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Same Potential (same + potential)
Selected AbstractsIntegrating an Enzyme-Entrapped Conducting Polymer Electrode and a Prereactor in a Microfluidic System for Sensing GlucoseELECTROANALYSIS, Issue 6 2008Po-Chin Nien Abstract In this study, the flow injection analysis was applied to the enzyme-entrapped electrode on a chip for sensing glucose. The on-chip microelectrode was fabricated by the standard photolithography in clean-room environment and the microfluidic channel height of 100,,m on the chip was formed by poly(dimethylsiloxane). The conducting polymer, poly(3,4-ethylenedioxythiophene), PEDOT, was electropolymerized to entrap the coexisting glucose oxidase (GOD) by cyclic voltammetry (CV). The amount of enzyme entrapped in the matrix measured spectroscopically was about 0.101,U/cm2. At a flow rate of 10,ml/hr, the working electrode (Pt/PEDOT/GOD, WE1) was set at 0.7,V (vs. Ag/AgCl) and sensing of H2O2 was carried out by injecting samples with various concentrations of glucose (Glu). A linear relationship between the sensing current and the glucose concentration, ranging from 1 to 20,mM, was obtained with a sensitivity of 8,nA mm,2 mM,1. The response time and the recovery time were about 30 and 230,s, respectively. For a single-potential test, the oxidation currents of 0.08,mM ascorbic acid (AA) and a blend of 0.08,mM AA and 10,mM Glu reached 31.3% and 145.5%, respectively, when compared with the oxidation current of 10,mM Glu alone. However, when a pre-reactor (WE2) was set at the same potential (0.7,V) before the main enzyme integrated electrode (WE1), the oxidation current for the above mixed solution reached 99.6% of the original one. [source] Multiple-point electrochemical detection for a dual-channel hybrid PDMS-glass microchip electrophoresis deviceELECTROPHORESIS, Issue 19 2009Mario Castaño-Álvarez Abstract A new PDMS-based dual-channel MCE with multiple-point amperometric detection has been evaluated. Electrophoresis has been optimised in a single-channel device. Pretreatment with 0.1,M NaOH is very important for increasing and stabilising the EOF. The precision is adequate for a day's work in terms of both peak current and migration time. The RSD of the peak current for five successive signals was 1.9, 2.4 and 3.1% for dopamine, p- aminophenol and hydroquinone. RSD for the migration time was always less than 1.3%, which demonstrates the stability of the EOF and the possibility of running multiple experiments in the same microchip. The adequate inter-microchip precision as well as the rapid and simple manufacturing procedure indicates the disposable nature of the PDMS microchips. A dual-channel device with very simple multiple-point amperometric detection is proposed here. Elasticity of the PDMS allows removing the polymer slightly and aligning gold wires working electrodes. Injection can be performed from each of the sample reservoirs or from both simultaneously. The distance between the separation channels is critical for obtaining adequate signals as well as the introduction of a high-voltage electrode in the buffer reservoir. Simultaneous measurement of the same analytes in both channels is possible by applying the same potential. Moreover, since no cross-separation is produced, different analytes or samples can be simultaneously measured. [source] Simple circuit to improve electric field homogeneity in contour-clamped homogeneous electric field chambersELECTROPHORESIS, Issue 7-8 2003José A. Herrera Abstract We redesigned contour-clamped homogeneous electric field (CHEF) circuitry to eliminate crossover distortion, to set identical potentials at electrodes of each equipotential pair and to drive pairs with transistors in emitter follower stages. An equipotential pair comprised the two electrodes set at the same potential to provide electric field homogeneity inside of the hexagonal array. The new circuitry consisted of two identical circuits, each having a resistor ladder, diodes and transistors. Both circuits were interconnected by diodes that controlled the current flow to electrodes when the array was energized in the ,A' or ,B' direction of the electric field. The total number of transistors was two-thirds of the total number of electrodes. Average voltage deviation from potentials expected at electrodes to achieve a homogeneous electric field was 0.06 V, whereas 0.44 V was obtained with another circuit that used transistors in push-pull stages. The new voltage clamp unit is cheap, generated homogeneous electric field, and gave reproducible and undistorted DNA band patterns. [source] Application of the anharmonic coherent states to the vibronic interactionFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2-3 2003C.N. Avram We calculated the vibronic reduction factor (Ham factor) for the physical system (molecules, crystals) with octahedral symmetry. The vibrations of the nuclei of the systems are described by the anharmonic states of the Morse potential and also by the anharmonic coherent states of the same potential. The linear vibronic coupling of these vibration states with the electronic states of the system are considered. [source] Experience, change and vulnerability: consumer education for older people revisitedINTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 3 2002Phil Lyon Abstract Everyday consumer transactions have the same potential for unexpected consequence whatever the age of the consumers involved. Young and old alike can find that products and services fail to live up to performance claims and that they are left with problems not easily resolved, or costs that are difficult to recover. While not overlooking consumer heterogeneity , especially on the basis of age , older consumers are arguably distinguishable in terms of the social and financial context in which they make decisions and attempt to redress problems. In 1988, attention was drawn to the need for consumer education to look beyond generic objectives to the specific situation of older people and their transactions. More than a decade later, in an allegedly consumer-oriented society, the issue is revisited here to assess the argument's current relevance. Despite the increased availability of information for decisions and consumer protection, difficulties persist in the way information is presented or accessed. Chameleon-like, old problems become manifest in new unfamiliar ways and invalidate experience. Consumer education today is as important as it was in 1988. Arguably, technological change means that the need for a better understanding of dangers, rights and redress procedures is greater than ever and the needs of older people in increasingly complex private and public sector transaction environments are all the more pressing. However, a fundamental revision of the way we approach the design of products, services and environments is needed to improve prospects for older consumers. [source] Rainfall effects on rare annual plantsJOURNAL OF ECOLOGY, Issue 4 2008Jonathan M. Levine Summary 1Variation in climate is predicted to increase over much of the planet this century. Forecasting species persistence with climate change thus requires understanding of how populations respond to climate variability, and the mechanisms underlying this response. Variable rainfall is well known to drive fluctuations in annual plant populations, yet the degree to which population response is driven by between-year variation in germination cueing, water limitation or competitive suppression is poorly understood. 2We used demographic monitoring and population models to examine how three seed banking, rare annual plants of the California Channel Islands respond to natural variation in precipitation and their competitive environments. Island plants are particularly threatened by climate change because their current ranges are unlikely to overlap regions that are climatically favourable in the future. 3Species showed 9 to 100-fold between-year variation in plant density over the 5,12 years of censusing, including a severe drought and a wet El Niño year. During the drought, population sizes were low for all species. However, even in non-drought years, population sizes and per capita growth rates showed considerable temporal variation, variation that was uncorrelated with total rainfall. These population fluctuations were instead correlated with the temperature after the first major storm event of the season, a germination cue for annual plants. 4Temporal variation in the density of the focal species was uncorrelated with the total vegetative cover in the surrounding community, suggesting that variation in competitive environments does not strongly determine population fluctuations. At the same time, the uncorrelated responses of the focal species and their competitors to environmental variation may favour persistence via the storage effect. 5Population growth rate analyses suggested differential endangerment of the focal annuals. Elasticity analyses and life table response experiments indicated that variation in germination has the same potential as the seeds produced per germinant to drive variation in population growth rates, but only the former was clearly related to rainfall. 6Synthesis. Our work suggests that future changes in the timing and temperatures associated with the first major rains, acting through germination, may more strongly affect population persistence than changes in season-long rainfall. [source] | ||||||||||