Effects of nitrogen sources on toluene degradation by Pseudomonas putida BZ918

For effective toluene degradation, the effects of a nitrogen source were studied with Pseudomonas putida BZ912, which was isolated from crude oil contaminated soil and is capable of degrading VOC. Two nitrogen sources, ammonia and nitrate, showed different effects on specific growth rates (0.25 hr⁻¹ and 0.12 hr⁻¹, respectively), biomass yields (0.56 vs. 0.39) and specific toluene degradation rates (0.51 hr⁻¹ vs. 0.26 hr⁻¹). Under the resting cell conditions, the cells pre-cultured in the ammonia-containing medium showed higher specific toluene degradation rate than that in nitrate-containing medium (0.045 hr⁻¹ vs. 0.038 hr⁻¹). Ammonia as a nitrogen source was effective for degradation in high toluene concentration because high cellular biomass was accomplished. Nitrate showed slow growth rate compared to ammonia. The resting cell conditions demonstrated that it was able to degrade toluene efficiently without increasing biomass. These conditions could be a solution for degrading VOC after high cellular biomass was obtained in a biofilter. By changing the nitrogen source and the growth conditions according to the toluene concentration, the control of cell biomass and the desired removal capacity were accomplished.     

Prediction of microstructure evolution during high temperature blade forging of a Ni−Fe based superalloy,Alloy 718

The mechanical properties of the Ni−Fe-based Alloy 718 depend very much on grain size, as well as the strengthening phases, γ’ and γ. The grain structure of the superalloy components is mainly controlled during thermo-mechanical processes by the dynamic, meta-dynamic recrystallization and grain growth. In this investigation, the evolution of the grain structure in the process of two-step blade forging was experimentally and numerically dealt with. The evolution of the grain structure in Alloy 718 during blade forging was predicted using a 2-DFE simulator with implemented constitutive models on dynamic recrystallization and grain growth. The comparison of the simulated microstructure with the actual grain structure of the forged parts validated the prediction of the grain structure evolution. The effect of dynamic recrystallization on the evolution of grain structure is highlighted in this article.     

Effects of the Domain Size on Local d33 in Tetragonal (Na0.53 K0.45Li0.02)(Nb0.8Ta0.2)O3 Ceramics

Lead‐free (Na_0.53K_0.45Li_0.02)(Nb_0.8Ta_0.2)O₃ (NKLNT) was prepared using a conventional cold‐pressing method. A commercial piezoresponse force microscope (PFM) was applied to observe the domain structures of NKLNT ceramics. The typical configuration of the ferroelectric domain was analyzed in abnormal grains with grain sizes that exceeded 40 μm, where tetragonal 90° domains are predominant. The local piezoresponse hysteresis loops were characterized and studied as a function of the domain width (dw) in the range 300–1000 nm. It was found that the amplitude signals increased and the coercive field reduced significantly with a decrease in the domain size. Finally, the local longitudinal piezoelectric coefficient (d₃₃) increased as the domain size decreased.     

Homogeneous charge compression ignition of LPG and gasoline using variable valve timing in an engine

The combustion characteristics and exhaust emissions in an engine were investigated under homogeneous charge compression ignition (HCCI) operation fueled with liquefied petroleum gas (LPG) and gasoline with regard to variable valve timing (VVT) and the addition of di-methyl ether (DME). LPG is a low carbon, high octane number fuel. These two features lead to lower carbon dioxide (CO₂) emission and later combustion in an LPG HCCI engine as compared to a gasoline HCCI engine. To investigate the advantages and disadvantages of the LPG HCCI engine, experimental results for the LPG HCCI engine are compared with those for the gasoline HCCI engine. LPG was injected at an intake port as the main fuel in a liquid phase using a liquefied injection system, while a small amount of DME was also injected directly into the cylinder during the intake stroke as an ignition promoter. Different intake valve timings and fuel injection amount were tested in order to identify their effects on exhaust emissions and combustion characteristics. Combustion pressure, heat release rate, and indicated mean effective pressure (IMEP) were investigated to characterize the combustion performance. The optimal intake valve open (IVO) timing for the maximum IMEP was retarded as the λ_TOTAL was decreased. The start of combustion was affected by the IVO timing and the mixture strength (λ_TOTAL) due to the volumetric efficiency and latent heat of vaporization. At rich operating conditions, the θ_90-20 of the LPG HCCI engine was longer than that of the gasoline HCCI engine. Hydrocarbon (HC) and carbon monoxide (CO) emissions were increased as the IVO timing was retarded. However, CO₂ was decreased as the IVO timing was retarded. CO₂ emission of the LPG HCCI engine was lower than that of the gasoline HCCI engine. However, CO and HC emissions of the LPG HCCI engine were higher than those of the gasoline HCCI engine.