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91.
Arsenic removal using polymer-supported hydrated iron(III) oxide nanoparticles: role of donnan membrane effect 总被引:1,自引:0,他引:1
The conditions leading to the Donnan membrane equilibrium arise from the inability of ions to diffuse out from one phase in a heterogeneous system. In a polymeric cation exchanger, negatively charged sulfonic acid groups are covalently attached to the polymer chains, and thus, they cannot permeate out of the polymer phase. Conversely, a polymeric anion exchanger contains a high concentration of non-diffusible positively charged quaternary ammonium functional groups. It is well-established that submicron or nanoscale hydrated iron(III) oxide (HFO) particles exhibit high sorption affinity toward both arsenates and arsenites. In this study, commercially available cation and anion exchangers were used as host materials for dispersing HFO nanoparticles within the polymer phase using a technique previously developed. The resulting polymeric/inorganic hybrid sorbent particles were subsequently used for arsenic removal in the laboratory. The most significant finding of the study is that the anion exchanger as a substrate containing dispersed HFO offered substantially higher arsenate removal capacity as compared to the cation exchanger, all other conditions remaining identical. In fact, HFO nanoparticles dispersed within the gel-type cation exchanger were unable to remove arsenic. The Donnan membrane effect resulting from the nondiffusible negatively charged sulfonic acid groups in the cation exchanger did not allow permeation of arsenate into the polymer phase (i.e., arsenate was excluded from the spherical beads dispersed with HFO nanoparticles). On the contrary, anion-exchanger-supported HFO particles or HAIX offered very high arsenic removal capacity; less than 10% of influent arsenic broke through after 10 000 bed vol. HAIX was also amenable to efficient regeneration with 2% NaOH and 3% NaCl and capable of simultaneously removing both perchlorate and arsenic selectively. According to the information in the open literature, HAIX is the first hybrid sorbent that utilizes the Donnan membrane effect of the host material for sorption enhancement. From a generic viewpoint, other metal oxide/metal nanoparticles may also be judiciously embedded in appropriate support materials that would reject or enhance permeation of targeted ionic solutes. 相似文献
92.
Sengupta N. Gupta M.D. Reddy B. Dutta H. Sarkar S. 《Antennas and Propagation, IEEE Transactions on》1983,31(4):620-624
A comparison of the signal intensity fluctuations or scintillation of signal level, observed over two line-of-sight links is presented. These links are situated over Calcutta, DumDum-Andul (6.7 GHz) and Delhi, Delhi-Sonepat (7.6 GHz). The study reveals departures, in the occurrence and variation of the scintillation over the Calcutta path as compared with the path over Delhi. This deviation has been attributed to the large variation in humidity which exists in the coastal region, and also which plays a major role in microwave propagation in the troposphere. 相似文献
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Melamed B. Raychaudhuri D. Sengupta B. Zdepski J. 《Communications, IEEE Transactions on》1994,42(10):2773-2777
The letter considers modeling methodologies of variable bit-rate (VBR) video sources for performance evaluation of integrated networks. The authors consider an example in which compressed H.261 standard VBR video is transmitted over a local area network carrying both video and data. A group-of-block (GOB) level source model has been constructed using TES (transform-expand-sample)-a new general methodology for generating stationary autocorrelated time series, which can simultaneously capture a prescribed marginal distribution and autocorrelation function. The TES model is used to drive CSMA/CD network simulations for a performance evaluation study. Numerical comparisons with a conventional autoregressive (AR) modeling approach are given 相似文献
95.
Feature-based stereo correspondence techniques suffer from the major limitation that it is difficult to match along epipolar
lines and this often results in a sparse set of depth points. Past researchers attempted to solve this problem through trinocular
stereo. In this paper, a new method has been proposed for reducing the sparsity of depth points by orienting the epipolar
line of the cameras in a direction that maximizes the number of feature points. The corresponding epipolar axis has been termed
as the optimal axis. Our analytical as well as simulation results have established that for a limited edge scenario, the proposed
approach can lead to considerable improvement in the number of feature points that can be matched. We have introduced a figure-of-merit
for the optimal axis and discussed how it is qualitatively related to the variance of the probability density function (pdf). We have also presented the results of our simulation experiment, termed as the random stick experiment. Finally, we have
also shown the results of improved reconstructed surface of a synthetic image using optimal axis alignment. 相似文献
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