34,904 research outputs found
Correlation function algebra for inhomogeneous fluids
We consider variational (density functional) models of fluids confined in
parallel-plate geometries (with walls situated in the planes z=0 and z=L
respectively) and focus on the structure of the pair correlation function
G(r_1,r_2). We show that for local variational models there exist two
non-trivial identities relating both the transverse Fourier transform G(z_\mu,
z_\nu;q) and the zeroth moment G_0(z_\mu,z_\nu) at different positions z_1, z_2
and z_3. These relations form an algebra which severely restricts the possible
form of the function G_0(z_\mu,z_\nu). For the common situations in which the
equilibrium one-body (magnetization/number density) profile m_0(z) exhibits an
odd or even reflection symmetry in the z=L/2 plane the algebra simplifies
considerably and is used to relate the correlation function to the finite-size
excess free-energy \gamma(L). We rederive non-trivial scaling expressions for
the finite-size contribution to the free-energy at bulk criticality and for
systems where large scale interfacial fluctuations are present. Extensions to
non-planar geometries are also considered.Comment: 15 pages, RevTex, 4 eps figures. To appear in J.Phys.Condens.Matte
Arrival direction distribution of cosmic rays of energy 10 (18) eV
The Haverah Park air-shower experiment recorded over 8500 events with primary energy 10 to the 18th power eV between 1963 and 1983. An analysis of these events for anisotropies in celestial and galactic coordinates is reported. No very striking anisotropies are observed
Theoretical and numerical studies of chemisorption on a line with precursor layer diffusion
We consider a model for random deposition of monomers on a line with
extrinsic precursor states. As the adsorbate coverage increases, the system
develops non-trivial correlations due to the diffusion mediated deposition
mechanism. In a numeric simulation, we study various quantities describing the
evolution of the island structure. We propose a simple, self-consistent theory
which incorporates pair correlations. The results for the correlations, island
density number, average island size and probabilities of island nucleation,
growth and coagulation show good agreement with the simulation data.Comment: 17 pages(LaTeX), 11 figures(1 PS file, uuencoded), submmited to Phys.
Rev.
Membrane geometry with auxiliary variables and quadratic constraints
Consider a surface described by a Hamiltonian which depends only on the
metric and extrinsic curvature induced on the surface. The metric and the
curvature, along with the basis vectors which connect them to the embedding
functions defining the surface, are introduced as auxiliary variables by adding
appropriate constraints, all of them quadratic. The response of the Hamiltonian
to a deformation in each of the variables is examined and the relationship
between the multipliers implementing the constraints and the conserved stress
tensor of the theory established.Comment: 8 page
Geometrical families of mechanically stable granular packings
We enumerate and classify nearly all of the possible mechanically stable (MS)
packings of bidipserse mixtures of frictionless disks in small sheared systems.
We find that MS packings form continuous geometrical families, where each
family is defined by its particular network of particle contacts. We also
monitor the dynamics of MS packings along geometrical families by applying
quasistatic simple shear strain at zero pressure. For small numbers of
particles (N < 16), we find that the dynamics is deterministic and highly
contracting. That is, if the system is initialized in a MS packing at a given
shear strain, it will quickly lock into a periodic orbit at subsequent shear
strain, and therefore sample only a very small fraction of the possible MS
packings in steady state. In studies with N>16, we observe an increase in the
period and random splittings of the trajectories caused by bifurcations in
configuration space. We argue that the ratio of the splitting and contraction
rates in large systems will determine the distribution of MS-packing
geometrical families visited in steady-state. This work is part of our
long-term research program to develop a master-equation formalism to describe
macroscopic slowly driven granular systems in terms of collections of small
subsystems.Comment: 18 pages, 23 figures, 5 table
Criterion for phase separation in one-dimensional driven systems
A general criterion for the existence of phase separation in driven
one-dimensional systems is proposed. It is suggested that phase separation is
related to the size dependence of the steady-state currents of domains in the
system. A quantitative criterion for the existence of phase separation is
conjectured using a correspondence made between driven diffusive models and
zero-range processes. Several driven diffusive models are discussed in light of
the conjecture
Fracture toughness of the cancellous bone of FNF femoral heads in relation to its microarchitecture
This study considers the relationship between microarchitecture and mechanical properties for cancellous bone specimens collected from a cohort of patients who had suffered fractured necks of femur. OP
is an acute skeletal condition with huge socioeconomic impact [1] and it is associated with changes in both bone quantity and quality [2], which affect greatly the strength and toughness of the tissue [3].Support was provided by the EPSRC (EP/K020196: Point-ofCare High Accuracy Fracture Risk Prediction), the UK Department of Transport under the BOSCOS (Bone Scanning for Occupant Safety) project, and approved by Gloucester and Cheltenham NHS Trust hospitals under ethical consent (BOSCOS – Mr. Curwen CI REC ref 01/179G)
Chemical Nanomachining of Silicon by Gold-Catalyzed Oxidation
A chemical nanomachining process for the rapid, scalable production of
nanostructure assemblies from silicon-on-insulator is demonstrated. The process
is based on the spontaneous, local oxidation of Si induced by Au, which is
selectively evaporated onto the Si surface. The Au-catalyzed oxide forms a
pattern that serves as a robust mask for the underlying Si, enabling the use of
simple wet chemistry to sculpt arrays of nanostructures of diverse shapes
including rings, pillars, wires, and nanopores. The remarkable simplicity of
this chemical nanomachining process makes it widely accessible as an enabling
technique for applications from photonics to biotechnology
Correlation functions in ionic liquid at coexistence with ionic crystal. Results of the Brazovskii-type field theory
Correlation functions in the restricted primitive model are calculated within
a field-theoretic approach in the one-loop self-consistent Hartree
approximation. The correlation functions exhibit damped oscillatory behavior as
found before in the Gaussian approximation [Ciach at. al., J. Chem. Phys. {\bf
118}, 3702 (2003)]. The fluctuation contribution leads to a renormalization of
both the amplitude and the decay length of the correlation functions. The
renormalized quantities show qualitatively different behavior than their
mean-field (MF) counterparts. While the amplitude and the decay length both
diverge in MF when the -line is approached, the renormalized
quantities remain of order of unity in the same dimensionless units down to the
coexistence with the ionic crystal. Along the line of the phase transition the
decay length and the period of oscillations are independent of density, and
their values in units of the diameter of the ions are
and respectively.Comment: 21 pages including 9 figure
Using the stated preference method for the calculation of social discount rate
The aim of this paper is to build the stated preference method into the social discount rate methodology. The first part of the paper presents the results of a survey about stated time preferences through pair-choice decision situations for various topics and time horizons. It is assumed that stated time preferences differ from calculated time preferences and that the extent of stated rates depends on the time period, and on how much respondents are financially and emotionally involved in the transactions. A significant question remains: how can the gap between the calculation and the results of surveys be resolved, and how can the real time preferences of individuals be interpreted using a social time preference rate. The second part of the paper estimates the social time preference rate for Hungary using the results of the survey, while paying special attention to the pure time preference component. The results suggest that the current method of calculation of the pure time preference rate does not reflect the real attitudes of individuals towards future generations
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