1,980 research outputs found
Note on clock synchronization and Edwards transformations
Edwards transformations relating inertial frames with arbitrary clock
synchronization are reminded and put in more general setting. Their group
theoretical context is described.Comment: 11 pages, no figures; final version, to appear in Foundations of
Physics Letter
Instability of spatial patterns and its ambiguous impact on species diversity
Self-arrangement of individuals into spatial patterns often accompanies and
promotes species diversity in ecological systems. Here, we investigate pattern
formation arising from cyclic dominance of three species, operating near a
bifurcation point. In its vicinity, an Eckhaus instability occurs, leading to
convectively unstable "blurred" patterns. At the bifurcation point, stochastic
effects dominate and induce counterintuitive effects on diversity: Large
patterns, emerging for medium values of individuals' mobility, lead to rapid
species extinction, while small patterns (low mobility) promote diversity, and
high mobilities render spatial structures irrelevant. We provide a quantitative
analysis of these phenomena, employing a complex Ginzburg-Landau equation.Comment: 4 pages, 3 figures and supplementary information. To appear in Phys.
Rev. Lett
Noncommutative Common Cause Principles in Algebraic Quantum Field Theory
States in algebraic quantum field theory "typically" establish correlation
between spacelike separated events. Reichenbach's Common Cause Principle,
generalized to the quantum field theoretical setting, offers an apt tool to
causally account for these superluminal correlations. In the paper we motivate
first why commutativity between the common cause and the correlating events
should be abandoned in the definition of the common cause. Then we show that
the Noncommutative Weak Common Cause Principle holds in algebraic quantum field
theory with locally finite degrees of freedom. Namely, for any pair of
projections A, B supported in spacelike separated regions V_A and V_B,
respectively, there is a local projection C not necessarily commuting with A
and B such that C is supported within the union of the backward light cones of
V_A and V_B and the set {C, non-C} screens off the correlation between A and B
Doppelniere mit Nierenbeckenabgangsstenose im Kindesalter: Retroperitoneoskopische Pyeloplastik
Zusammenfassung: Die laparoskopische Pyeloplastik für die Therapie der Nierenbeckenabgangsstenose bei Kindern gilt nach wie vor als einer der anspruchvollsten Eingriffe in der Urologie. Wir berichten über einen 12-jährigen Jungen mit Nierenbeckenabgangsstenose, Doppelniere und hohem Ureter fissus. Der Junge stellte sich wegen seit einem Jahr zunehmender Flankenschmerzen rechts und zuvor diagnostizierter Nierenbeckenabgangsstenose des unteren Doppelnierenanteils bei uns vor. Wir führten eine retroperitoneoskopische Pyeloplastik nach Anderson-Hynes durc
Coexistence in a One-Dimensional Cyclic Dominance Process
Cyclic (rock-paper-scissors-type) population models serve to mimic complex
species interactions. Focusing on a paradigmatic three-species model with
mutations in one dimension, we observe an interplay between equilibrium and
non-equilibrium processes in the stationary state. We exploit these insights to
obtain asymptotically exact descriptions of the emerging reactive steady state
in the regimes of high and low mutation rates. The results are compared to
stochastic lattice simulations. Our methods and findings are potentially
relevant for the spatio-temporal evolution of other non-equilibrium stochastic
processes.Comment: 4 pages, 4 figures and 2 pages of Supplementary Material. To appear
in Physical Review
Three-fold way to extinction in populations of cyclically competing species
Species extinction occurs regularly and unavoidably in ecological systems.
The time scales for extinction can broadly vary and inform on the ecosystem's
stability. We study the spatio-temporal extinction dynamics of a paradigmatic
population model where three species exhibit cyclic competition. The cyclic
dynamics reflects the non-equilibrium nature of the species interactions. While
previous work focusses on the coarsening process as a mechanism that drives the
system to extinction, we found that unexpectedly the dynamics to extinction is
much richer. We observed three different types of dynamics. In addition to
coarsening, in the evolutionary relevant limit of large times, oscillating
traveling waves and heteroclinic orbits play a dominant role. The weight of the
different processes depends on the degree of mixing and the system size. By
analytical arguments and extensive numerical simulations we provide the full
characteristics of scenarios leading to extinction in one of the most
surprising models of ecology
Simultaneity as an Invariant Equivalence Relation
This paper deals with the concept of simultaneity in classical and
relativistic physics as construed in terms of group-invariant equivalence
relations. A full examination of Newton, Galilei and Poincar\'e invariant
equivalence relations in is presented, which provides alternative
proofs, additions and occasionally corrections of results in the literature,
including Malament's theorem and some of its variants. It is argued that the
interpretation of simultaneity as an invariant equivalence relation, although
interesting for its own sake, does not cut in the debate concerning the
conventionality of simultaneity in special relativity.Comment: Some corrections, mostly of misprints. Keywords: special relativity,
simultaneity, invariant equivalence relations, Malament's theore
Noise and Correlations in a Spatial Population Model with Cyclic Competition
Noise and spatial degrees of freedom characterize most ecosystems. Some
aspects of their influence on the coevolution of populations with cyclic
interspecies competition have been demonstrated in recent experiments [e.g. B.
Kerr et al., Nature {\bf 418}, 171 (2002)]. To reach a better theoretical
understanding of these phenomena, we consider a paradigmatic spatial model
where three species exhibit cyclic dominance. Using an individual-based
description, as well as stochastic partial differential and deterministic
reaction-diffusion equations, we account for stochastic fluctuations and
spatial diffusion at different levels, and show how fascinating patterns of
entangled spirals emerge. We rationalize our analysis by computing the
spatio-temporal correlation functions and provide analytical expressions for
the front velocity and the wavelength of the propagating spiral waves.Comment: 4 pages of main text, 3 color figures + 2 pages of supplementary
material (EPAPS Document). Final version for Physical Review Letter
Controlling nuclear spin exchange via optical Feshbach resonances in Yb
Nuclear spin exchange occurs in ultracold collisions of fermionic
alkaline-earth-like atoms due to a difference between s- and p-wave phase
shifts. We study the use of an optical Feshbach resonance, excited on the
intercombination line of Yb, to affect a large
modification of the s-wave scattering phase shift, and thereby optically
mediate nuclear exchange forces. We perform a full multichannel calculation of
the photoassociation resonances and wave functions and from these calculate the
real and imaginary parts of the scattering length. As a figure of merit of this
interaction, we estimate the fidelity to implement a entangling
quantum logic gate for two atoms trapped in the same well of an optical
lattice. For moderate parameters one can achieve a gate fidelity of
in a time of s.Comment: 5 pages, 1 figur
All cause and disease specific mortality in patients with knee or hip osteoarthritis: Population based cohort study
Copyright © 2011 by the BMJ Publishing Group Ltd. This articles was first published in: BMJ, 2011, Vol. 342, Issue 7798, pp. 638 - 638To examine all cause and disease specific mortality in patients with osteoarthritis of the knee or hip
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