671 research outputs found
A new deep-bodied Late Permian actinopterygian fish from the Beaufort Group, South Africa
Anew genus of actinopterygian (ray-finned) fish, Blourugia seeleyi is described from Late Permian (Tatarian) fluvio-lacustrine, siltstone dominated
deposits within the lower Beaufort Group of South Africa. It was originally provisionally assigned to the globally known
genus Atherstonia by Woodward (1893), but indications are that the genus is distinct from Atherstonia on the basis of its deep-bodied form
and the associated skull characters; thus Blourugia seeleyi is placed in Gardiner&Schaeffer’s (1989) Platysomus Group. The new genus is
characterized by a uniquely shaped prominent high triangular posterior blade of the maxilla, dermosphenotic triangular shaped,
pointed marginal teeth, 8–10 branchiostegal rays, flank scales that exhibit a well-developed dermal ornamentation consisting of numerous
transverse ganoine ridges, and the presence of a dermopterotic that contacts the nasal. Blourugia appears to be a primitive
deep-bodied form, basal to lower actinopterygian deep-bodied forms such as Adroichthys, Amphicentrum, Cheirodopsis, Paramesolepis and
Platysomus. As a member of Gardiner & Schaeffer’s Platysomus Group, it is therefore derived relative to stem-actinopterans such as
Howqualepis, Mimia and Moythomasia, and also derived relative to earlier southern African Palaeozoic actinopterygians such as
Atherstonia scutata, Mentzichthys jubbi, Namaichthys schroederi and the newly/recently described lower Beaufort Group taxa
Bethesdaichthys kitchingi and Kompasia delaharpei, but basal to stem-neopterygians such as Australosomus and Saurichthys.South African Council for Geoscienc
A new late Permian ray-finned (actinopterygian) fish from the Beaufort Group, South Africa
Main articleA new genus and species of actinopterygian (ray-finned) fish, Kompasia delaharpei, is described
from Late Permian (Tatarian) fluvio-lacustrine, siltstone dominated deposits within the lower Beaufort
Group of South Africa. It is currently known from two localities on adjoining farms, Wilgerbosch and
Ganora, both in the New Bethesda district of the Eastern Cape Karoo region. The fossils were
recovered from an uncertain formation, possibly closely equivalent to the Balfour Formation, within the
Dicynodon Assemblage Zone. Kompasia delaharpei differs from previously described early
actinopterygians, including the recently described new lower Beaufort Group taxon Bethesdaichthys
kitchingi, on the basis of a combination of skull and post cranial characters. The genus is characterised
by: a uniquely shaped subrectangular posterior blade of the maxilla, a shortened dorsal limb of the
preopercular, and a dermopterotic and dermosphenotic contacting the nasal; furthermore, the
subopercular is equal to or longer than the opercular, the dorsal fin is situated in the posterior third of
the body, slightly behind the position of the anal fin, and the anterior midflank scales exhibit a smooth
dermal pattern or surface, with a number of faint ganoine ridges present parallel to the posterior and
ventral scale margins. Kompasia appears to exhibit a relatively conservative morphology similar to that
in the lower Beaufort Group taxon Bethesdaichthys kitchingi. As such, Kompasia is derived relative
to stem-actinopterans such as Howqualepis, Mimia and Moythomasia, and also derived relative to
earlier southern African Palaeozoic actinopterygians such as Mentzichthys jubbi and Namaichthys
schroederi, but basal to stem-neopterygians such as Australosomus and Saurichthys.Palaeo-Anthropology Scientific Trust; French Embassy in South Africa; Co-operation and Cultural Service
A new actinopterygian fish species from the Late Permian Beaufort Group, South Africa
A new genus and species of actinopterygian (ray-finned) fish, Bethesdaichthys kitchingi, is described from the Tatarian, Late Permian, Lower Beaufort Group of South Africa. Bethesdaichthys is presently known from three localities, two in the New Bethesda and one in the Victoria West districts of the Karoo region respectively. The fossils were recovered from within the Abrahamskraal Formation Tapinocephalus Assemblage Zone at the Victoria West locality, and from an uncertain Formation possibly closely equivalent to the Balfour Formation, within the Dicynodon Assemblage Zone at the New Bethesda sites. Bethesdaichthys kitchingi is a fusiform fish, up to approximately 300mm in total length, with the skull displaying a moderately oblique suspensorium, and a maxilla with a large sub-rectangular postorbital blade. Furthermore there is a complex of four suborbital bones adjacent to the orbit. The pectoral fin is large relative to body size and the tail is heterocercal with an elongate tapered dorsal body lobe. The anterior midflank scales in particular exhibit a distinctive dermal ornamentation consisting of numerous ganoine ridges. The phylogenetics and interrelationships of Bethesdaichthys kitchingiare examined. It appears to exhibit a relatively conservative morphology similar to that found in possibly related Carboniferous taxa such as the South African taxa Australichthys and Willomorichthys. Bethesdaichthys kitchingiis derived relative to stem-actinopterans such as the Howqualepis and Mimia, and also derived relative to southern African Palaeozoic actinoptyerygians such as Mentzichthys jubbi; and Namaichthys schroeden; but basal to stemneopterygians such as Australosomus, Perleldus and Saurichthys.The Council's Research Committee, University of the Witwatersrand; National Research Foundation (NRF); Palaeo-Anthropology Scientific Trust (PAST
A variational Monte Carlo algorithm for lattice gauge theories with continuous gauge groups: a study of (2+1)-dimensional compact QED with dynamical fermions at finite density
Lattice gauge theories coupled to fermionic matter account for many
interesting phenomena in both high energy physics and condensed matter physics.
Certain regimes, e.g. at finite fermion density, are difficult to simulate with
traditional Monte Carlo algorithms due to the so-called sign-problem. We
present a variational, sign-problem-free Monte Carlo method for lattice gauge
theories with continuous gauge groups and apply it to (2+1)-dimensional compact
QED with dynamical fermions at finite density. The variational ansatz is
formulated in the full gauge field basis, i.e. without having to resort to
truncation schemes for the gauge field Hilbert space. The ansatz
consists of two parts: first, a pure gauge part based on Jastrow-type ansatz
states (which can be connected to certain neural-network ansatz states) and
secondly, on a fermionic part based on gauge-field dependent fermionic Gaussian
states. These are designed in such a way that the gauge field integral over all
fermionic Gaussian states is gauge-invariant and at the same time still
efficiently tractable. To ensure the validity of the method we benchmark the
pure gauge part of the ansatz against another variational method and the full
ansatz against an existing Monte Carlo simulation where the sign-problem is
absent. Moreover, in limiting cases where the exact ground state is known we
show that our ansatz is able to capture this behavior. Finally, we study a
sign-problem affected regime by probing density-induced phase transitions.Comment: 14+6 pages, 9+1 figure
Real-time dynamics in 2+1d compact QED using complex periodic Gaussian states
We introduce a class of variational states to study ground state properties
and real-time dynamics in (2+1)-dimensional compact QED. These are based on
complex Gaussian states which are made periodic in order to account for the
compact nature of the gauge field. Since the evaluation of expectation
values involves infinite sums, we present an approximation scheme for the whole
variational manifold. We calculate the ground state energy density for lattice
sizes up to and extrapolate to the thermodynamic limit for the
whole coupling region. Additionally, we study the string tension both by
fitting the potential between two static charges and by fitting the exponential
decay of spatial Wilson loops. As the ansatz does not require a truncation in
the local Hilbert spaces, we analyze truncation effects which are present in
other approaches. The variational states are benchmarked against exact
solutions known for the one plaquette case and exact diagonalization results
for a lattice gauge theory. Using the time-dependent variational
principle, we study real-time dynamics after various global quenches, e.g. the
time evolution of a strongly confined electric field between two charges after
a quench to the weak-coupling regime. Up to the points where finite size
effects start to play a role, we observe equilibrating behavior.Comment: 20 pages, 16 figures, v2: as publishe
Engineering long-range molecular potentials by external drive
We report the engineering of molecular potentials at large interatomic
distances. The molecular states are generated by off-resonant optical coupling
to a highly excited, long-range Rydberg molecular potential. The coupling
produces a potential well in the low-lying molecular potential, which supports
a bound state. The depth of the potential well, and thus the binding energy of
the molecule, can be tuned by the coupling parameters. We characterize these
molecules and find good agreement with a theoretical model based on the
coupling of the two involved adiabatic potential energy curves. Our results
open numerous possibilities to create long-range molecules between ultracold
ground state atoms and to use them for ultracold chemistry and applications
such as Feshbach resonances, Efimov physics or the study of halo molecules
Genetic Analysis of Putative Familial Relationships in a Captive Chimpanzee (Pan troglodytes) Population
Twelve autosomal dinucleotide repeat loci were analyzed in chimpanzees genomes by DNA amplification using primers designed for analysis of human loci. The markers span the entire length of human chromosomes 21 and 22. Nine markers were polymorphic in chimpanzee as well, with a somewhat comparable level of polymorphism and allele size range. Even in the presence of very limited information and in spite of missing samples, it was possible to reconstruct a complex pedigree and to provide molecular data that corroborate family relationships that were deduced from cage history
and behavioral data. The conclusions were further supported by mitochondrial DNA analysis. The data presented in this report show that the extremely abundant source of human markers may be exploited to validate, with molecular evidence, hypotheses on individual relationship or alleged pedigrees, based upon behavioral observations
Genetic Analysis of Putative Familial Relationships in a Captive Chimpanzee (\u3ci\u3ePan troglodytes\u3c/i\u3e) Population
Twelve autosomal dinucleotide repeat loci were analyzed in chimpanzees genomes by DNA amplification using primers designed for analysis of human loci. The markers span the entire length of human chromosomes 21 and 22. Nine markers were polymorphic in chimpanzee as well, with a somewhat comparable level of polymorphism and allele size range. Even in the presence of very limited information and in spite of missing samples, it was possible to reconstruct a complex pedigree and to provide molecular data that corroborate family relationships that were deduced from cage history and behavioral data. The conclusions were further supported by mitochondrial DNA analysis. The data presented in this report show that the extremely abundant source of human markers may be exploited to validate, with molecular evidence, hypotheses on individual relationship or alleged pedigrees, based upon behavioral observations
Griffiths Phase in a Facilitated Rydberg Gas at Low Temperature
The spread of excitations by Rydberg facilitation bears many similarities to
epidemics. Such systems can be modeled with Monte-Carlo simulations of
classical rate equations to great accuracy as a result of high dephasing. In
this paper, we analyze the dynamics of a Rydberg many-body system in the
facilitation regime in the limits of high and low temperatures. While in the
high-temperature limit a homogeneous mean-field behaviour is recovered,
characteristic effects of heterogeneity can be seen in a frozen gas. At large
temperatures the system displays an absorbing-state phase transition and, in
the presence of an additional loss channel, self-organized criticality. In a
frozen or low-temperature gas, excitations are constrained to a network
resembling an Erd\"os-Renyi graph. We show that the absorbing-state phase
transition is replaced with an extended Griffiths phase, which we accurately
describe by a susceptible-infected-susceptible model on the Erd\"os-Renyi
network taking into account Rydberg blockade. Furthermore, we expand upon an
existing macroscopic Langevin equation to more accurately describe the density
of Rydberg atoms in the frozen and finite temperature regimes.Comment: 14 pages, 11 figure
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