6,303 research outputs found
Numerical study of dynamics of single bubbles and bubble swarms
No full textA systematic computational study of the dynamics of gas bubbles rising in a viscous liquid is presented. Two-dimensional simulations are carried out. Both the dynamics of single bubbles and small groups of bubbles (bubble swarms) are considered. This is a continuation of our previous studies on the two-bubble coalescence and vortex shedding [A. Smolianski, H. Haario, P. Luukka, Vortex shedding behind a rising bubble and two-bubble coalescence: a numerical approach, Appl. Math. Model. 29 (2005) 615–632]. The proposed numerical method allows us to simulate a wide range of flow regimes, accurately capturing the shape of the deforming interface of the bubble and the surface tension effect, while maintaining the mass conservation. The computed time-evolution of bubble’s position and rise velocity shows a good agreement with the available experimental data. At the same time, the results on the dynamics of bubble interface area, which are, up to our knowledge, presented for the first time, show how much the overall mass transfer would be affected by the interface deformation in the case of the bubble dissolution. Another set of experiments that are of interest for chemical engineers modelling bubbly flows concerns the bubble swarms and their behavior in different bubble-shape regimes. The ellipsoidal and spherical shape regimes are considered to represent, respectively, the coalescing and non-coalescing bubble swarms. The average rise velocities of the bubble swarms are computed and analyzed for both regimes
Characterization of Czochralski silicon detectors
No full textThis thesis describes the characterization of irradiated and non-irradiated segmented detectors made of high-resistivity (>1 kΩcm) magnetic Czochralski (MCZ) silicon. It is shown that the radiation hardness (RH) of the protons of these detectors is higher than that of devices made of traditional materials such as Float Zone (FZ) silicon or Diffusion Oxygenated Float Zone (DOFZ) silicon due to the presence of intrinsic oxygen (> 5 × 1017 cm−3). The MCZ devices therefore present an interesting alternative for future high-energy physics experiments. In the large hadron collider (LHC), the RH of the detectors is a critical issue due to the high luminosity (1034 cm−2s−1) corresponding to the expected total fluencies of fast hadrons above 1015 cm−2. This RH improvement is important since radiation damage in the detector bulk material reduces the detector performance and because some of the devices produced from standard detector-grade silicon, e.g. FZ silicon with negligible oxygen concentration, might not survive the planned operational period of the LHC experiments.
In this work, segmented detectors and test structures were processed, measured, irradiated with different particles (protons of different energies, neutrons and high-energy electrons) and tested with a 60Co gamma source and with high-energy muon and pion beams. The electrical characterizations show that, for proton irradiation, the MCZ silicon is significantly radiation harder than traditionally used detector materials. In gamma irradiation, MCZ silicon detectors behave similarly to the DOFZ silicon detectors. For neutron radiation, there is only a small difference between MCZ silicon and the reference devices made of standard FZ silicon. The beam test results with the full-size detectors show that the properties of the high-resistivity MCZ silicon are suitable for particle detection both before and after heavy proton irradiation.reviewe
Recent progress of CERN RD50 Collaboration
No full textThe objective of the CERN RD50 Collaboration is to develop radiation hard semiconductor detectors for very high luminosity colliders, in particular, for the upgrade of the large hadron collider (LHC) which itself is scheduled to be operational in 2007. The approach of the RD50 has two major research lines, material engineering and device engineering. These are further subdivided into projects covering defect characterization and engineering, new detector materials, detector characterization, new detector structures and full detector systems. Presently, 264 members from 53 institutes are actively participating in the RD50 Collaboration. Detectors made of defect engineered substrates, e.g. high resistivity magnetic Czochralski (MCz-Si), epitaxial silicon (Epi-Si) on Czochralski silicon (Cz-Si) substrate, intentionally thermal donor (TD) compensated p-type MCz-Si and oxygen enriched (DOFZ) silicon, have been demonstrated by the RD50 Collaboration. An overview and highlights of the results of these defect engineering techniques were given in this report
CMS inner tracker upgrade
No full textThe LHC is preparing an upgrade, which will bring the luminosity of the machine to 5-7 × 1034 cm−2s−1 reaching an integrated luminosity of 3000 fb-1 by the end of 2037. This High Luminosity LHC (HL-LHC) scenario will require extensive upgrades to the experiments to fully exploit the physics potential of the accelerator. In this so-called Phase-2 upgrade, CMS detector will require improved radiation hardness, higher detector granularity to reduce occupancy, increased bandwidth to accommodate higher data rates, and an improved trigger capability to maintain an acceptable trigger rate. Thus, the entire tracking system will need to be replaced to deal with the HL-LHC environment and to maintain the excellent performance of the current CMS detector. The Phase-2 Inner Tracker is designed to maintain or even improve the tracking and vertexing capabilities under the high pileup (140 - 200 collisions per bunch crossing) conditions of the HL-LHC. The detectors should have the required radiation tolerance and capability of delivering the desired performance in terms of detector resolution, occupancy, and track separation. The Inner Tracker will be built from thin silicon pixel detectors segmented into pixel sizes of 25 x 100 µm2 or 50 x 50 µm2. It is composed of a barrel part with four cylindrical layers and eight small and four large disc-like structures in each forward direction. The design also includes the possibility to extract and replace the degraded parts of the detector without removing the beam pipe. The Tracker Endcap Pixel detector, installed within the extended space, will enable the measurement of real-time instantaneous luminosity as an added functionality. The extended geometrical coverage of up to η < 4.0 provides large forward acceptance to mitigate the pileup, particularly in the endcap calorimeters. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).Peer reviewe
p/sup +//n/sup -//n/sup +/ Cz-Si detectors processed on p-type boron doped substrates with thermal donor induced space charge sign inversion
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Similarity Classifier with Generalized mean Applied to Medical Data Using Different Preprocessing Methods
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Comparison of two different dimension reduction methods in classification by arithmetic, geometric and harmonic similarity measure
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