Synthesis and Characterization of Porogen Based Porous Low-k Thin Films

The present work is focused towards the lowering of the k value of deposited SiO₂ thin films by varying solvent concentration i.e. ethanol in the range 4-10 ml. Porous low-k thin films were synthesized by using the sol-gel spinon technique. A non-ionic surfactant polysorbate 80 (Tween 80) was used as a porogen to generate the porosity in the film matrix. The lower values of refractive index and film density were measured to be 1.19 and 0.94 gm/cm³ respectively for 10 ml solvent concentration. Further, the lowest k value of 2.2 and highest porosity percentage of 58.5 % were obtained for the same film due to the dilution of coating solution at higher solvent concentration. The water contact angle of the film was observed to be increased to 106.3° which indicates the transformation of the deposited film surface from hydrophilic to hydrophobic. The change in chemical structure as an effect of solvent concentration is studied by using FTIR. From FTIR spectra the disappearance of Si-OH groups at higher solvent concentration reveals the increase in condensation rate. Overall in this study, the result shows the significant change in structural, chemical and optical properties of the deposited films at 10 ml solvent concentration. Such deposited porous thin films with lower k value and enhanced hydrophobicity can be used as an interlayer dielectric (ILD) for back end of line (BEOL) in CMOS technology.     

Bacterial synthesis of copper/copper oxide nanoparticles

A bacterial mediated synthesis of copper/copper oxide nanoparticle composite is reported. A Gram-negative bacterium belonging to the genus Serratia was isolated from the midgut of Stibara sp., an insect of the Cerambycidae family of beetles found in the Northwestern Ghats of India. This is a unique bacterium that is quite specific for the synthesis of copper oxide nanoparticles as several other strains isolated from the same insect and common Indian mosquitoes did not result in nanoparticle formation. By following the reaction systematically, we could delineate that the nanoparticle formation occurs intracellularly. However, the process results in the killing of bacterial cells. Subsequently the nanoparticles leak out as the cell wall disintegrates. The nanoparticles formed are thoroughly characterized by UV-Vis, TEM, XRD, XPS and FTIR studies.     

Assessment of a fuzzy logic based MRAS observer used in a photovoltaic array supplied AC drive

In this paper a fuzzy logic (FL) based model reference adaptive system (MRAS) speed observer for high performance AC drives is proposed. The error vector computation is made based on the rotor-flux derived from the reference and the adaptive model of the induction motor. The error signal is processed in the proposed fuzzy logic controller (FLC) for speed adaptation. The drive employs an indirect vector control scheme for achieving a good closed loop speed control. For powering the drive system, a standalone photovoltaic (PV) energy source is used. To extract the maximum power from the PV source, a constant voltage controller (CVC) is also proposed. The complete drive system is modeled in MATLAB/Simulink and the performance is analyzed for different operating conditions.     

Electrospun bioactive nanocomposite scaffolds of polycaprolactone and nanohydroxyapatite for bone tissue engineering

Nanocomposite scaffolds based on nanofibrous poly(epsilon-caprolactone) (PCL) and nanohydroxyapatite (nanoHA) with different compositions (wt%) were prepared by electrostatic co-spinning to mimic the nano-features of the natural extracellular matrix (ECM). NanoHA was found to be well dispersed in polymers up to the addition of 20 wt%, after ultrasonication. The composite scaffolds were characterized for structure and morphology using XRD, EDX, SEM, and DSC. The scaffolds have a porous nanofibrous morphology with fibers (majority) having diameters in the range of 450-650 nm, depending on composition, and interconnected pore structures. SEM, EDX, and XRD analyses have confirmed the presence of nanoHA in the fibers. As the nanoHA content in the fibers increases, the surface of fibers becomes rougher. The mechanical (tensile) property measurement of the electrospun composites reveals that as the nanoHA content increases, the ultimate strength increases from 1.68 MPa for pure PCL to 2.17, 2.65, 3.91, and 5.49 MPa for PCL/nanoHA composites with the addition of 5, 10, 15, and 20 wt% nanoHA, respectively. Similarly the tensile modulus also increases gradually from 6.12 MPa to 21.05 MPa with the increase of nanoHA content in the PCL/nanoHA fibers, revealing an increase in stiffness of the fibers due to the presence of HA. DSC analysis reveals that as nanoHA in the composite scaffolds increases, the melting point slightly increases due to the good dispersion and interface bonding between PCL and nanoHA.     

Convective heat transfer in pressure-driven nitrogen slip flows in long microchannels: The effects of pressure work and viscous dissipation

An analytical and numerical study is carried out to examine the convective heat transfer in two-dimensional pressure-driven nitrogen slip flows in long microchannels, whose length-to-height ratios are above 500. The momentum and the energy equations are solved, where variable properties, rarefaction that involves velocity slip, thermal creep and temperature jump, pressure work, and viscous dissipation are all taken into account. Nitrogen is assumed to be a perfect gas. The effects of pressure work and viscous dissipation, which are particularly significant for long microchannels, are examined by analyzing the uniform wall temperature and the uniform wall heat flux cases. It is found that the degree of rarefaction, which is characterized by the Knudsen number, is the key factor that determines the relative importance of pressure work and viscous dissipation. It is demonstrated that, for perfect gases, rarefaction promotes the conversion of internal energy to mechanical energy. Specifically, regardless of the fluid field development, pressure work and viscous dissipation cancel out in the absence of rarefaction, while pressure work is greater than viscous dissipation with rarefaction and its dominance increases as the Knudsen number increases. It is shown that the combination of pressure work and viscous dissipation makes a significant impact on the Nusselt number in both the continuum and the rarefaction cases. Therefore, it is concluded that for convective heat transfer in internal gas flows, both pressure work and viscous dissipation need to be considered in analysis.     

An efficient similarity measure technique for medical image registration

In this paper, an efficient similarity measure technique is proposed for medical image registration. The proposed approach is based on the Gerschgorin circles theorem. In this approach, image registration is carried out by considering Gerschgorin bounds of a covariance matrix of two compared images with normalized energy. The beauty of this approach is that there is no need to calculate image features like eigenvalues and eigenvectors. This technique is superior to other well-known techniques such as normalized cross-correlation method and eigenvalue-based similarity measures since it avoids the false registration and requires less computation. The proposed approach is sensitive to small defects and robust to change in illuminations and noise. Experimental results on various synthetic medical images have shown the effectiveness of the proposed technique for detecting and locating the disease in the complicated medical images.     

Bioenergy production from glycerol in hydrogen producing bioreactors (HPBs) and microbial fuel cells (MFCs)

The supply of glycerol has increased substantially in recent years as a by-product of biodiesel production. To explore the value of glycerol for further application, the conversion of glycerol to bioenergy (hydrogen and electricity) was investigated using Hydrogen Producing Bioreactors (HPBs) and Microbial Fuel Cells (MFCs). Pure-glycerol and the glycerol from biodiesel waste stream were compared as the substrates for bioenergy production. In terms of hydrogen production, the yields of hydrogen and 1,3-propanediol at a pure-glycerol concentration of 3 g/L were 0.20 mol/mol glycerol and 0.46 mol/glycerol, respectively. With glucose as the co-metabolism substrate at the ratio of 3:1 (glycerol:glucose), the yields of hydrogen and 1,3-propanediol from glycerol significantly increased to 0.37 mol/mol glycerol and 0.65 mol/glycerol, respectively. The glycerol from biodiesel waste stream had good hydrogen yields (0.17-0.18 mol H₂/mole glycerol), which was comparable with the pure-glycerol. In terms of power generation in MFCs, pure-glycerol was examined at concentrations of 0.5-5 g/L with the highest power density of 4579 mW/m³ obtained at a concentration of 2 g/L. The power densities from the biodiesel waste glycerol were 1614-2324 mW/m³, which were likely caused by the adverse effects of impurities on electrode materials. An economic analysis indicates that with the annual waste stream of 70 million gallons of glycerol, the expected values generated from HPBs and MFCs were $311 and $98 million, respectively.     

Detection of lead in water using laser-induced breakdown spectroscopy and laser-induced fluorescence

Laser-induced breakdown spectroscopy (LIBS) is a well-known technique for fast, stand-off, and nondestructive analysis of the elemental composition of a sample. We have been investigating micro-LIBS for the past few years and demonstrating its application to microanalysis of surfaces. Recently, we have integrated micro-LIBS with laser-induced fluorescence (LIF), and this combination, laser ablation laser-induced fluorescence (LA-LIF), allows one to achieve much higher sensitivity than traditional LIBS. In this study, we use a 170 microJ laser pulse to ablate a liquid sample in order to measure the lead content. The plasma created was re-excited by a 10 microJ laser pulse tuned to one of the lead resonant lines. Upon optimization, the 3sigma limit of detection was found to be 35 +/- 7 ppb, which is close to the EPA standard for the level of lead allowed in drinking water.     

Synthesis of economically viable biodiesel from waste frying oils (WFO)

In present communication, waste frying oil (WFO) has been used as a feedstock for biodiesel synthesis. WFO, procured from a local Indian restaurant possessed an acid value of 0.84 mg KOH/g, which is low enough for single step transesterification reaction. Biodiesel (fatty acid methyl esters) was washed after transesterification reaction and the yield got lowered substantially (from 96% to 86.36%) after water washing owing to loss of esters. 30:100 vol% (methanol to oil), 0.6 wt% NaOCH₃, 60°C temperature and 600 rpm agitation in 1 h reaction time was found to be optimum for transesterification reaction. ¹H NMR spectrum showed a high conversion (95.19%) of fatty acids in WFO to biodiesel in 2 h reaction time. Almost complete conversion (99.68%) was attained in 2 h reaction time. © 2011 Canadian Society for Chemical Engineering