1,257 research outputs found
The high-field polar RX J1007.5-2017
We report optical and X-ray observations of the high-field polar
RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of
208.60 min determined from the ellipsoidal modulation of the secondary star in
an extended low state. The spectral flux of the dM3- secondary star yields a
distance of 790+-105 pc. At low accretion levels, \RX{} exhibits pronounced
cyclotron emission lines. The second and third harmonic fall in the optical
regime and yield a field strength in the accretion spot of 94 MG. The source is
highly variable on a year-to-year basis and was encountered at visual
magnitudes between V \sim 20 and V \sim 16. In the intermediate state of 1992
and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the
cyclotron source, the hard X-ray source, and the accretion stream by an order
of magnitude. An X-ray high state, corresponding to the brightest optical
level, has apparently not been observed so far.Comment: To be published in A&
A new clue to the transition mechanism between optical high and low states of the supersoft X-ray source RX J0513.9-6951, implied from the recurrent nova CI Aquilae 2000 outburst model
We have found a new clue to the transition mechanism between optical
high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray
source RX J0513.9-6951. A sharp ~1 mag drop is common to the CI Aql 2000
outburst. These drops are naturally attributed to cessation of optically thick
winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that
the size of a disk drastically shrinks when the wind stops. This causes ~1-2
mag drop in the optical light curve. In RX J0513.9-6951, the same mechanism
reproduces sharp ~1 mag drop from optical high to low states. We predict this
mechanism also works on the transition from low to high states. Interaction
between the wind and the companion star attenuates the mass transfer and drives
full cycles of low and high states.Comment: 9 pages including 5 figures, to appear in the Astrophysical Journa
Supersoft X-ray sources in M31: II. ROSAT-detected supersoft sources in the ROSAT, Chandra and XMM eras
We have performed Chandra observations during the past 3 years of 5 of the
M31 supersoft X-ray sources (SSS) discovered with ROSAT. Surprisingly, only one
of these sources has been detected, despite a predicted detection of about
20-80 counts. This has motivated a thorough check of the ROSAT M31 survey I
data, including a relaxation of the hardness ratio requirement used to select
SSS. This increases the number of SSS identified in survey I by 7. We then
carried out a comparison with the ROSAT M31 survey II dataset which had
hitherto not been explicitly investigated for SSS. We find that most of the
ROSAT survey I sources are not detected, and only two new SSS are identified.
The low detection rate in the ROSAT survey II and our Chandra observations
implies that the variability time scale of SSS is a few months. If the majority
of these sources are close-binary SSS with shell hydrogen burning, it further
implies that half of these sources predominantly experience large mass transfer
rates.Comment: accepted for publ. in ApJ; 2 ps-figures; high-quality figures
available at http://www.mpe.mpg.de/~jcg/publis.htm
Mapping the porcine RN gene to chromosome 15
International audienc
Exploring the Case for Expanded Remote Texter Liability for Employers
In 2013, the New Jersey Appellate Court decided the potentially landmark case of Kubert v. Best, recognizing for the first time that a sender of a text may be held liable to an innocent third party injured in an automobile accident caused by a driver who was distracted by receiving the text. Other subsequent cases have both confirmed and limited the Kubert ruling. In this article, we explore possible further extensions of the Kubert ruling, anticipating that because of expanding employer liability for acts undertaken by their employees, the next step in the evolution of texting and driving law may likely hold employers liable for accidents caused by their employees whose employment-related texts to others result in accident and harm
Applying Indices Post-\u3ci\u3eGrutter\u3c/i\u3e to Monitor Progress Toward Attaining a Diverse Student Body
The Supreme Court decision in Grutter v. Bollinger provided more definitive guidance for institutions of higher education desiring to use racial preferences in an effort to achieve a diverse student body. This Article first examines Grutter and other relevant cases to set forth the parameters established by the Supreme Court concerning how university preferences, including but not limited to race, may be used in an admissions policy. This Article then provides a framework for creating and using diversity indices that can help institutions implement the guidelines found in these court decisions and monitor whether or not the goal of diversity has been met. The Article describes a hypothetical situation, illustrating how diversity indices can be used in a manner that conforms to the admissions policy parameters established by the Supreme Court
Applying Indices Post-\u3ci\u3eGrutter\u3c/i\u3e to Monitor Progress Toward Attaining a Diverse Student Body
The Supreme Court decision in Grutter v. Bollinger provided more definitive guidance for institutions of higher education desiring to use racial preferences in an effort to achieve a diverse student body. This Article first examines Grutter and other relevant cases to set forth the parameters established by the Supreme Court concerning how university preferences, including but not limited to race, may be used in an admissions policy. This Article then provides a framework for creating and using diversity indices that can help institutions implement the guidelines found in these court decisions and monitor whether or not the goal of diversity has been met. The Article describes a hypothetical situation, illustrating how diversity indices can be used in a manner that conforms to the admissions policy parameters established by the Supreme Court
An optimum time-stepping scheme for N-body simulations
We present a new time-stepping criterion for N-body simulations that is based
on the true dynamical time of a particle. This allows us to follow the orbits
of particles correctly in all environments since it has better adaptivity than
previous time-stepping criteria used in N-body simulations. Furthermore, it
requires far fewer force evaluations in low density regions of the simulation
and has no dependence on artificial parameters such as, for example, the
softening length. This can be orders of magnitude faster than conventional
ad-hoc methods that employ combinations of acceleration and softening and is
ideally suited for hard problems, such as obtaining the correct dynamics in the
very central regions of dark matter haloes. We also derive an eccentricity
correction for a general leapfrog integration scheme that can follow
gravitational scattering events for orbits with eccentricity e -> 1 with high
precision. These new approaches allow us to study a range of problems in
collisionless and collisional dynamics from few body problems to cosmological
structure formation. We present tests of the time-stepping scheme in N-body
simulations of 2-body orbits with eccentricity e -> 1 (elliptic and
hyperbolic), equilibrium haloes and a hierarchical cosmological structure
formation run.Comment: 15 pages, 10 figures, replaced with version that matches published
versio
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