4,932 research outputs found
Entropy-based characterizations of the observable-dependence of the fluctuation-dissipation temperature
The definition of a nonequilibrium temperature through generalized
fluctuation-dissipation relations relies on the independence of the
fluctuation-dissipation temperature from the observable considered. We argue
that this observable independence is deeply related to the uniformity of the
phase-space probability distribution on the hypersurfaces of constant energy.
This property is shown explicitly on three different stochastic models, where
observable-dependence of the fluctuation-dissipation temperature arises only
when the uniformity of the phase-space distribution is broken. The first model
is an energy transport model on a ring, with biased local transfer rules. In
the second model, defined on a fully connected geometry, energy is exchanged
with two heat baths at different temperatures, breaking the uniformity of the
phase-space distribution. Finally, in the last model, the system is connected
to a zero temperature reservoir, and preserves the uniformity of the
phase-space distribution in the relaxation regime, leading to an
observable-independent temperature.Comment: 15 pages, 7 figure
Stability of Monitoring Weak Changes in Multiply Scattering Media with Ambient Noise Correlation: Laboratory Experiments
Previous studies have shown that small changes can be monitored in a
scattering medium by observing phase shifts in the coda. Passive monitoring of
weak changes through ambient noise correlation has already been applied to
seismology, acoustics and engineering. Usually, this is done under the
assumption that a properly reconstructed Green function as well as stable
background noise sources are necessary. In order to further develop this
monitoring technique, a laboratory experiment was performed in the 2.5MHz range
in a gel with scattering inclusions, comparing an active (pulse-echo) form of
monitoring to a passive (correlation) one. Present results show that
temperature changes in the medium can be observed even if the Green function
(GF) of the medium is not reconstructed. Moreover, this article establishes
that the GF reconstruction in the correlations is not a necessary condition:
the only condition to monitoring with correlation (passive experiment) is the
relative stability of the background noise structure
Intertwined Orders in Heavy-Fermion Superconductor CeCoIn
The appearance of spin-density-wave (SDW) magnetic order in the
low-temperature and high-field corner of the superconducting phase diagram of
CeCoIn is unique among unconventional superconductors. The nature of this
magnetic phase is a matter of current debate. Here, we present the thermal
conductivity of CeCoIn in a rotating magnetic field, which reveals the
presence of an additional order inside the phase that is intimately
intertwined with the superconducting -wave and SDW orders. A discontinuous
change of the thermal conductivity within the phase, when the magnetic
field is rotated about antinodes of the superconducting -wave order
parameter, demands that the additional order must change abruptly together with
the recently observed switching of the SDW. A combination of interactions,
where spin-orbit coupling orients the SDW, which then selects the secondary
-wave pair-density-wave component (with an average amplitude of 20\% of the
primary -wave order parameter), accounts for the observed behavior
Hydrodynamic equations for self-propelled particles: microscopic derivation and stability analysis
Considering a gas of self-propelled particles with binary interactions, we
derive the hydrodynamic equations governing the density and velocity fields
from the microscopic dynamics, in the framework of the associated Boltzmann
equation. Explicit expressions for the transport coefficients are given, as a
function of the microscopic parameters of the model. We show that the
homogeneous state with zero hydrodynamic velocity is unstable above a critical
density (which depends on the microscopic parameters), signaling the onset of a
collective motion. Comparison with numerical simulations on a standard model of
self-propelled particles shows that the phase diagram we obtain is robust, in
the sense that it depends only slightly on the precise definition of the model.
While the homogeneous flow is found to be stable far from the transition line,
it becomes unstable with respect to finite-wavelength perturbations close to
the transition, implying a non trivial spatio-temporal structure for the
resulting flow. We find solitary wave solutions of the hydrodynamic equations,
quite similar to the stripes reported in direct numerical simulations of
self-propelled particles.Comment: 33 pages, 11 figures, submitted to J. Phys.
Ohm's Law for a Relativistic Pair Plasma
We derive the fully relativistic Ohm's law for an electron-positron plasma.
The absence of non-resistive terms in Ohm's law and the natural substitution of
the 4-velocity for the velocity flux in the relativistic bulk plasma equations
do not require the field gradient length scale to be much larger than the
lepton inertial lengths, or the existence of a frame in which the distribution
functions are isotropic.Comment: 12 pages, plain TeX, Phys. Rev. Lett. 71 3481 (1993
The business case for women leaders: Meta-analysis, research critique, and path forward
Since the 1990s, a growing body of research has sought to quantify the relationship between women’s representation in leadership positions and organizational financial performance. Commonly known as the “business case” for women’s leadership, the idea is that having more women leaders is good for business. Through meta-analysis ( k = 78, n = 117,639 organizations) of the direct effects of women’s representation in leadership (as CEOs, on top management teams, and on boards of directors) on financial performance, and tests that proxy theoretical arguments for moderated relationships, we call attention to equivocal findings. Our results suggest women’s leadership may affect firm performance in general and sales performance in particular. And women’s leadership—overall and, specifically, the presence of a female CEO—is more likely to positively relate to firms’ financial performance in more gender egalitarian cultures. Yet taking our findings as a whole, we argue that commonly used methods of testing the business case for women leaders may limit our ability as scholars to understand the value that women bring to leadership positions. We do not advocate that the business case be abandoned altogether but, rather, improved and refined. We name exemplary research studies to show how different perspectives on gender, alternative conceptualizations of value, and the specification of underlying mechanisms linking leadership to performance can generate changes in both the dominant ontology and the epistemology underlying this body of research.</jats:p
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