10,811 research outputs found
A Search for Stars of Very Low Metal Abundance. V. Photoelectric UBV Photometry of Metal-Weak Candidates from the Northern HK Survey
We report photoelectric UBV data for 268 metal-poor candidates chosen from
the northern HK objective-prism/interference-filter survey of Beers and
colleagues. Over 40 % of the stars have been observed on more than one night,
and most have at least several sets of photometric measurements. Reddening
estimates, preliminary spectroscopic measurements of abundance, and type
classifications are reported.Comment: To Appear in the Astronomical Journal, October 200
Avalanches in a Bose-Einstein condensate
Collisional avalanches are identified to be responsible for an 8-fold
increase of the initial loss rate of a large 87-Rb condensate. We show that the
collisional opacity of an ultra-cold gas exhibits a critical value. When
exceeded, losses due to inelastic collisions are substantially enhanced. Under
these circumstances, reaching the hydrodynamic regime in conventional BEC
experiments is highly questionable.Comment: 4 pages, 2 figures, 1 tabl
Triggering up states in all-to-all coupled neurons
Slow-wave sleep in mammalians is characterized by a change of large-scale
cortical activity currently paraphrased as cortical Up/Down states. A recent
experiment demonstrated a bistable collective behaviour in ferret slices, with
the remarkable property that the Up states can be switched on and off with
pulses, or excitations, of same polarity; whereby the effect of the second
pulse significantly depends on the time interval between the pulses. Here we
present a simple time discrete model of a neural network that exhibits this
type of behaviour, as well as quantitatively reproduces the time-dependence
found in the experiments.Comment: epl Europhysics Letters, accepted (2010
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uvbyCa H beta CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
CCD photometry on the intermediate-band uvbyCa H beta system is presented for
the anticenter, intermediate-age open cluster, Melotte 71. Restricting the data
to probable single members of the cluster using the color-magnitude diagram and
the photometric indices alone generates a sample of 48 F dwarfs on the
unevolved main sequence. The average E(b-y) = 0.148 +/- 0.003 (s.e.m.) or
E(B-V) = 0.202 +/- 0.004 (s.e.m.), where the errors refer to internal errors
alone. With this reddening, [Fe/H] is derived from both m1 and hk, using H beta
and b-y as the temperature index, with excellent agreement among the four
approaches and a final weighted average of [Fe/H] = -0.17 +/- 0.02 (s.e.m.) for
the cluster, on a scale where the Hyades has [Fe/H] = +0.12. When adjusted for
the higher reddening estimate, the previous metallicity estimates from
Washington photometry and from spectroscopy are now in agreement with the
intermediate-band result. From comparisons to isochrones of appropriate
metallicity, the cluster age and distance are determined as 0.9 +/- 0.1 Gyr and
(m-M) = 12.2 +/- 0.1 or (m-M)_0 = 11.6 +/- 0.1. At this distance from the sun,
Mel 71 has a galactocentric distance of 10.0 kpc on a scale where the sun is
8.5 kpc from the galactic center. Based upon its age, distance, and elemental
abundances, Mel 71 appears to be a less populous analog to NGC 3960.Comment: Accepted for Astronomical Journal. 38 page latex file includes 11
figures and short version of data table. Full table will appear in online AJ
or may be requested from author
Atomic layer deposition of titanium nitride for quantum circuits
Superconducting thin films with high intrinsic kinetic inductance are of
great importance for photon detectors, achieving strong coupling in hybrid
systems, and protected qubits. We report on the performance of titanium nitride
resonators, patterned on thin films (9-110 nm) grown by atomic layer
deposition, with sheet inductances of up to 234 pH/square. For films thicker
than 14 nm, quality factors measured in the quantum regime range from 0.4 to
1.0 million and are likely limited by dielectric two-level systems.
Additionally, we show characteristic impedances up to 28 kOhm, with no
significant degradation of the internal quality factor as the impedance
increases. These high impedances correspond to an increased single photon
coupling strength of 24 times compared to a 50 Ohm resonator, transformative
for hybrid quantum systems and quantum sensing.Comment: 10 pages, 8 figures including supplemental material
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