792 research outputs found
Characterizing Information Propagation in Plants
This paper considers an electro-chemical based communication model for
intercellular communication in plants. Many plants, such as Mimosa pudica (the
"sensitive plant"), employ electrochemical signals known as action potentials
(APs) for communication purposes. In this paper we present a simple model for
action potential generation. We make use of the concepts from molecular
communication to explain the underlying process of information transfer in a
plant. Using the information-theoretic analysis, we compute the mutual
information between the input and output in this work. The key aim is to study
the variations in the information propagation speed for varying number of plant
cells for one simple case. Furthermore we study the impact of the AP signal on
the mutual information and information propagation speed. We aim to explore
further that how the growth rate in plants can impact the information transfer
rate and vice versa.Comment: 6 pages, 5 Figures, Submitted to IEEE Conference, 201
Links between different analytic descriptions of constant mean curvature surfaces
Transformations between different analytic descriptions of constant mean
curvature (CMC) surfaces are established. In particular, it is demonstrated
that the system descriptive of CMC surfaces within the
framework of the generalized Weierstrass representation, decouples into a
direct sum of the elliptic Sh-Gordon and Laplace equations. Connections of this
system with the sigma model equations are established. It is pointed out, that
the instanton solutions correspond to different Weierstrass parametrizations of
the standard sphere
Self Interacting Dark Matter in the Solar System
Weakly coupled, almost massless, spin 0 particles have been predicted by many
extensions of the standard model of particle physics. Recently, the PVLAS group
observed a rotation of polarization of electromagnetic waves in vacuum in the
presence of transverse magnetic field. This phenomenon is best explained by the
existence of a weakly coupled light pseudoscalar particle. However, the
coupling required by this experiment is much larger than the conventional
astrophysical limits. Here we consider a hypothetical self-interacting
pseudoscalar particle which couples weakly with visible matter.
Assuming that these pseudoscalars pervade the galaxy, we show that the solar
limits on the pseudoscalar-photon coupling can be evaded.Comment: 17 pages, 2 figure
Metric of a tidally perturbed spinning black hole
We explicitly construct the metric of a Kerr black hole that is tidally
perturbed by the external universe in the slow-motion approximation. This
approximation assumes that the external universe changes slowly relative to the
rotation rate of the hole, thus allowing the parameterization of the
Newman-Penrose scalar by time-dependent electric and magnetic tidal
tensors. This approximation, however, does not constrain how big the spin of
the background hole can be and, in principle, the perturbed metric can model
rapidly spinning holes. We first generate a potential by acting with a
differential operator on . From this potential we arrive at the metric
perturbation by use of the Chrzanowski procedure in the ingoing radiation
gauge. We provide explicit analytic formulae for this metric perturbation in
spherical Kerr-Schild coordinates, where the perturbation is finite at the
horizon. This perturbation is parametrized by the mass and Kerr spin parameter
of the background hole together with the electric and magnetic tidal tensors
that describe the time evolution of the perturbation produced by the external
universe. In order to take the metric accurate far away from the hole, these
tidal tensors should be determined by asymptotically matching this metric to
another one valid far from the hole. The tidally perturbed metric constructed
here could be useful in initial data constructions to describe the metric near
the horizons of a binary system of spinning holes. This perturbed metric could
also be used to construct waveforms and study the absorption of mass and
angular momentum by a Kerr black hole when external processes generate
gravitational radiation.Comment: 17 pages, 3 figures. Final PRD version, minor typos, etc corrected.
v3: corrected typo in Eq. (35) and (57
Measurement of HbA1c in multicentre diabetes trials - should blood samples be tested locally or sent to a central laboratory: an agreement analysis (vol 17, pg 517, 2016)
Background
Glycated haemoglobin (HbA1c) is an important outcome measure in diabetes clinical trials. For multicentre designs, HbA1c can be measured locally at participating centres or by sending blood samples to a central laboratory. This study analyses the agreement between local and central measurements, using 1-year follow-up data collected in a multicentre randomised controlled trial (RCT) of newly diagnosed children with type I diabetes.
Methods
HbA1c measurements were routinely analysed both locally and centrally at baseline and then at 3, 6, 9 and 12 months and the data reported in mmol/mol. Agreement was assessed by calculating the bias and 95 % limits of agreement, using the Bland-Altman analysis method. A predetermined benchmark for clinically acceptable margin of error between measurements was subjectively set as ±10 % for HbA1c. The percentage of pairs of measurements that were classified as clinically acceptable was calculated. Descriptive statistics were used to examine the agreement within centres. Treatment group was not considered.
Results
Five hundred and ninety pairs of measurement, representing 255 children and 15 trial centres across four follow-up time points, were compared. There was no significant bias: local measurements were an average of 0.16 mmol/mol (SD = 4.5, 95 % CI −0.2 to 0.5) higher than central. The 95 % limits of agreement were −8.6 to 9.0 mmol/mol (local minus central). Eighty percent of local measurements were within ±10 % of corresponding central measurements. Some trial centres were more varied in the differences observed between local and central measurements: IQRs ranging from 3 to 9 mmol/mol; none indicated systematic bias.
Conclusions
Variation in agreement between HbA1c measurements was greater than had been expected although no overall bias was detected and standard deviations were similar. Discrepancies were present across all participating centres. These findings have implications for the comparison of standards of clinical care between centres, the design of future multicentre RCTs and existing quality assurance processes for HbA1c measurements. We recommend that centralised HbA1c measurement is preferable in the multicentre clinical trial setting
Gravitational collapse in asymptotically Anti-de Sitter/de Sitter backgrounds
We study here the gravitational collapse of a matter cloud with a
non-vanishing tangential pressure in the presence of a non-zero cosmological
term. Conditions for bounce and singularity formation are derived for the
model. It is also shown that when the tangential pressures vanish, the bounce
and singularity conditions reduce to that of the dust case studied earlier. The
collapsing interior is matched with an exterior which is asymptotically de
Sitter or anti de Sitter, depending on the sign of cosmological constant. The
junction conditions for matching the cloud to exterior are specified. The
effect of the cosmological term on apparent horizons is studied in some detail,
and the nature of central singularity is analyzed. We also discuss here the
visibility of the singularity and implications for the cosmic censorship
conjecture.Comment: 11 pages, 1 figure, Revtex
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