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- Carling, Tobias, et al.
(författare)
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Familial hypercalcemia and hypercalciuria caused by a novel mutation in the cytoplasmic tail of the calcium receptor
- 2000
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - 0021-972X .- 1945-7197. ; 85:5, s. 2042-7
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Tidskriftsartikel (refereegranskat)abstract
- Familial hyperparathyroidism (HPT), characterized by hypercalcemia and hypercalciuria, and familial benign hypocalciuric hypercalcemia (FHH) are the most common causes of hereditary hypercalcemia. The calcium-sensing receptor (CaR) regulates PTH secretion and renal calcium excretion. Heterozygous inactivating mutations of the gene cause FHH, whereas CaR gene mutations have not been demonstrated in HPT. In a kindred with 20 affected individuals, the hypercalcemic disorder segregated with inappropriately higher serum PTH and magnesium levels and urinary calcium levels than in unaffected members. Subtotal parathyroidectomy revealed parathyroid gland hyperplasia/adenoma and corrected the biochemical signs of the disorder in seven of nine individuals. Linkage analysis mapped the condition to markers flanking the CaR gene on chromosome 3q. Sequence analysis revealed a mutation changing phenylalanine to leucine at codon 881 of the CaR gene, representing the first identified point mutation located within the cytoplasmic tail of the CaR. A construct of the mutant receptor (F881L) was expressed in human embryonic kidney cells (HEK 293), and demonstrated a right-shifted dose-response relationship between the extracellular and intracellular calcium concentrations. The hypercalcemic disorder of the present family is caused by an inactivating point mutation in the cytoplasmic tail of the CaR and displays clinical characteristics atypical of FHH and primary HPT.
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- Gustavsson, Jonas, 1973, et al.
(författare)
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3-D Modeling of Conventional and HCCI Combustion Diesel Engines
- 2004
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Ingår i: SAE, Tampa 25-28 oct 2004. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Konferensbidrag (refereegranskat)abstract
- Operation of a Diesel engine in HCCI combustion mode is typically restricted to moderate engine loads. For practical applications, an engine switching from HCCI to conventional Diesel combustion mode at higher loads appears to be the most plausible solution. In this light, modeling applicable to both combustion modes is favourable. The performance of Diesel engines is affected by chemical kinetics of fuel oxidation through correct prediction of auto-ignition, especially at complicated injection scenarios such as those for HCCI. Thus, the modeling exploits the advantage of the detailed chemistry approach which incorporates a generalized partially stirred reactor, (PaSR), model coupled with a surrogate diesel fuel oxidation mechanism as a substitute of real hydrocarbon fuel. The surrogate Diesel fuel is assumed to be a 70/30 % mixture of n-heptane and toluene, consisting of 68 species participating in 279 reactions. PaSR assumes that chemical processes proceed in two successive steps: the reaction act follows after the micro-mixing simulated on a sub-grid scale. Consistently evaluated time scales for micro-mixing and limiting reaction rates gives a combustion model in a "well-closed" form incorporated into the KIVA-3V code. The results of the model were verified by experimental results obtained from a direct injection Diesel engine operated in conventional and HCCI combustion mode. The engine is a single cylinder version of a passenger car type common rail engine with a displacement of 480 cc. Split injection was used for conventional Diesel operation. For HCCI operation, fuel was injected in multiple steps during the compression stroke creating a homogeneous mixture avoiding spray interaction with the cylinder liner and piston. As a measure to properly phase the combustion process in the engine cycle and to prevent knock, a combination of a reduced geometric compression ratio and high rates of cooled EGR was investigated.
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- Gustavsson, Jonas, 1973, et al.
(författare)
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3 D Simulation of Multiple Injections in DI Diesel Engine
- 2004
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Ingår i: COMODIA 2004.
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Konferensbidrag (refereegranskat)abstract
- In numerical simulation of spray combustion in DI Diesel engines, a correctly modeled spray behavior is essential, since it forms a fundamental basis for the combustion process. Droplet penetration and vapor distribution determines combustion characteristics such as ignition delay and position, flame lift-off, heat release rate, emissions formation, etc. The process of spray combustion development is modeled in several distinctive stages and much research has been devoted to this area. Stages such as spray primary- and secondary -break-up, droplet collision and evaporation can all be modeled in various ways with not always consistent results. In this paper, among these stages, a special attention is paid on the development of a new collision model and it's effect on spray combustion in both the 2-D constant volume vessel and in DI Diesel engine combustion chamber represented on a 3-D sector grid.The calculations were performed using the KIVA3V, release 2, CFD code supplemented by the Partially Stirred Reactor (PaSR) model for turbulence-chemistry interaction coupled with the detailed chemical mechanism (68 species, 280 reactions) of diesel oil surrogate represented by a mixture of n-heptane and toluene. The modified collision model (Nordin, 2001) includes elements of a classic collision theory to calculate a probability of droplet collision/coalescence with a highly reduced grid dependence compared with the original ORourke model. The model has a considerable impact on the spray development, and it has been validated using constant volume experimental data.When simulating the Volvo NED5 DI Diesel engine in a split injection mode, it was found that the collisions play a crucial role in predicting the rate of heat release during the pilot injection. More specifically, if a collision probability is over-predicted, it causes a droplet cluster formation and too fuel lean conditions resulting in a decrease in combustion intensity. Since the O'Rourke collision probability is proportional to the number of droplets in the cell, the droplet displacement volume based on relative velocity of colliding droplets and inverse proportional to the cell volume, it causes both high grid dependence and does not discriminate droplet trajectories which are not intersecting each other. In a new grid independent formulation, two vital requirements have to be met for collision between two droplets to occur: first, they have to travel towards each other being in a so-called collision cone and second, all these colliding droplets are constrained to a certain exponential time-decaying probability.The former weak rate of heat release for the pilot injection (Gustavsson, Golovitchev, 2003) related to the O´Rourke collision model has been replaced by better predictions of cylinder pressure and heat release rate resulting in a closer agreement to experimental data from the single cylinder engine.
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- Gustavsson, Jonas
(författare)
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The development of streamwise streaky structures in the suction boundary layer
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An analytical solution is sought for the perturbation velocity field in a boundary layer with prescribed suction through a porous surface. Addressing the problem as an initial value problem, using stream- and spanwise Fourier transforms and Laplace transformation in time, yields solutions for the vertical velocity and the normal vorticity. Comparisons with the suction-free case are made and conclusions are drawn regarding the stabilizing effects of the suction motion. It is found that the analytical solutions give support to the theory that the presence of a porous boundary with suction acts stabilizing.
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- Gustavsson Tingvall, Patrik, et al.
(författare)
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The impact of seasonal unit roots and vector ARMA modelling on forecasting monthly tourism flows
- 2001
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Ingår i: Tourism Economics. - : SAGE Publications. - 1354-8166 .- 2044-0375. ; 7:2, s. 117-134
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Tidskriftsartikel (refereegranskat)abstract
- The effect of imposing different numbers of unit roots on forecasting accuracy is examined using univariate ARMA models. To see whether additional information improves forecasting accuracy and increases the informative forecast horizon, the authors cross-relate the time series for inbound tourism in Sweden for different visitor categories and estimate vector ARMA models. The mean-squared forecast error for different filters indicates that models in which unit roots are imposed at all frequencies have the smallest forecast errors. The results from the vector ARMA models with all roots imposed indicate that the informative forecast horizon is greater than for the univariate models. Out-of-sample evaluations indicate, however, that the univariate modelling approach may be preferable.
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