The growth kinetics and optical confinement studies of porous Si for application in terrestrial Si solar cells as antireflection coating

The mesoporous porous-silicon (PS) layers were grown on 1 0 0, 1 1 0, and 1 1 1 oriented wafers at constant current density of 20 mA cm⁻². The pore sizes and surface morphologies were measured by atomic force and scanning electron microscopes. The thickness x of the PS formed and the refractive index were measured by an ellipsometer as a function of time duration t (in min) of anodization. The x vs. t data were fitted into a power law x=at^c where c is a dimensionless constant and growth kinetics was established. The growth is practically independent of orientation. This is due the reason that the growth rate is controlled largely by the availability of holes which exchange their charge with oxidizing species and desirably large concentrations of holes were available at current density of 20 mA cm⁻². For a similar reason the growth of PS layer on the front surface of the n⁺ region of n⁺–p solar cells could also be done at current density of 20 mA cm⁻² nearly at the same rate. A large concentration of holes could be injected from p region into the n⁺ region because the positive contact was made on the p side and thus the junction was forward biased. The PS ARC of thickness 70 nm showed increase 26% in the short circuit current density J_sc and 24% in efficiency of the cells. However, the improvement in the values of the open circuit voltage V_oc were lower than the expected value indicating that the PS layers had enhanced recombination of minority carriers at the front surface or in the front emitter region immediately below the PS layer.     

Optimization of organic solar cells with thin film Au as anode

Optical transmittance and conductivity for thin metallic films, such as Au, are two inversely related and extremely important parameters for its application in organic photovoltaics as the front electrode. We report our findings on how these parameters have been optimized to attain maximum possible efficiencies by fabricating organic solar cells with thin Au film anodes of differing optical transmittances and consequently due to scaling at the nanolevel, varying electrical conductivities. There was an extraordinary improvement in the overall solar cell efficiency (to the order of 49%) when the Au thin film transmittance was increased from 38% to 54%. Surface morphologies of these thin films also have an effect on the critical parameters including, V_oc, J_sc and FF.     

Percolation bacterial leaching of low-grade chalcopyrite using acidophilic microorganisms

Bioleaching studies were carried out in percolation columns using low-grade copper containing rock (granite). The lixiviant consisted of acidified ferric sulfate containing acidophilic microorganisms. The iron oxidizing strain was isolated from Malanjkhand mine water and after adaptation the iron oxidation observed to be 500 mg/L/h. Leaching parameters studied were lixiviant flow rate, particle size and bed height. It was observed that leaching efficiency increased with decrease of particle size and lixiviant flow rate. The precipitation of iron during leaching observed to be low as pH was maintained at 2. Based on the leaching kinetics, a unified rate equation was developed and shown as rά(d _p )^−0.61 (F)^−0.76 (H _b )^0.97.     

Intramedullary nailing technique and its effect on union rates of tibial shaft fractures

Seventy tibial shaft fractures treated by intramedullary nailing using two different techniques were compared. The first group (35 cases) was treated with a Herzog intramedullary nail following hand reaming and minimal traction. The second group (35 cases) had a Grosse and Kempf or AO nail inserted following power reaming and skeletal traction. Fracture patterns were similar in both groups. In the hand-reamed group, the mean time to union was 15.2 weeks with two delayed unions and no non-unions. In the power-reamed group, the mean time to union was 19.9 weeks with 10 delayed unions and two non-unions. These differences were statistically significant. Complications in the hand-reamed group included a Sudecks atrophy and one mal-union. In the power-reamed group, there were three transient foot drops, two compartment syndromes and one pulmonary embolus. This difference was not statistically significant. Our findings suggest that surgical technique has an important effect on the healing rates of nailed tibial shaft fractures. When intramedullary nailing is performed, minimal reaming is required and skeletal traction should be avoided if possible.     

Control of colonic variceal haemorrhage with a somatostatin analogue

Carbamazepine is a drug commonly used in the treatment of neuropathic pain. It is an iminostilbene derivative that is extensively metabolized by the liver. We describe a 66-year-old man with dysesthetic pain from cervical myelopathy who developed cholestatic hepatitis, skin rash, and eosinophilia after carbamazepine was administered for 5 weeks (total dose of 18.9gm). Withdrawal of carbamazepine led to complete resolution of both clinical and biochemical abnormalities within 3 weeks. Clinicians should be alert to this rare complication because it can be confused clinically with biliary tract sepsis and viral hepatitis.     

Multiproduct purchase scheduling with limited budget and/or group discounts

A grouping scheme is employed whereby the products are ranked by the ratio of the inventory carrying cost per period and the order placing cost, and are assigned to the groups so that the products belonging to a group are consecutive in their rank-order. The product to group assignment is achieved using a “shortest-path” approach. We show that the above grouping scheme minimizes the total cost composed of the order placing cost, inventory carrying cost and purchase cost with group discounts. We also establish a powerful and somewhat surprising result that the composition of the optimal groups is not affected even if a limit is placed on the purchase budget.     

A study on arsenic adsorption on polymetallic sea nodule in aqueous medium

A detailed study on As(III) and As(V) adsorption on polymetallic sea nodule in aqueous medium has been reported. Elemental composition of sea nodule comprises primarily, iron, manganese and silicon with trace quantities of aluminium, copper, cobalt and nickel. As(V) adsorption on sea nodule is dependent on pH while As(III) is insensitive to it. Adsorption data broadly follow Langmuir isotherm. Kinetic data follow a pseudo-second-order model for both As(III) and As(V). Arsenic loading on sea nodule is dependent on initial arsenic concentration. Optimum As(III) loading is 0.74 mg/g at 0.34 mg/L and for As(V) it is 0.74 mg/g at 0.78mg/L. As(III) adsorption is broadly independent of ionic environment. Except for PO(4)(3-), As(III) adsorption is not influenced by anions but cations influence it significantly. As(V) adsorption, on the other hand, is influenced by anions and not by cations. Experimental evidence indicates an inner sphere complex for As(III) and partial inner and partial outer sphere complex for As(V). Both As(III) and As(V) adsorptions are marked with very little desorption in the pH range of 2-10. Sea nodule can speciate As(III) and As(V) in groundwater at or above pH 6. Sea nodule was successfully tested as an adsorbent for the removal of arsenic from six contaminated groundwater samples of West Bengal, India, containing arsenic in the range 0.04-0.18mg/L.     

Removal of arsenic from groundwater using low cost ferruginous manganese ore

A low cost ferruginous manganese ore (FMO) has been studied for the removal of arsenic from groundwater. The major mineral phases present in the FMO are pyrolusite and goethite. The studied FMO can adsorb both AS(III) and As(V) without any pre-treatment, adsorption of As(III) being stronger than that of As(V). Both As(II) and As(V) are adsorbed by the FMO in the pH range of 2-8. Once adsorbed, arsenic does not get desorbed even on varying the pH in the range of 2-8. Presence of bivalent cations, namely, Ni2+, Co2+ Mg2+ enhances the adsorption capability of the FMO. The FMO has been successfully used for the removal of arsenic from six real groundwater samples containing arsenic in the range of 0.04-0.18 ppm. Arsenic removals are almost 100% in all the cases. The cost of the FMO is about 50-56 US$ per metric tonne.     

High strength porous alumina by spark plasma sintering

High strength porous alumina was fabricated by spark plasma sintering (SPS) at temperatures between 1000 and 1200 °C with nanocrystalline Al(OH)₃ as the starting powder without any seeds, dopants or inclusions. Decomposition of the Al(OH)₃ produced a series of transitional alumina phases depending on sintering temperature and pressure and finally the stable α-alumina phase was obtained. A network of continuous pores with unimodal pore size distribution was estimated by mercury porosimetry and BET surface area measurements, with the porosity ranging between 20% and 60% based on sintering conditions. Predominance of fine grains and extensive necking between them led to better strength in the sintered samples. The bending strength of the sintered compacts rapidly increased with sintering temperature while retaining reasonable porosity suitable for practical applications. The results clearly indicate that in situ phase formation of α-Al₂O₃ and θ-Al₂O₃ provides strength and porosity, respectively. Phase transformation, pore morphology and microstructure evolution were also studied.