Effect of complexing agent on the chemically deposited ZnS thin film

Zinc sulfide (ZnS) thin films have been deposited onto fluorine doped tin oxide and microscopic glass substrates from an aqueous alkaline reaction by chemical bath deposition. The effect of concentrations of hydrazine hydrate (HyH) (complexing agent) on the deposit is studied. X-ray analysis confirm the growth of nanocrystalline ZnS thin films with reflections (111), (220) and (311) correspond to cubic crystalline phase. TEM results support the growth of cubic ZnS layers. The energy band gap was successfully tailored from 2.77 to 3.80 eV. Photoluminescence study indicates a strong band-edge emission with some defect like vacancies. It was also noticed that HyH plays an important role on the nucleation. The remarkable improvement in the growth rate of ZnS thin films have been observed upon increasing the contents of HyH. Nearly stoichiometric ZnS layer was obtained upon annealing prepared with 2.5 M HyH. The crystallinity was found to be increased upon annealing the layers. The ideality factor for the ZnS layers prepared with 0 and 1.0 M HyH were obtained?~1.71 and 1.24, respectively. The capacitance–voltage plots behave according to Schottky–Mott theory. The doping concentrations?~10¹⁷ and 10¹⁸ cm^?3 were calculated for the layers deposited with 0 and 1.0 M HyH, respectively.     

The Misprediction Recovery Cache

In modern processors, deep pipelines couple with superscalar techniques to allow each pipe stage to process multiple instructions. When such a pipe must be flushed and refilled, as when predicted program flow beyond a branch is subsequently recognized as wrong, the temporary performance loss is significant. While modern branch target buffer (BTB) technology makes this flush/refill penalty fairly rare, the penalty that accrues from the remaining branch mispredictions is a serious impediment to even higher processor performance. Advanced mechanisms that can reduce this residual misprediction penalty can be of enormous value in future microprocessor designs. In this paper we describe the design and performance of a promising new mechanism called the Misprediction Recovery Cache (MRC). The key results of our study are. (1) Small, finite sized MRCs (16 to 256 entry) can effectively reduce branch penalty in deeply pipelined processors. (2) Commercial Benchmarks such as the Winstone benchmarks make better use of larger M RCs due to large number of unique branch instructions unlike the predominantly technical SPECint benchmarks. (3) The MRC hit rates increase with increasing BTB prediction accuracy (5-200% depending on MRC size) due to fewer residual mispredictions associated with better prediction. (4) For the processor architecture we studied, the M RC resulted in up to 20% improvement in cpi(cycles per instruction). (5) The incremental performance gain achievable by adding an MRC to a modern CISC processor (which uses a BTB with a two-level predictor) is two to three times of what was achievable by going from a one-level predictor to a two-level predictor.     

Uses of α-Fe2O3 and fly ash as solid adsorbents

Solid adsorbents have shown great promise for control of particulate and non-particulate matter and as gas sensing devices in recent times. In the present study, adsorption of environmental toxic pollutant such as lead ions on solid adsorbents viz. α-Fe₂O₃ and fly ash, are reported. Considerable adsorption was observed on fly ash when compared to α-Fe₂O₃ surface. These studies are characterized by employing solid state and solution studies.     

Enhancement of luminescence intensity and spectroscopic analysis of Eu3+ activated and Li+ charge-compensated Bi2O3 nanophosphors for solid-state lighting

The present work reports the synthesis, characterization, photoluminescence and photocatalytic activity of Eu~(3+)(1 mol%-11 mol%) doped and Li~+(0.5 mol%-5 mol%) co-doped Bi_2 O_3 nanophosphors(NPs) by sonochemical method. The average particle size was estimated using powder X-ray diffraction(PXRD)and transmission electron microscopy(TEM) and is found to be in the range of 30-35 nm. The scanning electron microscopy(SEM) images were highly dependent on sonication time and concentration of epigallocatechin gallate(EGCG) bio-surfactant. The energy gap of doped and co-doped Bi_2 O_3 nanophosphors was estimated using Kubelka-Munk(K-M) function and is found to be in the range of2.9-3.08 eV. The effect of Li+ co-doping on luminescence of optimized Bi_2 O_3:Eu~(3+) was studied and is found about more than 3 fold enhancement of emission intensity. Judd-Ofelt parameters(Ω_2, Ω_4 and Ω_6).transition probabilities(A_T), quantum efficiency(η), luminescence lifetime(τ_(rad)), color chromaticity coordinates(CIE) and correlated color temperature(CCT) values were estimated from the emission spectra and are discussed in detail. The estimated CIE chromaticity co-ordinates are very close to the NTSC(National Television Standard Committee) standard value of red emission. The synthesized NPs show excellent photocatalytic activity of acid red-88 under UV-light irradiation, which can degrade 98.1% in60 min. The decreasing electron-hole pair recombination rate with quick electron transfer ability is predominantly ascribed to the balance between crystallite size, morphology, band gap, defects, surface area, etc. These results show a light for the use of sonochemical route of Bi_2 O_3:Eu~(3+):Li~+ in solid state display and photocatalytic applications.     

Particle size distribution control in emulsion polymerization

Effects of the operating policies—the initial initiator amount; the initial emulsifier amount; the monomer addition mode: batch or semibatch; and the monomer addition rate under “monomer‐starved conditions” for the control of particle size distribution (PSD)—were studied through a model that simulates batch and semibatch reactor operations in conventional emulsion polymerization. The population balance model incorporates both the nucleation stage and the growth stage. The full PSDs were reported, which have normally been omitted in earlier studies. It was shown through simulations that the broadness of the distributions, both initial (obtained after the end of nucleation) and final (after complete conversion of monomer), can be controlled by the initial initiator amount and the emulsifier amount. The higher initiator amounts and the lower emulsifier amounts favor narrower initial and final distributions. The shape of the initial PSDs and the trends in the average size and range were preserved with subsequent addition of monomer in the batch or in the semibatch mode, although the final PSD was always considerably narrower than that of the initial PSD. The addition of monomer in the semibatch mode gave narrower distribution compared to that of the batch mode, and also, lower monomer addition rates gave narrower distributions (larger average sizes), which was a new result. It was further shown through simulations that, under monomer‐starved conditions, the reaction rate closely matched the monomer feed rate. These conclusions are explained (1) qualitatively—the shorter the length of the nucleation stage and the larger the length of the growth stage (provided the number of particles remains the same), the narrower is the distribution; and (2) mathematically—in terms of the “self‐sharpening” effect. Experimental evidence in favor of the self‐sharpening effect was given by analyzing the experimental particle size distributions in detail. The practical significance of this work was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2884–2902, 2004     

Chemical Composition and Fatty Acid Profile of Khat (Catha edulis) Seed Oil

The proximate, physicochemical, and fatty acid compositions of seed oil extracted from khat (Catha edulis) were determined. The oil, moisture, crude protein, crude fiber, crude carbohydrate, and ash content in seeds were 35.54, 6.63, 24, 1.01, 30.4 %, and 1.32 g/100 g DW respectively. The free fatty acids, peroxide value, saponification value, and iodine value were 2.98 %, 12.65 meq O₂/kg, 190.60 mg KOH/g, and 145 g/100 g oil, respectively. Linolenic acid (C_18:3, 50.80 %) and oleic (C_18:1, 16.96 %) along with palmitic acid (C_16:0, 14.60 %) were the dominant fatty acids. The seed oil of khat can be used in industry for the preparation of liquid soaps and shampoos. Furthermore, high levels of unsaturated fatty acids make it an important source of nutrition especially as an animal product substitute for omega‐3 fatty acids owing to the high content of linolenic acid.     

Stimuli sensitive copolymer poly(N-tert-butylacrylamide-ran-acrylamide): processing into thin films and their transitional behaviour

Temperature sensitive polymer hydrogels are being extensively studied because of their potential applications in biomedical, robotics, and chemical industry. However, major hurdles in their development have been their slow response, low efficiency, and poor mechanical properties. One of the main reasons for these shortcomings is the difficulty of processing them into mechanically fine structures in polymer gel form. In this work, a novel approach has been developed to process temperature sensitive copolymers based on acrylamide into mechanically stable thin films. A series of temperature sensitive random linear copolymers of N-tert-butylacrylamide (NTBA) and acrylamide (Am) were synthesized by solution polymerization method, using regulated dosing of comonomer Am having a higher reactivity ratio (r_Am=1.5) than NTBA (r_NTBA=0.5). Copolymers with varying feed ratios of NTBA and Am (80:20 to 20:80 mol%) were synthesized and characterized. The actual incorporation of less reactive comonomer NTBA was found to be lower than the feed and was found to vary between 75 mol% with feed of 80 and 11 mol% for a feed of 20%. Linear copolymer with 40:60 feed ratio of NTBA and Am monomers, with actual incorporation of NTBA to the extent of 27 mol%, was selected for processing. The copolymer films of thickness in the range of 10–200 microns could be obtained from aqueous solution in the presence of citric acid or 1,2,3,4-butane tetracarboxylic acid as crosslinkers and sodium hypophosphite as catalyst. Subsequently, the films were crosslinked at 150–160 °C to obtain mechanically strong insoluble films. The crosslinks were formed between reactive amide side groups of the acrylamide moiety of the polymer and the carboxylic acid group of the crosslinker. The transition temperatures of the crosslinked films were found to shift towards the lower temperature from 37 °C (in linear copolymer) to 22–25 °C. High surface to volume ratio of the prepared films lead to significant increase in swelling percentage from 490 to 2980% and faster response time from 1280 min (in the first cycle) to 5 min compared to polymerized-gel samples (2 mm disc) of the same composition.     

Convective nanofluid flow over a vertical cone with a rough surface

In recent literature, the analysis of a combined convective flow over a cone has received a lot of attention. To explore the convection effects of flow over a cone in greater detail, in this investigation, we have considered a cone with a rough surface, which is entirely a new flow problem. Recent studies have shown the influence of roughness on fluid flow over several geometries, but flow over a rough conical surface has not been studied so far. In addition, we have analyzed the effects of nanoparticles, magnetohydrodynamic (MHD), and suction/blowing, which could have significant impacts on characteristics of fluid flow over the cone with a rough surface. Initially, the governing equations, which are partial differential equations with a high degree of nonlinearity, are nondimensionalized through Mangler's transformations. Later, linear equations are obtained via the method of quasilinearization, which is then solved numerically through finite difference approximations. The roughness of the cone's surface has notable effects on fluid flow, that too away from the origin. In fact, the roughness increases the friction at the cone's surface. Furthermore, the magnetic field applied at the wall increases the surface friction. Thus, the combination of roughness and MHD helps delay the boundary layer separation. On the other hand, the suction reduces the temperature of the fluid and increases the energy transport strength, while the thermophoresis parameter exhibits the contrary nature. Therefore, the combined consideration of these two could enhance energy transport strength in several industrial applications.     

Shear Reversible Alumina Gels for Direct Writing

Phase diagram of alumina sol has been investigated, wherein a unique region of shear reversible gels has been discovered. In this region, rapid transformation from gel to sol was observed, where the viscosity shows a sudden drop by six orders of magnitude on application of shear stress. The sol to gel transformation was observed to depend on the composition of the sol and could be tuned in the range of few seconds to hours. These gels are suitable for fabricating complex three‐dimensional structures using advanced technology of direct write and ink‐jet printing.