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  • Abdalla, M. A., et al. (författare)
  • A CMOS APS for dental X-ray imaging using scintillating sensors
  • 2001
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 460:1, s. 197-203
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we present an integrating CMOS Active Pixel Sensor (APS) circuit to be used with scintillator type X-ray sensors for intra oral dental X-ray imaging systems. Different pixel architectures were constructed to explore their performance characteristics and to study the feasibility of the development of such systems using the CMOS technology. A prototype 64 x 80 pixel array has been implemented in a CMOS 0.8 mum double poly n-well process with a pixel pitch of 50 mum. A spectral sensitivity measurement for the different pixels topologies, as well as measured X-ray direct absorption in the different APSs are presented. A measurement of the output signal showed a good linearity over a wide dynamic range. This chip showed that the very low sensitivity of the CMOS APSs to direct X-ray exposure adds a great advantage to the various CMOS advantages over CCD-based imaging systems,
  • Abdalla, M. A., et al. (författare)
  • An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier
  • 2001
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 466:1, s. 232-236
  • Tidskriftsartikel (refereegranskat)abstract
    • We present in this paper an integrating CMOS Active Pixel Sensor (APS) circuit coated with scintillator type sensors for intra-oral dental X-ray imaging systems. The photosensing element in the pixel is formed by the p-diffusion on the n-well diode. The advantage of this photosensor is its very low direct absorption of X-rays compared to the other available photosensing elements in the CMOS pixel. The pixel features an integrating capacitor in the feedback loop of a preamplifier of a finite gain in order to increase the optical sensitivity. To verify the effectiveness of this in-pixel preamplification, a prototype 32 x 80 element CMOS active pixel array was implemented in a 0.8 mum CMOS double poly, n-well process with a pixel pitch of 50 mum. Measured results confirmed the improved optical sensitivity performance of the APS. Various measurements on device performance are presented.
  • Aboelfotoh, M O, et al. (författare)
  • Schottky-barrier behavior of metals on n- and p-type 6H-SiC
  • 2003
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 67:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The Schottky-barrier height of a number of metals (Ti, Ni, Cu, and Au) on n- and p-type Si-terminated 6H-SiC has been measured in the temperature range 150-500 K. It is found that the barrier height to n-type 6H-SiC does not exhibit a temperature dependence, while for p-type 6H-SiC the change in the barrier height with temperature follows very closely the change in the indirect energy gap in 6H-SiC. These results are inconsistent with models of Schottky-barrier formation based on the concept of a charge neutrality level. Furthermore, the present results cannot be reconciled with a defect pinning mechanism, contrary to the conclusions of earlier studies on III-V compound semiconductors. We suggest that chemical bonding at the metal-semiconductor interface plays an important role in determining the Schottky-barrier height.
  • Amon, B., et al. (författare)
  • From first-order logic to automated word generation for Lyee
  • 2003
  • Ingår i: Knowledge-Based Systems. - 0950-7051. ; 16:07-8, s. 413-429
  • Tidskriftsartikel (refereegranskat)abstract
    • A conceptual schema can be viewed as a language to describe the phenomena in a system to be modelled, i.e. a set of derivation rules and integrity constraints as well as a set of event-rules describing the behaviour of an object system. In this paper, we investigate the relationship between the Lyee software requirements concepts with various constructs in conceptual modelling. Within our work we choose the Unified Modelling Language (UML) as a modelling notation for explaining conceptual models. The result obtained models a fully expressive set of UML and First Order Logic constructs mapped into Lyee concepts.
  • Andersson, J, et al. (författare)
  • Ageing of Flexographic Printed Model Cellulose Surfaces and Determination of the Mechanisms Behind Ageing
  • 2009
  • Ingår i: Pulp & paper Canada. - 0316-4004. ; 110:6, s. 34-38
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of storage conditions on the ink detachment efficiency of water-based flexographic ink printed onto model cellulose surfaces and handsheets was investigated. It was shown that UV light, elevated temperatures, longer storage time, increasing surface roughness, and increasing surface hydrophobicity all had a negative effect on ink detachment. It was also shown that the ink's chemical and structural characteristics changed when stored at elevated temperatures. No chemical or structural changes could be observed for the ink when stored under UV light.
  • Andreasson, B., et al. (författare)
  • Determination of fibre pore structure : influence of salt, pH and conventional wet strength resins
  • 2005
  • Ingår i: Cellulose (London). - 0969-0239. ; 12:3, s. 253-265
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However, the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength, measured as zero span-strength of the sheets.
  • Andreasson, B., et al. (författare)
  • The porous structure of pulp fibres with different yields and its influence on paper strength
  • 2003
  • Ingår i: Cellulose (London). - 0969-0239. ; 10:2, s. 111-123
  • Tidskriftsartikel (refereegranskat)abstract
    • The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of H-2 in fibres saturated with (H2O)-H-2. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/ lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.
  • Badel, X, et al. (författare)
  • Improvement of an X-ray imaging detector based on a scintillating guides screen
  • 2002
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 487:1-2, s. 129-135
  • Tidskriftsartikel (refereegranskat)abstract
    • An X-ray imaging detector has been developed for dental applications. The principle of this detector is based on application of a silicon charge coupled device covered by a scintillating wave-guide screen. Previous studies of such a detector showed promising results concerning the spatial resolution but low performance in terms of signal to noise ratio (SNR) and sensitivity. Recent results confirm the wave-guiding properties of the matrix and show improvement of the detector in terms of response uniformity, sensitivity and SNR. The present study is focussed on the fabrication of the scintillating screen where the principal idea is to fill a matrix of Si pores with a CsI scintillator. The photoluminescence technique was used to prove the wave-guiding property of the matrix and to inspect the filling uniformity of the pores. The final detector was characterized by X-ray evaluation in terms of spatial resolution, light output and SNR. A sensor with a spatial resolution of 9 LP/mm and a SNR over 50 has been achieved using a standard dental X-ray source and doses in the order of those used at the moment by dentists (around 25 mR).
  • Badel, X., et al. (författare)
  • Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors
  • 2004
  • Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499. ; 51:3, s. 1001-1005
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon charge-coupled devices (CCDs) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this paper, such waveguides were fabricated by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using scanning electron microscopy and tested under X-ray exposure. Theoretical efficiencies of macropore arrays filled with CsI(TI) were also calculated, indicating that the optimal pore depth for metallized macropore arrays is about 80 mum while it is around 350 mum for oxidized ones. This result, together with the roughness of the metal coating, explains why lower SNR values were measured with the metallized macropores. Indeed, the macropore arrays had depths in the range of 210-390 mum, which is favorable to oxidized structures.
  • Badel, X, et al. (författare)
  • Performance of scintillating waveguides for CCD-based X-ray detectors
  • 2006
  • Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499. ; 53:1, s. 3-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Scintillating films are usually used to improve the sensitivity of CCD-based X-ray imaging detectors. For an optimal spatial resolution and detection efficiency, a tradeoff has to be made on the film thickness. However, these scintillating layers can also be structured to provide a pixellated screen. In this paper, the study of CsI(TI)-filled pore arrays is reported. The pores are first etched in silicon, then oxidized and finally filled with CsI(TI) to form scintillating waveguides. The dependence of the detector sensitivity on pore depth, varied from 40 to 400 mu m here, follows rather well theoretical predictions. Most of the detectors produced in this work have a detective quantum efficiency of the incoming X-ray photons of about 25%. However, one detector shows that higher efficiency can be achieved approaching almost the theoretical limit set by Poisson statistics of the incoming X-rays. Thus, we conclude that it is possible to fabricate scintillating waveguides with almost ideal performance. Imaging capabilities of the detectors are demonstrated.
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