17,554 research outputs found
The distribution of information for sEMG signals in the rectal cancer treatment process
The electrical activity of external anal sphincter can be registered with
surface electromyography. This signals are known to be highly complex and
nonlinear. This work aims in characterisation of the information carried in the
signals by harvesting the concept of information entropy. We will focus of two
classical measures of the complexity. Firstly the Shannon entropy is addressed.
It is related to the probability spectrum of the possible states. Secondly the
Spectral entropy is described, as a simple frequency-domain analog of the
time-domain Shannon characteristics. We discuss the power spectra for separate
time scales and present the characteristics which can represent the dynamics of
electrical activity of this specific muscle group. We find that the rest and
maximum contraction states represent rather different spectral characteristic
of entropy, with close-to-normal contraction and negatively skewed rest state.Comment: 6 pages, 5 figures, 1 tabl
Identifying the quantum correlations in light-harvesting complexes
One of the major efforts in the quantum biological program is to subject
biological systems to standard tests or measures of quantumness. These tests
and measures should elucidate if non-trivial quantum effects may be present in
biological systems. Two such measures of quantum correlations are the quantum
discord and the relative entropy of entanglement. Here, we show that the
relative entropy of entanglement admits a simple analytic form when dynamics
and accessible degrees of freedom are restricted to a zero- and
single-excitation subspace. We also simulate and calculate the amount of
quantum discord that is present in the Fenna-Matthews-Olson protein complex
during the transfer of an excitation from a chlorosome antenna to a reaction
center. We find that the single-excitation quantum discord and relative entropy
of entanglement are equal for all of our numerical simulations, but a proof of
their general equality for this setting evades us for now. Also, some of our
simulations demonstrate that the relative entropy of entanglement without the
single-excitation restriction is much lower than the quantum discord. The first
picosecond of dynamics is the relevant timescale for the transfer of the
excitation, according to some sources in the literature. Our simulation results
indicate that quantum correlations contribute a significant fraction of the
total correlation during this first picosecond in many cases, at both cryogenic
and physiological temperature.Comment: 15 pages, 7 figures, significant improvements including (1) an
analytical formula for the single-excitation relative entropy of entanglement
(REE), (2) simulations indicating that the single-excitation REE is equal to
the single-excitation discord, and (3) simulations indicating that the full
REE can be much lower than the single-excitation RE
Quantum entanglement in photosynthetic light harvesting complexes
Light harvesting components of photosynthetic organisms are complex, coupled,
many-body quantum systems, in which electronic coherence has recently been
shown to survive for relatively long time scales despite the decohering effects
of their environments. Within this context, we analyze entanglement in
multi-chromophoric light harvesting complexes, and establish methods for
quantification of entanglement by presenting necessary and sufficient
conditions for entanglement and by deriving a measure of global entanglement.
These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to
extract the initial state and temperature dependencies of entanglement. We show
that while FMO in natural conditions largely contains bipartite entanglement
between dimerized chromophores, a small amount of long-range and multipartite
entanglement exists even at physiological temperatures. This constitutes the
first rigorous quantification of entanglement in a biological system. Finally,
we discuss the practical utilization of entanglement in densely packed
molecular aggregates such as light harvesting complexes.Comment: 14 pages, 7 figures. Improved presentation, published versio
Intermittent chaos for ergodic light trapping in a photonic fiber plate
Extracting the light trapped in a waveguide, or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction, is essential for optimal energetic performance in illumination, display or light harvesting devices. Here we demonstrate that the paradoxical goal of letting as much light in or out while maintaining the wave effectively trapped can be achieved with a periodic array of interpenetrated fibers forming a photonic fiber plate. Photons entering perpendicular to that plate may be trapped in an intermittent chaotic trajectory, leading to an optically ergodic system. We fabricated such a photonic fiber plate and showed that for a solar cell incorporated on one of the plate surfaces, light absorption is greatly enhanced. Confirming this, we found the unexpected result that a more chaotic photon trajectory reduces the production of photon scattering entropy.Peer ReviewedPostprint (published version
The Binary Energy Harvesting Channel with a Unit-Sized Battery
We consider a binary energy harvesting communication channel with a
finite-sized battery at the transmitter. In this model, the channel input is
constrained by the available energy at each channel use, which is driven by an
external energy harvesting process, the size of the battery, and the previous
channel inputs. We consider an abstraction where energy is harvested in binary
units and stored in a battery with the capacity of a single unit, and the
channel inputs are binary. Viewing the available energy in the battery as a
state, this is a state-dependent channel with input-dependent states, memory in
the states, and causal state information available at the transmitter only. We
find an equivalent representation for this channel based on the timings of the
symbols, and determine the capacity of the resulting equivalent timing channel
via an auxiliary random variable. We give achievable rates based on certain
selections of this auxiliary random variable which resemble lattice coding for
the timing channel. We develop upper bounds for the capacity by using a
genie-aided method, and also by quantifying the leakage of the state
information to the receiver. We show that the proposed achievable rates are
asymptotically capacity achieving for small energy harvesting rates. We extend
the results to the case of ternary channel inputs. Our achievable rates give
the capacity of the binary channel within 0.03 bits/channel use, the ternary
channel within 0.05 bits/channel use, and outperform basic Shannon strategies
that only consider instantaneous battery states, for all parameter values.Comment: Submitted to IEEE Transactions on Information Theory, August 201
Energy Sharing for Multiple Sensor Nodes with Finite Buffers
We consider the problem of finding optimal energy sharing policies that
maximize the network performance of a system comprising of multiple sensor
nodes and a single energy harvesting (EH) source. Sensor nodes periodically
sense the random field and generate data, which is stored in the corresponding
data queues. The EH source harnesses energy from ambient energy sources and the
generated energy is stored in an energy buffer. Sensor nodes receive energy for
data transmission from the EH source. The EH source has to efficiently share
the stored energy among the nodes in order to minimize the long-run average
delay in data transmission. We formulate the problem of energy sharing between
the nodes in the framework of average cost infinite-horizon Markov decision
processes (MDPs). We develop efficient energy sharing algorithms, namely
Q-learning algorithm with exploration mechanisms based on the -greedy
method as well as upper confidence bound (UCB). We extend these algorithms by
incorporating state and action space aggregation to tackle state-action space
explosion in the MDP. We also develop a cross entropy based method that
incorporates policy parameterization in order to find near optimal energy
sharing policies. Through simulations, we show that our algorithms yield energy
sharing policies that outperform the heuristic greedy method.Comment: 38 pages, 10 figure
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