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, $P(\eta)$, based on large deviation statistics of work and heat, that remains very accurate even when $P(\eta)$ 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.