The use of methyl tertiary butyl ether (MTBE) as a gasoline additive has resulted in serious environmental problems following spills and leaks, primarily due to MTBE's high solubility in water. Remediation technologies have involved air stripping, advanced oxidation, and sorption on granular activated carbons (GAC). Hydrophobic zeolites, such as silicalite, dealuminated Y, mordenite, and beta, have been of interest in recent studies for the removal of MTBE from water. Some of these materials have shown a better performance than GAC particularly in the microg/L range. We made Monte Carlo and molecular dynamics simulations of the adsorption of pure MTBE in silicalite, mordenite, and zeolite beta with different Na+ loadings at room temperature to reveal the factors affecting the adsorption process. The results show that although the three zeolites studied here have similar pore volumes, the pore structure of zeolite beta causes a significant difference on the predicted amount of MTBE adsorbed. It was found that the position of the Na+ cations has an important effect at lower pressures. Within the range of [Na+] studied, the amount of Na+ was not found to be critical on the adsorption capacity of any of the zeolites studied, except at very low pressures in silicalite and zeolite beta. 相似文献
In the proposed work, the simultaneous analysis of amlodipine–rosuvastatin and amlodipine–atorvastatin in their dosage forms was achieved. Simultaneous dissolution profiles of the amlodipine–rosuvastatin and amlodipine–atorvastatin tablets are realized using Apparatus II with a simple, accurate and precise RP-LC method. The mobile phase consisting of 0.2 % H3PO4 and pH 5:methanol:acetonitrile (46:27:27) was used. The samples of 10 µL were injected onto a Zorbax SB C18 (100 mm, 4.6 mm, 3.5 µm particle size) column with 1.2 µL min−1 flow rate. The samples were detected at 236 nm. By plotting peak area ratios vs. concentration, the linearity for amlodipine–rosuvastatin and amlodipine–atorvastatin was determined. With the developed RP-LC method, AML, ROS and ATOR were detected within the range of 0.25–10, 0.5–10 and 0.25–25 µg mL−1, respectively. LOD and LOQ values were also calculated as 0.028, 0.058, 0.021 and 0.095 µg mL−1, 0.195 µg mL−1, 0.070 µg mL−1 for AML, ROS and ATOR, respectively. System suitability tests parameters, such as capacity factor, selectivity to previous peak, selectivity to next peak, resolution to previous peak, resolution to next peak, tailing factor, theoretical number of plates, were performed and found coherent with the ICH guideline parameters. The proposed method has been extensively validated in terms of recovery, and recovery results were between 99 and 101 %. For proving the precision, between-day and within-day repeatability results of the method were proposed. The method can be used for the simultaneous determination of amlodipine–rosuvastatin and amlodipine–atorvastatin.
An analytical study is performed on steady, laminar, and fully developed forced convection heat transfer in a parallel plate
channel with asymmetric uniform heat flux boundary conditions. The channel is filled with a saturated porous medium, and the
lower and upper walls are subjected to different uniform heat fluxes. The dimensionless form of the Darcy–Brinkman momentum
equation is solved to determine the dimensionless velocity profile, while the dimensionless energy equation is solved to obtain
temperature profile for a hydrodynamically and thermally fully developed flow in the channel. Nusselt numbers for the lower
and upper walls and an overall Nusselt number are defined. Analytical expressions for determination of the Nusselt numbers
and critical heat flux ratio, at which singularities are observed for individual Nusselt numbers, are obtained. Based on the
values of critical heat flux ratio and Darcy number, a diagram is provided to determine the direction of heat transfer between
the lower or upper walls while the fluid is flowing in the channel. 相似文献
Angle-resolved X-ray photoelectron spectroscopy and contact-angle measurements guided by a signal attenuation model are utilized to extract molar composition and anion enrichment in the vacuum interface of a binary ionic liquid mixture, having a common quaternary ammonium cation and two different anions. By using the intensity ratio of the F1s peaks belonging to the two different anions recorded at the full electron take-off angle range, from 0° to 80°, we have determined that only a fractionally covered and anion enriched surface layer can predict the AR-XPS data, which is also consistent with surface tension measurements. Moreover, the more bulky and non-spherical anion enrichment is evident even at the conventional and the so assumed bulk sensitive take-off angle of 0°. This methodology provides a surface enrichment factor of the molecular ions and clearly serves as an experimental evidence for recently debated surface layering and/or island structure in ionic liquid systems. 相似文献
The variability associated with the aflatoxin test procedure used to estimate aflatoxin levels in bulk shipments of hazelnuts was investigated. Sixteen 10 kg samples of shelled hazelnuts were taken from each of 20 lots that were suspected of aflatoxin contamination. The total variance associated with testing shelled hazelnuts was estimated and partitioned into sampling, sample preparation, and analytical variance components. Each variance component increased as aflatoxin concentration (either B1 or total) increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. The sampling, sample preparation, and analytical variances associated with estimating aflatoxin in a hazelnut lot at a total aflatoxin level of 10 ng/g and using a 10 kg sample, a 50 g subsample, dry comminution with a Robot Coupe mill, and a high-performance liquid chromatographic analytical method are 174.40, 0.74, and 0.27, respectively. The sampling, sample preparation, and analytical steps of the aflatoxin test procedure accounted for 99.4, 0.4, and 0.2% of the total variability, respectively. 相似文献
Titanium tetra-n-butoxide, Ti(OBun)4, and zirconium tetra-n-butoxide, Zr(OBun)4, were reacted with some well-known dioxime and monoxime ligands such as dimethylglyoxime (DMG), salicylaldoxime (SO) and
acetone oxime (AO). The structures of the resulting complexes have been determined by elemental analysis, i.r. and 1H-n.m.r. spectroscopy. The complexation ratio of both Ti(OBun)4 and Zr(OBun)4 was found to be 1:2 with DMG and SO. On the other hand, both 1:1 and 1:2 complexation ratios of the same metal alkoxides
were observed with the ligand AO. 相似文献
Modeling and control of vehicle suspension system are high noteworthy from safety to comfort. In this paper, an analytical
nonlinear half-vehicle model which is included quadratic tire stiffness, cubic suspension stiffness, and coulomb friction
is derived based on fundamental physics. A hybrid fuzzy logic approach which combines fuzzy logic and PID controllers is designed
for reducing the vibration levels of passenger seat and vehicle body. Performances of designed controllers have been evaluated
by numerical simulations. Comparisons with classical PID control, Fuzzy Logic Control (FLC) and Hybrid Fuzzy-PID control (HFPID)
have also been provided. Results of numerical simulations are evaluated in terms of time histories of displacement and acceleration
responses and ride index comparison. A good performance for the Hybrid Fuzzy-PID controller with coupled rules (HFPIDCR) is
achieved in simulation studies despite the nonlinearities. 相似文献
Two chaotic indicators namely the correlation dimension and the Lyapunov exponent methods are investigated for the daily river flow of Kizilirmak River. A delay time of 60 days used for the reconstruction is chosen after examining the first minimum of the average mutual information of the data. The sufficient embedding dimension is estimated using the false nearest neighbor algorithm, which has a value of 11. Based on these embedding parameters the correlation dimension of the resulting attractor is calculated, as well as the average divergence rate of nearby orbits given by the largest Lyapunov exponent. The presence of chaos in the examined river flow time series is evident with the low correlation dimension (2.4) and the positive value of the largest Lyapunov exponent (0.0061). 相似文献