Convex cone-based ranking of decision-making units in DEA

OR Spectrum - One of the major research streams in data envelopment analysis (DEA) is ranking decision-making units (DMUs). Utilizing a multicriteria decision-making technique, we develop a novel...     

The road user behaviour of school students in Iran

The present study developed a Persian version of the Adolescent Road User Behaviour Questionnaire (ARBQ) and investigated the psychometric properties of the scale in a sample of school students in the province of Tehran (Iran). In total 1111 adolescents completed the Persian version of the ARBQ. Exploratory factor analysis, using the shortened 21-item version of the scale revealed the presence of three reliable factors which were also supported using confirmatory factor analysis.     

The Use of Probability Limits of COM–Poisson Charts and their Applications

The conventional c and u charts are based on the Poisson distribution assumption for the monitoring of count data. In practice, this assumption is not often satisfied, which requires a generalized control chart to monitor both over‐dispersed as well as under‐dispersed count data. The Conway–Maxwell–Poisson (COM–Poisson) distribution is a general count distribution that relaxes the equi‐dispersion assumption of the Poisson distribution and in fact encompasses the special cases of the Poisson, geometric, and Bernoulli distributions. In this study, the exact k‐sigma limits and true probability limits for COM–Poisson distribution chart have been proposed. The comparison between the 3‐sigma limits, the exact k‐sigma limits, and the true probability limits has been investigated, and it was found that the probability limits are more efficient than the 3‐sigma and the k‐sigma limits in terms of (i) low probability of false alarm, (ii) existence of lower control limits, and (iii) high discriminatory power of detecting a shift in the parameter (particularly downward shift). Finally, a real data set has been presented to illustrate the application of the probability limits in practice. Copyright © 2012 John Wiley & Sons, Ltd.     

Structure and electrochemical performance of ZnO/CNT composite as anode material for lithium-ion batteries

Metal oxides are well-known potential alternatives to graphite as anode materials of lithium-ion batteries, and they can deliver much higher reversible capacities than graphite even at high current densities. In this study, hexagonal disk-shaped ZnO are synthesized by a facile solution reaction of ZnCl₂ and its composite is prepared in the presence of carbon nanotubes (CNTs). The as prepared ZnO/CNT composite has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, fourier transform-infrared spectroscopy and Rutherford backscattering spectroscopy. Electrochemical characterization by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge tests demonstrate that the conversion reactions in ZnO and ZnO/CNT electrodes enable reversible capacity of 478 and 602 mAh g^?1, respectively for up to 50 cycles. Our investigation highlights the importance of anchoring of small ZnO particles on CNTs for maximum utilization of electrochemically active ZnO and CNTs for energy storage application in lithium-ion batteries.     

An efficient synthesis of quinoxalinone derivatives as potent inhibitors of aldose reductase

A novel and facile synthesis of quinoxalinone derivatives was developed in which a wide range of 3-chloroquinoxalin-2(1H)-ones as key intermediates can be generated chemo- and regioselectively in good yields from corresponding quinoxaline-2,3(1H,4H)-diones. This new protocol is arguably superior, as it allows the design and preparation of a variety of bioactive quinoxaline-based compounds, which are particularly effective in the treatment of diabetes and its complications. Through this procedure, a new class of quinoxalinone-based aldose reductase inhibitors were synthesized successfully. Most of the inhibitors, with an N1-acetic acid head group and a substituted C3-phenoxy side chain, proved to be potent and selective. Their IC(50) values ranged from 11.4 to 74.8 nM. Among them, 2-(3-(4-bromophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic acid and 2-(6-bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic acid were the most active. Structure-activity relationship and molecular docking studies highlighted the importance of the ether spacer in the C3-phenoxy side chains, and provided clear guidance on the contribution of substitutions both at the core structure and the side chain to activity.     

Finite element modeling of low speed reaming vibrations with reamer geometry modifications

Reaming is a finishing process used to remove a small amount of material from a predrilled hole. In low speed cutting processes, it is the formation of lobed or multi-cornered holes that is of concern, rather than tool chatter, which occurs at high speed near the natural frequency of the tool. Using a quasi-static model in the characteristic form for the reaming process, a finite element modeling for the low speed reaming process, based on the Euler–Bernoulli beam model, was developed. Cutting and rubbing forces were applied as concentrated and distributed forces on a variable engagement length of the reamer. The variable engagement length is considered to simulate the actual applied forces length as the reamer advances to the workpiece. The time dependant changes in the bending stiffness of the reamer were included in the governing equation of the equilibrium of the reamer, and its stability analysis was performed at different time steps. Using this model, the vibration damping effect of uneven spacing of reamer teeth was investigated. The results demonstrate that uneven spacing of reamer teeth reduces the tool vibration, and therefore leads to a more stable condition. Finally, the optimum configuration of uneven tooth pitch angles for a six-flute reamer, in order to have the highest vibration decay rate during the reaming, was presented.     

Spin Polarization Dependence of Zero Bias Conductance in Ferromagnetic Quantum Wire/ D-wave Superconductor Junctions

A relation between the zero-bias conductance and spin polarization in a ferromagnetic quantum wire/ d-wave superconductor junction at finite temperature is studied, theoretically. In contrast to conventional d-wave superconductors which zero bias conductance peaks appear in tunneling spectra, we have found a disappearance of zero bias peak in tunneling spectra, in a way that it will be zero for all of barriers and polarizations parameters. Also, different temperature dependencies of zero bias conductance will be discussed.     

Low-temperature synthesis of bioactive glass-ceramic microspheres: Effect of processing parameters on the size and morphology

A low-temperature method was developed to produce bioactive glass microspheres (BGMs). The microspheres were fabricated by dispersing the prepared sol in silicon oil, a process called the sol-microemulsion-gel method. The resulting microspheres were characterized by X-ray diffractometry (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Brunauer-Emmett-Teller (BET) techniques. Furthermore, the effect of various processing parameters such as reaction chamber size and the stirring rate on microspheres diameter was investigated. The results indicated that under optimized conditions, one could obtain BGMs with acceptable sphericity having a narrow size distribution. The obtained microspheres had diameters in the range of 19.3 ± 9.3 μm. The BET specific surface area was 240.33 m²/g. The results also showed that the increase in the reaction chamber size had interesting contradictory effects on BGMs diameter. The increase in the stirring rate intensified the shear forces exerted on the water-based phase and caused the generation of smaller droplets and microspheres.