Phylogenetic placement and the timing of diversification in Australia's endemic Vachellia (Caesalpinioideae, Mimosoid Clade, Fabaceae) species

The genus Vachellia Wight & Arn. has a pantropical distribution, with species being distributed through Africa, the Americas, Asia and Australia. The relationships among the lineages from Africa and America are well understood, but the phylogenetic placement and evolutionary origins of the Australian species of Vachellia are not known. We, therefore, sequenced four plastid genes from representatives of each of the nine Australian species of Vachellia, and used Bayesian inference to assess the phylogenetic placement of these lineages, and a relaxed molecular clock to assess the timing of diversification. The Australian species of Vachellia form a well-supported monophyletic clade, with molecular-dating analysis suggesting a single dispersal into Australia 6.5 million years ago (95% range 13.9-2.7 million years ago). Diversification of the Australian clade commenced more recently, c. 3.1 million years ago (95% range 9.2-1.2 million years ago), perhaps driven by the increased aridification of Australia at this time. The closest relatives to the Australian Vachellia were not from the Malesian bioregion, suggesting either a long-distance dispersal from Africa, or two separate migrations through Asia. These results not only improve our understanding of the biogeography of Vachellia species, but also have significant implications for the biological control of invasive Vachellia species in Australia. © 2020 CSIRO

Light propagation in non-trivial QED vacua

Within the framework of effective action QED, we derive the light cone condition for homogeneous non-trivial QED vacua in the geometric optics approximation. Our result generalizes the ``unified formula'' suggested by Latorre, Pascual and Tarrach and allows for the calculation of velocity shifts and refractive indices for soft photons travelling through these vacua. Furthermore, we clarify the connection between the light velocity shift and the scale anomaly. This study motivates the introduction of a so-called effective action charge that characterizes the velocity modifying properties of the vacuum. Several applications are given concerning vacuum modifications caused by, e.g., strong fields, Casimir systems and high temperature.Comment: 13 pages, REVTeX, 3 figures, to appear in Phys. Rev.

Ornithology of the Kelabit Highlands of Sarawak, Malaysia

The Kelabit Highlands played a key role in the development of modern Bornean ornithology. The Highlands consist of a plateau at 1000-1200 m with substantial wet rice paddy and surrounding taller mountains. These physical features lead to an unusual combination of montane, lowland, and migratory birds. This avifauna was studied in the 1940s to 1950s by two ornithologists whose collaboration helped usher in the modern era of Bornean ornithology: Tom Harrisson of the Sarawak Museum and Dean Amadon of the American Museum of Natural History. We examine their collaboration and explain how these men contributed to Bertram Smythies' milestone book, The Birds of Borneo (1960). Although the roles of Harrisson and Smythies in Bornean ornithology are well known, the contribution of Dean Amadon is not generally appreciated, and we clarify it. In the process, we also consider modern work on the Kelabit avifauna, including our own expedition in 2011, and the current status of Kelabit birds and issues relating to their conservation and potential for further stud

On the stability of Dirac sheet configurations

Using cooling for SU(2) lattice configurations, purely Abelian constant magnetic field configurations were left over after the annihilation of constituents that formed metastable Q=0 configurations. These so-called Dirac sheet configurations were found to be stable if emerging from the confined phase, close to the deconfinement phase transition, provided their Polyakov loop was sufficiently non-trivial. Here we show how this is related to the notion of marginal stability of the appropriate constant magnetic field configurations. We find a perfect agreement between the analytic prediction for the dependence of stability on the value of the Polyakov loop (the holonomy) in a finite volume and the numerical results studied on a finite lattice in the context of the Dirac sheet configurations

Dynamical measure and field theory models free of the cosmological constant problem

Summary of abstract Field theory models including gauge theories with SSB are presented where the energy density of the true vacuum state (TVS) is zero without fine tuning. The above models are constructed in the gravitational theory where a measure of integration \Phi in the action is not necessarily \sqrt{-g} but it is determined dynamically through additional degrees of freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in terms of the matter degrees of freedom due to the existence of a constraint. We study a few explicit field theory models where it is possible to combine the solution of the cosmological constant problem with: 1) possibility for inflationary scenario for the early universe; 2) spontaneously broken gauge unified theories (including fermions). The models are free from the well known problem of the usual scalar-tensor theories in what is concerned with the classical GR tests. The only difference of the field equations in the Einstein frame from the canonical equations of the selfconsistent system of Einstein's gravity and matter fields, is the appearance of the effective scalar field potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander Friedmann International Seminar on Gravitation and Cosmology; accepted for publication in Phys. Rev. D; 31 page

Observations of quasi-periodic solar X-ray emission as a result of MHD oscillations in a system of multiple flare loops

We investigate the solar flare of 20 October 2002. The flare was accompanied by quasi-periodic pulsations (QPP) of both thermal and nonthermal hard X-ray emissions (HXR) observed by RHESSI in the 3-50 keV energy range. Analysis of the HXR time profiles in different energy channels made with the Lomb periodogram indicates two statistically significant time periods of about 16 and 36 seconds. The 36-second QPP were observed only in the nonthermal HXR emission in the impulsive phase of the flare. The 16-second QPP were more pronounced in the thermal HXR emission and were observed both in the impulsive and in the decay phases of the flare. Imaging analysis of the flare region, the determined time periods of the QPP and the estimated physical parameters of magnetic loops in the flare region allow us to interpret the observations as follows. 1) In the impulsive phase energy was released and electrons were accelerated by successive acts with the average time period of about 36 seconds in different parts of two spatially separated, but interacting loop systems of the flare region. 2) The 36-second periodicity of energy release could be caused by the action of fast MHD oscillations in the loops connecting these flaring sites. 3) During the first explosive acts of energy release the MHD oscillations (most probably the sausage mode) with time period of 16 seconds were excited in one system of the flare loops. 4) These oscillations were maintained by the subsequent explosive acts of energy release in the impulsive phase and were completely damped in the decay phase of the flare.Comment: 14 pages, 4 figure

Entanglement and localization of wavefunctions

We review recent works that relate entanglement of random vectors to their localization properties. In particular, the linear entropy is related by a simple expression to the inverse participation ratio, while next orders of the entropy of entanglement contain information about e.g. the multifractal exponents. Numerical simulations show that these results can account for the entanglement present in wavefunctions of physical systems.Comment: 6 pages, 4 figures, to appear in the proceedings of the NATO Advanced Research Workshop 'Recent Advances in Nonlinear Dynamics and Complex System Physics', Tashkent, Uzbekistan, 200

Energy States of Colored Particle in a Chromomagnetic Field

The unitary transformation, which diagonalizes squared Dirac equation in a constant chromomagnetic field is found. Applying this transformation, we find the eigenfunctions of diagonalized Hamiltonian, that describe the states with definite value of energy and call them energy states. It is pointed out that, the energy states are determined by the color interaction term of the particle with the background chromofield and this term is responsible for the splitting of the energy spectrum. We construct supercharge operators for the diagonal Hamiltonian, that ensure the superpartner property of the energy states.Comment: 25 pages, some calculation details have been removed, typos correcte

A LOW COST PHYSICS AND ENGINEERING TRAINING REACTOR. Reactor Design and Feasibility Study

The conceptual design of a low cost training reactor for the instruction of physicists and engineers is covered. It is conceived as an instructional tool for a course such as that given at the Oak Ridge School of Reactor Technology. The reactor is of a modified pool type, and is designed for a maximum power level of one Mw. This arrangement will accommodate engineering experiments, shielding experiments, and critical experiments as well as being useful as a neutron and gamma source. (auth