22 research outputs found

    The interfacial stability of magnetically stabilized fluidized beds

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    The study concerns a phenomenon in which the magnetization of ferromagnetic particles stabilizes the state of uniform fluidization in gas-solid, liquid-solid and gas-liquid-solid fluidized beds. Fluidization regimes and bed structure are functions of the intensity of an external magnetic field and the magnetic propererties of the particles. A fluidized bed of magnetized ferromagnetic particles can be regarded as a ferromagnet, with the permeability proportional to the ferromagnetic material magnetization properties, the intensity of the magnetic field applied by the solenoid, particle diameter and fluidized bed porosity. Stability analysis was performed using mean field theory to determine the magnetic forces acting at the gas-ferromagnet and liquid-ferromagnet surface, a discontinuity boundary, and to predict the mechanism of transition from the unstably fluidized to the stably fluidized sate

    Structure optimization of polylactide microcapsules for controlled drug release

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    The influence of starting material properties on physical characteristics and drug release kinetics of poly-L-lactide microcapsules was investigated. The density, the distribution of the diameter size of microcapsules, the voidage and the active substance (methylene blue and Sudan III tracers) released concentrations, in paralel with microcapsules structure were studied. It was found that the density, size and structure of the microcapsules influenced in the polymer molar weight. In the case of the voidage, it exist the influence of the tracer and the polymer molar weight. The kinetic studies showed that the release patterns were similar and controllable. It was concluded that PLLA microcapsules showed a great potential for utilization in the active substance administration

    An investigation of the synthesis of poly(L-lactide) as a biodegradable polymer for orthopaedic applications

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    The investigation is based upon recent research in the area of the synthesis of biodegradable poly(L-lactide) (PLLA) for biomedical applications using stannous octoate (SnOct) as an initiator. The objective was to investigate factors that affect the synthesis of poly(L-lactide), such as monomer purification, vacuum required for monomer drying, polymerization reacton time and catalyst concentration. Complete polymer characterization was done by 1H-NMR, IR spectroscopy and light scattering, in order to reveal the polymerization mechanism. An attempt was made to obtain a polymer of high molecular weight and good mechanical properties that could be used for the processing of biodegradable surgical sutures. Experiments showed that the optimum conditions to obtain polymer of high molecular weight (≈ 30 × 104) are: vacuum required for monomer drying (0.2 mmHg), purification of both monomer and polymer by recrystallization/precipitation, monomer/initiator mole ratio ([M]/[I] about 5000 and a polymerization time of approximately 50 h

    Production of anthraquinones by immobilized Frangula alnus Mill. plant cells in a four-phase air-lift bioreactor

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    The production of anthraquinones by Frangula alnus Mill. plant cells was used as a model system to evaluate the performance of a liquid-liquid extractive product-recovery process. The shake flask experiments have shown higher production of anthraquinones in cell suspension and flask cultures of calcium-alginate-immobilized cells when silicone oil was incorporated into the medium, compared to a control without silicone oil. An external-loop air-lift bioreactor, developed and designed for the production and simultaneous extraction of extracellular plant cell products, was regarded as a four-phase system, with dispersed gas, non-aqueous solvent and calcium-alginate-immobilized plant cells in Murashige and Skoog medium. Continuous extraction of anthraquinones by silicone oil and n-hexadecane inside the bioreactor resulted in 10–30 times higher cell productivity, compared to that of immobilized cells in a flask. Based on the mixing pattern, immobilized biocatalyst extraparticle and intraparticle diffusional constraints and the kinetics of growth, substrate consumption and product formation, a mathematical model was developed to describe the time course of a batch plant cell culture

    Hydrodynamics and Mass Transfer in a Four‐Phase External Loop Air Lift Bioreactor

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    An external loop air lift reactor (ELALR) was developed and designed for continuous production and extraction of extracellular secondary metabolites by immobilized Frangula alnus Mill. plant cells. This system was considered as a four‐phase system, with dispersed gas, nonaqueous liquid solvent, and calcium alginate particles in water or Murashige and Skoog medium. Analysis of the four‐phase ELALR revealed the influence of gas, solvent, calcium alginate particles and MS medium composition on gas and solvent holdup, liquid circulation velocity, mixing in aqueous liquid phase, and mass transfer coefficients of oxygen and plant cell product. It was shown that the gas holdup appears to be the principal variable determining the properties of the four‐phase system. An unified correlation for the gas holdup, based on drift flux flow in a three‐phase system, has been extended to the four‐phase system. Bubble size and bubble size distribution observed in the bubbly flow regime were the same in water as in the MS medium system (Sauter mean diameter 2.5 mm). Consequently, gas holdup and all related parameters, such as liquid circulation velocity, oxygen mass transfer coefficient, and axial liquid dispersion in MS medium, were similar to those in water for the four‐phase system

    Effect of nitric oxide - releasing compounds on phytochrome - controlled germination of Empress tree seeds

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    Using different nitric oxide releasing compounds and appropriate controls we have obtained data strongly suggesting the involvement of nitric oxide in the phytochrome controlled germination of Paulownia tomentosa seeds. Direct detection of nitric oxide, under various experimental conditions, was performed by a spin-trapping technique combined with electron paramagnetic resonance (EPR) spectroscopy. The addition of methylene blue prevented light-induced and NO donors-potentiated germination of P. tomentosa seeds. This inhibition could be completely overcome by addition of gibberellin. The promotive effect of nitrite was pH dependent, maximally pronounced at the pH range where nitrite undergoes dismutation and liberates nitric oxide. Under these conditions, nitrite exerted its efficacy at the same concentrations at which nitric oxide releasing compounds such as sodium nitroprusside (SNP), S-nitroso acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1), were the most effective. Likewise, the potentiation of P. tomentosa seed germination could be achieved by chemical reduction of nitrite with Na2S2O4 during which liberation of nitric oxide could be detected.nul
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