462 research outputs found
Study of X-ray emission from the old open cluster, M67
We present an X-ray analysis of a 4 Gyr old open cluster, M67, using archival
XMM-Newton data. The aim of this study was to find new X-ray members of M67,
and to use the updated member list for studying X-ray variability, and derive
the X-ray luminosity functions (XLFs) of different stellar types and compare
them with other star clusters of similar age. We report the detection of X-ray
emission from 25 members of M67, with membership based primarily on their
proper motion, of which one X-ray source is a new member. Supplementing this
study with previous ROSAT and Chandra studies of M67, and using the most recent
proper motion study by Vereshchagin et al., we have compiled a revised list of
X-ray emitting members of M67 consisting of 43 stars. Sixteen of these are
known RS CVn type binaries having orbital periods 10 days, and
near-circular orbits, 5 are contact binaries with orbital periods 6 hours,
5 are yellow and blue stragglers, 2 are Algol-type binaries, and one source is
a cataclysmic variable. Fourteen members do not have any orbital information
and cannot be classified. Fourteen of the X-ray sources detected do not have
any optical counterpart down to a magnitude of , and their
membership is uncertain. Finally, we report the X-ray luminosity functions of
RS CVn type and other types of stars in M67 and compare them with other open
clusters of intermediate-to-old age.Comment: 13 pages, 8 figures, 5 tables. Accepted for publication in MNRA
Universal R operator with deformed conformal symmetry
We study the general solution of the Yang-Baxter equation with deformed
symmetry. The universal R operator acting on tensor products of
arbitrary representations is obtained in spectral decomposition and in integral
forms. The results for eigenvalues, eigenfunctions and integral kernel appear
as deformations of the ones in the rational case. They provide a basis for the
construction of integrable quantum systems generalizing the XXZ spin models to
the case of arbitrary not necessarily finite-dimensional representations on the
sites.Comment: 18 pages LaTex, revised, to be publ. in Nucl. Phy
OVERCONFIDENCE AND TRADING VOLUME: EVIDENCE FROM AN EMERGENT MARKET
It has been a challenge for financial economists to explain some stylized factsobserved in securities markets, among them, high levels of trading volume. The mostprominent explanation of excess volume is overconfidence. High market returns makeinvestors overconfident and as a consequence, these investors trade more subsequently andmake some transactions more aggressively. The aim of our paper is to study the impact of thephenomenon of overconfidence on the trading volume and its role in the formation of theexcess volume on the Tunisian stock market. Based on the work of Statman, Thorley andVorkink (2006) and by using VAR models and impulse response functions, we find a littleevidence of the overconfidence hypothesis when we use volume (shares traded) as proxy oftrading volume.overconfidence, disposition effect, trading volume, emergent market
Numerical solution for the temperature distribution in a cooled guide vane blade of a radial gas turbine
A two dimensional finite difference numerical technique is presented to determine the temperature distribution of an internal cooled blade of radial turbine guide vanes. A simple convection cooling is assumed inside the guide vane blade. Such cooling has relatively small cooling effectiveness at the leading edge and at the trailing edge. Heat transfer augmentation in these critical areas may be achieved by using impingement jets and film cooling. A computer program is written in FORTRAN IV for IBM 370/165 computer
On Better Approximation Order for the Nonlinear Meyer-K\"onig and Zeller Operator of Maximum Product Kind
Using maximum instead of sum, nonlinear Meyer-K\"onig and Zeller operator of
maximum product kind is introduced by Bede et al. The present paper deals with
the approximation processes for this operator. Especially in, it was indicated
that the order of approximation of this operator to the function f under the
modulus is and it could not be improved except for some subclasses of
functions. Contrary to this claim, we will show that a better order of
approximation can be obtained with the help of classical modulus of continuity
An investigation of temperature distribution in cooled guide vanes
A numerical study to determine the temperature distribution in the guide vane blades of a radial inflow turbine is presented. A computer program was developed which permits the temperature distribution to be calculated when the blade is cooled internally using a combination of impingement and film cooling techniques. The study is based on the use of the finite difference method in a two dimensional heat conduction problem. The results are then compared to determine the best cooling configuration for a certain coolant to primary mass flow ratio
Whistler Waves: Modeling and Observations
The thesis presents the results of all the research from the published and in publication process research in the Journal of Geophysical Research [1]. This research focuses on whistler wave ducting events in the equatorial magnetosphere. High-density ducts are the main focus of whistler study in both studies as they are commonly observed by the Van Allen Probe satellites. A three-step procedure based on the analysis of the whistler wave dispersion relation and numerical simulations of the electron magnetohydrodynamics model. We use this model to identify the parallel and perpendicular wave numbers of the âmost trappedâ wave in an attempt to understand the filtering aspects of HDD. Statistical analysis was done in a separate study to determine common parameters and characteristics of narrow and wide ducting events. A total of 213 events were cataloged where 164 were narrow events. The narrow HDD were found to most commonly have a duct size between 0-50 km with a density increase of 161% in the background magnetic field range of 100-300 nT. Wide events are events were the background magnetic field and the density gradient vary in the same direction, either both increases or decreases. The results from the studies show a robust three-step procedure that was applied to an observed event as well as the common characteristics and catalog of events in which this procedure is applicable
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