1,765 research outputs found
A Comparative Study of Mammalian Diversification Pattern
Although mammals have long been regarded as a successful radiation, the diversification pattern among the clades is still poorly known. Higher-level phylogenies are conflicting and comprehensive comparative analyses are still lacking. Using a recently published supermatrix encompassing nearly all extant mammalian families and a novel comparative likelihood approach (MEDUSA), the diversification pattern of mammalian groups was examined. Both order- and family-level phylogenetic analyses revealed the rapid radiation of Boreoeutheria and Euaustralidelphia in the early mammalian history. The observation of a diversification burst within Boreoeutheria at approximately 100 My supports the Long Fuse model in elucidating placental diversification progress, and the rapid radiation of Euaustralidelphia suggests an important role of biogeographic dispersal events in triggering early Australian marsupial rapid radiation. Diversification analyses based on family-level diversity tree revealed seven additional clades with exceptional diversification rate shifts, six of which represent accelerations in net diversification rate as compared to the background pattern. The shifts gave origin to the clades Muridae+Cricetidae, Bovidae+Moschidae+Cervidae, Simiiformes, Echimyidae, Odontoceti (excluding Physeteridae+Kogiidae+Platanistidae), Macropodidae, and Vespertilionidae. Moderate to high extinction rates from background and boreoeutherian diversification patterns indicate the important role of turnovers in shaping the heterogeneous taxonomic richness observed among extant mammalian groups. Furthermore, the present results emphasize the key role of extinction on erasing unusual diversification signals, and suggest that further studies are needed to clarify the historical radiation of some mammalian groups for which MEDUSA did not detect exceptional diversification rates
Large shift current via in-gap and charge-neutral exciton excitations in BN nanotubes and single BN layer
We perform {\it ab initio} many-body calculations to investigate the exciton
shift current in small diameter zigzag BN nanotubes and also single BN sheet,
using the GW plus Bethe-Salpeter equation (GW-BSE) method with the newly
developed efficient algorithms. Our GW-BSE calculations reveal a giant in-gap
peak in the shift current spectrum in all the studied BN systems due to the
excitation of the A exciton. The peak value of the excitonic shift current is
more than three times larger than that of the quasiparticle shift current, and
is attributed to the gigantic enhancement of the optical dipole matrix element
by the A exciton resonance. The effective exciton shift current conductivity is
nearly ten times larger than the largest shift conductivity observed in
ferroelectric semiconductors. Importantly, the direction of the shift current
in the BN nanotubes is found to be independent of the tube chirality ()
(or diameter), contrary to the simple rule of predicted by previous model Hamiltonian
studies. Finally, our {\it ab initio} calculations also show that the exciton
excitation energies decrease significantly with the decreasing diameter due to
the curvature-induced orbital rehybridization in small diameter zigzag BN
nanotubes.Comment: 12 pages, 8 figures and 2 table
A Study of Lateral Bearing Capacity of Pile by Dynamic Test
In order to improve the knowledge of the Lateral Loading behavior of artificially drilled cast-in-place concrete piles, the full-scale lateral static and dynamic loading tests of eleven piles had been carried out by the authors in Louyang, China. In this paper, the principle of laterally dynamic pile test is discussed. The results of the static and dynamic tests performed in the light of different diameter piles are analyzed comparatively. It is found that the critical loads defined by the dynamic testing are almost identical with results of the static testing ones. Thus we come to a conclusion that the lateral critical loading of the single pile in the area can be determined by dynamic testing method
Minimal effective model and possible high- mechanism for superconductivity of LaNiO under high pressure
The recent discovery of high- superconductivity in bilayer nickelate
LaNiO under high pressure has stimulated great interest
concerning its pairing mechanism. We argue that the weak coupling model from
the almost fully-filled bonding band cannot give rise to its high
, and thus propose a strong coupling model based on local inter-layer
spin singlets of Ni- electrons due to their strong on-site Coulomb
repulsion. This leads to a minimal effective model that contains local pairing
of electrons and a considerable hybridization with near
quarter-filled itinerant electrons on nearest-neighbor sites.
The strong coupling between two components provides a composite scenario to
achieve high- superconductivity. Our theory highlights the importance of
the bilayer structure of superconducting LaNiO and points out
a potential route for the exploration of more high- superconductors.Comment: 6 pages, 3 figure
A convenient basis for the Izergin-Korepin model
We propose a convenient orthogonal basis of the Hilbert space for the
Izergin-Korepin model (or the quantum spin chain associated with the
algebra). It is shown that the monodromy-matrix elements acting
on the basis take relatively simple forms (c.f. acting on the original basis ),
which is quite similar as that in the so-called F-basis for the quantum spin
chains associated with -type (super)algebras. As an application, we present
the recursive expressions of Bethe states in the basis for the Izergin-Korepin
model.Comment: 24 pages, no figure
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