Indigenous design and development of a micro-pulse lidar for atmospheric studies

A sophisticated micro-pulse lidar (MPL) has been designed and developed for the study of the atmospheric boundary layer (ABL) and clouds. The developed MPL uses a low energy pico-second pulsed Nd:YAG laser at 532 nm. The conventional receiver optic is used along with a photomultiplier tube in single photon detection mode. Stanford Research Systems' multi-channel scalar (MCS) is used with a personal computer for data acquisition. Due to the short laser pulse and a fast MCS, a spatial resolution of 0.75 m has been achieved. The control circuit has been designed to sense telescope cover status (open or closed) to avoid any mistakes in dark count and background data acquisition. The complete control software and Graphical User Interface (GUI) has been developed in Visual Basic. The lidar system has been tested both for its functionality to detect the variation in ABL and cloud height and also for its capability to acquire continuous night-time data without user interaction. In this article the design details and some preliminary results are discussed.     

Probing Aromaticity of Borozene Through Optical and Dielectric Response: A Theoretical Study

In this work, we report electronic structure calculations aimed at computing the linear optical absorption spectrum and static dipole polarizablity of a newly proposed boron-based planar aromatic compound borozene (B ₁₂ H ₆). For the purpose, we use the semiempirical INDO model Hamiltonian, accompanied by large-scale correlation calculations using the multi-reference singles-doubles configuration-interaction (MRSDCI) approach. We present detailed predictions about the energetics, polarization properties, and the nature of many-particle states contributing to various peaks in the linear absorption spectrum. Our results can be used to characterize this material in future optical absorption experiments. We also argue that one can deduce the aromaticity of the cluster from the optical absorption and static polarizability results.     

Effect of silica doping on the densification and grain growth in zinc oxide

The ability of silica (SiO₂) in controlling the densification and grain growth behavior of nano crystalline zinc oxide (ZnO) has been systematically studied. It has been observed that SiO₂ acts as a sintering inhibitor in the ZnO–SiO₂ system up to 4 wt.% limiting value beyond which densification behavior of the system remains almost unchanged, especially above 1100 °C. The addition of SiO₂ to ZnO retards grain growth which in turn results a finer ultimate grain size as compared to the undoped ZnO. However, stabilization in grain size occurs at ≥4 wt.% SiO₂ addition. It has been observed that SiO₂ incorporation changes the grain growth mechanism up to 4 wt.% addition, beyond which no remarkable changes was noticed. The grain growth (n) shows distinctly different slopes as a function of sintering time for the SiO₂ doped ZnO systems than undoped ZnO. The different slopes tend to indicate that different diffusion mechanisms and probably the formation of a secondary phase (Zn–Si–O) at the grain boundary control the densification and grain growth. The thermal expansion coefficient of the system has been found to decrease substantially beyond 4 wt.% SiO₂ addition to ZnO.     

Vinyl carbazole (VC) functionalized mesoporous silica polymer nanocomposites (SBA/VC) for the antibacterial activity studies

Vinyl carbazole (VC) functionalized ordered mesoporous silica polymer nanocomposites (SBA/VC) were synthesized by in situ radical polymerization of monomers inside the mesoporous framework and characterized for the antibacterial activity studies against gram positive and gram negative bacteria. Powder X-ray diffraction and N₂ adsorption isotherms of SBA/VC nanocomposites showed the presence of mesoporous nature. The antimicrobial activity results showed increasing trend with the increase in the concentration of vinyl carbazole (VC) and the maximum antibacterial activity was achieved with SBA/VC₆₄ nanocomposites.     

Analysis of Scanning DMA Transfer Functions

A new approach to determine transfer functions of scanning differential mobility analyzers (DMAs) is introduced. An expression for non-diffusive particle trajectories in a cylindrical DMA operating in a scanning voltage mode is obtained analytically. Particle trajectory simulations are then used to determine the scanning DMA transfer functions. The results suggest that the shape of the scanning DMA transfer functions may vary with mobility for scan times smaller than a certain value, which depends on the DMA flowrates, and this provides one criteria limiting the fastest scan possible with the conventional DMAs. A simple approach to determine upscan scanning DMA transfer functions in near real-time with minimal number of simulations is described. For upscan operation, the choice of the scantime is seen to impose upper and lower limits on the particle mobility range classified by a scanning DMA. The predicted effect of voltage scanning on altering DMA transfer functions is validated with fast scan experiments.     

A One-Dimensional Model for Particulate Deposition and Hydrocarbon Condensation in Exhaust Gas Recirculation Coolers

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NO_x (oxides of nitrogen) emissions. A portion of the exhaust gases is recirculated into the intake manifold of the engine after cooling it through a heat exchanger. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface. This adversely affects the combustion process, engine durability, and emissions. In this study, a 1-D model was developed to simulate soot deposition, soot removal, and condensation of several hydrocarbon (HC) species in a circular tube with turbulent gas flow at constant wall temperature. The circular tube, which makes up the computational domain in the model, represents a single channel from any EGR cooler geometry. The model takes into account soot particle deposition due to thermophoresis, diffusion, turbulent impaction, and gravitational drift. However, thermophoresis was found to be the most dominant deposition mechanism for boundary conditions at which EGR coolers typically operate. Soot removal was modeled by considering a force balance between the drag and van der Waals forces. A lognormal distribution of particles was assumed at the tube inlet. The evolution of the particle distribution in the bulk flow along the tube as well as the mass distribution in the deposit layer on the tube walls is predicted by the model. Condensation of six HC species between C₁₅-C₂₄ alkanes was also modeled. Predictions made by the model are in reasonably good agreement with experimental data obtained from a laboratory reactor under the same boundary conditions. There are several assumptions and simplifications built into the model, which can be refined further to improve it.

Copyright 2012 American Association for Aerosol Research     

Antibacterial activity of silver‐doped manganese dioxide nanoparticles on multidrug‐resistant bacteria

BACKGROUND: As a result of evolution of multiple drug resistance in human pathogens (bacteria) there is increasing demand for novel antibacterial agents, and recently, due to their high antibacterial and catalytic activities, metal nanoparticles have attracted the attention of researchers and medical microbiologists worldwide. RESULTS: Ni‐, Ce‐ and Ag‐doped MnO₂ nanoparticles were synthesized by a co‐precipitation method. Antibacterial activity of these synthesized nanoparticles on methicillin‐resistant Staphylococcus aureus and lead‐resistant Pseudomonas aeruginosa strain 4EA was investigated using a disc diffusion method. Only Ag‐doped MnO₂ nanoparticles showed an antibacterial property against methicillin‐resistant Staphylococcus aureus and lead‐resistant Pseudomonas aeruginosa strain 4EA at low levels of 60 µg/disc and 85 µg/disc, respectively. Scanning electron microscopy and transmission electron microscopy (SEM‐TEM) coupled with energy dispersive X‐ray (EDX) analysis revealed the nano‐size and composition of these synthesized nanoparticles. CONCLUSION: It was confirmed through a disc diffusion method that chemically synthesized silver doped MnO₂ nanoparticles have antibacterial activity against multidrug‐resistant Staphylococcus aureus and lead‐resistant Pseudomonas aeruginosa strain 4EA at low levels therefore these nanoparticles can be employed to fight and prevent infections caused by multidrug‐resistant bacterial pathogens. © 2012 Society of Chemical Industry     

Gender difference in color preference across cultures: An archetypal pattern modulated by a female cultural stereotype

A gender difference in color preference among British participants has been repeatedly reported, in which both males and females show a preference for blue‐green colors, while females express an additional preference for pink‐purple colors. To investigate the robustness of gender difference in color preference in a different culture, we tested 81 young adult Indians from a school of design and compared them to 80 young British students in Psychology. The 35‐item International Personality Item Pool (IPIP) and Bem Sex Role Inventory (BSRI) questionnaires were also administered to explore possible links between personality traits, gender schemata, and color preferences. Results confirmed a gender difference in both cultures; participants collectively expressed a preference for cool over warm colors, while in addition females showed a preference for pink colors, with a warm bias for Indian females and a cool bias for British females. While these results extend gender difference to Indian culture and support the universality of an underlying pattern they also reveal a culture‐specific contribution essentially observed in females. In British participants, color preference was correlated exclusively with BSRI scores in females and overwhelmingly with IPIP scores in males; this gender‐specific pattern of correlation was not replicated in the Indian sample. Results point to an archetypal pattern of gender difference in color preference with a remarkable cross‐cultural similarity in men and a subtle but significant cultural difference in women whose origin is yet to be explained.