31 research outputs found
Tubulization with chitosan guides for the repair of long gap peripheral nerve injury in the rat
Biosynthetic guides can be an alternative to nerve grafts for reconstructing severely injured peripheral nerves. The aim of this study was to evaluate the regenerative capability of chitosan tubes to bridge critical nerve gaps (15 mm long) in the rat sciatic nerve compared with silicone (SIL) tubes and nerve autografts (AGs). A total of 28 Wistar Hannover rats were randomly distributed into four groups (n = 7 each), in which the nerve was repaired by SIL tube, chitosan guides of low (∼2%, DAI) and medium (∼5%, DAII) degree of acetylation, and AG. Electrophysiological and algesimetry tests were performed serially along 4 months follow-up, and histomorphometric analysis was performed at the end of the study. Both groups with chitosan tubes showed similar degree of functional recovery, and similar number of myelinated nerve fibers at mid tube after 4 months of implantation. The results with chitosan tubes were significantly better compared to SIL tubes (P < 0.01), but lower than with AG (P < 0.01). In contrast to AG, in which all the rats had effective regeneration and target reinnervation, chitosan tubes from DAI and DAII achieved 43 and 57% success, respectively, whereas regeneration failed in all the animals repaired with SIL tubes. This study suggests that chitosan guides are promising conduits to construct artificial nerve grafts
High-speed, energy-resolved, STJ observations of the AM Her system V2301 Oph
We present high time-resolution optical energy-resolved photometry of the
eclipsing cataclysmic variable V2301 Oph made using the ESA S-Cam detector, an
array of photon counting super-conducting tunnel junction (STJ) devices with
intrinsic energy resolution. Three eclipses were observed, revealing
considerable variation in the eclipse shape, particularly during ingress. The
eclipse shape is shown to be understood in terms of AM Her accretion via a
bright stream, with very little contribution from the white dwarf photosphere
and/or hotspot. About two thirds of the eclipsed light arises in the threading
region. Variation in the extent of the threading region can account for most of
the variations observed between cycles. Spectral fits to the data reveal a
10,000K blackbody continuum with strong, time-varying emission lines of
hydrogen and helium. This is the first time that stellar emission lines have
been detected in the optical band using a non-dispersive photon-counting
system.Comment: Accepted A&
Quasi-periodic oscillations in accreting magnetic white dwarfs II. The asset of numerical modelling for interpreting observations
Magnetic cataclysmic variables are close binary systems containing a strongly
magnetized white dwarf that accretes matter coming from an M-dwarf companion.
High-energy radiation coming from those objects is emitted from the accretion
column close to the white dwarf photosphere at the impact region. Its
properties depend on the characteristics of the white dwarf and an accurate
accretion column model allows the properties of the binary system to be
inferred, such as the white dwarf mass, its magnetic field, and the accretion
rate. We study the temporal and spectral behaviour of the accretion region and
use the tools we developed to accurately connect the simulation results to the
X-ray and optical astronomical observations. The radiation hydrodynamics code
Hades was adapted to simulate this specific accretion phenomena. Classical
approaches were used to model the radiative losses of the two main radiative
processes: bremsstrahlung and cyclotron. The oscillation frequencies and
amplitudes in the X-ray and optical domains are studied to compare those
numerical results to observational ones. Different dimensional formulae were
developed to complete the numerical evaluations. The complete characterization
of the emitting region is described for the two main radiative regimes: when
only the bremsstrahlung losses and when both cyclotron and bremsstrahlung
losses are considered. The effect of the non-linear cooling in- stability
regime on the accretion column behaviour is analysed. Variation in luminosity
on short timescales (~ 1 s quasi-periodic oscillations) is an expected
consequence of this specific dynamic. The importance of secondary shock
instability on the quasi-periodic oscillation phenomenon is discussed. The
stabilization effect of the cyclotron process is confirmed by our numerical
simulations, as well as the power distribution in the various modes of
oscillation.Comment: 13 pages, 13 figures, 2 tables. Accepted for publication in A&
Long-term eclipse timing of white dwarf binaries: an observational hint of a magnetic mechanism at work
We present a long-term programme for timing the eclipses of white dwarfs in close binaries to measure apparent and/or real variations in their orbital periods. Our programme includes 67 close binaries, both detached and semi-detached and with M-dwarfs, K-dwarfs, brown dwarfs or white dwarfs secondaries. In total, we have observed more than 650 white dwarf eclipses. We use this sample to search for orbital period variations and aim to identify the underlying cause of these variations. We find that the probability of observing orbital period variations increases significantly with the observational baseline. In particular, all binaries with baselines exceeding 10 yr, with secondaries of spectral type K2 – M5.5, show variations in the eclipse arrival times that in most cases amount to several minutes. In addition, among those with baselines shorter than 10 yr, binaries with late spectral type (>M6), brown dwarf or white dwarf secondaries appear to show no orbital period variations. This is in agreement with the so-called Applegate mechanism, which proposes that magnetic cycles in the secondary stars can drive variability in the binary orbits. We also present new eclipse times of NN Ser, which are still compatible with the previously published circumbinary planetary system model, although only with the addition of a quadratic term to the ephemeris. Finally, we conclude that we are limited by the relatively short observational baseline for many of the binaries in the eclipse timing programme, and therefore cannot yet draw robust conclusions about the cause of orbital period variations in evolved, white dwarf binaries
Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae
We report precise measures of the orbital and superhump period in twenty more
dwarf novae. For ten stars, we report new and confirmed spectroscopic periods -
signifying the orbital period P_o - as well as the superhump period P_sh. These
are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, and
RZ Sge. For the remaining ten, we report a medley of P_o and P_sh measurements
from photometry; most are new, with some confirmations of previous values.
These are KV And, LL And, WX Cet, MM Hya, AO Oct, V2051 Oph, NY Ser, KK Tel, HV
Vir, and RX J1155.4-5641.
Periods, as usual, can be measured to high accuracy, and these are of special
interest since they carry dynamical information about the binary. We still have
not quite learned how to read the music, but a few things are clear. The
fractional superhump excess epsilon [=(P_sh-P_o)/P_o] varies smoothly with P_o.
The scatter of the points about that smooth curve is quite low, and can be used
to limit the intrinsic scatter in M_1, the white dwarf mass, and the
mass-radius relation of the secondary. The dispersion in M_1 does not exceed
24%, and the secondary-star radii scatter by no more than 11% from a fixed
mass-radius relation. For the well-behaved part of epsilon(P_o) space, we
estimate from superhump theory that the secondaries are 18+-6% larger than
theoretical ZAMS stars. This affects some other testable predictions about the
secondaries: at a fixed P_o, it suggests that the secondaries are (compared
with ZAMS predictions) 40+-14% less massive, 12+-4% smaller, 19+-6% cooler, and
less luminous by a factor 2.5(7). The presence of a well-defined mass-radius
relation, reflected in a well-defined epsilon(P_o) relation, strongly limits
effects of nuclear evolution in the secondaries.Comment: PDF, 62 pages, 7 tables, 21 figures; accepted, in press, to appear
November 2003, PASP; more info at http://cba.phys.columbia.edu
The underluminous Type Ia Supernova 2005bl and the class of objects similar to SN 1991bg
Optical observations of the Type Ia supernova (SN Ia) 2005bl in NGC 4070,
obtained from -6 to +66 d with respect to the B-band maximum, are presented.
The photometric evolution is characterised by rapidly-declining light curves
and red colours at peak and soon thereafter. With M_B,max = -17.24 the SN is an
underluminous SN Ia, similar to the peculiar SNe 1991bg and 1999by. This
similarity also holds for the spectroscopic appearance, the only remarkable
difference being the likely presence of carbon in pre-maximum spectra of SN
2005bl. A comparison study among underluminous SNe Ia is performed, based on a
number of spectrophotometric parameters. Previously reported correlations of
the light-curve decline rate with peak luminosity and R(Si) are confirmed, and
a large range of post-maximum Si II lambda6355 velocity gradients is
encountered. 1D synthetic spectra for SN 2005bl are presented, which confirm
the presence of carbon and suggest an overall low burning efficiency with a
significant amount of leftover unburned material. Also, the Fe content in
pre-maximum spectra is very low, which may point to a low metallicity of the
precursor. Implications for possible progenitor scenarios of underluminous SNe
Ia are briefly discussed.Comment: 24 pages, 24 figures, accepted for publication in MNRA
SN 2005cs in M51 II. Complete Evolution in the Optical and the Near-Infrared
We present the results of the one year long observational campaign of the
type II-plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the
Whirlpool Galaxy). This extensive dataset makes SN 2005cs the best observed
low-luminosity, 56Ni-poor type II-plateau event so far and one of the best
core-collapse supernovae ever. The optical and near-infrared spectra show
narrow P-Cygni lines characteristic of this SN family, which are indicative of
a very low expansion velocity (about 1000 km/s) of the ejected material. The
optical light curves cover both the plateau phase and the late-time radioactive
tail, until about 380 days after core-collapse. Numerous unfiltered
observations obtained by amateur astronomers give us the rare opportunity to
monitor the fast rise to maximum light, lasting about 2 days. In addition to
optical observations, we also present near-infrared light curves that (together
with already published UV observations) allow us to construct for the first
time a reliable bolometric light curve for an object of this class. Finally,
comparing the observed data with those derived from a semi-analytic model, we
infer for SN 2005cs a 56Ni mass of about 0.003 solar masses, a total ejected
mass of 8-13 solar masses and an explosion energy of about 3 x 10^50 erg.Comment: 18 pages, 18 figures, accepted for publication in MNRA
WeCAPP -Wendelstein Calar Alto pixellensing project I
We present WeCAPP, a long term monitoring project searching for microlensing events towards M 3