905 research outputs found
The Quiescent Spectrum of the AM CVn star CP Eri
We used the 6.5m MMT to obtain a spectrum of the AM CVn star CP Eri in
quiescence. The spectrum is dominated by He I emission lines, which are clearly
double peaked with a peak-to-peak separation of ~1900 km/s. The spectrum is
similar to that of the longer period AM CVn systems GP Com and CE 315, linking
the short and the long period AM CVn systems. In contrast with GP Com and CE
315, the spectrum of CP Eri does not show a central 'spike' in the line
profiles, but it does show lines of SiII in emission. The presence of these
lines indicates that the material being transferred is of higher metallicity
than in GP Com and CE 315, which, combined with the low proper motion of the
system, probably excludes a halo origin of the progenitor of CP Eri. We
constrain the primary mass to M_1>0.27 M_sun and the orbital inclination to 33
degr < i < 80 degr. The presence of the He I lines in emission opens up the
possibility for phase resolved spectroscopic studies which allows a
determination of the system parameters and a detailed study of helium accretion
disks under highly varying circumstances.Comment: 12 pages, 2 figures, accepted for publication in ApJ Letter
KUV 01584-0939: A Helium-transferring Cataclysmic Variable with an Orbital Period of 10 Minutes
High speed photometry of KUV 01584-0939 (alias Cet3) shows that is has a
period of 620.26 s. Combined with its hydrogen-deficient spectrum, this implies
that it is an AM CVn star. The optical modulation is probably a superhump, in
which case the orbital period will be slightly shorter than what we have
observed.Comment: Published by PASP. See also the latest Early-Release Research Paper
website of the PAS
Neurocognitive factors in sensory restoration of early deafness: a connectome model
Progress in biomedical technology (cochlear, vestibular, and retinal implants) has led to remarkable success in neurosensory restoration, particularly in the auditory system. However, outcomes vary considerably, even after accounting for comorbidity-for example, after cochlear implantation, some deaf children develop spoken language skills approaching those of their hearing peers, whereas other children fail to do so. Here, we review evidence that auditory deprivation has widespread effects on brain development, affecting the capacity to process information beyond the auditory system. After sensory loss and deafness, the brain's effective connectivity is altered within the auditory system, between sensory systems, and between the auditory system and centres serving higher order neurocognitive functions. As a result, congenital sensory loss could be thought of as a connectome disease, with interindividual variability in the brain's adaptation to sensory loss underpinning much of the observed variation in outcome of cochlear implantation. Different executive functions, sequential processing, and concept formation are at particular risk in deaf children. A battery of clinical tests can allow early identification of neurocognitive risk factors. Intervention strategies that address these impairments with a personalised approach, taking interindividual variations into account, will further improve outcomes
The Helium-Rich Cataclysmic Variable ES Ceti
We report photometry of the helium-rich cataclysmic variable ES Ceti during
2001-2004. The star is roughly stable at V ~ 17.0 and has a light curve
dominated by a single period of 620 s, which remains measurably constant over
the 3 year baseline. The weight of evidence suggests that this is the true
orbital period of the underlying binary, not a "superhump" as initially
assumed. We report GALEX ultraviolet magnitudes, which establish a very blue
flux distribution (F_nu ~ nu^1.3), and therefore a large bolometric correction.
Other evidence (the very strong He II 4686 emission, and a ROSAT detection in
soft X-rays) also indicates a strong EUV source, and comparison to
helium-atmosphere models suggests a temperature of 130+-10 kK. For a distance
of 350 pc, we estimate a luminosity of (0.8-1.7)x10^34 erg/s, yielding a mass
accretion rate of (2-4)x10^-9 M_sol/yr onto an assumed 0.7 M_sol white dwarf.
This appears to be about as expected for white dwarfs orbiting each other in a
10 minute binary, assuming that mass transfer is powered by gravitational
radiation losses. We estimate mean accretion rates for other helium-rich
cataclysmic variables, and find that they also follow the expected M-dot ~
P_o^-5 relation. There is some evidence (the lack of superhumps, and the small
apparent size of the luminous region) that the mass transfer stream in ES Cet
directly strikes the white dwarf, rather than circularizing to form an
accretion disk.Comment: PDF, 26 pages, 3 tables, 9 figures; accepted, in press, to appear
February 2005, PASP; more info at http://cba.phys.columbia.edu
Persistence in q-state Potts model: A Mean-Field approach
We study the Persistence properties of the T=0 coarsening dynamics of one
dimensional -state Potts model using a modified mean-field approximation
(MMFA). In this approximation, the spatial correlations between the interfaces
separating spins with different Potts states is ignored, but the correct time
dependence of the mean density of persistent spins is imposed. For this
model, it is known that follows a power-law decay with time, where is the -dependent persistence exponent. We
study the spatial structure of the persistent region within the MMFA. We show
that the persistent site pair correlation function has the scaling
form for all values of the persistence
exponent . The scaling function has the limiting behaviour () and (). We then show within the
Independent Interval Approximation (IIA) that the distribution of
separation between two consecutive persistent spins at time has the
asymptotic scaling form where the
dynamical exponent has the form =max(). The behaviour of
the scaling function for large and small values of the arguments is found
analytically. We find that for small separations where =max(), while for large
separations , decays exponentially with . The
unusual dynamical scaling form and the behaviour of the scaling function is
supported by numerical simulations.Comment: 11 pages in RevTeX, 10 figures, submitted to Phys. Rev.
"Remember Everything": things past in Station Island
Book synopsis: Seamus Heaney: Poet, Critic, Translator explores the range of Heaney's writing, emphasizing significant intersections in his work - meeting places; spaces between; tradition meeting the contemporary context as life meets death; liminal poetic representations and political divisions; town and woods, absence and presence; inner reality facing external reality; the timely and the transcendent; region and wider world; Irish tradition encountering Polish tradition; the space between modern English and ancient Greek; the meeting of personal and formal in the translation of Beowulf; different times and perceptions meeting problematic memory; Heaney's Leavisite stance in the face of contemporary critical currents; and Heaney's imagination approaching the imaginations of other poets
Persistence in Cluster--Cluster Aggregation
Persistence is considered in diffusion--limited cluster--cluster aggregation,
in one dimension and when the diffusion coefficient of a cluster depends on its
size as . The empty and filled site persistences are
defined as the probabilities, that a site has been either empty or covered by a
cluster all the time whereas the cluster persistence gives the probability of a
cluster to remain intact. The filled site one is nonuniversal. The empty site
and cluster persistences are found to be universal, as supported by analytical
arguments and simulations. The empty site case decays algebraically with the
exponent . The cluster persistence is related to the
small behavior of the cluster size distribution and behaves also
algebraically for while for the behavior is
stretched exponential. In the scaling limit and with fixed the distribution of intervals of size between
persistent regions scales as , where is the average interval size and . For finite the
scaling is poor for , due to the insufficient separation of the two
length scales: the distances between clusters, , and that between
persistent regions, . For the size distribution of persistent regions
the time and size dependences separate, the latter being independent of the
diffusion exponent but depending on the initial cluster size
distribution.Comment: 14 pages, 12 figures, RevTeX, submitted to Phys. Rev.
Fraction of uninfected walkers in the one-dimensional Potts model
The dynamics of the one-dimensional q-state Potts model, in the zero
temperature limit, can be formulated through the motion of random walkers which
either annihilate (A + A -> 0) or coalesce (A + A -> A) with a q-dependent
probability. We consider all of the walkers in this model to be mutually
infectious. Whenever two walkers meet, they experience mutual contamination.
Walkers which avoid an encounter with another random walker up to time t remain
uninfected. The fraction of uninfected walkers is investigated numerically and
found to decay algebraically, U(t) \sim t^{-\phi(q)}, with a nontrivial
exponent \phi(q). Our study is extended to include the coupled
diffusion-limited reaction A+A -> B, B+B -> A in one dimension with equal
initial densities of A and B particles. We find that the density of walkers
decays in this model as \rho(t) \sim t^{-1/2}. The fraction of sites unvisited
by either an A or a B particle is found to obey a power law, P(t) \sim
t^{-\theta} with \theta \simeq 1.33. We discuss these exponents within the
context of the q-state Potts model and present numerical evidence that the
fraction of walkers which remain uninfected decays as U(t) \sim t^{-\phi},
where \phi \simeq 1.13 when infection occurs between like particles only, and
\phi \simeq 1.93 when we also include cross-species contamination.Comment: Expanded introduction with more discussion of related wor
Coaxial Jets and Sheaths in Wide-Angle-Tail Radio Galaxies
We add 20, 6 and 3.6 cm wavelength VLA observations of two WATs, 1231+674 and
1433+553, to existing VLA data at 6 and 20 cm, in order to study the variations
of spectral index as a function of position. We apply the spectral tomography
process that we introduced in our analysis of 3C67, 3C190 and 3C449. Both
spectral tomography and polarization maps indicate that there are two distinct
extended components in each source. As in the case of 3C449, we find that each
source has a flat spectrum jet surrounded by a steeper spectrum sheath. The
steep components tend to be more highly polarized than the flat components. We
discuss a number of possibilities for the dynamics of the jet/sheath systems,
and the evolution of their relativistic electron populations. While the exact
nature of these two coaxial components is still uncertain, their existence
requires new models of jets in FR I sources and may also have implications for
the dichotomy between FR Is and FR IIs.Comment: 29 text pages plus 13 figures. Scheduled for publication in May 10,
1999 Ap
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