4,951 research outputs found
On positivity and roots in operator algebras
In earlier papers the second author and Charles Read have introduced and
studied a new notion of positivity for operator algebras, with an eye to
extending certain C*-algebraic results and theories to more general algebras.
The present paper consists of complements to some facts in the just mentioned
papers, concerning this notion of positivity. For example we prove a result on
the numerical range of products of the roots of commuting operators with
numerical range in a sector.Comment: 11 pages, to appear Integral Equations Operator Theor
Charge Particle Multiplicity and Transverse Energy Measurements in Au-Au collisions in PHENIX at RHIC
We present results on charged particle and transverse energy densities
measured at mid-rapidity in Au-Au collisions at sqrt(s_{NN})=200 GeV. The mean
transverse energy per charged particle is derived. The results are presented as
a function of centrality, which is defined by the number of participating
nucleons, and compared to results obtained in Au-Au collisions at
sqrt{s_{NN})=130 GeV. A comparison with calculations from various theoretical
models is performed.Comment: 4 pages, 5 figures. Talk presented at Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
Anomalous diffusion in non-equilibrium relativistic heavy-ion rapidity spectra
There is experimental and theoretical evidence that the broad rapidity
distribution of net proton yield in central heavy-ion collisions at SPS
energies could be a signal of non-equilibrium properties of the system. We show
that the broad rapidity shape can be well reproduced in the framework of a
non-linear relativistic Fokker-Planck dynamics which incorporates non-extensive
statistics and anomalous diffusion.Comment: 4 pages, 1 figure, elsart style. To appear in Physica A (proceeding
of the conference NEXT2001).
Disrupted working memory circuitry and psychotic symptoms in 22q11.2 deletion syndrome.
22q11.2 deletion syndrome (22q11DS) is a recurrent genetic mutation that is highly penetrant for psychosis. Behavioral research suggests that 22q11DS patients exhibit a characteristic neurocognitive phenotype that includes differential impairment in spatial working memory (WM). Notably, spatial WM has also been proposed as an endophenotype for idiopathic psychotic disorder, yet little is known about the neurobiological substrates of WM in 22q11DS. In order to investigate the neural systems engaged during spatial WM in 22q11DS patients, we collected functional magnetic resonance imaging (fMRI) data while 41 participants (16 22q11DS patients, 25 demographically matched controls) performed a spatial capacity WM task that included manipulations of delay length and load level. Relative to controls, 22q11DS patients showed reduced neural activation during task performance in the intraparietal sulcus (IPS) and superior frontal sulcus (SFS). In addition, the typical increases in neural activity within spatial WM-relevant regions with greater memory load were not observed in 22q11DS. We further investigated whether neural dysfunction during WM was associated with behavioral WM performance, assessed via the University of Maryland letter-number sequencing (LNS) task, and positive psychotic symptoms, assessed via the Structured Interview for Prodromal Syndromes (SIPS), in 22q11DS patients. WM load activity within IPS and SFS was positively correlated with LNS task performance; moreover, WM load activity within IPS was inversely correlated with the severity of unusual thought content and delusional ideas, indicating that decreased recruitment of working memory-associated neural circuitry is associated with more severe positive symptoms. These results suggest that 22q11DS patients show reduced neural recruitment of brain regions critical for spatial WM function, which may be related to characteristic behavioral manifestations of the disorder
Increasing Doctoral Student Completion Rates Within the College of Humanities and Sciences at Virginia Commonwealth University
Research on doctoral education primarily focuses on broad fields of study and general attrition. Often overlooked, is an examination of the student at each stage of their program and the challenges they face that can potentially lead to stopping out. This capstone project explored the doctoral student experience within the Department of Humanities and Sciences at Virginia Commonwealth University. A mixed method study via an online survey was utilized to gather data about the student experience on their path towards candidacy. Quantitative and qualitative data was analyzed through Chi-square tests and thematic coding to identify answers to each research question. This paper aims to inform students, faculty, and administrators, of common attrition points on a doctoral student’s path to completion. In addition, this research aims to use the data to identify interventions that will support doctoral students in their journey and increase retention rates
(Anti)Proton and Pion Source Sizes and Phase Space Densities in Heavy Ion Collisions
NA44 has measured mid-rapidity deuteron spectra from AA collisions at
sqrt{s}=18GeV/A at the CERN SPS. Combining these spectra with published proton,
antiproton and antideuteron data allows us to calculate, within a coalescence
framework, proton and antiproton source sizes and phase space densities. These
results are compared to pion source sizes and densities, pA results and to
lower energy (AGS) data. The antiproton source is larger than the proton source
at sqrt{s}=18GeV/A. The phase space densities of pions and protons are not
constant but grow with system size. Both pi+ and proton radii decrease with
transverse mass and increase with sqrt{s}. Pions and protons do not freeze-out
independently. The nature of their interaction changes as sqrt{s}, and the
pion/proton ratio increases.Comment: 4 pages, Latex 2.09, 3 eps figures. Changes for January 2001. The
proton source size is now calculated assuming a more realistic Hulthen,
rather than Gaussian, wavefunction. A new figure shows the effect of this
change which is important for small radii. A second new figure shows the
results of RQMD calculations of the proton source size and phase density.
Because of correlations between position and momentum coalesence does not
show the full proton source size. The paper has been streamlined and
readability improve
The relationship between particle freeze-out distributions and HBT radius parameters
The relationship between pion and kaon space-time freeze-out distributions
and the HBT radius parameters in high-energy nucleus-nucleus collisions is
investigated. We show that the HBT radius parameters in general do not reflect
the R.M.S. deviations of the single particle production points. Instead, the
HBT radius parameters are most closely related to the curvature of the
two-particle space-time relative position distribution at the origin. We
support our arguments by studies with a dynamical model (RQMD 2.4).Comment: RevTex, 10 pages including 3 figures. v2: Discussion of the lambda
parameter has been added. PRC, in prin
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