Unsteady hydromagnetic flow of a reactive variable viscosity third‐grade fluid in a channel with convective cooling

This paper examines the combined effects of a transverse magnetic field and variable viscosity on unsteady flow of a reactive third‐grade electrically conducting fluid and heat transfer in a channel with convective cooling at the surface. It is assumed that the fluid has small electrical conductivity and the electromagnetic force produced is very small. The coupled nonlinear partial differential equations governing the problem are derived and solved numerically using a semi‐implicit finite‐difference scheme. Both numerical and graphical results are presented and physical aspects of the problem are discussed with respect to various parameters embedded in the system. It is in general noted that those parameters that increase/decrase one flow quantity (velocity or temperature) also lead to the increase/decrease respectively of the other quantity. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of the size and geometry of the anion binding pocket of sugar–urea anion receptors on chiral recognition

Three new chiral urea-type anion receptors were synthesized from aromatic diamines and 1-amino-1-deoxyglucose. The anion binding properties of these receptors were studied using chiral carboxylates derived from mandelic acid and three α-amino acids. We found that the size of the anion binding pocket played an important role in chiral recognition processes. The best results were obtained for 1,8-diaminoanthracene and α-amino acid anions.     

Covalent Organic Frameworks(COFs) for Sequestration of99TcO4–

Covalent organic frameworks(COFs), as a class of crystalline porous materials with periodic lattices and porous structures, have received extensive attention in the fields of gas storage and separation, energy storage, catalysis and optoelectronics and so on. However, COFs are still in their infancy in the field of nuclear waste treatment, especially for sequestration of long-live problematic radionuclides, such as ⁹⁹Tc. Battle of decontamination of pertechnetate(TcO₄^–), a main existence of ⁹⁹Tc under aerobic environments, is far from finished. In this review, recent progresses of COFs and some relative materials in the sequestration of pertechnetate, and perspective on surmounting the unmet issues are elucidated.     

UV–vis and fluorescence detection by receptors based on an isophthalamide bearing a phenylethynyl group

We have successfully prepared 5-(2-phenylethynyl)isophathalilc acid as a signaling unit and the corresponding derivatives for an anion receptor 2 and a barbiturate receptor 4. Receptor 2 showed characteristic UV–vis changes and dramatic fluorescence quenching upon the addition of anions and receptor 4 showed UV–vis and an OFF-ON fluorescence changes upon the addition of dibutylbarbituric acid based on the diphenylethyne moiety.     

Joint impact of nodes-mobility and channel estimation error on the performance of two-way relay systems

This paper presents the performance analysis of a two-way relay system with nodes-mobility (NM) and channel estimation errors (CEE) under time-varying Rayleigh fading. Herein, analog network coding protocol is employed at the relay node. All the participating nodes are half-duplex and equipped with single-antenna devices. Specifically, we utilize first-order Markovian model to characterize the impact of NM in the channel. Along with the NM, we also consider that the CEE may exist in practical scenarios, where nodes require to estimate the channel state information. By incorporating these factors, we first derive the instantaneous end-to-end (e2e) signal-to-noise ratios (SNRs) at two source nodes. Then, we obtain the exact closed-form expressions for distribution and density functions of the two e2e SNRs. After that, we derive the accurate expressions of various performance metrics, viz., sum-bit error rate, overall outage probability, and ergodic sum-rate. Further, to attain more insights into the considered system, we deduce the asymptotic behavior of these performance metrics. Finally, numerical and Monte-Carlo simulation results are provided to validate our theoretical analysis and to illustrate the impact of NM and CEE on the performance measures of the considered system.     

Anion Receptor with Xylene Bridged Two Imidazolium Rings

A m-xylene bridged imidazolium receptor 1 has been designed and synthesized. The receptor 1 utilizes two imidazole (C–H)⁺—anion hydrogen bonds and one aromatic hydrogen—anion hydrogen bond. The major driving force of complexation between the receptor 1 and anions comes from two imidazole (C–H)⁺—anion hydrogen bonding. However, some hydrogen bonding energy between aromatic hydrogen and anion exists, although it is expected to be much smaller than that of imidazole (C–H)⁺—anion hydrogen bonds.

     

Cobalt(III) Supramolecuar Complex: Synthesis,Crystal Structure and Anions Recognition Properties of 6,7-Dinitroquinoxaline-2,3-dione

A 3D supramolecular complex [Co(III)(Phen)₂Cl₂][DNQ]Cl·H₂O (DNQ = 6,7-dinitroquinoxaline-2,3-dione) has been synthesized and determined by single-crystal X-ray analysis. Anion binding studies carried out using ¹H NMR and UV-visible revealed that a genuine hydrogen bond interaction between anion receptor 2 and Cl^?  can be detected, but fluoride is deprotonating the anion receptor 2. X-ray analysis results show that it is not possible for the two amide nitrogen atoms of anion receptor to form hydrogen bonds to a chloride ion in the presence of small aliquots of water.     

A New Phosphonium Calix[4]arene for Selective Anion Recognition: Synthesis and Studies in Solution and in Ion Selective Electrodes

The synthesis and characterization of a new tetra (triphenylphosphonium) p-tert-butylcalix[4]arene 2 is presented. Its interactions with anions were studied by ¹H and ³¹P NMR and UV absorption spectrophotometry, showing the biggest interaction with ClO₄ ^? , I^?  and SCN^? . Anion selectivity in ion-selective PVC-membrane electrodes (ISEs) plasticized with o-NPOE containing ionophore 2 was also investigated. Compound 2 shows a potentiometric response for various anions with the following selectivity pattern: ClO₄ ^?  > SCN^?  > I^?  > Cr₂O₇ ^2 ?  > NO₃ ^?  > Br^?  > Cl^? .