| 1. |
- Bruzzi, M, et al.
(author)
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Radiation-hard semiconductor detectors for SuperLHC
- 2005
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In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 541:1-2, s. 189-201
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Journal article (peer-reviewed)abstract
- An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
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| 4. |
- Kuzenko, S. M., et al.
(author)
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4D N=2 supergravity and projective superspace
- 2008
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In: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media LLC. - 1126-6708 .- 1029-8479. ; :9, s. 051-
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Journal article (peer-reviewed)abstract
- This paper presents a projective superspace formulation for 4D N = 2 matter-coupled supergravity. We first describe a variant superspace realization for the N = 2 Weyl multiplet. It differs from that proposed by Howe in 1982 by the choice of the structure group SO(3, 1) x SU(2) versus SO(3, 1) x U( 2)), which implies that the super-Weyl transformations are generated by a covariantly chiral parameter instead of a real unconstrained one. We introduce various off-shell supermultiplets which are curved superspace analogues of the superconformal projective multiplets in global supersymmetry and which describe matter fields coupled to supergravity. A manifestly locally supersymmetric and super-Weyl invariant action principle is given. Off-shell locally supersymmetric nonlinear sigma models are presented in this new superspace.
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| 5. |
- Kuzenko, S. M., et al.
(author)
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On conformal supergravity and projective superspace
- 2009
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In: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media LLC. - 1126-6708 .- 1029-8479. ; :8, s. 023-
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Journal article (peer-reviewed)abstract
- The projective superspace formulation for four-dimensional N = 2 matter-coupled supergravity presented in arXiv:0805.4683 makes use of the variant superspace realization for the N = 2 Weyl multiplet in which the structure group is SL(2, C) x SU(2) and the super-Weyl transformations are generated by a covariantly chiral parameter. An extension to Howe's realization of N = 2 conformal supergravity in which the tangent space group is SL(2, C) x U(2) and the super-Weyl transformations are generated by a real unconstrained parameter was briefly sketched. Here we give the explicit details of the extension.
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| 6. |
- Lôpez-Rubio, A., et al.
(author)
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Enhanced film forming and film properties of amylopectin using micro-fibrillated cellulose
- 2007
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 68:4, s. 718-727
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Journal article (peer-reviewed)abstract
- This work describes a novel approach to produce amylopectin films with enhanced properties by the addition of micro fibrillated cellulose (MFC). Aqueous dispersions of gelatinized amylopectin, glycerol (0-38 wt%) and MFC (0-10 wt%) were cast at ambient temperature and 50% relative humidity and, after 10 days of storage, the tensile properties were investigated. The structure of the composite films was revealed by optical, atomic force and transmission electron microscopy. The moisture content was determined by thermogravimetry and the temperature-dependent film rigidity was measured by thermal mechanical analysis. Synchrotron simultaneous small- and wide-angle X-ray measurements revealed that the solutions had to be heated to above 85 degrees C in order to achieve complete gelatinization. Optical microscopy and atomic force microscopy revealed uniformly distributed MFC aggregates in the films, with a length of 10-90 mu m and a width spanning from a few hundred nanometers to several microns. Transmission electron microscopy showed that, in addition to aggregates, single MFC microfibrils were also embedded in the amylopectin matrix. It was impossible to cast antylopectin films of sufficient quality with less than 38 wt% glycerol. However, when MFC was added it was possible to produce high quality films even without glycerol. The film without glycerol was stiff and strong but not brittle. It was suggested that this remarkable effect was due to its comparatively high moisture content. Consequently MFC acted both as a "conventional" reinforcement because of its fibrous structure and also indirectly as a plasticiser because its presence led to an increase in film moisture content.
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| 9. |
- Nordqvist, David, et al.
(author)
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Enhancement of the wet properties of transparent chitosan-acetic-acid-salt films using microfibrillated cellulose
- 2007
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:8, s. 2398-2403
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Journal article (peer-reviewed)abstract
- This report presents a new route to enhance the wet properties of chitosan-acetic-acid-salt films using microfibrillated cellulose (MFC). The enhancement makes it easier to form chitosan-acetic-acid-salt films into various shapes at room temperature in the wet state. Chitosan with MFC was compared with the well-known buffer treatment. It was observed that films containing 5 wt % MFC were visually identical to the buffered/unbuffered films without MFC. Field-emission scanning electron microscopy indicated that MFC formed a network with uniformly distributed fibrils and fibril bundles in the chitosan matrix. The addition of MFC reduced the risk of creases and deformation in the wet state because of a greater wet stiffness. The wet films containing MFC were also extensible. Although the stiffness, strength and extensibility were highest for the buffered films, the wet strength of the MFC-containing unbuffered films was sufficient for wet forming operations. The effects of MFC on the mechanical properties of the dry chitosan films were small or absent. It was concluded that the addition of MFC is an acceptable alternative to buffering for shaping chitosan films/products in the wet state. The advantages are that the "extra" processing step associated with buffering is unnecessary and that the film matrix remains more water-soluble.
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| 10. |
- Pääkkö, M., et al.
(author)
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Enzymatic hydrolysis combined with mechanical shearing and high-pressure homogenization for nanoscale cellulose fibrils and strong gels
- 2007
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:6, s. 1934-1941
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Journal article (peer-reviewed)abstract
- Toward exploiting the attractive mechanical properties of cellulose I nanoelements, a novel route is demonstrated, which combines enzymatic hydrolysis and mechanical shearing. Previously, an aggressive acid hydrolysis and sonication of cellulose I containing fibers was shown to lead to a network of weakly hydrogen-bonded rodlike cellulose elements typically with a low aspect ratio. On the other hand, high mechanical shearing resulted in longer and entangled nanoscale cellulose elements leading to stronger networks and gels. Nevertheless, a widespread use of the latter concept has been hindered because of lack of feasible methods of preparation, suggesting a combination of mild hydrolysis and shearing to disintegrate cellulose I containing fibers into high aspect ratio cellulose I nanoscale elements. In this work, mild enzymatic hydrolysis has been introduced and combined with mechanical shearing and a high-pressure homogenization, leading to a controlled fibrillation down to nanoscale and a network of long and highly entangled cellulose I elements. The resulting strong aqueous gels exhibit more than 5 orders of magnitude tunable storage modulus G' upon changing the concentration. Cryotransmission electron microscopy, atomic force microscopy, and cross-polarization/magic-angle spinning (CP/MAS) C-13 NMR suggest that the cellulose I structural elements obtained are dominated by two fractions, one with lateral dimension of 5-6 nm and one with lateral dimensions of about 10-20 nm. The thicker diameter regions may act as the junction zones for the networks. The resulting material will herein be referred to as MFC (microfibrillated cellulose). Dynamical rheology showed that the aqueous suspensions behaved as gels in the whole investigated concentration range 0.125-5.9% w/w, G' ranging from 1.5 Pa to 10(5) Pa. The maximum G' was high, about 2 orders of magnitude larger than typically observed for the corresponding nonentangled low aspect ratio cellulose I gels, and G' scales with concentration with the power of approximately three. The described preparation method of MFC allows control over the final properties that opens novel applications in materials science, for example, as reinforcement in composites and as templates for surface modification.
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