4,076 research outputs found
Casimir interaction of rod-like particles in a two-dimensional critical system
We consider the fluctuation-induced interaction of two thin, rod-like
particles or "needles" immersed in a two-dimensional critical fluid of Ising
symmetry right at the critical point. Conformally mapping the plane containing
the needles onto a simpler geometry in which the stress tensor is known, we
analyze the force and torque between needles of arbitrary length, separation,
and orientation. For infinite and semi-infinite needles we utilize the mapping
of the plane bounded by the needles onto the half plane, and for two needles of
finite length the mapping onto an annulus. For semi-infinite and infinite
needles the force is expressed in terms of elementary functions, and we also
obtain analytical results for the force and torque between needles of finite
length with separation much greater than their length. Evaluating formulas in
our approach numerically for several needle geometries and surface universality
classes, we study the full crossover from small to large values of the
separation to length ratio. In these two limits the numerical results agree
with results for infinitely long needles and with predictions of the
small-particle operator expansion, respectively.Comment: 68 pages, 9 figure
A Correlation Between Inclination and Color in the Classical Kuiper Belt
We have measured broadband optical BVR photometry of 24 Classical and
Scattered Kuiper belt objects (KBOs), approximately doubling the published
sample of colors for these classes of objects. We find a statistically
significant correlation between object color and inclination in the Classical
Kuiper belt using our data. The color and inclination correlation increases in
significance after the inclusion of additional data points culled from all
published works. Apparently, this color and inclination correlation has not
been more widely reported because the Plutinos show no such correlation, and
thus have been a major contaminant in previous samples. The color and
inclination correlation excludes simple origins of color diversity, such as the
presence of a coloring agent without regard to dynamical effects.
Unfortunately, our current knowledge of the Kuiper belt precludes us from
understanding whether the color and inclination trend is due to environmental
factors, such as collisional resurfacing, or primordial population effects. A
perihelion and color correlation is also evident, although this appears to be a
spurious correlation induced by sampling bias, as perihelion and inclination
are correlated in the observed sample of KBOs.Comment: Accepted to Astrophysical Journal Letter
First-passage and extreme-value statistics of a particle subject to a constant force plus a random force
We consider a particle which moves on the x axis and is subject to a constant
force, such as gravity, plus a random force in the form of Gaussian white
noise. We analyze the statistics of first arrival at point of a particle
which starts at with velocity . The probability that the particle
has not yet arrived at after a time , the mean time of first arrival,
and the velocity distribution at first arrival are all considered. We also
study the statistics of the first return of the particle to its starting point.
Finally, we point out that the extreme-value statistics of the particle and the
first-passage statistics are closely related, and we derive the distribution of
the maximum displacement .Comment: Contains an analysis of the extreme-value statistics not included in
first versio
Biomass partitioning and gas exchange parameters in different Musa cultivars as influenced by natural shade
Poster presented at Tropentag 2011 Development on the Margin. Bonn (Germany), 3-7 Oct 2011
Two-dimensional critical systems with mixed boundary conditions: Exact Ising results from conformal invariance and boundary-operator expansions
With conformal-invariance methods, Burkhardt, Guim, and Xue studied the
critical Ising model, defined on the upper half plane with different
boundary conditions and on the negative and positive axes. For
and , they determined the one and two-point averages of the spin
and energy . Here , , and stand for spin-up,
spin-down, and free-spin boundaries, respectively. The case , where
the boundary conditions switch between and at arbitrary points,
, , on the axis was also analyzed.
In this paper the alternating boundary conditions and the case
of three different boundary conditions are considered. Exact results for
the one and two-point averages of , , and the stress tensor
are derived. Using the results for , the critical Casimir
interaction with the boundary of a wedge-shaped inclusion is analyzed for mixed
boundary conditions.
The paper also includes a comprehensive discussion of boundary-operator
expansions in two-dimensional critical systems with mixed boundary conditions.
Two types of expansions - away from switching points of the boundary condition
and at switching points - are considered. The asymptotic behavior of two-point
averages is expressed in terms of one-point averages with the help of the
expansions. We also consider the strip geometry with mixed boundary conditions
and derive the distant-wall corrections to one-point averages near one edge due
to the other edge using the boundary-operator expansions. The predictions of
the boundary-operator expansions are consistent with exact results for Ising
systems.Comment: 50 pages, 1 figur
The response of Musa cultivar root systems to a tree shade gradient
Poster presented at Tropentag 2011 - Development on the Margin. Bonn (Germany), 3-7 Oct 2011
Scar appearance of different skin and subcutaneous tissue closure techniques in caesarean section: a randomized study
OBJECTIVES: To determine the role of skin and subcutaneous space closure in caesarean section on the cosmetic appearance of the scar and the patients' satisfaction. STUDY DESIGN: 153 patients undergoing caesarean section without prior abdominal delivery were included and randomly assigned in a non-blinded study to four different combinations of skin and subcutaneous tissue closure. The scar was assessed after a period of at least 4 months by a self-developed protocol and the patient was asked to complete a survey regarding her satisfaction with the scar. RESULTS: One hundred patients were eligible for long-term evaluation of the scar. Skin closure by either staples or intracutaneous suture in combination with closure or non-closure of the subcutaneous space has a comparable outcome in view of cosmetic outcome and patient satisfaction. CONCLUSIONS: All four methods of skin closure seem to be a reasonable choice in caesarean section because they have comparable cosmetic outcome, do not differ with respect to the patients' satisfaction and bear comparable costs
Local functional models of critical correlations in thin-films
Recent work on local functional theories of critical inhomogeneous fluids and
Ising-like magnets has shown them to be a potentially exact, or near exact,
description of universal finite-size effects associated with the excess
free-energy and scaling of one-point functions in critical thin films. This
approach is extended to predict the two-point correlation function G in
critical thin-films with symmetric surface fields in arbitrary dimension d. In
d=2 we show there is exact agreement with the predictions of conformal
invariance for the complete spectrum of correlation lengths as well as the
detailed position dependence of the asymptotic decay of G. In d=3 and d>=4 we
present new numerical predictions for the universal finite-size correlation
length and scaling functions determining the structure of G across the
thin-film. Highly accurate analytical closed form expressions for these
universal properties are derived in arbitrary dimension.Comment: 4 pages, 1 postscript figure. Submitted to Phys Rev Let
Winner-Take-All? Visibility, Availability, and Heterogeneity on Webcam Sex Platforms
Online platforms have profoundly changed the organization of work in many economic sectors, and the sex industry is no exception. Webcam sex platforms, in particular, host large and heterogeneous populations of workers who are not formally employed and rely heavily on algorithmic systems to manage this workforce. These systems are often said to produce or reinforce unpredictable and unequal winner-take-all effects, contributing to economic pressure and precarity. Most research trying to empirically assess these claims has focused on single platforms and on the experiences of limited samples of regular workers, excluding more sporadic performers that nonetheless compete for visibility within the same ranking systems. In this article, we seek to address these limitations through a multi-platform study based on systematic ranking data collected by scraping the complete homepages of five webcam platforms over 11 weeks. The article proceeds in four steps. We first discuss existing work on algorithmic workplace management and webcam sex platforms. We then introduce the case studies, present our empirical approach, and discuss ethical considerations. The findings section is organized around two complementary lines of inquiry: an examination of visibility distributions across our sample of websites, as well as their connection with viewer numbers, and an exploration of the relationship between visibility and labor practices, which allows us to link performer availability to ranking outcomes. We conclude by highlighting the substantial differences between these designed marketplaces and discuss repercussions for both webcam sex research and the broader field of platform studies
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