10,065 research outputs found
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
Perturbation theory of the mass enhancement for a polaron coupled to acoustic phonons
We use both a perturbative Green's function analysis and standard
perturbative quantum mechanics to calculate the decrease in energy and the
effective mass for an electron interacting with acoustic phonons. The
interaction is between the difference in lattice displacements for neighbouring
ions, and the hopping amplitude for an electron between those two sites. The
calculations are performed in one, two, and three dimensions, and comparisons
are made with results from other electron-phonon models. We also compute the
spectral function and quasiparticle residue, as a function of characteristic
phonon frequency. There are strong indications that this model is always
polaronic on one dimension, where an unusual relation between the effective
mass and the quasiparticle residue is also found.Comment: 9 pages, 5 figures, submitted to PR
Thermodynamic equilibrium and its stability for Microcanonical systems described by the Sharma-Taneja-Mittal entropy
It is generally assumed that the thermodynamic stability of equilibrium state
is reflected by the concavity of entropy. We inquire, in the microcanonical
picture, on the validity of this statement for systems described by the
bi-parametric entropy of Sharma-Taneja-Mittal. We analyze
the ``composability'' rule for two statistically independent systems, A and B,
described by the entropy with the same set of the deformed
parameters. It is shown that, in spite of the concavity of the entropy, the
``composability'' rule modifies the thermodynamic stability conditions of the
equilibrium state. Depending on the values assumed by the deformed parameters,
when the relation holds (super-additive systems), the concavity
conditions does imply the thermodynamics stability. Otherwise, when the
relation holds (sub-additive systems), the concavity
conditions does not imply the thermodynamical stability of the equilibrium
state.Comment: 13 pages, two columns, 1 figure, RevTex4, version accepted on PR
Implementation of the Hierarchical Reference Theory for simple one-component fluids
Combining renormalization group theoretical ideas with the integral equation
approach to fluid structure and thermodynamics, the Hierarchical Reference
Theory is known to be successful even in the vicinity of the critical point and
for sub-critical temperatures. We here present a software package independent
of earlier programs for the application of this theory to simple fluids
composed of particles interacting via spherically symmetrical pair potentials,
restricting ourselves to hard sphere reference systems. Using the hard-core
Yukawa potential with z=1.8/sigma for illustration, we discuss our
implementation and the results it yields, paying special attention to the core
condition and emphasizing the decoupling assumption's role.Comment: RevTeX, 16 pages, 2 figures. Minor changes, published versio
Derivation of Boltzmann Principle
We present a derivation of Boltzmann principle
based on classical mechanical models of thermodynamics. The argument is based
on the heat theorem and can be traced back to the second half of the nineteenth
century with the works of Helmholtz and Boltzmann. Despite its simplicity, this
argument has remained almost unknown. We present it in a modern, self-contained
and accessible form. The approach constitutes an important link between
classical mechanics and statistical mechanics
DE 1 RIMS operational characteristics
The Retarding Ion Mass Spectrometer (RIMS) on the Dynamics Explorer 1 spacecraft observes both the thermal and superthermal (50 eV) ions of the ionosphere and inner magnetosphere. It is capable of measuring the detailed species distribution function of these ions in many cases. It was equipped with an integral electrometer to permit in-flight calibration of the detector sensitivities and variations thereof. A guide to understanding the RIMS data set is given. The reduction process from count rates to physical quantities is discussed in some detail. The procedure used to establish in-flight calibration is described, and results of a comparison with densities from plasma wave measurements are provided. Finally, a discussion is provided of various anomalies in the data set, including changes of channeltron efficiency with time, spin modulation of the axial sensor heads, apparent potential differences between the sensor heads, and failures of the radial head retarding potential sweep and of the -Z axial head aperture plane bias. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented here, or in collaboration with one of the scientists actively involved with RIMS data analysis
Entropy and density of states from isoenergetic nonequilibrium processes
Two identities in statistical mechanics involving entropy differences (or
ratios of density of states) at constant energy are derived. The first provides
a nontrivial extension of the Jarzynski equality to the microcanonical ensemble
[C. Jarzynski, Phys. Rev. Lett. 78, 2690 (1997)], which can be seen as a
``fast-switching'' version of the adiabatic switching method for computing
entropies [M. Watanabe, W. P. Reinhardt, Phys. Rev. Lett. 65, 3301 (1990)]. The
second is a thermodynamic integration formula analogous to a well-known
expression for free energies, and follows after taking the quasistatic limit of
the first. Both identities can be conveniently used in conjunction with a
scaling relation (herein derived) that allows one to extrapolate measurements
taken at a single energy to a wide range of energy values. Practical aspects of
these identities in the context of numerical simulations are discussed.Comment: 5 pages, no figure
Estimation of near-surface attenuation in bedrock for analysis of intraplate seismic hazard
The significance of near-surface attenuation in bedrock, as distinct from attenuation in unconsolidated soft soil sediments, has been identified. The k parameter, which characterizes the extent of this attenuation mechanism, is generally difficult to measure, particularly in regions of low and moderate seismicity. Empirical correlation of k with the near-surface shear wave velocity parameter in rock has been developed using global information obtained from limited independent studies. The influence of shaking intensity on the value of k has been found to be negligible in conditions that are consistent with the average seismicity of Australia (as also for other intraplate regions). Thus, adjustment in the value of k to account for variations in earthquake magnitude, or the intensity of ground shaking, has not been recommended for intraplate conditions. In parallel with the empirical correlations, values of k have also been obtained from calibration analyses employing stochastic simulations of the seismological model, along with onedimensional non-linear shear wave analyses of the rock layers. Good agreement in the values of k obtained from the different approaches has been demonstrated. The correlation of k with the near-surface shear wave velocity of rock, as recommended in this paper, has thereby been reaffirmed
COP 26: Pavilion Proposals
There is considerable interest in having a Peatland Pavilion at the up-coming UNFCCC COP26 to be held in Glasgow in November 2021. The purpose of the pavilion would be to provide a focus for discussions about the increasingly recognised importance of peatlands and their role as major global stores of soil carbon but also, in their damaged state, as large sources of carbon emissions. UEL Architecture Masters students were set the task of developing potential designs for such a pavilion with the requirement that it incorporate an installation designed by the artist and UEL lecturer Michael Pinsky. The architectural concept drawn up by Hussein Ail Kassim and Mohammed Patel offers some thought-provoking ideas for such a Peatland Pavilion and thus opens up the debate about what form, both conceptually and architecturally, such a pavilion might take. It is worth highlighting that the themes of the different environment domes envisaged by Hussein and Mohammed can each be related to particular aspects of importance to peatlands
- …