Effect of Ca Substitution on the Superconductivity of La2.5Y0.5CaBa3(Cu0.88Fe0.12)7Oz

The structural and superconducting properties of single-phase La_2.5–y Y_0.5Ca_1+y Ba₃ (Cu_0.88Fe_0.12)₇O _z (LYCaBCuFe) (y= 0.0–1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T _c ^R=0 shows a marginal increase from 31 K to 37 K for y = 0.0–0.21 and thereafter it decreases with increasing y leading to zero T _c ^R=0 at y 0.84. This shows that the suppression of T _c from 80 K to 31 K by Fe doping at x = 0.12 La_2.5Y_0.5CaBa₃(Cu_1–x Fe _x )₇O _z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.     

Swelling behavior and diffusion studies of high‐water‐retaining acrylamide/potassium methacrylate hydrogels

Poly(acrylamide‐co‐potassium methacrylate) hydrogels were prepared by free‐radical simultaneous polymerization with aqueous solutions of acrylamide (AAm) and potassium methacrylate (KMA) with a redox initiator. The copolymerization was performed with eight different compositions of KMA at a fixed concentration of oil‐soluble crosslinkers, including 1,4‐butanediol diacrylate and ethylene glycol dimethacrylate (EGDMA). For every composition of AAm/KMA copolymer, the percentage swelling, swelling equilibrium, and diffusion characteristics were investigated. The copolymers were further studied for deswelling properties. The power law relationships of the hydrogels were evaluated for variation in terms of saline concentration. The AAm/KMA copolymers were confirmed by IR spectroscopy. Thermal studies of hydrogels were performed with differential scanning calorimetry and thermogravimetric analysis. EGDMA was found to be a better crosslinker for obtaining higher swelling and deswelling properties for the AAm/KMA hydrogels. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1153–1164, 2005     

Characteristics of ZnS films pulse plated using non-aqueous electrolytes

Thin films of ZnS were deposited by the pulse electrodeposition technique employing zinc sulphate and sodium thiosulphate in diethylene glycol solution at 80°C and at different duty cycles in the range 6–50%. The films were polycrystalline exhibiting cubic structure. The intensity of the peaks increased with duty cycle. Transmission measurements indicated interference fringes from which the refractive index fo the films were calculated to be in the range of 2.30–2.70. The band gap of the films was in the range of 3.66–3.62 eV with increase of duty cycle. The films exhibited resistivities in the range of 400–50 ohm cm with increase of duty cycle. The films exhibited higher Photoelectrochemical cell output compared to earlier reports.     

Enhancement of entrainment rates in liquid–gas ejectors

Ejectors are widely used as effective distributors in many chemical and bioprocess industries. Gas entrainment rate as a function of liquid flow rate in ejectors is investigated using nozzles of different geometries. The data are analyzed through macro-energy balance for each phase considering air and water inlet line discharge coefficients. Nozzles with smaller discharge coefficients are effective in producing higher vacuum and hence higher entrainment rates. It has been observed that the factor limiting the air entrainment rate is the low discharge coefficient in the air inlet line. Higher air inlet line discharge coefficients can increase the entrainment rate.     

Characteristics of pulse plated ZnTe films

Stoichiometric films of ZnTe are electrodeposited on stainless steel and conducting glass substrates from an aqueous solution consisting of ZnSO₄ (50 mM), TeO₂ (17 μM) and H₂SO₄ to maintain a pH of 2.5. Structure, morphology, composition, and optical are studied using XRD, SEM, EDAX and optical transmittance spectroscopy The films are composed of small crystallites (50 nm) with cubic crystal structure. The films were polycrystalline in nature with peaks corresponding to the cubic phase. Direct band gap of 2.30 eV was observed. XPS studiers indicated the formation of ZnTe. EDAX measurements were made on the films and it was found that there was a slight excess of Te. AFM studies indicated a surface roughness of 15 nm and a crystallite size of 10–50 nm.     

Locality optimization in a compiler for wireless applications

A strong need exists now for compilers of embedded systems to find effective ways of optimizing series of loop-nests. This is especially so for applications wherein the majority of the memory references occurs in the form of multi-dimensional arrays, indexed primarily with linear functions of iterators and parameterized constants. One major reason is the emergence of the new wireless standards, e.g. 802.11n, WiMAX, Bluetooth, HIPERMAN, 3GPP-LTE and WiBro, where the codes are predominantly of the type described above. These standards provide high bitrate and mobility but are also extremely power and performance hungry. For an even wider commercial applicability of these standards it is important to heavily optimize their energy consumption, so as to increase the mobile battery life time. We propose a novel solution to the multiple loop-nest optimization problem by using the concept of propagating constraints, and by splitting the problem into an access and layout locality-optimization phase, instead of adhering to the traditional split of temporal and spatial locality optimization. Experiments show that our technique leads to 47.5% reduction in external memory accesses over state-of-the-art.     

Efficient distributed simulation through dynamic load balancing

With recent advances in parallel computation, distributed simulation has become a viable way of dealing with time-consuming simulations. For distributed simulations to run efficiently, care must be taken in assigning the tasks (work) in the simulated system to the available physical processors in the computer system. An inefficient assignment can result in excessive communication times between processors and unfavorable load conditions. This leads to long run times, possibly giving performance worse than that with a uniprocessor sequential event-list implementation. This paper establishes the feasibility, and in some cases the necessity, of using dynamic task allocation (rather than a-priori static allocation) in distributed simulation. A dynamic reallocation strategy is developed, and experiments on an iPSC/2 Hypercube indicate that significant improvements in run time can be achieved at low cost.     

Numerical estimation of pillar strength in coal mines

Results of numerical modelling of failed and stable cases of pillars from Indian coal mines are reported in this paper. The complete procedure for modelling using FLAC^3D in the strain-softening mode is given. It is shown that estimation of pillar strength is possible using numerical modelling and it may provide a viable, and perhaps better, alternative to earlier conventional pillar strength approaches. Methods are given to estimate the large number of input parameters required in the models. Because of the paucity of rock characterisation and in situ stress data, some approximations and assumptions were made in all the cases based on earlier experience. The modelling work leads to the conclusion that such data are necessary for the success of this method. Areas for further research related to this subject are given in the end.     

Elimination of intergranular corrosion susceptibility of cold-worked and sensitized AlSl 316 SS by laser surface melting

Susceptibility to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) due to sensitization is one of the major problems associated with austenitic stainless steels. Thermal exposures encountered during fabrication (welding, hot working, etc.) and elevated temperature service may lead to sensitization of components of austenitic stainless steels. Laser surface melting (LSM) is an in-situ method to increase the life of a sensitized component by modifying the surface microstructure without affecting the bulk properties. In this paper, the results obtained in the attempt to improve IGC resistance of coldworked and sensitized 316 SS by LSM are presented. Type 316 SS specimens cold worked to various degrees ranging from 5 to 25% reduction in thickness and sensitized to different degrees by exposing at 898 K for different durations were laser surface melted using continuous wave (cw) CO₂ laser. ASTM standard A262 practice A, optical metallography, and ASTM standard G108 were used to characterize the specimens before and after LSM. Influence of prior deformation on the desensitization behavior was evaluated for the laser melting conditions adopted during the investigation. Complete dissolution of M₂₃C₆ due to laser melting and suppression of re-precipitation due to rapid quenching result in a desensitized homogenous microstructure, which is immune to IGC. Under identical laser melting conditions, the extent of desensitization decreases with an increase in the degree of cold work, and hence, higher power levels and an extended interaction time must be adopted to homogenize the sensitized microstructure with prior cold work.