An exact solution of the metric-affine gauge theory with dilation, shear, and spin charges

The spacetime of the metric-affine gauge theory of gravity (MAG) encompasses {\it nonmetricity} and {\it torsion} as post-Riemannian structures. The sources of MAG are the conserved currents of energy-momentum and dilation, shear and spin. We present an exact static spherically symmetric vacuum solution of the theory describing the exterior of a lump of matter carrying mass and dilation, shear and spin charges.Comment: 13 pages, RevTe

Density and conformation with relaxed substrate, bulk, and interface electrophoretic deposition of polymer chains

Characteristics of relaxed density profile and conformation of polymer chains are studied by a Monte Carlo simulation on a discrete lattice in three dimensions using different segmental (kink-jump $K$, crank-shaft $C$, reptation $R$) dynamics. Three distinct density regimes, substrate, bulk, and interface, are identified. With the $KC$ segmental dynamics we find that the substrate coverage grows with a power-law, $d_s \propto t^{\gamma}$ with a field dependent nonuniversal exponent $\gamma = 0.23 + 0.7 E$. The bulk volume fraction $d_b$ and the substrate polymer density ($d_s$) increases exponentially with the field ($d_b \propto E^{0.4}$, $d_s \propto E^{0.2}$) in the low field regime. The interface polymer density $d_f$ increases with the molecular weight. With the $KCR$ segmental dynamics, bulk and substrate density decreases linearly with the temperature at high temperatures. The bulk volume fraction is found to decay with the molecular weight, $d_b \propto L_c^{-0.11}$. The radius of gyration remains Gaussian in all density regions.Comment: Changed double to single spacin

Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates

We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor, using high precision torsional oscillator and DC calorimetry techniques. Our investigation focused on the onset of superfluidity at low temperatures as the 4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel system were used to determine the superfluid density of films with transition temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor system probed the excitation spectrum of both non-superfluid and superfluid films for temperatures down to 10 mK. Both sets of measurements suggest that the critical coverage for the onset of superfluidity corresponds to a mobility edge in the chemical potential, so that the onset transition is the bosonic analog of a superconductor-insulator transition. The superfluid density measurements, however, are not in agreement with the scaling theory of an onset transition from a gapless, Bose glass phase to a superfluid. The heat capacity measurements show that the non-superfluid phase is better characterized as an insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript

Contribution to the Knowledge of the Floral Structure in Sabal palmetto (Walter) Lodd. Ex Schult. (Arecaceae: Coryphoideae)

The floral structure of the neotropical palm Sabal palmetto is described. The species is characterized by the presence of hermaphrodite solitary flowers; congenitally united imbricate sepals and free imbricate petals. The six stamens are fertile, with filaments congenitally united towards the base. Contrary to previous reports indicating complete syncarpy, the three carpels are free in the basal region and postgenitally fused above the level of the septal nectary; they are ascidiate throughout the ovary and plicate from the style base up to the stigma. Our study supports the close relationships between Sabaleae and the rest of Cryosophileae

The roles of dispersal and mass extinction in shaping palm diversity across the Caribbean

Aim: The rich flora of the Caribbean islands and surrounding mainland evolved in a context of isolation alternated with phases of terrestrial connectivity between landmasses, climatic fluctuations and episodes of mass extinctions during the Cenozoic. We explored how these events affected the evolution of the sister palm tribes Cryosophileae and Sabaleae, and how continent-island exchanges, endemic radiations and mass extinction shaped their extant diversity. Location: The American continent including the Caribbean region. Methods: We reconstructed a time-calibrated phylogeny of the palm tribes Cryosophileae and Sabaleae using 84% of the known species. We inferred ancestral distribution and tested the effect of island colonization and mass extinction on extant diversity. Results: Our results indicate that Cryosophileae and Sabaleae originated c. 77 Ma most probably in Laurasia, and their extant species started to diversify between 5635 Ma and 19-10 Ma respectively. Biogeographical state reconstruction estimated that Cryosophileae dispersed to South America between 56-35 Ma, then dispersed to North-Central America between 39-25 Ma and the Caribbean islands between 3421 Ma. We detected a possible signature of a mass extinction event at the end of the Eocene, affecting the diversification of Cryosophileae and Sabaleae and we did not detect a diversification rate shift related to the colonization of the Caribbean islands. Main conclusions: Species of Cryosophileae in the Caribbean islands are probably derived from a single Oligocene dispersal event that likely occurred overwater from North-Central America rather than through the hypothesized GAARlandia land bridge. Contrastingly, three independent Miocene dispersal events from North-Central America explain the occurrence of Sabaleae in the Caribbean islands. Contrary to our expectations, island colonization did not trigger increased diversification. Instead, we find that diversification patterns in this clade, and its disappearance from northernmost latitudes, could be the signature of a mass extinction triggered by the global temperature decline at the end of the Eocene

Evaluation of palm swamps palaeocology related to past climatic and human practices variability: The study case of the Orinoco Delta

PROJECT AIMS: The paucity of palaeoecological data is acute in the Neotropics, where the low number of good quality records (with reliable dating and continuous sedimentation) prevents the development of a regional understanding of the vegetation and climate dynamics. Within the Neotropics, low wetlands are particularly poorly known due to the scarcity of potential archives. We present here an ongoing project designed to improve the understanding of wetland forests' responses to changes in climatic and human variability by studying their long-term dynamics. The project will focus on specific scales for maximising the accuracy of the outputs: I) the geographic area (northern South American wetlands), and ii) the time period (last 6 kyr). The region has been chosen because of the occurrence of globally important big wetland areas dominated by the palm Mauritania flexuosa and the perceived threats to the fluvial-linked systems. Within this broad area, two specific locations have been chosen that represent the northern limit of M. flexuosa current distribution. Time frame has been selected to allow: i) the comparison between intervals with and without human activity, and ii) covering the establishment of Mauritania which will allow a better understanding of the current trends (communities in expansion or reduction). The knowledge of past interactions between wetlands, seasonality changes and human practices will provide new insights into how this poorly understood community could face future projections of climatic and land use changes. In addition, emphasis will be placed on studying what influenced the composition of modern plant communities, to analyse their sensitivity to external drivers and to identify the occurrence of irreversible tipping points or thresholds in the recent past. The research will be addressed by using a combination of indicators (proxies) of past environmental change in sedimentary sequences, including: vegetation (pollen), erosion/run-off/sedimentation (palaeomagnetism, XRD), and human impacts (non-pollen palynomorphs, charcoal particles). Funding project reference: 2014 BP-B-00094.Peer Reviewe