Composition and Tribological Properties of Hardened Cutting Blades of Tillage Machines under Abrasive Deterioration

The article presents the results of metallographic study of low-carbon 20 steel grade and high-carbon 70 and 65G steel grades upon carburizing, heat treatment, and laser hardening. The change in the microhardness through the depth of the surface layer of steels and their abrasion resistance upon hardening under different conditions has been measured. Optimal hardening conditions have been proposed for steels for cutting blades of tillage machines that enable the durability of the blades to be improved.     

Control of the Machining Precision in Thread Cutting

Russian Engineering Research - In research on thread cutting, the flaws inevitably arising in the first two and last two turns of the thread, when the process is unsteady, are analyzed....     

Thermal Properties of (Zr,TM)B2 Solid Solutions with TM = Hf,Nb, W,Ti, and Y

The thermal properties were investigated for hot‐pressed zirconium diboride—transition‐metal boride solid solutions. The transition‐metal additives included hafnium, niobium, tungsten, titanium, and yttrium. The nominal additions were equivalent to 3 at.% of each metal with respect to zirconium. Powders were hot‐pressed to nearly full density at 2150°C using 0.5 wt% carbon as a sintering aid. Thermal diffusivity was measured using the laser flash method. Thermal conductivity was calculated from the thermal diffusivity results using temperature‐dependent values for density and heat capacity. At 25°C, the thermal conductivity ranged from 88 to 34 W·(m·K)^?1 for specimens with various additives. Electrical resistivity measurements and the Wiedemann–Franz law were used to calculate the electron contribution of the thermal conductivity and revealed that thermal conductivity was dominated by the electron contribution. The decrease in thermal conductivity correlated with a decrease in unit cell volume, indicating that lattice strain may affect both phonon and electron transport in ZrB₂.     

Brassica Plant Responses to Mild Herbivore Stress Elicited by Two Specialist Insects from Different Feeding Guilds

Compensation growth and chemical defense are two components of plant defense strategy against herbivores. In this study, compensation growth and the response of primary and secondary metabolites were investigated in Brassica rapa plants subjected to infestation by two herbivores from contrasting feeding guilds, the phloem-feeding aphid Brevicoryne brassicae and the leaf-feeding caterpillar Pieris brassicae. These specialist herbivores were used at two different densities and allowed to feed for seven days on a young caged leaf. Changes in growth rates were assessed for total leaf area and bulb mass, whereas changes in primary and secondary metabolites were evaluated in young and mature leaves, roots, and bulbs. Mild stress by caterpillars on young plants enhanced mean bulb mass and elicited a contrasting regulation of aliphatic and indolic glucosinolates in the leaves. In contrast, mild stress by aphids enhanced leaf growth and increased glucosinolate concentrations in the bulb, the most important storage organ of B. rapa. A similar mild stress by either herbivore to older plants did not alter plant growth parameters or concentrations of the metabolites analyzed. In conclusion, Brassica plant growth was either maintained or enhanced under mild herbivore stress, and defense patterns differed strongly in response to herbivore type and plant development stage. These results have implications for the understanding of plasticity in plant defenses against herbivores and for the management of Brassica rapa in agroecosystems.     

Regioselective Synthesis of Naphtho‐fused Heterocycles via Palladium(0)‐Catalyzed Tandem Reaction of N‐Tosylhydrazones

We have developed a palladium(0)‐catalyzed tandem process which involves the cross‐coupling reaction of N‐tosylhydrazones with dibromide compounds followed by a sequence of intramolecular 5‐exo‐trig, 3‐exo‐trig cyclization, ring opening, and β‐hydride elimination to produce 6‐endo‐trig cyclized products. The strategy was successfully applied for the regioselective synthesis of substituted benzo[b]naphtho[2,1‐d]thiophenes, naphtho[1,2‐b]benzofurans, and benzo[a]carbazoles in moderate to excellent yields.

     

Expeditious Synthesis of Functionalized 1‐Arylcyclooctadienes via Palladium‐Catalyzed Lithium Cross‐Coupling

The palladium‐catalyzed direct cross‐coupling of aryl bromides and (1Z,5Z)‐cycloocta‐1,5‐dien‐1‐yllithium is described as an important method to synthesize 1‐arylcyclooctadienes. The use of a well‐established Pd₂dba₃/XPhos catalytic system affords the desired new compounds in good to excellent yields; the reaction proceeds at room temperature with both high efficiency and selectivity. Finally we found the best conditions to combine a suitable lithium‐halogen exchange with a cross‐coupling reaction.

     

Obtaining and Studying Films of Tungsten,Titanium and Their Oxides

Glass Physics and Chemistry - The initial polycrystalline films of tungsten and titanium, whose surface has predominantly ultrananodispersed morphology and a thickness of 50 to 100 nm, are obtained...