Structure and Properties of Heat-Resistant Alloys NiAl–Cr–Co–X (X = La,Mo, Zr,Ta, Re) and Fabrication of Powders for Additive Manufacturing

The NiAl–Cr–Co–X alloys were produced by centrifugal self-propagating high-temperature synthesis (SHS) casting. The effects of dopants X = La, Mo, Zr, Ta, and Re on combustion, as well as the phase composition, structure, and properties of the resulting cast alloys, have been studied. The greatest improvement in overall properties was achieved when the alloys were co-doped with 15% Mo and 1.5% Re. By forming a ductile matrix, molybdenum enhanced strength characteristics up to the values σ_ucs = 1604 ± 80 MPa, σ_ys = 1520 ± 80 MPa, and ε_pd = 0.79%, while annealing at T = 1250 ℃ and t = 180 min improved strength characteristics to the following level: σ_ucs = 1800 ± 80 MPa, σ_ys = 1670 ± 80 MPa, and ε_pd = 1.58%. Rhenium modified the structure of the alloy and further improved its properties. The mechanical properties of the NiAl, ZrNi₅, Ni_0.92Ta_0.08, (Al,Ta)Ni₃, and Al(Re,Ni)₃ phases were determined by nanoindentation. The three-level hierarchical structure of the NiAl–Cr–Co+15%Mo alloy was identified. The optimal plasma treatment regime was identified, and narrow-fraction powders (fraction 8–27 µm) characterized by 95% degree of spheroidization and the content of nanosized fraction <5% were obtained.     

Mathematical Modeling and Experimental Substantiation of the Gas Release Process in the Production of Non-Autoclaved Aerated Concrete

The widespread use of aerated concrete in construction has led to the emergence of many types and compositions. However, additional research should fill theoretical gaps in the phenomenon of gas release during the formation of the structure of aerated concrete. Based on theoretical analysis and experimental studies, the article proposes a mathematical model of the swelling process based on the physicochemical laws of convection and molecular diffusion of hydrogen from a mixture and the conditions of swelling, precipitation, and stabilization of the mixture. An improved method for the manufacture of aerated concrete is proposed, which consists of introducing cement pre-hydrated for 20–30 min into the composition of the aerated concrete mixture and providing improved gas-holding capacity and increased swelling of the mixture, reducing the average density of aerated concrete up to 29% and improving heat-shielding properties up to 31%. At the same time, the small dynamics of a decrease in the strength properties of aerated concrete were observed, which is confirmed by an increased structural quality factor (CSQ) of up to 13%. As a result, aerated concrete has been obtained that meets the requirements of environmental friendliness and has improved mechanical and physical characteristics. Economic efficiency is to reduce the cost of production of aerated concrete and construction in general by about 15%.     

Improved Mechanical and Tribological Properties of Metal-Matrix Composites Dispersion-Strengthened by Nanoparticles

Co- and Fe-based alloys produced by powder technology are being widely used as a matrix for diamond-containing composites in cutting, drilling, grinding pplications, etc. The severe service conditions demand that the mechanical and tribological properties of these alloys be improved. Development of metal-matrix composites (MMCs) and alloys reinforced with nanoparticles is a promising way to resolve this problem. In this work, we have investigated the effect of nano-sized WC, ZrO₂, Al₂O₃, and Si₃N₄ additives on the properties of sintered dispersion-strengthened Co- and Fe-based MMCs. The results show an increase in the hardness (up to 10 HRB), bending strength (up to 50%), wear resistance (by a factor of 2–10) and a decrease in the friction coefficient (up to 4-fold) of the dispersion-strengthened materials. The use of designed alloys as a binder of cutting diamond tools gave a 4-fold increment in the service life, without reduction in their cutting speed.     

The mechanism of rate-limiting motions in enzyme function

The ability to use conformational flexibility is a hallmark of enzyme function. Here we show that protein motions and catalytic activity in a RNase are coupled and display identical solvent isotope effects. Solution NMR relaxation experiments identify a cluster of residues, some distant from the active site, that are integral to this motion. These studies implicate a single residue, histidine-48, as the key modulator in coupling protein motion with enzyme function. Mutation of H48 to alanine results in loss of protein motion in the isotope-sensitive region of the enzyme. In addition, k(cat) decreases for this mutant and the kinetic solvent isotope effect on k(cat), which was 2.0 in WT, is near unity in H48A. Despite being located 18 A from the enzyme active site, H48 is essential in coordinating the motions involved in the rate-limiting enzymatic step. These studies have identified, of approximately 160 potential exchangeable protons, a single site that is integral in the rate-limiting step in RNase A enzyme function.     

Epidemiology of small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth(SIBO) is defined as an increase in the bacterial content of the small intestine above normal values. The presence of SIBO is detected in 33.8% of patients with gastroenterological complaints who underwent a breath test, and is significantly associated with smoking, bloating, abdominal pain, and anemia. Proton pump inhibitor therapy is a significant risk factor for SIBO. The risk of SIBO increases with age and does not depend on gender or race. SIBO complicat...     

EPR Identification of Zr(III) Complexes Formed upon Interaction of (2-PhInd)2ZrCl2 and rac-Me2Si(1-Ind)2ZrCl2 with MAO and MMAO

Reactions of 1 and 2 with MAO and MMAO were monitored by EPR. It was found that MMAO is a stronger reducing agent than MAO. 1 is more prone to reduction than 2 . The reduction of Zr^IV to Zr^III seems to be the essential pathway of some zirconocene catalysts' deactivation. Zr^III species with the following proposed structures can be identified in the 1 /MMAO system: (2-PhInd)₂Zr^III(ⁱBu), (2-PhInd)₂Zr^III(µ-Cl)₂AlⁱBu₂, (2-PhInd)₂Zr^III(µ-Cl)(ⁱBu)AlⁱBu₂, and [(2-PhInd)₂Zr^III]⁺[Me-MAO]⁻. The degree of reduction of Zr^IV species determined by EPR in the catalytic system 2 /MMAO can be masked by the formation of diamagnetic Zr^III/Zr^III dimers. Addition of monomers to the 2 /MAO system promotes reduction ot the zirconium species.

     

Evidence for correlation between the intensities of adjuvant effects and NOD2 activation by monomeric, dimeric and lipophylic derivatives of N-acetylglucosaminyl-N-acetylmuramyl peptides

Adjuvanticity of a series of peptidoglycan fragments-known as muramyl peptides-and their lipophylic derivatives was examined and compared with the ability of these compounds to activate NF-kB pathway through NOD2. The adjuvant activity of di, tetrasaccharide peptides and stearoyl containing derivatives has at least two peaks in dose-response curves and the greater of them correlates with respective dose-response data for NF-kB stimulation through NOD2. Introduction of stearoyl moiety, with the aim of improving muramyl peptide interaction with the cell membrane and subsequent intracellular delivery, influenced the corresponding activities in vitro, but did not correlate with improved effects in vivo experiments. IgG subtypes tests indicate that muramyl peptides preferentially stimulate IgG(1) production, whereas the tetrasaccharide containing muramyl peptide additionally induces production of IgG(2b) subclasses. On the whole, comparison of the adjuvanticity in vivo and the NOD2 activation in vitro revealed a clear correlation between the two responses. These findings confirm the view that NOD2 pathway activation should account, at least in part, for the adjuvant effects of these compounds.