414 research outputs found
P-wave tomography of the mantle beneath the South Pacific Superswell revealed by joint ocean floor and islands broadband seismic experiments
International audienceThree-dimensional P-wave velocity structure of the mantle beneath the South Pacific Superswell is determined through passive broadband seismic experiments on the ocean floor and islands between 2003 and 2005. We collected approximately 1500 relative times of long-period teleseismic P-waves by using a waveform cross-correlation. We analyzed this data set with relative time tomography to depths of 2000 km. The resultant structure shows lateral heterogeneity of approximately +/- 2%, in which a distinct low velocity region is found beneath the center of the Superswell at a depth of 1600 km. At 1200km depth, an elongated low velocity region is found beneath the Society to Pitcairn hotspots. At 800 km depth, two linear low velocity regions are located beneath Tuamotu and Austral islands. Isolated low velocity regions are identified beneath the Society, Marquesas, and Macdonald hotspots at 400 km depth. Our new tomographic images reveal that the large low velocity region rooted in the deep lower mantle is split into two sheets at 1200 km depth and these terminate at approximately 800 km depth. This feature appears to be consistent with the characteristics of a thermo-chemical pile or dome
Depth of the 660-km discontinuity near the Mariana slab from an array of ocean bottom seismographs,
[1] High frequency records of deep Mariana earthquakes from a dense array of ocean bottom seismographs deployed in the Mariana arc and back-arc regions are stacked and searched for the phases P660p and S660p to constrain the depth of the 660-km discontinuity near the Mariana slab. Results of the high-resolution study suggest that around 18°N the 660-km discontinuity lies at about 710-730 km (±14 km) depth within or in the vicinity of the slab core. In the region seismicity ceases at 100 km above the base of the transition zone. These findings and similar observations in Tonga argue that factors other than the phase transition at the base of the upper mantle may control the maximum down-dip extent of the deep seismogenic region in the slab
Net Charge Fluctuations in Au + Au Interactions at sqrt(s_NN) = 130 GeV
Data from Au + Au interactions at sqrt(s_NN) = 130 GeV, obtained with the
PHENIX detector at RHIC, are used to investigate local net charge fluctuations
among particles produced near mid-rapidity. According to recent suggestions,
such fluctuations may carry information from the Quark Gluon Plasma. This
analysis shows that the fluctuations are dominated by a stochastic distribution
of particles, but are also sensitive to other effects, like global charge
conservation and resonance decays.Comment: 6 pages, RevTeX 3, 3 figures, 307 authors, submitted to Phys. Rev.
Lett. on 21 March, 2002. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (will be made) publicly
available at http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
Flow Measurements via Two-particle Azimuthal Correlations in Au + Au Collisions at sqrt(s_NN) = 130 GeV
Two particle azimuthal correlation functions are presented for charged
hadrons produced in Au + Au collisions at RHIC sqrt(s_NN) = 130 GeV. The
measurements permit determination of elliptic flow without event-by-event
estimation of the reaction plane. The extracted elliptic flow values v_2 show
significant sensitivity to both the collision centrality and the transverse
momenta of emitted hadrons, suggesting rapid thermalization and relatively
strong velocity fields. When scaled by the eccentricity of the collision zone,
epsilon, the scaled elliptic flow shows little or no dependence on centrality
for charged hadrons with relatively low p_T. A breakdown of this epsilon
scaling is observed for charged hadrons with p_T > 1.0 GeV/c for the most
central collisions.Comment: 6 pages, RevTeX 3, 4 figures, 307 authors, submitted to Phys. Rev.
Lett. on 11 April 2002. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (will be made) publicly
available at http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
Centrality Dependence of Charged Particle Multiplicity in Au-Au Collisions at sqrt(s_NN)=130 GeV
We present results for the charged-particle multiplicity distribution at
mid-rapidity in Au - Au collisions at sqrt(s_NN)=130 GeV measured with the
PHENIX detector at RHIC. For the 5% most central collisions we find
. The results,
analyzed as a function of centrality, show a steady rise of the particle
density per participating nucleon with centrality.Comment: 307 authors, 43 institutions, 6 pages, 4 figures, 1 table Minor
changes to figure labels and text to meet PRL requirements. One author added:
M. Hibino of Waseda Universit
Measurement of the mid-rapidity transverse energy distribution from GeV Au+Au collisions at RHIC
The first measurement of energy produced transverse to the beam direction at
RHIC is presented. The mid-rapidity transverse energy density per participating
nucleon rises steadily with the number of participants, closely paralleling the
rise in charged-particle density, such that E_T / N_ch remains relatively
constant as a function of centrality. The energy density calculated via
Bjorken's prescription for the 2% most central Au+Au collisions at
sqrt(s_NN)=130 GeV is at least epsilon_Bj = 4.6 GeV/fm^3 which is a factor of
1.6 larger than found at sqrt(s_NN)=17.2 GeV (Pb+Pb at CERN).Comment: 307 authors, 6 pages, 4 figures, 1 table, submitted to PRL 4/18/2001;
revised version submitted to PRL 5/24/200
Centrality dependence of pi^[+/-], K^[+/-], p and p-bar production from sqrt(s_NN)=130 GeV Au + Au collisions at RHIC
Identified pi^[+/-] K^[+/-], p and p-bar transverse momentum spectra at
mid-rapidity in sqrt(s_NN)=130 GeV Au-Au collisions were measured by the PHENIX
experiment at RHIC as a function of collision centrality. Average transverse
momenta increase with the number of participating nucleons in a similar way for
all particle species. The multiplicity densities scale faster than the number
of participating nucleons. Kaon and nucleon yields per participant increase
faster than the pion yields. In central collisions at high transverse momenta
(p_T greater than 2 GeV/c), anti-proton and proton yields are comparable to the
pion yields.Comment: 6 pages, 3 figures, 1 table, 307 authors, accepted by Phys. Rev.
Lett. on 9 April 2002. This version has minor changes made in response to
referee Comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
Laser-chemical vapor deposition of W Schottky contacts on GaAs\ud using WF6 and SiH4
Reports on the deposition of tungsten on gallium arsenide (GaAs) using a low-temperature laser-chemical vapor deposition process. Induction of metallic W formation from a gas mixture; Columnar structure shown by scanning electron microscopy of the W films; Schottky diodes obtained during a laser based resistless projection patterning process on GaAs
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