Superexchange interactions in AgMF4 (M = Co, Ni, Cu) polymorphs

Magnetic properties of silver(II) compounds have been of interest in recent years. In covalent compounds, the main mechanism of interaction between paramagnetic sites is the superexchange via the connecting ligand. To date, little is known of magnetic interactions between Ag(II) cations and other paramagnetic centres. It is because only a few compounds bearing a Ag(II) cation and other paramagnetic transition metal cation are known from experimental work. Recently the high-pressure synthesis of ternary silver(II) fluoridometallates with 3d metal cations AgMF4 (M = Co, Ni, Cu) was predicted to be feasible. Here, we investigate the magnetic properties of these compounds in their diverse polymorphic forms. Using well-established computational methods we predict superexchange pathways in AgMF4 compounds, evaluate coupling constants and calculate the impact of the Ag(II) presence on superexchange between the other cations. The results indicate that the low-pressure form of AgCuF4, the only one composed of stacked layers like the parent AgF2, would show mainly Ag–Ag and Cu–Cu superexchange interactions. Upon compression, or with the nickel(II) cation, the Ag–M interactions in AgMF4 compounds are intensified, which is emphasized by an increase of Ag–M superexchange coupling constants and Ag–F–M angles. All the strongest Ag–M superexchange pathways are quasi-linear, leading to the formation of antiferromagnetic chains along the crystallographic directions. The impact of Ag(II) on M–M superexchange turns out to be moderate, due to factors connected to the crystal structure.

Helium incorporation induced direct-gap silicides

The search of direct-gap Si-based semiconductors is of great interest due to the potential application in many technologically relevant fields. This work examines the incorporation of He as a possible route to form a direct band gap in Si. Structure predictions and first-principles calculations show that He and Si, at high pressure, form four dynamically stable phases of Si2He (oP36-Si2He, tP9-Si2He, mC18-Si2He, and mC12-Si2He). All phases adopt host–guest structures consisting of a channel-like Si host framework filled with He guest atoms. The Si frameworks in oP36-Si2He, tP9-Si2He, and mC12-Si2He could be retained to ambient pressure after removal of He, forming three pure Si allotropes. Among them, oP36-Si2He and mC12-Si2He exhibit direct band gaps of 1.24 and 1.34 eV, respectively, close to the optimal value (~1.3 eV) for solar cell applications. Analysis shows that mC12-Si2He with an electric dipole transition allowed band gap possesses higher absorption capacity than cubic diamond Si, which makes it to be a promising candidate material for thin-film solar cell.

Adaptation and the Brain

The rationale for this work is to make some sort of sense of the seeming myriad of adaptive explanations for why vertebrate brains vary in size. The role that natural selection has played in brain size has been addressed using the comparative method, which allows identification of evolutionary patterns across species. One starting assumption is that brain size is a useful proxy for intelligence and therefore that large-brained animals are more intelligent than smaller-brained animals. Five classes of selection pressure form the majority of explanations: ecology, technology, innovation, sex, and sociality. After chapters in which I describe the difficulties of measuring both brain size and intelligence (cognition), I address the evidence for each of the five factors in turn, reaching the conclusion that although ecology provides the best explanations for variation in the size of brain regions, none of the factors yet offers a robust and compelling explanation for variation in whole brain size. I end by providing the steps I consider necessary to reach such an explanation, steps that I suggest are feasible, if challenging.

High-temperature, high-pressure hydrothermal synthesis, crystal structure, and infrared and NMR spectroscopy of a barium lead borate with a 2D layer structure: [Ba3Pb(H2O)][B11O19(OH)3]

The structure of the hydrothermally synthesized barium lead borate contains an unusual fundamental building block, 2Δ4□:〈Δ2□〉–〈3□〉Δ, which was also found in the high-pressure form of CaB2O4 synthesized at 900 °C under a pressure of 15–25 kbar.

The Influence of Yard Trucks on Berth Operations in Smaller Container Terminals

Nowadays smaller container terminals are facing an increase in traffic and ship sizes and are consequently subject to extreme pressure form ship-owners that require rapid and efficient transhipment operations in the port, the achievement of which is only possible with the assignment of the proper type and number of quay cranes to each ship and with a good level of synergy between the cranes and the transfer mechanisation. The latter has a significant impact on the cranes working and waiting times and affects the entirety of berth operations. Existing terminals that cannot afford to invest in new modern horizontal transport technologies are most commonly using yard trucks that provide less efficient port transfer operations. That is why in the paper a simulation approach has been used in order to determine how a different number of yard trucks assigned to a single quay crane can affect the productivity of that crane and the productivity of the whole berth subsystem.

Pressure-Induced Polymorphism of Caprolactam: A Neutron Diffraction Study

Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam; two new high pressure solid forms were observed. The transition between each of the forms requires a substantial rearrangement of the molecules and we observe that the kinetic barrier to the conversion can aid retention of phases beyond their region of stability. Form II of caprolactam shows a small pressure region of stability between 0.5 GPa and 0.9 GPa with Form III being stable from 0.9 GPa to 5.4 GPa. The two high-pressure forms have a catemeric hydrogen-bonding pattern compared with the dimer interaction observed in ambient pressure Form I. The interaction between the chains has a marked effect on the directions of maximal compressibility in the structure. Neither of the high-pressure forms can be recovered to ambient pressure and there is no evidence of any polymerization occurring.