Counterfactual Learning from Bandit Feedback under Deterministic Logging: A Case Study in Statistical Machine Translation

The goal of counterfactual learning for statistical machine translation (SMT) is to optimize a target SMT system from logged data that consist of user feedback to translations that were predicted by another, historic SMT system. A challenge arises by the fact that risk-averse commercial SMT systems deterministically log the most probable translation. The lack of sufficient exploration of the SMT output space seemingly contradicts the theoretical requirements for counterfactual learning. We show that counterfactual learning from deterministic bandit logs is possible nevertheless by smoothing out deterministic components in learning. This can be achieved by additive and multiplicative control variates that avoid degenerate behavior in empirical risk minimization. Our simulation experiments show improvements of up to 2 BLEU points by counterfactual learning from deterministic bandit feedback.Comment: Conference on Empirical Methods in Natural Language Processing (EMNLP), 2017, Copenhagen, Denmar

The Economic Effects of Direct Democracy – A First Global Assessment

This is the first study that assesses the economic effects of direct democratic institutions on a cross country basis. Its results are based on up to six new measures produced to reflect the legislative basis for using direct democratic institutions as well as their factual use. In addition, a more general overall indicator is used. On the basis of these two different data sets only some of the results of the former intra-country studies are confirmed. An analysis based on the more general democracy index for 87 countries shows that a higher degree of direct democracy leads to lower budget deficits and higher government effectiveness. The effects on government expenditure, corruption and productivity have the expected signs but do not reach conventional levels of significance. A more fine grained analysis for a cross section of 88 countries based on the second data set shows that institutional detail matters a great deal. In particular, the mere possibility of drawing on direct-democratic institutions is often not sufficient to induce significant effects whereas the frequency of their factual use has a number of substantive effects on economic variables.direct democracy, economic effects of constitutions, positive constitutional economics

White Heterosexual Men, Athletic Bodies, and the Pleasure of Unruly Racialization

In recent times, the semi-naked male athletic body has become central to the cultural imagination of late modern societies, in turn, inviting comment from social scientists of different shades on the changing gazes of heterosexual men. Interestingly, and despite frequently appearing in sport and leisure media, the racialized aspects of this change are yet to be explored fully. This article, therefore, considers how white heterosexual men (de)construct and (re)attach gendered and sexualized meanings to those male athletic bodies they struggle to define “racially.” Borrowing Gilroy’s use of the term “unruly,” which he employs to capture those moments of multiculture that are hard to “home” culturally or geographically, I refer to this struggle as a process of unruly racialization. After analyzing interviews with twentytwo self-identifying white, British, heterosexual men, this article argues that male bodies racialized as unruly are marked with varying degrees of intrigue, jealously, admiration, and fear. I conclude by reflecting on the extent to which this cultural shift can be read as a move toward a future beyond “race.

Well-Pointed Coalgebras

For endofunctors of varieties preserving intersections, a new description of the final coalgebra and the initial algebra is presented: the former consists of all well-pointed coalgebras. These are the pointed coalgebras having no proper subobject and no proper quotient. The initial algebra consists of all well-pointed coalgebras that are well-founded in the sense of Osius and Taylor. And initial algebras are precisely the final well-founded coalgebras. Finally, the initial iterative algebra consists of all finite well-pointed coalgebras. Numerous examples are discussed e.g. automata, graphs, and labeled transition systems

Analysis and Comparison of Two-Phase Ejector Performance Metrics for R134a and CO2 Ejectors

Two-phase ejectors have been gaining increased attention in recent years due to their ability to directly improve the COP of the cycle. Of common interest in two-phase ejector studies is how the ejector improves cycle COP. However, less emphasis is often given to the performance of the two-phase ejector itself. The amount of COP improvement offered by an ejector cycle is very strongly influenced by the performance of the two-phase ejector; thus, it is important to understand the operation and performance of the two-phase ejector. Defining the performance of a two-phase ejector is not as straightforward as for an isentropic expander because there are multiple fluid streams in an ejector and because it is difficult to obtain flow properties at some locations in the ejector. As a result, there are a variety of performance metrics that have been proposed for use with ejectors in general and specifically for two-phase ejectors. In the present study, several different metrics that have been proposed for measuring the performance of ejectors are presented and analyzed. Performance metrics that were originally proposed for single-phase ejectors as well as those proposed specifically for two-phase ejectors are both considered. A simple numerical ejector model is used to simulate ejector operation and calculate the performance of the ejector based on the various performance metrics. The various ejector performance metrics are then compared based on the numerical results. Experimental data for R134a and CO2 two-phase ejectors is also presented, and the ejector performance metrics are compared based on the available experimental data as well. It is seen that R134a and CO2 offer somewhat similar ejector performance, though the CO2 ejector does seem to have noticeably better performance. CO2 has significantly higher throttling loss than R134a, meaning that there is more work available for the two-phase ejector to recover with CO2 and larger potential COP improvement for a CO2 cycle

Experimental and Numerical Study on the Performance of R410A Liquid Recirculation Cycles with and without Ejectors

Liquid recirculation is a method of improving evaporator performance by supplying the evaporator with more liquid than is evaporated. The excess liquid, which is generally provided by means of an externally driven, mechanical pump, eliminates dryout and increases overall heat transfer coefficient in the evaporator. Liquid recirculation is common in large-scale industrial refrigeration systems, where the additional cost and complexity of the pump is justified by the large size of the system. However, liquid recirculation has yet to gain widespread application in small-scale systems, such as residential or automotive air conditioning. The use of an ejector to provide the recirculation effect rather than a mechanical pump can help liquid recirculation systems gain consideration for small-scale systems. However, the performance of liquid recirculation cycles with and without ejectors for small-scale systems has yet to be thoroughly investigated. This paper presents the results of an experimental and numerical study of the effect of liquid recirculation on the performance of air condition cycles. The refrigerant R410A, commonly considered for residential systems, is used as the working fluid. A numerical model of a liquid recirculation cycle, capable of accounting for heat transfer and pressure drop effects in the evaporator, was developed and used to predict the effect that recirculation ratio (ratio of total evaporator mass flow rate to mass flow rate of vaporized liquid) has on cycle COP. A liquid recirculation cycle with a mechanical pump was constructed and tested at various evaporator mass flow rates for a fixed cooling capacity in order to see experimentally the effect of recirculation ratio on the COP of the cycle. Cycles in which the work recovered by the expansion process in the ejector is used to provide the pumping effect, instead of the mechanical pump, are then presented and analyzed, and the ability of the ejector to act as a viable replacement for the mechanical pump in liquid recirculation systems is discussed

Numerical Study on the Design of Microchannel Evaporators for Ejector Refrigeration Cycles

Two-phase ejectors are devices capable of improving the performance of refrigeration and air conditioning cycles by means of expansion work recovery. Ejector studies often focus on the design and performance of the two-phase ejector and the effect it can have on the performance of the ejector cycle. However, the ejector is not the only component of the system that can have a significant influence on the performance of the ejector cycle. Recent experimental work has shown that the effect of evaporator design on ejector cycle performance can be quite significant, though there is very little research available on the relation between evaporator design and ejector cycle performance. In this paper, a numerical model of a microchannel air-to-refrigerant evaporator, capable of accounting for heat transfer and pressure drop effects, is developed and used to investigate the effect that different evaporator dimensions have on the performance of ejector cycles. The model is validated with experimental data from previous ejector cycle studies. There are two ejector cycles of interest: The standard ejector cycle, in which the ejector is used to directly lift the compressor suction pressure, and the ejector recirculation cycle, in which the ejector recirculates excess liquid through the evaporator but does not directly lift compressor suction pressure. The effects of microchannel port hydraulic diameter, number of evaporator passes, refrigerant outlet state, and air-side resistance are investigated. The analysis is performed with refrigerants R134a and CO2 (R744) in order to demonstrate how proper evaporator and ejector cycle design is different for different refrigerants