This paper presents an adaptive sliding-mode (ASM) control methodology for a vehicle steer-by-wire (SbW) system. First, the SbW system is modeled as a second-order system from the steering motor ...input voltage to the front-wheel steering angle. For simplicity, the self-aligning torque and friction arising from the tire-to-ground contact are regarded as external disturbance acting on the SbW system. Next, an ASM controller is designed for the SbW system, which can not only cope with the parametric uncertainties in the plant model but also estimate the coefficient of the self-aligning torque effectively. The stability of the ASM control system is proved in the sense of Lyapunov and the guidelines for selecting the control parameters are given. Finally, experiments are carried out for steering control to respectively follow a slalom path and a circular path under various road conditions. It is shown that the proposed ASM controller can achieve stronger robustness against various road conditions leading to significantly smaller tracking errors in comparison with a conventional sliding-mode controller and a linear H ∞ controller.
Inflammatory bowel disease (IBD) is an increasing global burden and a predisposing factor to colorectal cancer. Although a number of treatment options are available, the side effects could be ...considerable. Studies on fecal microbiota transplantation (FMT) as an IBD intervention protocol require further validation as the underlying mechanisms for its attenuating effects remain unclear. This study aims to demonstrate the ameliorative role of FMT in an ulcerative colitis (UC) model induced by dextran sulfate sodium (DSS) and elucidate its relative mechanisms in a mouse model. It was shown that FMT intervention decreased disease activity index (DAI) levels and increased the body weight, colon weight and colon length of experimental animals. It also alleviated histopathological changes, reduced key cytokine expression and oxidative status in the colon. A down-regulated expression level of genes associated with NF-κB signaling pathway was also observed. The results of 16S rRNA gene sequencing showed that FMT intervention restored the gut microbiota to the pattern of the control group by increasing the relative abundance of Firmicutes and decreasing the abundances of Bacteroidetes and Proteobacteria. The relative abundances of the genera
,
,
,
and
were upregulated but
,
and
were reduced after FMT administration. Furthermore, FMT administration elevated the concentrations of SCFAs in the colon. In conclusion, FMT intervention could be suitable for UC control, but further validations via clinical trials are recommended.
Permafrost on the Qinghai–Tibet Plateau (QTP) has undergone degradation as a result of recent climate change. This may alter the thermo‐hydrological processes and unlock soil organic carbon, and ...thereby affect local hydrological, ecological, and climatic systems. The relationships between permafrost and climate change have received extensive attention, and in this paper we review climate change for permafrost regions of the QTP over the past 30 years. We summarize the current state and changes in permafrost distribution and thickness, ground temperature, and ground ice conditions. We focus on changes in permafrost thermal state and in active‐layer thickness (ALT). Possible future changes in ground temperature and ALT are also discussed. Finally, we discuss the changes in hydrological processes and to ecosystems caused by permafrost degradation. Air temperature and ground temperature in the permafrost regions of the QTP have increased from 1980 to 2018, and the active layer has been thickening at a rate of 19.5 cm per decade. The response of permafrost to climate change is not as fast as in some reports, and permafrost degradation is slower than projected by models that do not account for conditions deep in permafrost.
In this paper, an innovative multitasking device (MTD) regulated by the gravity field realizing the functions of metamaterial absorber (MMA) and linear polarization converter (LPC) is proposed and ...theoretically investigated. When the device operates in the function of MMA, the engineered SRR structure offers robust conditions for the formation of anapole mode. The anapole mode can lead to destructive interference in the far‐field and constructive interference within the configuration synchronously; thereby, the incident wave energy can be consumed strongly. It is verified that the proposed MTD in the MMA state can acquire a high absorption rate exceeding 0.9 from 10.82 to 13.55 GHz, with a broad relative bandwidth (RBW) of 22.4%. While in the LPC state, the utilization of the “L”‐shaped structure successfully introduces an equivalent magnetic resonance to achieve the translation of the incident wave polarization state. In this case, the orthogonal state of the incident beam can be obtained by the MTD with the polarization conversion ratio (PCR) over 0.9 in the range of 2.62–3.72 GHz, whose RBW is 34.7%. The design accomplishes the functional combination of MMA and LPC through the gravity field regulation, simultaneously staggering the operating bands to guarantee their independence and anti‐interference.
An innovative multitasking device regulated by the gravity field realizing the functions of metamaterial absorber (MMA) and linear polarization converter (LPC) is proposed and theoretically investigated. In the MMA state, the anapole mode is excited and leads to broadband absorption. While in the LPC state, an equivalent magnetic resonance is introduced to achieve the conversion of the polarization state.
In the era of big data, with the increasing number of audit data features, human-centered smart intrusion detection system performance is decreasing in training time and classification accuracy, and ...many support vector machine (SVM)-based intrusion detection algorithms have been widely used to identify an intrusion quickly and accurately. This paper proposes the FWP-SVM-genetic algorithm (GA) (feature selection, weight, and parameter optimization of support vector machine based on the genetic algorithm) based on the characteristics of the GA and the SVM algorithm. The algorithm first optimizes the crossover probability and mutation probability of GA according to the population evolution algebra and fitness value; then, it subsequently uses a feature selection method based on the genetic algorithm with an innovation in the fitness function that decreases the SVM error rate and increases the true positive rate. Finally, according to the optimal feature subset, the feature weights and parameters of SVM are simultaneously optimized. The simulation results show that the algorithm accelerates the algorithm convergence, increases the true positive rate, decreases the error rate, and shortens the classification time. Compared with other SVM-based intrusion detection algorithms, the detection rate is higher and the false positive and false negative rates are lower.
Abstract
Developing highly efficient catalyst for selective oxidation of benzene to phenol (SOBP) with low H
2
O
2
consumption is highly desirable for practical application, but challenge remains. ...Herein, we report unique single-atom Cu
1
-N
1
O
2
coordination-structure on N/C material (Cu-N
1
O
2
SA/CN), prepared by water molecule-mediated pre-assembly-pyrolysis method, can efficiently boost SOBP reaction at a 2:1 of low H
2
O
2
/benzene molar ratio, showing 83.7% of high benzene conversion with 98.1% of phenol selectivity. The Cu
1
-N
1
O
2
sites can provide a preponderant reaction pathway for SOBP reaction with less steps and lower energy barrier. As a result, it shows an unexpectedly higher turnover frequency (435 h
−1
) than that of Cu
1
-N
2
(190 h
−1
), Cu
1
-N
3
(90 h
−1
) and Cu nanoparticle (58 h
−1
) catalysts, respectively. This work provides a facile and efficient method for regulating the electron configuration of single-atom catalyst and generates a highly active and selective non-precious metal catalyst for industrial production of phenol through selective oxidation of benzene.
•An algorithm is proposed to identify track irregularities using vehicle responses.•TThe VB interaction is taken into account in the proposed algorithm.•A railway bridge is employed as an ...illustrative example to validate its accuracy.
Track irregularities affect the running safety of railway vehicles and ride comfort, hence track irregularity identification using the dynamic responses of in-service vehicles is of great interest. Because the high-speed rail lines mainly consist of bridges in China, vehicle-bridge (VB) interactions which significantly influence the vehicle dynamic responses should be taken into account in the track irregularity identification. This paper proposes a Kalman filter algorithm to identify the track irregularities of railway bridges using vehicle dynamic responses considering the VB interactions in real-time. A state space model is established to represent a time-dependent VB system subjected to unknown track irregularity excitations. A Kalman filter algorithm is proposed to estimate optimally the state vector of the VB system and to identify the track irregularities subsequently. Two numerical examples including a real railway bridge constructed in China are presented to validate the accuracy of the proposed algorithm. A parametric study is also conducted to demonstrate the effects of measurement noise, vehicle running state, parameter uncertainty and model uncertainty on the identification of track irregularities. Comparison results demonstrate that the proposed track irregularity identification algorithm outperforms the conventional approaches mainly because of considering the VB interaction. The proposed algorithm enables efficient monitoring the track irregularities of railway bridges using the acceleration responses of in-service vehicles.
Dye-sensitized solar cells (DSCs) have gained widespread attentions owing to their low production cost, tunable optical response, and high light-to-electricity conversion. In DSCs, the performance of ...redox mediators with iodide/triiodide or iodine-free redox couples is vital to internal quantum efficiency. For a long time, iodide/triiodide based electrolytes are the most widely used mediators because of their desirable kinetics. Recently, exciting progress has been made with respect to iodine-free metallorganic and pure organic redox shuttles. Their tunable redox potential and diverse electron transfer behaviors enable the rational screening of electrolyte composition for enhancing the light-to-electricity conversion efficiency of DSCs toward the Shockley–Queisser limit. In this Account, we emphasize on current knowledge of two distinct but interrelated interfacial processes (electron recombination and dye regeneration), particularly for DSCs with iodine-free redox couples. We show that a deeper understanding of electron transfer kinetics of the alternative redox couples is fundamental to develop rational strategies for cell optimization. Compared with iodine electrolyte, iodine-free metallorganic redox couples such as iron, cobalt, and nickel complexes display much faster electron transfer kinetics in dye regeneration and interfacial recombination. Evidently, rapid regeneration enables the employment of more positive metal complex for attaining a higher photovoltage. However, severe recombination reactions have to be well controlled by using several effective surface treatments such as the addition of Brönsted bases and atomic layer deposition. Although these methods offer different pathways in surface passivation, a trade-off between charge injection efficiency and electron diffusion length is always observed. It follows that an appropriate LUMO level of sensitizer is essential to ensure efficient electron injection at the passivated TiO2 surface. Apart from fast recombination behavior, bulky metal complexes suffer from inefficient charge transport. Thus, the combination of thinner TiO2 film and sensitizers with high mole extinction coefficient has been employed for both enhancing diffusion-limited current and maintaining light-harvesting efficiency. Unlike metal complexes, most of organic sulfur redox couples in DSCs exhibit slow recombination kinetics. This allows the use of thicker TiO2 film to achieve an optimized light harvesting. However, the concomitant sluggish behavior of dye regeneration requires the use of sensitizers with more positive HOMO level, which is beneficial to efficient regeneration. Moreover, lower level of TiO2 band edge in DSCs based on organic sulfur mediators hinders the achievement of desirable photovoltage, spurring future explorations on this class of redox mediator. Based on the comparison of electron transfer behavior between iodine-free metallorganic complexes and pure organic redox couples, we aim to provide a comprehensive Account of the intriguing interfacial processes in iodine-free DSCs as the key scientific point is linked with the kinetics of interfacial reactions. This demonstrates the advantages as well as disadvantages of each class of iodine-free electrolyte and should shed light on to judicious selection of the energy levels for redox mediators, sensitizers, and the conduction band of TiO2 for DSCs. The knowledge of the reaction kinetics in DSCs should be also beneficial to the interface engineering on recent developed perovskite cells.
Abstract
Topological semimetals have recently attracted extensive research interests as host materials to condensed matter physics counterparts of Dirac and Weyl fermions originally proposed in high ...energy physics. Although Lorentz invariance is required in high energy physics, it is not necessarily obeyed in condensed matter physics, and thus Lorentz-violating type-II Weyl/Dirac fermions could be realized in topological semimetals. The recent realization of type-II Weyl fermions raises the question whether their spin-degenerate counterpart—type-II Dirac fermions—can be experimentally realized too. Here, we report the experimental evidence of type-II Dirac fermions in bulk stoichiometric PtTe
2
single crystal. Angle-resolved photoemission spectroscopy measurements and first-principles calculations reveal a pair of strongly tilted Dirac cones along the Γ-A direction, confirming PtTe
2
as a type-II Dirac semimetal. Our results provide opportunities for investigating novel quantum phenomena (e.g., anisotropic magneto-transport) and topological phase transition.
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