1,383 research outputs found
The Cryogenic AntiCoincidence detector for ATHENA X-IFU: a scientific assessment of the observational capabilities in the hard X-ray band
ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028
towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a
cryogenic spectrometer based on a large array of TES microcalorimeters, able to
perform integral field spectrography in the 0.2-12 keV band (2.5 eV FWHM at 6
keV). The X-IFU sensitivity is highly degraded by the particle background
expected in the L2 orbit, which is induced by primary protons of both galactic
and solar origin, and mostly by secondary electrons. To reduce the particle
background level and enable the mission science goals, the instrument
incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES
based detector, placed <1 mm below the main array. In this paper we report a
scientific assessment of the CryoAC observational capabilities in the hard
X-ray band (E>10 keV). The aim of the study has been to understand if the
present detector design can be improved in order to enlarge the X-IFU
scientific capability on an energy band wider than the TES array. This is
beyond the CryoAC baseline, being this instrument aimed to operate as
anticoincidence particle detector and not conceived to perform X-ray
observations.Comment: Accepted for publication on Experimental Astronom
First assessment of non-X-ray background in Line Emission Mapper (LEM) focal plane detector.
The LEM (Line Emission Mapper) mission proposal envisions a cryogenic microcalorimeter array optimized for the 0.2–2 keV energy band, based on the X-IFU heritage. The array will consist of 13,806 absorber pixels with a 290 µm pitch, in hexagonal arrangement, that for a 4 m focal length will cover a solid angle equal to 29.4 square degrees. The orbit for LEM is currently under study with the Sun-Earth Lagrange points L1 and L2 possible candidates.
For what concerns the non X-Ray background (NXB), the premises are very similar to the X-IFU case. The background estimates are performed using Monte Carlo simulations with the Geant4 software [RD1] and, as a consequence, minor modifications to the X-IFU simulations can give precious insights on the NXB level to be expected for the instrument.
Furthermore, it is possible to test the effect of changes to the instrument mass model (sensitivity analysis) and identify the configuration that optimizes the detector performances
Impact of chronic exposure to bevacizumab on EpCAM-based detection of circulating tumor cells
BACKGROUND:
Circulating tumor cells (CTCs) are often undetected through the immunomagnetic epithelial cell adhesion molecule (EpCAM)-based CellSearch(®) System in breast and colorectal cancer (CRC) patients treated with bevacizumab (BEV), where low CTC numbers have been reported even in patients with evidence of progression of disease. To date, the reasons for this discrepancy have not been clarified. This study was carried out to investigate the molecular and phenotypic changes in CRC cells after chronic exposure to BEV in vitro.
METHODS:
The human CRC cell line WiDr was exposed to a clinically relevant dose of BEV for 3 months in vitro. The expression of epithelial and mesenchymal markers and EpCAM isoforms was determined by western blotting and immunofluorescence. To evaluate the impact of EpCAM variant isoforms expression on CTC enumeration by CellSearch(®), untreated and treated colon cancer cells were spiked into 7.5 mL of blood from a healthy donor and enumerated by CellSearch(®).
RESULTS:
Chronic exposure of CRC cell line to BEV induced decreased expression of EpCAM 40 kDa isoform and increased expression EpCAM 42 kDa isoform, together with a decreased expression of cytokeratins (CK), while no evidence of epithelial to mesenchymal transition (EMT) in treated cells was observed. The recovery rate of cells through CellSearch(®) was gradually reduced in course of treatment with BEV, being 84%, 70% and 40% at 1, 2 and 3 months, respectively.
CONCLUSIONS:
We hypothesize that BEV may prevent CellSearch(®) from capturing CTCs through altering EpCAM isoforms
Results of a research regarding the variability of spring depletion curves
Springs, no recharge periods, discharge process, depletion coefficient
Geant4 simulations of soft proton scattering in X-ray optics. A tentative validation using laboratory measurements
Low energy protons (< 300 keV) can enter the field of view of X-ray space
telescopes, scatter at small incident angles, and deposit energy on the
detector, causing intense background flares at the focal plane or in the most
extreme cases, damaging the X-ray detector. A correct modelization of the
physics process responsible for the grazing angle scattering processes is
mandatory to evaluate the impact of such events on the performance of future
X-ray telescopes as the ESA ATHENA mission. For the first time the Remizovich
model, in the approximation of no energy losses, is implemented top of the
Geant4 release 10.2. Both the new scattering physics and the built-in Coulomb
scattering are used to reproduce the latest experimental results on grazing
angle proton scattering. At 250 keV multiple scattering delivers large proton
angles and it is not consistent with the observation. Among the tested models,
the single scattering seems to better reproduce the scattering efficiency at
the three energies but energy loss obtained at small scattering angles is
significantly lower than the experimental values. In general, the energy losses
obtained in the experiment are higher than what obtained by the simulation. The
experimental data are not completely representative of the soft proton
scattering experienced by current X-ray telescopes because of the lack of
measurements at low energies (< 200 keV) and small reflection angles, so we are
not able to address any of the tested models as the one that can certainly
reproduce the scattering behavior of low energy protons expected for the ATHENA
mission. We can, however, discard multiple scattering as the model able to
reproduce soft proton funneling, and affirm that Coulomb single scattering can
represent, until further measurements, the best approximation of the proton
scattered angular distribution at the exit of X-ray optics.Comment: submitted to Experimental Astronom
Laboratory evolution of copper tolerant yeast strains
<p>Abstract</p> <p>Background</p> <p>Yeast strains endowed with robustness towards copper and/or enriched in intracellular Cu might find application in biotechnology processes, among others in the production of functional foods. Moreover, they can contribute to the study of human diseases related to impairments of copper metabolism. In this study, we investigated the molecular and physiological factors that confer copper tolerance to strains of baker's yeasts.</p> <p>Results</p> <p>We characterized the effects elicited in natural strains of <it>Candida humilis </it>and <it>Saccharomyces cerevisiae </it>by the exposure to copper in the culture broth. We observed that, whereas the growth of <it>Saccharomyces </it>cells was inhibited already at low Cu concentration, <it>C. humilis </it>was naturally robust and tolerated up to 1 g · L<sup>-1 </sup>CuSO<sub>4 </sub>in the medium. This resistant strain accumulated over 7 mg of Cu per gram of biomass and escaped severe oxidative stress thanks to high constitutive levels of superoxide dismutase and catalase. Both yeasts were then "evolved" to obtain hyper-resistant cells able to proliferate in high copper medium. While in <it>S. cerevisiae </it>the evolution of robustness towards Cu was paralleled by the increase of antioxidative enzymes, these same activities decreased in evolved hyper-resistant <it>Candida </it>cells. We also characterized in some detail changes in the profile of copper binding proteins, that appeared to be modified by evolution but, again, in a different way in the two yeasts.</p> <p>Conclusions</p> <p>Following evolution, both <it>Candida </it>and <it>Saccharomyces </it>cells were able to proliferate up to 2.5 g · L<sup>-1 </sup>CuSO<sub>4 </sub>and to accumulate high amounts of intracellular copper. The comparison of yeasts differing in their robustness, allowed highlighting physiological and molecular determinants of natural and acquired copper tolerance. We observed that different mechanisms contribute to confer metal tolerance: the control of copper uptake, changes in the levels of enzymes involved in oxidative stress response and changes in the copper-binding proteome. However, copper elicits different physiological and molecular reactions in yeasts with different backgrounds.</p
Thermal assessment of the ATHENA X-IFU passive shielding for the particles background reduction.
Updates on the background estimates for the X-IFU instrument onboard of the ATHENA mission
ATHENA, with a launch foreseen in 2028 towards the L2 orbit, addresses the
science theme "The Hot and Energetic Universe", coupling a high-performance
X-ray Telescope with two complementary focal-plane instruments. One of these,
the X-ray Integral Field Unit (X-IFU) is a TES based kilo-pixel array providing
spatially resolved high-resolution spectroscopy (2.5 eV at 6 keV) over a 5
arcmin FoV. The background for this kind of detectors accounts for several
components: the diffuse Cosmic X-ray Background, the low energy particles
(<~100 keV) focalized by the mirrors and reaching the detector from inside the
field of view, and the high energy particles (>~100 MeV) crossing the
spacecraft and reaching the focal plane from every direction. Each one of these
components is under study to reduce their impact on the instrumental
performances. This task is particularly challenging, given the lack of data on
the background of X-ray detectors in L2, the uncertainties on the particle
environment to be expected in such orbit, and the reliability of the models
used in the Monte Carlo background computations. As a consequence, the
activities addressed by the group range from the reanalysis of the data of
previous missions like XMM-Newton, to the characterization of the L2
environment by data analysis of the particle monitors onboard of satellites
present in the Earth magnetotail, to the characterization of solar events and
their occurrence, and to the validation of the physical models involved in the
Monte Carlo simulations. All these activities will allow to develop a set of
reliable simulations to predict, analyze and find effective solutions to reduce
the particle background experienced by the X-IFU, ultimately satisfying the
scientific requirement that enables the science of ATHENA. While the activities
are still ongoing, we present here some preliminary results already obtained by
the group
An XMM-Newton proton response matrix
Soft protons constitute an important source of background in focusing X-ray telescopes, as Chandra and XMM-Newton experience has shown. The optics in fact transmit them to the focal plane with efficiency similar to the X-ray photon one. This effect is a good opportunity to study the environment of the Earth magnetosphere crossed by the X-ray satellite orbits, provided that we can link the spectra detected by the instruments with the ones impacting on the optics. For X-ray photons this link has the form of the so-called response matrix that includes the optics effective area and the energy redistribution in the detectors. Here we present a first attempt to produce a proton response matrix exploiting ray-tracing and GEANT4 simulations with the final aim to be able to analyse XMM-Newton soft proton data and link them to the external environment. If the procedure is found to be reliable, it can be applied to any future X-ray missions to predict the soft particles spectra impacting on the focal plane instruments
- …