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Träfflista för sökning "FÖRF:(Bertil Persson) srt2:(2000-2004)"

Sökning: FÖRF:(Bertil Persson) > (2000-2004)

  • Resultat 1-10 av 56
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1.
  • Munck af Rosenschöld, Per, et al. (författare)
  • Quality assurance of patient dosimetry in boron neutron capture therapy
  • 2004
  • Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 43:4, s. 404-411
  • Tidskriftsartikel (refereegranskat)abstract
    • The verification of the correctness of planned and executed treatments is imperative for safety in radiotherapy. The purpose of the present work is to describe and evaluate the quality assurance (QA) procedures for patient dosimetry implemented at the boron neutron capture therapy (BNCT) facility at Studsvik, Sweden. The dosimetric complexity of the mixed neutron-photon field during BNCT suggests a careful verification of routine procedures, specifically the treatment planning calculations. In the present study, two methods for QA of patient dosimetry are presented. The first is executed prior to radiotherapy and involves an independent check of the planned absorbed dose to be delivered to a point in the patient for each treatment field. The second QA procedure involves in vivo dosimetry measurements using posttreatment activation analysis. Absorbed dose conversion factors taking the difference in material composition and geometry of the patient and the PMMA phantom used for reference dosimetry were determined using the Monte Carlo method. The agreement of the QA procedure prior to radiotherapy reveals an acceptably small deviation for 60 treatment fields of ±4.2% (1 SD), while the in vivo dosimetry method presented may benefit from improvements, as the deviations observed were quite substantial (±12%, 1 SD), and were unlikely to be due to actual errors in the clinical dosimetry.
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  • Persson, Bertil (författare)
  • Chloride migration coefficient of self-compacting concrete
  • 2004
  • Ingår i: Materials and Structures. - 1359-5997. ; 37:2, s. 82-91
  • Tidskriftsartikel (refereegranskat)abstract
    • In this article laboratory and analytical studies of the chloride migration coefficient, D, are presented. The result of studies on chloride migration of Self-Compacting Concrete, SCC, are compared with the corresponding properties of normal concrete with the same water-cement ratio, w/c and air content. Both 28 and 90 days' age applied at the start of the testing. Six SCC were studied and 2 NC, all with w/c = 0.39. The effect of normal and reversed order of mixing (filler last), increased amount of filler, type of filler, limestone powder, increased air content and large hydrostatic concrete pressure were investigated.
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4.
  • Persson, Bertil (författare)
  • Fire resistance of self-compacting concrete, SCC
  • 2004
  • Ingår i: Materials and Structures. - 1359-5997. ; 37:9, s. 575-584
  • Tidskriftsartikel (refereegranskat)abstract
    • This article outlines laboratory and full-scale studies on fire resistance of SCC. For this purpose 40 pre-stressed columns and 140 cylinders of concrete were subjected to compressive loading at high temperature. The SCC included water-binder ratios, w/b, between 0.40 and 0.70 and large amount limestone powder. Comparison was done with vibrated concrete, VC, with the same w/b. Mix proportions were chosen as regards tunnel concrete (w/b = 0.40), prefabricated concrete (w/b = 0.55) and concrete for production of dwelling houses (w/b = 0.70). The water-powder ratio, w/p varied between 0.28 and 0.70. The fullscale behaviour showed extensive fire spalling for water-cured concrete at w/p < 0.40 and for air-cured concrete at w/p < 0.35. One way of avoiding the fire spalling was to introduce polypropylene fibres, PPF, in the mix proportions, which was chosen to be very effective. The laboratory results on small cylinders indicated similar material behaviour of SCC and VC at high temperature when spalling did not occur. The project was performed 1999-2002.
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5.
  • Persson, Bertil (författare)
  • Justification of Federation International de Beton, fib, 2000 model for elastic modulus of normal and high-performance concrete, HPC
  • 2004
  • Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 34:4, s. 651-655
  • Tidskriftsartikel (refereegranskat)abstract
    • This article outlines an experimental and theoretical comparison between the fib 2000 model for elastic modulus of normal concrete, NC, and HPC and 144 laboratory tests. Two dimensions of specimen were studied (diameters 56 and 100 mm) and one climate (20 degreesC, sealed or with ambient relative humidity, RE, 60%). The age dependence did not seem to be well correlated between the derived and the measured elastic modulus. The fib 2000 model overestimated the elastic modulus of mature concrete and in contrast slightly underestimated the elastic modulus of young NC. As a whole, the derived modulus when using the fib model was about 110% of the elastic modulus measured at loading. A relationship to strength was found for this diversity with an increasing overestimation of the E-modulus at lower strength. (C) 2004 Published by Elsevier Ltd.
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  • Sarimov, R, et al. (författare)
  • Nonthermal GSM microwaves affect chromatin conformation in human lymphocytes similar to heat shock
  • 2004
  • Ingår i: IEEE Transactions on Plasma Science. - 0093-3813. ; 32:4, s. 1600-1608
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we investigated whether microwaves (MWs) of Global System for Mobile Communication (GSM) induce changes in chromatin conformation in human lymphocytes. Effects of MWs were studied at different frequencies in the range of 895-915 MHz in experiments with lymphocytes from seven healthy persons. Exposure was performed in transverse electromagnetic transmission line cell (TEM-cell) using a GSM test-mobile phone. All standard modulations included 2 W output power in the pulses, specific absorbed rate (SAR) being 5.4 mW/kg. Changes in chromatin conformation, which are indicative of stress response and genotoxic effects, were measured by the method of anomalous viscosity time dependencies (AVTD). Heat shock and treatment with the genotoxic agent camptothecin, were used as positive controls. 30-min exposure to MWs at 900 and 905 MHz resulted in statistically significant condensation of chromatin in lymphocytes from 1 of 3 tested donors. This condensation was similar to effects. of heat shock within the temperature window of 40degreesC-44degreesC. Analysis of pooled data from all donors showed statistically significant effect of 30-min exposure to MWs. Stronger effects of MWs was found following I-h exposure. In replicated experiments, cells from four out of five donors responded to 905 MHz. Responses to 915 MHz were observed in cells from I out of 5 donors, p < 0.002. Dependent on donor, condensation, 3 donors, or decondensation, 1 donor, of chromatin was found in response to I-h exposure. Analysis of pooled data from all donors showed statistically significant effect of 1-h exposure to MWs. In cells from one donor, this effect was frequency-dependent (p < 0.01). Effects of MWs correlated statistically significantly with effects of heat shock and initial state of chromatin before exposure. MWs at 895 and 915 MHz affected chromatin conformation in transformed lymphocytes. The conclusion-GSM microwaves under specific conditions of exposure affected human lymphocytes similar to stress response. The data suggested that the MW effects differ at various GSM frequencies and vary between donors.
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