Investigation on thermal-hydraulic performance of outdoor heat exchanger in air sources heat pump

A plethora of findings exists on the decreasing heat transfer performance of ASHP under frosting condition. This study investigates, using field and laboratory experiments, the frosting behavior and heat transfer performance of fin-tube exchangers. Findings from our initial observation revealed the severity of frosting phenomenon during winter in hot summer and cold winter zone of China; for avoiding the lower COP, defrosting period of ASHP was not longer than 60 min. The results showed that the basic tube surface temperature decreases with running time and remains stable after 70 min, and an adverse pressure drop ensued. The findings, thereby suggests a 70 min defrosting period in ASHP. Comparing jH/fH and COP between exchangers revealed an improved performance of plain fin-tube exchanger over that of louver fin-tube exchanger in all the test conditions. Therefore, under frosting condition, plain fin-tube heat exchanger provides a superior thermal-hydraulic performance over louver fin-tube heat exchanger. Findings from this study will help designers and facility managers in taking a more informed decision when selecting heat exchanger types for ASHP

Assortative Mixing Equilibria in Social Network Games

It is known that individuals in social networks tend to exhibit homophily (a.k.a. assortative mixing) in their social ties, which implies that they prefer bonding with others of their own kind. But what are the reasons for this phenomenon? Is it that such relations are more convenient and easier to maintain? Or are there also some more tangible benefits to be gained from this collective behaviour? The current work takes a game-theoretic perspective on this phenomenon, and studies the conditions under which different assortative mixing strategies lead to equilibrium in an evolving social network. We focus on a biased preferential attachment model where the strategy of each group (e.g., political or social minority) determines the level of bias of its members toward other group members and non-members. Our first result is that if the utility function that the group attempts to maximize is the degree centrality of the group, interpreted as the sum of degrees of the group members in the network, then the only strategy achieving Nash equilibrium is a perfect homophily, which implies that cooperation with other groups is harmful to this utility function. A second, and perhaps more surprising, result is that if a reward for inter-group cooperation is added to the utility function (e.g., externally enforced by an authority as a regulation), then there are only two possible equilibria, namely, perfect homophily or perfect heterophily, and it is possible to characterize their feasibility spaces. Interestingly, these results hold regardless of the minority-majority ratio in the population. We believe that these results, as well as the game-theoretic perspective presented herein, may contribute to a better understanding of the forces that shape the groups and communities of our society

Antioxidant activity of longan (Dimocarpus longan) barks and leaves

In this paper, the barks and leaves of longan (Dimocarpus longan Lour.) were extracted with 80% methanol. The antioxidant activity and the contents of ellagic acid (EA) in the extracts were investigated. For the evaluation of antioxidant activities, the extracts possess almost the same 2,2- diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and reducing power. Besides, the antioxidant activity was concomitant with the development of the reducing power with high correlation coefficients. The contents of EA in the extracts were 0.91 and 3.723 mg/g dry samples, respectively. After hydrolysis, the EA contents increased almost three and four times. Therefore, the ellagic acid in longan barks and leaves exist mostly in the form of ellagitannins. The research showed that longan barks and leaves not only were excellent sources of free-radical inhibitors, but also had potential use in the production of ellagic acid.Key words: Antioxidant activity, ellagic acid, longan, barks, leaves

On optimality of jury selection in crowdsourcing

Recent advances in crowdsourcing technologies enable computationally challenging tasks (e.g., sentiment analysis and entity resolution) to be performed by Internet workers, driven mainly by monetary incentives. A fundamental question is: how should workers be selected, so that the tasks in hand can be accomplished successfully and economically? In this paper, we study the Jury Selection Problem (JSP): Given a monetary budget, and a set of decision-making tasks (e.g., “Is Bill Gates still the CEO of Microsoft now?”), return the set of workers (called jury), such that their answers yield the highest “Jury Quality” (or JQ). Existing JSP solutions make use of the Majority Voting (MV) strategy, which uses the answer chosen by the largest number of workers. We show that MV does not yield the best solution for JSP. We further prove that among all voting strategies (including deterministic and randomized strategies), Bayesian Voting (BV) can optimally solve JSP. We then examine how to solve JSP based on BV. This is technically challenging, since computing the JQ with BV is NP-hard. We solve this problem by proposing an approximate algorithm that is computationally efficient. Our approximate JQ computation algorithm is also highly accurate, and its error is proved to be bounded within 1%. We extend our solution by considering the task owner’s “belief” (or prior) on the answers of the tasks. Experiments on synthetic and real datasets show that our new approach is consistently better than the best JSP solution known.published_or_final_versio

Atomic structure of Ge quantum dots on the Si(001) surface

In situ morphological investigation of the {105} faceted Ge islands on the Si(001) surface (hut clusters) have been carried out using an ultra high vacuum instrument integrating a high resolution scanning tunnelling microscope and a molecular beam epitaxy vessel. Both species of hut clusters--pyramids and wedges--were found to have the same structure of the {105} facets which was visualized. Structures of vertexes of the pyramidal clusters and ridges of the wedge-shaped clusters were revealed as well and found to be different. This allowed us to propose a crystallographic model of the {105} facets as well as models of the atomic structure of both species of the hut clusters. An inference is made that transitions between the cluster shapes are impossible.Comment: 6 pages, 6 figures. Accepted to JETP Letters (publication date 2010-03-25

Simultaneous estimation of attenuation and structure parameters of aggregated red blood cells from backscatter measurements

The analysis of the ultrasonic frequency-dependent backscatter coefficient of aggregating red blood cells reveals information about blood structural properties. The difficulty to apply this technique in vivo is due to the frequency-dependent attenuation caused by intervening tissue layers that distorts the spectral content of backscattering properties from blood microstructures. An optimization method is proposed to simultaneously estimate tissue attenuation and blood structure factor. In an in vitro experiment, the method gave satisfactory estimates with relative errors below 22% for attenuations between 0.101 and 0.317 dB/cm/MHz, signal-to-noise ratios>28 dB and kR<2.7 (k being the wave number and R the aggregate radius)

Comparison and analysis of flux-switching permanent-magnet double-rotor machine with 4QT used for HEV

This journal issue contains selected papers from the 2014 IEEE International Magnetics (INTERMAG) ConferenceCQ - Motors, generators and actuators VIpublished_or_final_versio