197 research outputs found
On The Low Frequency Quasi Periodic Oscillations of X-ray Sources
Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations
(kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries
(LMXBs) to the Keplerian and the periastron precession frequencies at the
magnetosphere-disk of X-ray neutron star (NS) respectively, we ascribe the low
frequency Quasi Periodic Oscillations (LFQPO) and HBO (15-60 Hz QPO for Z
sources or Atoll sources) to the periastron precession at some outer disk
radius.
The obtained conclusions include: all QPO frequencies increase with
increasing the accretion rate. The obtained theoretical relations between HBO
(LFQPO) frequency and the kHz QPO frequency are similar to the measured
empirical formula. Further, the possible dynamical mechanism for QPO production
is discussed.Comment: 6 pages, 2 figures, accepted by APSS, 200
Intraâclinothem variability in sedimentary texture and process regime recorded down slope profiles
Shelfâmargin clinothem successions can archive process interactions at the shelf to slope transition, and their architecture provides constraints on the interplay of factors that control basinâmargin evolution. However, detailed textural analysis and facies distributions from shelf to slope transitions remain poorly documented. This study uses quantitative grainâsize and sorting data from coeval shelf and slope deposits of a single clinothem that crops out along a 5 km long, dipâparallel transect of the Eocene Sobrarbe Deltaic Complex (Ainsa Basin, southâcentral Pyrenees, Spain). Systematic sampling of sandstone beds tied to measured sections has captured vertical and basinward changes in sedimentary texture and facies distributions at an intraâclinothem scale. Two types of hyperpycnal flowârelated slope deposits, both rich in mica and terrestrial organic matter, are differentiated according to grain size, sorting and bed geometry: (i) sustained hyperpycnal flow deposits, which are physically linked to coarse channelized sediments in the shelf setting and which deposit sand down the complete slope profile; (ii) episodic hyperpycnal flow deposits, which are disconnected from, and incise into, shelf sands and which are associated with sediment bypass of the proximal slope and coarseâgrained sand deposition on the medial and distal slope. Both types of hyperpycnites are interbedded with relatively homogenous, organicâfree and micaâfree, wellâsorted, very fineâgrained sandstones, which are interpreted to be remobilized from waveâdominated shelf environments; these waveâdominated deposits are found only on the proximal and medial slope. Coarseâgrained sediment bypass into the deeperâwater slope settings is therefore dominated by episodic hyperpycnal flows, whilst sustained hyperpycnal flows and turbidity currents remobilizing waveâdominated shelf deposits are responsible for the full range of grain sizes in the proximal and medial slope, thus facilitating clinoform progradation. This novel dataset highlights previously undocumented intraâclinothem variability related to updip changes in the shelf processâregime, which is therefore a key factor controlling downdip architecture and resulting sedimentary texture
Incised valley paleoenvironments interpreted by seismic stratigraphic approach in Patos Lagoon, Southern Brazil
<div><p>ABSTRACT: The Rio Grande do Sul (RS) coastal plain area (33,000 km 2 ) had its physiography modified several times through the Quaternary, responding to allogenic and autogenic forcings. The Patos Lagoon covers a significant area of RS coastal plain (10,000 km 2 ), where incised valleys were identified in previous works. About 1,000 km of high resolution (3.5 kHz) seismic profiles, radiocarbon datings, Standard Penetration Test (SPT) and gravity cores were analyzed to interpret the paleoenvironmental evolution as preserved in incised valley infills. Seismic facies were recognized by seismic parameters. The sediment cores were used to ground-truth the seismic interpretations and help in the paleoenvironmental identification. Key surfaces were established to detail the stratigraphical framework, and seismic facies were grouped into four seismic units, which one classified in respective system tracts within three depositional sequences. The oldest preserved deposits are predominantly fluvial and estuarine facies, representing the falling stage and lowstand system tracts. The Holocene transgressive records are dominated by muddy material, mainly represented by estuarine facies with local variations. The transgression culminated in Late Holocene deposits of Patos Lagoon, representing the highstand system tract. The depositional pattern of the vertical succession was controlled by eustatic variations, while the autogenic forcing (paleogeography and sediment supply) modulated the local facies variation.</p></div
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Gravitational Radiation Theory and Light Propagation
The paper gives an introduction to the gravitational radiation theory of isolated sources and to the propagation properties of light rays in radiative gravitational fields. It presents a theoretical study of the generation, propagation, back-reaction, and detection of gravitational waves from astrophysical sources. After reviewing the various quadrupole-moment laws for gravitational radiation in the Newtonian approximation, we show how to incorporate post-Newtonian corrections into the source multipole moments, the radiative multipole moments at infinity, and the back-reaction potentials. We further treat the light propagation in the linearized gravitational field outside a gravitational wave emitting source. The effects of time delay, bending of light, and moving source frequency shift are presented in terms of the gravitational lens potential. Time delay results are applied in the description of the procedure of the detection of gravitational waves
Measurement of the CP-Violating Asymmetry Amplitude sin2
We present results on time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 88 million Y(4S) --> B Bbar decays collected between 1999 and 2002 with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We study events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B0 or B0bar from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay-time distributions in such events. We measure sin2beta = 0.741 +/- 0.067 (stat) +/- 0.033 (syst) and |lambda| = 0.948 +/- 0.051 (stat) +/- 0.017 (syst). The magnitude of lambda is consistent with unity, in agreement with the Standard Model expectation of no direct CP violation in these modes
A search for the decay
We search for the rare flavor-changing neutral-current decay in a data sample of 82 fb collected with the {\sl BABAR}
detector at the PEP-II B-factory. Signal events are selected by examining the
properties of the system recoiling against either a reconstructed hadronic or
semileptonic charged-B decay. Using these two independent samples we obtain a
combined limit of
at the 90% confidence level. In addition, by selecting for pions rather than
kaons, we obtain a limit of using only the hadronic B reconstruction method.Comment: 7 pages, 8 postscript figures, submitted to Phys. Rev. Let
High-reflectivity broadband distributed Bragg reflector lattice matched to ZnTe
We report on the realization of a high quality distributed Bragg reflector
with both high and low refractive index layers lattice matched to ZnTe. Our
structure is grown by molecular beam epitaxy and is based on binary compounds
only. The high refractive index layer is made of ZnTe, while the low index
material is made of a short period triple superlattice containing MgSe, MgTe,
and ZnTe. The high refractive index step of Delta_n=0.5 in the structure
results in a broad stopband and the reflectivity coefficient exceeding 99% for
only 15 Bragg pairs.Comment: 4 pages, 3 figure
EuFeAs under high pressure: an antiferromagnetic bulk superconductor
We report the ac magnetic susceptibility and resistivity
measurements of EuFeAs under high pressure . By observing nearly
100% superconducting shielding and zero resistivity at = 28 kbar, we
establish that -induced superconductivity occurs at ~30 K in
EuFeAs. shows an anomalous nearly linear temperature dependence
from room temperature down to at the same . indicates that
an antiferromagnetic order of Eu moments with ~20 K persists
in the superconducting phase. The temperature dependence of the upper critical
field is also determined.Comment: To appear in J. Phys. Soc. Jpn., Vol. 78 No.
Measurement of the electron energy spectrum and its moments in inclusive B -> Xe nu decays
We report a measurement of the inclusive electron energy spectrum for semileptonic decays of B mesons in a data sample of 52 million Y(4S)-->B(B) over bar decays collected with the BABAR detector at the PEP-II asymmetric-energy B-meson factory at SLAC. We determine the branching fraction, first, second, and third moments of the spectrum for lower cutoffs on the electron energy between 0.6 and 1.5 GeV. We measure the partial branching fraction to be B(B-->Xenu,E-e>0.6 GeV)=[10.36+/-0.06(stat.)+/-0.23(sys.)]%
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