The role of Harper–Dorn creep at high temperatures and very low stresses

Creep experiments were conducted on single crystals of very high purity aluminum to evaluate the validity of the Harper–Dorn region of flow which occurs at very low stresses and high homologous temperatures. The results confirm the existence of a different flow process under these conditions but with a stress exponent closer to ∼3 rather than 1. Measurements show that the dislocation density within this low stress region varies with stress in a manner consistent with the behavior anticipated from an extrapolation of data reported in the regime of conventional power-law creep at high stresses. All of the experimental results are in reasonable agreement with earlier published data, including with the original data of Harper and Dorn when their results are plotted without incorporating a threshold stress.     

Ontological analysis of web surf history to maximize the click-through probability of web advertisements

Due to an enormous influx of capital over the past decade, the online advertising industry has become extremely robust and competitive. The difference between success and failure in such a competitive market often rests in the ability to deliver advertisements that are closely in line with a user's interests. In this work, we propose and test a new online advertisement targeting technique which adapts and utilizes several powerful and well tested information retrieval and lexical techniques to develop an estimate of a user's affinity for particular products and services based on an analysis of a user's web surfing behavior. This new online ad targeting technique performs extremely well in our empirical tests.     

Effect of annealing on electrical conductivity and morphology of polyaniline films

We report structure–property relationships of polyaniline emeraldine base (EB) films that were produced by combining different processing steps in various sequences. The effect of annealing and doping processes on the surface structure of the films was investigated by atomic force microscopy (AFM), and the corresponding changes to the chemical structure of the EB films were monitored by Fourier transform infrared spectroscopy. AFM results indicate that after doping polyaniline (EB) films with HCl, the root mean square (rms) roughness of the surface of EB film increased ～ 46%. When the doped films were annealed at 180°C under a nitrogen atmosphere for 3 h, the rms roughness was essentially unchanged from that of the initial, undoped films. The electrical conductivity of the films also showed a significant dependence on the processing sequence. When the doped polyaniline (EB) films were annealed, no electrical conductivity was observed. When these films were redoped, only ～ 6% of the initial conductivity could be recovered. In another processing sequence in which the polyaniline (EB) films were first annealed and then doped, the electrical conductivity was only ～ 12% relative to the film that was doped immediately after being cast. From this work, a strategy to reduce the surface roughness of films made from electrically conducting polyaniline (EB) is proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3602–3610, 2001     

Current and future linked responses of ozone and PM2.5 to emission controls

Responses of ozone and PM2.5 to emission changes are coupled because of interactions between their precursors. Here we show the interdependencies of ozone and PM2.5 responses to emission changes in 2001 and 2050, with the future case accounting for both currently planned emission controls and climate change. Current responses of ozone and PM2.5 to emissions are quantified and linked on a daily basis for five cities in the continental United States: Atlanta, Chicago, Houston, Los Angeles, and NewYork. Reductions in anthropogenic NO(x) emissions decrease 24-h average PM2.5 levels but may either increase or decrease daily maximum 8-h average ozone levels. Regional ozone maxima for all the cities are more sensitive to NO(x) reductions than at the city center, particularly in New York and Chicago. Planned controls of anthropogenic NO(x) emissions lead to more positive responses to NO(x) reductions in the future. Sensitivities of ozone and PM2.5 to anthropogenic VOC emissions are predicted to decrease between 2001 and 2050. Ammonium nitrate formation is predicted to be less ammonia-sensitive in 2050 than 2001 while the opposite is true for ammonium sulfate. Sensitivity of PM2.5 to SO2 and NO(x) emissions changes little between 2001 and 2050. Both ammonium sulfate and ammonium nitrate are predicted to decrease in sensitivity to SO2 and NO(x) emissions between 2001 and 2050. The complexities, linkages, and daily changes in the pollutant responses to emission changes suggest that strategies developed to meet specific air quality standards should consider other air quality impacts as well.     

Methane hydrates: A future clean energy resource

Natural gas has been considered as the best transition fuel into the future carbon constraint world. The ever-increasing demand for natural gas has prompted expanding research and development activities worldwide for exploring methane hydrates as a future energy resource. With its vast global resource volume (~ 3000 trillion cubic meter CH₄) and high energy storage capacity (170 CH₄ v/v methane hydrate), recovering energy from naturally-occurring methane hydrate has attracted both academic and industry interests to demonstrate the technical feasibility and economic viability. In this review paper, we highlight the recent advances in fundamental researches, seminal discoveries and implications from on-going drilling programs and field production tests, the impending knowledge gaps and the future perspectives of recovering energy from methane hydrates. We further emphasize the current scientific, technological and economic challenges in realizing long-term commercial gas production from methane hydrate reservoir. The continuous growth of the corresponding experimental studies in China should target these specific challenges to narrow the knowledge gaps between laboratory-scale investigations and reservoir-scale applications. Furthermore, we briefly discuss both the environmental and geomechanical issues related to exploiting methane hydrate as the future energy resource and believe that they should be of paramount importance in the future development of novel gas production technologies.     

Cross‐Linked Amorphous Nitrilase Aggregates for Enantioselective Nitrile Hydrolysis

A recombinant Escherichia coli strain was constructed which efficiently expressed the enantioselective nitrilase from Alcaligenes faecalis DSMZ 30030 as a hisitidine‐tagged enzyme variant under the control of a rhamnose inducible promoter. The enzyme was purified from cell extracts and used for the preparation of cross‐linked enzyme aggregates (CLEAs). The conditions for the preparation of the CLEAs were optimized using various organic solvents and cross‐linking agents and a procedure was developed which combined a precipitation with 85 % (v/v) isopropyl alcohol and a cross‐linking with 30 mM glutaraldehyde. Thus, about 80 % of the initial nitrilase activity could be incorporated into the CLEAs. The hydrolysis of racemic mandelonitrile to (R)‐mandelic acid was compared between the soluble nitrilase preparations and their CLEAs (nit‐CLEAs). The nitrilase activity in the CLEAs was at 30 °C and 60 °C about 5 times more stable than in the soluble preparations. The CLEAs could be reused 5 times with only about 10 % reduction in activity. The enantioselectivity of the nitrilase for the formation of (R)‐mandelic acid from racemic mandelonitrile decreased for both preparations with increasing temperatures (10 °C to 50 °C), but this effect was significantly less pronounced for the CLEAs. A detailed analysis of solvent effects on nitrilase enantioselectivity allowed thermodynamic insights into contributions from free energy component (activation enthalpy and entropy) to chiral preference of nitrilase in such non conventional media.     

Electrodeposition and properties of Zn–Ni–CNT composite coatings

Zn–Ni–CNT composite coatings were prepared by electrodeposition from a sulphate bath. The effect of CNTs on the corrosion behavior, wear resistance and hardness of the composite coatings was investigated. Their corrosion properties were evaluated by polarization, impedance, weight loss and salt spray tests. The CNT particles inclusion improved the corrosion resistance, hardness and wear resistance of the coating. The grain size of the composite coating was smaller than that of a pure Zn–Ni coating with the same Zn/Ni ratio. Scanning electron microscope images and X-ray diffraction patterns of coating revealed its fine-grain nature.     

Response surface methodological approach for the decolorization of simulated dye effluent using Aspergillus fumigatus fresenius

The aim of our research was to study, effect of temperature, pH and initial dye concentration on decolorization of diazo dye Acid Red 151 (AR 151) from simulated dye solution using a fungal isolate Aspergillus fumigatus fresenius have been investigated. The central composite design matrix and response surface methodology (RSM) have been applied to design the experiments to evaluate the interactive effects of three most important operating variables: temperature (25-35 degrees C), pH (4.0-7.0), and initial dye concentration (100-200 mg/L) on the biodegradation of AR 151. The total 20 experiments were conducted in the present study towards the construction of a quadratic model. Very high regression coefficient between the variables and the response (R(2)=0.9934) indicated excellent evaluation of experimental data by second-order polynomial regression model. The RSM indicated that initial dye concentration of 150 mg/L, pH 5.5 and a temperature of 30 degrees C were optimal for maximum % decolorization of AR 151 in simulated dye solution, and 84.8% decolorization of AR 151 was observed at optimum growth conditions.     

Molecular Dynamics Modeling of Latent Heat Enhancement in Nanofluids

A discrete computational approach based on molecular dynamics (MD) simulations is proposed for evaluating the latent heat of vaporization of nanofluids. The computational algorithm, which considers the interaction of the solid and the fluid molecules, is used for obtaining the enhancement of the latent heat of a base fluid due to the suspension of nanoparticles. The method is validated by comparing the computed latent heat values of water with standard values at different saturation temperatures. Simulation of a water–platinum nanofluid system is performed, treating the volume fraction and size of nanoparticles as parameters. The trends in the variation are found to match well with experimental results on nanofluids. Discussions are also presented on the limitations of the proposed model, and on methods to overcome them.