9,438 research outputs found
Phase separation of a multiple occupancy lattice gas
A binary lattice gas model that allows for multiple occupancy of lattice
sites, inspired by recent coarse-grained descriptions of solutions of
interacting polymers, is investigated by combining the steepest descent
approximation with an exploration of the multidimensional energy landscape, and
by Gibbs ensemble Monte Carlo simulations. The one-component version of the
model, involving on site and nearest neighbour interactions, is shown to
exhibit microphase separation into two sub-lattices with different mean
occupation numbers. The symmetric two-component version of the multiple
occupancy lattice gas is shown to exhibit a demixing transition into two phases
above a critical mean occupation number.Comment: submitted to Journal of Physics
The self-assembly of DNA Holliday junctions studied with a minimal model
In this paper, we explore the feasibility of using coarse-grained models to
simulate the self-assembly of DNA nanostructures. We introduce a simple model
of DNA where each nucleotide is represented by two interaction sites
corresponding to the phosphate-sugar backbone and the base. Using this model,
we are able to simulate the self-assembly of both DNA duplexes and Holliday
junctions from single-stranded DNA. We find that assembly is most successful in
the temperature window below the melting temperatures of the target structure
and above the melting temperature of misbonded aggregates. Furthermore, in the
case of the Holliday junction, we show how a hierarchical assembly mechanism
reduces the possibility of becoming trapped in misbonded configurations. The
model is also able to reproduce the relative melting temperatures of different
structures accurately, and allows strand displacement to occur.Comment: 13 pages, 14 figure
Multiple Quantum Oscillations in the de Haas van Alphen Spectra of the Underdoped High Temperature Superconductor YBa_2Cu_3O_6.5
By improving the experimental conditions and extensive data accumulation, we
have achieved very high-precision in the measurements of the de Haas-van Alphen
effect in the underdoped high-temperature superconductor
YBaCuO. We find that the main oscillation, so far believed
to be single-frequency, is composed of three closely spaced frequencies. We
attribute this to bilayer splitting and warping of a single quasi-2D Fermi
surface, indicating that \emph{c}-axis coherence is restored at low temperature
in underdoped cuprates. Our results do not support the existence of a larger
frequency of the order of 1650 T reported recently in the same compound [S.E.
Sebastian {\it et al}., Nature {\bf 454}, 200 (2008)]
Two types of nematicity in the phase diagram of the cuprate superconductor YBaCuO
Nematicity has emerged as a key feature of cuprate superconductors, but its
link to other fundamental properties such as superconductivity, charge order
and the pseudogap remains unclear. Here we use measurements of transport
anisotropy in YBaCuO to distinguish two types of nematicity. The
first is associated with short-range charge-density-wave modulations in a
doping region near . It is detected in the Nernst coefficient, but
not in the resistivity. The second type prevails at lower doping, where there
are spin modulations but no charge modulations. In this case, the onset of
in-plane anisotropy - detected in both the Nernst coefficient and the
resistivity - follows a line in the temperature-doping phase diagram that
tracks the pseudogap energy. We discuss two possible scenarios for the latter
nematicity.Comment: 8 pages and 7 figures. Main text and supplementary material now
combined into single articl
Onset of a boson mode at superconducting critical point of underdoped YBa2Cu3Oy
The thermal conductivity of underdoped \Y was measured in the limit as a function of hole concentration across the superconducting
critical point at = 5.0%. ``Time doping'' was used to resolve the
evolution of bosonic and fermionic contributions with high accuracy. For , we observe an additional contribution to
which we attribute to the boson excitations of a phase with long-range spin or
charge order. Fermionic transport, manifest as a linear term in , is
seen to persist unaltered through , showing that the state just below
is a thermal metal. In this state, the electrical resistivity varies
as log and the Wiedemann-Franz law is violated
Structure and thermodynamics of colloid-polymer mixtures: a macromolecular approach
The change of the structure of concentrated colloidal suspensions upon
addition of non-adsorbing polymer is studied within a two-component,
Ornstein-Zernicke based liquid state approach. The polymers' conformational
degrees of freedom are considered and excluded volume is enforced at the
segment level. The polymer correlation hole, depletion layer, and excess
chemical potentials are described in agreement with polymer physics theory in
contrast to models treating the macromolecules as effective spheres. Known
depletion attraction effects are recovered for low particle density, while at
higher densities novel many-body effects emerge which become dominant for large
polymers.Comment: 7 pages, 4 figures; to be published in Europhys. Let
Metallization of Fluid Hydrogen
The electrical resistivity of liquid hydrogen has been measured at the high
dynamic pressures, densities and temperatures that can be achieved with a
reverberating shock wave. The resulting data are most naturally interpreted in
terms of a continuous transition from a semiconducting to a metallic, largely
diatomic fluid, the latter at 140 GPa, (ninefold compression) and 3000 K. While
the fluid at these conditions resembles common liquid metals by the scale of
its resistivity of 500 micro-ohm-cm, it differs by retaining a strong pairing
character, and the precise mechanism by which a metallic state might be
attained is still a matter of debate. Some evident possibilities include (i)
physics of a largely one-body character, such as a band-overlap transition,
(ii) physics of a strong-coupling or many-body character,such as a Mott-Hubbard
transition, and (iii) processes in which structural changes are paramount.Comment: 12 pages, RevTeX format. Figures available on request; send mail to:
[email protected] To appear: Philosophical Transaction of the Royal
Society
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Clinical Classification of Borderline Cases in the Family Study of Essential Tremor: An Analysis of Phenotypic Features
Background: In genetic research on essential tremor (ET), certain individuals may be particularly challenging to categorize diagnostically.
Methods: In the Family Study of Essential Tremor (>200 enrollees), 28 participants with borderline clinical findings who did not meet strict criteria for ET were assigned final diagnoses of ET. We scrutinized the clinical features of these cases and the sensitivity/specificity of certain features that best separated them from 19 unaffected individuals.
Results: Borderline ET cases differed from unaffected individuals in eight features: total tremor score, at least one kinetic tremor rating ≥1.5, at least one kinetic tremor rating ≥1.5 in the dominant arm, tremor rating during spiral drawing ≥1.5, higher spiral axis score, head tremor, complaint of tremor, and comment on tremor by others. The combination of at least one kinetic tremor rating ≥1.5 in the dominant arm and the presence of at least three of the remaining seven features predicted the clinician‐assigned diagnosis in 88.6% of borderline ET vs. unaffected individuals (sensitivity 84.6%, specificity 94.4%).
Discussion: In a family study, a small number of clinical features characterized borderline ET, and a particular combination of these separated the majority of these borderline cases from normals. These analyses may help researchers minimize diagnostic misclassification
Influence of polymer excluded volume on the phase behavior of colloid-polymer mixtures
We determine the depletion-induced phase-behavior of hard sphere colloids and
interacting polymers by large-scale Monte Carlo simulations using very accurate
coarse-graining techniques. A comparison with standard Asakura-Oosawa model
theories and simulations shows that including excluded volume interactions
between polymers leads to qualitative differences in the phase diagrams. These
effects become increasingly important for larger relative polymer size. Our
simulations results agree quantitatively with recent experiments.Comment: 5 pages, 4 figures submitted to Physical Review Letter
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