1,380 research outputs found
Spin up and phase fluctuations in the timing of the accreting millisecond pulsar XTE J1807-294
We performed a timing analysis of the 2003 outburst of the accreting X-ray
millisecond pulsar XTE J1807-294 observed by RXTE. Using recently refined
orbital parameters we report for the first time a precise estimate of the spin
frequency and of the spin frequency derivative. The phase delays of the pulse
profile show a strong erratic behavior superposed to what appears as a global
spin-up trend. The erratic behavior of the pulse phases is strongly related to
rapid variations of the light curve, making it very difficult to fit these
phase delays with a simple law. As in previous cases, we have therefore
analyzed separately the phase delays of the first harmonic and of the second
harmonic of the spin frequency, finding that the phases of the second harmonic
are far less affected by the erratic behavior. In the hypothesis that the
second harmonic pulse phase delays are a good tracer of the spin frequency
evolution we give for the first time a estimation of the spin frequency
derivative in this source. The source shows a clear spin-up of Hz sec (1 confidence level). The
largest source of uncertainty in the value of the spin-up rate is given by the
uncertainties on the source position in the sky. We discuss this systematics on
the spin frequency and its derivative.Comment: 17 pages, 4 figures, Accepted by Ap
Effects of different simplified milk recording methods on genetic evaluation with test-day animal model
The aims of the present study were to compare estimated breeding values (EBV) for milk yield using different testing schemes with a test-day animal model and to evaluate the effect of different testing schemes on the ranking of top sheep. Alternative recording schemes that use less information than that currently obtained with a monthly test-day schedule were employed to estimate breeding values. A random regression animal mixed model that used a spline function of days in milk was fitted. EBVs obtained with alternative recording schemes showed different degrees of Spearman correlation with EBVs obtained using the monthly recording scheme. These correlations ranged from 0.77 to 0.92. A reduction in accuracy and intensity of selection could be anticipated if these alternative schemes are used; more research in this area is needed to reduce the costs of test-day recording
Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305
We perform a timing analysis on RXTE data of the accreting millisecond pulsar
XTE J1751-305 observed during the April 2002 outburst. After having corrected
for Doppler effects on the pulse phases due to the orbital motion of the
source, we performed a timing analysis on the phase delays, which gives, for
the first time for this source, an estimate of the average spin frequency
derivative = (3.7 +/- 1.0)E-13 Hz/s. We discuss the torque resulting
from the spin-up of the neutron star deriving a dynamical estimate of the mass
accretion rate and comparing it with the one obtained from X-ray flux.
Constraints on the distance to the source are discussed, leading to a lower
limit of \sim 6.7 kpc.Comment: 7 pages, 3 figures, Accepted for publication by MNRA
Timing of the Accreting Millisecond Pulsar XTE J1814-338
We present a precise timing analysis of the accreting millisecond pulsar XTE
J1814-338 during its 2003 outburst, observed by RXTE. A full orbital solution
is given for the first time; Doppler effects induced by the motion of the
source in the binary system were corrected, leading to a refined estimate of
the orbital period, P_orb=15388.7229(2)s, and of the projected semimajor axis,
a sini/c= 390.633(9) lt-ms. We could then investigate the spin behaviour of the
accreting compact object during the outburst. We report here a refined value of
the spin frequency (nu=314.35610879(1) Hz) and the first estimate of the spin
frequency derivative of this source while accreting (nu^dot=(-6.7 +/- 0.7)
10^(-14) Hz/s). This spin down behaviour arises when both the fundamental
frequency and the second harmonic are taken into consideration. We discuss this
in the context of the interaction between the disc and the quickly rotating
magnetosphere, at accretion rates sufficiently low to allow a threading of the
accretion disc in regions where the Keplerian velocity is slower than the
magnetosphere velocity. We also present indications of a jitter of the pulse
phases around the mean trend, which we argue results from movements of the
accreting hotspots in response to variations of the accretion rate.Comment: 7 pages, 4 figures, Accepted for publication by MNRA
Protein adsorption onto Fe3O4 nanoparticles with opposite surface charge and its impact on cell uptake
Nanoparticles (NPs) engineered for biomedical applications are meant to be in
contact with protein-rich physiological fluids. These proteins are usually
adsorbed onto the NP surface, forming a swaddling layer called protein corona
that influences cell internalization. We present a study on protein adsorption
onto different magnetic NPs (MNPs) when immersed in cell culture medium, and
how these changes affect the cellular uptake. Two colloids with magnetite cores
of 25 nm, same hydrodynamic size and opposite surface charge were in situ
coated with (a) positive polyethyleneimine (PEI-MNPs) and (b) negative
poly(acrylic acid) (PAA-MNPs). After few minutes of incubation in cell culture
medium the wrapping of the MNPs by protein adsorption resulted in a 5-fold size
increase. After 24 h of incubation large MNP-protein aggregates with
hydrodynamic sizes 1500 to 3000 nm (PAA-MNPs and PEI-MNPs respectively) were
observed. Each cluster contained an estimated number of magnetic cores between
450 and 1000, indicating the formation of large aggregates with a "plum
pudding" structure of MNPs embedded into a protein network of negative surface
charge irrespective of the MNP_core charge. We demonstrated that PEI-MNPs are
incorporated in much larger amounts than the PAA-MNPs units. Quantitative
analysis showed that SH-SY5Y cells can incorporate 100 per cent of the added
PEI-MNPs up to about 100 pg per cell, whereas for PAA-MNPs the uptake was less
than 50 percent. The final cellular distribution showed also notable
differences regarding partial attachment to the cell membrane. These results
highlight the need to characterize the final properties of MNPs after protein
adsorption in biological media, and demonstrate the impact of these properties
on the internalization mechanisms in neural cells.Comment: 32 pages, 10 figure
Estimation of genetic and phenotypic parameters for bacteriological status of the udder,somatic cell score,and milk yield in dairy sheep using a threshold animal model
The objective of this study was to estimate the genetic parameters for infection status (INF), as indicator of mastitis, SCS (i.e., log-transformed SCC), and milk yield (MY), by using a Gibbs sampling algorithm. The data comprised 17,843 test-day records of 2,040 ewes. The pedigree file included 2,948 animals. A bivariate variance component analysis was performed using the TM software. Fixed effects considered in the analysis were litter size, parity, flock by test-day interaction, year by season of lambing interaction, and stage of lactation; whereas the animal, and the permanent environmental effect within and across lactations were considered as random as well as the error. Flat priors were used for both fixed effects and variance components. Parameters were drawn from the posterior conditional distributions. The posterior means of heritability for MY, SCS and INF were equal to 0.14, 0.09, and 0.09, respectively; whereas the repeatability within lactation was around 0.30 for the three traits, and ranged between 0.29 and 0.41 across lactations. The genetic correlation between INF and SCS was equal to 0.93, suggesting that selection for low SCS would also lead to a reduced incidence of mastitis. On the other hand, the positive and moderate genetic correlation between mastitis and milk yield (0.59) confirms the antagonistic association between udder health and milk yield. Therefore, in breeding programs that emphasize milk yield, the unfavorable genetic correlation between milk yield and mastitis, may result in an increased incidence of the latter
Genetic parameters for milk somatic cell score and relationships with production traits in primiparous dairy sheep
A total of 13,066 first-lactation test-day records of 2,277 Valle del Belice ewes from 17 flocks were used to estimate genetic parameters for somatic cell scores (SCS) and milk production traits, using a repeatability test-day animal model. Heritability estimates were low
and ranged from 0.09 to 0.14 for milk, fat, and protein yields, and contents. For SCS, the heritability of 0.14 was relatively high. The repeatabilities were moderate and ranged from 0.29 to 0.47 for milk production traits. The repeatability for SCS was 0.36. Flock-test-day explained a large proportion of the variation for milk production traits, but it did not have a big effect on SCS. The genetic correlations of fat and protein yields with fat and protein percentages were positive and high,indicating a strong association between these traits. The genetic correlations of milk production traits with SCS were positive and ranged from 0.16 to 0.31. The results showed that SCS is a heritable trait in Valle del Belice sheep and that single-trait selection for increased milk production will also increase SCS
Timing of the accreting millisecond pulsar IGR~J17511--3057
{Timing analysis of Accretion-powered Millisecond Pulsars (AMPs) is a
powerful tool to probe the physics of compact objects. The recently discovered
\newigrj is the 12 discovered out of the 13 AMPs known. The Rossi XTE satellite
provided an extensive coverage of the 25 days-long observation of the source
outburst.} {Our goal is to investigate the complex interaction between the
neutron star magnetic field and the accretion disk, determining the angular
momentum exchange between them. The presence of a millisecond coherent flux
modulation allows us to investigate such interaction from the study of pulse
arrival times. In order to separate the neutron star proper spin frequency
variations from other effects, a precise set of orbital ephemeris is
mandatory.} {Using timing techniques, we analysed the pulse phase delays
fitting differential corrections to the orbital parameters. To remove the
effects of pulse phase fluctuations we applied the timing technique already
successfully applied to the case of an another AMP, XTE J1807-294.} {We report
a precise set of orbital ephemeris. We demonstrate that the companion star is a
main sequence star. We find pulse phase delays fluctuations on the first
harmonic with a characteristic amplitude of about 0.05, similar to what also
observed in the case of the AMP XTE J1814-338. For the second time an AMP shows
a third harmonic detected during the entire outburst. The first harmonic phase
delays show a puzzling behaviour, while the second harmonic phase delays show a
clear spin-up. Also the third harmonic shows a spin-up, although not highly
significant (3 c.l.). The presence of a fourth harmonic is also
reported. In the hypothesis that the second harmonic is a good tracer of the
spin frequency of the neutron star, we find a mean spin frequency derivative
for this source of \np{1.65(18)}{-13} Hz s.} (continue ...)Comment: 9 pages, 12 figures, A&A accepted on 23/10/201
A re-analysis of the NuSTAR and XMM-Newton broad-band spectrum of Ser~X-1
Context: Ser X-1 is a well studied LMXB which clearly shows a broad iron
line. Recently, Miller et al. (2103) have presented broad-band, high quality
NuSTAR data of SerX-1.Using relativistically smeared self-consistent reflection
models, they find a value of R_in close to 1.0 R_ISCO (corresponding to 6 R_g),
and a low inclination angle, less than 10 deg. Aims: The aim of this paper is
to probe to what extent the choice of reflection and continuum models (and
uncertainties therein) can affect the conclusions about the disk parameters
inferred from the reflection component. To this aim we re-analyze all the
available public NuSTAR and XMM-Newton. Ser X-1 is a well studied source, its
spectrum has been observed by several instruments, and is therefore one of the
best sources for this study. Methods: We use slightly different continuum and
reflection models with respect to those adopted in literature for this source.
In particular we fit the iron line and other reflection features with
self-consistent reflection models as reflionx (with a power-law illuminating
continuum modified with a high energy cutoff to mimic the shape of the incident
Comptonization spectrum) and rfxconv. With these models we fit NuSTAR and
XMM-Newton spectra yielding consistent spectral results. Results: Our results
are in line with those already found by Miller et al. (2013) but less extreme.
In particular, we find the inner disk radius at about 13 R_g and an inclination
angle with respect to the line of sight of about 27 deg. We conclude that,
while the choice of the reflection model has little impact on the disk
parameters, as soon as a self-consistent model is used, the choice of the
continuum model can be important in the precise determination of the disk
parameters from the reflection component. Hence broad-band X-ray spectra are
highly preferable to constrain the continuum and disk parameters.Comment: 13 pages including 8 figures. Accepted for publication in A&
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