Advanced robust control strategies of mechatronic suspensions for cars

Two novel mechatronic suspensions for road vehicles are studied in this thesis: the Series Active Variable Geometry Suspension (SAVGS) and the Parallel Active Link Suspension (PALS). The SAVGS and the PALS complement each other in terms of the vehicle categories they serve, which range from light high-performance vehicles (the Grand Tourer) to heavy SUV vehicles, respectively, based on the sprung mass and the passive suspension stiffness. Previous work developed various control methodologies for these types of suspension. Compared to existing active suspension solutions, both the SAVGS and the PALS are capable of low-frequency chassis attitude control and high-frequency ride comfort and road holding enhancement. In order to solve the limitation of both SAVGS and PALS robustness, mu-synthesis control methodologies are first developed for SAVGS and PALS, respectively, to account for structured uncertainties arising from changes to system parameters within realistic operating ranges. Subsequently, to guarantee robustness of both low-frequency and high-frequency vehicle dynamics for PALS, the mu-synthesis scheme is combined with proportional-integral-derivative (PID) control, employing a frequency separation paradigm. Moreover, as an alternative robustness guaranteeing scheme that captures plant nonlinearities and road unevenness as uncertainties and disturbances, a novel robust model predictive control (RMPC) based methodology is proposed for the SAVGS, motivated by the promise shown by RMPC in other industrial applications. Finally, aiming to provide further performance stability and improvements, feedforward control is developed for the PALS. Nonlinear simulations with a set of ISO driving situations are performed to evaluate the efficiency and effectiveness of the proposed control methods in this thesis.Open Acces

Learning When to See for Long-term Traffic Data Collection on Power-constrained Devices

Collecting traffic data is crucial for transportation systems and urban planning, and is often more desirable through easy-to-deploy but power-constrained devices, due to the unavailability or high cost of power and network infrastructure. The limited power means an inevitable trade-off between data collection duration and accuracy/resolution. We introduce a novel learning-based framework that strategically decides observation timings for battery-powered devices and reconstructs the full data stream from sparsely sampled observations, resulting in minimal performance loss and a significantly prolonged system lifetime. Our framework comprises a predictor, a controller, and an estimator. The predictor utilizes historical data to forecast future trends within a fixed time horizon. The controller uses the forecasts to determine the next optimal timing for data collection. Finally, the estimator reconstructs the complete data profile from the sampled observations. We evaluate the performance of the proposed method on PeMS data by an RNN (Recurrent Neural Network) predictor and estimator, and a DRQN (Deep Recurrent Q-Network) controller, and compare it against the baseline that uses Kalman filter and uniform sampling. The results indicate that our method outperforms the baseline, primarily due to the inclusion of more representative data points in the profile, resulting in an overall 10\% improvement in estimation accuracy. Source code will be publicly available.Comment: Accepted by IEEE 26th International Conference on Intelligent Transportation System

Experimental study on the hydraulic fracture propagation of laminar argillaceous limestone continental shale

Laminar argillaceous limestone continental shale is an important oil reservoir in Jiyang Depression, Bohai Bay Basin of China. Affected by the laminar structure, the spatial propagation morphology of hydraulic fracturing is not clear. To reveal the propagation law of hydraulic fracturing pathway in laminar marl continental shale, the mineral content and basic rock mechanics test are firstly carried out on the cores from the wells in Jiyang Depression. Secondly the similar material cores with standard-size and large-size are manufactured and processed. Finally, combined with physical model experiments, acoustic emission and moment tensor inversion techniques, the hydraulic fracturing experiments on the large-size cores under different stress differences are conducted. The experimental results show that the in situ stress (confining stresses), laminar structure, and lithological distribution jointly affect the propagation mode of fractures. As the horizontal stress difference increases, the stimulated reservoir volume gradually decreases, and the number of shear fractures decreases accordingly. Macroscopically, the pump pressure curve shows obvious fluctuation in the case with lower horizontal stress difference, which is the external performance of hydraulic fracture initiation–obstruction–turning–penetrating–obstruction–turning. The content of brittle and plastic minerals has a significant impact on the fracture complexity, particularly the layers with high argillaceous content have a significant inhibitory effect on fracture propagation. The weakly cemented lamination or bedding plane is easy to capture the fracture and make it propagate along the bedding plane, thereby increasing the complexity of fracture network. The research results are expected to provide a theoretical reference for design and optimization of hydraulic fracturing parameter in continental shale oil exploration and development

LMI-based robust model predictive control for a quarter car with series active variable geometry suspension

This paper proposes a robust model predictive control-based solution for the recently introduced series active variable geometry suspension (SAVGS) to improve the ride comfort and road holding of a quarter car. In order to close the gap between the nonlinear multi-body SAVGS model and its linear equivalent, a new uncertain system characterization is proposed that captures unmodeled dynamics, parameter variation, and external disturbances. Based on the newly proposed linear uncertain model for the quarter car SAVGS system, a constrained optimal control problem (OCP) is presented in the form of a linear matrix inequality (LMI) optimization. More specifically, utilizing semidefinite relaxation techniques a state-feedback robust model predictive control (RMPC) scheme is presented and integrated with the nonlinear multi-body SAVGS model, where state-feedback gain and control perturbation are computed online to optimise performance, while physical and design constraints are preserved. Numerical simulation results with different ISO-defined road events demonstrate the robustness and significant performance improvement in terms of ride comfort and road holding of the proposed approach, as compared to the conventional passive suspension, as well as, to actively controlled SAVGS by a previously developed conventional H-infinity control scheme.Comment: 13 pages, 11 figures, 2 tables, IEEE Transactions on Control Systems Technolog

Policy-driven food security: investigating the impact of China’s maize subsidy policy reform on farmer’ productivity

IntroductionChina is the largest producer, consumer, and trader of grain. Changes in China’s agricultural policies will affect global food trade and thus impact food security. In this paper, we use China’s maize subsidy system reform (MSSR) as a quasi-natural experiment to investigate the impact of market-oriented reforms in price support policy on the productivity of grain.MethodsWe use official Chinese government panel data on farm households and a PSM-DID model to overcome the endogeneity problem of policy change.Results and discussionThe empirical results show that MSSR can increase maize productivity. The MSSR is divided into two phases: eliminating the maize purchase price and implementing maize producer subsidies. The policy effect of eliminating the purchase price exceeds the implementation of producer subsidies. Further analysis reveals that for farmers with a larger scale of cultivation, higher level of specialization, and higher degree of part-time employment, the MSSR enhances their productivity more significantly. In the high quartile, the MSSR reduces farmers’ productivity. In the low quartile, the MSSR raises farmers’ productivity, suggesting that the MSSR reduces the productivity differences among farmers. The results of our study suggest that market-based reform of price subsidies is an effective institutional arrangement to mitigate resource mismatch and increase food productivity, and point to the need to continue to improve the MSSR, explore diversified maize producer subsidy policies, and take into account the impact of other subsidies on farmers’ maize production behavior

Dampak Pembangunan Infrastruktur Perdesaan Pada Program PNPM Mandiri Perdesaan Di Kabupaten Toli Toli

The purpose of this study was to determine the Development Impact of Rural Infrastructure in PNPM RuralProgram in Toli-Toli. Research conducted on the implementation of PNPM Rural Program in Toli-Toli forfiscal year 2007 and 2008.Primary data obtained from interviews with relevant parties and direct observation in the field, then the datais processed with Descriptive Analysis.The results showed the impact of rural infrastructure development in poor communities in Toli Toli, namely:increasing revenue, impoving public education, improving health and improving the public midset. Impact onvillage institutions, namely: the function and role of local government to be effective, institutions ofparticipatory development and improvement of the quality of facilities.and social infrastructure andeconomic base of societ

Achieving high-quality silver sintered joint for highly-reliable schottky barrier diodes via pressureless method

The fabrication of silver joints was done using the pressureless sintering technology to suit the demand of high-reliability schottky barrier diodes (SBD). Porosity of 10.6% and shear strength of 39.6 MPa were reached under the optimized parameters of 290°C sintering temperature and 40 min residence time. The sintered joint demonstrated good mechanical/thermal/electrical performance in the ultimate reliability assessment testing, including the temperature cycling test, second sintering test, steady-state lifetime test, and intermittent lifetime test. This study demonstrated the viability of pressureless sintering of silver joints with good high-temperature reliability, which has significant application potential for aeronautical high-reliability power electronics

Pancreatic Stellate Cells: A Rising Translational Physiology Star as a Potential Stem Cell Type for Beta Cell Neogenesis

The progressive decline and eventual loss of islet β-cell function underlies the pathophysiological mechanism of the development of both type 1 and type 2 diabetes mellitus. The recovery of functional β-cells is an important strategy for the prevention and treatment of diabetes. Based on similarities in developmental biology and anatomy, in vivo induction of differentiation of other types of pancreatic cells into β-cells is a promising avenue for future diabetes treatment. Pancreatic stellate cells (PSCs), which have attracted intense research interest due to their effects on tissue fibrosis over the last decade, express multiple stem cell markers and can differentiate into various cell types. In particular, PSCs can successfully differentiate into insulin- secreting cells in vitro and can contribute to tissue regeneration. In this article, we will brings together the main concepts of the translational physiology potential of PSCs that have emerged from work in the field and discuss possible ways to develop the future renewable source for clinical treatment of pancreatic diseases

Isomerization of sp2-hybridized carbon nanomaterials: structural transformation and topological defects of fullerene, carbon nanotube, and graphene

The structural transformation of various carbon nanomaterials, such as fullerene, carbon nanotube (CNT), and graphene, has been extensively studied both experimentally and theoretically. It was broadly recognized that the isomerization of the sp2-hybridized carbon network through the generalized Stone–Wales transformation (GSWT), which is equivalent to a CC bond's in-plane rotation, is the key mechanism facilitating most structural revolutions in carbon materials. The GSWT process also plays a crucial role in the shape change, defect healing and the growth in these carbon materials and may greatly affect their mechanical, chemical, and electronic performances. In this review, we summarize the previous studies on the GSWT and topological defects in the sp2 carbon network as well as the consequent results of sp2-hybridized carbon materials??? isomerization, including structural shrinkage of the giant fullerenes and CNTs at high temperature, plastic deformation of CNTs, coalescence of the fullerenes and carbon peapods, topological defects evolution under high energetic irradiation, and healing of the defects during the chemical vapor deposition growth of CNT and graphene. This review provides a clear picture of the isomerization of the sp2-hybridized carbon materials, from single step process until the large-scale structural transformation, and many examples for the readers to get into the topic deeply step by step. WIREs Comput Mol Sci 2017, 7:e1283. doi: 10.1002/wcms.1283. For further resources related to this article, please visit the WIREs website.clos

Atomistic simulation and the mechanism of graphene amorphization under electron irradiation

Real-time reconstruction of a divacancy in graphene under electron irradiation (EI) is investigated by nonequilibrium molecular dynamic simulation (NEMD). The formation of the amorphous structure is found to be driven by the generalized Stone-Wales transformations (GSWTs), i.e. C-C bond rotations, around the defective area. The simulation reveals that each step of the reconstruction can be viewed as a quasi-thermal process and thus the reconstruction from a point defect to an amorphous structure favors the minimum energy path. On the other hand, the formation of a high energy large defective area is kinetically dominated by the balance between its expansion and shrinkage, and a kinetic model was proposed to understand the size of the defective area. The current study demonstrates that the route of the reconstruction from the point defective graphene toward an amorphous structure is predictive, though under stochastic EI