Results 1 - 10 of 92468
Results 1 - 10 of 92468. Search took: 0.095 seconds
|Sort by: date | relevance|
[en] FAIR - the Facility for Antiproton and Ion Research is a new international accelerator facility which is built in Darmstadt, Germany. The core machines of the project are the superconducting synchrotron SIS100 and the superconducting fragment separator Super-FRS. Design and construction of superconducting machines require a comprehensive study of cases when the superconducting state is lost (quench). This dissertation covers two subjects. The first subject aims the development of a novel calculation tool (called GSI quench software) dedicated to the quench study of the FAIR magnets. Quench calculations done with the GSI software serve as an input for the proper design of SIS100 and Super-FRS quench detection and energy extraction systems. The software uses the unconditionally stable implicit scheme for the solution of the partial-differential equations that describe the thermal model of the coil. An innovative adaptive time stepping algorithm is used in order to limit the maximum temperature increase of the individual mesh elements to a predefined level. The thermal model of the coil gives the possibility to include the cooling by a liquid helium bath. The electrical circuit topology including the magnet protection system (energy extraction resistors and/or by-pass diodes) is implemented. The properties of the magnet's yoke are taken into account in the inductance function Ld(I). The implemented electro-thermal model was verified and validated by comparison to quench measurements conducted on SIS100 dipole and Super-FRS dipole prototypes. The testing campaign on the SIS100 dipole prototype (magnet training, quench propagation velocity, hot-spot temperature, MIITs, RRRCu, inductance, splice resistance, current leads) was performed in the scope of this work. The quench measurements on the Super-FRS dipole prototype were received from the FAIR China Group. The results of calculations performed with the GSI software are either in good agreement with the measurement data or they represent the worst case scenario, e.g. the calculated hot-spot temperature or quench voltage is higher than measured. The second subject concerns the design challenges of the SIS100 quench detection system. An outstanding cycling rate of the dipole circuit (4 T/s), high voltage (U0/U=1 kV/2 kV), radiation hardness required for the equipment to be installed in the accelerator tunnel (≥1 MGy) and long signal lines between the magnets and quench detection racks (up to 200 m) implies a customised design of the key components of the system. Selected contributions to the SIS100 quench detection system, concerning the reduction of the parasitic capacitance in the main magnet circuits (by utilising magnetic amplifiers and a new overlapping structure of balance bridges) and the development of a quench detector dedicated to corrector magnets (mutual inductance detector) are presented.
[en] After a presentation of some key figures characterising the organisation and process of the public debate launched by the French government on the Energy Multi-Year Programming (PPE), a first document describes the debate process and context (recall of the PPE, role of the public debate, preliminary meetings, limited means for the public debate, fruitful initiatives of the Commission, lessons learned from technical work groups, documentation published by interest groups, disputes about the Commission). Results are then discussed by describing how the law on energy transition is facing difficulties for its application, and how the law and associated authorities (ADEME, Ministry) have been disputed, and by outlining that, while suggesting improvement, the public kept on giving importance to the compromise present within the law. Recommendations are then made to the Ministry. Then, about two hundred documents are proposed, each one being a 'cahier d'acteur' (actor leaflet) published by the Commission, each issue being written by an actor involved in the energy sector (industrial actor, environmental association, and so on) and giving its opinion and propositions regarding the energy issue.
[en] This work describes the development of an instrument for radiological monitoring, identified as Gamma Alarm (GAMAL01). These monitors detect the increase in intensity radiation and emit an alarm when this magnitude exceeds a certain threshold. Threshold for the emission of the alarm is fixed, so that it occurs when it is considered that the intensity of radiation may cause unacceptable exposure of personnel to radiation, in accordance with the provisions of the radiological safety regulations in force in the country. The alarm signal indicates the need to evacuate personnel from the affected site.
[en] The objective of this work is to relate the accumulated effective dose of workers occupationally exposed (TOE's) in public versus private organizations, of two Nuclear Medicine services -Camera Gamma area- in Bolivia. Retrospective analysis of dosimetric history, sent by the Dosimetry Laboratory of the Bolivian Institute of Science and Nuclear Technology, provided by the Radiological Protection Officers of the Nuclear Medicine of Sucre (A) and the Center for Molecular Imaging of La Paz (B), from the years 2014 to 2016 they refer that: In group (A) of a total of 48 samples, 4.17 percent are considered recordable (less than 0.2 mSv are not reported) with a maximum accumulated value of 0.6 mSv, in relation to group (B) of 30 samples, 66.67 percent are recordable with a maximum accumulated of 12.5 mSv. Therefore, it is concluded that a higher estimate of the cumulative effective dose in the TOE‘s of the Private Institution in relation to that of the Institution Public, representing an increase of 2083.33 percent and corresponding to the personnel that carries out the activity of elution of radioactive material, preparation and administration of radiopharmaceutical. Cause attributable to use of radioactive material with higher energy (Mo99-Tc99m / I131) and / or activity (frequency of weekly / monthly reception).
[en] Nanotechnology applied to polymer foams is an emerging field. The possibility to add nanofillers to polymers and to expand them by supercritical carbon dioxide represents an important development in polymer foam production, tailoring the foams’ properties. In this study, polystyrene (PS) composites with cellulose nanofibers (CNF) were obtained by producing PS/CNF nanocomposites and subsequently expanding them with supercritical CO2. The viscosity, mechanical and dynamic-mechanical properties of non-expanded composites were obtained. The morphology and compressive strength of the expanded composites were evaluated. The non-expanded composites’ mechanical properties remained unchanged, and the viscosity increased with the addition of CNF. PS/CNF non-expanded composites displayed higher storage modulus in the rubbery region with increasing CNF content. The expanded foams displayed smaller cell size as CNF is introduced, which increased the compressive strength and decreased the deformation at 5 wt% CNF. This allows the tailoring of the mechanical properties and cell size with varying CNF content to better suit a wide range of applications.
[en] In this research, the preparation, application and optimization of catalytic membrane based on nickel–palladium–tin-coated carbon nanotubes/polyethersulfone-hyperbranched polyol (Ni–Pd–Sn@MWCNT/PES-HBAPO) were assessed. The nickel nanoparticles were coated on the carbon nanotubes by an electroless plating method. Later, Ni–Pd–Sn@MWCNT was mixed with the polyethersulfone modified with hyperbranched polymer, and membrane samples were prepared by a phase inversion process. For improvement of the membrane properties including thermal and chemical stability, an aromatic hyperbranched polymer was synthesized and was utilized in the membrane blend. For evaluation of the properties of the resultant membranes, FE-SEM, SEM-Mapping, TEM, FTIR, ICP-OES, DSC and 1H NMR tests were used. The catalytic activity of the obtained membranes in Ullmann-type coupling reaction was studied. High reaction yields were obtained with no significant catalyst leaching.
[en] An ion exchange membrane is a polymer matrix of cross-linked polyvinyl chloride macromolecular chains, on which are grafted ionic functional sites. The transport numbers of two metal ions and proton through these membranes were determined using the well-known electrochemical Hittorf’s method. The cation exchange membrane Nafion, having sulfonic reactional site (–SO3−), yielded the transport number of copper relatively less than that of sodium, leaving way to proton to be transported. In contrast, the anion membrane of alkyl ammonium reactional site (–NR4+) prevented the transfer of cation metals and allowed the proton to displace by defect of permselectivity. These two membranes were used as separators in microbial fuel cells (MFC). In effect, the MFC with the anion membrane AMX, gave relatively higher power density (1.10 mW/m2) compared to the cation exchange membrane Nafion (0.45 mW/m2). Really, with the AMX separator, the metal ions present in the wastewater anolyte compartment were blocked by the membrane giving way to the protons to displace freely and be reduced efficiently at the cathode. In the mono-compartment cell, the ions moved sideways between anode and cathode, yielding the highest power density (11.90 mW/m2) so far obtained. The pH adjustment of anolyte and cathode compartments support, therefore, strongly the cell voltage evolutions. In addition, the cyclic voltammetry results showed that the electroactive biofilm of the bioanode using the AMX membrane described a diffusion-limited process, while that of the Nafion membrane made in evidence the adsorption monolayer of redox species. Besides, the electrochemical impedance spectroscopy revealed that the charge transfer resistance at the interface bioanode/biofilm decreased drastically from 728 to 18 Ω cm2 for Nafion MFC during 11 days of functioning.
[en] The performances of UV-curable waterborne polyurethane-acrylate (WPUA) composite modified with nano calcium carbonate (NCA) were highlighted in this work. The γ-methacryloxy propyl trimethoxyl silane (KH-570) and polysorbate 80 (Tween-80) were used to enhance interfacial interaction between NCA and WPUA matrix. Transmission electron microscopy (TEM), particle size analysis and Fourier transfer infrared (FT-IR) spectrometry were employed to examine the micromorphology and the variation of function group of modified nano calcium carbonate (MNCA). Three different WPUA oligomers were investigated to obtain the optimized R value (the molar ratio of –NCO:–OH) via in situ polymerization and anion self-emulsification process. Results showed that WPUA displayed excellent film-forming ability and mechanical properties when R value was 2.2:1.0. These UV-curable WPUA films modified with MNCA (UV-MNCA/WPUA) were prepared through environmentally friendly UV-curable technology and investigated by thermogravimetric (TG) analysis, scanning electron microscope (SEM), X-ray diffractometer (XRD) and FT-IR. UV-MNCA/WPUA-3-3 film had the best overall performances with MNCA-2 and UV-WPUA at the mass ratio of 3.6%. Finally, the experimental results demonstrated that the as-obtained UV-curable coating had outstanding conservation effect to iron surface, providing a promising way for protection of iron cultural relics.
[en] In this study, effects of coupling agent addition on adhesive wear, thermal and morphological properties of glass fiber-reinforced polyamide 6,6 (PA6,6) composites were investigated. 1,4-Phenylene-bis-oxazoline (PBO) was used as coupling agent to improve the interfacial adhesion between glass fiber and PA6,6 matrix. While coupling agent loading level was changed as 0.5, 1.0 and 2.0 wt%, glass fiber loading level was fixed at 10 wt% in the composites. For tribological characterization of prepared composites, adhesive wear test was performed. Differential scanning calorimeter analysis and thermogravimetric analysis were performed for thermal characterization. In addition to this, scanning electron microscopy analysis was applied to investigate the worn surfaces and fracture surfaces of samples. Applied test results revealed that 2 wt% PBO addition improved the fiber–matrix adhesion and correspondingly adhesive wear resistance of glass fiber-reinforced PA6,6 matrix composites.
[en] In this study, nanocomposite samples based on polymethylmethacrylate/poly (lactic acid)/graphene nanoplatelets (PMMA/PLA/GNP) were prepared via melt mixing method and thermal multiple shape memory was induced. Dynamic mechanical thermal analysis results showed that two polymers are miscible in the selected blend ratio (70/30, 50/50, 30/70 w/w; PLA/PMMA) and was not affected by the presence of GNP (1 and 2 phr). The dispersion and distribution status of GNP were observed by scanning electron microscopy (SEM). The co-continuous morphology was dominant in all samples due to complete miscibility of two phases. Multi-shape memory was induced using a tensile test machine equipped with the hot oven at 65 and 100 °C. The results revealed that shape recovery was affected by the presence of GNP at high temperature(for example increasing from 93.34% in neat PLA/PMMA(50/50 w/w) to 96.67% in the sample containing 1 phr of GNP) while there was no considerable effect at low temperature. At high temperature, amorphous phases of two polymers are extended and un-melted chains of PMMA can be as hard segment and leads to good recovery. Due to nucleation and reinforcement effects of GNP, the higher degree of crystallization of PLA and higher storage modulus were obtained and caused to the enhancement of the shape fixity values at the presence of GNP.