Evaluation of microchamber geometries and surface conditions for electrokinetic driven mixing

The paper presents numerical simulations and analysis of electrokinetic induced mixing in a microchamber in the presence of a fluctuating electric field. Two microchamber geometries are investigated; one plain and the other with strategically placed microbaffles. Both geometries are tested for two extreme surface conditions: a charged surface with induced electrokinesis and another with a neutral or passive surface. Through order of magnitude analysis and numerical experiments it is found that there is an optimal choice of nondimensional frequency and driving potential which leads to the best mixing characteristics. This is given by the relationship Re(eof)/f*< 5 and the condition that f*= O(1), where Re(eof) is the ratio of electrokinetic forces to viscous forces and f*is the nondimensional frequency. Optimal mixing is shown to occur at Re(eof) = 100 and f*= 30. In all cases, best mixing is found to occur when conditions are favorable for the establishment and sustenance of a rotational cell in the chamber driven by the fluctuating ac current. It is shown that the plain microchamber performs better under conditions of surface neutrality while microbaffles enhance mixing substantially in a charged microchamber. In the presence of a rotational cell, the characteristic time scale for mixing is reduced by 2-3 orders of magnitude compared to plain diffusion and is calculated to be between 5 and 10 s for aqueous buffers.     

High-transfer-rate high-capacity holographic disk data-storage system

We describe the design and implementation of a high-data-rate high-capacity digital holographic storage disk system. Various system design trade-offs that affect density and data-rate performance are described and analyzed. In the demonstration system that we describe, high-density holographic recording is achieved by use of high-resolution short-focal-length optics and correlation shift multiplexing in photopolymer disk media. Holographic channel decoding at a 1-Gbit/s data rate is performed by custom-built electronic hardware. A benchmark sustained optical data-transfer rate of 10 Gbits/s has been successfully demonstrated.     

High-pressure high-temperature (HPHT) synthesis and magnetism of MSr2Y1.5Ce0.5Cu2O10 compounds with M = Ru, Mn, and Cr

We report synthesis and magnetization of MSr₂Y_1.5Ce_0.5Cu₂O₁₀ (M/Y-1222) compounds with M = Ru, Mn and Cr by HPHT. They are synthesized at high-pressure of 6 GPa in optimized temperatures of up to 1450 °C, for Ru, Mn and 1550 °C in the case of Cr based Y/1222, for a time duration of three hours for all the samples. All the samples crystallized with tetragonal structure in I4/mmm space group. Few minor impurities are also seen in the case of Mn,Cr/Y-1222 samples. DC magnetic susceptibility measurements exhibited ferromagnetic like transition for all the three compounds at low temperatures. At 5 K, the magnetization M(H) experiments showed clear ferromagnetic like hysteresis loops for Ru and Mn samples with sizeable returning moment (M_r) and coercive field (H_c). In the case of Cr/Y-1222 system though, ferromagnetism is visible below around 45 K in susceptibility measurements, the characteristic M_r and H_c are not seen. To the best of our knowledge the Mn,Cr/Y-1222 phases are synthesized for the first time and the quality of our earlier reported Ru/Y-1222 is improved.     

Process Parameter Optimization in Jatropha Methyl Ester Yield Using Taguchi Technique

Among all alternate fuel sources available, the biodiesel of Jatropha curcas appears to be a potential fuel as it widely exists in Asia. The Jatropha methyl ester (JME) is produced by transesterification process. In the transesterification process, alkyl group of ester exchanges with that of an alcohol. This work focuses on optimizing various parameters like quantities of methanol, KOH, and stirrer speed, which influence high JME yield. Based on L₉ orthogonal array, experiments are conducted by using Taguchi technique. All the nine combinations of L₉ orthogonal array are experimentally done for extraction of JME, and then it is used for analysis in Taguchi technique. The analysis of maximum yield is done on the basis of “larger is better” signal to noise ratio (S/N ratio). The best combination in the L₉ orthogonal array is found to be methanol (110 ml), KOH (1.306 gm), and stirrer speed (1200 rpm). The influence of methanol, KOH, and stirrer speed on the yield is found by analysis of variance (ANOVA). Based on the results of ANOVA, it is found that the influence of methanol, KOH, and stirrer speed on the yield are obtained as 70.10%, 20.35%, and 5.78%, respectively.     

Growth of unidirectional potassium dihydrogen orthophosphate single crystal by SR method and its characterization

Unidirectional <100> potassium dihydrogen orthophosphate (KDP) single crystals were grown for the first time by Sankaranarayanan-Ramasamy (SR) method. The <100> oriented seed crystals were mounted at the bottom of the glass ampoules and the crystal of 15 mm diameter, 65 mm height were grown by SR method. The grown crystals were characterized by high-resolution X-ray diffraction (HRXRD), etching studies. The HRXRD analysis indicates that the crystalline perfection is excellent without having any very low angle internal structural grain boundaries. Dislocation density is less in SR grown KDP compared to conventional method grown KDP.     

Effect of a high energy electrical pulse on the dynamic stress-strain behavior of a copper alloy

Electromagnetic launchers (EML) dispatch projectiles at extreme velocities (Mach 7-8), using copper/copper alloy rails which are subjected to high rates of loading under a high energy electrical pulse. Results from Split Hopkinson Pressure Bar (SHPB) testing of a copper alloy at high strain rates in the order of 10³ s^− 1 with simultaneous application of a high energy electrical pulse show that the plastic deformation of the copper alloy is increased and a higher degree of work hardening is observed under these conditions.     

Dynamics of growth and weight transitions in a pediatric cohort from India

Background  

There is paucity of information regarding time trends of weight status in children from rapidly developing economies like India. The aim of the study was to analyse the dynamics of growth and weight transitions in a cohort of school children from India.     

A non-quasi-static small-signal model for metal-semiconductor junction diodes

The quasi-static approximation, which assumes that free-carrier propagation delay in the semiconductor device is zero, is often used in device modeling. Consequently, the quasi-static model is adequate only for low-frequency excitations for which free-carrier propagation delay is very small compared to the variation of the excitations. This paper develops a non-quasi-static model suitable for metal-semiconductor junction diodes subjected to small-signal excitation. We show that the predictions of the non-quasi-static model agree more favourably with experimental data taken from Al---Si diodes than that of the quasi-static model, particularly when the frequency of the excitation is high.     

MATLAB modelling and examination of the effect of heat capacity of basin and glass cover on performance of solar still by thermal models

There are numerous researcher-developed mathematical models for single slope passive solar stills which considered the effect of heat capacities of basin and glass cover as negligible. The negligence parameter also plays a vital role in the prediction of the thermal performance of the system. In this paper, an effort has been made to evaluate the cumulative yield, energy efficiency and exergy efficiency of a single slope passive solar still with and without considering the heat capacities of basin and glass cover by using various thermal models such as Dunkle’s model, Zheng Hongfei et al.’s model and Tsilingiris model. These models were studied and compared with and without considering the heat capacity of solar components such as basin and glass cover. The thermodynamic model of this system is developed, and executed in a MATLAB code. By comparing the theoretical values of the cumulative yield, energy efficiency and exergy efficiency, it was found that consideration of the heat capacities of glass cover and basin gives a higher output in all the thermal models.     

Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SR_K2SO4 > SR_KCl and SR_Na2SO4 > SR_NaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010