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The importance of plant richness to enhance the presence, biodiversity and efficiency of natural enemies in agricultural systems has largely been studied and demonstrated these last decades. Planting and preserving non-crop plants or manipulating crop richness in fields are practices that have proven their efficiency. However, the impact of crop-richness continuity in space and time on pests and natural enemies at a landscape scale remains poorly studied. In a two-year study, we assessed the effect of crop richness (single crop vs. multiple crops) on pest and natural enemy abundance and spillover in a field experiment in north-east China. Overall, we found crop diversity had a limited impact on pest and natural enemy abundance at the spatial scale tested (0.025 vs. 0.2 ha). The total pest and natural enemy abundances were not different between single-crop and multi-crop plots in either year, and the community composition at the functional group level was mostly determined by the crop but not crop diversity. However, we found that crop diversity influenced the numeric response of ladybirds to aphids in wheat; their negative response (higher abundance where aphid abundance was lower, suggesting predation) was attenuated in multi-crop plots (no correlation of aphid and ladybird abundance, suggesting the use of alternative resources). This pattern was not found in maize. Finally, crop succession enhanced the spillover of ladybirds from wheat and maize to cotton plots but with limited benefits for aphid control. Because of these limited impacts, we hypothesized that crop diversity may benefit natural enemy populations and enhance pest control at larger spatial scales; while we found similar abundances of ladybirds between our small (0.025–0.2 ha) plots and in large (2 ha) close-by cotton fields, aphid abundances were more than ten times higher in large cotton fields. Our study highlights the need to accurately estimate the spatial scale at which crop biodiversity may benefit pest control, in relation to the ecology of the target pest and natural enemies.

Semi-active devices have been widely investigated and applied due to their advantages in control systems. However, for satisfying complicated applications, some semi-active devices need to be capable of controlling multiple mechanical properties, which is hard to implement with a mechanical network considering the space limitation. In this paper, a semi-active variable equivalent stiffness and inertance (VESI) device is developed by an electrical network and an electromagnetic device instead of a mechanical system. Due to that the inerter and spring can store energy, the dynamic control of their mechanical properties without the external power to compensate the stored energy will cause the system discontinuity, which will affect the control performance. Therefore, the variable damping (VD) device is applied to connect with spring or inerter in series to obtain variable equivalent stiffness or inertance properties. Then, according to the force-current analogy, an electrical “VESI” network is designed to simulate the mechanical VESI network. An electromagnetic device equips with the variable electrical system can achieve the VESI mechanical properties, which is validated with experiments. The imaginary part of the admittance of the proposed device can vary to the positive phase and also the negative phase by controlling two resistors. The application of VESI device in the vehicle is investigated and analysed. A semi-active control strategy is designed for vibration control and rollover prevention of vehicles with VESI suspensions. According to the simulation result, the proposed semi-active system can significantly improve the vibration reduction performance at both vertical and roll directions; also, it can decrease the roll angel when vehicles in the cornering maneuver. Besides, the semi-active VESI device with an electrical network has the advantages in installation and maintenance. It has great potential in practical applications.

This paper proposes a hybrid controller for a seat suspension equipped with an advanced electromagnetic damper (EMD) system to meet the requirement with vibration isolation and energy saving. The friction of seat suspension has considerable influence on the system dynamic. Applying a constant model to describe the friction is unreliable due to the long term wear and tear. Therefore, an observer is designed to estimate seat suspension friction, and it is used to compensate for the frictional influence in a H∞ controller. The friction observer applies the acceleration, relative displacement and circuit current, which are measurable in engineering. Then, a hybrid controller is further proposed, in which the low-frequency vibration is controlled with the friction observer-based H∞ controller, and the system will switch to passive state with low damping at high frequency based on the dominant frequency of the vibration. In order to validate the effectiveness of the proposed friction observer, the Bouc-Wen friction model is selected to describe actual seat suspension friction, and it is compared with the estimated friction by the observer. Experimental results show that the friction observer has similar performance and less computational complexity compared with the Bouc-Wen friction model. The effectiveness of the proposed hybrid controller is validated on a six-degree of freedom vibration platform with the bump and random excitation. This friction observer-based hybrid controller is helpful for the engineering application as it applies practically measurable variables as feedback and considers the performance of the semi-active device in reality.

The recently discovered material Cs$_3$Fe$_2$Br$_9$ contains Fe$_2$Br$_9$ bi-octahedra forming triangular layers with hexagonal stacking along the $c$ axis. In contrast to isostructural Cr-based compounds, the zero-field ground state is not a nonmagnetic $S=0$ singlet-dimer state. Instead, the Fe$_2$Br$_9$ bi-octahedra host semiclassical $S=5/2$ Fe$^{3+}$ spins with a pronounced easy-axis anisotropy along $c$ and interestingly, the intra-dimer spins are ordered ferromagnetically. The high degree of magnetic frustration due to (various) competing intra- and inter-dimer couplings leads to a surprisingly rich magnetic phase diagram. Already the zero-field ground state is reached via an intermediate phase, and the high-field magnetization and thermal expansion data for $H\parallel c$ identify ten different ordered phases. Among them are phases with constant magnetization of 1/3, respectively 1/2 of the saturation value, and several transitions are strongly hysteretic with pronounced length changes reflecting strong magnetoelastic coupling., 11 pages, 12 figures (minor corrections and 3 additional have been included in V3)

The hydrodynamic performance of a floating cylindrical oscillating water column (OWC) wave energy converter is investigated experimentally and numerically. The physical experiment is carried out in a wave flume at Dalian University of Technology. The floating cylindrical OWC device is constrained by springs and only moves vertically. A second-order time-domain Higher-Order Boundary Element Method, based on the perturbation expansion technique, is used to simulate the nonlinear wave interaction with the floating OWC device. The nonlinear terms concerning the pneumatic and viscous damping are introduced to the free surface boundary conditions inside the OWC chamber. The chamber surface elevation and air pressure, the hydrodynamic efficiency, and the vertical displacement of the OWC device are examined in detail. Good agreements are obtained between experimental data and numerical results. Then, the effects of opening ratio, wave steepness, mooring stiffness and chamber draft on the hydrodynamic performance are then investigated. It is found that the optimal opening ratio is between 0.02 and 0.03. The mooring stiffness plays an important role on the hydrodynamic response of the OWC device. The hydrodynamic efficiency and effective frequency bandwidth increase with the mooring stiffness.

The crystal and magnetic structure of multiferroic LiFe(WO$_4$)$_2$ were investigated by temperature and magnetic-field dependent specific heat, susceptibility and neutron diffraction experiments on single crystals. Considering only the two nearest-neighbour magnetic interactions, the system forms a $J_1$, $J_2$ magnetic chain but more extended interactions are sizeable. Two different magnetic phases exhibiting long-range incommensurate order evolve at $T_{\text{N}1}\approx 22.2 \text{ K}$ and $T_{\text{N}2}\approx 19 \text{ K}$. First, a spin-density wave develops with moments lying in the $ac$ plane. In its multiferroic phase below $T_{\text{N}2}$, LiFe(WO$_4$)$_2$ exhibits a spiral arrangement with an additional spin-component along $b$. Therefore, the inverse Dzyaloshinskii-Moriya mechanism fully explains the multiferroic behavior in this material. A partially unbalanced multiferroic domain distribution was observed even in the absence of an applied electric field. For both phases only a slight temperature dependence of the incommensurability was observed and there is no commensurate phase emerging at low temperature or at finite magnetic fields up to $6\text{ T}$. LiFe(WO$_4$)$_2$ thus exhibits a simple phase diagram with the typical sequence of transitions for a type-II multiferroic material., This manuscript has been accepted as a regular article in PRB: https://journals.aps.org/prb/accepted/fb07cO25Le41de3ae74211d6e869185cdc06df242

Multi-functional platform is a promising way to enhance the economic power production from multiple renewable energy sources. This paper investigates numerically and experimentally the hydrodynamic performance of an oscillating water column (OWC) wave energy converter (WEC), integrated into a monopile-mounted offshore wind turbine (OWT). Based on linear potential flow theory, a 3D time-domain numerical model was developed, based on the higher-order boundary element method, to investigate the coupled hydrodynamic response of a cylindrical-type OWC device. A nonlinear pneumatic model was utilized to simulate the turbine damping. Experiments on the integrated system were carried out in a wave flume at Dalian University of Technology. The numerical results agree well with the experimental studies, including i) the surface elevation and air pressure inside the chamber, ii) wave pressure on the OWT monopile and iii) hydrodynamic efficiency. Furthermore, the effects of the OWC damping and wave steepness on the OWC-OWT system were investigated. It was found that the introduction of the OWC can significantly reduce the horizontal force and overturning moment on the OWT monopile, and that the wave steepness has a significant influence on the OWC efficiency, especially at resonance.

In this chapter, a novel electromagnetic variable inertance (EMVI) device is designed for vehicle vibration reduction, which consists of a controllable damper and an inerter in serial. First, the composition of the EMVI system is introduced and its mathematical model is established. Next, based on the time and frequency domain simulation, the control methods and dynamic control effects of the EMVI device are studied. Simulation results show that the EMVI device can achieve variable inertance by PWM signal control. To verify the performance of the EMVI device for vehicle suspension, a quadratic optimal controller was designed for real-time control of the EMVI suspension. The overall performance of EMVI suspension and conventional suspension under sinusoidal and random road excitation is compared. The results confirmed that the EMVI device can improve the suspension performance of a vehicle. Furthermore, it can effectively reduce the vibration of the vehicle body in the frequency range of 1 to 3 Hz.

© 2019 Elsevier Ltd This paper designs and builds an electromagnetic variable inertance (VI) device for a heavy duty vehicle seat suspension to reduce the vibration transferred to driver bodies. The conventional semi-active vibration control mainly applies the variable damping (VD) and variable stiffness (VS) devices. The VI device is equivalent to an inerter with the capability to vary its inertance, which is a new semi-active system inspired by the VS device design. The VI device consists of a transmission device, a VD device and two flywheels. By varying the damping of the VD device, the equivalent inertance of the VI device is controllable in real time. The VI device prototype is built with an electromagnetic VD device which is controlled by the duty cycle of the pulse width modulation signal. The test results verify the proposed system model and identify the unknown model parameters. Then, a seat suspension applies the VI device prototype for improving the ride comfort. Based on the system model, an implementable controller is proposed and experimentally validated. The proposed seat suspension system shows excellent performance in a random vibration experiment. Compared with a conventional passive seat suspension, the frequency-weighted root mean square acceleration of the proposed one reduces 35.7%. The VI device has expanded the application of the inerter and the area of the semi-active research; it shows great potential in vibration control.

© 2019 Elsevier Ltd In this paper, a novel resistance switching method is proposed to control an electromagnetic damper (EMD) system of a vehicle seat suspension, and torque response characteristics of the EMD system are investigated in detail. First, the relationship between electromagnetic torque and circuit resistance of the EMD system is established. The basic parameters of the EMD system are identified by least squares fitting, and the resistance distribution is optimized to meet the demand damping of seat suspension. Second, the electromagnetic torque response time and the continuously dynamic torque tracking performance of the EMD system are investigated experimentally. The time required for the torque change from its initial to 80% of the final state and the final state is measured, respectively. The results show that the response time required for torque decrease is shorter than the response time required for torque increase; the EMD system has excellent torque response and torque tracking performance and is suitable for seat suspension vibration control. Finally, two typical vehicle body vibration excitations are exerted on the EMD seat suspension. The test results verify that the EMD seat suspension has excellent controllable damping and can significantly isolate the vibration of driver body when applying a sliding mode control method.

Microorganisms in wastewater treatment plants (WWTPs) are essential for water purification to protect public and environmental health. However, the diversity of microorganisms and the factors that control it are poorly understood. Using a systematic global-sampling effort, we analysed the 16S ribosomal RNA gene sequences from similar to 1,200 activated sludge samples taken from 269 WWTPs in 23 countries on 6 continents. Our analyses revealed that the global activated sludge bacterial communities contain similar to 1 billion bacterial phylotypes with a Poisson lognormal diversity distribution. Despite this high diversity, activated sludge has a small, global core bacterial community (n = 28 operational taxonomic units) that is strongly linked to activated sludge performance. Meta-analyses with global datasets associate the activated sludge microbiomes most closely to freshwater populations. In contrast to macroorganism diversity, activated sludge bacterial communities show no latitudinal gradient. Furthermore, their spatial turnover is scale-dependent and appears to be largely driven by stochastic processes (dispersal and drift), although deterministic factors (temperature and organic input) are also important. Our findings enhance our mechanistic understanding of the global diversity and biogeography of activated sludge bacterial communities within a theoretical ecology framework and have important implications for microbial ecology and wastewater treatment processes.