4,327 research outputs found
Analysis of reaction dynamics at RHIC in a combined parton/hadron transport approach
We introduce a transport approach which combines partonic and hadronic
degrees of freedom on an equal footing and discuss the resulting reaction
dynamics. The initial parton dynamics is modeled in the framework of the parton
cascade model, hadronization is performed via a cluster hadronization model and
configuration space coalescence, and the hadronic phase is described by a
microscopic hadronic transport approach. The resulting reaction dynamics
indicates a strong influence of hadronic rescattering on the space-time pattern
of hadronic freeze-out and on the shape of transverse mass spectra. Freeze-out
times and transverse radii increase by factors of 2 - 3 depending on the hadron
species.Comment: 10 pages, 4 eps figures include
What Does an Exemplary Middle School Mathematics Teacher Look Like? The Use of a Professional Development Rubric
A School University Research Network (SURN) committee composed of current mathematics teachers, central office math supervisors, building administrators, mathematicians, and mathematics educators researched numerous sources regarding best practices in mathematics instruction. The resulting professional development rubric synthesizes their findings and can serve a professional development role by providing teachers and administrators with a tool to develop clarity and consensus on best mathematics instructional practices, and how these practices are implemented in the classroom. It is also being used as a tool for cooperating teachers in their supervision of student teachers and as a reflective method for self-evaluation
Chiral Behaviour of the Rho Meson in Lattice QCD
In order to guide the extrapolation of the mass of the rho meson calculated
in lattice QCD with dynamical fermions, we study the contributions to its
self-energy which vary most rapidly as the quark mass approaches zero; from the
processes and . It turns out that in
analysing the most recent data from CP-PACS it is crucial to estimate the
self-energy from using the same grid of discrete momenta as
included implicitly in the lattice simulation. The correction associated with
the continuum, infinite volume limit can then be found by calculating the
corresponding integrals exactly. Our error analysis suggests that a factor of
10 improvement in statistics at the lowest quark mass for which data currently
exists would allow one to determine the physical rho mass to within 5%.
Finally, our analysis throws new light on a long-standing problem with the
J-parameter.Comment: 13 pages, 7 figures. Full analytic forms of the self-energies are
included and a correction in the omega-pi self-energ
Unpolarized structure functions at Jefferson Lab
Over the past decade measurements of unpolarized structure functions at
Jefferson Lab with unprecedented precision have significantly advanced our
knowledge of nucleon structure. These have for the first time allowed
quantitative tests of the phenomenon of quark-hadron duality, and provided a
deeper understanding of the transition from hadron to quark degrees of freedom
in inclusive scattering. Dedicated Rosenbluth-separation experiments have
yielded high-precision transverse and longitudinal structure functions in
regions previously unexplored, and new techniques have enabled the first
glimpses of the structure of the free neutron, without contamination from
nuclear effects.Comment: 21 pages, 9 figures; typo in Eq. (3) corrected, references added; to
appear in J. Phys. Conf. Proc. "New Insights into the Structure of Matter:
The First Decade of Science at Jefferson Lab", eds. D. Higinbotham, W.
Melnitchouk, A. Thoma
Non-equilibrium dynamics in quantum field theory at high density: the tsunami
The dynamics of a dense relativistic quantum fluid out of thermodynamic
equilibrium is studied in the framework of the Phi^4 scalar field theory in the
large N limit. The time evolution of a particle distribution in momentum space
(the tsunami) is computed. The effective mass felt by the particles in such a
high density medium equals the tree level mass plus the expectation value of
the squared field. The case of negative tree level squared mass is particularly
interesting. In such case dynamical symmetry restoration as well as dynamical
symmetry breaking can happen. Furthermore, the symmetry may stay broken with
vanishing asymptotic squared mass showing the presence of out of equilibrium
Goldstone bosons. We study these phenomena and identify the set of initial
conditions that lead to each case. We compute the equation of state which turns
to depend on the initial state. Although the system does not thermalize, the
equation of state for asymptotically broken symmetry is of radiation type. We
compute the correlation functions at equal times. The two point correlator for
late times is the sum of different terms. One stems from the initial particle
distribution. Another term accounts for the out of equilibrium Goldstone bosons
created by spinodal unstabilities when the symmetry is asymptotically
broken.Both terms are of the order of the inverse of the coupling for distances
where causal signals can connect the two points. The contribution of the out of
equilibrium Goldstones exhibits scaling behaviour in a generalized sense.Comment: LaTex, 49 pages, 15 .ps figure
Nonresonant Semileptonic Heavy Quark Decay
In both the large N_c limit and the valence quark model, semileptonic decays
are dominated by resonant final states. Using Bjorken's sum rule in an
"unquenched" version of the quark model, I demonstrate that in the heavy quark
limit nonresonant final states should also be produced at a significant rate.
By calculating the individual strengths of a large number of exclusive two-body
nonresonant channels, I show that the total rate for such processes is highly
fragmented. I also describe some very substantial duality-violating suppression
factors which reduce the inclusive nonresonant rate to a few percent of the
total semileptonic rate for the finite quark masses of B decay, and comment on
the importance of nonresonant decays as testing grounds for very basic ideas on
the structure, strength, and significance of the quark-antiquark sea and on
quark-hadron duality in QCD.Comment: 51 pages, 2 Postscript figure
Critique of a Pion Exchange Model for Interquark Forces
I describe four serious defects of a widely discussed pion exchange model for
interquark forces: it doesn't solve the "spin-orbit problem" as advertised, it
fails to describe the internal structure of baryon resonances, it leads to
disastrous conclusions when extended to mesons, and it is not reasonably
connected to the physics of heavy-light systems.Comment: 20 pages, 6 figures; some clarifications and references adde
Studies of parton thermalization at RHIC
We consider the evolution of a parton system which is formed in the central
region just after a relativistic heavy ion collision. The parton consist of
mostly gluons, minijets, which are produced by elastic scattering between
constituent partons of the colliding nuclei. We assume the system can be
described by a semi-classical Boltzmann transport equation, which we solve by
means of the test particle Monte-Carlo method including retardation. The
partons proliferate via secondary radiative processes until the
thermalization is reached for some assumptions. The extended system is
thermalized at about fm/ with MeV and stays in equilibrium
for about 2 fm/ with breaking temperature MeV in the rapidity
central region.Comment: 14 page
Insulin Receptor Substrate 2 Expression and Involvement in Neuronal Insulin Resistance in Diabetic Neuropathy
Insulin signaling depends on tyrosine phosphorylation of insulin receptor substrates (IRSs) to mediate downstream effects; however, elevated serine phosphorylation of IRS impairs insulin signaling. Here, we investigated IRS protein expression patterns in dorsal root ganglia (DRG) of mice and whether their signaling was affected by diabetes. Both IRS1 and IRS2 are expressed in DRG; however, IRS2 appears to be the prevalent isoform and is expressed by many DRG neuronal subtypes. Phosphorylation of Ser(731)IRS2 was significantly elevated in DRG neurons from type 1 and type 2 diabetic mice. Additionally, Akt activation and neurite outgrowth in response to insulin were significantly decreased in DRG cultures from diabetic ob/ob mice. These results suggest that DRG neurons express IRS proteins that are altered by diabetes similar to other peripheral tissues, and insulin signaling downstream of the insulin receptor may be impaired in sensory neurons and contribute to the pathogenesis of diabetic neuropathy
Gluon Radiation and Coherent States in Ultrarelativistic Nuclear Collisions
We explore the correspondence between classical gluon radiation and quantum
radiation in a coherent state for gluons produced in ultrarelativistic nuclear
collisions. The expectation value of the invariant momentum distribution of
gluons in the coherent state is found to agree with the gluon number
distribution obtained classically from the solution of the Yang-Mills
equations. A criterion for the applicability of the coherent state formalism to
the problem of radiation in ultrarelativistic nucleus-nucleus collisions is
discussed. This criterion is found to be fulfilled for midrapidity gluons with
perturbative transverse momenta larger than about 1-2 GeV and produced in
collisions between valence partons.Comment: 15 pages, 6 figures, RevTeX (with epsf, psfig style files
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