| 1. |
- Riley, M A, et al.
(författare)
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Beyond band termination in Er-157 and the search for wobbling excitations in strongly deformed Hf-174
- 2005
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. 1735-1740
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Tidskriftsartikel (refereegranskat)abstract
- High-spin terminating bands in heavy nuclei were first identified in nuclei around Er-158(90). While examples of special terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work the high-spin structure of Er-157 has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently, four strongly or superdeformed (SD) sequences have been observed in Hf-174 and ultimate cranker calculations predict, such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment was run to search for linking transitions between the SD bands and possible wobbling modes.
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| 2. |
- Riley, M. A., et al.
(författare)
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Observation of states beyond band termination in Er-156,Er-157,Er-158 and strongly deformed structures in Hf-173,Hf-174,Hf-175
- 2006
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Ingår i: Physica Scripta. - 0031-8949. ; T125, s. 123-126
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Tidskriftsartikel (refereegranskat)abstract
- High-spin terminating bands in heavy nuclei were first identified in nuclei around Er-158(90). While examples of terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work, the high-spin structure of Er-156,Er-157,Er-158 has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently four strongly or superdeformed (SD) sequences have been observed in Hf-174, and cranking calculations using the Ultimate Cranker code predict that such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment took place to search for linking transitions between the SD bands, possible wobbling modes, and new SD band structures.
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| 3. |
- Saric, Fikret
(författare)
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A Detailed Kinetic Model for Calculation of the Soot Particle Size Distribution Function
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The soot particle size distribution was studied via numerical simulation under diesel like engine conditions using a detailed kinetic soot model. Two different mathematical methods of the soot model description have been used in this work. In the first part of the work, the method of moments is presented. In addition, a so called sectional method for the soot particle size distribution function in diffusion flames has been developed. Both of the methods have been employed for simulations in diesel like engine operating conditions. The commercial computational fluid dynamics (CFD) codes have been used in order to obtain more information of temporal and spatial soot particles size distribution inside the enclosed chamber. The predictive capabilities of the model have been validated versus experimental data for different fuels and different initial and boundary conditions. The subject of the calculations was the influence of these different values on the soot particle formation. The sectional model was validated with laboratory diesel fuel jet flame data for an optically accessible constant-volume combustion vessel, where test data at high pressure and high temperature are available. For the validation of the soot method of moments, different optical measurements of the in-cylinder soot have been presented. The combustion process itself is simulated using a progress variable model for the auto ignition of a diffusion flamelet, with the sectional model calculations. Source terms for soot particle inception, surface growth, and oxidation describing the interaction of the particles with the gas phase are taken from a flamelet library for both models. The coagulation of particles is calculated as part of the CFD calculations, based on the mean of the weighted soot mass fractions. The computations demonstrate the complex interaction between gaseous species, soot production, temperature, etc. Exclusion of any of the above effects can lead to significant errors.
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| 4. |
- Tuovinen, H, et al.
(författare)
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Modelling of hydrogen cyanide formation in room fires
- 2004
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Ingår i: Fire Safety Journal. - : Elsevier BV. - 0379-7112. ; 39:8, s. 737-755
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Tidskriftsartikel (refereegranskat)abstract
- A chemical kinetics model for calculation of the formation of hydrogen cyanide (HCN) has been made. The combustion of a mixture of methylamine and ethylene has been modelled using the stationary laminar flamelet concept. The flamelet calculations are based on several thousand elementary reaction steps including the chemical kinetics of HCN in combustion. The flamelets for both cold (293 K) and hot (1000 K) combustion product recycling have been calculated. The effect of strain is also included in the flamelet calculations. Scalar dissipation rates from 0.01 s(-1) to extinction values have been varied. Also the effect of radiation is included in the flamelet state relationships. Separate flamelet sets for various levels of radiation, from adiabatic up to 30% radiation losses, incremented by 1%, have been made. In the flow field calculation, the flamelet options may be used either as adiabatic, constant radiation or an interpolation between flamelet sets of different radiation. The chemical kinetics model, incorporated into a Reynolds-Averaging Navier-Stoke (RANS) type CFD code, has been used to simulate two laboratory fire tests of the combustion of nylon. Changing the size of the opening in the test room varied the ventilation between the two tests. Flamelet sets for a mixture of methylamine and ethylene with nitrogen content close to that of nylon were used in these simulations. The simulations were made with and without recycling the combustion products back to the fire. The calculations show that recycling of the combustion products to the fire increases the formation of HCN and CO. Similarly, a lowered ventilation rate increases the formation of these species. The calculated temperatures and main species concentrations, including HCN, agree reasonably well with the trends in the laboratory measurements.
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