8,601 research outputs found
Exploration of jet energy loss via direct -charged particle azimuthal correlation measurements
The multiplicities of charged particles azimuthally associated with direct
photons and have been measured for Au+Au, p+p, and d+Au collisions at
= 200 GeV in the STAR experiment. Charged particles with
transverse momentum 0.5 16 GeV/c for p+p and d+Au, and
3 16 GeV/c for Au+Au and pseudorapidity
1.5 in coincidence with direct photons and of high transverse
momentum 8 16 GeV/c at 0.9
have been used for this analysis. Within the considered range of kinematics,
the observed suppressions of the associated yields per direct in
central Au+Au relative to p+p and d+Au are similar and constant with direct
photon fractional energy (). The
measured suppressions of the associated yields with direct are
comparable to those with . The data are compared to theoretical
predictions.Comment: 4 pages, 5 figures, Quark Matter 2009, March 30 - April 4, Knoxville,
Tennesse
Black Hole Feedback On The First Galaxies
We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.Astronom
Can Recent Charge Fluctuations Be a Reliable signal for a QGP at RHIC?
The recent papers of Jeon and Koch [1] and Asakawa, Heinz, and Muller [2]
argue that the event by event fluctuations of the ratio of the positively
charged and negatively charged pions provide a distinct signal for a QGP at
RHIC/LHC due to differences in those from the QGP phase and the Hadron Gas
Phase.In this paper we point out that aside from the questionability of the
many assumptions in the treatment used,even following their approach there are
other effects not considered, e.g. color charge fluctuations, which could
significantly or even completely wash out the proposed signal.Therefore lack of
observation of these charge fluctuation signals cannot lead one to conclude
that a QGP is not formed at RHIC. A general discussion of experimental
requirements for observation of such signals(if they exist),annd how to
interpret them is included.Comment: 9 pages and 2 Fig
Growth Of Antimony Doped P-type Zinc Oxide Nanowires For Optoelectronics
In a method of growing p-type nanowires, a nanowire growth solution of zinc nitrate (Zn(NO₃)₂), hexamethylenetetramine (HMTA) and polyethylenemine (800 Mw PEI) is prepared. A dopant solution to the growth solution, the dopant solution including an equal molar ration of sodium hydroxide (NaOH), glycolic acid (C₂H₄O₃) and antimony acetate (Sb(CH₃COO)₃) in water is prepared. The dopant solution and the growth solution combine to generate a resulting solution that includes antimony to zinc in a ratio of between 0.2% molar to 2.0% molar, the resulting solution having a top surface. An ammonia solution is added to the resulting solution. A ZnO seed layer is applied to a substrate and the substrate is placed into the top surface of the resulting solution with the ZnO seed layer facing downwardly for a predetermined time until Sb-doped ZnO nanowires having a length of at least 5 μm have grown from the ZnO seed layer.Georgia Tech Research Corporatio
InGaN nano-ring structures for high-efficiency light emitting diodes
A technique based on the Fresnel diffraction effect for the fabrication of nano-scale site-controlled ring structures in InGaN/GaN multi-quantum well structures has been demonstrated. The ring structures have an internal diameter of 500 nm and a wall width of 300 nm. A 1 cm-1 Raman shift has been measured, signifying substantial strain relaxation from the fabricated structure. The 9 nm blueshift observed in the cathodoluminescence spectra can be attributed to band filling and/or screening of the piezoelectric field. A light emitting diode based on this geometry has been demonstrated
Hierarchical Network Data Analytics Framework for B5G Network Automation: Design and Implementation
5G introduced modularized network functions (NFs) to support emerging
services in a more flexible and elastic manner. To mitigate the complexity in
such modularized NF management, automated network operation and management are
indispensable, and thus the 3rd generation partnership project (3GPP) has
introduced a network data analytics function (NWDAF). However, a conventional
NWDAF needs to conduct both inference and training tasks, and thus it is
difficult to provide the analytics results to NFs in a timely manner for an
increased number of analytics requests. In this article, we propose a
hierarchical network data analytics framework (H-NDAF) where inference tasks
are distributed to multiple leaf NWDAFs and training tasks are conducted at the
root NWDAF. Extensive simulation results using open-source software (i.e.,
free5GC) demonstrate that H-NDAF can provide sufficiently accurate analytics
and faster analytics provision time compared to the conventional NWDAF.Comment: 7 page
J/psi Production and Absorption in High Energy Proton-Nucleus Collisions
Measured J/Psi production cross sections for 200 and 450 GeV/c protons
incident on a variety of nuclear targets are analyzed within a Glauber
framework which takes into account energy loss of the beam proton, the time
delay of particle production due to quantum coherence, and absorption of the
J/Psi on nucleons. The best representation is obtained for a coherence time of
0.5 fm/c, previously determined by Drell-Yan production in proton-nucleus
collisions, and an absorption cross section of 3.6 mb, which is consistent with
the value deduced from photoproduction of the J/Psi on nuclear targets.Comment: LaTeX2e, 7 pages, 4 PS figures. Typos removed, minor change
Quantifying Baryon Stopping in High Energy Nuclear Collisions
We propose a numerical definition for baryon stopping in relativistic heavy
ion collisions that is obtainable from final hadron rapidity distributions as
well as from bremsstrahlung measurements. Thus a new channel of communication
is opened between the two methods.Comment: latex 9 pages, 2 embedded PS figure
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