335 research outputs found
Effects of Electron Correlations on Hofstadter Spectrum
By allowing interactions between electrons, a new Harper's equation is
derived to examine the effects of electron correlations on the Hofstadter
energy spectra. It is shown that the structure of the Hofstadter butterfly ofr
the system of correlated electrons is modified only in the band gaps and the
band widths, but not in the characteristics of self-similarity and the Cantor
set.Comment: 13 pages, 5 Postscript figure
The structure of fluid trifluoromethane and methylfluoride
We present hard X-ray and neutron diffraction measurements on the polar
fluorocarbons HCF3 and H3CF under supercritical conditions and for a range of
molecular densities spanning about a factor of ten. The Levesque-Weiss-Reatto
inversion scheme has been used to deduce the site-site potentials underlying
the measured partial pair distribution functions. The orientational
correlations between adjacent fluorocarbon molecules -- which are characterized
by quite large dipole moments but no tendency to form hydrogen bonds -- are
small compared to a highly polar system like fluid hydrogen chloride. In fact,
the orientational correlations in HCF3 and H3CF are found to be nearly as small
as those of fluid CF4, a fluorocarbon with no dipole moment.Comment: 11 pages, 9 figure
Sound-propagation gap in fluid mixtures
We discuss the behavior of the extended sound modes of a dense binary
hard-sphere mixture. In a dense simple hard-sphere fluid the Enskog theory
predicts a gap in the sound propagation at large wave vectors. In a binary
mixture the gap is only present for low concentrations of one of the two
species. At intermediate concentrations sound modes are always propagating.
This behavior is not affected by the mass difference of the two species, but it
only depends on the packing fractions. The gap is absent when the packing
fractions are comparable and the mixture structurally resembles a metallic
glass.Comment: Published; withdrawn since ordering in archive gives misleading
impression of new publicatio
FS Poseidon Cruise Report P340 [POS340] TYMAS "Tyrrhenian Sea Massive Sulfides", Messina - Messina, 06.07.-17.07.2006
Phase Separation Based on U(1) Slave-boson Functional Integral Approach to the t-J Model
We investigate the phase diagram of phase separation for the hole-doped two
dimensional system of antiferromagnetically correlated electrons based on the
U(1) slave-boson functional integral approach to the t-J model. We show that
the phase separation occurs for all values of J/t, that is, whether or with J, the Heisenberg coupling constant and t, the hopping
strength. This is consistent with other numerical studies of hole-doped two
dimensional antiferromagnets. The phase separation in the physically
interesting J region, is examined by introducing
hole-hole (holon-holon) repulsive interaction. We find from this study that
with high repulsive interaction between holes the phase separation boundary
tends to remain robust in this low region, while in the high J region, J/t
> 0.4, the phase separation boundary tends to disappear.Comment: 4 pages, 2 figures, submitted to Phys. Rev.
On the Origin of Peak-dip-hump Structure in the In-plane Optical Conductivity of the High Cuprates; Role of Antiferromagnetic Spin Fluctuations of Short Range Order
An improved U(1) slave-boson approach is applied to study the optical
conductivity of the two dimensional systems of antiferromagnetically correlated
electrons over a wide range of hole doping and temperature. Interplay between
the spin and charge degrees of freedom is discussed to explain the origin of
the peak-dip-hump structure in the in-plane conductivity of high
cuprates. The role of spin fluctuations of short range order(spin singlet pair)
is investigated. It is shown that the spin fluctuations of the short range
order can cause the mid-infrared hump, by exhibiting a linear increase of the
hump frequency with the antiferromagnetic Heisenberg coupling strength
Role of spinon and spinon singlet pair excitations on phase transitions in superconductors
We examine the roles of massless Dirac spinon and spin singlet pair
excitations on the phase transition in superconductors. Although the
massless spinon excitations in the presence of the spin singlet pair
excitations do not alter the nature of the phase transition at , that
is, the XY universality class, they are seen to induce an additional attractive
interaction potential between vortices, further stabilizing vortex-antivortex
pairs at low temperature for lightly doped high samples.Comment: 5 pages, 1 figur
Cryo-EM structure of a helicase loading intermediate containing ORC-Cdc6-Cdt1-MCM2-7 bound to DNA
In eukaryotes, the Cdt1-bound replicative helicase core MCM2-7 is loaded onto DNA by the ORC-Cdc6 ATPase to form a prereplicative complex (pre-RC) with an MCM2-7 double hexamer encircling DNA. Using purified components in the presence of ATP-γS, we have captured in vitro an intermediate in pre-RC assembly that contains a complex between the ORC-Cdc6 and Cdt1-MCM2-7 heteroheptamers called the OCCM. Cryo-EM studies of this 14-subunit complex reveal that the two separate heptameric complexes are engaged extensively, with the ORC-Cdc6 N-terminal AAA+ domains latching onto the C-terminal AAA+ motor domains of the MCM2-7 hexamer. The conformation of ORC-Cdc6 undergoes a concerted change into a right-handed spiral with helical symmetry that is identical to that of the DNA double helix. The resulting ORC-Cdc6 helicase loader shows a notable structural similarity to the replication factor C clamp loader, suggesting a conserved mechanism of action
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