Band Gap and Diameter Modulation of Quantum Dots in Glasses

Modulation of the band gap energy and diameter of quantum dots (QDs) formed in glasses is important to achieve the optimized performance for applications as infrared light sources, lasers, saturable absorbers, etc. Absorption and photoluminescence of PbS QDs were extended into mid-infrared wavelength range in glasses containing small amount of lead but oversaturated with sulfur. Dual-band photoluminescence of PbSe QDs was prepared in oxyfluoride glass-ceramics containing BaF₂ nanocrystals. By introducing SnO in the glasses, alloyed Pb_1-xSn_xSe QDs with smaller band gap energies were formed in glasses, and mid-infrared photoluminescence of Pb_1-xSn_xSe QDs at ~2570 nm in wavelength was achieved.     

Wear resistance characteristics of materials used in oil sands plants

The surge in demand for natural resources has shifted the focus of the international community toward the development of oil sands, shale oil, shale gas and other non-traditional energy sources. In extreme environments, materials used in petroleum gas plant modules are accompanied by various problems caused by low-temperature brittleness such as damage, corrosion and wear. Many researchers have been conducting studies to discover a suitable material whose lifespan could be improved by performing characteristics analyses and performance assessments. In this study, a material characteristics assessment was conducted based on a wear resistance test on materials that are commonly used at oil sands plants. Prior to a wear resistance test, a chemical composition analysis was performed on each of the specimens, and tensile, impact, hardness and corrosion tests were carried out to examine the correlation between their results with the results of the wear resistance test. Each test was performed according to ASTM G 105 standards, and the change in weight according to wear length was analysed for each material to determine the related tendencies. In addition, the results of the wear test were derived by analysing the change in the mass of the specimen before and after the test, and the surface roughness was assessed to analyse the performance related to wear and define the service life. The aim was to use these results to select a material that would be suitable for the abrasive environment of the key equipment and materials of plants.     

Quantitative analysis of microbial community structure in two-phase anaerobic digesters treating food wastewater

An acidogenic reactor with a 0.5-L working volume and a methanogenic digester with a 5-L of working volume were operated for 150 days on a continuous mode to investigate the structure of a microbial community during food wastewater treatment. During the steady state of anaerobic digestion, volatile solids (VS) removal efficiency in the pilot plant was approximately 65%. The bacterial population was higher than any other methanogens detected during the entire anaerobic process and treatment of raw food wastewater. Methanomicrobiales (MMB), Methanosarcinales (MSL), and Methanobacteriales (MBT) were detected during digestion. The methanogenic population present in the acidogenic reactor was directly affected by the archaeal community in raw food wastewater. However, the shift of microbial community in the methanogenic digester was relatively gradual. The performance of methanogenic digester might be more related to the change of microbial metabolism affected by the physicochemical properties of the input substrate.     

A methodology for determining the true stress-strain curve of SA-508 low alloy steel from a tensile test with finite element analysis

The true stress-strain curve of a material should be determined for plastic property input to numerical analysis. This study proposes a simple methodology for determining the true stress-strain curve of SA-508 Grade 3 Class 1 low alloy steel using limited information from a general tensile test with finite element analysis. Measured engineering stresses and strains can be reasonably converted to true stresses and strains under uniform deformation before necking. True stress-strains are difficult to determine after necking because of nonuniform deformation without specialized measurement techniques. Five post-necking strain hardening models are considered, namely, linear, swift, Ludwick, Hollomon-linear (HL) and Hollomon-linear-constant (HLC) models. The equations for each model can be determined using the results of the tensile test, which include the true stress-strain value at the maximum load point and the corrected true stress-strain value at the fracture point plus the Considere instability criterion. The HL and HLC models suggested that the engineering stress-strains from the finite element analysis are consistent with the experimental results.     

Impacts of climate and land‐cover changes on water resources in a humid subtropical watershed: a case study from East Texas,USA

This study investigates the response of water resources regarding the climate and land‐cover changes in a humid subtropical watershed during the period 1970–2009. A 0.7°C increase in temperature and a 16.3% increase in precipitation were observed. Temperature had a lower increase trend, and precipitation showed definite increasing trend compared to previous studies. The main trend of land‐cover change was conversion of vegetation and barren lands to developed and crop lands affected by human intervention, and forest and grass to bush/shrub which considered to be caused by natural climate system. Hydrologic responses to climate and land‐cover changes resulted in increases of surface run‐off (15.0%), soil water content (2.7%), evapotranspiration (20.1%) and a decrease in groundwater discharge (9.2%). We found that surface run‐off is relatively stable with precipitation, whereas groundwater discharge and soil water content are sensitive to changes in land cover, especially land cover brought about by human intervention.     

Simvastatin Attenuates the Oxidative Stress,Endothelial Thrombogenicity and the Inducibility of Atrial Fibrillation in a Rat Model of Ischemic Heart Failure

Increased atrial oxidative stress has an important role in inducing and maintaining atrial fibrillation (AF), and the activation of the small GTPase Rac1 contributes to the oxidative stress. We investigated the relationship of Rac1, atrial endothelial thromboprotective markers and AF inducibility and if simvastatin has a potential beneficial effect on a myocardial infarction (MI)-induced heart failure (HF) rat model. Rats were randomized into three groups (shams, MI group and simvastatin treatment group) and underwent echocardiography, AF induction studies and left atrial (LA) fibrosis analysis. Atrial Rac 1, sodium calcium exchanger (I_NCX), sarcoplasmic reticulum calcium ATPase (SERCA), endothelial nitric oxide synthase (eNOS) and induced nitric oxide synthase (iNOS) were measured. AF inducibility, AF duration and LA fibrosis were significantly higher in the MI group (p < 0.001 vs. sham), which were significantly reduced by simvastatin (p < 0.05 vs. MI). The reduced expressions of atrial eNOS, SERCA, thrombomodulin, tissue factor pathway inhibitor and tissue plasminogen activator in the MI group were significantly improved by simvastatin. Furthermore, the increased expression of atrial iNOS, I_NCX and Rac1 activity were significantly decreased by the simvastatin. Oxidative stress, endothelial dysfunction and thrombogenicity are associated with the promotion of AF in a rat model of ischemic HF. These were associated with increased Rac1 activity, and simvastatin treatment prevents these changes.     

Pr3+/Er3+ Codoped Ge-As-Ga-S Glasses as Dual-Wavelength Fiber-optic Amplifiers for 1.31 and 1.55 μm Windows

Fluorescence emissions at both 1.31 and 1.55 μm communication windows were observed from Pr³⁺/Er³⁺ codoped Ge-As-Ga-S glasses with a single wavelength pumping at 986 nm. The lifetime of the Er³⁺:⁴ I _11/2 level decreased as the Pr³⁺ concentration increased, and that of the Pr³⁺:¹ G ₄ level increased as the Er³⁺ concentration increased. Energy transfer from the Er³⁺:⁴ I _11/2 level to the Pr³⁺:¹ G ₄ level was responsible for emission of the 1.31 μm fluorescence from the Pr³⁺:¹ G ₄ level. Ge-As-Ga-S glasses that have been doped with Pr³⁺ and Er³⁺ cations are promising amplifier materials for both 1.31 and 1.55 μm communication windows.