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| 2. |
- Correa, J., et al.
(författare)
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The PERCIVAL detector : first user experiments
- 2023
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 30, s. 242-250
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Tidskriftsartikel (refereegranskat)abstract
- The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science.
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| 3. |
- Hubert, D., et al.
(författare)
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Ground-based assessment of the bias and long-term stability of 14 limb and occultation ozone profile data records
- 2016
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 9:6, s. 2497-2534
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Tidskriftsartikel (refereegranskat)abstract
- The ozone profile records of a large number of limb and occultation satellite instruments are widely used to address several key questions in ozone research. Further progress in some domains depends on a more detailed understanding of these data sets, especially of their long-term stability and their mutual consistency. To this end, we made a systematic assessment of 14 limb and occultation sounders that, together, provide more than three decades of global ozone profile measurements. In particular, we considered the latest operational Level-2 records by SAGE II, SAGE III, HALOE, UARS MLS, Aura MLS, POAM II, POAM III, OSIRIS, SMR, GOMOS, MIPAS, SCIAMACHY, ACE-FTS and MAESTRO. Central to our work is a consistent and robust analysis of the comparisons against the ground-based ozonesonde and stratospheric ozone lidar networks. It allowed us to investigate, from the troposphere up to the stratopause, the following main aspects of satellite data quality: long-term stability, overall bias and short-term variability, together with their dependence on geophysical parameters and profile representation. In addition, it permitted us to quantify the overall consistency between the ozone profilers. Generally, we found that between 20 and 40km the satellite ozone measurement biases are smaller than ±5%, the short-term variabilities are less than 5-12% and the drifts are at most ±5%decade-1 (or even ±3%decade-1 for a few records). The agreement with ground-based data degrades somewhat towards the stratopause and especially towards the tropopause where natural variability and low ozone abundances impede a more precise analysis. In part of the stratosphere a few records deviate from the preceding general conclusions; we identified biases of 10% and more (POAM II and SCIAMACHY), markedly higher single-profile variability (SMR and SCIAMACHY) and significant long-term drifts (SCIAMACHY, OSIRIS, HALOE and possibly GOMOS and SMR as well). Furthermore, we reflected on the repercussions of our findings for the construction, analysis and interpretation of merged data records. Most notably, the discrepancies between several recent ozone profile trend assessments can be mostly explained by instrumental drift. This clearly demonstrates the need for systematic comprehensive multi-instrument comparison analyses.
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| 4. |
- Kirkwood, S., et al.
(författare)
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Polar mesosphere winter echoes by ESRAD, EISCAT and lidar
- 2002
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- The ESRAD 52 MHz MST radar (67° 53 ‘ N, 21 ° 06 ‘ E) has observed thin layers of enhanced radar echoes in the winter mesosphere during several recent solar proton events. The detection of these polar mesosphere winter echoes (PMWE) is generally found to correlates well with low values of λ (the ratio of negative ion density to electron density). However PMWE are found to persist for values of λ up to ~100. Present knowledge of the nature of neutral turbulence in the winter mesosphere suggests that such turbulence cannot generate electron density fluctuations with scale-sizes as short as the 3 m needed to produce radar echoes at 52 MHz. This is particularly true as λ increases to ~100. Joint observations from ESRAD and the EISCAT 224 MHz radar suggest that PMWE is also detectable at 67 cm scale-sizes, further increasing the difficulty in explaining the echoes by neutral turbulence. Joint observations from ESRAD and lidar are also inconsistent with the expected behaviour of turbulence. Together with results concerning the thickness, echo aspect-sensitivity and echo spectral-width of the PMWE, these observation leads to the conclusion that the layers cannot be explained by turbulence alone. A role for charged aerosols in creating PMWE is proposed. The presence of aerosols is supported by the lidar observations.
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| 5. |
- Marras, A., et al.
(författare)
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Percival P2M-FSI detector : First test at a Synchrotron Ring beamline with tender x-ray photons
- 2019
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Ingår i: 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS/MIC 2019. - : IEEE. - 9781728141640
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Konferensbidrag (refereegranskat)abstract
- In this paper, we are presenting the results of the first test of the Percival P2M-FSI detector with tender x-rays photons at a synchrotron beamline. Percival is a monolithic CMOS Imager for detection of x-rays in Synchrotron Rings and Free Electron Lasers: the Front-Side-Illuminated (FSI) version of the detector has been proven able to successfully distinguish tender (2keV) x-ray single photons.
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| 6. |
- Pinaroli, G., et al.
(författare)
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PERCIVAL : Possible applications in X-ray micro-tomography
- 2020
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Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 15:2
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Tidskriftsartikel (refereegranskat)abstract
- X-ray computed micro-tomography (μCT) is one of the most advanced and common non-destructive techniques in the field of medical imaging and material science. It allows recreating virtual models (3D models), without destroying the original objects, by measuring three-dimensional X-ray attenuation coefficient maps of samples on the (sub) micrometer scale. The quality of the images obtained using μCT is strongly dependent on the performance of the associated X-ray detector i.e. to the acquisition of information of the X-ray beam traversing the patient/sample being precise and accurate. Detectors for μCT have to meet the requirements of the specific tomography procedure in which they are going to be used. In general, the key parameters are high spatial resolution, high dynamic range, uniformity of response, high contrast sensitivity, fast acquisition readout and support of high frame rates. At present the detection devices in commercial μCT scanners are dominated by charge-coupled devices (CCD), photodiode arrays, CMOS acquisition circuits and more recently by hybrid pixel detectors. Monolithic CMOS imaging sensors, which offer reduced pixel sizes and low electronic noise, are certainly excellent candidates for μCT and may be used for the development of novel high-resolution imaging applications. The uses of monolithic CMOS based detectors such as the PERCIVAL detector are being recently explored for synchrotron and FEL applications. PERCIVAL was developed to operate in synchrotron and FEL facilities in the soft X-ray regime from 250 eV to 1 keV and it could offer all the aforementioned technical requirements needed in μCT experiments. In order to adapt the system for a typical tomography application, a scintillator is required, to convert incoming X-ray radiation (∼ tens of KeV) into visible light which may be detected with high efficiency. Such a taper-based scintillator was developed and mounted in front of the sensitive area of the PERCIVAL imager. In this presentation we will report the setup of the detector system and preliminary results of first μCTs of reference objects, which were performed in the TomoLab at ELETTRA.
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| 7. |
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| 8. |
- Wunderer, C. B., et al.
(författare)
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The Percival 2-Megapixel monolithic active pixel imager
- 2019
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Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- The peak brilliance reached by today's Free-Electron Laser and Synchrotron light sources requires photon detectors matching their output intensity and other characteristics in order to fully realize the sources' potential. The Pixellated Energy Resolving CMOS Imager, Versatile And Large (Percival) is a dedicated soft X-ray imager (0.25-1 keV) developed for this purpose by a collaboration of DESY, Rutherford Appleton Laboratory/STFC, Elettra Sincrotrone Trieste, Diamond Light Source, and Pohang Accelerator Laboratory. Following several generations of prototypes, the Percival "P2M" 2-Megapixel imager - a 4.5x5 cm monolithic, stitched sensor with an uninterrupted imaging area of 4x4 cm(2) (1408x1484 pixels of 27x27 mu m - was produced and has demonstrated basic functionality with a first-light image using visible light. It is currently being brought to full operation in a front-illuminated configuration. The readout system being commissioned in parallel has been developed specifically for this imager which will produce - at full 300 Hz frame rate - data at 20 Gbit/s. A first wafer with eight Percival P2M chips has undergone backthinning to enable soft X-ray detection. It has been diced and chips are currently being wirebonded. We summarize here the P2M system, the project status, and show the P2M sensor's first response to visible light.
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| 9. |
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| 10. |
- Blum, Ulrich, et al.
(författare)
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Simultaneous lidar observations of a polar stratospheric cloud on the east and west side of the Scandinavian mountains and microphysical box model simulations
- 2006
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Ingår i: Annales Geophysicae. ; 24, s. 3267-3277
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Tidskriftsartikel (refereegranskat)abstract
- The importance of polar stratospheric clouds (PSC) for polar ozone depletion is well established. Lidar experiments are well suited to observe and classify polar stratospheric clouds. On 5 January 2005 a PSC was observed simultaneously on the east and west sides of the Scandinavian mountains by ground-based lidars. This cloud was composed of liquid particles with a mixture of solid particles in the upper part of the cloud. Multi-colour measurements revealed that the liquid particles had a mode radius of r~300 nm, a distribution width of ~1.04 and an altitude dependent number density of N~2–20 cm−3. Simulations with a microphysical box model show that the cloud had formed about 20 h before observation. High HNO3 concentrations in the PSC of 40–50 weight percent were simulated in the altitude regions where the liquid particles were observed, while this concentration was reduced to about 10 weight percent in that part of the cloud where a mixture between solid and liquid particles was observed by the lidar. The model simulations also revealed a very narrow particle size distribution with values similar to the lidar observations. Below and above the cloud almost no HNO3 uptake was simulated. Although the PSC shows distinct wave signatures, no gravity wave activity was observed in the temperature profiles measured by the lidars and meteorological analyses support this observation. The observed cloud must have formed in a wave field above Iceland about 20 h prior to the measurements and the cloud wave pattern was advected by the background wind to Scandinavia. In this wave field above Iceland temperatures potentially dropped below the ice formation temperature, so that ice clouds may have formed which can act as condensation nuclei for the nitric acid trihydrate (NAT) particles observed at the cloud top above Esrange.
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