21,047 research outputs found
Rare Earth Abundances in Meteoritic Chondrules
Rare earth elements abundance in meteoritic chondrites determined by radiochemical neutron activation analysi
The Spectral Energy Distribution of Normal, Starburst and Active Galaxies
We present the results of an extensive literature search of multiwavelength
data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2's,
5 LINER's, 6 normal spirals and 7 normal elliptical galaxies. The data include
soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared
photometry and radio measurements, selected to match as closely as possible the
IUE aperture (10" X 20"). The galaxies are separated into 6 groups with similar
characteristics, namely, Ellipticals, Spirals, LINER's, Seyfert 2's, Starbursts
of Low and High reddening, for which we create average spectral energy
distributions (SED). The individual groups SED's are normalized to the
7000\AA flux and compared, looking for similarities and differences
among them.The bolometric fluxes of different types of galaxies were calculated
integrating their SED's. These values are compared with individual waveband
flux densities, in order to determine the wavebands which contribute most to
the bolometric flux. Linear regressions were performed between the bolometric
and individual band fluxes for each kind of galaxy. These fits can be used in
the calculation of the bolometric flux for other objects of similar activity
type, but with reduced waveband information. We have also collected
multiwavelength data for 4 HII regions, a thermal supernova remnant, and a
non-thermal supernova remnant (SNR), which are compared with the Starburst
SED's.Comment: 29 pages, 13 postscript figures and 10 tables. To appear in The
Astronomical Journa
Non-equilibrium structural phase transitions of the vortex lattice in MgB2
We have studied non-equilibrium phase transitions in the vortex lattice in
superconducting MgB2, where metastable states are observed in connection with
an intrinsically continuous rotation transition. Using small-angle neutron
scattering and a stop-motion technique, we investigated the manner in which the
metastable vortex lattice returns to the equilibrium state under the influence
of an ac magnetic field. This shows a qualitative difference between the
supercooled case which undergoes a discontinuous transition, and the
superheated case where the transition to the equilibrium state is continuous.
In both cases the transition may be described by an an activated process, with
an activation barrier that increases as the metastable state is suppressed, as
previously reported for the supercooled vortex lattice [E. R. Louden et al.,
Phys. Rev. B 99, 060502(R) (2019)]. Separate preparations of superheated
metastable vortex lattices with different domain populations showed an
identical transition towards the equilibrium state. This provides further
evidence that the vortex lattice metastability, and the kinetics associated
with the transition to the equilibrium state, is governed by nucleation and
growth of domains and the associated domain boundaries.Comment: 27 pages, 10 figures. arXiv admin note: text overlap with
arXiv:1812.0597
Characterization of a two-transmon processor with individual single-shot qubit readout
We report the characterization of a two-qubit processor implemented with two
capacitively coupled tunable superconducting qubits of the transmon type, each
qubit having its own non-destructive single-shot readout. The fixed capacitive
coupling yields the \sqrt{iSWAP} two-qubit gate for a suitable interaction
time. We reconstruct by state tomography the coherent dynamics of the two-bit
register as a function of the interaction time, observe a violation of the Bell
inequality by 22 standard deviations after correcting readout errors, and
measure by quantum process tomography a gate fidelity of 90%
Structural Transition Kinetics and Activated Behavior in the Superconducting Vortex Lattice
Using small-angle neutron scattering, we investigated the behavior of a
metastable vortex lattice state in MgB2 as it is driven towards equilibrium by
an AC magnetic field. This shows an activated behavior, where the AC field
amplitude and cycle count are equivalent to, respectively, an effective
"temperature" and "time". The activation barrier increases as the metastable
state is suppressed, corresponding to an aging of the vortex lattice.
Furthermore, we find a cross-over from a partial to a complete suppression of
metastable domains depending on the AC field amplitude, which may empirically
be described by a single free parameter. This represents a novel kind of
collective vortex behavior, most likely governed by the nucleation and growth
of equilibrium vortex lattice domains.Comment: 5 pages plus 3 pages of supplemental materia
Stellar population gradients in Seyfert 2 galaxies. Northern sample
We use high signal-to-noise ratio long-slit spectra in the 3600-4700A range
of the twenty brightest northern Seyfert 2 galaxies to study the variation of
the stellar population properties as a function of distance from the nucleus.
In order to characterize the stellar population and other continuum sources
(e.g. featureless continuum FC) we have measured equivalent widths Ws of six
absorption features, four continuum colours and their radial variations, and
performed spectral population synthesis as a function of distance from the
nucleus. About half the sample has CaIIK and G-band W values smaller at the
nucleus than at 1 kpc from it, due to a younger population and/or FC. The
stellar population synthesis shows that, while at the nucleus, 75% of the
galaxies present contribution > 20% of ages younger or equal than 100Myr and/or
of a FC, this proportion decreases to 45% at 3 kpc. In particular, 55% of the
galaxies have contribution > 10% of the 3 Myr/FC component (a degenerate
component in which one cannot separate what is due to a FC or to a 3 Myr
stellar population) at the nucleus, but only 25% of them have this contribution
at 3 kpc. As reference, the stellar population of 10 non-Seyfert galaxies,
spanning the Hubble types of the Seyfert (from S0 to Sc) was also studied. A
comparison between the stellar population of the Seyferts and that of the
non-Seyferts shows systematic differences: the contribution of ages younger
than 1 Gyr is in most cases larger in the Seyfert galaxies than in
non-Seyferts, not only at the nucleus but up to 1 kpc from it.Comment: 23 pages, 18 figures, MNRAS in pres
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