1,109 research outputs found
Computational inference in systems biology
Parameter inference in mathematical models of biological pathways, expressed as coupled ordinary differential equations (ODEs), is a challenging problem. The computational costs associated with repeatedly solving the ODEs are often high. Aimed at reducing this cost, new concepts using gradient matching have been proposed. This paper combines current adaptive gradient matching approaches, using Gaussian processes, with a parallel tempering scheme, and conducts a comparative evaluation with current methods used for parameter inference in ODEs
Alexander representation of tangles
A tangle is an oriented 1-submanifold of the cylinder whose endpoints lie on
the two disks in the boundary of the cylinder. Using an algebraic tool
developed by Lescop, we extend the Burau representation of braids to a functor
from the category of oriented tangles to the category of Z[t,t^{-1}]-modules.
For (1,1)-tangles (i.e., tangles with one endpoint on each disk) this invariant
coincides with the Alexander polynomial of the link obtained by taking the
closure of the tangle. We use the notion of plat position of a tangle to give a
constructive proof of invariance in this case.Comment: 13 pages, 5 figure
Analysis of No-Difference Findings in Evaluation Research
Conclusions of no difference are becoming increasingly important in evaluation research. We delineate three major uses of no-difference findings and analyze their meanings. (1) No-differ ence findings in randomized experiments can be interpreted as support for conclusions of the absence of a meaningful treatment effect, but only if the proper analytic methods are used. (2) Statistically based conclusions in quasi-experiments do not allow causal statements about the treatment impact but do provide a metric to judge the size of the resulting difference. (3) Using no-difference findings to conclude equivalence on control variables is inefficient and potentially misleading. The final section of the article presents alternative methods by which conclusions of no difference may be supported when applicable. These methods include the use of arbitrarily high alpha levels, interval estimation, and power analysis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67182/2/10.1177_0193841X8901300604.pd
Studying the vertical extent of the ground layer turbulence using sonic-anemometers
The optical turbulence above Dome C in winter is mainly concentrated in the first tens of meters above the ground. The properties of this so-called surface layer were investigated during the last two winterover by a set of sonics anemometers placed on a 45 m high tower. These anemometers provide measurements of the temperature and the wind speed vector. The sampling rate of 10 Hz allows to derivate the refractive index structure constant C_n^2. We report here the first analysis of these data
Neuropsychological constraints to human data production on a global scale
Which are the factors underlying human information production on a global
level? In order to gain an insight into this question we study a corpus of
252-633 Million publicly available data files on the Internet corresponding to
an overall storage volume of 284-675 Terabytes. Analyzing the file size
distribution for several distinct data types we find indications that the
neuropsychological capacity of the human brain to process and record
information may constitute the dominant limiting factor for the overall growth
of globally stored information, with real-world economic constraints having
only a negligible influence. This supposition draws support from the
observation that the files size distributions follow a power law for data
without a time component, like images, and a log-normal distribution for
multimedia files, for which time is a defining qualia.Comment: to be published in: European Physical Journal
The Taming of Closed Time-like Curves
We consider a orbifold, where acts by time and space
reversal, also known as the embedding space of the elliptic de Sitter space.
The background has two potentially dangerous problems: time-nonorientability
and the existence of closed time-like curves. We first show that closed causal
curves disappear after a proper definition of the time function. We then
consider the one-loop vacuum expectation value of the stress tensor. A naive
QFT analysis yields a divergent result. We then analyze the stress tensor in
bosonic string theory, and find the same result as if the target space would be
just the Minkowski space , suggesting a zero result for the
superstring. This leads us to propose a proper reformulation of QFT, and
recalculate the stress tensor. We find almost the same result as in Minkowski
space, except for a potential divergence at the initial time slice of the
orbifold, analogous to a spacelike Big Bang singularity. Finally, we argue that
it is possible to define local S-matrices, even if the spacetime is globally
time-nonorientable.Comment: 37 pages, LaTeX2e, uses amssymb, amsmath and epsf macros, 8 eps and 3
ps figures; (v2): Two additional comments + one reference added; (v3):
corrections in discussion of CTCs + some clarification
Magnetic Resonance Imaging of Plantar Plate Rupture
Degenerative plantar plate failure is an under-recognized cause of lesser metatarsalgia. We performed magnetic resonance imaging (MRI) with a small receiver coil in 13 patients in whom plantar plate ruptures of the second or third metatarsophalangeal joint were clinically suspected. In eight patients, MRI showed focal hyperintensity in the plantar plate that was interpreted as a rupture of the plate. Ruptures were confirmed in all five patients who underwent an operative procedure to treat the unstable, painful metatarsophalangeal joint. MRI is a noninvasive technique that can visualize plantar plate abnormalities and aid the clinical evaluation of problematic lesser metatarsalgia
Multi-Leg One-Loop Gravity Amplitudes from Gauge Theory
By exploiting relations between gravity and gauge theories, we present two
infinite sequences of one-loop n-graviton scattering amplitudes: the `maximally
helicity-violating' amplitudes in N=8 supergravity, and the `all-plus' helicity
amplitudes in gravity with any minimally coupled massless matter content. The
all-plus amplitudes correspond to self-dual field configurations and vanish in
supersymmetric theories. We make use of the tree-level Kawai-Lewellen-Tye (KLT)
relations between open and closed string theory amplitudes, which in the
low-energy limit imply relations between gravity and gauge theory tree
amplitudes. For n < 7, we determine the all-plus amplitudes explicitly from
their unitarity cuts. The KLT relations, applied to the cuts, allow us to
extend to gravity a previously found `dimension-shifting' relation between (the
cuts of) the all-plus amplitudes in gauge theory and the maximally
helicity-violating amplitudes in N=4 super-Yang-Mills theory. The gravitational
version of the relation lets us determine the n < 7 N=8 supergravity amplitudes
from the all-plus gravity amplitudes. We infer the two series of amplitudes for
all n from their soft and collinear properties, which can also be derived from
gauge theory using the KLT relations.Comment: Minor errors corrected, Latex, 53 page
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