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排序方式: 共有816条查询结果,搜索用时 15 毫秒
91.
de Jesus DP Brito-Neto JG Richter EM Angnes L Gutz IG do Lago CL 《Analytical chemistry》2005,77(2):607-614
The use of two additional reservoirs to accommodate the electrodes of the power source is proposed to improve the stability of the running electrolyte in capillary electrophoresis. The basic idea is to use salt bridges to connect those reservoirs to the ones containing the capillary ends. Although simple, there are several issues that can be considered in the design and implementation of such system in order to prevent undesired transference of material between the electrolysis and the main reservoirs. The use of a sealed electrolysis reservoir without a gas phase, the use of materials that ensure volume stability, and the use of bridges as long as possible are three basic directions. A compromise is involved in the dimensions of the sectional area of the bridge, because a small area diminishes the amount of a species transferred by diffusion but leads to an undesirable increase of the electrical field during the electrophoretic running. Thus, a bridge composed of a main wide-bore tube connected to a small-bore capillary seems to give the best performance for practical use. A simple electrolysis-separated system was adapted to a preexisting capillary electrophoresis system, and its performance was evaluated with a mixture of tartaric, malic, and succinic acids that was separated in sodium benzoate solution (pH 5.5) using the original equipment and the modified one. Due to the water electrolysis and the small buffering capacity of the electrolyte, there was a significant pH change and consequently changes in the effective mobilities of the analytes and loss of resolution after a few runs using the original equipment. Using the electrolysis-separated system, no significant change in the migration time and resolution was observed even after 15 runs. Besides the freedom to prepare running electrolytes with electroactive species or unbuffered solution, high throughput and the use of small reservoirs, such as the ones used in microfluidic devices, are the main advantages of the system. 相似文献
92.
93.
Marta Dizy Pedro Jesus Martín-Alvarez María Dolores Cabezudo M. Carmen Polo 《Journal of the science of food and agriculture》1992,60(1):47-53
Several multivariate statistical methods (principal component, cluster, stepwise discriminant and multiple linear regression analysis) were applied to analytical data obtained by conventional methods and to analytical data for free amino acids, in an attempt to distinguish between grape, apple and pineapple juice. Analysis for methionine, proline, asparagine, arginine and glutamic acid made it possible to differentiate among the 34 samples of grape, apple and pineapple juices studied. Multiple linear regression analysis of computer-simulated mixtures of grape and apple juices made it possible to detect the proportion of each fruit within the blend. 相似文献
94.
Jesus Rooney Rivera-Guillen Rene de Jesus Romero-Troncoso Roque Alfredo Osornio-Rios Arturo Garcia-Perez Gilberto Herrera-Ruiz 《The International Journal of Advanced Manufacturing Technology》2010,51(5-8):723-737
High speed and high precision on computer numerically controlled (CNC) machines are major issues for most industrial automation processes. Among the most important factors for precise motion control are the control law, the controller implementation, and the profile reference. The effects of the control law and controller implementation on the tracking error in CNC machines have been widely studied, while the issue of profile reference has not received the required attention. To improve the dynamics provided by the conventional profile reference, several techniques have been proposed, focusing on peak jerk limitation. The novelty of this work is to develop a generalized methodology designed for producing dynamically constrained higher degree piecewise polynomial profiles, without limits in maximum polynomial degrees. They lead to define in an arbitrary way the dynamics shape, while the peak dynamics values constrained are maintained in order to improve the tracking error on CNC systems and giving the possibility to design fully dynamic-controlled trajectories. For experimentation purposes, a two-axis proportional–integral–derivative controller and profile reference generator are implemented in a low-cost field programmable gate array. The experimentation demonstrates the efficiency of the proposed methodology, showing the peak jerk and tracking error reduction, compared against recent reports from literature. 相似文献
95.
Karla Bigetti Guergoletto Marciane Magnani Juca San Martin Celia Guadalupe Tardeli de Jesus Andrade Sandra Garcia 《Innovative Food Science and Emerging Technologies》2010,11(2):415-421
This study evaluated the survival of Lactobacillus casei (LC-1) when adhered to four different dehydrated prebiotic fibers. After vacuum drying in oat bran with 9% β-glucan and green banana flour, LC-1 viability was 79% and 76%, respectively. Scanning electron microscopy images revealed no morphological changes in the cells adhered to these fibers, and the addition of trehalose as a cell protectant had a positive and significant effect on the survival of LC-1. At different storage temperatures, oat bran had the highest stability as well as in simulated gastrointestinal conditions, where LC-1 that adhered to the oat bran had greater viability (7.1 log CFU g? 1) than in the free form (2.4 log CFU g? 1). In the sensory evaluation, the probiotic oat bran added to a dairy fruit beverage was well accepted by consumers.Industrial relevanceThe diversification of food products and the growing interest in health life requires from food industry innovations and new products for this. Probiotic cultures into non-dairy products is still an innovation and a challenge to the functional food segment. The development of an oat bran with LC-1 adhered is important for the functional food industries because the probiotic can be viable during dehydration and storage at room temperature. In addition the LC-1 is protected under simulated gastrointestinal conditions without compromising sensory acceptability. 相似文献
96.
Inorganic ligand-modified, colloid-enhanced ultrafiltration (ILM-CEUF) is as a novel membrane-based separation method for selectively removing target ions from aqueous solution. Traditional colloid-enhanced ultrafiltration (CEUF) is a well-established membrane-based separation technique that can be used to separate metal ions from other aqueous solution components. Ligand-modified, colloid-enhanced ultrafiltration (LM-CEUF) uses organic ligands that selectively complex target ions and also associate with a water-soluble colloid, such as a surfactant micelle or polyelectrolyte. The colloid, associated -ligand, and target ion are then concentrated using an ultrafilter, producing a filtrate with a low concentration of the target ion. While traditional LM-CEUF techniques are able to provide quantitative separations of a variety of ionic pollutants, the high costs of the chelating agents make such techniques nonviable in most remediation schemes. This study investigated the replacement of organic ligands with carbonate for the selective removal of U(VI) from aqueous solution.In slightly to moderately basic solutions containing carbonate, UO2(CO3)34− can be made to dominate the U(VI) speciation. Using poly(diallyldimethylammonium) chloride, the effectiveness and efficiency of ILM-CEUF for removing U(VI) from other aqueous solution components was investigated as a function of carbonate concentration, pH, and ionic strength. Uranium separations of greater than 99.6% were achieved; even in the presence of large excesses of competing ions. The specific separation of U(VI) from Sr2+ was also examined. 相似文献
97.
Miguel Such Jesus R. Jimenez-Octavio Alberto Carnicero Oscar Lopez-Garcia 《Engineering Structures》2009,31(9):2162-2170
In this paper a novel method to solve three dimensional cable structures based on the catenary equation is proposed. The method is a generalization of a previous engineering application to compute the initial equilibrium of railway overheads. The major contributions of this paper are: the extension of the previous engineering application to simulate arbitrary three dimensional cable structures; cable elasticity is incorporated into the formulation; and due to the fact that the method relies on the analytical catenary equations, high numerical efficiency is exhibited. In order to show the validity of the method, comparisons with several well reported cable structure problems are presented. The agreement between the proposed method and published results is excellent. 相似文献
98.
99.
Mohammad S. Yalfani Sandra Contreras Francesc Medina Jesus Sueiras 《Applied catalysis. B, Environmental》2009,89(3-4):519-526
The recent reported pathway using oxygen and formic acid at ambient conditions has been utilized to generate hydrogen peroxide in situ for the degradation of phenol. An alumina supported palladium catalyst prepared via impregnation was used for this purpose. Almost full destruction of phenol was carried out within 6 h corresponding to the termination of 100 mM formic acid at the same time. In addition, a significant mineralization (60%) was attained. A simulated conventional Fenton process (CFP) using continuous addition of 300 ppm H2O2 displayed maximum 48% mineralization. Study of different doses of formic acid showed that decreasing the initial concentration of formic acid caused faster destruction of phenol and its toxic intermediates. The catalytic in situ generation of hydrogen peroxide system demonstrated interesting ability to oxidize phenol without the addition of Fenton's catalyst (ferrous ion). Lower Pd content catalysts (Pd1/Al and Pd0.5/Al) despite of producing higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the Pd5/Al catalyst in phenol degradation. The later catalyst showed a remarkable repeatability so that more than 90% phenol degradation along with 57% mineralization was attained by the used catalyst after twice recovery. Higher temperature (45 °C) gave rise to faster degradation of phenol resulting to almost the same mineralization degree as obtained at ambient temperature. Meanwhile, Pd leaching studied by atomic adsorption proved excellent stability of the catalysts. 相似文献
100.
Soft magnetic alloys are limited to lower frequencies because of increased eddy-current losses at higher frequencies. A simple low-temperature solvent-based process was developed to coat permalloy powder with a benzocyclobutene insulating layer to reduce interparticle eddy-current loss. Low-signal measurements show that the permeability of the cured composite exhibits a bandwidth beyond 10 MHz. In contrast, the permeability of the pure powder rolled off well below 1 MHz with a corresponding increase in the imaginary permeability. Measurements of the core loss density at 5 MHz on pressed composite cores show a core loss of 300 mW/cm3 at more than 90 gauss, while the pure powder core achieved the same core loss density at just over 10 gauss. The results demonstrate that the polymer coating process is an effective way of reducing the interparticle eddy-current loss in powdered magnetic cores at high frequencies. 相似文献