Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires

We report the fabrication of degenerately doped silicon (Si) nanowires of different aspect ratios using a simple, low-cost and effective technique that involves metal-assisted chemical etching (MacEtch) combined with soft lithography or thermal dewetting metal patterning. We demonstrate sub-micron diameter Si nanowire arrays with aspect ratios as high as 180:1, and present the challenges in producing solid nanowires using MacEtch as the doping level increases in both p- and n-type Si. We report a systematic reduction in the porosity of these nanowires by adjusting the etching solution composition and temperature. We found that the porosity decreases from top to bottom along the axial direction and increases with etching time. With a MacEtch solution that has a high [HF]:[H(2)O(2)] ratio and low temperature, it is possible to form completely solid nanowires with aspect ratios of less than approximately 10:1. However, further etching to produce longer wires renders the top portion of the nanowires porous.     

Hydrodynamic analysis of flow fields for redox flow battery applications

Electrolyte flow distribution is an important factor that contributes to the performance of the overall efficiency of a redox flow battery system. In the present paper, a comparative study of the hydrodynamics of the serpentine and interdigitated flow fields has been performed. Ex situ experiments were conducted using the two flow fields in conditions typical of flow battery applications. Limited in situ testing has also been conducted. These bring out the surprising result that the pressure drop in the interdigitated flow field is less than that in the serpentine for the same flow rate. Computational fluid dynamics studies show strong under-the-rib convection in the reaction zone exists in both flow fields but with a shorter residence time in case of the interdigitated. It is posited that this may explain the superior electrochemical performance of cells with interdigitated flow fields.     

Physicochemical properties of the starchy flour extracted from sweet potato tubers through lactic acid fermentation

The efficiency of starch extraction from sweet potato tubers was improved by lactic acid fermentation using a mixed culture inoculum. Study of the properties of the starchy flour showed that there was a significant reduction in the starch content and consequently the soluble and apparent amylose contents of fermented samples from all six varieties used. A fall in peak viscosity and viscosity breakdown was observed for fermented samples, while the pasting temperature was enhanced significantly. The fermented flour showed greater solubility and reduced swelling. Differential scanning calorimetry studies indicated a delay in gelatinisation and a fall in enthalpy of gelatinisation of the starch on fermentation. Unlike cassava, all the properties of the starch from sweet potato tubers, ie viscosity, swelling, solubility, gelatinisation temperature, amylose content and starch content, were affected by fermentation, and variation was also observed among cultivars. Copyright © 2005 Society of Chemical Industry     

Application of artificial neural networks for the development of a signal monitoring system

A prototype of a Signal Monitoring System (SMS) utilizing artificial neural networks is developed in this work. The prototype system is unique in: 1) its utilization of state-of-the-art technology in pattern recognition such as the Adaptive Resonance Theory family of neural networks, and 2) the integration of neural network results of pattern recognition and fault identification databases.
The system is developed in an X-windows environment that offers an excellent Graphical User Interface (GUI). Motif software is used to build the GUI. The system is user-friendly, menu-driven, and allows the user to select signals and paradigms of interest. The system provides the status or condition of the signals tested as either normal or faulty. In the case of faulty status, SMS, through an integrated database, identifies the fault and indicates the progress of the fault relative to the normal condition as well as relative to the previous tests.
Nuclear reactor signals from an Experimental Breeder Reactor are analyzed to closely represent actual reactor operational data. The signals are both measured signals collected by a Data Acquisition System as well as simulated signals.     

Inhibitive action of the acid extract of Luffa aegyptiaca leaves on the corrosion of mild steel in acidic medium

The inhibitive effect of the acid extract of Luffa aegyptiaca (LA) leaves on the corrosion of mild steel (MS) in the hydrochloric acid medium was studied using mass loss, colorimetric and electrochemical methods. The inhibition efficiency, increased with increase in concentration of the extract, but decreased with a raise in temperature and increase in acid strength. Polarization measurement studies revealed that LA extract act as a mixed-type inhibitor but predominantly control the anodic reaction. Furthermore, the inhibition efficiency synergistically increased with the addition of halide ions. Physical adsorption mechanism is proposed from the trend in inhibition efficiency with the change in temperature and from thermodynamic parameters. It has been found that the adsorption of LA on MS complies with Langmuir adsorption isotherm and follows the kinetic thermodynamic model of El-Awady at all temperatures studied. Fourier transform infrared spectroscopy and optical profiler images confirmed the adsorption of LA on MS surface.     

Nutritional potential,bioaccessibility of minerals and antioxidant properties of niger (Guizotia abyssinicacass.) seed protein

The investigation aimed at preparing protein isolate from niger seeds and determining its nutritional profile, functional properties and antioxidant potential. Niger seeds with 25.5% protein, 30% fat and 21.8% fibre were used for preparation of dehulled, defatted niger seed flour (DNF) and protein isolate (NPI). Protein content of DNF was 53.8% and NPI was 85.7%. Minerals, crude fiber and carbohydrate content reduced from DNF to NPI. In vitro protein digestibility, iron and zinc dialysability increased significantly from DNF to NPI with a corresponding decrease in fibre, tannin and phytate. Water and fat absorption capacity (FAC) was higher in DNF and foaming and emulsification index was better in NPI. Polyphenol content of NPI was higher than DNP. NPI exhibited significantly higher free radical scavenging ability and metal chelating ability, hydroxyl radical scavenging activity was comparable to DNP. Studies on organo‐leptic evaluation and utilisation of NPI as a protein source in food formulations are warranted.     

Corrosion Inhibition of Mild Steel in Sulphuric Acid Using Luffa Aegyptiaca Leaves Extract

The corrosion inhibition of mild steel（MS） in sulphuric acid using Luffa aegyptiaca（LA） leaves extract was investigated by weight loss studies, colorimetric measurements, potentiodynamic polarisation and electrochemical impedance spectroscopy. The adsorption of LA leaves extract was confirmed by Fourier transform infrared spectroscopy and optical profilometry. The inhibition efficiency increased with increasing concentration of the extract but decreased with rise in temperature and with the increase in acid strength. Furthermore, the inhibition efficiency synergistically increased on the addition of halide ions. Polarisation studies revealed that the LA extract acts as mixed- type inhibitor. Physical adsorption mechanism is proposed from the trend in inhibition efficiency with the change in temperature and from thermodynamic parameters. The adsorption of LA on MS surface obeys Langmuir adsorption isotherm and follows the kinetic thermodynamic model of ElAwady at all temperatures studied.     

Synthesis,characterization and swelling behaviour of superabsorbent polymers from cassava starch‐graft‐poly(acrylamide)

Superabsorbent polymers (SAPs) were prepared from cassava starch by graft copolymerization of acrylamide on to starch using ceric ammonium nitrate (CAN) as free radical initiator, followed by alkali saponification. The reaction parameters such as concentration of acrylamide, concentration of CAN, temperature, and duration of polymerization reaction were optimized for maximum water absorbency using a 4‐factor 3‐level Box‐Behnken design. The highest values of percentage grafting and absorbency obtained were 174.8% and 425.2 g/g, respectively. The polymers were characterized by determination of grafting efficiency, N‐content, acrylamide content, FTIR analysis, SEM and XRD analyses. Thermogravimetric analysis (TG) showed that the SAP has higher thermal stability. The rate of water absorbency and the swelling behaviour of the SAP under different conditions of pH, and different salts were determined. The de‐swelling pattern of the hydrogels over different time durations was also determined.     

Water sorption kinetics of superabsorbent hydrogels of saponified cassava starch‐graft‐poly(acrylamide)

Superabsorbent polymers (SAPs) are hydrophilic polymeric networks that can absorb, swell and retain large quantity of water and other physiological fluids. In this paper, the water sorption pattern and kinetics of cassava starch based SAP hydrogels were studied under different conditions of swelling such as soaking duration, pH, presence of salts, and particle size of the hydrogel. The kinetics was studied using Voigt‐based viscoelastic model to determine the rate parameter and the swelling rate (SR). It was noted that under all conditions, the water sorption followed a second order kinetics. The absorbency was directly proportional to the rate of swelling. But when the sample was allowed to swell in aqueous solutions of CaCl₂ and AlCl₃, the absorbency as well as the SR was irregular. The particle size also had significant effect on water absorption by the SAP and the polymer with smaller particles showed more absorption than those with larger particle size. The solvent induced phase transition of the superabsorbent hydrogel was also studied.     

Rheological,mechanical and moisture sorption characteristics of cassava starch‐konjac glucomannan blend films

Cassava starch (ST)‐konjac glucomannan (KGM) blend films were prepared and their thermal, rheological, mechanical, moisture sorption properties and water vapour transmission rate were determined. Response surface methodology was employed for the preparation of films using different levels of ST, KGM and glycerol. All the filmogenic solutions exhibited shear thinning behaviour. Apparent viscosity and the dynamic rheological properties of filmogenic solutions varied considerably with KGM content. Rheological analysis revealed that the blend films are more appropriate than neat ST film for controlled drug release studies and for food coating. The melting temperature and enthalpy of fusion of the blend films were lower than that of neat ST film. When compared to neat starch film, the blend films showed broader peaks in DSC patterns, which suggests that incorporation of KGM decreased the crystallinity of ST. Mechanical properties, elongation at break and tensile strength of blend films were significantly higher (112.8% and 22.5 MPa, respectively) than those of neat ST film. Due to the more hydrophilic nature of KGM when compared to ST, the WVTR and moisture absorption of blend films were greater than that of neat ST film. Though KGM is more hydrophillic in nature, blend films with higher amount of KGM (0.643g) showed comparably lower values for both WVTR and moisture absorption than other blends. The solubility of the blend films was lower than that of neat starch film which also confirmed the strong intramolecular attraction between ST and KGM.