Extended vertical lists for temporal pattern mining from multivariate time series

In this paper, the problem of mining complex temporal patterns in the context of multivariate time series is considered. A new method called the Fast Temporal Pattern Mining with Extended Vertical Lists is introduced. The method is based on an extension of the level‐wise property, which requires a more complex pattern to start at positions within a record where all of the subpatterns of the pattern start. The approach is built around a novel data structure called the Extended Vertical List that tracks positions of the first state of the pattern inside records and links them to appropriate positions of a specific subpattern of the pattern called the prefix. Extensive computational results indicate that the new method performs significantly faster than the previous version of the algorithm for Temporal Pattern Mining; however, the increase in speed comes at the expense of increased memory usage.     

Querying on large and complex databases by content: Challenges on variety and veracity regarding real applications

The amount and variety of digital data currently being generated, stored and analyzed, including images, videos, and time series, have brought challenges to data administrators, analysts and developers, who struggle to comply with the expectations of both data owners and end users. The majority of the applications demand searching complex data by taking advantage of queries that analyze different aspects of the data, and need the answers in a timely manner. Content-based similarity retrieval techniques are well-suited to handle large databases, because they enable performing queries and analyses using features automatically extracted from the data, without users’ intervention. In this paper, we review and discuss the challenges posed to the database and related communities in order to provide techniques and tools that can meet the variety and veracity characteristics of big and complex data, while also considering the aspects of semantical preservation and completeness of the data. Examples and results obtained over a two-decade-long experience with real applications are presented and discussed.     

Numerical investigations on the Dish–Stirling engine system

The Stirling engine is an environmentally friendly external combustion heat engine and reduces the complexities of the combustion process, and indirectly helps in reduction of CO₂ emission. Modelling based on cyclic analysis is performed for a Beta configuration Stirling engine of 1.5?kW_e capacity using a rhombic drive for the solar-dish-supported Stirling engine. The analysis helps in estimating the overall efficiency of the system using the experimental correlation of the solar concentrator ARUN160 at the engine operating temperature. The analysis shows that the system will have overall efficiency around 25% in the range of 750–1050?K at the expansion space. The degradation of performance compared to that at an operating temperature of 1025?K is only marginal and makes 750?K a more preferred temperature. The present study evaluates a range of possible design goals and provides suitable alternatives and thus provides a clear understanding of the system design considerations.     

Why stop after 20 minutes? Breaks and target prevalence in a 60-minute X-ray baggage screening task

Current EU regulation restricts continuously reviewing X-ray images of passenger baggage to 20-min duration as a precautionary measure to prevent performance decrements in airport security officers (screeners). However, this 20-min limit is not based on clear empirical evidence on how well screeners can sustain their performance over time. Our study tested screeners in a 60-min simulated X-ray cabin baggage screening task. One group took 10-min breaks after 20 min of screening; the other group worked without breaks. We found no decrease in performance over 60 min in either group. Breaks did not affect performance, but they did reduce the amount of subjective distress. By varying target prevalence, we found that d_a with a slope of about 0.6 is a more valid measure of detection performance than d'. Target prevalence caused a criterion shift. Our results provide a basis for conducting field studies of prolonged screening durations, and open the discussion on whether more flexible break policies and work schedules should be considered.     

Heterogeneity in zooplankton distributions and vertical migrations: Application of a laser optical plankton counter in offshore Lake Michigan

Zooplankton distributions are patchy due to multiple physical, chemical, and biological processes, including diel vertical migration (DVM) behavior. Heterogeneity in the offshore environment is difficult to study with net tows, but newer technologies measure finer-scale distributions. Here, we use laser optical plankton counter (LOPC) data, informed by net tows, to study distributions and DVM of zooplankton in offshore Lake Michigan during July and September 2015. Water column (5–60 m) zooplankton biomass varied by an order of magnitude among transects and a factor of two within individual transects (6–19 km distances); transect coefficients of variation (SD/mean) ranged from 7 to 22% (~0.5 km scale). Horizontal patterns in zooplankton biomass varied among size groups but were consistent from day to night, suggesting that processes driving heterogeneity persist for hours to days. Fine-scale LOPC data show that zooplankton often aggregate in thin layers (1–3 m) within the metalimnion, a feature undetectable by coarser net sampling. Although DVM was not consistently observed, some patterns emerged. Small zooplankton including copepodites, diaptomids (Leptodiaptomus ashlandi, L. minutus), and Diacyclops thomasi often migrated to surface waters at night, and large zooplankton (Limnocalanus macrurus) migrated upward at night in most cases. Beam attenuation coefficient (proxy for phytoplankton biomass) was a significant predictor for zooplankton mean depth (p < 0.001) although it explained more of the variation for night data (R² = 0.72) than day data (R² = 0.53). The heterogeneity observed in zooplankton distributions has implications for planktivorous fish feeding in the offshore zone, as prey density varies greatly with depth.     

An improved cuckoo search algorithm and its application in vibration fault diagnosis for a hydroelectric generating unit

This article presents an improved cuckoo search (ICS) algorithm based on the parametric adaptation mechanism and non-uniform mutation. In the ICS algorithm, the biased random walk operator is modified to take advantage of the neighbourhood information of the current solution, and then the control parameters of step size, discovery probability and scaling factor are directly integrated into the optimized problems. Meanwhile, the non-uniform mutation operation is used to adaptively tune the search step of the current optimal solution. To evaluate the feasibility and efficiency of the presented algorithm, three groups of benchmark test functions are employed to perform the validation analysis. Subsequently, to diagnose the vibration fault of a hydroelectric generating unit, a combinational model is built, which combines ICS with a back-propagation neural network (ICSBP). The experimental results indicate that ICS is competitive on the optimization problems, and the ICSBP approach can effectively improve the accuracy of vibration fault diagnosis for a hydroelectric generating unit.     

一种基于MEMS工艺的365 GHz硅微波导垂直转接结构

基于微电子机械系统(MEMS)工艺设计并制作了一种THz垂直转接结构,该结构采用6层硅片堆叠的硅微波导形式。理论分析计算了垂直转接结构的参数,并使用三维电磁场分析软件HFSS对该结构进行了模拟仿真。设计得到了中心频率为365 GHz、带宽为80 GHz、芯片尺寸为10 mm×7 mm×2.7 mm的THz垂直转接结构。给出了一套基于MEMS工艺的硅微波导的制作流程,制作了365 GHz垂直转接结构并对其进行测试。获得的THz垂直转接结构的回波损耗随频率变化的测试结果与仿真结果基本一致。采用MEMS工艺制作的硅微波导垂直转接结构具有精度高、一致性好、成本低的特点,满足THz器件的发展需求。     

User-friendly search interface for older adults: supporting search goal refreshing in working memory to improve information search strategies

ABSTRACT

This study investigates how a search interface that displays users’ ultimate query (i.e. users’ current search goal) can cope with the age-related decrease of fluid abilities and support older users’ search behaviours. 30 young and 18 older adults completed 9 search problems with a regular web browser or with the experimental search interface. Results showed that older adults spent longer time on the search engine result pages, they needed more time to reformulate, and they had more difficulties exploring the search paths elaborated. Age-differences also appeared as soon as the beginning of the search. The support tool helped older users reformulate their queries more rapidly and elaborate more flexible search strategies at the beginning of the activity. Indeed, older adults who interacted with the support tool switched to the processing of a new search path more rapidly instead of exploiting their initial query (i.e. they visited fewer websites for the initial query produced and reformulated a query instead of keeping on conducting a deeper investigation of the search results provided in the search engine result page). Implications of these findings for the design of effective support tools for older users are discussed.     

浅谈船用主机使用低硫燃油面临的挑战与应对措施

介绍了低硫燃油和传统的船用高硫燃油在化学成分和物理特性方面存在的诸多不同;指出:IMO2020限硫令对船舶运营带来了很大的挑战。基于两大主机制造商的相关文件和实际服务经验，归纳总结了船用主机使用低硫燃油运营时应注意的事项及应对措施，为船舶安全稳定运营提供参考。     

Second order velocity slip and thermal jump of Cu–water nanofluid over a cone in the presence of nonlinear radiation and nonuniform heat source/sink using homotopy analysis method

The purpose of the present paper is to explore the second order slip effects on nanofluid flow over a vertical cone. The effects of nonlinear thermal radiation and nonuniform heat source/sink are also taken into account. Water with copper nanoparticles is used as nanofluid in this investigation. The governing partial differential equations for the flow are converted into ordinary differential equations by using transformations and then are solved using homotopy analysis method. The influence of various important parameters on velocity, temperature, skin‐friction, and Nusselt number are presented through graphs. Results indicate that the velocity and magnitude of skin friction decrease with a rise in first and second order velocity slips. A raise in either first or second order temperature jump causes a fall in temperature. Nonlinear radiation increases the more rapidly when compared to the linear radiation case.