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Various Samples (various + sample)
Selected AbstractsMulti-walled carbon nanotube composites with polyacrylate prepared for open-tubular capillary electrochromatographyELECTROPHORESIS, Issue 19 2010Jian-Lian Chen Abstract A new phase containing immobilized carbon nanotubes (CNTs) was synthesized by in situ polymerization of acid-treated multi-walled CNTs using butylmethacrylate (BMA) as the monomer and ethylene dimethacrylate as the crosslinker on a silanized capillary, forming a porous-layered open-tubular column for CEC. Incorporation of CNT nanomaterials into a polymer matrix could increase the phase ratio and take advantage of the easy preparation of an OT-CEC column. The completed BMA-CNT column was characterized by SEM, ATR-IR, and EOF measurements, varying the pH and the added volume organic modifier. In the multi-walled CNTs structure, carboxylate groups were the major ionizable ligands on the phase surface exerting the EOF having electroosmotic mobility, 4.0×104,cm2,V,1,S,1, in the phosphate buffer at pH 2.8 and RSD values (n=5), 3.2, 4.1, and 4.3%, for three replicate capillaries at pH 7.6. Application of the BMA-CNT column in CEC separations of various samples, including nucleobases, nucleosides, flavonoids, and phenolic acids, proved satisfactory upon optimization of the running buffers. Their optima were found in the borate buffers at pH 9.0/50,mM, pH 9.5/10,mM/50% v/v ACN, and pH 9.5/30,mM/10% v/v methanol, respectively. The separations could also be used to assess the relative contributions of electrophoresis and chromatography to the CEC mechanism by calculating the corresponding velocity and retention factors. Discussions about interactions between the probe solutes and the bonded phase included the ,,, interactions, electrostatic repulsion, and hydrogen bonding. Furthermore, a reversed-phase mode was discovered to be involved in the chromatographic retention. [source] Aerogel and Xerogel Catalysts Based on ,-Alumina Doped with Silicon for High Temperature ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005Aurelien Florin Popa Abstract Numerous materials (supports and catalysts) based on alumina have been prepared using the sol-gel process and carbon dioxide supercritical drying. In this work two types of solids, i.e. xerogels and aerogels, were systematically compared and a way of introducing platinum metal with a content of 5% percent by weight was examined. The structural data, the surface area, Pt dispersion and catalytic activity for the decomposition of the propellant were measured for the various samples. The (Al2O3)0.88(SiO2)0.12 samples prepared show very interesting porosity values, especially for the aerogel. For this reason, they were chosen as supports for the synthesis of 5 wt% platinum on alumina catalysts. The results presented in this work allowed us to obtain an overall view of the influence of the preparation mode on the properties of platinum on alumina supported catalysts. The dispersion of the metal phase is directly dependent on the specific surface of the support. A significant value for the surface area implies a large amount of centers for interaction with the metal precursor and, consequently, the appearance of more centres of simultaneous germination. Although aerogels obtained by carbon dioxide supercritical drying always show superior properties compared with xerogels, for catalytic decompositions the xerogels still remain superior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Production and sensory characteristics of flavoured soymilk samplesINTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 3 2003Christina Antwiwaa Nti Abstract The sensory quality characteristics of four flavoured soymilk samples including vanilla, banana, coffee and chocolate were evaluated at varying concentrations of the flavour. This was done to establish the most acceptable flavour and desired concentration for commercial production of soymilk and also to facilitate increased consumption of soymilk for improved nutrition. Hot extraction of the milk from blanched soybeans was achieved by blending in hot water and sieving through muslin cloth. Different concentration levels of the flavours being assessed, namely chocolate, coffee, vanilla and banana, were added. Consumer preference for the various samples was assessed using a nine-point hedonic scale. Addition of flavours was found to improve the sensory characteristics and consumer preference of soymilk. Colour, taste, aroma, mouthfeel and hence overall acceptability of the soymilk samples were improved significantly by the addition of vanilla, banana, coffee and chocolate flavours. The maximum concentrations of the individual flavours for optimal sensory impact were established. Based on the results, the following flavour concentrations are recommended per 100 ml of soymilk: 0.03% vanilla, 0.01% banana, 1.5% coffee and 4% chocolate. [source] Application of the accelerated shelf life testing method (ASLT) to study the survival rates of freeze-dried Lactococcus starter culturesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2001M Achour Abstract The survival rates of two freeze-dried strains, Lactococcus lactis var diacetylactis and Lactococcus lactis var lactis, were evaluated using the Accelerated Shelf Life Testing (ASLT) method. The strains were initially isolated from a brand of a Tunisian fermented milk product. Lactococcus cell survival observed at higher temperatures was used to extrapolate to shelf life at a lower storage temperature of 4,°C. The apparent kinetics of the survival rate loss were estimated and the effect of storage temperature was quantified by determining the inactivation energies for various samples. The work has shown an overall higher survival rate of the strain Lactococcus lactis var diacetylactis. An average half-life of a strain maintained at 25,°C was equal to about 7 days as compared with about 43 days at 4,°C. The addition of lyoprotectants such glycerol, saccharose and calcium carbonate to the drying medium, improved the survival of such bacteria. © 2001 Society of Chemical Industry [source] High-performance liquid chromatography with sequential injection for online precolumn derivatization of some heavy metalsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 16 2007Rodjana Burakham Abstract HPLC was coupled with sequential injection (SI) for simultaneous analyses of some heavy metals, including Co(II), Ni(II), Cu(II), and Fe(II). 2-(5-Nitro-2-pyridylazo)-5-[N -propyl- N -(3-sulfopropyl)amino]phenol (nitro-PAPS) was employed as a derivatizing reagent for sensitive spectrophotometric detection by online precolumn derivatization. The SI system offers an automated handling of sample and reagent, online precolumn derivatization, and propulsion of derivatives to the HPLC injection loop. The metal,nitro-PAPS complexes were separated on a C18 -,Bondapak column (3.9×300 mm2). Using the proposed SI-HPLC system, determination of four metal ions by means of nitro-PAPS complexes was achieved within 13 min in which the parallel of derivatization and separation were processed at the same time. Linear calibration graphs were obtained in the ranges of 0.005,0.250 mg/L for Cu(II), 0.007,1.000 mg/L for Co(II), 0.005,0.075 mg/L for Ni(II), and 0.005,0.100 mg/L for Fe(II). The system provides means for automation with good precision and minimizing error in solution handling with the RSD of less than 6%. The detection limits obtained were 2 ,g/L for Cu(II) and Co(II), and 1 ,g/L for Ni(II) and Fe(II). The method was successfully applied for the determination of metal ions in various samples, including milk powder for infant, mineral supplements, local wines, and drinking water. [source] FTIR Microanalysis and Phase Behaviour of Ethylene/1-Hexene Random CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2007Mariano Pracella Abstract Ethylene/1-hexene random copolymers with 1-hexene content in the range of 1,5 mol-%, synthesised in the presence of new heterogeneous catalyst systems based on bis-carboxylato and -bis-chloro-carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR-M), DSC calorimetry and X-ray scattering. The co-monomer content and sequence distribution in the various samples were determined by means of both FTIR-M and 13C NMR spectroscopy. The deformation bands of methyl groups in the region of 1,400,1,330 cm,1 were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1,500,1,300 and 760,690 cm,1 frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1,378 cm,1 was recorded between 110 and 130,°C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co-monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches. [source] MMIC's characterization by very near-field techniqueMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2004L. Nativel Abstract This paper shows a method to characterize microwave circuits using a near-field scanning microscope. Applied on various samples, it shows good resolution and weak disturbance for ICs operating with very common microwave components. Here, it is applied in an industrial surrounding to characterize the Bluetooth CMOS power amplifier. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 209,213, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20096 [source] Mechanism of excitation and relaxation in Er,O-codoped GaAs for 1.5 ,m light-emitting devices with extremely stable wavelengthPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008Yasufumi Fujiwara Abstract Energy-transfer processes in Er,O-codoped GaAs (GaAs:Er,O) have been investigated by means of a pump and probe reflection technique. Time-resolved reflectivity exhibited a characteristic dip; a negative signal due to bandgap renormalization in less than 1 ps and then a gradual recovery. In the recovery process, there were two components, fast and slow. The fast recovery time (several ps) was inversely proportional to Er concentration. The analysis based on a rate equation indicated that it is due to the capture of electrons by charged traps. The slow recovery (30,60 ps) was well coincident with the time (54 ps) predicted theoretically in the framework of a multiphonon-assisted model. Optical excitation cross section of Er ions in GaAs:Er,O has also been studied in various samples and shown to depend strongly on Er concentration. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of ZnMgTe/ZnTe layered structures grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010S. Imada Abstract ZnMgTe/ZnTe layered structures were grown on ZnTe substrates by molecular beam epitaxy, and the crystal structures were characterized using X-ray diffraction methods. This structure would be the waveguide for various optoelectronic devices. Therefore, the crystal quality of this layered structure would be very crucial for the realization of high performance devices. ZnMgTe is lattice mismatched to ZnTe, and the increase of the ZnMgTe layer thickness or Mg mole fraction ratio would result in the crystal quality deterioration of the layered structure. The critical layer thickness (CLT) was theoretically derived, and various structures with various ZnMgTe layer thickness and Mg mole fraction were grown. The lattice mismatch strain relief and crystal quality of those samples were investigated by means of X-ray reciprocal space mapping (RSM) and cross sectional transmission electron microscopy (TEM). The dislocation formation and the lattice mismatch relaxation were confirmed for various samples and it was revealed that the calculated CLT values could be used as an appropriate guideline to design the dislocation free and high performance device structures (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Probiotic effect of Bacillus NL110 and Vibrio NE17 on the survival, growth performance and immune response of Macrobrachium rosenbergii (de Man)AQUACULTURE RESEARCH, Issue 9 2010K M Mujeeb Rahiman Abstract Eight hundred and eighty-five strains of bacterial isolates from various samples associated with the natural habitat of Macrobrachium rosenbergii were screened for their probiotic potential. Two putative probionts namely Bacillus NL110 and Vibrio NE17 isolated from the larvae and egg samples, respectively, were selected for experimental studies and were introduced to the juveniles of M. rosenbergii (0.080±0.001 g) through different modes such as through feed, water and both. The probiotic potential of the above bacteria in terms of improvements in water quality, growth, survival, specific growth rate (SGR), feed conversion ratio and immune parameters was evaluated. The treatment groups showed a significant improvement in SGR and weight gain (P<0.001). Survival among different treatment groups was better than that in the control group. There were also significant improvements in the water quality parameters such as the concentration of nitrate and ammonia in the treatment groups (P<0.05). Improvements in immune parameters such as the total haemocyte count (P<0.05), phenoloxidase activity and respiratory burst were also significant (P<0.001). It is concluded that screening of the natural microflora of cultured fish and shellfish for putative probionts might yield probiotic strains of bacteria that could be utilized for an environment-friendly and organic mode of aquaculture. [source] Glass Transition Temperatures and Fermentative Activity of Heat-Treated Commercial Active Dry YeastsBIOTECHNOLOGY PROGRESS, Issue 2 2000Carolina Schebor Differential scanning calorimetry thermograms of various samples of commercial instant active dry yeasts revealed a clear glass transition typical of amorphous carbohydrates and sugars. The resulting glass transition temperatures were found to decrease with increasing moisture content. The observed glass curve was similar to that of pure trehalose, which is known to accumulate in large amounts in baker's yeast. The effect of heat treatment at various temperatures on the fermentative activity (as measured by the metabolic production of CO2) of dry yeast was studied. First-order plots were obtained representing the loss of fermentative activity as a function of heating time at the various temperatures assayed. Significant losses of fermentative activity were observed in vitrified yeast samples. The dependence of rate constants with temperature was found to follow Arrhenius behavior. The relationship between the loss of fermentative activity and glass transition was not verified, and the glass transition was not reflected on the temperature dependence of fermentative activity loss. [source] | ||||||||||||||||