309 research outputs found
Reading a GEM with a VLSI pixel ASIC used as a direct charge collecting anode
In MicroPattern Gas Detectors (MPGD) when the pixel size is below 100 micron
and the number of pixels is large (above 1000) it is virtually impossible to
use the conventional PCB read-out approach to bring the signal charge from the
individual pixel to the external electronics chain. For this reason a custom
CMOS array of 2101 active pixels with 80 micron pitch, directly used as the
charge collecting anode of a GEM amplifying structure, has been developed and
built. Each charge collecting pad, hexagonally shaped, realized using the top
metal layer of a deep submicron VLSI technology is individually connected to a
full electronics chain (pre-amplifier, shaping-amplifier, sample and hold,
multiplexer) which is built immediately below it by using the remaining five
active layers. The GEM and the drift electrode window are assembled directly
over the chip so the ASIC itself becomes the pixelized anode of a MicroPattern
Gas Detector. With this approach, for the first time, gas detectors have
reached the level of integration and resolution typical of solid state pixel
detectors. Results from the first tests of this new read-out concept are
presented. An Astronomical X-Ray Polarimetry application is also discussed.Comment: 11 pages, 14 figures, presented at the Xth Vienna Conference on
Instrumentation (Vienna, February 16-21 2004). For a higher resolution paper
contact [email protected]
Single-shot X-ray phase-contrast computed tomography with non-microfocal laboratory sources
We present a method that enables performing x-ray phase-contrast imaging (XPCI) computed tomography with a laboratory setup using a single image per projection angle, eliminating the need to move optical elements during acquisition. Theoretical derivation of the method is presented, and its validity conditions are provided. The object is assumed to be quasihomogeneous, i.e., to feature a ratio between the refractive index and the linear attenuation coefficient that is approximately constant across the field of view. The method is experimentally demonstrated on a plastics phantom and on biological samples using a continuous rotation acquisition scheme achieving scan times of a few minutes. Moreover, we show that such acquisition times can be further reduced with the use of a high-efficiency photon-counting detector. Thanks to its ability to substantially simplify the image-acquisition procedure and greatly reduce collection times, we believe this method represents a very important step towards the application of XPCI to real-world problems
Spectral and polarimetric characterization of the Gas Pixel Detector filled with dimethyl ether
The Gas Pixel Detector belongs to the very limited class of gas detectors
optimized for the measurement of X-ray polarization in the emission of
astrophysical sources. The choice of the mixture in which X-ray photons are
absorbed and photoelectrons propagate, deeply affects both the energy range of
the instrument and its performance in terms of gain, track dimension and
ultimately, polarimetric sensitivity. Here we present the characterization of
the Gas Pixel Detector with a 1 cm thick cell filled with dimethyl ether (DME)
at 0.79 atm, selected among other mixtures for the very low diffusion
coefficient. Almost completely polarized and monochromatic photons were
produced at the calibration facility built at INAF/IASF-Rome exploiting Bragg
diffraction at nearly 45 degrees. For the first time ever, we measured the
modulation factor and the spectral capabilities of the instrument at energies
as low as 2.0 keV, but also at 2.6 keV, 3.7 keV, 4.0 keV, 5.2 keV and 7.8 keV.
These measurements cover almost completely the energy range of the instrument
and allows to compare the sensitivity achieved with that of the standard
mixture, composed of helium and DME.Comment: 20 pages, 11 figures, 5 tables. Accepted for publication by NIM
Low energy polarization sensitivity of the Gas Pixel Detector
An X-ray photoelectric polarimeter based on the Gas Pixel Detector has been
proposed to be included in many upcoming space missions to fill the gap of
about 30 years from the first (and to date only) positive measurement of
polarized X-ray emission from an astrophysical source. The estimated
sensitivity of the current prototype peaks at an energy of about 3 keV, but the
lack of readily available polarized sources in this energy range has prevented
the measurement of detector polarimetric performances.
In this paper we present the measurement of the Gas Pixel Detector
polarimetric sensitivity at energies of a few keV and the new, light, compact
and transportable polarized source that was devised and built to this aim.
Polarized photons are produced, from unpolarized radiation generated with an
X-ray tube, by means of Bragg diffraction at nearly 45 degrees.
The employment of mosaic graphite and flat aluminum crystals allow the
production of nearly completely polarized photons at 2.6, 3.7 and 5.2 keV from
the diffraction of unpolarized continuum or line emission. The measured
modulation factor of the Gas Pixel Detector at these energies is in good
agreement with the estimates derived from a Monte Carlo software, which was up
to now employed for driving the development of the instrument and for
estimating its low energy sensitivity. In this paper we present the excellent
polarimetric performance of the Gas Pixel Detector at energies where the peak
sensitivity is expected. These measurements not only support our previous
claims of high sensitivity but confirm the feasibility of astrophysical X-ray
photoelectric polarimetry.Comment: 15 pages, 12 figures. Accepted for publication in NIM
XPOL-III: a New-Generation VLSI CMOS ASIC for High-Throughput X-ray Polarimetry
While the successful launch and operation in space of the Gas Pixel Detectors
onboard the PolarLight cubesat and the Imaging X-ray Polarimetry Explorer
demonstrate the viability and the technical soundness of this class of
detectors for astronomical X-ray polarimetry, it is clear that the current
state of the art is not ready to meet the challenges of the next generation of
experiments, such as the enhanced X-ray Timing and Polarimetry mission,
designed to allow for a significantly larger data throughput.
In this paper we describe the design and test of a new custom,
self-triggering readout ASIC, dubbed XPOL-III, specifically conceived to
address and overcome these limitations. While building upon the overall
architecture of the previous generations, the new chip improves over its
predecessors in several, different key areas: the sensitivity of the trigger
electronics, the flexibility in the definition of the readout window, as well
as the maximum speed for the serial event readout. These design improvements,
when combined, allow for almost an order of magnitude smaller dead time per
event with no measurable degradation of the polarimetric, spectral, imaging or
timing capability of the detector, providing a good match for the next
generation of X-ray missions.Comment: accepted for publication at Nuclear Inst. and Methods in Physics
Research Section
Acute mammary and liver transcriptome responses after an intramammary Escherichia coli lipopolysaccharide challenge in postpartal dairy cows
The study investigated the effect of an intramammary lipopolysaccharide (LPS) challenge on the bovine mammary and liver transcriptome and its consequences on metabolic biomarkers and liver tissue composition. At 7 days of lactation, 7 cows served as controls (CTR) and 7 cows (LPS) received an intramammary Escherichia coli LPS challenge. The mammary and liver tissues for transcriptomic profiling were biopsied at 2.5 h from challenge. Liver composition was evaluated at 2.5 h and 7 days after challenge, and blood biomarkers were analyzed at 2, 3, 7 and 14 days from challenge. In mammary tissue, the LPS challenge resulted in 189 differentially expressed genes (DEG), with 20 down-regulated and 169 up-regulated. In liver tissue, there were 107 DEG in LPS compared with CTR with 42 down-regulated and 65 up-regulated. In mammary, bioinformatics analysis highlighted that LPS led to activation of NOD-like receptor signaling, Toll-like receptor signaling, RIG-I-like receptor signaling and apoptosis pathways. In liver, LPS resulted in an overall inhibition of fatty acid elongation in mitochondria and activation of the p53 signaling pathway. The LPS challenge induced changes in liver lipid composition, a systemic inflammation (rise of blood ceruloplasmin and bilirubin), and an increase in body fat mobilization. The data suggest that cells within the inflamed mammary gland respond by activating mechanisms of pathogen recognition. However, in the liver the response likely depends on mediators originating from the udder that affect liver functionality and specifically fatty acid metabolism (b-oxidation, ketogenesis, and lipoprotein synthesis).Fil: Minuti, Andrea. Universita Cattolica del Sacro Cuore; ItaliaFil: Zhou, Zheng. University Of Illinois At Urbana; Estados UnidosFil: Graugnard, Daniel E. University Of Illinois At Urbana; Estados UnidosFil: Rodriguez Zas, Sandra L.. University Of Illinois At Urbana; Estados UnidosFil: Palladino, Rafael Alejandro. Universidad de Buenos Aires. Facultad de Agronomia; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Cardoso, Felipe C.. University Of Illinois At Urbana; Estados UnidosFil: Trevisi, Erminio. Universita Cattolica del Sacro Cuore; ItaliaFil: Loor, Juan J. University Of Illinois At Urbana; Estados Unido
The imaging properties of the Gas Pixel Detector as a focal plane polarimeter
X-rays are particularly suited to probe the physics of extreme objects.
However, despite the enormous improvements of X-ray Astronomy in imaging,
spectroscopy and timing, polarimetry remains largely unexplored. We propose the
photoelectric polarimeter Gas Pixel Detector (GPD) as an instrument candidate
to fill the gap of more than thirty years of lack of measurements. The GPD, in
the focus of a telescope, will increase the sensitivity of orders of magnitude.
Moreover, since it can measure the energy, the position, the arrival time and
the polarization angle of every single photon, allows to perform polarimetry of
subsets of data singled out from the spectrum, the light curve or the image of
source. The GPD has an intrinsic very fine imaging capability and in this work
we report on the calibration campaign carried out in 2012 at the PANTER X-ray
test facility of the Max-Planck-Institut f\"ur extraterrestrische Physik of
Garching (Germany) in which, for the first time, we coupled it to a JET-X
optics module with a focal length of 3.5 m and an angular resolution of 18
arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-ray
Imaging Polarimetry Explorer (XIPE) in response to the ESA call for a small
mission. We derived the imaging and polarimetric performance for extended
sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the
XIPE configuration, discussing also possible improvements by coupling the
detector with advanced optics, having finer angular resolution and larger
effective area, to study with more details extended objects.Comment: Accepted for publication in The Astrophysical Journal Supplemen
Reliable protocol for sample preparation to observe nanomaterial adherence to the surface of biological cells by using scanning electron microscopy
Background. When assessing the interaction between nanomaterials and cells, an important step is to
image the effects induced by the material to the cell membrane. In order to evaluate the results of the
interaction process, scanning electron microscopy (SEM) is typically used. Commonly, an important step
during the preparation of biological cell samples for SEM is represented by the critical point drying,
which involves the replacement of the alcohol used for dehydration with an inert gas. This conventional
drying method is not only hard to accomplish, but it can lead to sample destruction if specific parameters
are not met. On the other hand, when assessing nanomaterials adhered to the cell membrane, the integrity
of the cell is not necessarily important, so a little cell deflation doesn’t affect the intended purpose of the
evaluation. Here, we describe a simple and more cost efficient method to prepare biological samples for
SEM imaging that preserves cell integrity and can be used to describe nanomaterials interaction with cell
surface.
Methods. Cells were grown on sterilized silica chips, after which the evaluated nanomaterial was added
to the cell culture media at least 24h for incubation. Afterwards, the samples were washed to eliminate
non-adhered nanomaterials, fixed with glutaraldehyde and osmium tetroxide, and dehydrated with
increasing concentrations of alcohol. The silica chips were then air dried in the biological safety hood
and in vacuum, followed by a sputter coat film of 5 nm of gold. The samples were imaged with a
scanning electron microscope.
Results. We were able to obtain well preserved biological cell samples, both with and without
nanomaterials adhered to the cell membrane surface. Nanomaterials such as magnetic nanoparticles and
magnetic nanowires were easily traceable on cell surface. Furthermore, the nanomaterials were clearly
observed in the images obtained, while the cell surface was not affected by the drying process applied.
Although the samples obtained using our method were characterized by a slight deflation of the cells, the
morphology of the cells is well preserved and the method is suitable for the evaluation of the interaction
between nanomaterials and cell surfaces.
Conclusions: We have described a novel cost efficient and easy to perform method for processing
biological samples for SEM imaging that preserves cell morphology and can be used for analyzing
nanoparticle and nanowires interaction with cell surface
Imaging with the invisible light
We describe a UV photo-detector with single photon(electron) counting and
imaging capability. It is based on a CsI photocathode, a GEM charge multiplier
and a self triggering CMOS analog pixel chip with 105k pixels at 50 micron
pitch. The single photoelectron produced by the absorption of a UV photon is
drifted to and multiplied inside a single GEM hole. The coordinates of the GEM
avalanche are reconstructed with high accuracy (4 micron rms) by the pixel
chip. As a result the map of the GEM holes, arranged on a triangular pattern at
50micron pitch, is finely imaged.Comment: 6 pages, 14 figures, presented at the 11th Vienna Conference on
Instrumentation VIC 2007, submitted to Nuclear Instruments and Methods
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