ASEAN will be weakened by internal strains

Significance This year, it plans to hold its 38th and 39th summits back-to-back on October 26-28. The decision to postpone the first meeting is likely a response to internal strains. The bloc is struggling to deal will the ongoing COVID-19 crisis, increased jockeying among the region’s powers and the fallout of the February 1 coup in Myanmar. Impacts Subregional initiatives such as the US-Mekong Partnership and the China-led Lancang-Mekong Cooperation mechanism will become more prominent. China will push to elevate the ASEAN-China strategic partnership to a comprehensive strategic partnership. With several small states in line to chair ASEAN, some of the bloc's larger members such as Indonesia will assume informal leadership roles.

Incredible internal strains within a biogenic single crystal viewed by X-ray diffraction tomography

The dorsal arm plates (DAPs) of the Ophiocoma Wendtii brittle star are highly functional single crystalline biominerals whose optimized structure and nanostructure enable them to fullfill mechanical and optical functions in the organism. Here, a large DAP bulk piece is characterized by means of synchrotron X-ray Diffraction Tomography (XRDT). This non-destructive crystallographic characterization revealed an astounding feature: the presence of very high compressive strains which relax when the mineral is cracked or grinded into a powder. Thus, previous destructive characterization techniques did not allow their detection. We attribute the compressive strains to the previously identified high-Mg calcite particles, which are coherently included and thereby compress the low-Mg calcite matrix. The measured slice contained both the bulk DAP sample as well as DAP powder. The data generated by the bulk piece could be separated from those by the powder, and the latter was used to calibrate and interprete the former. This study reveals yet another awe-inspiring feature of a biogenic structure, highlights the importance of non-destructive crystallographic characterization for biominerals, and exemplifies the potential of XRDT use in studying a single crystalline material, as well as the advantage of complementary measurement of bulk and powder for data calibration and interpretation.

Mechanism of Interaction between Concrete Cement Matrix and Mineral Additive Particles

A nature of the forces, which act between the concrete cement matrix and entrained mineral particles (ground additives, fine and coarse additives), has been considered. It has been shown that the adhesion between them is attributable to the forces of different nature. The strongest adhesion between the particles of the hydrated binding material and mineral additives occurs, when materials, which react with calcium hydrate of the pore fluid, are used. The latter includes glassy wollastonite, which is part of granulated blast furnace slag. Even at a temperature of 25 °C, an aggressive interaction between them is observed and firm chemical bonds occur. In such case, the dissociation energy of such bonds ranges from 400 to 500 kJ per bond. Between materials, such as crystalline wollastonite and the concrete cement matrix, there is an epitaxial coalescence of its basal surfaces and tobermorite calcium hydrosilicates formed by the interaction of the binder with water. A direct contact is required between the reacting surfaces for such interaction. This is implemented by virtue of the bond, which is attributable to contraction forces resulting from shrinkage strains of the hydrated particles in the concrete cement matrix. Internal strains of the cement that are attributable to contraction, shrinkage, and carbonization of hydrated compounds result in the cement sheath contracting around the aggregate grains and steel reinforcement. Internal strains of the cement stone can be calculated using the Lame equation. We have reviewed the role of the factors, which are most critical for contraction of the cement ring around coarse particles of the aggregate and for stress-strain properties of artificial conglomerates, which have different composition and purpose.

Anisotropic Plastic Behavior in an Extruded Long-Period Ordered Structure Mg90Y6.5Ni3.5 (at.%) Alloy

The Mg90Y6.5Ni3.5 alloy composed almost completely of the Long-Period-Stacking-Ordered (LPSO) phase has been prepared by casting and extrusion at high temperature. An elongated microstructure is obtained where the LPSO phase with 18R crystal structure is oriented with its basal plane parallel to the extrusion direction. Islands of α-magnesium are located between the LPSO grains. The mechanical properties of the alloy are highly anisotropic and depend on the stress sign as well as the relative orientation between the stress and the extrusion axes. The alloy is stronger when it is compressed along the extrusion direction. Under this configuration, the slip of <a> dislocations in the basal plane is highly limited. However, the activation of kinking induces an increase in the plastic deformation. In the transversal extrusion direction, some grains deform by the activation of basal slip. The difference in the yield stress between the different stress configurations decreases with the increase in the test temperature. The evolution of internal strains obtained during in-situ compressive experiments reveals that tensile twinning is not activated in the LPSO phase.

Practical Liberators

During the first fifteen months of the Civil War, the policies and attitudes of Union officers toward emancipation in the western theater were, at best, inconsistent and fraught with internal strains. But after Congress passed the Second Confiscation Act in 1862, army policy became mostly consistent in its support of liberating the slaves in general, in spite of Union army officers' differences of opinion. By 1863 and the final Emancipation Proclamation, the army had transformed into the key force for instituting emancipation in the West. However, Kristopher Teters argues that the guiding principles behind this development in attitudes and policy were a result of military necessity and pragmatic strategies, rather than an effort to enact racial equality. Through extensive research in the letters and diaries of western Union officers, Teters demonstrates how practical considerations drove both the attitudes and policies of Union officers regarding emancipation. Officers primarily embraced emancipation and the use of black soldiers because they believed both policies would help them win the war and save the Union, but their views on race actually changed very little. In the end, however, despite its practical bent, Teters argues, the Union army was instrumental in bringing freedom to the slaves.