959 research outputs found
Novel nitrogen-based organosulfur electrodes for advanced intermediate temperature batteries
Advanced secondary batteries operating at intermediate temperatures (100 to 200 C) have attracted considerable interest due to their inherent advantages (reduced corrosion and safety risks) over higher temperature systems. Current work in this laboratory has involved research on a class of intermediate temperature Na/beta double prime- alumina/RSSR batteries conceptually similar to Na/S cells, but operating within a temperature range of 100 to 150 C, and having an organosulfur rather than inorganic sulfur positive electrode. The organosulfur electrodes are based on the reversible, two electron eduction of organodisulfides to the corresponding thiolate anions, RSSR + 2 electrons yield 2RS(-), where R is an organic moiety. Among the advantages of such a generic redox couple for battery research is the ability to tailor the physical, chemical, and electrochemical properties of the RSSR molecule through choice of the organic moiety. The viscosity, liquidus range, dielectric constant, equivalent weight, and redox potential can in fact be verified in a largely predictable manner. The current work concerns the use of multiple nitrogen organosulfur molecules, chosen for application in Na/RSSR cells for their expected oxidizing character. In fact, a Na/RSSR cell containing one of these materials, the sodium salt of 5-mercapto 1-methyltetrazole, yielded the highest open circuit voltage obtained yet in the laboratory; 3.0 volts in the charged state and 2.6 volts at 100 percent discharge. Accordingly, the cycling behavior of a series of multiple nitrogen organodisulfides as well as polymeric organodisulfides are presented in this manuscript
Two brains in action: joint-action coding in the primate frontal cortex
Daily life often requires the coordination of our actions with those of another partner. After sixty years (1968-2018) of behavioral neurophysiology of motor control, the neural mechanisms which allow such coordination in primates are unknown. We studied this issue by recording cell activity simultaneously from dorsal premotor cortex (PMd) of two male interacting monkeys trained to coordinate their hand forces to achieve a common goal. We found a population of 'joint-action cells' that discharged preferentially when monkeys cooperated in the task. This modulation was predictive in nature, since in most cells neural activity led in time the changes of the "own" and of the "other" behavior. These neurons encoded the joint-performance more accurately than 'canonical action-related cells', activated by the action per se, regardless of the individual vs. interactive context. A decoding of joint-action was obtained by combining the two brains activities, using cells with directional properties distinguished from those associated to the 'solo' behaviors. Action observation-related activity studied when one monkey observed the consequences of the partner's behavior, i.e. the cursor's motion on the screen, did not sharpen the accuracy of 'joint-action cells' representation, suggesting that it plays no major role in encoding joint-action. When monkeys performed with a non-interactive partner, such as a computer, 'joint-action cells' representation of the "other" (non-cooperative) behavior was significantly degraded. These findings provide evidence of how premotor neurons integrate the time-varying representation of the self-action with that of a co-actor, thus offering a neural substrate for successful visuo-motor coordination between individuals.SIGNIFICANT STATEMENTThe neural bases of inter-subject motor coordination were studied by recording cell activity simultaneously from the frontal cortex of two interacting monkeys, trained to coordinate their hand forces to achieve a common goal. We found a new class of cells, preferentially active when the monkeys cooperated, rather than when the same action was performed individually. These 'joint-action neurons' offered a neural representation of joint-behaviors by far more accurate than that provided by the canonical action-related cells, modulated by the action per se regardless of the individual/interactive context. A neural representation of joint-performance was obtained by combining the activity recorded from the two brains. Our findings offer the first evidence concerning neural mechanisms subtending interactive visuo-motor coordination between co-acting agents
Fluctuation-response relations for nonequilibrium diffusions with memory
Strong interaction with other particles or feedback from the medium on a
Brownian particle entail memory effects in the effective dynamics. We discuss
the extension of the fluctuation-dissipation theorem to nonequilibrium Langevin
systems with memory. An important application is to the extension of the
Sutherland-Einstein relation between diffusion and mobility. Nonequilibrium
corrections include the time-correlation between the dynamical activity and the
velocity of the particle, which in turn leads to information about the
correlations between the driving force and the particle's displacement
Fluctuation relation for a L\'evy particle
We study the work fluctuations of a particle subjected to a deterministic
drag force plus a random forcing whose statistics is of the L\'evy type. In the
stationary regime, the probability density of the work is found to have ``fat''
power-law tails which assign a relatively high probability to large
fluctuations compared with the case where the random forcing is Gaussian. These
tails lead to a strong violation of existing fluctuation theorems, as the ratio
of the probabilities of positive and negative work fluctuations of equal
magnitude behaves in a non-monotonic way. Possible experiments that could probe
these features are proposed.Comment: 5 pages, 2 figures, RevTeX4; v2: minor corrections and references
added; v3: typos corrected, new conclusion, close to published versio
Modeling the dynamics of a tracer particle in an elastic active gel
The internal dynamics of active gels, both in artificial (in-vitro) model
systems and inside the cytoskeleton of living cells, has been extensively
studied by experiments of recent years. These dynamics are probed using tracer
particles embedded in the network of biopolymers together with molecular
motors, and distinct non-thermal behavior is observed. We present a theoretical
model of the dynamics of a trapped active particle, which allows us to quantify
the deviations from equilibrium behavior, using both analytic and numerical
calculations. We map the different regimes of dynamics in this system, and
highlight the different manifestations of activity: breakdown of the virial
theorem and equipartition, different elasticity-dependent "effective
temperatures" and distinct non-Gaussian distributions. Our results shed light
on puzzling observations in active gel experiments, and provide physical
interpretation of existing observations, as well as predictions for future
studies.Comment: 11 pages, 6 figure
First test of a BAE transducing scheme on a Resonant Gravitational-Wave Antenna
We present the results obtained with a resonant capacitive transducer, suitable for Back Action Evasion (BAE) measurements, coupled for the first time to a
gravitational-wave antenna. This scheme was developed in collaboration with the
Group of the University of Rome La Sapienza. The antenna is a 270 kg aluminum 5056 alloy cylinder, with a resonant frequency of 1805 Hz, operating at 4.2K in the ALTAIR
cryostat, located in Frascati (Italy) at the IFSI-CNR laboratory. The apparatus was able to work continuously for periods as long as days, both in up-conversion and BAE
configurations, with good stability. The behaviour of the system is in reasonable Agreement with a proposed model of a double harmonic oscillator in a BAE readout scheme. The limits on the sensitivity of this set-up are discussed as well as the possible future improvements
Activity driven fluctuations in living cells
We propose a model for the dynamics of a probe embedded in a living cell,
where both thermal fluctuations and nonequilibrium activity coexist. The model
is based on a confining harmonic potential describing the elastic cytoskeletal
matrix, which undergoes random active hops as a result of the nonequilibrium
rearrangements within the cell. We describe the probe's statistics and we bring
forth quantities affected by the nonequilibrium activity. We find an excellent
agreement between the predictions of our model and experimental results for
tracers inside living cells. Finally, we exploit our model to arrive at
quantitative predictions for the parameters characterizing nonequilibrium
activity, such as the typical time scale of the activity and the amplitude of
the active fluctuations.Comment: 6 pages, 4 figure
Dynamics of a tracer granular particle as a non-equilibrium Markov process
The dynamics of a tracer particle in a stationary driven granular gas is
investigated. We show how to transform the linear Boltzmann equation describing
the dynamics of the tracer into a master equation for a continuous Markov
process. The transition rates depend upon the stationary velocity distribution
of the gas. When the gas has a Gaussian velocity probability distribution
function (pdf), the stationary velocity pdf of the tracer is Gaussian with a
lower temperature and satisfies detailed balance for any value of the
restitution coefficient . As soon as the velocity pdf of the gas
departs from the Gaussian form, detailed balance is violated. This
non-equilibrium state can be characterized in terms of a Lebowitz-Spohn action
functional defined over trajectories of time duration . We
discuss the properties of this functional and of a similar functional
which differs from the first for a term which is non-extensive
in time. On the one hand we show that in numerical experiments, i.e. at finite
times , the two functionals have different fluctuations and
always satisfies an Evans-Searles-like symmetry. On the other hand we cannot
observe the verification of the Lebowitz-Spohn-Gallavotti-Cohen (LS-GC)
relation, which is expected for at very large times . We give
an argument for the possible failure of the LS-GC relation in this situation.
We also suggest practical recipes for measuring and
in experiments.Comment: 16 pages, 3 figures, submitted for publicatio
Spatial fluctuations at vertices of epithelial layers: quantification of regulation by Rho pathway
In living matter, shape fluctuations induced by acto-myosin are usually
studied in vitro via reconstituted gels, whose properties are controlled by
changing the concentrations of actin, myosin and cross-linkers. Such an
approach deliberately avoids to consider the complexity of biochemical
signaling inherent to living systems. Acto-myosin activity inside living cells
is mainly regulated by the Rho signaling pathway which is composed of multiple
layers of coupled activators and inhibitors. We investigate how such a pathway
controls the dynamics of confluent epithelial tissues by tracking the
displacements of the junction points between cells. Using a phenomenological
model to analyze the vertex fluctuations, we rationalize the effects of
different Rho signaling targets on the emergent tissue activity by quantifying
the effective diffusion coefficient, the persistence time and persistence
length of the fluctuations. Our results reveal an unanticipated correlation
between layers of activation/inhibition and spatial fluctuations within
tissues. Overall, this work connects the regulation via biochemical signaling
with mesoscopic spatial fluctuations, with potential application to the study
of structural rearrangements in epithelial tissues.Comment: 8 pages, 3 figure
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