8,233 research outputs found
Craton-scale variations in crustal evolution: new insights from Scottish Highland detrital zircon
Saddle-point van Hove singularity and the phase diagram of high-Tc cuprates
We examine the generic phase behavior of high-Tc cuprate superconductors in
terms a universal van Hove singularity in the strongly overdoped region. Using
a rigid ARPES-derived dispersion we solve the BCS gap equation and show that
the pairing interaction or pairing energy cutoff must be a rapidly declining
function of doping. This result is prejudicial to a phonon-based pairing
interaction and more consistent with a magnetic or magnetically enhanced
interaction.Comment: 5 pages, 2 figures, submitted to Physical Review
Observations of far-infrared fine structure lines: o III88.35 micrometer and oI 63.2 micrometer
Observations of the O III 88.35 micrometer line and the O I63.2 micrometer were made with a far infrared spectrometer. The sources M17, NGC 7538, and W51 were mapped in the O III line with 1 arc minute resolution and the emission is found to be quite widespread. In all cases the peak of the emission coincides with the maximum radio continuum. The far infrared continuum was mapped simultaneously and in M17, NGC 7538, and W51 the continuum peak is found to be distinct from the center of ionization. The O III line was also detected in W3, W49, and in a number of positions in the Orion nebula. Upper limits were obtained on NGS 7027, NGC 6572, DR21, G29.9-0.0 and M82. The 63.2 micrometer O I line was detected in M17, M42, and marginally in DR21. A partial map of M42 in this line shows that most of the emission observed arises from the Trapezium and from the bright optical bar to the southeast
Rip/singularity free cosmology models with bulk viscosity
In this paper we present two concrete models of non-perfect fluid with bulk
viscosity to interpret the observed cosmic accelerating expansion phenomena,
avoiding the introduction of exotic dark energy. The first model we inspect has
a viscosity of the form by
taking into account of the decelerating parameter q, and the other model is of
the form . We give out the
exact solutions of such models and further constrain them with the latest
Union2 data as well as the currently observed Hubble-parameter dataset (OHD),
then we discuss the fate of universe evolution in these models, which confronts
neither future singularity nor little/pseudo rip. From the resulting curves by
best fittings we find a much more flexible evolution processing due to the
presence of viscosity while being consistent with the observational data in the
region of data fitting. With the bulk viscosity considered, a more realistic
universe scenario is characterized comparable with the {\Lambda}CDM model but
without introducing the mysterious dark energy.Comment: 9 pages, 6 figures, submitted to EPJ-
Pulse Profiles, Accretion Column Dips and a Flare in GX 1+4 During a Faint State
The Rossi X-ray Timing Explorer (RXTE) spacecraft observed the X-ray pulsar
GX 1+4 for a period of 34 hours on July 19/20 1996. The source faded from an
intensity of ~20 mCrab to a minimum of <~0.7 mCrab and then partially recovered
towards the end of the observation. This extended minimum lasted ~40,000
seconds. Phase folded light curves at a barycentric rotation period of
124.36568 +/- 0.00020 seconds show that near the center of the extended minimum
the source stopped pulsing in the traditional sense but retained a weak dip
feature at the rotation period. Away from the extended minimum the dips are
progressively narrower at higher energies and may be interpreted as
obscurations or eclipses of the hot spot by the accretion column. The pulse
profile changed from leading-edge bright before the extended minimum to
trailing-edge bright after it. Data from the Burst and Transient Source
Experiment (BATSE) show that a torque reversal occurred <10 days after our
observation. Our data indicate that the observed rotation departs from a
constant period with a Pdot/P value of ~-1.5% per year at a 4.5 sigma
significance. We infer that we may have serendipitously obtained data, with
high sensitivity and temporal resolution about the time of an accretion disk
spin reversal. We also observed a rapid flare which had some precursor
activity, close to the center of the extended minimum.Comment: 19 pages, 6 figures, accepted for publication in Astrophysical
Journal (tentatively scheduled for vol. 529 #1, 20 Jan 2000
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