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Two results on evolutionary processes on general non-directed graphs
Structural and Physical Properties of CaFe4As3 Single Crystals
We report the synthesis, and structural and physical properties of CaFe4As3
single crystals. Needle-like single crystals of CaFe4As3 were grown out of Sn
flux and the compound adopts an orthorhombic structure as determined by X-ray
diffraction measurements. Electrical, magnetic, and thermal properties indicate
that the system undergoes two successive phase transitions occurring at TN1 ~
90 K and TN2 ~ 26 K. At TN1, electrical resistivities (\rho(b) and \rho(ac))
are enhanced while magnetic susceptibilities (\chi(b) and \chi(ac)) are reduced
in both directions parallel and perpendicular to the b-axis, consistent with
the scenario of antiferromagnetic spin-density-wave formation. At TN2, specific
heat reveals a slope change, and \chi(ac) decreases sharply but \chi(b) has a
clear jump before it decreases again with decreasing temperature. Remarkably,
both \rho(b) and \rho(ac) decrease sharply with thermal hysteresis, indicating
the first-order nature of the phase transition at TN2. At low temperatures,
\rho(b) and \rho(ac) can be described by {\rho} = {\rho}0 + AT^\alpha ({\rho}0,
A, and {\alpha} are constants). Interestingly, these constants vary with
applied magnetic field. The ground state of CaFe4As3 is discussed.Comment: 15 pages, 8 figures, Submitted to Physical Review
Covariant equations for the three-body bound state
The covariant spectator (or Gross) equations for the bound state of three
identical spin 1/2 particles, in which two of the three interacting particles
are always on shell, are developed and reduced to a form suitable for numerical
solution. The equations are first written in operator form and compared to the
Bethe-Salpeter equation, then expanded into plane wave momentum states, and
finally expanded into partial waves using the three-body helicity formalism
first introduced by Wick. In order to solve the equations, the two-body
scattering amplitudes must be boosted from the overall three-body rest frame to
their individual two-body rest frames, and all effects which arise from these
boosts, including the Wigner rotations and rho-spin decomposition of the
off-shell particle, are treated exactly. In their final form, the equations
reduce to a coupled set of Faddeev-like double integral equations with
additional channels arising from the negative rho-spin states of the off-shell
particle.Comment: 57 pages, RevTeX, 6 figures, uses epsf.st
Triton calculations with and exchange three-nucleon forces
The Faddeev equations are solved in momentum space for the trinucleon bound
state with the new Tucson-Melbourne and exchange three-nucleon
potentials. The three-nucleon potentials are combined with a variety of
realistic two-nucleon potentials. The dependence of the triton binding energy
on the cut-off parameter in the three-nucleon potentials is studied
and found to be reduced compared to the case with pure exchange. The
exchange parts of the three-nucleon potential yield an overall repulsive
effect. When the recommended parameters are employed, the calculated triton
binding energy turns out to be very close to its experimental value.
Expectation values of various components of the three-nucleon potential are
given to illustrate their significance for binding.Comment: 17 pages Revtex 3.0, 4 figures. Accepted for publication in Phys.
Rev.
Three-Nucleon Force and the -Mechanism for Pion Production and Pion Absorption
The description of the three-nucleon system in terms of nucleon and
degrees of freedom is extended to allow for explicit pion production
(absorption) from single dynamic de-excitation (excitation) processes.
This mechanism yields an energy dependent effective three-body hamiltonean. The
Faddeev equations for the trinucleon bound state are solved with a force model
that has already been tested in the two-nucleon system above pion-production
threshold. The binding energy and other bound state properties are calculated.
The contribution to the effective three-nucleon force arising from the pionic
degrees of freedom is evaluated. The validity of previous coupled-channel
calculations with explicit but stable isobar components in the
wavefunction is studied.Comment: 23 pages in Revtex 3.0, 9 figures (not included, available as
postscript files upon request), CEBAF-TH-93-0
Long-term follow up after non-myeloablative allogeneic stem cell transplantation for renal cell carcinoma: the university of Chicago experience
Landscape statistics of the low autocorrelated binary string problem
The statistical properties of the energy landscape of the low autocorrelated
binary string problem (LABSP) are studied numerically and compared with those
of several classic disordered models. Using two global measures of landscape
structure which have been introduced in the Simulated Annealing literature,
namely, depth and difficulty, we find that the landscape of LABSP, except
perhaps for a very large degeneracy of the local minima energies, is
qualitatively similar to some well-known landscapes such as that of the
mean-field 2-spin glass model. Furthermore, we consider a mean-field
approximation to the pure model proposed by Bouchaud and Mezard (1994, J.
Physique I France 4 1109) and show both analytically and numerically that it
describes extremely well the statistical properties of LABSP
Momentum and Coordinate Space Three-nucleon Potentials
In this paper we give explicit formulae in momentum and coordinate space for
the three-nucleon potentials due to and meson exchange, derived
from off-mass-shell meson-nucleon scattering amplitudes which are constrained
by the symmetries of QCD and by the experimental data. Those potentials have
already been applied to nuclear matter calculations. Here we display additional
terms which appear to be the most important for nuclear structure. The
potentials are decomposed in a way that separates the contributions of
different physical mechanisms involved in the meson-nucleon amplitudes. The
same type of decomposition is presented for the TM force: the
, the chiral symmetry breaking and the nucleon pair terms are isolated.Comment: LATEX, 33 pages, 3 figures (available as postscript files upon
request
Ancient Yersinia pestis genomes from across Western Europe reveal early diversification during the First Pandemic (541â750)
The first historically documented pandemic caused by Yersinia pestis began as the Justinianic Plague in 541 within the Roman Empire and continued as the so-called First Pandemic until 750. Although paleogenomic studies have previously identified the causative agent as Y. pestis, little is known about the bacteriumâs spread, diversity, and genetic history over the course of the pandemic. To elucidate the microevolution of the bacterium during this time period, we screened human remains from 21 sites in Austria, Britain, Germany, France, and Spain for Y. pestis DNA and reconstructed eight genomes. We present a methodological approach assessing single-nucleotide polymorphisms (SNPs) in ancient bacterial genomes, facilitating qualitative analyses of low coverage genomes from a metagenomic background. Phylogenetic analysis on the eight reconstructed genomes reveals the existence of previously undocumented Y. pestis diversity during the sixth to eighth centuries, and provides evidence for the presence of multiple distinct Y. pestis strains in Europe. We offer genetic evidence for the presence of the Justinianic Plague in the British Isles, previously only hypothesized from ambiguous documentary accounts, as well as the parallel occurrence of multiple derived strains in central and southern France, Spain, and southern Germany. Four of the reported strains form a polytomy similar to others seen across the Y. pestis phylogeny, associated with the Second and Third Pandemics. We identified a deletion of a 45-kb genomic region in the most recent First Pandemic strains affecting two virulence factors, intriguingly overlapping with a deletion found in 17th- to 18th-century genomes of the Second Pandemic. © 2019 National Academy of Sciences. All rights reserved
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