2,036 research outputs found
Eclipse Timings of the Transient Low Mass X-ray Binary EXO0748-676. IV. The Rossi X-Ray Timing Explorer Eclipses
We report our complete database of X-ray eclipse timings of the low mass
X-ray binary EXO0748-676 observed by the Rossi X-Ray Timing Explorer (RXTE)
satellite. As of this writing we have accumulated 443 full X-ray eclipses, 392
of which have been observed with the Proportional Counter Array on RXTE. These
include both observations where an eclipse was specifically targeted and those
eclipses found in the RXTE data archive. Eclipse cycle count has been
maintained since the discovery of the EXO0748-676 system in February 1985. We
describe our observing and analysis techniques for each eclipse and describe
improvements we have made since the last compilation by Wolff et al. (2002).
The principal result of this paper is the database containing the timing
results from a seven-parameter fit to the X-ray light curve for each observed
eclipse along with the associated errors in the fitted parameters. Based on the
standard O-C analysis, EXO0748-676 has undergone four distinct orbital period
epochs since its discovery. In addition, EXO0748-676 shows small-scale events
in the O-C curve that are likely due to short-lived changes in the secondary
star.Comment: Accepted for publication in The Astrophysical Journal Supplement
Series, 5 figures. Analysis revised. Tables 1 & 3 update
A New Insight into the Classification of Type Ia Supernovae
Type Ia Supernovae (SNe Ia) spectra are compared regarding the coefficient of
the largest wavelet scale in their decomposition. Two distinct subgroups were
identified and their occurrence is discussed in light of use of SNe Ia as
cosmological probes. Apart from the group of normal SNe, another trend
characterised by intrinsically redder colours is consisted of many different SN
events that exhibit diverse properties, including the interaction with the
circumstellar material, the existence of specific shell-structure in or
surrounding the SN ejecta or super-Chandrasekhar mass progenitors. Compared
with the normal objects, these SNe may violate the standard width-luminosity
correction, which could influence the cosmological results if they were all
calibrated equally, since their fraction among SNe Ia is not negligible when
performing precision cosmology. Using largest wavelet scale coefficient in
combination with long-baseline B-I colours, we show how to disentangle SN
intrinsic colour from the part that corresponds to the reddening due to dust
extinction in the host galaxy in the SALT2 colour parameter c, discussing how
the intrinsic colour differences may explain the different reddening laws for
two subsamples. There are wavelength intervals for which the measured largest
scale coefficient is invariant to the additional extinction applied to a
spectrum. Combination of wavelet coefficients measured in different wavelength
intervals can be used to develop a technique that allows for estimation of
extinction.Comment: 10 pages, 5 figures, 1 table; accepted for publication in MNRAS; v2:
one reference added and changed comment on SN 2009d
Evidence for Insulating Behavior in the Electric Conduction of (NH)KC Systems
Microwave study using cavity perturbation technique revealed that the
conductivity of antiferromagnet (NH)KRbC at 200K is
already 3-4 orders of magnitude smaller than those of superconductors,
KC and (NH)NaRbC, and that the antiferromagnetic
compounds are {\it insulators} below 250K without metal-insulator transitions.
The striking difference in the magnitude of the conductivity between these
materials strongly suggests that the Mott-Hubbard transition in the ammoniated
alkali fullerides is driven by a reduction of lattice symmetry from
face-centered-cubic to face-centered-orthorhombic, rather than by the magnetic
ordering.Comment: accepted for publication in PR
Bird Cryptochrome 1a Is Excited by Blue Light and Forms Long-Lived Radical- Pairs
Cryptochromes (Cry) have been suggested to form the basis of light-dependent
magnetic compass orientation in birds. However, to function as magnetic
compass sensors, the cryptochromes of migratory birds must possess a number of
key biophysical characteristics. Most importantly, absorption of blue light
must produce radical pairs with lifetimes longer than about a microsecond.
Cryptochrome 1a (gwCry1a) and the photolyase-homology-region of Cry1
(gwCry1-PHR) from the migratory garden warbler were recombinantly expressed
and purified from a baculovirus/Sf9 cell expression system. Transient
absorption measurements show that these flavoproteins are indeed excited by
light in the blue spectral range leading to the formation of radicals with
millisecond lifetimes. These biophysical characteristics suggest that gwCry1a
is ideally suited as a primary light-mediated, radical-pair-based magnetic
compass recepto
The Effect of Higher-Order Curvature Terms on String Quantum Cosmology
Several new results regarding the quantum cosmology of the quadratic gravity
theory derived from the heterotic string effective action are presented. After
describing techniques for solving the Wheeler-De Witt equation with appropriate
boundary conditions, it is shown that this quantum cosmological model may be
compared with semiclassical theories of inflationary cosmology. In particular,
it should be possible to compute corrections to the standard inflationary model
perturbatively about a stable exponentially expanding classical background.Comment: 24 pages, TeX. Several remarks on operator ordering, the complete
computation of , and approximate solutions of the and
equations of motion, which are stable and exponentially expanding, have been
included. Substantial revision of equations (5)-(7), (10)-(20) from version
Supersymmetric Intersecting Branes on the Waves
We construct a general family of supersymmetric solutions in time- and
space-dependent wave backgrounds in general supergravity theories describing
single and intersecting p-branes embedded into time-dependent dilaton-gravity
plane waves of an arbitrary (isotropic) profile, with the brane world-volume
aligned parallel to the propagation direction of the wave. We discuss how many
degrees of freedom we have in the solutions. We also propose that these
solutions can be used to describe higher-dimensional time-dependent "black
holes", and discuss their property briefly.Comment: 12 pages, LaTe
Stability of the non-extremal enhancon solution I: perturbation equations
We consider the stability of the two branches of non-extremal enhancon
solutions. We argue that one would expect a transition between the two branches
at some value of the non-extremality, which should manifest itself in some
instability. We study small perturbations of these solutions, constructing a
sufficiently general ansatz for linearised perturbations of the non-extremal
solutions, and show that the linearised equations are consistent. We show that
the simplest kind of perturbation does not lead to any instability. We reduce
the problem of studying the more general spherically symmetric perturbation to
solving a set of three coupled second-order differential equations.Comment: 20 pages, 1 figure, references added, typos fixed, version to appear
in PR
All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz
Aims: We study the Galactic large-scale synchrotron emission by generating a
reliable all-sky spectral index map and temperature map at 45 MHz. Methods: We
use our observations, the published all-sky map at 408 MHz, and a
bibliographical compilation to produce a map corrected for zero-level offset
and extragalactic contribution. Results: We present full sky maps of the
Galactic emission at 45 MHz and the Galactic spectral index between 45 and 408
MHz with an angular resolution of 5\degs. The spectral index varies between 2.1
and 2.7, reaching values below 2.5 at low latitude because of thermal free-free
absorption and its maximum in the zone next to the Northern Spur.Comment: A&A accepte
Contact-controlled amoeboid motility induces dynamic cell trapping in 3D-microstructured surfaces.
On flat substrates, several cell types exhibit amoeboid migration, which is characterized by restless stochastic successions of pseudopod protrusions. The orientation and frequency of new membrane protrusions characterize efficient search modes, which can respond to external chemical stimuli as observed during chemotaxis in amoebae. To quantify the influence of mechanical stimuli induced by surface topography on the migration modes of the amoeboid model organism Dictyostelium discoideum, we apply high resolution motion analysis in microfabricated pillar arrays of defined density and geometry. Cell motion is analyzed by a two-state motility-model, distinguishing directed cellular runs from phases of isotropic migration that are characterized by randomly oriented cellular protrusions. Cells lacking myosin II or cells deprived of microtubules show significantly different behavior concerning migration velocities and migrational angle distribution, without pronounced attraction to pillars. We conclude that microtubules enhance cellular ability to react with external 3D structures. Our experiments on wild-type cells show that the switching from randomly formed pseudopods to a stabilized leading pseudopod is triggered by contact with surface structures. These alternating processes guide cells according to the available surface in their 3D environment, which we observed dynamically and in steady-state situations. As a consequence, cells perform "home-runs" in low-density pillar arrays, crawling from pillar to pillar, with a characteristic dwell time of 75 s. At the boundary between a flat surface and a 3D structured substrate, cells preferentially localize in contact with micropillars, due to the additionally available surface in the microstructured arrays. Such responses of cell motility to microstructures might open new possibilities for cell sorting in surface structured arrays
A new model for magnetoreception
Certain migratory birds can sense the earth's magnetic field. The nature of
this process is not yet properly understood. Here we offer a simple explanation
according to which birds literally `see' the local magnetic field: Our model
relates the well-established radical pair hypothesis to the phenomenon of
Haidinger's brush, a capacity to see the polarisation of light. This new
picture explains recent surprising experimental data indicating long lifetimes
for the radical pair. Moreover there is a clear evolutionary path toward this
field sensing mechanism: it is an enhancement of a weak effect that may be
present in many species.Comment: 8 pages, 5 figures, version of final published pape
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