Multiscale micro-patterned polymeric and carbon substrates derived from buckled photoresist films: fabrication and cytocompatibility

We report here a novel and simple buckling-based multiscale patterning of negative photoresist films which were subsequently pyrolyzed to yield complex micro-patterned carbon surfaces. Unlike other polymers, the use of a photoresist layer allows the overall pattern definition by photolithography on which the geometry and length scale of the buckling-instability are superimposed. The photoresist film swells anisotropically during developing and buckles after subsequent drying due to the difference in the shrinkage of the hard cross-linked layer on top of a softer native pre-polymer. We studied the conditions for the formation of a wide variety of complex, fractal buckling patterns as well as directionally aligned zigzag patterns over a large area. For example, the buckling diminished for the films below a critical thickness and after a prolonged UV exposure, both of which eliminate the softer under-layer. These patterned carbon substrates are also shown to be biocompatible for the cellular adhesion and viability by using L929 mouse fibroblast cells, thus indicating their potential use in bio-MEMS platforms with a conductive substrate. The buckled carbon patterns were found to be a better choice of a substrate for cell growth and viability as compared to flat and simply periodic patterned carbon surfaces.     

In-situ measurements of concentration and temperature during transient solidification of aqueous solution of ammonium chloride using laser interferometry

The variation in temperature and concentration plays a crucial role in predicting the final microstructure during solidification of a binary alloy. Most of the experimental techniques used to measure concentration and temperature are intrusive in nature and affect the flow field. In this paper, the main focus is laid on in-situ, non-intrusive, transient measurement of concentration and temperature during the solidification of a binary mixture of aqueous ammonium chloride solution (a metal-analog system) in a top cooled cavity using laser based Mach–Zehnder Interferometric technique. It was found from the interferogram, that the angular deviation of fringe pattern and the total number of fringes exhibit significant sensitivity to refractive index and hence are functions of the local temperature and concentration of the NH₄Cl solution inside the cavity. Using the fringe characteristics, calibration curves were established for the range of temperature and concentration levels expected during the solidification process. In the actual solidification experiment, two hypoeutectic solutions (5% and 15% NH₄Cl) were chosen. The calibration curves were used to determine the temperature and concentration of the solution inside the cavity during solidification of 5% and 15% NH₄Cl solution at different instants of time. The measurement was carried out at a fixed point in the cavity, and the concentration variation with time was recorded as the solid–liquid interface approached the measurement point. The measurement exhibited distinct zones of concentration distribution caused by solute rejection and Rayleigh Benard convection. Further studies involving flow visualization with laser scattering confirmed the Rayleigh Benard convection. Computational modeling was also performed, which corroborated the experimental findings.     

Engineered anode structure for enhanced electrochemical performance of anode-supported planar solid oxide fuel cell

A novel approach of fabricating SOFC anode comprising graded compositions in constituent phases having layer wise microstructural variation is reported. Such anode encompasses conventional NiO–YSZ (40 vol% Ni) with higher porosity at the fuel inlet side and Ni–YSZ electroless cermet (28–32 vol% Ni) with less porosity toward the electrolyte. Microstructures and thicknesses of the bilayer anodes (BLA) are varied sequentially from 50 to 250 μm for better thermal compatibility and cell performance. Significant augmentation in performance (3.5 A cm⁻² at 800 °C, 0.7 V) is obtained with engineered trilayer anode (TLA) having conventional anode support in conjunction with layers of electroless cermet each of 50 μm having 28 and 32 vol% Ni. Engineered TLA accounts for substantial reduction both in cell polarization (ohmic ASR: 78 mΩ cm² versus 2835 mΩ cm²; cell impedance: 0.35 Ω cm² versus 0.9 Ω cm²) and degradation rate (76 μV h⁻¹ versus 219 μV h⁻¹) compared to cells fabricated with conventional cermet.     

Dependence of Protein Adsorption on Wetting Behavior of UHMWPE–HA–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CNT Hybrid Biocomposites

Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as an articulating surface in total hip and knee joint replacement. In order to enhance long-term durability/wear resistance properties, UHMWPE-based polymer–ceramic hybrid composites are being developed. Surface properties such as wettability and protein adsorption alter with reinforcement or with change in surface chemistry. From this perspective, the wettability and protein adsorption behavior of compression-molded UHMWPE–hydroxyapatite (HA)–aluminum oxide (Al₂O₃)–carbon nanotube (CNT) composites were analyzed in conjunction with surface roughness. The combined effect of Al₂O₃ and CNT shows enhancement of the contact angle by ~37° compared with the surface of the UHMWPE matrix reinforced with HA. In reference to unreinforced UHMWPE, protein adsorption density also increased by ~230% for 2 wt.%HA–5 wt.%Al₂O₃–2 wt.%CNT addition to UHMWPE. An important conclusion is that the polar and dispersion components of the surface free energy play a significant role in wetting and protein adsorption than do the total free energy or chemistry of the surface. The results of this study have major implications for the biocompatibility of these newly developed biocomposites.     

Wave‐current interaction effects on structural responses of floating offshore wind turbines

This paper proposes a model considering the wave‐current interactions in dynamic analyses of floating offshore wind turbines (FOWTs) and investigates the interaction effects on the FOWT responses. Waves when traveling on current are affected by the current, leading to frequency shift and shape modification. To include such interactions in FOWT analysis, which has not been considered by the researchers till date, a nonlinear hydrodynamic model for multicable mooring systems is presented that is able to consider the cable geometric nonlinearity, seabed contact, and the current effect. The mooring model is then coupled with a spar‐type FOWT model that handles the structural dynamics of turbine blades and tower, aerodynamics of the wind‐blade interaction, and wave‐current effects on the spar. The analytical wave‐current interaction model based on Airy theory considering the current effect is used in the computation of flow velocity and acceleration. Numerical studies are then carried out based on the NREL offshore 5‐MW baseline wind turbine supported on top of the OC3‐Hywind spar buoy. Two cases, (1) when the currents are favorable and (2) when the currents are adverse, are examined. Differences of up to 15% have been observed by comparing the cable fairlead tension obtained excluding and including the wave‐current interactions. In particular, when irregular waves interact with adverse current, a simple superposition treatment of the wave and the current effects seems to underestimate the spar motion and the cable fairlead tension. This indicates that the wave‐current interaction is an important aspect and is needed to be considered in FOWT analysis.     

The fatty acid composition of cottonseed oil at various stages of solvent extraction

The variation in the fatty acid composition of the glyceride portion of cottonseed oil at various stages of solvent extraction has been investigated. Prime cottonseed meats were flaked and extracted in glassware rate extraction apparatus, using commercial hexane up to different degrees of extractions. The fatty acid composition of cottonseed oil obtained after extracting the flakes to different residual oil contents was determined by gas-liquid partition chromatography. No difference was found.     

Integrated biofilter-immersed membrane system for the treatment of humic waters

An integrated biofilter-immersed membrane study was conducted to determine the effect of placing a biofilter before or after a membrane for the treatment of a humic type water. The parameters measured included total organic carbon (TOC), organic acids, and specific ultraviolet absorbance (SUVA). The difference in membrane fouling and microbial growth for the two configurations was also examined. Greater TOC and organic acid removal occurred when the biofilter was located ahead of the membrane. The greatest decrease in SUVA values was associated with the membrane. The membrane located after the biofilter fouled at a slower rate than the membrane ahead of the biofilter. Fouling was slower when turbidity was present in the synthetic feedwater. A new method is proposed for determining the operational cleaning frequency of membranes, using an empirical model.     

Rise-Time Calibration of 50-GHz Sampling Oscilloscopes: Intercomparison Between PTB and NPL

The paper presents the results of the first intercomparison of the rise-time calibration of a 50-GHz sampling oscilloscope between Physikalisch-Technische Bundesanstalt, Germany, and National Physical Laboratory, U.K. (EUROMET project 641). Rise-times between 6.0 and 6.6 ps were obtained using optoelectronic techniques. Detailed uncertainty budgets are given, which yield typical rise-time uncertainties of 1.2 ps. The absolute values of the degree of equivalence are les 0.3 ps with an expanded uncertainty of 1.0 ps and, thus, validate the experimental techniques     

Deposition of nanocrystalline ZnO thin films on p-Si by novel galvanic method and application of the heterojunction as methane sensor

Undoped nanocrystalline n-ZnO thin films were deposited by a novel galvanic technique at room temperature on p-Si 〈100 〉 substrates to fabricate ZnO–Si heterojunctions. The I–V characteristics were studied at different temperatures with two different metallic contacts e.g., gold and palladium–silver (26%), in air and in presence of different concentrations (0.1, 0.5 and 1%) of methane gas. A shift in I–V characteristics in presence of methane was observed. The sensitivity and response time were studied at different temperatures (30 through 350 °C). Pd–Ag (26%) catalytic contacts showed much improved sensor performance.     

Nonstationary seismic response of a tank on a bilinear hysteretic soil using wavelet transform

A wavelet based nonlinear random vibration theory has been proposed in the present study to obtain responses of liquid storage tanks in form of instantaneous root mean square displacements of impulsive modes of the tank-liquid system supported on bilinear hysteretic (elasto-perfectly plastic) soil medium. The superstructure has been modeled by a combination of mass-spring-damper system. In order to evaluate the instantaneous root mean square values of the displacement responses of the tanks, zeroth moments of instantaneous power spectral density function (PSDF) have been evaluated. The hysteretic displacement is assumed to follow a truncated mixed Gaussian distribution. The evaluation of this zeroth moment depends on the post-yield or the pre-yield state of the hysteretic spring. The instantaneous root-mean-square (r.m.s) impulsive displacement response of the tank has been validated by simulation. A parametric study has been carried out to see the effects of the soil nonlinearity, the shear wave velocity in the soil and the height of the tank on tank responses.