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| 2. |
- Balthasar, Michael, et al.
(författare)
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Detailed Modeling of soot formation in a partially stirred plug flow reactor
- 2002
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Ingår i: Combustion and Flame. - 0010-2180. ; 128:4, s. 395-409
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work is to propose a detailed model for the formation of soot in turbulent reacting flow and to use this model to study a carbon black furnace. The model is based on a combination of a detailed reaction mechanism to calculate the gas phase chemistry, a detailed kinetic soot model based on the method of moments, and the joint composition probability density function (PDF) of these scalar quantities. Two problems, which arise when modeling the formation of soot in turbulent flows using a PDF approach, are studied. A consistency study of the combined scalar-soot moment approach reveals that the molecular diffusion term in the PDF-equation can be closed by the IEM and Curl-type mixing models. An investigation of different kernels for the collision frequency of soot particles shows that the influence of turbulence on particle coagulation is negligible for typical flame conditions and the particle size range considered. The model is used as a simple toot to simulate a furnace black process, which is the most important industrial process for the production of carbon blacks. Despite the simplifications in the modeling of the turbulent flow reasonable agreement between the calculated soot yield and data measured in an industrial furnace black reactor is achieved although no adjustments were made to the kinetic parameters of the soot model. The effect of the mixing intensity on soot yield and different soot formation rates is investigated. In addition the influence of different operating conditions such as temperature and equivalence ratio in the primary zone of the reactor is studied.
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| 3. |
- Beck, O, et al.
(författare)
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Frontline immunochromatographic device for on-site urine testing of amphetamines: laboratory validation using authentic specimens
- 2000
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Ingår i: Annals of clinical biochemistry. - : SAGE Publications. - 0004-5632. ; 3737 ( Pt 2), s. 199-204
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated a new test device for amphetamines and methamphetamines (Frontline ®, cut-off limit 300 ng/mL) using authentic clinical and forensic specimens. The device is based on immunochromatography and is dipped into urine and read visually by comparison with a colour scale after a few minutes. A total of 658 specimens were tested by comparing results of the screening procedure with established immunoassays. Discordant results were further investigated by gas chromatography- mass spectrometry or gas chromatography (with flame ionization detector). The Frontline device had a sensitivity of 93% and a specificity of 98%. When specimens were classified by urine amphetamine concentration, close agreement was obtained at concentrations below 150 ng/mL and above 1000 ng/mL. A small number of specimens with amphetamine concentrations between 300 and 1000 ng/mL tested negative in the Frontline test. This finding could to some extent be explained by the enantioselectivity of the antibodies in the Frontline test to d-amphetamine. We conclude that the performance of the Frontline test device for amphetamines is adequate for presumptive clinical and forensic screening.
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| 5. |
- Maigaard, P, et al.
(författare)
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Homogeneous charge compression ignition engine: A simulation study on the effects of inhomogeneities
- 2003
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Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 125:2, s. 466-471
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Tidskriftsartikel (refereegranskat)abstract
- A stochastic model for the HCCI engine is presented The model is based on the PaSPFR-IEM model and accounts for inhomogeneities in the combustion chamber while including a detailed chemical model for natural gas combustion, consisting of 53 chemical species and 590 elementary chemical reactions. The model is able to take any type of inhomogeneities in the initial gas composition into account, such as inhomogeneities in the temperature field, in the air-fuel ratio or in the concentration of the recirculated exhaust gas. With this model the effect of temperature differences caused by the thermal boundary layer and crevices in the cylinder for a particular engine speed and fuel to air ratio is studied. The boundary layer is divided into a viscous sublayer and a turbulent buffer zone. There are also colder zones due to crevices. All zones are modeled by a characteristic temperature distribution. The simulation results are compared with experiments and a previous numerical study employing a PFR model. In all cases the PaSPFR-IEM model leads to a better agreement between simulations and experiment for temperature and pressure. In addition a sensitivity study on the effect of different intensities of turbulent mixing on the combustion is performed. This study reveals that the ignition delay is a Junction of turbulent mixing of the hot bulk and the colder boundary layer.
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| 7. |
- Nevskaya, Natasha, et al.
(författare)
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Archaeal ribosomal protein L1: the structure provides new insights into RNA binding of the L1 protein family
- 2000
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Ingår i: Structure. - 0969-2126. ; 8:4, s. 363-371
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Tidskriftsartikel (refereegranskat)abstract
- Background: L1 is an important primary rRNA-binding protein, as well as a translational repressor that binds mRNA. It was shown that L1 proteins from some bacteria and archaea are functionally interchangeable within the ribosome and in the repression of translation. The crystal structure of bacterial L1 from Thermus thermophilus (TthL1) has previously been determined. Results: We report here the first structure of a ribosomal protein from archaea, L1 from Methanococcus jannaschii (MjaL1). The overall shape of the two-domain molecule differs dramatically from that of its bacterial counterpart (TthL1) because of the different relative orientations of the domains. Two strictly conserved regions of the amino acid sequence, each belonging to one of the domains and positioned close to each other in the interdomain cavity of TthL1, are separated by about 25 Å in MjaL1 owing to a significant opening of the structure. These regions are structurally highly conserved and are proposed to be the specific RNA-binding sites. Conclusions: The unusually high RNA-binding affinity of MjaL1 might be explained by the exposure of its highly conserved regions. The open conformation of MjaL1 is strongly stabilized by nonconserved interdomain interactions and suggests that the closed conformations of L1 (as in TthL1) open upon RNA binding. Comparison of the two L1 protein structures reveals a high conformational variability of this ribosomal protein. Determination of the MjaL1 structure offers an additional variant for fitting the L1 protein into electron-density maps of the 50S ribosomal subunit.
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