581 research outputs found
Electron Spectroscopy for Chemical Analysis (ESCA) study of atmospheric particles
The results of analyses by ESCA (Electron Spectroscopy for Chemical Analysis) on several Nuclepore filters which were exposed during air pollution studies are presented along with correlative measurements by Neutron Activation Analysis and Scanning Electron Microscopy. Samples were exposed during air pollution studies at Norfolk, Virginia and the NASA Kennedy Space Center (KSC). It was demonstrated that with the ESCA technique it was possible to identify the chemical (bonding) state of elements contained in the atmospheric particulate matter collected on Nuclepore filters. Sulfur, nitrogen, mercury, chlorine, alkali, and alkaline earth metal species were identified in the Norfolk samples. ESCA binding energy data for aluminum indicated that three chemically different types of aluminum are present in the launch and background samples from NASA-KSC
Superoxide Signaling in Perivascular Adipose Tissue Promotes Age-Related Artery Stiffness
We tested the hypothesis that superoxide signaling within aortic perivascular adipose tissue (PVAT) contributes to large elastic artery stiffening in old mice. Young (4-6 months), old (26-28 months), and old treated with 4-Hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL), a superoxide scavenger (1 mm in drinking water for 3 weeks), male C57BL6/N mice were studied. Compared with young, old had greater large artery stiffness assessed by aortic pulse wave velocity (aPWV, 436 ± 9 vs. 344 ± 5 cm s(-1)) and intrinsic mechanical testing (3821 ± 427 vs. 1925 ± 271 kPa) (both P \u3c 0.05). TEMPOL treatment in old reversed both measures of arterial stiffness. Aortic PVAT superoxide production was greater in old (P \u3c 0.05 vs. Y), which was normalized with TEMPOL. Compared with young, old controls had greater pro-inflammatory proteins in PVAT-conditioned media (P \u3c 0.05). Young recipient mice transplanted with PVAT from old compared with young donors for 8 weeks had greater aPWV (409 ± 7 vs. 342 ± 8 cm s(-1)) and intrinsic mechanical properties (3197 ± 647 vs. 1889 ± 520 kPa) (both P \u3c 0.05), which was abolished with TEMPOL supplementation in old donors. Tissue-cultured aortic segments from old in the presence of PVAT had greater mechanical stiffening compared with old cultured in the absence of PVAT and old with PVAT and TEMPOL (both, P \u3c 0.05). In addition, PVAT-derived superoxide was associated with arterial wall hypertrophy and greater adventitial collagen I expression with aging that was attenuated by TEMPOL. Aging or TEMPOL treatment did not affect blood pressure. Our findings provide evidence for greater age-related superoxide production and pro-inflammatory proteins in PVAT, and directly link superoxide signaling in PVAT to large elastic artery stiffness
Charged-Particle Pseudorapidity Distributions in Au+Au Collisions at sqrt(s_NN)=62.4 GeV
The charged-particle pseudorapidity density for Au+Au collisions at
sqrt(s_NN)=62.4 GeV has been measured over a wide range of impact parameters
and compared to results obtained at other energies. As a function of collision
energy, the pseudorapidity distribution grows systematically both in height and
width. The mid-rapidity density is found to grow approximately logarithmically
between AGS energies and the top RHIC energy. As a function of centrality,
there is an approximate factorization of the centrality dependence of the
mid-rapidity yields and the overall multiplicity scale. The new results at
sqrt(s_NN)=62.4 GeV confirm the previously observed phenomenon of ``extended
longitudinal scaling'' in the pseudorapidity distributions when viewed in the
rest frame of one of the colliding nuclei. It is also found that the evolution
of the shape of the distribution with centrality is energy independent, when
viewed in this reference frame. As a function of centrality, the total charged
particle multiplicity scales linearly with the number of participant pairs as
it was observed at other energies.Comment: 6 pages, 7 figures, submitted to Phys. Rev. C - Rapid Communication
System Size, Energy, Pseudorapidity, and Centrality Dependence of Elliptic Flow
This paper presents measurements of the elliptic flow of charged particles as
a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and
200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider
(RHIC). The elliptic flow in Cu-Cu collisions is found to be significant even
for the most central events. For comparison with the Au-Au results, it is found
that the detailed way in which the collision geometry (eccentricity) is
estimated is of critical importance when scaling out system-size effects. A new
form of eccentricity, called the participant eccentricity, is introduced which
yields a scaled elliptic flow in the Cu-Cu system that has the same relative
magnitude and qualitative features as that in the Au-Au system
Event-by-event fluctuations of azimuthal particle anisotropy in Au+Au collisions at sqrt(s_NN) = 200 GeV
This paper presents the first measurement of event-by-event fluctuations of
the elliptic flow parameter v_2 in Au+Au collisions at sqrt(s_NN) = 200GeV as a
function of collision centrality. The relative non-statistical fluctuations of
the v_2 parameter are found to be approximately 40%. The results, including
contributions from event-by-event elliptic flow fluctuations and from azimuthal
correlations that are unrelated to the reaction plane (non-flow correlations),
establish an upper limit on the magnitude of underlying elliptic flow
fluctuations. This limit is consistent with predictions based on spatial
fluctuations of the participating nucleons in the initial nuclear overlap
region. These results provide important constraints on models of the initial
state and hydrodynamic evolution of relativistic heavy ion collisions.Comment: 5 pages, 2 figures, Published in Phys. Rev. Lett
Latest Results from PHOBOS
This manuscript contains a summary of the latest physics results from PHOBOS,
as reported at Quark Matter 2006. Highlights include the first measurement from
PHOBOS of dynamical elliptic flow fluctuations as well as an explanation of
their possible origin, two-particle correlations, identified particle ratios,
identified particle spectra and the latest results in global charged particle
production.Comment: 9 pages, 7 figures, PHOBOS plenary proceedings for Quark Matter 200
System size, energy, centrality and pseudorapidity dependence of charged-particle density in Au+Au and Cu+Cu collisions at RHIC
Charged particle pseudorapidity distributions are presented from the PHOBOS
experiment at RHIC, measured in Au+Au and Cu+Cu collisions at sqrt{s_NN}=19.6,
22.4, 62.4, 130 and 200 GeV, as a function of collision centrality. The
presentation includes the recently analyzed Cu+Cu data at 22.4 GeV. The
measurements were made by the same detector setup over a broad range in
pseudorapidity, |eta|<5.4, allowing for a reliable systematic study of particle
production as a function of energy, centrality and system size. Comparing Cu+Cu
and Au+Au results, we find that the total number of produced charged particles
and the overall shape (height and width) of the pseudorapidity distributions
are determined by the number of nucleon participants, N_part. Detailed
comparisons reveal that the matching of the shape of the Cu+Cu and Au+Au
pseudorapidity distributions over the full range of eta is better for the same
N_part/2A value than for the same N_part value, where A denotes the mass
number. In other words, it is the geometry of the nuclear overlap zone, rather
than just the number of nucleon participants that drives the detailed shape of
the pseudorapidity distribution and its centrality dependence.Comment: 5 pages, 4 figures. Presented at the 20th International Conference on
Nucleus-Nucleus Collisions (Quark Matter 2008), Jaipur, Rajasthan, India,
4-10 February 200
Non-flow correlations and elliptic flow fluctuations in gold-gold collisions at sqrt(s_NN)= 200 GeV
This paper presents results on event-by-event elliptic flow fluctuations in
Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow
correlations has been subtracted. An analysis method is introduced to measure
non-flow correlations, relying on the assumption that non-flow correlations are
most prominent at short ranges (Delta eta < 2). Assuming that non-flow
correlations are of the order that is observed in p+p collisions for long range
correlations (Delta eta > 2), relative elliptic flow fluctuations of
approximately 30-40% are observed. These results are consistent with
predictions based on spatial fluctuations of the participating nucleons in the
initial nuclear overlap region. It is found that the long range non-flow
correlations in Au+Au collisions would have to be more than an order of
magnitude stronger compared to the p+p data to lead to the observed azimuthal
anisotropy fluctuations with no intrinsic elliptic flow fluctuations.Comment: 9 pages, 7 figures, Published in Phys. Rev.
Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at RHIC
This paper describes the measurement of the energy dependence of elliptic
flow for charged particles in Au+Au collisions using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of
19.6, 62.4, 130 and 200 GeV are shown over a wide range in
pseudorapidity. These results, when plotted as a function of
, scale with approximate linearity throughout ,
implying no sharp changes in the dynamics of particle production as a function
of pseudorapidity or increasing beam energy.Comment: 5 pages, 4 figure
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