+âŻAu and dâŻ+âŻAu collisions at RHIC
Quark interactions with topological gluon configurations can induce chirality imbalance and local parity violation in quantum chromodynamics. This can lead to electric charge separation along the strong magnetic field in relativistic heavy-ion collisions â the chiral magnetic effect (CME). We report measurements by the STAR collaboration of a CME-sensitive observable in p+Au and d+Au collisions at 200 GeV, where the CME is not expected, using charge-dependent pair correlations relative to a third particle. We observe strong charge-dependent correlations similar to those measured in heavy-ion collisions. This bears important implications for the interpretation of the heavy-ion data
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Longitudinal double-spin asymmetry for inclusive jet and dijet production in pp collisions at s =510 GeV
We report the first measurement of the inclusive jet and the dijet longitudinal double-spin asymmetries, ALL, at midrapidity in polarized pp collisions at a center-of-mass energy s=510 GeV. The inclusive jet ALL measurement is sensitive to the gluon helicity distribution down to a gluon momentum fraction of xâ0.015, while the dijet measurements, separated into four jet-pair topologies, provide constraints on the x dependence of the gluon polarization. Both results are consistent with previous measurements made at s=200 GeV in the overlapping kinematic region, x>0.05, and show good agreement with predictions from recent next-to-leading order global analyses
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