Enhancement of Elevated-Temperature Strength in Al–Cu–Ce–Mn–Zr Cast Aluminum Alloy Through Ni Alloying

Herein, to enhance the elevated-temperature strength of heat-resistant aluminum alloys to satisfy application requirements, the effect of Ni content (0.5, 1.0, 2.0, 4.0 wt%) on the microstructures and tensile properties of Al–8.4Cu–2.3Ce–1.0Mn–0.2Zr alloy is investigated. The metallographic analysis techniques are used to quantitatively examine the microstructural changes. The skeleton-like Al₇Cu₄Ni phase is formed after the addition of Ni and its morphology is gradually transformed into a coarse reticular-like shape with Ni content increasing. However, the thermally stable Al₈CeCu₄ and Al₂₄MnCu₈Ce₃ phases disappear when Ni content exceeds 1.0%. Al–8.4Cu–2.3Ce–1.0Mn–0.2Zr–0.5Ni alloy exhibits the optimal elevated-temperature tensile performance at 400 °C, and its ultimate tensile strength, yield strength, and elongation at 400 °C reach 105, 85 MPa, and 16.5%, respectively. The optimal tensile performance is attributed to synergistic enhancing action of the thermostable Al₈CeCu₄, Al₂₄MnCu₈Ce₃, Al₁₆Cu₄Mn₂Ce, and Al₇Cu₄Ni phases at the grain boundaries and the nano-sized Al₂₀Cu₂Mn₃ and Al₂Cu precipitates inside the grains. The typical brittle fracture is dominating in the five alloys with different Ni contents at ambient temperature, but the fracture mode at 400 °C is changed from ductile fracture to ductile and brittle mixed fracture with the increase of Ni.     

Investigation of nerve injury through microfluidic devices

Traumatic injuries, both in the central nervous system (CNS) and peripheral nervous system (PNS), can potentially lead to irreversible damage resulting in permanent loss of function. Investigating the complex dynamics involved in these processes may elucidate the biological mechanisms of both nerve degeneration and regeneration, and may potentially lead to the development of new therapies for recovery. A scientific overview on the biological foundations of nerve injury is presented. Differences between nerve regeneration in the central and PNS are discussed. Advances in microtechnology over the past several years have led to the development of invaluable tools that now facilitate investigation of neurobiology at the cellular scale. Microfluidic devices are explored as a means to study nerve injury at the necessary simplification of the cellular level, including those devices aimed at both chemical and physical injury, as well as those that recreate the post-injury environment.     

Abrasion resistance and mechanical properties of high-volume fly ash concrete

The abrasion resistance and mechanical properties of concrete containing high-volume fly ash (HVFA) were investigated. Sand (fine aggregate) was replaced with 35, 45, and 55% of Class F fly ash by mass. The water to cement ratio and the workability of mixtures were maintained constant at 0.46 and 55 ± 5 mm respectively. Properties examined were compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and abrasion resistance expressed as depth of wear. Test results indicated that replacement of sand with fly ash enhanced the 28-day compressive strength by 25–41%, splitting tensile strength by 12–21%, flexural strength by 14–17%, and modulus of elasticity by 18–23% depending upon the fly ash content, and showed continuous improvement in mechanical properties up to the ages of 365 days. Replacing fly ash with sand significantly improved the abrasion resistance of concrete at all ages. Strong correlation exists between the abrasion resistance and each of the mechanical properties investigated.     

Determinants of Post‐flood Social and Institutional Trust Among Disaster Victims

The 2010 Pakistan floods affected a tenth of the population of that nation and one‐fifth of its land, killing more than 1,700 people. Many observers have wondered the degree to which mass emergencies affect how residents see their decision‐makers. We use original survey data from 450 Pakistan residents to evaluate the degree to which social and institutional trust were correlated with flood damage. Controlling for gender, educational level, occupation and flood experience, high material loss during the flood was negatively correlated with postflood trust levels. In contrast, housing stability and perceived fairness in the distribution of disaster aid were positively correlated with postflood levels of trust. Our study confirms past research on the variability of trust in postdisaster situations and the importance of investing in state–civil society relations.     

Optical Investigation of Sm<Superscript>3+</Superscript> Doped in Phosphate Glass

Samarium doped zinc-magnesium-phosphate glasses having composition (60 – x)P₂O₅–10MgO–30ZnO–xSm₂O₃ where x = 0.1, 0.3, 0.6, 1.0 mol % were prepared by melt quenching technique. Archimedes method was used to measure their densitieswhich are lying in the range 2.65–2.91 g/cm³. On the basis of the increasing trend in the density while increasing the content of Sm₂O₃ it can be concluded that the bridging oxygen is converted to non-bridging oxygen The UV-Vis absorption spectroscopy was carried on in the wavelength range 310–900 nm where the absorption spectra consist of six absorption peaks corresponding to the transitions from the ground state ⁶H_5/2 to various excited energy levels. The optical band gaps are calculated to be 3.93–4.41 eV, 3.31–3.73 eV and 0.27–0.29 eV for direct band gap, indirect band gap and Urbach energy, respectively. The physical parameters like oxygen packing density, refractive index, molar refractivity, metallization, and electronic polarizability are also studied. The Differential Scanning Calorimetry (DSC) technique is used to evaluate the thermal stability.     

Approaches to enzyme and substrate design of the murine Dnmt3a DNA methyltransferase

Dnmt3a‐C, the catalytic domain of the Dnmt3a DNA‐(cytosine‐C5)‐methyltransferase, is active in an isolated form but, like the full‐length Dnmt3a, shows only weak DNA methylation activity. To improve this activity by directed evolution, we set up a selection system in which Dnmt3a‐C methylated its own expression plasmid in E. coli, and protected it from cleavage by methylation‐sensitive restriction enzymes. However, despite screening about 400 clones that were selected in three rounds from a random mutagenesis library of 60 000 clones, we were not able to isolate a variant with improved activity, most likely because of a background of uncleaved plasmids and plasmids that had lost the restriction sites. To improve the catalytic activity of Dnmt3a‐C by optimization of the sequence of the DNA substrate, we analyzed its flanking‐sequence preference in detail by bisulfite DNA‐methylation analysis and sequencing of individual clones. Based on the enrichment and depletion of certain bases in the positions flanking >1300 methylated CpG sites, we were able to define a sequence‐preference profile for Dnmt3a‐C from the ?6 to the +6 position of the flanking sequence. This revealed preferences for T over a purine at position ?2, A over G at ?1, a pyrimidine at +1, and A and T over G at +3. We designed one “good” substrate optimized for methylation and one “bad” substrate designed not to be efficiently methylated, and showed that the optimized substrate is methylated >20 times more rapidly at its central CpG site. The optimized Dnmt3a‐C substrate can be applied in enzymatic high‐throughput assays with Dnmt3a‐C (e.g., for inhibitor screening), because the increased activity provides an improved dynamic range and better signal/noise ratio.     

Origin of anomalous octahedral distortions and collapse of magnetic ordering in Nd1−xSrxFeO3 (0≤x≤0.5)

The effects of strontium doping on the structural properties and magnetic ordering of Nd_1?xSr_xFeO₃ orthoferrite system have been studied by employing macroscopic and microscopic structural techniques like X-ray diffraction, scanning electron microscopy and ⁵⁷Fe Mössbauer spectroscopy. X-ray diffraction confirmed that single phase materials have been synthesized. It has been observed that orthorhombic distortion, density and porosity have decreased; whereas, grain size, tolerance factor and symmetry have increased with increase in the strontium concentration. Mössbauer results showed an increase in the Fe⁴⁺/Fe³⁺ ratio, sagging and local octahedral distortions while decrease in the magnetic ordering with increase in the strontium content. The origin behind anomalous octahedral distortions in this system has been attributed to the decrease in the oxidation state and mismatch in the ionic radii of A-site cations and increase in the concentration of Fe⁴⁺, due to Sr²⁺ doping at Nd³⁺ sites. The collapse of magnetic ordering has been ascribed to the weakening of super-exchange interactions, dilution of strong long range magnetic sub-lattice of high spin Fe³⁺ (five unpaired electrons) by relatively lower spin of high spin Fe⁴⁺ (four unpaired electrons) and increase in the spin–spin relaxation frequency.     

Microstructure and Chemical Properties of Cement Treated Soft Bangladesh Clays

This paper examines the relationship between the microstructure and chemical properties of soft Bangladesh clays due to cementation. The microstructure was investigated using X-ray diffraction, scanning electron microscopy, pH measurement, specific surface area and soil chemical tests. The results indicate that a multitude of changes occurred in the properties and behavior of cement-treated clays that can be explained by the interaction between four underlying microstructural mechanisms. That is, it is suggested that the hydrated lime is formed by hydration, which causes the flocculation of the little clay particles, by the preferential attack of the calcium ions on kaolinite rather than on illite and monmorillinite in the pozzolanic reaction, by surface deposition and shallow infilling by cementitious products such as calcium silicate hydrate and calcium alumino silicate hydrate (CSH and CASH) on clay clusters, and finally, by the presence of water trapped within the clay clusters. The chemical properties of the cement-treated clays were found to depend on the plasticity of soil.