16,965 research outputs found
Efficiency and Large Deviations in Time-Asymmetric Stochastic Heat Engines
In a stochastic heat engine driven by a cyclic non-equilibrium protocol,
fluctuations in work and heat give rise to a fluctuating efficiency. Using
computer simulations and tools from large deviation theory, we have examined
these fluctuations in detail for a model two-state engine. We find in general
that the form of efficiency probability distributions is similar to those
described by Verley et al. [2014 Nat Comm, 5 4721], in particular featuring a
local minimum in the long-time limit. In contrast to the time-symmetric engine
protocols studied previously, however, this minimum need not occur at the value
characteristic of a reversible Carnot engine. Furthermore, while the local
minimum may reside at the global minimum of a large deviation rate function, it
does not generally correspond to the least likely efficiency measured over
finite time. We introduce a general approximation for the finite-time
efficiency distribution, , based on large deviation statistics of work
and heat, that remains very accurate even when deviates significantly
from its large deviation form.Comment: 10 pages, 3 figure
Near-optimal protocols in complex nonequilibrium transformations
The development of sophisticated experimental means to control nanoscale
systems has motivated efforts to design driving protocols which minimize the
energy dissipated to the environment. Computational models are a crucial tool
in this practical challenge. We describe a general method for sampling an
ensemble of finite-time, nonequilibrium protocols biased towards a low average
dissipation. We show that this scheme can be carried out very efficiently in
several limiting cases. As an application, we sample the ensemble of
low-dissipation protocols that invert the magnetization of a 2D Ising model and
explore how the diversity of the protocols varies in response to constraints on
the average dissipation. In this example, we find that there is a large set of
protocols with average dissipation close to the optimal value, which we argue
is a general phenomenon.Comment: 6 pages and 3 figures plus 4 pages and 5 figures of supplemental
materia
Young Stars with SALT
We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77
systems. All are low-proper-motion southern hemisphere objects and were
identified in a nearby star survey with a demonstrated sensitivity to young
stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph
(RSS) on the South African Large Telescope (SALT), we have determined radial
velocities, H-alpha, Lithium 6708\AA, and Potassium 7699\AA~equivalent widths
linked to age and activity, and spectral types for all our targets. Combined
with astrometric information from literature sources, we identify 44 young
stars. Eighteen are previously known members of moving groups within 100
parsecs of the Sun. Twelve are new members, including one member of the TW
Hydra moving group, one member of the 32 Orionis moving group, nine members of
Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We
also find fourteen young star systems that are not members of any known groups.
The remaining 33 star systems do not appear to be young. This appears to be
evidence of a new population of nearby young stars not related to the known
nearby young moving groups.Comment: 23 pages, 11 figures, 6 tables. Accepted to Ap
Contractile units in disordered actomyosin bundles arise from F-actin buckling
Bundles of filaments and motors are central to contractility in cells. The
classic example is striated muscle, where actomyosin contractility is mediated
by highly organized sarcomeres which act as fundamental contractile units.
However, many contractile bundles in vivo and in vitro lack sarcomeric
organization. Here we propose a model for how contractility can arise in
actomyosin bundles without sarcomeric organization and validate its predictions
with experiments on a reconstituted system. In the model, internal stresses in
frustrated arrangements of motors with diverse velocities cause filaments to
buckle, leading to overall shortening. We describe the onset of buckling in the
presence of stochastic actin-myosin detachment and predict that
buckling-induced contraction occurs in an intermediate range of motor
densities. We then calculate the size of the "contractile units" associated
with this process. Consistent with these results, our reconstituted actomyosin
bundles contract at relatively high motor density, and we observe buckling at
the predicted length scale.Comment: 5 pages, 4 figures, Supporting text and movies attache
Bounded Rationality\u27s Account for the Influence of Group Identification on Ingroup Favoritism: A Field Investigation Using Jewish and Arab Populations in Israel
We used the bounded rationality approach to explore the impact of group identification on intergroup relations. 1,289 Jewish and Arab citizens completed assessments of group identification, functional relations, and indices of ingroup favoritism. Results provided evidence of (a) a positive relation between group identification and ingroup favoritism; (b) perceptions of more positive functional relations that were associated with less ingroup favoritism; and (c) that high-identifiers who evaluated relations as positive experienced the lowest levels of ingroup favoritism. We discuss how the results clarify the complex relation between group identification and ingroup favoritism
A Fundamental Comparison of International Real Estate Returns
This study analyzes commercial real estate returns in Australia, Canada, the United Kingdom, and the United States over the period 1985-95, from the perspective of a U.S. investor. Because national indices can consist of differing property mixes, this study separately analyzes the office, retail, and warehouse sectors. Moreover, these analyses also convert total returns into their fundamental components: initial yield, growth in income, and shifts in capitalization rates. The paths of currency-adjusted income and asset values and, therefore, capitalization rates are also presented. Generally speaking, the fundamental components of retail returns across the four countries exhibit greater divergence than the office and warehouse sectors. It is interesting that the U.S. property sectors showed the worst performance, while the Australian retail and the British office and warehouse sectors were the best performers (both before and after currency adjustments). Additionally, the currency-adjusted Australian returns were adversely effected by exchange rate movements, while the British returns were positively effected. Lastly, the correlation of the quarterly percentage change in income was generally lower and less statistically significant that the correlation patterns observed among the other components of return. This might suggest that more idiosyncratic risk can be found in the real estate space markets (as proxied by income changes) than in the real estate capital markets (as proxied by the pricing of the income--that is, capitalization rates), which appear to be more globally influenced.
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