| 1. |
- Karlsson, Magnus G, et al.
(författare)
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Semi-conductor detectors in output factor measurements
- 1997
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 42:3, s. 293-296
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Output factors are generally measured with cylindrical ionization chambers. It was investigated if Si-diodes of p-type instead could be used. The advantage would be the small detector size and the robust construction of the detector. Materials and methods: Two types of diodes were studied, one with a shielding layer of tungsten specially made to reduce the excess response for scattered photons and one standard diode without any extra shielding. The measurements were performed at accelerating potentials between 4 and 50 MV and beam sizes between 4 cm x 4 cm and 40 cm x 40 cm. Results: The results showed that both types of diodes are suitable for measurements of head scatter factors in mini-phantoms. However, the diodes were found inappropriate for measurement of output factors for large fields in extended water phantoms. For small fields (<10 cm x 10 cm) a small detector is advantageous and no errors due to the scatter contribution were seen. Conclusions: An cylindrical ionization chamber is the best choice for output factor measurements in extended water phantoms for large field sizes while diodes are an alternative in small fields. There were negligible differences between the detectors in head scatter measurements in mini phantoms.
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| 2. |
- Sjögren, Rickard, et al.
(författare)
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Depth for dose calibration in high energy photon beams
- 1997
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 43:3, s. 311-313
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: The normalisation depth for determination of output factors in photon fields has frequently been the depth of dose maximum. At high energies the contribution from contaminating electrons is significant at dose maximum and is critically dependent on the beam geometry parameters, which is why a larger depth should be preferred. Materials and methods: The effect of electron contamination was studied using a purging magnet to remove charged particles from the treatment head and a helium bag to minimise production between the head and the phantom. Results: A depth of 10 cm was found to be beyond the range of the contaminating electrons for photon energies up to 20 MV (TPR1020 = 0.772). However, at 50 MV (TPR1020 = 0.810) contaminating electrons contribute 2-3% to the absorbed dose at 10 cm depth. Conclusions: 10 cm is recommended as both reference and normalisation depth for all megavoltage photon beam qualities, i.e. Co-60 and X-rays from accelerators up to 50 MV. (C) 1997 Elsevier Science Ireland Ltd.
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| 3. |
- Akhmediev, N., et al.
(författare)
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Cherenkov radiation emitted by solitons in optical fibers
- 1995
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 51:3, s. 2602-2607
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a simple, fully analytic method of calculating the amount of radiation emitted by optical solitons perturbed by higher-order dispersion effects in fibers and find good agreement with numerical results. It is pointed out that this radiation mechanism is analogous to the well-known Cherenkov radiation processes in nonlinear optics. © 1995 The American Physical Society.
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| 4. |
- Anders, Berntson, et al.
(författare)
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Self-phase modulation in dispersion compensated optical fibre transmission systems
- 1996
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Ingår i: Optics Communications. - : Elsevier. - 0030-4018 .- 1873-0310. ; 130:1-3, s. 153-162
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Tidskriftsartikel (refereegranskat)abstract
- An analysis is made of the influence of self-phase modulation on optical fibre communication systems where the chromatic dispersion is compensated for by a dispersion compensation fibre. In particular we derive a simple and useful expression for the optimal fibre length in the presence of nonlinearities.
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| 5. |
- Anders, Berntson, et al.
(författare)
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Self-phase modulation in dispersion compensated optical fibre transmission systems
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An analysis is made of the influence of self-phase modulation on optical fibre communication systems where the chromatic dispersion is compensated for by a dispersion compensation fibre. In particular we derive a simple and useful expression for the optimal fibre length in the presence of nonlinearities.
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| 6. |
- Anders, Berntson, et al.
(författare)
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Self-phase modulation in dispersion-compensating systems
- 1996
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Ingår i: Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS. - : IEEE. ; , s. 405-406
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Konferensbidrag (refereegranskat)abstract
- The effects of SPM in a dispersion-compensation system are investigated. An explicit and compact formula is presented for the optimal length of the DCF. In particular, it is shown that the order of the fibers is important when SPM is considered. Using precompensation SPM effects can improve system performance. A qualitative comparison between the analytical predictions and previously presented experimental results show good agreement.
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| 7. |
- Bakhshi, Bamdad, 1970, et al.
(författare)
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Experimental observation of soliton robustness to polarisation dispersion pulse broadening
- 1999
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 35:1, s. 65-66
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Tidskriftsartikel (refereegranskat)abstract
- Soliton robustness to polarisation dispersion pulse broadening in a 400km installed optical fibre is experimentally demonstrated. With 10ps input pulses and a differential group delay of 7.6ps, the soliton pulsewidth at the receiver is maintained within 10-11ps when the input polarisation is changed, while the corresponding range for dispersion-compensated linear pulses is 10.5-15.5ps.
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| 8. |
- Bakhshi, Bamdad, 1970, et al.
(författare)
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Measurement of the differential group delay in installed optical fibers using polarization multiplexed solitons
- 1999
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Ingår i: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1041-1135 .- 1941-0174. ; 11:5, s. 593-595
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally demonstrate a new technique for measurement of the differential group delay (DGD) in optical fibers using polarization-division multiplexed (PDM) solitons: the change in the separation of orthogonally polarized solitons propagating along different principal axes in a fiber equals the DGD at the signal wavelength. Based on this principle, we use PDM solitons to measure the accumulated DGD at different distances along a 400-km installed fiber. The measured DGD exhibits the expected square-root-of-length dependence, corresponding to a polarization-mode dispersion of 0.26 ps/km1/2. The results are in excellent agreement with those obtained by a commercial instrument utilizing Jones matrix eigenanalysis.
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| 9. |
- Bakhshi, Bamdad, 1970, et al.
(författare)
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Soliton interaction penalty reduction by receiver filtering
- 1998
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Ingår i: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1041-1135 .- 1941-0174. ; 10:7, s. 1042-1044
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Tidskriftsartikel (refereegranskat)abstract
- We present the first detailed numerical study of the impact of receiver low-pass filtering in soliton interaction-limited communication systems. We propagate 40-Gb/s pseudorandom bit sequences (PRBS's) of 28-1 solitons up to one soliton collision distance (Zc-) and optimize the filter bandwidth to minimize the interaction induced eye opening penalty. The distance at 0.5-dB penalty is increased over 40% through filtering. The penalty is essentially pulsewidth independent when considering distances normalized by Zc. We also show that PRBS's of at least 28 - 1 solitons are required to accurately simulate random data.
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| 10. |
- Bengtsson, C, et al.
(författare)
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Co-operation of the MIND-method and the Pinch Technology : Energy Efficient Pre-evaporation of Bleach Plant Filtrate Using Waste Heat
- 1999
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- In order to decrease the environmental impacts caused by the pulp- and paper industry it is nowadays more or less common to perform a closure of the mill. The closure of the bleach plant will result in a minimal intake of fresh water and thereby the effluent will be contaminated to a greater extent. The bleach plant filtrate can be mixed with the black liquor and combusted in the soda recovery boilers. The necessity of pre-evaporating the bleach plant filtrate will thereby arise. In this study some alternatives have been investigated how to process integrate a pre-evaporation plant. Three alternatives have been investigated where the pre-evaporation can be fulfilled by using live steam only or live steam combined with waste heat. It can also be achieved by using a mechanical vapour recompression unit, which uses low temperature waste heat to accomplish the pre-evaporation. Due to the complexity of the mill two different methods have been used to evaluate the alternatives for pre-evaporation. The pinch-method is used on a lower aggregation level where the different components for pre-evaporation is considered, while the MIND-method is used on the higher aggregation level to take into account the whole mill. Two different scenarios have been studied, one with the existing electricity prices and one with an increase of the electricity prices with 50%. In both scenarios it is shown preferable to use the live steam/waste heat alternative compared to the ”worst case”, using mere live steam. The investment costs for the live steam/waste heat case will imply that the payback period will be approximately 3.5 years. The mechanical vapour recompression alternative is shown profitable with the existing electricity prices, compared to the live steam case. But due to the high investment costs it gives an unacceptable payback period. When the electricity price is increased by 50% it shows not profitable. In case of an increase of the fuel prices the mechanical vapour recompression alternative will be more profitable due to the usage of less fuel compared to the other cases.
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