402 research outputs found
PHYSIOLOGICAL AND INDUCED APOPTOSIS IN SEA URCHIN LAEVAE UNDERGOING METAMORPHOSIS
Paracentrotus lividus embryos at the early pluteus stage undergo spontaneous apoptosis. Using a TUNEL (TdT-mediated dUTP Nick-End Labelling) assay on whole mount embryos, we showed that there was a different distribution of the apoptotic cells in different optical sections. Not more than 20% of cells in plutei were spontaneously apoptotic, as confirmed by the counts of dissociated ectoderm and intestine cells. Observation of larva stages closer to metamorphosis confirmed that apoptosis is a physiological event for the development of the adult. In particular, larvae at different developmental stages showed apoptotic cells in the oral and aboral arms, intestine, ciliary band and both apical and oral ganglia. Moreover, we found that the number of apoptotic cells decreased in later larva stages, possibly because in the organism approaching metamorphosis, a smaller number of cells needs to be eliminated. Furthermore, combined phorbol ester (TPA) and heat shock treatment enhanced apoptosis by increasing the number of cells involved in the phenomenon
Adult exposures from MDCT including multiphase studies: first Italian nationwide survey.
OBJECTIVES:
To evaluate the radiation dose in routine multidetector computed tomography (MDCT) examinations in Italian population.
METHODS:
This was a retrospective multicentre study included 5,668 patients from 65 radiology departments who had undergone common CT protocols: head, chest, abdomen, chest–abdomen–pelvis (CAP), spine and cardiac. Data included patient characteristics, CT parameters, volumetric CT dose index (CTDIvol) and dose length product (DLP) for each CT acquisition phase. Descriptive statistics were calculated, and a multi-regression analysis was used to outline the main factors affecting exposure.
RESULTS:
The 75th percentiles of CTDIvol (mGy) and DLP (mGy cm) for whole head were 69 mGy and 1,312 mGy cm, respectively; for chest, 15 mGy and 569 mGy cm; spine, 42 mGy and 888 mGy cm; cardiac, 7 mGy and 131 mGy cm for calcium score, and 61 mGy and 1,208 mGy cm for angiographic CT studies. High variability was present in the DLP of abdomen and CAP protocols, where multiphase examinations dominated (71 % and 73 % respectively): for abdomen, 18 mGy, with 555 and 920 mGy cm in abdomen and abdomen–pelvis acquisitions respectively; for CAP, 17 mGy, with 508, 850 and 1,200 mGy cm in abdomen, abdomen–pelvis and CAP acquisitions respectively.
CONCLUSION:
The results of this survey could help in the definition of updated diagnostic reference levels (DRL)
Radiation dose from multidetector CT studies in children: results from the first Italian nationwide survey
Background Multidetector CT (MDCT) scanners have con- tributed to the widespread use of CT in paediatric imaging. However, concerns are raised for the associated radiation exposure. Very few surveys on radiation exposure from MDCT studies in children are available.
Objective The aim of this study was to outline the status of radiation exposure in children from MDCT practice in Italy. Materials and methods In this retrospective multicentre study we asked Italian radiology units with an MDCT scanner with at least 16 slices to provide dosimetric and acquisition param- eters of CT examinations in three age groups (1–5, 6–10, 11– 15 years) for studies of head, chest and abdomen. The dosi- metric results were reported in terms of third-quartile volu- metric CT dose index (CTDIvol) (mGy), size-specific dose estimate (SSDE) (mGy), dose length product (DLP) (mGy cm), and total DLP for multiphase studies. These results were compared with paediatric European and adult Italian published data. A multivariate analysis assessed the association of CTDIvol with patient characteristics and scanning modalities.
Results We collected data from 993 MDCT examinations performed at 25 centres. For age groups 1–5 years, 6–10 years and 11–15 years, the CTDIvol, DLP and total DLP values were statistically significantly below the values observed in our analogous national survey in adults, although the difference decreased with increasing age. CTDIvol variability among centres was statistically significant (variance = 0.07; 95% confidence interval = 0.03–0.16; P < 0.001).
Conclusions This study reviewed practice in Italian centres performing paediatric imaging with MDCT scanners. The variability of doses among centres suggests that the use of standardised CT protocols should be encourage
A possible cyclotron resonance scattering feature near 0.7 keV in X1822-371
We analyse all available X-ray observations of X1822-371 made with
XMM-Newton, Chandra, Suzaku and INTEGRAL satellites. The observations were not
simultaneous. The Suzaku and INTEGRAL broad band energy coverage allows us to
constrain the spectral shape of the continuum emission well. We use the model
already proposed for this source, consisting of a Comptonised component
absorbed by interstellar matter and partially absorbed by local neutral matter,
and we added a Gaussian feature in absorption at keV. This addition
significantly improves the fit and flattens the residuals between 0.6 and 0.8
keV. We interpret the Gaussian feature in absorption as a cyclotron resonant
scattering feature (CRSF) produced close to the neutron star surface and derive
the magnetic field strength at the surface of the neutron star, G for a radius of 10 km. We derive the pulse period in the
EPIC-pn data to be 0.5928850(6) s and estimate that the spin period derivative
of X1822-371 is s/s using all available
pulse period measurements. Assuming that the intrinsic luminosity of
X1822-371is at the Eddington limit and using the values of spin period and spin
period derivative of the source, we constrain the neutron star and companion
star masses. We find the neutron star and the companion star masses to be M and M, respectively, for a
neutron star radius of 10 km.In a self-consistent scenario in which X1822-371
is spinning-up and accretes at the Eddington limit, we estimate that the
magnetic field of the neutron star is G for a
neutron star radius of 10 km. If our interpretation is correct, the Gaussian
absorption feature near 0.7 keV is the very first detection of a CRSF below 1
keV in a LMXB. (abridged)Comment: 14 pages, 12 figures, accepted for publication in A&
An XMM-Newton and INTEGRAL view on the hard state of EXO 1745-248 during its 2015 outburst
CONTEXT - Transient low-mass X-ray binaries (LMXBs) often show outbursts
lasting typically a few-weeks and characterized by a high X-ray luminosity
( erg/sec), while for most of the time they are
found in X-ray quiescence ( erg/sec). EXO 1745-248
is one of them. AIMS - The broad-band coverage, and the sensitivity of
instrument on board of {\xmm} and {\igr}, offers the opportunity to
characterize the hard X-ray spectrum during {\exo} outburst. METHODS - In this
paper we report on quasi-simultaneous {\xmm} and {\igr} observations of the
X-ray transient {\exo} located in the globular cluster Terzan 5, performed ten
days after the beginning of the outburst (on 2015 March 16th) shown by the
source between March and June 2015. The source was caught in a hard state,
emitting a 0.8-100 keV luminosity of ~{\lumcgs}. RESULTS - The
spectral continuum was dominated by thermal Comptonization of seed photons with
temperature keV, by a cloud with moderate optical depth
and electron temperature keV. A weaker soft
thermal component at temperature --0.7 keV and compatible
with a fraction of the neutron star radius was also detected. A rich emission
line spectrum was observed by the EPIC-pn on-board {\xmm}; features at energies
compatible with K- transitions of ionized sulfur, argon, calcium and
iron were detected, with a broadness compatible with either thermal Compton
broadening or Doppler broadening in the inner parts of an accretion disk
truncated at gravitational radii from the neutron star. Strikingly, at
least one narrow emission line ascribed to neutral or mildly ionized iron is
needed to model the prominent emission complex detected between 5.5 and 7.5
keV. (Abridged)Comment: 14 pages, 6 figure, 2 tables. Accepted for publication on A&A
(21/03/2017
GRO J1744-28: an intermediate B-field pulsar in a low mass X-ray binary
The bursting pulsar, GRO J1744-28, went again in outburst after 18
years of quiescence in mid-January 2014. We studied the broad-band, persistent,
X-ray spectrum using X-ray data from a XMM-Newton observation, performed almost
at the peak of the outburst, and from a close INTEGRAL observation, performed 3
days later, thus covering the 1.3-70.0 keV band. The spectrum shows a complex
continuum shape that cannot be modelled with standard high-mass X-ray pulsar
models, nor by two-components models. We observe broadband and peaked residuals
from 4 to 15 keV, and we propose a self-consistent interpretation of these
residuals, assuming they are produced by cyclotron absorption features and by a
moderately smeared, highly ionized, reflection component. We identify the
cyclotron fundamental at 4.7 keV, with hints for two possible harmonics
at 10.4 keV and 15.8 keV. The position of the cyclotron fundamental allows an
estimate for the pulsar magnetic field of (5.27 0.06) 10
G, if the feature is produced at its surface. From the dynamical and
relativistic smearing of the disk reflected component, we obtain a lower limit
estimate for the truncated accretion disk inner radius, ( 100 R),
and for the inclination angle (18-48). We also detect the
presence of a softer thermal component, that we associate with the emission
from an accretion disk truncated at a distance from the pulsar of 50-115 R.
From these estimates, we derive the magneto-spheric radius for disk accretion
to be 0.2 times the classical Alfv\'en radius for radial accretion.Comment: Accepted for publication in MNRA
Signature of the presence of a third body orbiting around XB 1916-053
The ultra-compact dipping source \object{XB 1916-053} has an orbital period
of close to 50 min and a companion star with a very low mass (less than 0.1
M). The orbital period derivative of the source was estimated to be
s/s through analysing the delays associated with the
dip arrival times obtained from observations spanning 25 years, from 1978 to
2002. The known orbital period derivative is extremely large and can be
explained by invoking an extreme, non-conservative mass transfer rate that is
not easily justifiable. We extended the analysed data from 1978 to 2014, by
spanning 37 years, to verify whether a larger sample of data can be fitted with
a quadratic term or a different scenario has to be considered. We obtained 27
delays associated with the dip arrival times from data covering 37 years and
used different models to fit the time delays with respect to a constant period
model.We find that the quadratic form alone does not fit the data. The data are
well fitted using a sinusoidal term plus a quadratic function or,
alternatively, with a series of sinusoidal terms that can be associated with a
modulation of the dip arrival times due to the presence of a third body that
has an elliptical orbit. We infer that for a conservative mass transfer
scenario the modulation of the delays can be explained by invoking the presence
of a third body with mass between 0.10-0.14 M, orbital period around
the X-ray binary system of close to 51 yr and an eccentricity of . In a non-conservative mass transfer scenario we estimate that the
fraction of matter yielded by the degenerate companion star and accreted onto
the neutron star is , the neutron star mass is
M, and the companion star mass is 0.028 M. (Abridged)Comment: 13 pages, 9 figures. Accepted for publication in A&
Cellular and molecular bases of biomineralization in sea urchin embryos
Sea urchin embryos construct their skeleton following a precise gene-regulated time- and space-dependent
programme, in concert with factors promoting cell adhesion and differentiation. The biomineral is deposited in a privileged extracellular space produced by the fused filopodia processes of the primary mesenchyme cells, the only cells producing a set of necessary matrix proteins. More than ten years ago we showed for the first time that signals from ectoderm cells promoted the expression of one of the major skeleton matrix genes by the primary mesenchyme cells. Since then, many of the crucial steps of this complex activation cascade, from ectoderm cells to embryonic spicules, have been elucidated. The experimental production of skeleton malformations, induced by the exposure to toxic metals or ionizing radiations, served as model to dissect the molecular mechanisms leading to biomineralization. With the aim of understanding the sea urchin
skeleton physiology, we analysed the expression of well-known and newly-identified biomineral-related genes, including
those coding for growth and transcription factors as well as for skeleton matrix proteins. This review summarizes our recent findings on sea urchin embryo skeletogenesis, with a particular attention to the role played by cellular and molecular signaling, approached by the use of experimentally induced skeleton malformations
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