20,791 research outputs found
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
A cyclic bipolar wind in the interacting binary V393 Scorpii
V393 Scorpii is a Double Periodic Variable characterized by a relatively
stable non-orbital photometric cycle of 253 days. Mennickent et al. argue for
the presence of a massive optically thick disc around the more massive B-type
component and describe the evolutionary stage of the system. In this paper we
analyze the behavior of the main spectroscopic optical lines during the long
non-orbital photometric cycle. We study the radial velocity of the donor
determining their orbital elements and find a small but significant orbital
eccentricity (e = 0.04). The donor spectral features are modeled and removed
from the spectrum at every observing epoch using the light-curve model given by
Mennickent et al. We find that the line emission is larger during eclipses and
mostly comes from a bipolar wind. We find that the long cycle is explained in
terms of a modulation of the wind strength; the wind has a larger line and
continuum emissivity on the high state. We report the discovery of highly
variable chromospheric emission in the donor, as revealed by Doppler maps of
the emission lines MgII 4481 and CI 6588. We discuss notable and some novel
spectroscopic features like discrete absorption components, especially visible
at blue-depressed OI 7773 absorption wings during the second half-cycle, Balmer
double emission with V/R-curves showing "Z-type" and "S-type" excursions around
secondary and main eclipse, respectively, and H_beta emission wings extending
up to +- 2000 km/s. We discuss possible causes for these phenomena and for
their modulations with the long cycle.Comment: 19 pages, 22 figures, accepted for publication in MNRA
Universality of rain event size distributions
We compare rain event size distributions derived from measurements in
climatically different regions, which we find to be well approximated by power
laws of similar exponents over broad ranges. Differences can be seen in the
large-scale cutoffs of the distributions. Event duration distributions suggest
that the scale-free aspects are related to the absence of characteristic scales
in the meteorological mesoscale.Comment: 16 pages, 10 figure
Linear optics and quantum maps
We present a theoretical analysis of the connection between classical
polarization optics and quantum mechanics of two-level systems. First, we
review the matrix formalism of classical polarization optics from a quantum
information perspective. In this manner the passage from the
Stokes-Jones-Mueller description of classical optical processes to the
representation of one- and two-qubit quantum operations, becomes
straightforward. Second, as a practical application of our
classical-\emph{vs}-quantum formalism, we show how two-qubit maximally
entangled mixed states (MEMS), can be generated by using polarization and
spatial modes of photons generated via spontaneous parametric down conversion.Comment: 13 pages, 8 figure
Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC 5548
We present the results of three years of ground-based observations of the
Seyfert 1 galaxy NGC 5548, which combined with previously reported data, yield
optical continuum and broad-line H-beta light curves for a total of eight
years. The light curves consist of over 800 points, with a typical spacing of a
few days between observations. During this eight-year period, the nuclear
continuum has varied by more than a factor of seven, and the H-beta emission
line has varied by a factor of nearly six. The H-beta emission line responds to
continuum variations with a time delay or lag of 10-20 days, the precise value
varying somewhat from year to year. We find some indications that the lag
varies with continuum flux in the sense that the lag is larger when the source
is brighter.Comment: 29 pages, 6 figures. Accepted for publication in ApJ (1999 Jan 10
Optimizing tuning masses for helicopter rotor blade vibration reduction including computed airloads and comparison with test data
The development and validation of an optimization procedure to systematically place tuning masses along a rotor blade span to minimize vibratory loads are described. The masses and their corresponding locations are the design variables that are manipulated to reduce the harmonics of hub shear for a four-bladed rotor system without adding a large mass penalty. The procedure incorporates a comprehensive helicopter analysis to calculate the airloads. Predicting changes in airloads due to changes in design variables is an important feature of this research. The procedure was applied to a one-sixth, Mach-scaled rotor blade model to place three masses and then again to place six masses. In both cases the added mass was able to achieve significant reductions in the hub shear. In addition, the procedure was applied to place a single mass of fixed value on a blade model to reduce the hub shear for three flight conditions. The analytical results were compared to experimental data from a wind tunnel test performed in the Langley Transonic Dynamics Tunnel. The correlation of the mass location was good and the trend of the mass location with respect to flight speed was predicted fairly well. However, it was noted that the analysis was not entirely successful at predicting the absolute magnitudes of the fixed system loads
On the relative expressiveness of higher-order session processes
By integrating constructs from the λ-calculus and the Ï-calculus, in higher-order process calculi exchanged values may contain processes. This paper studies the relative expressiveness of HOÏ, the higher-order Ï-calculus in which communications are governed by session types. Our main discovery is that HO, a subcalculus of HOÏ which lacks name-passing and recursion, can serve as a new core calculus for session-typed higher-order concurrency. By exploring a new bisimulation for HO, we show that HO can encode HOÏ fully abstractly (up to typed contextual equivalence) more precisely and efficiently than the first-order session Ï-calculus (Ï). Overall, under session types, HOÏ, HO, and Ï are equally expressive; however, HOÏ and HO are more tightly related than HOÏ and Ï
An atmospheric perspective on North American carbon dioxide exchange: CarbonTracker
We present an estimate of net CO2 exchange between the terrestrial biosphere and the atmosphere across North America for every week in the period 2000 through 2005. This estimate is derived from a set of 28,000 CO2 mole fraction observations in the global atmosphere that are fed into a state-of-the-art data assimilation system for CO2 called CarbonTracker. By design, the surface fluxes produced in CarbonTracker are consistent with the recent history of CO2 in the atmosphere and provide constraints on the net carbon flux independent from national inventories derived from accounting efforts. We find the North American terrestrial biosphere to have absorbed â0.65 PgC/yr (1 petagram = 10^15 g; negative signs are used for carbon sinks) averaged over the period studied, partly offsetting the estimated 1.85 PgC/yr release by fossil fuel burning and cement manufacturing. Uncertainty on this estimate is derived from a set of sensitivity experiments and places the sink within a range of â0.4 to â1.0 PgC/yr. The estimated sink is located mainly in the deciduous forests along the East Coast (32%) and the boreal coniferous forests (22%). Terrestrial uptake fell to â0.32 PgC/yr during the large-scale drought of 2002, suggesting sensitivity of the contemporary carbon sinks to climate extremes. CarbonTracker results are in excellent agreement with a wide collection of carbon inventories that form the basis of the first North American State of the Carbon Cycle Report (SOCCR), to be released in 2007. All CarbonTracker results are freely available at http://carbontracker.noaa.gov
Folates provoke cellular efflux and drug resistance of substrates of the multidrug resistance protein 1 (MRP1)
Cellular folate concentration was earlier reported to be a critical factor in the activity and expression of the multidrug resistance protein MRP1 (ABCC1). Since MRP1 mediates resistance to a variety of therapeutic drugs, we investigated whether the cellular folate concentration inf
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