1,612 research outputs found
A PVC Detection Program
journal articleBiomedical Informatic
An Analysis of Granulocyte Kinetics in Blood and Bone Marrow
journal articleBiomedical Informatic
High-Density Medical Data Management by Computer
journal articleBiomedical Informatic
The Dwarf Nova PQ Andromedae
We report a photometric study of the WZ Sagittae-type dwarf nova PQ
Andromedae. The light curve shows strong (0.05 mag full amplitude) signals with
periods of 1263(1) and 634(1) s, and a likely double-humped signal with
P=80.6(2) min. We interpret the first two as nonradial pulsation periods of the
underlying white dwarf, and the last as the orbital period of the underlying
binary. We estimate a distance of 150(50) pc from proper motions and the two
standard candles available: the white dwarf and the dwarf-nova outburst. At
this distance, the K magnitude implies that the secondary is probably fainter
than any star on the main sequence -- indicating a mass below the Kumar limit
at 0.075 M_sol. PQ And may be another "period bouncer", where evolution now
drives the binary out to longer period.Comment: PDF, 13 pages, 2 figures; accepted, in press, to appear September
2005, PASP; more info at http://cba.phys.columbia.edu
Spectroscopy of Seven Cataclysmic Variables with Periods Above Five Hours
We present spectroscopy of seven cataclysmic variable stars with orbital
periods P(orb) greater than 5 hours, all but one of which are known to be dwarf
novae. Using radial velocity measurements we improve on previous orbital period
determinations, or derive periods for the first time. The stars and their
periods are
TT Crt, 0.2683522(5) d;
EZ Del, 0.2234(5) d;
LL Lyr, 0.249069(4) d;
UY Pup, 0.479269(7) d;
RY Ser, 0.3009(4) d;
CH UMa, 0.3431843(6) d; and
SDSS J081321+452809, 0.2890(4) d.
For each of the systems we detect the spectrum of the secondary star,
estimate its spectral type, and derive a distance based on the surface
brightness and Roche lobe constraints. In five systems we also measure the
radial velocity curve of the secondary star, estimate orbital inclinations, and
where possible estimate distances based on the MV(max) vs.P(orb) relation found
by Warner. In concordance with previous studies, we find that all the secondary
stars have, to varying degrees, cooler spectral types than would be expected if
they were on the main sequence at the measured orbital period.Comment: 25 pages, 2 figures, accepted for Publications of the Astronomical
Society of the Pacifi
Sediment transport due to extreme events : the Hudson River estuary after tropical storms Irene and Lee
Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 5451–5455, doi:10.1002/2013GL057906.Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 megaton, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that approximately two thirds of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms and only about one fifth of the new sediment reached the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest that this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.This research was supported by grants from
the Hudson Research Foundation (002/07A) and the National Science
Foundation (1232928).2014-04-1
Flow convergence caused by a salinity minimum in a tidal channel
© 2006 The Author et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The definitive version was published in San Francisco Estuary and Watershed Science 4 (2006): Issue 3, Article 1.Residence times of dissolved substances and sedimentation rates in tidal channels are affected by residual (tidally averaged) circulation patterns. One influence on these circulation patterns is the longitudinal density gradient. In most estuaries the longitudinal density gradient typically maintains a constant direction. However, a junction of tidal channels can create a local reversal (change in sign) of the density gradient. This can occur due to a difference in the phase of tidal currents in each channel. In San Francisco Bay, the phasing of the currents at the junction of Mare Island Strait and Carquinez Strait produces a local salinity minimum in Mare Island Strait. At the location of a local salinity minimum the longitudinal density gradient reverses direction. This paper presents four numerical models that were used to investigate the circulation caused by the salinity minimum: (1) A simple one-dimensional (1D) finite difference model demonstrates that a local salinity minimum is advected into Mare Island Strait from the junction with Carquinez Strait during flood tide. (2) A three-dimensional (3D) hydrodynamic finite element model is used to compute the tidally averaged circulation in a channel that contains a salinity minimum (a change in the sign of the longitudinal density gradient) and compares that to a channel that contains a longitudinal density gradient in a constant direction. The tidally averaged circulation produced by the salinity minimum is characterized by converging flow at the bed and diverging flow at the surface, whereas the circulation produced by the constant direction gradient is characterized by converging flow at the bed and downstream surface currents. These velocity fields are used to drive both a particle tracking and a sediment transport model. (3) A particle tracking model demonstrates a 30 percent increase in the residence time of neutrally buoyant particles transported through the salinity minimum, as compared to transport through a constant direction density gradient. (4) A sediment transport model demonstrates increased deposition at the near-bed null point of the salinity minimum, as compared to the constant direction gradient null point. These results are corroborated by historically noted large sedimentation rates and a local maximum of selenium accumulation in clams at the null point in Mare Island Strait.The authors acknowledge support for this research
from the California Department of Fish and Game, the
California Coastal Conservancy, the U.S. Fish and
Wildlife Service Coastal Program, and the U.S.
Geological Survey Federal/State Cooperative and
Priority Ecosystem Science Programs
1RXS J232953.9+062814: A Dwarf Nova with a 64-minute Orbital Period and a Conspicuous Secondary Star
We present spectroscopy and time-series photometry of the newly discovered
dwarf nova 1RXS J232953.9+062814. Photometry in superoutburst reveals a
superhump with a period of 66.06(6) minutes. The low state spectrum shows
Balmer and HeI emission on a blue continuum, and in addition shows a rich
absorption spectrum of type K4 +- 2. The absorption velocity is modulated
sinusoidally at P_orb = 64.176(5) min, with semi-amplitude K = 348(4) km/s. The
low-state light curve is double-humped at this period, and phased as expected
for ellipsoidal variations. The absorption strength does not vary appreciably
around the orbit. The orbital period is shorter than any other cataclysmic
variable save for a handful of helium-star systems and V485 Centauri (59
minutes). The secondary is much hotter than main sequence stars of similar
mass, but is well-matched by helium-enriched models, indicating that the
secondary evolved from a more massive progenitor. A preliminary calculation in
which a 1.2 solar-mass star begins mass transfer near the end of H burning
matches this system's characteristics remarkably well.Comment: accepted to Astrophysical Journal Letters; 14 pages, 3 eps figures +
1 jpg greyscale figur
Parallax and Distance Estimates for Twelve Cataclysmic Variable Stars
We report parallax and distance estimates for twelve more cataclysmic
binaries and related objects observed with the 2.4m Hiltner telescope at MDM
Observatory. The final parallax accuracy is typically about 1 mas. For only one
of the twelve objects, IR Gem, do we fail to detect a significant parallax.
Notable results include distances for V396 Hya (CE 315), a helium double
degenerate with a relatively long orbital period, and for MQ Dra
(SDSSJ155331+551615), a magnetic system with a very low accretion rate. We find
that the Z Cam star KT Persei is physically paired with a K main-sequence star
lying 15 arcsec away. Several of the targets have distance estimates in the
literature that are based on the white dwarf's effective temperature and flux;
our measurements broadly corroborate these estimates, but tend to put the stars
a bit closer, indicating that the white dwarfs may have rather larger masses
than assumed. As a side note, we briefly describe radial velocity spectroscopy
that refines the orbital period of V396 Hya to 65.07 +- 0.08 min.Comment: Accepted for Astronomical Journal. 19 pages, no figure
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