Determination of gamma-emitting radionuclides in the inter-tidal sediments off Balochistan (Pakistan) Coast, Arabian Sea

Natural radionuclide contents of 226Ra, 228Ra and (40)K were studied for inter-tidal sediments collected from selected locations off the745 km long Balochistan Coast using HPGe detector based gamma-spectrometry system. The sampling zone extends from the beaches of Sonmiani (near Karachi metropolis) through Jiwani (close to the border of Iran). The natural radioactivity levels detected in various sediment samples range from 14.4 +/- 2.5 to 36.6 +/- 3.8 Bq kg(-1) for 226Ra, 9.8 +/- 1.2 to 35.2 +/- 2.0 Bq kg(-1) for (228)Ra and 144.6 +/- 9.4 to 610.5 +/- 23.9 Bq kg(-1) for (40)K. No artificial radionuclide was detected in any of the marine coastal sediment samples. 137Cs, (60)Co, 106Ru and 144Ce contents in sediment samples were below the limit of detection. The measured radioactivity levels are compared with those reported in the literature for coastal sediments in other parts of the world. The information presented in this paper will serve as the first ever local radioactivity database for the Balochistan/Makran Coastal belt of Pakistan. The presented data will also contribute to the IAEA's, Asia-Pacific Marine Radioactivity Database (ASPAMARD) and the Global Marine Radioactivity Database (GLOMARD).     

Hexavalent chromium reduction by Acinetobacter haemolyticus isolated from heavy-metal contaminated wastewater

Possible application of a locally isolated environmental isolate, Acinetobacter haemolyticus to remediate Cr(VI) contamination in water system was demonstrated. Cr(VI) reduction by A. haemolyticus seems to favour the lower concentrations (10-30 mg/L). However, incomplete Cr(VI) reduction occurred at 70-100 mg/L Cr(VI). Initial specific reduction rate increased with Cr(VI) concentrations. Cr(VI) reduction was not affected by 1 or 10 mM sodium azide (metabolic inhibitor), 10 mM of PO(4)3-, SO4(2-), SO(3)2-, NO3- or 30 mg/L of Pb(II), Zn(II), Cd(II) ions. However, heat treatment caused significant dropped in Cr(VI) reduction to less than 20% only. A. haemolyticus cells loses its shape and size after exposure to 10 and 50 mg Cr(VI)/L as revealed from TEM examination. The presence of electron-dense particles in the cytoplasmic region of the bacteria suggested deposition of chromium in the cells.     

Kinetic analysis of competition between aerosol particle removal and generation by ionization air purifiers

Ionization air purifiers are increasingly used to remove aerosol particles from indoor air. However, certain ionization air purifiers also emit ozone. Reactions between the emitted ozone and unsaturated volatile organic compounds (VOC) commonly found in indoor air produce additional respirable aerosol particles in the ultrafine (<0.1 microm) and fine (<2.5 microm) size domains. A simple kinetic model is used to analyze the competition between the removal and generation of particulate matter by ionization air purifiers under conditions of a typical residential building. This model predicts that certain widely used ionization air purifiers may actually increase the mass concentration of fine and ultrafine particulates in the presence of common unsaturated VOC, such as limonene contained in many household cleaning products. This prediction is supported by an explicit observation of ultrafine particle nucleation events caused by the addition of D-limonene to a ventilated office room equipped with a common ionization air purifier.     

Predicting Separation of Lower Hydrocarbon from Natural Gas by a Nano‐Porous Membrane using Capillary Condensation

In the present work, the potential of a nano‐porous membrane for predicting the separation of lower hydrocarbons from natural gas by capillary condensation was explored. While a gas permeates through a capillary at a suitable pressure, the adsorbed layer may attain a thickness enough to fill the entire membrane pore. Poiseuille flow of the condensed phase follows. Our computed results have established that for a passage through a nano‐porous membrane, gas having lower condensation pressure condenses in the pores at a pressure which is about an order of magnitude lower than its vapor pressure at the concerned temperature. In the case of propane/methane and butane/methane binary mixtures, propane and butane are preferentially condensed and permeation rates up to 700 g mol/m² s bar for propane and 600 g mol/m² s bar for butane have been achieved at a temperature lower than the critical temperature of the permeating species and higher than the critical temperature of the non‐permeating species. Since methane has a much lower critical temperature than both propane and butane, it gets physically dissolved in the condensed phase of propane, butane in the case of propane/methane and butane/methane binary mixtures, respectively. An equation of state (EOS) approach has been adopted to calculate the fugacity of methane in the gas, as well as in the condensed phase, in order to estimate its solubility. The Peng‐Robinson equation of state was used. Computation of the separation factor for methane/propane and methane/butane was performed over a wide range of temperature, pressure, and gas composition. The separation factor which is expectedly a function of these variables ranged from 0.3–75 for methane/propane and 0.7–140 for methane/butane binary mixtures. It has been established that an acceptable degree of separation is achievable at moderate pressure and at low temperature for the removal of propane and butane from natural gas. The results have the potential to be used for further refinement and optimization of the process conditions so that this strategy can be exploited for large‐scale removal of lower hydrocarbon from natural gas at a low cost.     

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO2, a hazardous pollutant. We also use SiO2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors.     

Mimicking the biomineralization of aragonite (calcium carbonate) using reverse-micelles under ambient conditions

Reverse micelles have been used, for the first time, to mimic the conditions suitable for the low-temperature (40 degrees C) synthesis of the high temperature and high pressure orthorhombic phase of calcium carbonate (aragonite) normally crystallizing in the sea as abalone shells and as natural pearls. The aragonite phase undergoes morphological changes under higher temperatures with long Y-junctions (at 40 degrees C) to shorter rod-like structures (at 85 degrees C). Pure calcite is obtained at higher reaction temperature. At a lower temperature (5 degrees C) homogeneous and monodisperse spheres of vaterite is obtained. The spherical particles after longer aging (168 h) aggregate to form nanorods and the self assembly is clearly seen at various stages by electron microscopic images.     

In vitro Digestibility of Raw Starches Extracted from five Yam (Dioscorea spp.) Species Grown in Jamaica

Starch granules from Round leaf yellow yam, Negro yam, Sweet yam, Bitter yam and Chinese yam grown in Jamaica were isolated and characterized. The amylose content, granular size, crystallinity, and digestibility by α‐amylase were determined. The granules obtained were of three crystalline types. Round leaf yellow yam, Negro yam and Sweet yam were found to be type‐B, while Chinese yam and Bitter yam were type‐C and type‐A, respectively. Round leaf yellow yam had the highest amylose content (26.5%) while Chinese yam had the lowest (11.1%). The granule size varied between 1–3 μm for Chinese yam and 16–42 μm for Round leaf yellow yam. Significant variations in digestibility of the granules were observed. Raw starches from Chinese yam and Bitter yam were the most susceptible to α‐amylase digestion (porcine pancreatic α‐amylase, pH 5.5, 0.02% CaCl₂, 40°C, 24 h) with 21.27 ± 0.01% and 18.11 ± 0.02% degradation, respectively, while Round leaf yellow yam, Negro yam and Sweet yam starches were the least susceptible, with 13.74 ± 0.03%, 14.98 ± 0.08%, and 15.32 ± 0.04% enzymatic degradation, respectively.     

A design and implementation of fully programmable switched-currentIIR filters

An approach to switched-current filter design based on digital multiply-accumulator and delay blocks is presented. The characteristics of the filter are made fully programmable by simply changing the ratios of the coefficient transistors. To reduce the effect of switch charge injection and channel-length modulation, a high-performance, single-ended differential, switched-current memory cell is developed and used as a basic building block. To reduce the chip area and to maintain the required accuracy of the coefficients, an array consisting of three different sizes of transistors is designed instead of using a unit transistor array as coefficient transistors. An experimental prototype infinite impulse response filter array consisting of six second-order switched-current sections is designed and fabricated with a standard 1.2-μ CMOS process technology. A hard-wiring technique is used to program the filters. The test results show that the characteristics of the filters satisfy the design requirements     

Microstructure-Property Relations of Hot-Pressed Silicon Carbide-Aluminum Nitride Compositions at Room and Elevated Temperatures

A series of SiC-AlN compositions of 0, 10, 25, 50, 75, 90, and 100 mol% AlN were hot pressed at 2100°C for a 1 h soak at a pressure of 35 MPa under vacuum. 2H-wurtzite SiC-AlN solid-solution structures were formed for compositions with 25-100 mol% AlN. The associated lattice parameters for these solid solutions followed Vegard's law. The microstructures varied with composition; the number of needlelike grains decreased for compositions up to 25 mol% AlN and the amount of equiaxed grains increased for compositions with 25–100 mol% AlN. Densities for all the specimens were >99% of the theoretical density. Coefficients of thermal expansion varied from 4.80 × 10^-6/°C to 6.25 × 10^-6/°C in the 20°-1400°C range. Young's moduli varied from 451 GPa to 320 GPa at room temperature (RT) and retained 98%, 96%, and 94% of their RT values at 500°, 1000°, and 1250°C, respectively. These three properties correlated linearly with composition. RT microhardness varied from 21.6 GPa to 11.2 GPa and correlated linearly with composition within the solid-solution range. Flexural strengths increased from 487 MPa to 604 MPa from 0 mol% AlN to 25 mol% AlN and then decreased to 284 MPa for 100 mol% AlN. At 1250°C, flexural strengths decreased from 90% to 65% of the RT values. Fracture toughness increased from 3.6 MPa·m^1/2 to 4.2 MPa·m^1/2 from 0 mol% AlN to 10 mol% AlN and then decreased to 2.5 MPa·m^1/2 for 100 mol% AlN.