Density functional study of Aun_n (n=2-20) clusters: lowest-energy structures and electronic properties

We have investigated the lowest-energy structures and electronic properties of the Au$_n$(n=2-20) clusters based on density functional theory (DFT) with local density approximation. The small Au$_n$ clusters adopt planar structures up to n=6. Tabular cage structures are preferred in the range of n=10-14 and a structural transition from tabular cage-like structure to compact near-spherical structure is found around n=15. The most stable configurations obtained for Au$_{13}$ and Au$_{19}$ clusters are amorphous instead of icosahedral or fcc-like, while the electronic density of states sensitively depend on the cluster geometry. Dramatic odd-even alternative behaviors are obtained in the relative stability, HOMO-LUMO gaps and ionization potentials of gold clusters. The size evolution of electronic properties is discussed and the theoretical ionization potentials of Au$_n$ clusters compare well with experiments.Comment: 6 pages, 7 figure

Eigenvalue Problem in Two Dimensions for an Irregular Boundary II: Neumann Condition

We formulate a systematic elegant perturbative scheme for determining the eigenvalues of the Helmholtz equation (\bigtriangledown^{2} + k^{2}){\psi} = 0 in two dimensions when the normal derivative of {\psi} vanishes on an irregular closed curve. Unique feature of this method, unlike other perturbation schemes, is that it does not require a separate formalism to treat degeneracies. Degenerate states are handled equally elegantly as the non-degenerate ones. A real parameter, extracted from the parameters defining the irregular boundary, serves as a perturbation parameter in this scheme as opposed to earlier schemes where the perturbation parameter is an artificial one. The efficacy of the proposed scheme is gauged by calculating the eigenvalues for elliptical and supercircular boundaries and comparing with the results obtained numerically. We also present a simple and interesting semi-empirical formula, determining the eigenspectrum of the 2D Helmholtz equation with the Dirichlet or the Neumann condition for a supercircular boundary. A comparison of the eigenspectrum for several low-lying modes obtained by employing the formula with the corresponding numerical estimates shows good agreement for a wide range of the supercircular exponent.Comment: 26 pages, 12 figure

Stratigraphy and Geologic History of the InSight Landing Site, Mars

We describe the local stratigraphy and geologic history of a regolith-covered lava plain at the InSight landing site using orbital and lander observations

Effect of surrounding environment on atomic structure and equilibrium shape of growing nanocrystals: gold in/on SiO2

We report on the equilibrium shape and atomic structure of thermally-processed Au nanocrystals (NCs) as determined by high resolution transmission electron microscopy (TEM). The NCs were either deposited on SiO2surface or embedded in SiO2layer. Quantitative data on the NCs surface free energy were obtained via the inverse Wulff construction. Nanocrystals inside the SiO2layer are defect-free and maintain a symmetrical equilibrium shape during the growth. Nanocrystals on SiO2surface exhibit asymmetrical equilibrium shape that is characterized by the introduction of twins and more complex atomic defects above a critical size. The observed differences in the equilibrium shape and atomic structure evolution of growing NCs in and on SiO2is explained in terms of evolution in isotropic/anisotropic environment making the surface free energy function angular and/or radial symmetric/asymmetric affecting the rotational/translational invariance of the surface stress tensor

The characteristics of SARS-CoV-2-positive children in Australian hospitals: a PREDICT network study

Published June 2023Objectives: To examine the clinical characteristics and short term outcomes for children with severe acute respiratory syndrome coronavirus 2 (SARS-CoV- 2) infections who presented to Australian hospitals during 2020 and 2021. Design, setting: Retrospective case review study in nineteen hospitals of the Paediatric Research in Emergency Departments International Collaborative (PREDICT) network from all Australian states and territories, including seven major paediatric tertiary centres and eight Victorian hospitals. Participants: SARS-CoV- 2- positive people under 18 years of age who attended emergency departments or were admitted to hospital during 1 February 2020 –31 December 2021. Main outcome measures: Epidemiological and clinical characteristics, by hospital care type (emergency department [ED] or inpatient care). Results: A total of 1193 SARS-CoV- 2- positive children and adolescents (527 girls, 44%) attended the participating hospitals (107 in 2020, 1086 in 2021). Their median age was 3.8 years (interquartile range [IQR], 0.8–11.4 years); 63 were Aboriginal or Torres Strait Islander people (5%). Other medical conditions were recorded for 293 children (25%), including asthma (86, 7%) and premature birth (68, 6%). Medical interventions were not required during 795 of 1181 ED presentations (67%); children were discharged directly home in 764 cases (65%) and admitted to hospital in 282 (24%; sixteen to intensive care units). The 384 admissions to hospital (including 102 direct admissions) of 341 children (25 infants under one month of age) included 23 to intensive care (6%); the median length of stay was three days (IQR, 1–9 days). Medical interventions were not required during 261 admissions (68%); 44 children received respiratory support (11%) and 21 COVID-19- specific treatments, including antiviral and biologic agents (5%). Being under three months of age (v one year to less than six years: odds ratio [OR], 2.6; 95% confidence interval [CI], 1.7–4.0) and pre-existing medical conditions (OR, 2.5; 95% CI, 1.9–3.2) were the major predictors of hospital admission. Two children died, including one without a known pre-existing medical condition. Conclusion: During 2020 and 2021, most SARS-CoV- 2- positive children and adolescents who presented to participating hospitals could be managed as outpatients. Outcomes were generally good, including for those admitted to hospital.Laila Ibrahim, Catherine Wilson, Doris Tham, Mark Corden, Shefali Jani, Michael Zhang, Amit Kochar, Ker Fern Tan, Shane George, Natalie T Phillips, Paul Buntine, Karen Robins-Browne, Vimuthi Chong, Thomas Georgeson, Anna Lithgow, Sarah Davidson, Sharon O, Brien, Viet Tran, Franz E Bab

Organic Superconductors: when correlations and magnetism walk in

This survey provides a brief account for the start of organic superconductivity motivated by the quest for high Tc superconductors and its development since the eighties'. Besides superconductivity found in 1D organics in 1980, progresses in this field of research have contributed to better understand the physics of low dimensional conductors highlighted by the wealth of new remarkable properties. Correlations conspire to govern the low temperature properties of the metallic phase. The contribution of antiferromagnetic fluctuations to the interchain Cooper pairing proposed by the theory is borne out by experimental investigations and supports supercondutivity emerging from a non Fermi liquid background. Quasi one dimensional organic superconductors can therefore be considered as simple prototype systems for the more complex high Tc materials.Comment: 41 pages, 21 figures to be published in Journal of Superconductivity and Novel Magnetis