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Performance Deterioration (performance + deterioration)
Selected AbstractsIn-capillary solid-phase extraction,capillary electrophoresis for the determination of chlorophenols in waterELECTROPHORESIS, Issue 16 2006Luo-Hong Zhang Abstract A novel CE method combined with SPE in a single capillary was developed for analysis of chlorophenols in water. A frit of 0.5,mm was first made by a sol-gel method, followed by packing a SPE sorbent in the inlet end of the capillary. Two phenol derivatives, 2,4-dichlorophenol and 2,4,5-trichlorophenol, were used as the model compounds. By loading sample solutions into the capillary, the two chlorophenols were extracted into the sorbent. They were desorbed by injecting only about 4,nL of methanol. Finally, the analytes were separated by conventional CE. The technique provided a concentration enhancement factor of over 4000-fold for both chlorophenols. The detection limits (S/N,=,3) of 2,4-dichlorophenol and 2,4,5-trichlorophenol were determined to be 0.1,ng/mL and 0.07,ng/mL, respectively. For replicate analyses of 5,ng/mL of 2,4-dichlorophenol, within-day and between-day RSDs of migration time, peak height and peak area were in the range of 1.8,2.0%, 4.0,4.4% and 4.1,4.6%, respectively. The method shows wide linear range, acceptable reproducibility and excellent sensitivity, and it was applied to the analyses of spiked river water samples. The capillary packed with the SPE sorbents can be used for more than 400 runs without performance deterioration. [source] Electrochemical performance and microstructure characterization of nickel yttrium-stabilized zirconia anodeAICHE JOURNAL, Issue 6 2010Jingbo Liu Abstract A nickel and yttrium-stabilized zirconia (Ni-YSZ) composite is one of the most commonly used anode materials in solid oxide fuel cells (SOFCs). One of the drawbacks of the Ni-YSZ anode is its susceptibility to deactivation due to the formation of carbonaceous species when hydrocarbons are used as fuel supplies. We therefore initiated an electrochemical study of the influence of methane (CH4) on the performance of Ni-YSZ anodes by examining the kinetics of the oxidation of CH4 and H2 over operating temperatures of 600,800°C. Anode performance deterioration was then correlated with the degree of carbonization observed on the anode using ex-situ X-ray powder diffraction and scanning electron microscopy techniques. Results showed that carbonaceous species led to a significant deactivation of Ni-YSZ anode toward methane oxidation. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] The application of novel 1.7 ,m ethylene bridged hybrid particles for hydrophilic interaction chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2008Eric S. Grumbach Abstract An un-derivatized 1.7 ,m ethylene bridged hybrid (BEH) particle was evaluated for its utility in retaining polar species in hydrophilic interaction chromatography (HILIC), and was compared to a 3 ,m un-derivatized silica material. Retentivity as a function of mobile phase pH, polar modifier and ACN content was examined. Also, the efficiency of the two particle substrates was compared by plotting HETP vs. linear velocity. Improved chemical resistance of the un-derivatized BEH particle was compared to un-derivatized silica at pH 5, demonstrating no performance deterioration over the course of 2000 injections for the BEH particle, while the silica particle deteriorated rapidly after 800 injections. Lastly, ESI-MS sensitivity as a function of particle size and separation mode was demonstrated. A 2.2 to 4.7-times higher ESI-MS response was observed on the 1.7 ,m particle compared to the 3 ,m particle, whereas a 5.6 to 8.8-times higher ESI-MS response was observed using HILIC as when compared to traditional RP chromatography. [source] Rhythms of Mental PerformanceMIND, BRAIN, AND EDUCATION, Issue 1 2008Pablo Valdez ABSTRACT, Cognitive performance is affected by an individual's characteristics and the environment, as well as by the nature of the task and the amount of practice at it. Mental performance tests range in complexity and include subjective estimates of mood, simple objective tests (reaction time), and measures of complex performance that require decisions to be made and priorities set. Mental performance tasks show 2 components, a circadian rhythm and the effects of time awake. The circadian rhythm is in phase with the rhythm of core temperature and there is evidence for a causal link. Increasing time awake results in performance deterioration and is attributed to fatigue. The relative contribution of these 2 components depends upon the task under consideration; simple tasks generally show smaller effects due to increasing time awake. These contributions have been assessed by constant routines and forced desynchronization protocols and have formed the basis of several mathematical models that attempt to predict performance in a variety of field conditions. Mental performance is negatively affected by sleep loss; although short naps are beneficial, sleep inertia limits their value immediately after waking. The processes involved in cognition include attention (tonic and phasic alertness, and selective and sustained attention), working memory (phonological, used for speech, reading, and writing; and visuospatial, used for spatial processing, drawing, and mathematics), and executive function (initiative, decision making, and problem solving). These processes are illuminated by analysis of the regions of the brain involved, the presence of circadian rhythmicity, and the effects of sleep loss. The results from such laboratory- and field-based observations are relevant to the issue of learning in schoolchildren and lead to suggestions for improving their performance. [source] Combustion of Environmentally Altered Molybdenum Trioxide NanocompositesPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 3 2006Kevin Moore Abstract Nanocomposite thermite mixtures are currently under development for many primer applications due to their high energy densities, high ignition sensitivity, and low release of toxins into the environment. However, variability and inconsistencies in combustion performance have not been sufficiently investigated. Environmental interactions with the reactants are thought to be a contributing factor to these variabilities. Combustion velocity experiments were conducted on aluminum (Al) and molybdenum trioxide (MoO3) mixtures to investigate the role of environmental interactions such as light exposure and humidity. While the Al particles were maintained in an ambient, constant environment, the MoO3 particles were exposed to UV or fluorescent light, and highly humid environments. Results show that UV and fluorescent lighting over a period of days does not significantly contribute to performance deterioration. However, a humid environment severely decreases combustion performance if the oxidizer particles are not heat-treated. Heat treatment of the MoO3 greatly increases the material's ability to resist water absorption, yielding more repeatable combustion performance. This work further quantifies the role of the environment in the decrease of combustion performance of nanocomposites over time. [source] State estimation for time-delay systems with probabilistic sensor gain reductionsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Xiao He Abstract This paper presents a new state estimation problem for a class of time-delay systems with probabilistic sensor gain faults. The sensor gain reductions are described by a stochastic variable that obeys the uniform distribution in a known interval [,, ,], which is a natural reflection of the probabilistic performance deterioration of sensors when gain reduction faults occur. Attention is focused on the design of a state estimator such that for all possible sensor faults and all external disturbances, the filtering error dynamic is asymptotically mean-square stable as well as fulfils a prescribed disturbance attenuation level. The existence of desired filters is proved to depend on the feasibility of a certain linear matrix inequality (LMI), and a numerical example is given to illustrate the effectiveness of the proposed design approach. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||