30,183 research outputs found
Theoretical studies of chromospheres and winds in cool stars
Propagation of pulsational waves through the atmosphere of the M supergiant alpha Ori was explored using a time dependent hydrodynamic code. Wind properties for three FU Orionis objects were determined using radiative transfer models based on optical line profiles. The effects of varying wind temperature while keeping the velocity steady were considered. Using the premise that FU Orionis eruptions result from massive accretions from a disk into a T Tauri star explains a variety of observational peculiarities of FU Orionis objects
Theoretical studies of chromospheres and winds in cool stars
The atmospheres of hot pre-main sequence stars are discussed along with FU Orionis winds, h alpha emission from M dwarfs, and envelopes of T Tauri stars. In addition, extended chromospheres of M supergiants and metal deficiency giants are considered
The analytic torsion of the finite metric cone over a compact manifold
We give an explicit formula for the analytic torsion of the finite
metric cone over an oriented compact connected Riemannian manifold. We provide
an interpretation of the different factors appearing in this formula. We prove
that the analytic torsion of the cone is the finite part of the limit obtained
collapsing one of the boundaries, of the ratio of the analytic torsion of the
frustum to a regularising factor. We show that the regularising factor comes
from the set of the non square integrable eigenfunctions of the Laplace
Beltrami operator on the cone.Comment: To appear in Journal of the Mathematical Society of Japa
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AGM, a dataflow database machine
In recent years, a number of database machines consisting of large numbers of parallel processing elements have been proposed. Unfortunately, one of the main limitations to parallelism in database processing is the I/O bandwidth of the underlying storage devices. One way to solve this problem is to use multiple parallel disk units. The main problem with this approach, however, is the lack of a computational model capable of utilizing the potential of any significant number of such devices.This paper presents a database model which is based on the principles of data-driven computation. According to this model, the database is represented as a network in which each node is conceptually an independent processing element, capable of communicating with other nodes by exchanging messages along the network arcs. To answer a query, one or more such messages, called tokens, are created and injected into the network. These then propagate asynchronously through the network in the search of results satisfying the given query.To investigate the performance of the proposed system, we have implemented the model on a simulated computer architecture. The results of the simulation ex-periments indicate that the model is capable of exploiting the potential I/O band-width of a large number of disk units as well as the computational power of the associated processing elements
Molecular Dynamics in grafted layers of poly(dimethylsiloxane) (PDMS)
Dielectric relaxation spectroscopy 10^-1 Hz to 10^6 Hz) is employed to study
the molecular dynamics of poly(dimethylsiloxane) (PDMS, Mw=1.7 10^5 g/mol and
Mw=9.6 10^4 g/mol as grafted films with thicknesses d below and above the
radius of gyration Rg. For d smaller than Rg the molecular dynamics becomes
faster by up to three orders of magnitude with respect to the bulk resulting in
a pronounced decrease of the Vogel temperature T0 and hence the calorimetric
glass transition temperature Tg. For d larger than Rg the molecular dynamics is
comparable to that of the bulk melt. The results are interpreted in terms of a
chain confinement effect and compared with the findings for low molecular eight
glass forming liquids contained in nanoporous glasses and zeolites.
Crystallization effects - well known for PDMS - are observed for films of
thicknesses above and below Rg.Comment: 20 pages, 4 figure
Observations of cataclysmic variables with IUE
Observations are reported of the cataclysmic variables AN UMa, 2AO311-227, VV Pup, DQ Her, and GK Per. Continuum emission was detected in the short wavelength region in DQ Her. This object exhibits a quasi-blackbody spectrum at short wavelengths, such blackbody components are a common property of the variables AM Her, SS Cyg, and U Gem, suggesting an underlying similarity in the activity of these diverse systems. Flat continuum components at longer wavelengths in general are not compatible with standard disk models. The emission line ratios in AE Aqr are anomalous in that C IV is absent to a very low level relative to N V
Properties of GRB Host Galaxies
The transients following GRB970228 and GRB970508 showed that these (and
probably all) GRBs are cosmological. However, the host galaxies expected to be
associated with these and other bursts are largely absent, indicating that
either bursts are further than expected or the host galaxies are underluminous.
This apparent discrepancy does not invalidate the cosmological hypothesis, but
instead host galaxy observations can test more sophisticated models.Comment: 5 pages, AIPPROC LaTeX, to appear in "Gamma-Ray Bursts, 4th
Huntsville Symposium," eds. C. Meegan, R. Preece and T. Koshu
F-8C adaptive flight control extensions
An adaptive concept which combines gain-scheduled control laws with explicit maximum likelihood estimation (MLE) identification to provide the scheduling values is described. The MLE algorithm was improved by incorporating attitude data, estimating gust statistics for setting filter gains, and improving parameter tracking during changing flight conditions. A lateral MLE algorithm was designed to improve true air speed and angle of attack estimates during lateral maneuvers. Relationships between the pitch axis sensors inherent in the MLE design were examined and used for sensor failure detection. Design details and simulation performance are presented for each of the three areas investigated
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