Emergence of topological electronic phases in elemental lithium under pressure

Lithium, a prototypical simple metal under ambient conditions, has a surprisingly rich phase diagram under pressure, taking up several structures with reduced symmetry, low coordination numbers, and even semiconducting character with increasing density. Using first-principles calculations, we demonstrate that some predicted high-pressure phases of elemental Li also host topological electronic structures. Beginning at 80 GPa and coincident with a transition to the Pbca phase, we find Li to be a Dirac nodal line semimetal. We further calculate that Li retains linearly-dispersive energy bands in subsequent predicted higher pressure phases, and that it exhibits a Lifshitz transition between two Cmca phases at 220 GPa. The Fd-3m phase at 500 GPa forms buckled honeycomb layers that give rise to a Dirac crossing 1 eV below the Fermi energy. The well-isolated topological nodes near the Fermi level in these phases result from increasing p-orbital character with density at the Fermi level, itself a consequence of rising 1s core wavefunction overlap, and a preference for nonsymmorphic symmetries in the crystal structures favored at these pressures. Our results provide evidence that under pressure, bulk 3D materials with light elements, or even pure elemental systems, can undergo topological phase transitions hosting nontrivial topological properties near the Fermi level with measurable consequences; and that, through pressure, we can access these novel phases in elemental lithium.Comment: 5 pages, 5 figures, accepted for publicatio

Butter increases high-density lipoprotein functional capacity: is this compensation for its adverse effect on serum low-density lipoprotein cholesterol?

Credencia o curso "Depoimento Especial de Crianças e Adolescentes" compartilhado pela Enfam, promovido pela Escola Judicial do Tribunal de Justiça do Estado de Goiás - Ejug

Single-particle and collective excitations in a charged Bose gas at finite temperature

The main focus of this work is on the predictions made by the dielectric formalism in regard to the relationship between single-particle and collective excitation spectra in a gas of point-like charged bosons at finite temperature $T$ below the critical region of Bose-Einstein condensation. Illustrative numerical results at weak coupling ($r_s = 1$) are presented within the Random Phase Approximation. We show that within this approach the single-particle spectrum forms a continuum extending from the transverse to the longitudinal plasma mode frequency and leading to a double-peak structure as $T$ increases, whereas the density fluctuation spectrum consists of a single broadening peak. We also discuss the momentum distribution and the superfluidity of the gas.Comment: 15 pages, 5 figure

Structure determination from powder data : Mogul and CASTEP

When solving the crystal structure of complex molecules from powder data, accurately locating the global minimum can be challenging, particularly where the number of internal degrees of freedom is large. The program Mogul provides a convenient means to access typical torsion angle ranges for fragments related to the molecule of interest. The impact that the application of modal torsion angle constraints has on the structure determination process of two structure solution attempts using DASH is presented. Once solved, accurate refinement of a molecular structure against powder data can also present challenges. Geometry optimisation using density functional theory in CASTEP is shown to be an effective means to locate hydrogen atom positions reliably and return a more accurate description of molecular conformation and intermolecular interactions than global optimisation and Rietveld refinement alone

Regional Invasive Species & Climate Change Management Challenge: Prioritizing range-shifting invasive plants High-impact species coming to the Northeast

Prevention of new invasions is a cost-effective way to manage invasive species and is most effective when emerging invaders are identified and prioritized before they arrive. Climate change is projected to bring nearly 100 new invasive plants to the Northeast. However, these plants are likely to have different types of impacts, making some a higher concern than others. Here, we summarize the results of original RISCC research that identifies high priority, range-shifting invasive plants based on their potential impacts

Information activity in serious leisure

Background. In the past decade, scholars of information science have started to conduct research on information behaviour in serious leisure. Presently, these studies lack common concepts and terms and empirical discoveries are not easy to assemble into theory. Aim. This conceptual and methodological paper surveys the aforementioned research area and introduces Anders Hektor’s model of information behaviour in conjunction with the serious leisure perspective as a means to systematically study information behaviour in serious leisure. Method. Three methods are employed. The first is a selective literature review and intellectual history of research into information behaviour in serious leisure. The second is a conceptual analysis of Hektor’s model that relates its key features to the serious leisure perspective. The third consists of a deductive audit of three forms of serious leisure (the liberal arts hobby, amateur musicianship, and the hobby of running), utilizing the frameworks, concepts, and terms outlined in the paper. Results. Studies of information behaviour in serious leisure have increased and deepened in the past decade, largely through ideographic case studies. Hektor’s model of information behaviour, with its locus in everyday life and precise delineation of eight information activities, can complement such research designs. A deductive audit guided by Hektor’s model illuminated information activities within the three forms of serious leisure and enabled comparative observations. Conclusions. When combined with the serious leisure perspective, Hektor’s model enables research that is comparative and more precise. However, the extent to which this model captures physical or embodied information should be further examined