432 research outputs found
The thermoelectric working fluid: thermodynamics and transport
Thermoelectric devices are heat engines, which operate as generators or
refrigerators using the conduction electrons as a working fluid. The
thermoelectric heat-to-work conversion efficiency has always been typically
quite low, but much effort continues to be devoted to the design of new
materials boasting improved transport properties that would make them of the
electron crystal-phonon glass type of systems. On the other hand, there are
comparatively few studies where a proper thermodynamic treatment of the
electronic working fluid is proposed. The present article aims to contribute to
bridge this gap by addressing both the thermodynamic and transport properties
of the thermoelectric working fluid covering a variety of models, including
interacting systems.Comment: 15 pages, 2 figure
Thermodynamics of Thermoelectric Phenomena and Applications
Fifty years ago, the optimization of thermoelectric devices was analyzed by considering the relation between optimal performances and local entropy production. Entropy is produced by the irreversible processes in thermoelectric devices. If these processes could be eliminated, entropy production would be reduced to zero, and the limiting Carnot efficiency or coefficient of performance would be obtained. In the present review, we start with some fundamental thermodynamic considerations relevant for thermoelectrics. Based on a historical overview, we reconsider the interrelation between optimal performances and local entropy production by using the compatibility approach together with the thermodynamic arguments. Using the relative current density and the thermoelectric potential, we show that minimum entropy production can be obtained when the thermoelectric potential is a specific, optimal value
Closed-loop approach to thermodynamics
We present the closed loop approach to linear nonequilibrium thermodynamics
considering a generic heat engine dissipatively connected to two temperature
baths. The system is usually quite generally characterized by two parameters:
the output power and the conversion efficiency , to which we add a
third one, the working frequency . We establish that a detailed
understanding of the effects of the dissipative coupling on the energy
conversion process, necessitates the knowledge of only two quantities: the
system's feedback factor and its open-loop gain , the product of
which, , characterizes the interplay between the efficiency, the
output power and the operating rate of the system. By placing thermodynamics
analysis on a higher level of abstraction, the feedback loop approach provides
a versatile and economical, hence a very efficient, tool for the study of
\emph{any} conversion engine operation for which a feedback factor may be
defined
Rotational Splitting of Pulsational Modes
Mode splittings produced by uniform rotation and a particular form of
differential rotation are computed for two-dimensional rotating 10 Mo ZAMS
stellar models. The change in the character of the mode splitting is traced as
a function of uniform rotation rate, and it is found that only relatively slow
rotation rates are required before the mode splitting becomes asymmetric about
the azimuthally symmetric (m=0) mode. Increased rotation produces a
progressively altered pattern of the individual modes with respect to each
other. Large mode splittings begin to overlap with the mode splittings produced
by different radial and latitudinal modes at relatively low rotation rates. The
mode splitting pattern for the differentially rotating stars we model is
different than that for uniformly rotating stars, making the mode splitting a
possible discriminant of the internal angular momentum distribution if one
assumes the formidable challenge of mode identification can be overcome.Comment: 6 journal pages, 7 Figures, accepted by Ap
The influence of twin boundaries on the Flux Line Lattice structure in YBaCuO: a study by Small Angle Neutron Scattering
The influence of Twin Boundaries (TB) on the Flux Line Lattice(FLL) structure
was investigated by Small Angle Neutron Scattering (SANS). YBaCuO single
crystals possessing different TB densities were studied. The SANS experiments
show that the TB strongly modify the structure of the FLL. The flux lines
meander as soon as the magnetic field makes an angle with the TB direction.
According to the value of this angle but also to the ratio of the flux lines
density over the TB density, one observes that the FLL exhibits two different
unit cells in the plane perpendicular to the magnetic field. One is the
classical hexagonal and anisotropic cell while the other is affected by an
additional deformation induced by the TB. We discuss a possible relation
between this deformation and the increase of the critical current usually
observed in heavily twinned samples.Comment: accepted for publication in Phys Rev
Seismic evidence for a weak radial differential rotation in intermediate-mass core helium burning stars
The detection of mixed modes that are split by rotation in Kepler red giants
has made it possible to probe the internal rotation profiles of these stars,
which brings new constraints on the transport of angular momentum in stars.
Mosser et al. (2012) have measured the rotation rates in the central regions of
intermediate-mass core helium burning stars (secondary clump stars). Our aim
was to exploit& the rotational splittings of mixed modes to estimate the amount
of radial differential rotation in the interior of secondary clump stars using
Kepler data, in order to place constraints on angular momentum transport in
intermediate-mass stars. We selected a subsample of Kepler secondary clump
stars with mixed modes that are clearly rotationally split. By applying a
thorough statistical analysis, we showed that the splittings of both
gravity-dominated modes (trapped in central regions) and p-dominated modes
(trapped in the envelope) can be measured. We then used these splittings to
estimate the amount of differential rotation by using inversion techniques and
by applying a simplified approach based on asymptotic theory (Goupil et al.
2013). We obtained evidence for a weak radial differential rotation for six of
the seven targets that were selected, with the central regions rotating
to times faster than the envelope. The last target was
found to be consistent with a solid-body rotation. This demonstrates that an
efficient redistribution of angular momentum occurs after the end of the main
sequence in the interior of intermediate-mass stars, either during the
short-lived subgiant phase, or once He-burning has started in the core. In
either case, this should bring constraints on the angular momentum transport
mechanisms that are at work.Comment: 16 pages, 8 figures, accepted in A&
Publisher Correction: Listeners’ perceptions of the certainty and honesty of a speaker are associated with a common prosodic signature
Correction to: Nature Communications https://doi.org/10.1038/s41467-020-20649-4, published online 8 February 2021.
The original version of the Supplementary Information associated with this Article contained errors in Supplementary Figures 1, 3, 4, 5, 7 and 8 and an error in the figure legend of Supplementary Figure 8. The HTML has been updated to include a corrected version of the Supplementary Information; the original incorrect version of the Supplementary Information file can be found as Supplementary Information associated with this Correction
Listeners’ perceptions of the certainty and honesty of a speaker are associated with a common prosodic signature
The success of human cooperation crucially depends on mechanisms enabling individuals to detect unreliability in their conspecifics. Yet, how such epistemic vigilance is achieved from naturalistic sensory inputs remains unclear. Here we show that listeners’ perceptions of the certainty and honesty of other speakers from their speech are based on a common prosodic signature. Using a data-driven method, we separately decode the prosodic features driving listeners’ perceptions of a speaker’s certainty and honesty across pitch, duration and loudness. We find that these two kinds of judgments rely on a common prosodic signature that is perceived independently from individuals’ conceptual knowledge and native language. Finally, we show that listeners extract this prosodic signature automatically, and that this impacts the way they memorize spoken words. These findings shed light on a unique auditory adaptation that enables human listeners to quickly detect and react to unreliability during linguistic interactions
Musical coordination in a large group without plans nor leaders
A widespread belief is that large groups engaged in joint actions that require a high level of flexibility are unable to coordinate without the introduction of additional resources such as shared plans or hierarchical organizations. Here, we put this belief to a test, by empirically investigating coordination within a large group of 16 musicians performing collective free improvisation—a genre in which improvisers aim at creating music that is as complex and unprecedented as possible without relying on shared plans or on an external conductor. We show that musicians freely improvising within a large ensemble can achieve significant levels of coordination, both at the level of their musical actions (i.e., their individual decisions to play or to stop playing) and at the level of their directional intentions (i.e., their intentions to change or to support the music produced by the group). Taken together, these results invite us to reconsider the range and scope of actions achievable by large groups, and to explore alternative organizational models that emphasize decentralized and unscripted forms of collective behavior
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