Workflow resource pattern modelling and visualization

Workflow patterns have been recognized as the theoretical basis to modeling recurring problems in workflow systems. A form of workflow patterns, known as the resource patterns, characterise the behaviour of resources in workflow systems. Despite the fact that many resource patterns have been discovered, people still preclude them from many workflow system implementations. One of reasons could be obscurityin the behaviour of and interaction between resources and a workflow management system. Thus, we provide a modelling and visualization approach for the resource patterns, enabling a resource behaviour modeller to intuitively see the specific resource patterns involved in the lifecycle of a workitem. We believe this research can be extended to benefit not only workflow modelling, but also other applications, such as model validation, human resource behaviour modelling, and workflow model visualization

Pollution level and risk assessment of heavy metals in sewage sludge from eight wastewater treatment plants in Wuhu City, China

Aim of study: To investigate the content, contamination levels and potential sources of five heavy metals (Hg, Pb, Cd, Cr, As) in sewage sludge from eight wastewater treatment plants (W1 to W8).Area of study: Wuhu, located in southeastern Anhui Province, southeastern China.Material and methods: The sewage sludge pollution assessment employed the single-factor pollution index, Nemerow’s synthetic pollution index, monomial potential ecological risk coefficient and potential ecological risk index. The potential sources among the five heavy metals were determined using the Pearson’s correlation analysis and principal component analysis (PCA).Main results: The mean concentrations of the heavy metals were 0.27 mg/kg (Hg), 70.78 mg/kg (Pb), 3.48 mg/kg (Cd), 143.65 mg/kg (Cr) and 22.17 mg/kg (As). W1, W5 and W6 sewage sludge samples showed the highest levels of heavy metal contamination, and cadmium had the highest contamination level in the study area. Pearson’s correlation analysis and PCA revealed that Pb and Cd mainly derived from traffic emissions and the manufacturing industry and that As and Cr originated from agricultural discharges.Research highlights: The pollution of cadmium in Wuhu should be controlled preferentially. The heavy metal pollution of W1, W5 and W6 sewage treatment plants is relatively high, they should be key prevention targets

Co-existence of Anaerobic Ammonium Oxidation Bacteria and Denitrifying Anaerobic Methane Oxidation Bacteria in Sewage Sludge: Community Diversity and Seasonal Dynamics

Anaerobic ammonium oxidation (ANAMMOX) and denitrifying anaerobic methane oxidation (DAMO) have been recently discovered as relevant processes in the carbon and nitrogen cycles of wastewater treatment plants. In this study, the seasonal dynamics of ANAMMOX and DAMO bacterial community structures and their abundance in sewage sludge collected from wastewater treatment plants were analysed. Results indicated that ANAMMOX and DAMO bacteria co-existed in sewage sludge in different seasons and their abundance was positively correlated (P < 0.05). The high abundance of ANAMMOX and DAMO bacteria in autumn and winter indicated that these seasons were the preferred time to favour the growth of ANAMMOX and DAMO bacteria. The community structure of ANNAMOX and DAMO bacteria could also shift with seasonal changes. The "Candidatus Brocadia" genus of ANAMMOX bacteria was mainly recovered in spring and summer, and an unknown cluster was primarily detected in autumn and winter. Similar patterns of seasonal variation in the community structure of DAMO bacteria were also observed. Group B was the dominant in spring and summer, whereas in autumn and winter, group A and group B presented almost the same proportion. The redundancy analysis revealed that pH and nitrate were the most significant factors affecting community structures of these two groups (P < 0.01). This study reported the diversity of ANAMMOX and DAMO in wastewater treatment plants that may be the basis for new nitrogen removal technologies

Numerical study on explosion characteristics of wind turbine blade under lightning induced arc

For enhancing the lightning protection abilities of wind turbine blades, there is the need to study the mechanical explosion characteristics when the blades suffer from lightning induced arc intrusion. In this paper, a magnetohydrodynamic (MHD) model of lightning induced arc intrusion into the blade was developed, and the airflow and gas pressure distribution were calculated accordingly. The simulation results show that the huge pressure generated at the trailing edge of the blade should be the main cause of the trailing edge cracking. The research presented in this paper provides a theoretical basis for improving the structural design of the blade from the lightning protection perspective

A gate-programmable van der Waals metal-ferroelectric-semiconductor memory

Ferroelecticity, one of the keys to realize nonvolatile memories owing to the remanent electric polarization, has been an emerging phenomenon in the two-dimensional (2D) limit. Yet the demonstrations of van der Waals (vdW) memories using 2D ferroelectric materials as an ingredient are very limited. Especially, gate-tunable ferroelectric vdW memristive device, which holds promises in future neuromorphic applications, remains challenging. Here, we show a prototype gate-programmable memory by vertically assembling graphite, CuInP2S6, and MoS2 layers into a metal-ferroelectric-semiconductor architecture. The resulted devices exhibit two-terminal switchable electro-resistance with on-off ratios exceeding 105 and long-term retention, akin to a conventional memristor but strongly coupled to the ferroelectric characteristics of the CuInP2S6 layer. By controlling the top gate, Fermi level of MoS2 can be set inside (outside) of its band gap to quench (enable) the memristive behaviour, yielding a three-terminal gate programmable nonvolatile vdW memory. Our findings pave the way for the engineering of ferroelectric-mediated memories in future implementations of nanoelectronics

Experimental study on lightning attachment manner to wind turbine blades with lightning protection system

Different types of lightning protection systems (LPSs) have been developed for wind turbines to protect the blades from lightning strikes. However, severe damages caused by lightning strikes still happen frequently, which creates huge costs. Experiments using a 5-m blade specimen with tip receptors from 1.5-MW wind turbine blades under 3-m air gap were conducted to investigate the lightning attachment manner to the wind turbine blade with LPS in different situations. Factors including the polarity of the lightning strikes, the orientation of the blade, and the lateral distances (LDs) between the wind turbine blade and the lightning downward leader were taken into account. It was found that the types of discharge paths under positive and negative lightning strikes are quite different, and the positive discharges are much more dangerous to wind turbine blade than the negative ones. The LD between the downward leader and the wind turbine blade is a key factor that influences the interception efficiency. Three types of receptor interception failures were discovered. Multiple upward leaders may incept from the blade body as to intercept the downward leader. However, the protection range of the tip receptor is quite limited, and the connection of the tip receptor and the blade body is the most vulnerable position hit by the lightning strikes. The results present the useful reference to the optimal design of the wind turbine blade LPS

An improved bipolar-type AC-AC converter topology based on non-differential dual-buck PWM AC choppers

A novel single-phase pulse width modulation (PWM) direct ac-ac converter based on two-level non-differential dual-buck ac chopper legs with inverting and non-inverting operations is first proposed in this paper. It has the ability to resolve both voltage sag and swell problems at the same time when used as distributed flexible voltage conditioner (DFVC).Compared to the traditional ac-ac converter, it has much enhanced system reliability thanks to no shoot-through problems even when all switches of each ac chopper legs are turned on, and therefore, the PWM dead-time is not needed leading to improving the utilization of the duty cycles. Only half of the switches in the proposed converter are switched at high frequency during a switching period at most, which significantly reduces the total switching loss. In particularly, the converter has two greatest advantages that it retains the common sharing ground of the input and output and has the same buck/boost operation process for non-inverting and inverting modes. In order to fully testify the performance of the proposed converter, a 500W experimental prototype is built and tested at different conditions