Transport Phenomena and Electrode Reactions Generated by an Electric Field in Colloidal Silica.

The kinetics of transport phenomena generated by an electric field and leading to the formation of density gradients in suspensions of charged colloidal silica were studied by using various electrodes. The rate of approach to a steady-state density gradient was found to be much higher when using metallic electrodes (Cu, Fe, and Pt) in comparison with graphite (C) electrodes. Nevertheless, the initial rate with C electrodes was substantially increased by the addition of hydroquinone-quinone because the redox reactions, necessary for electrode-electrolyte current transfer, occur at lower potential compared with the electrolysis of water. On the other hand, the products of oxidation of hydroquinone which accumulate in the system bring about an important decrease of the zeta potential of silica particles and progressive deceleration of their electrophoretic mobility. A detailed study was carried out, by using thin-layer isoperichoric focusing, UV-vis spectrophotometry, and voltamperometry, to explain the observed phenomena which can interfere in electric polarization or focusing field-flow fractionation. Copyright 2000 Academic Press.

Effect of Ionic and Nonionic Solutes on the Transient and Steady States in the Settling of Charged Colloidal Particles.

Centrifugation was applied to study the transport phenomena in various suspensions of charged colloidal silica particles. Isopycnic focusing of colored density marker beads was used to view the evolution of the density gradient and to determine its steady-state shape from the measured positions of the focused zones. The effect of the ionic and nonionic solutes on the transient and steady states was studied. The experimental results are discussed in relation with the published theoretical dependence of the transport coefficients on the volume fraction of the settling particles. The understanding of the transport phenomena and of the interfering particle interactions governing the formation of the density gradient and the subsequent isopycnic focusing under model static conditions is necessary for the optimization of the isoperichoric focusing field-flow fractionation dynamic experiments, but it should allow a more accurate description of the relaxation phenomena and retention in polarization field-flow fractionation as well. Some previous experimental results concerning the study of the transport phenomena of the charged silica particles in an electric field are exploited here to demonstrate the general character of the observed behavior, independent of the field nature. Copyright 2000 Academic Press.

[Treatment of multiple myeloma with high-dose chemotherapy and transplantation of autologous hematopoietic stem cells and subsequent maintenance therapy with interferon alfa-2b or interferon alfa 2b and dexamethasone. Report of the ongoing study of the "4W" Czech Myeloma Group]. / Lécba mnohocetného myelomu vysokodávkovanou chemoterapií s transplantací autologních kmenových hemopoetických bunek a následující udrzovací lécbou interferonem alfa-2b nebo interferonem alfa-2b a dexametazonem. Zpráva o probíhající studii "4w" Ceské myelomové skupiny.

We report our results with high-dose chemotherapy in previously untreated multiple myeloma patients (4 courses of VAD chemotherapy, collection of PBSC after priming with cyclophosphamide, 5 g/m2, high-dose chemotherapy with melphalan, 200 mg/m2). Second transplantation was indicated only for patients who did not achieve remission after the first high-dose therapy (paraprotein lower than 25% of the pretreatment value). For the second transplantation melphalan (200 mg/m2) with methylprednisolone (1.5 g for 5 days) were used as conditioning regimen. After high-dose therapy all patients were randomized into two arms of maintenance therapy: interferon alpha-2b or sequential maintenance therapy (interferon alpha-2b for 3 months followed after 4 week pause by 40 mg of dexamethasone days 1-4, 10-13 and 20-23. The administration of interferon alpha was resumed four weeks after the last dexamethasone for next three months. The maintenance therapy continued for 48 months or until the progression. Fifty-five patients were enrolled in the study from January 1996 to August 1997. Thirty-five patients have undergone the first transplantation and 57% of them reached complete remission. There were 10% of non-responders after the first high-dose regimen. The mean time to reach white blood cell count above 1 x 10(9)/L after the application of high dose melphalan and platelets more than 50 x 10(9)/L were 12.2 (range 6-16 days) and 12.4 (range 0-25 days), respectively. Grade 4 mucositis according to SWOG classification requiring total parenteral nutrition was presented in 40% of the patients. The mean number of 1 unit of platelets and 2 units of packed red blood cells transfusions were given within the posttransplant period. Early transplant related mortality was 3%. This paper describes the response and tolerance of each particular step of therapy. The follow-up has been too short to evaluate event-free and overall survivals.

Isopycnic Focusing Study of the Transient State in the Settling of Colloidal Particles

Various effective field forces can generate the concentrating flux of the colloidal particles. Centrifugal field forces were used in this work to study the kinetics of the transport phenomena and the effect of interparticle interactions of the model silica suspension. Isopycnic focusing of the colored density marker beads was used to visualize the evolution and final quasi-equilibrium shape of the density gradient formed in silica suspension. Many operational parameters and experimental conditions (thickness of the liquid layer in measuring cells, intensity of the centrifugal forces, average concentration of the silica particles, and geometrical shape of the measuring cells) were tested to evidence their influence on the concentration and density gradient formation. The main objective was to apprehend the processes governing isoperichoric focusing in thin layers under model static conditions which is necessary for the optimization of isoperichoric focusing field-flow fractionation dynamic experiments carried out under conditions of hydrodynamical flow as an active factor of the separation by focusing effect. The experimental results were compared with the hypothetical model of noninteracting particles to demonstrate the effect of the actual interparticle interactions.

Change in the content of oxidation and oligomeric products of sunflower oil during hydrogenation.

Oxidation and oligomeric products of sunflower oil were determined by gel permeation chromatography after transformation into methyl esters and prefractionation by urea. During oil refining the content of oxidation monomeric products increased from 0.9% to 1.5%, the dimer content from 0.06% to 0.32%, and the trimer content from 0.02% to 0.10%. During hydrogenation the content of polar monomeric oxidation products decreased to 0.9%, the dimer content to 0.28% and that of trimers to 0.03%. Oligomers were partly adsorbed on the surface of catalyst and carrier, because fat isolated from the catalyst contained more than 3% of oligomers. The content of oligomers established in the refined sunflower oil and in the hydrogenated sunflower oil produced on an industrial scale was lower than values given as limiting with respect to hygiene safety, sensory value and stability against oxidative rancidity.