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A Koponen

Publications and source records attributed to A Koponen.

16 recordsLinked to original sources
PubMed2006

Simulation of liquid penetration in paper.

Capillary penetration of a wetting liquid in a microtomographic image of paper board, whose linear dimension was close to the average length of wood fibers, was simulated by the lattice-Boltzmann method. In spite of the size of the system not being large with respect to the size of structural inhomogeneities in the sample, for unidirectional penetration the simulated behavior was described well by that of the Lucas-Washburn equation, while for radial penetration a radial capillary equation described the behavior. In both cases the average penetration depth of the liquid front as a function of time followed a power law over many orders of magnitude. Capillary penetration of small droplets of liquid was also simulated in the same three-dimensional image of paper. In this case the simulation results could be described by a generalized form of the radial-penetration equation.

Journal Article↗
PubMed2005

Strain hardening in liquid-particle suspensions.

The behavior of a liquid-particle suspension induced to sheared motion was analyzed by numerical simulations. When the velocity (strain) of the suspension began to increase, its viscosity first stayed almost constant, but increased then rapidly to a clearly higher level. This increase in viscosity is shown to be related to formation of clusters of suspended particles. Clusters are shown to increase the viscosity by enhanced momentum transfer though clustered particles. This is the mechanism behind the strain-hardening phenomenon observed in small-strain experiments on liquid-particle suspensions.

Journal Article↗
PubMed2004

Oral treatment of acute myeloid leukaemia with etoposide, thioguanine, and idarubicin (ETI) in elderly patients: a prospective randomised comparison with intravenous cytarabine, idarubicin, and thioguanine in the second and third treatment cycle.

A randomised multicentre study was conducted among patients over 65 yr of age with newly diagnosed acute myeloid leukaemia (AML) to compare oral treatment with etoposide 80 mg/m(2) and thioguanine 100 mg/m(2) twice daily on 5 d and idarubicin 15 mg/m(2) on 3 d (ETI) to a mainly i.v. combination of cytarabine 100 mg/m(2) twice daily on 5 d, idarubicin 12 mg/m(2) x 1, and thioguanine (TAI). Ninety-two patients were enrolled. Their median age was 72 yr, range 65-84 yr. Sixty-five patients had de novo AML, 21 AML subsequent to myelodysplastic syndrome, and six treatment-related AML. They received at first a 6-d i.v. treatment with cytarabine and idarubicin. After the first treatment, 68 patients were randomised to receive two cycles of ETI (n = 36) or TAI (n = 32) and thereafter maintenance with mercaptopurine and methotrexate. Of the 92 patients, 52 (57%) achieved remission at some stage. The median survival was 10 months. There were no significant differences between the patients randomised to ETI or TAI in the remission rate (67% vs. 72%), survival (12 months from randomisation in both arms), event-free survival or relapse rate. The patients randomised to receive ETI spent significantly fewer days at hospital during the two randomised cycles (20 vs. 41 d, P = 0.010), and they had fewer days with infusions, shorter neutropenias and thrombocytopenias and fewer and less severe infections. In conclusion, treatment with oral ETI resulted in a similar antileukaemic effect as obtained with mainly i.v. TAI, with less toxicity and reduced need for hospitalisation.

Administration, Oral↗
PubMed2003

Clustering and viscosity in a shear flow of a particulate suspension.

A shear flow of particulate suspension is analyzed for the qualitative effect of particle clustering on viscosity using a simple kinetic clustering model and direct numerical simulations. The clusters formed in a Couette flow can be divided into rotating chainlike clusters and layers of particles at the channel walls. The size distribution of the rotating clusters is scale invariant in the small-cluster regime and decreases rapidly above a characteristic length scale that diverges at a jamming transition. The behavior of the suspension can qualitatively be divided into three regimes. For particle Reynolds number Re(p) less than or approximately equal 0.1, viscosity is controlled by the characteristic cluster size deduced from the kinetic clustering model. For Re(p) approximately 1, clustering is maximal, but the simple kinetic model becomes inapplicable presumably due to onset of instabilities. In this transition regime viscosity begins to increase. For Re(p) greater than or approximately equal 10, inertial effects become important, clusters begin to breakup, and suspension displays shear thickening. This phenomenon may be attributed to enhanced contribution of solid phase in the total shear stress.

Journal Article↗
PubMed2002

Lattice-Boltzmann and finite-difference simulations for the permeability for three-dimensional porous media.

Numerical micropermeametry is performed on three-dimensional porous samples having a linear size of approximately 3 mm and a resolution of 7.5 microm. One of the samples is a microtomographic image of Fontainebleau sandstone. Two of the samples are stochastic reconstructions with the same porosity, specific surface area, and two-point correlation function as the Fontainebleau sample. The fourth sample is a physical model that mimics the processes of sedimentation, compaction, and diagenesis of Fontainebleau sandstone. The permeabilities of these samples are determined by numerically solving at low Reynolds numbers the appropriate Stokes equations in the pore spaces of the samples. The physical diagenesis model appears to reproduce the permeability of the real sandstone sample quite accurately, while the permeabilities of the stochastic reconstructions deviate from the latter by at least an order of magnitude. This finding confirms earlier qualitative predictions based on local porosity theory. Two numerical algorithms were used in these simulations. One is based on the lattice-Boltzmann method, and the other on conventional finite-difference techniques. The accuracy of these two methods is discussed and compared, also with experiment.

Journal Article↗
PubMed2002

Allogeneic blood stem cell transplantation following non-myeloablative conditioning for hypereosinophilic syndrome.

A male patient with hypereosinophilic syndrome (HES) underwent an allogeneic blood stem cell transplantation from a female donor following non-myeloablative conditioning consisting of a 2 Gy dose of TBI and fludarabine 30 mg/m(2) intravenously on three days. Before transplantation 100% of the mitotic bone marrow cells of the patient showed a clonal karyotype abnormality. Three months after the transplantation eosinophilia had resolved and a chromosome analysis revealed normal female karyotype. The present study shows that stem cell transplantation after non-myeloablative conditioning may have curative potential for HES.

Adult↗
PubMed2002

Fouling dynamics in suspension flows.

A particle suspension flowing in a channel in which fouling layers are allowed to form on the channel walls is investigated by numerical simulation. A two-dimensional phase diagram with at least four different behaviors is constructed. The fouling is modeled by attachment during collision with the deposits and by detachment caused by large enough hydrodynamic drag. For fixed total number of particles and small Reynolds numbers, the relevant parameters governing the fouling dynamics are the solid volume fraction of the suspension and the detachment drag force threshold. Below a critical curve in this 2D phase space only transient fouling takes place when the suspension is accelerated from rest by a pressure gradient. Above the fouling transition line, persistent fouling layers are formed via ballistic deposition for low and via homogeneous deposition for large solid volume fractions. Close to the fouling transition line, the flow path between the deposited layers meanders, while necking appears for increasing distance from the transition. Finally, another transition to a fully blocked flow path takes place. As determined by the estimated amount of deposited particles at saturation, both transitions seem to be discontinuous. Large fluctuations and long saturation times are typical of the dynamics of the system.

Journal Article↗
PubMed1998

ADD1/SREBP-1c mediates insulin-induced gene expression linked to the MAP kinase pathway.

The aim of this study was to define the role of sterol regulatory element binding protein (SREBP)-1c, the human homologue to ADD1 (adipocyte determination- and differentiation-dependent factor 1), in insulin-induced gene expression. Transfection studies using SREBP-1-deficient cells and a LDL receptor promoter fragment containing the ADD1/SREBP-1c binding side showed that the effects of insulin and PDGF were abolished compared to control cells and completely reconstituted by overexpressing ADD1/SREBP-1c. Overexpression of upstream activators of MAP kinases, like MEKK1 or MEK1, demonstrated that ADD1/SREBP-1c-mediated effects of insulin and PDGF might be linked to the MAP kinase cascade. The recombinant N-terminal domain of ADD1/SREBP-1c was phosphorylated predominantly on serine and slightly on threonine residues by MAP kinases ERK1 and ERK2 in vitro. This was reversible by alkaline phosphatase. We conclude that ADD1/SREBP-1c mediates gene regulatory effects of insulin as well as PDGF and that this signalling is linked to the MAP kinase cascade.

Alkaline Phosphatase↗
PubMed1998

Serious adverse events after HPA-incompatible platelet transfusions in an alloimmunized patient with leukaemia.

We describe an alloimmunized female patient who developed serious adverse reactions when receiving HPA-incompatible platelet transfusions. She had received 13 transfusions with random platelets before the first allergic reactions. Antibodies against both the human leucocyte antigens (HLA) and several human platelet antigens (HPA) were detected at the time of transfusions. When the patient received HLA- and HPA-compatible platelets, no reactions followed the transfusions and platelet count increments were good. When she was transfused with platelets from donors with one foreign HLA antigen, her reactions were fever, chills and headache and the response to platelet transfusions was poor. When the platelets were HLA compatible but HPA incompatible, the reactions were repeatedly rapid pulse, shortness of breath, tightness of chest and wheezing interpretable as anaphylactoid reactions. Platelet count increments were satisfactory. When rare side-effects occur after transfusion, detailed immunohaematological studies are indicated.

Aged↗
PubMed1983

Pharmacokinetic interactions of timolol with vasodilating drugs, food and phenobarbitone in healthy human volunteers.

Pharmacokinetic interactions of oral timolol maleate 10 mg, with food (3566 kJ), single oral doses of prazosin 1 mg and dihydralazine 25 mg, and with a 1 week pretreatment with phenobarbitone 100 mg daily were examined in a randomized crossover study in 12 healthy volunteers. After fasting, the peak level (Cmax = 29.1 +/- 3.2 ng/ml; mean +/- SEM) was reached at 1.3 +/- 0.1 h (Tmax). The total area under the serum concentration-time curve (AUC0-infinity) was 154.4 +/- 33.8 ng x h/ml, total clearance (Cltot) 751.5 +/- 90.6 ml/min, renal clearance (Clren) 97.2 +/- 10.1 ml/min, elimination half-life (t1/2) 2.9 +/- 0.3 h and 24-h recovery in urine (X0u-24) 11.1 +/- 1.4% of the dose. Food and prazosin did not significantly affect the fate of timolol maleate. Dihydralazine enhanced Cmax (38.2 +/- 4.6 ng/ml) only when compared to phenobarbitone treatment, and did not affect any other parameters. Phenobarbitone pretreatment somewhat lowered Cmax (25.5 +/- 3.9 ng/ml), AUC0-infinity (117.5 +/- 22.1; p less than 0.05 vs food) and X0u-24 (8.7 +/- 1.2%), evidently by increasing Cltot (957.5 +/- 116.9 ml/min; p less than 0.05 vs food), but it did not affect Clren. It is concluded that the pharmacokinetics of timolol maleate can be altered to a limited extent in opposite directions by dihydralazine and phenobarbitone.

Adult↗