Electron spin resonance studies of 199HgH, 201HgH, 199HgD and 201HgD isolated in neon and argon matrices at 4K: an electronic structure investigation

Various isotopomers of the mercury hydride radical (HgH) have been generated in a microwave discharge and trapped in neon and argon matrices at 4 K for electron spin resonance (ESR) investigations. Both the dipolar (A_dip) and isotropic (A_iso) components of the nuclear hyperfine interactions have been directly measured for ¹⁹⁹Hg, ²⁰¹Hg, H and D. Electronic structure information for HgH in its X²Σ ground state obtained from the hyperfine data is compared with theoretical results from several different computational methods. The hyperfine interactions in HgH are unusually large with A_iso(¹⁹⁹Hg) = 6859(3), A_dip(¹⁹⁹Hg) = 446(3), A_iso(H) = 730(2) and A_dip(H) = 0(2) MHz. A standard analysis of the hyperfine interactions demonstrates the need for a more in-depth theoretical treatment of HgH that should include relativistic effects. An interesting shift in spin density is observed when deuterium replaces hydrogen in HgH. The decreased spin density on deuterium, which was demonstrated in earlier studies, can now be more fully investigated since these new measurements confirm an associated increase in spin density on mercury     

Improved models for the phase behaviour of hydrogen fluoride: chain and ring aggregates in the SAFT approach and the AEOS model

Hydrogen fluoride presents one of the strongest hydrogen bonds known. Ring aggregates exist both in the vapour and liquid phases at low temperatures resulting in an anomalously high low-temperature vapour pressure. The effect of ring-like aggregates on the vapour—liquid phase equilibria of associating fluids is studied within the framework of the statistical associating fluid theory (SAFT) and in the chemical model of Lencka and Anderko (AEOS). The SAFT approach incorporates separate contributions to describe chain formation, association (hydrogen bonding), and long range dispersion forces. The treatment of the association interactions stems from the thermodynamic perturbation theory of Wertheim. At the first level of approximation the contribution of ring-like aggregates is neglected and only chain- and treelike structures are treated. In this work an earlier extension of the approach to incorporate ring aggregates is used to model the phase behaviour of hydrogen fluoride. The chemical model of Lencka and Anderko for associating fluids is also considered together with a modification that takes into account the formation of ring aggregates. Vapour pressures and coexistence densities are examined together with heats of vapourization, and the calculations are compared with experimental data.     

The influence of efficient atomic packing on the constitution of metallic glasses

Efficient atomic packing is shown to be a fundamental consideration in the formation of metallic glasses. A simple concept of packing efficiency, based on atom packing in the first coordination shell of solute-centred clusters, is proposed and developed. This model leads to the prediction that specific radius ratios, defined as the radius of the solute atom divided by the radius of the solvent atom, are preferred in the constitution of metallic glasses. Analysis of a large number of binary and complex metallic glasses shows that these specific critical radius ratios R* are indeed preferred in known metallic glasses. The predictions of this model extend previous proposals to describe the influence of topology on the formation of metallic glasses. Although this model represents a simple idealization, the strong agreement with published metallic glasses suggests that efficient atomic packing, enabled by solute-centred clusters, forms a fundamental consideration in the constitution of metallic glasses.     

Coherent phonons, nanoseismology and THz radiation in InGaN/GaN heterostructures

The ultrafast optical photoexcitation of hot electrons and holes in semiconductors by femtosecond laser pulses can trigger coherent phonon oscillations. We discuss the huge coherent acoustic phonons which have been generated in InGaN/GaN heterostructures and epilayers and how they might be used in imaging of surfaces and interfaces in nanostructures. We also discuss the THz radiation emitted from these phonons.     

Search for cluster emission and extremely deformed shapes using charged-particle spectroscopy

The possible occurrence of highly deformed configurations is investigated in the N=Z nuclei ⁴⁰Ca, ⁴⁴Ti, and ⁵⁶Ni as formed in the ²⁸Si+¹²C, ¹⁶O+²⁸Si, and ²⁸Si+²⁸Si reactions by using the properties of the emitted light charged particles (LCP). The energy spectra, in-plane and out-of-plane angular correlations of LCP’s are analysed for each of the 3 studied reactions within the framework of the statistical model. Strong deformation effects are deduced from Hauser-Feshbach calculations performed with the Monte Carlo code CACARIZO by using a consistent set of parameters with spin-dependent level densities. The analysis of α particles in coincidence with ³²S fragments emitted in ²⁸Si+¹²C shows a strong contribution from a ⁸Be cluster emission. The binary nature of this cluster emission has been verified in three other reactions involving a ¹²C target: ²⁷A1+¹²C, ³¹P+¹²C, and ³²S+¹²C.     

Disjoint spine phenomena in certain contractible n-manifolds (n5)

If M is a compact PL manifold with boundary containing a subpolyhedron K in its interior, then K is said to be a PL spine of M provided M collapses to K (MK). Guilbault [Topology 34 (1) (1995) 99–108] has shown that certain nontrivial contractible manifolds possess disjoint spines. His results stem from a standing conjecture regarding disjoint spines in contractible 4-manifolds constructed by Mazur. More to the point, there is a dimensional requirement introduced by his techniques; Guilbault produces such manifolds in dimensions n9. We shall provide techniques which allow the construction of examples in dimensions n5 following the path laid out by Guilbault. The new techniques will provide a slight strengthening of some other Guilbault results as well.     

Behavior of gold nanoparticles in an experimental algal–zooplankton food chain

Journal of Nanoparticle Research - The first-order semiconductor–metal Mott transition in single nano-crystal of VO2 has been observed using scanning tunneling spectroscopy. The variation of...     

A radioactive tracer dilution method to determine the mass of molten salt

A new technique for molten salt mass determination, termed radioactive tracer dilution, that uses ²²Na as a tracer was validated at bench scale. It has been a challenging problem to determine the mass of molten salt in irregularly shaped containers, where a highly radioactive, high-temperature molten salt was used to process nuclear spent/used fuel during electrochemical recycling (pyro-processing) or for coolant/fuel salt from molten salt reactors. A radioactive source with known activity is dissolved into the salt. After a complete mixture, a small amount of the salt is sampled and measured in terms of its mass and radioactivity. By finding the ratio of the mass to radioactivity, the unknown salt mass in the original container can be precisely determined.