4,061 research outputs found
Critical Exponents for Diluted Resistor Networks
An approach by Stephen is used to investigate the critical properties of
randomly diluted resistor networks near the percolation threshold by means of
renormalized field theory. We reformulate an existing field theory by Harris
and Lubensky. By a decomposition of the principal Feynman diagrams we obtain a
type of diagrams which again can be interpreted as resistor networks. This new
interpretation provides for an alternative way of evaluating the Feynman
diagrams for random resistor networks. We calculate the resistance crossover
exponent up to second order in , where is the spatial
dimension. Our result verifies a
previous calculation by Lubensky and Wang, which itself was based on the
Potts--model formulation of the random resistor network.Comment: 27 pages, 14 figure
Lack of self-averaging of the specific heat in the three-dimensional random-field Ising model
We apply the recently developed critical minimum energy subspace scheme for
the investigation of the random-field Ising model. We point out that this
method is well suited for the study of this model. The density of states is
obtained via the Wang-Landau and broad histogram methods in a unified
implementation by employing the N-fold version of the Wang-Landau scheme. The
random-fields are obtained from a bimodal distribution (), and the
scaling of the specific heat maxima is studied on cubic lattices with sizes
ranging from to . Observing the finite-size scaling behavior of the
maxima of the specific heats we examine the question of saturation of the
specific heat. The lack of self-averaging of this quantity is fully illustrated
and it is shown that this property may be related to the question mentioned
above.Comment: 8 pages, 7 figures, extended version with two new figures, version as
accepted for publication to Physical Review
Quantifying traces of tool use: a novel morphometric analysis of damage patterns on percussive tools
Percussive technology continues to play an increasingly important role in understanding the evolution of tool use. Comparing the archaeological record with extractive foraging behaviors in nonhuman primates has focused on percussive implements as a key to investigating the origins of lithic technology. Despite this, archaeological approaches towards percussive tools have been obscured by a lack of standardized methodologies. Central to this issue have been the use of qualitative, non-diagnostic techniques to identify percussive tools from archaeological contexts. Here we describe a new morphometric method for distinguishing anthropogenically-generated damage patterns on percussive tools from naturally damaged river cobbles. We employ a geomatic approach through the use of three-dimensional scanning and geographical information systems software to statistically quantify the identification process in percussive technology research. This will strengthen current technological analyses of percussive tools in archaeological frameworks and open new avenues for translating behavioral inferences of early hominins from percussive damage patterns.Palaeontological Scientific Trust; National Research Foundation; National Science Foundation [BCS-1128170, BCS-0924476]; Integrative Graduate Education and Research Traineeship Program [DGE-0801634]; George Washington University's Selective Excellence Fund; George Washington University Columbian College Facilitating Fund; Clare Hall College [JRF]; Newnham College [Gibbs Travelling Fellowship] Cambridge; European Research Council [283959]info:eu-repo/semantics/publishedVersio
Critical Behavior of Random Bond Potts Models
The effect of quenched impurities on systems which undergo first-order phase
transitions is studied within the framework of the q-state Potts model. For
large q a mapping to the random field Ising model is introduced which provides
a simple physical explanation of the absence of any latent heat in 2D, and
suggests that in higher dimensions such systems should exhibit a tricritical
point with a correlation length exponent related to the exponents of the random
field model by \nu = \nu_RF / (2 - \alpha_RF - \beta_RF). In 2D we analyze the
model using finite-size scaling and conformal invariance, and find a continuous
transition with a magnetic exponent \beta / \nu which varies continuously with
q, and a weakly varying correlation length exponent \nu \approx 1. We find
strong evidence for the multiscaling of the correlation functions as expected
for such random systems.Comment: 13 pages, RevTeX. 4 figures included. Submitted to Phys.Rev.Let
Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and their Isotopes
A solar photospheric "thermal profiling" analysis is presented, exploiting
the infrared rovibrational bands of carbon monoxide (CO) as observed with the
McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above
the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum
intensities and center-limb behavior constrained the temperature profile of the
deep photosphere, while CO center-limb behavior defined the thermal structure
at higher altitudes. The oxygen abundance was self consistently determined from
weak CO absorptions. Our analysis was meant to complement recent studies based
on 3-D convection models which, among other things, have revised the historical
solar oxygen (and carbon) abundance downward by a factor of nearly two;
although in fact our conclusions do not support such a revision. Based on
various considerations, an oxygen abundance of 700+/-100 ppm (parts per million
relative to hydrogen) is recommended; the large uncertainty reflects the model
sensitivity of CO. New solar isotopic ratios also are reported for 13C, 17O,
and 18O.Comment: 90 pages, 19 figures (some with parts "a", "b", etc.); to be
published in the Astrophysical Journal Supplement
Off-shell effects in dilepton production from hot interacting mesons
The production of dielectrons in reactions involving a_1 mesons and pions is
studied. We compare results obtained with different phenomenological
Lagrangians that have been used in connection with hadronic matter and finite
nuclei. We insist on the necessity for those interactions to satisfy known
empirical properties of the strong interaction. Large off-shell effects in
dielectron production are found and some consequences for the interpretation of
heavy ion data are outlined. We also compare with results obtained using
experimentally-extracted spectral functions.Comment: 14 pages, LaTeX2e, 2 figure
The polaroid image as photo-object
This article is part of a larger project on the cultural history of Polaroid photography and draws on research done at the Polaroid Corporate archive at Harvard and at the Polaroid company itself. It identifies two cultural practices engendered by Polaroid photography, which, at the point of its extinction, has briefly flared into visibility again. It argues that these practices are mistaken as novel but are in fact rediscoveries of practices that stretch back as many as five decades. The first section identifies Polaroid image-making as a photographic equivalent of what Tom Gunning calls the ‘cinema of attractions’. That is, the emphasis in its use is on the display of photographic technologies rather than the resultant image. Equally, the common practice, in both fine art and vernacular circles, of making composite pictures with Polaroid prints, draws attention from image content and redirects it to the photo as object
Double Twist in Helical Polymer Soft Crystals
In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first time a double-twist molecular orientation in a helical crystal has been observed
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