Iskanje po katalogu digitalne knjižnice

Opis: This article describes experimental determination of the relative impact of significant process parameters that influence volumetric oxygen mass transfer coefficient (kLa) using Taguchi design methodology. For this purpose an automated RC1 reaction calorimeter (Mettler-Toledo), which was originally developed for chemical processes, was modified for the bioprocesses. Simple fermentation using Baker's yeast was studied to illustrate the design procedure. Orthogonal array L25 was selected for the proposed design and ANOVA method was used for recognizing the relative influence of the process parameters. Within the observed range of temperature (?), fermentation media volume (VFM), and yeast mass concentration (?Y), these process parameters were found to be unimportant compared to the volumetric air flow rate (qV,a) and rotational frequency of the stirrer (fm). The qV,a had a substantial effect on the kLa value (89.2 %) and the fm had just a small one (3.6 %), meanwhile the remain fraction to 100 % represents error. The results refer strictly to the selected case study. Anyhow, the proposed procedure shows that application of the Taguchi approach for analyzing the oxygen mass transfer based on the experimental data obtained from a highly-automated laboratory reactor appears to have potential usage in general biopharmaceutical process design.
Ključne besede: bioprocess parameters, mass transfer, volumetric oxygen mass transfer coefficient, process parameters, Taguchi method, analysis of variance
Objavljeno: 31.05.2012; Ogledov: 1484; Prenosov: 23
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Opis: Modification of surface properties of poly(ethyleneterephtalate) (PET) thin films by treatment with weakly ionized oxygen plasma was studied by contact angles of water and diiodomethane (DIM) drops. Samples were exposed to oxygen plasma with the ion density of 5 x 1015/m[sup]3 and the neutral oxygen atom density of 3 x 1021/m[sup]3. Just after the treatment they were characterized by contact angle measurements. Results showed a quick decrease of the water contact angle in the first few seconds of plasma treatment, while prolonged treatment did not cause any substantiated modification. The contact angles of DIM, on the other hand, remained rather constant for the first several secondsof plasma treatment, and increased after prolonged treatment. It was found that the dispersion component of the surface free energy decreased with increasing treatment time, while the polar component increased with treatment time. The results were explained by surface functionalization as well as by roughness effects.
Ključne besede: poly(ethylene terephtalante), PET, oxygen plasma, contact angle, hydrophilic, functionalization
Objavljeno: 01.06.2012; Ogledov: 1124; Prenosov: 22
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Opis: This paper presents the use of a non-equilibrium gaseous plasma technique for the activation of regenerated non-woven cellulose, as used in the preparation of wound-dressing materials. Plasma technology provides surface modification according to the required quality in terms of speed, homogeneity, process stability, and efficiency. In this study the non-woven cellulose was exposed to oxygen plasma (O2) in order to acquire the natural polymer's super-hydrophilicity which, among others, defines the materials' usability forwound-dressing. The influence of the plasma parameters on the material's hydrophilicity was studied; and the optimal plasma conditions defined. Combinations of different experimental techniques (contact angle, water retention value, and moisture content) were studied and correlated with the mechanical properties, as a function of plasma modification. The specific adsorption capacity of the non-woven cellulose using oxygen plasma treatment was achieved. In the next step, this material with increased hydrophilicity and improved mechanical properties will be used in the preparation of multilayered wound-dressing materials for specific functionalities (incorporation of drugs, specific functional properties).
Ključne besede: plasma, oxygen, regenerated non-woven cellulose, super-hydrophilicity, mechanical properties
Objavljeno: 10.07.2015; Ogledov: 444; Prenosov: 41
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Opis: Commercially pure (CP) titanium was surface modified with nitrogen-, argon- and oxygen-ion implantations in order to investigate the material's corrosion resistance in a simulated body fluid. Five doses were chosen for the ions, ranging from 5.1015 cm-2 to 2.5-1017 cm-2. In-vitro open-cyclic potential-timemeasurements and cyclic polarization studies were carried out to evaluate the corrosion resistance of the modified surface in comparison to an unmodified surface. Specimens implanted at 4.1016 cm-2 and 7.1016 cm-2 showed the optimum corrosion resistance, higher doses showed a detrimental effect on the corrosion resistance. Argon- and oxygen-ion implantation at these doses did not show any improved corrosion resistance, indicating the beneficial role of nitrogen on the corrosion resistance of titanium in the simulated body-fluid environment. Grazing-incidence X-ray diffraction (GIXD) was employed on the implanted specimens to determine the phases formed with the increasing doses. X-ray photoelectron spectroscopy (XPS) studies on the passive film of the implanted samples and on the unimplanted samples were analyzed in order to understand the role of nitrogen in improving the corrosion resistance. The results of the present investigation indicated that nitrogen-ion implantation can be used as a viable method for improving the corrosion resistance of titanium. The nature of the surface and the reason for the variation and the improvement in the corrosion resistance are discussed in detail.
Ključne besede: metallurgy, ion implantation, orthopedic implants, corrosion, titanium, nitrogen, oxygen, argon
Objavljeno: 10.07.2015; Ogledov: 1296; Prenosov: 51
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Opis: Non-woven cellulose material was functionalized using two techniques, i.e. the coating with AgCl via sol-gel and oxygen plasma. The treatment effects were studied regarding the wound fluid adsorption potential using physiological saline, synthetic exudate and synthetic blood. Plasma treatment was most efficient since a significant improvement by absorbency rate and capacity was evident, less pronounced in case of synthetic blood. The combination of both treatments showed a similar trend, while the effects were less prominent, but still sufficient by managing fluid-associated as well as infected wounds.
Ključne besede: non-woven cellulose fabric, sol-gel, oxygen plasma, absorption, synthetic wound fluids
Objavljeno: 31.08.2017; Ogledov: 317; Prenosov: 189
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