17,353 research outputs found
The Inhomogeneous Hall's Ray
We show that the inhomogenous approximation spectrum, associated to an
irrational number \alpha\ always has a Hall's Ray; that is, there is an
\epsilon>0 such that [0,\epsilon) is a subset of the spectrum. In the case when
\alpha\ has unbounded partial quotients we show that the spectrum is just a
ray.Comment: Fixed typos in bibliograph
V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary
(Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT
Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution
from a late-type secondary star in its optical spectrum, which led Schwope et
al. to suggest it to be among the nearest cataclysmic binaries. We present
extensive optical observations of V405 Peg. Time-series spectroscopy shows the
orbital period, Porb, to be 0.1776469(7) d (= 4.2635 hr), or 5.629 cycle/d. We
classify the secondary as M3 - M4.5. Astrometry with the MDM 2.4m telescope
gives a parallax 7.2 +- 1.1 milli-arcsec, and a relative proper motion of 58
mas/yr. Our best estimate of the distance yields d = 149 (+26, -20) pc. The
secondary stars's radial velocity has K2 = 92 +- 3 km/s, indicating a fairly
low orbital inclination if the masses are typical. Extensive I-band time-series
observations in the show the system varying between a minimum brightness level
of I = 14.14 and states of enhanced activity about 0.2 mag brighter. While the
low-state shows an ellipsoidal modulation, an additional photometric modulation
appears in the high state, with 0.1 mag amplitude and period 220-280 min. The
frequency of this modulation appears to be stable for a month or so, but no
single period was consistently detected from one observing season to the next.
We estimate the system luminosity by combining optical measurements with the
archival X-ray spectrum. The implied mass accretion rate is orders of
magnitudes below the predictions for the standard angular momentum loss above
the period gap. The system may possibly belong to a largely undiscovered
population of hibernating CVs.Comment: 11 figures; 7 of these are .png or .jpg to save space. In press for
Publications of the Astronomical Society of the Pacifi
Reconciling taxonomy and phylogenetic inference: formalism and algorithms for describing discord and inferring taxonomic roots
Although taxonomy is often used informally to evaluate the results of
phylogenetic inference and find the root of phylogenetic trees, algorithmic
methods to do so are lacking. In this paper we formalize these procedures and
develop algorithms to solve the relevant problems. In particular, we introduce
a new algorithm that solves a "subcoloring" problem for expressing the
difference between the taxonomy and phylogeny at a given rank. This algorithm
improves upon the current best algorithm in terms of asymptotic complexity for
the parameter regime of interest; we also describe a branch-and-bound algorithm
that saves orders of magnitude in computation on real data sets. We also
develop a formalism and an algorithm for rooting phylogenetic trees according
to a taxonomy. All of these algorithms are implemented in freely-available
software.Comment: Version submitted to Algorithms for Molecular Biology. A number of
fixes from previous versio
Precision electromagnetic structure of decuplet baryons in the chiral regime
The electromagnetic properties of the baryon decuplet are calculated in
quenched QCD on a 20^3 x 40 lattice with a lattice spacing of 0.128 fm using
the fat-link irrelevant clover (FLIC) fermion action with quark masses
providing a pion mass as low as 300 MeV. Magnetic moments and charge radii are
extracted from the electric and magnetic form factors for each individual quark
sector. From these, the corresponding baryon properties are constructed. We
present results for the higher order moments of the spin-3/2 baryons, including
the electric quadrupole moment E2 and the magnetic octupole moment M3. The
world's first determination of a non-zero M3 form factor for the Delta baryon
is presented. With these results we provide a conclusive analysis which shows
that decuplet baryons are deformed. We compare the decuplet baryon results from
a similar lattice calculation of the octet baryons. We establish that the
environment sensitivity is far less pronounced in the case of the decuplet
baryons compared to that in the octet baryons. A surprising result is that the
charge radii of the decuplet baryons are generally smaller than that of the
octet baryons. The magnetic moment of the Delta^+ reveals a turn over in the
low quark mass region, making it smaller than the proton magnetic moment. These
results are consistent with the expectations of quenched chiral perturbation
theory. A similar turn over is also noticed in the magnetic moment of the
Sigma^*0, but not for Xi^* where only kaon loops can appear in quenched QCD.
The electric quadrupole moment of the Omega^- baryon is positive when the
negative charge factor is included, and is equal to 0.86 +- 0.12 x 10^-2 fm^2,
indicating an oblate shape.Comment: 30 pages, 32 figure
High resolution structural characterisation of laser-induced defect clusters inside diamond
Laser writing with ultrashort pulses provides a potential route for the
manufacture of three-dimensional wires, waveguides and defects within diamond.
We present a transmission electron microscopy (TEM) study of the intrinsic
structure of the laser modifications and reveal a complex distribution of
defects. Electron energy loss spectroscopy (EELS) indicates that the majority
of the irradiated region remains as bonded diamond.
Electrically-conductive paths are attributed to the formation of multiple
nano-scale, -bonded graphitic wires and a network of strain-relieving
micro-cracks
String effects and the distribution of the glue in mesons at finite temperature
The distribution of the gluon action density in mesonic systems is
investigated at finite temperature. The simulations are performed in quenched
QCD for two temperatures below the deconfinment phase. Unlike the gluonic
profiles displayed at T=0, the action density iso-surfaces display a
prolate-spheroid like shape. The curved width profile of the flux-tube is found
to be consistent with the prediction of the free Bosonic string model at large
distances.Comment: 14 pages,10 figure
Sun-Sized Water Vapor Masers in Cepheus A
We present the first VLBI observations of a Galactic water maser (in Chepeus
A) made with a very long baseline interferometric array involving the
RadioAstron Earth-orbiting satellite station as one of its elements. We
detected two distinct components at -16.9 and 0.6 km/s with a fringe spacing of
66 microarcseconds. In total power, the 0.6 km/s component appears to be a
single Gaussian component of strength 580 Jy and width of 0.7 km/s.
Single-telescope monitoring showed that its lifetime was only 8~months. The
absence of a Zeeman pattern implies the longitudinal magnetic field component
is weaker than 120 mG. The space-Earth cross power spectrum shows two
unresolved components smaller than 15 microarcseconds, corresponding to a
linear scale of 1.6 x 10^11 cm, about the diameter of the Sun, for a distance
of 700 pc, separated by 0.54 km/s in velocity and by 160 +/-35 microarcseconds
in angle. This is the smallest angular structure ever observed in a Galactic
maser. The brightness temperatures are greater than 2 x 10^14K, and the line
widths are 0.5 km/s. Most of the flux (about 87%) is contained in a halo of
angular size of 400 +/- 150 microarcseconds. This structure is associated with
the compact HII region HW3diii. We have probably picked up the most prominent
peaks in the angular size range of our interferometer. We discuss three
dynamical models: (1) Keplerian motion around a central object, (2) two chance
overlapping clouds, and (3) vortices caused by flow around an obstacle (i.e.,
von Karman vortex street) with Strouhal number of about~0.3.Comment: 15 pages, 9 figures. Accepted for publication in ApJ, February 16,
201
Polarized Broad H-alpha Emission from the LINER Nucleus of NGC 1052
Optical spectropolarimetry of the nucleus of the LINER NGC 1052, obtained at
the Keck Observatory, reveals a rise in polarization in the wings of the
H-alpha line profile. The polarization vector of H-alpha is offset by 67
degrees from the parsec-scale radio axis and by 83 degrees from the
kiloparsec-scale radio axis, roughly in accord with expectations for scattering
within the opening cone of an obscuring torus. The broad component of H-alpha
has FWHM ~ 2100 km/s in total flux and FWHM ~ 5000 km/s in polarized light.
Scattering by electrons is the mechanism most likely responsible for this
broadening, and we find T_e ~ 10^5 K for the scattering medium, similar to
values observed in Seyfert 2 nuclei. This is the first detection of a polarized
broad emission line in a LINER, demonstrating that unified models of active
galactic nuclei are applicable to at least some LINERs.Comment: 6 pages, 2 figures, prepared using the emulateapj style file,
accepted for publication in The Astrophysical Journal Letter
Random division of an interval
The well-known relation between random division of an interval and the Poisson process is interpreted as a Laplace transformation. With the use of this interpretation a number of (in part known) results is derived very easily
- …