Electro-hydraulic position servo system of valve-controlled symmetrical cylinder (EPSSVCS) is a very important and widely used electro-hydraulic servo system, the performance of which is often ...affected by friction nonlinearity and external random disturbances together with unmodeled dynamic factors such as parameter uncertainty in practical work. To improve the tracking performance of the system, a backstepping sliding mode control algorithm (BSMC) based on an extended state observer was presented in this paper. Firstly, a nonlinear mathematical model of the EPSSVCS was established which takes into account the composite disturbance induced by the systematic friction nonlinearity, external disturbances and unmodeled dynamic factors. Then, an extended state observer (ESO) was designed which can effectively estimate the velocity, acceleration, and composite disturbance of the valve-controlled cylinder online. Furthermore, a kind of BSMC was presented based on the online ESO estimates and the displacement feedback signals. The control law was given and the system stability was proved. The analysis results showed that the output signal of the system can effectively track the input signal under the influence of typical external disturbances and unmodeled dynamic factors, which illustrated the effectiveness of the established nonlinear mathematical model and the stability of the designed control system. Moreover, by taking the parameters of the electro-hydraulic servo system of a certain type of CNC machine tool as a real example, the proposed algorithm (BSMC) was compared with the conventional PID control algorithm, the backstepping sliding mode control algorithm (BSC), and the adaptive robust control algorithm (ARC), and the results verified the superiority of the BSMC. This work may provide a useful reference for the research in the field of related control systems.
Confining photons in a finite volume is highly desirable in modern photonic devices, such as waveguides, lasers and cavities. Decades ago, this motivated the study and application of photonic ...crystals, which have a photonic bandgap that forbids light propagation in all directions
. Recently, inspired by the discoveries of topological insulators
, the confinement of photons with topological protection has been demonstrated in two-dimensional (2D) photonic structures known as photonic topological insulators
, with promising applications in topological lasers
and robust optical delay lines
. However, a fully three-dimensional (3D) topological photonic bandgap has not been achieved. Here we experimentally demonstrate a 3D photonic topological insulator with an extremely wide (more than 25 per cent bandwidth) 3D topological bandgap. The composite material (metallic patterns on printed circuit boards) consists of split-ring resonators (classical electromagnetic artificial atoms) with strong magneto-electric coupling and behaves like a 'weak' topological insulator (that is, with an even number of surface Dirac cones), or a stack of 2D quantum spin Hall insulators. Using direct field measurements, we map out both the gapped bulk band structure and the Dirac-like dispersion of the photonic surface states, and demonstrate robust photonic propagation along a non-planar surface. Our work extends the family of 3D topological insulators from fermions to bosons and paves the way for applications in topological photonic cavities, circuits and lasers in 3D geometries.
We propose a single low-profile skin metasurface carpet cloak to hide objects with arbitrary shape and size under three different waves, i.e., electromagnetic (EM) waves, acoustic waves and water ...waves. We first present a metasurface which can control the local reflection phase of these three waves. By taking advantage of this metasurface, we then design a metasurface carpet cloak which provides an additional phase to compensate the phase distortion introduced by a bump, thus restoring the reflection waves as if the incident waves impinge onto a flat mirror. The finite element simulation results demonstrate that an object can be hidden under these three kinds of waves with a single metasurface cloak.
Abstract
The recently discovered non-Hermitian skin effect (NHSE) manifests the breakdown of current classification of topological phases in energy-nonconservative systems, and necessitates the ...introduction of non-Hermitian band topology. So far, all NHSE observations are based on one type of non-Hermitian band topology, in which the complex energy spectrum winds along a closed loop. As recently characterized along a synthetic dimension on a photonic platform, non-Hermitian band topology can exhibit almost arbitrary windings in momentum space, but their actual phenomena in real physical systems remain unclear. Here, we report the experimental realization of NHSE in a one-dimensional (1D) non-reciprocal acoustic crystal. With direct acoustic measurement, we demonstrate that a twisted winding, whose topology consists of two oppositely oriented loops in contact rather than a single loop, will dramatically change the NHSE, following previous predictions of unique features such as the bipolar localization and the Bloch point for a Bloch-wave-like extended state. This work reveals previously unnoticed features of NHSE, and provides the observation of physical phenomena originating from complex non-Hermitian winding topology.
Origami is the art of folding two‐dimensional (2D) materials, such as a flat sheet of paper, into complex and elaborate three‐dimensional (3D) objects. This study reports origami‐based metamaterials ...whose electromagnetic responses are dynamically controllable via switching the folding state of Miura‐ori split‐ring resonators. The deformation of the Miura‐ori unit along the third dimension induces net electric and magnetic dipoles of split‐ring resonators parallel or anti‐parallel to each other, leading to the strong chiral responses. Circular dichroism as high as 0.6 is experimentally observed while the chirality switching is realized by controlling the deformation direction and kinematics. In addition, the relative density of the origami metamaterials can be dramatically reduced to only 2% of that of the unfolded structure. These results open a new avenue toward lightweight, reconfigurable, and deployable metadevices with simultaneously customized electromagnetic and mechanical properties.
An approach toward reconfigurable metamaterials with simultaneously customized electromagnetic and mechanical properties is presented. Strong chiroptical responses are induced when transforming a planar, achiral metasurface into 3D origami metamaterials, and breaking the mirror symmetry of the folded origami metamaterials. The relative density of the origami metamaterials can be dramatically reduced to only 2% of that of the unfolded structure.
Although a plethora of studies have investigated the association between green exposure and mental health in developed countries, it is only recently that academics and policymakers have paid ...attention to how this association works in rapidly urbanizing and developing countries. This study aims to explore biopsychosocial pathways linking residential greenness exposure to depression in the Chinese context using data from the 2016 wave of China Labour-force Dynamics Survey. Results from multilevel models along with mediation analysis show that exposure to residential greenness is negatively associated with depression, and that physical activity, stress and neighbourhood social cohesion altogether have a complete mediation effect on this association. Results from moderation analysis suggest that urbanicity moderates the relationship between greenness exposure and depression, and that the relationship is strongest at the upper level of urbanicity. Our findings suggest the necessity of increasing the provision of recreational green spaces and improving the quality of green spaces in Chinese less urbanized areas.
•Exposure to residential greenness is negatively associated with depression in China.•Physical activity, stress and neighbourhood social cohesion mediate the above relationship.•Urbanicity moderates the linkage between greenness exposure and depression.•Greenness exposure has the strongest association with depression at the upper level of urbanicity.
Inferring optical response from other correlated optical response is highly demanded for vast applications such as biological imaging, material analysis, and optical characterization. This is ...distinguished from widely-studied forward and inverse designs, as it is boiled down to another different category, namely, spectra-to-spectra design. Whereas forward and inverse designs have been substantially explored across various physical scenarios, the spectra-to-spectra design remains elusive and challenging as it involves intractable many-to-many correspondences. Here, we first dabble in this uncharted area and propose a generation-elimination framework that can self-orient to the best output candidate. Such a framework has a strong built-in stochastically sampling capability that automatically generate diverse nominations and eliminate inferior nominations. As an example, we study terahertz metasurfaces to correlate the reflection spectra from low to high frequencies, where the inaccessible spectra are precisely forecasted without consulting structural information, reaching an accuracy of 98.77%. Moreover, an innovative dimensionality reduction approach is executed to visualize the distribution of the abstract correlated spectra data encoded in latent spaces. These results provide explicable perspectives for deep learning to parse complex physical processes, rather than "brute-force" black box, and facilitate versatile applications involving cross-wavelength information correlation.
Recently, liquid flow over monolayer graphene has been experimentally demonstrated to generate an induced voltage in the flow direction, and various physical mechanisms have been proposed to explain ...the electricity‐generating process between liquid and graphene. However, there are significant discrepancies in the reported results with non‐ionic liquid: the observed voltage responses with deionized (DI) water vary from lab to lab under presumably similar flowing conditions. Here, a graphene‐piezoelectric material heterostructure is proposed for harvesting energy from water flow; it is shown that the introduction of a piezoelectric template beneath graphene results in an obvious voltage output up to 0.1 V even with DI water. This potential arises from a continuous charging–discharging process in graphene, which is suggested to be a result of a relatively retarded screening effect of the water for the generated piezoelectric charges than that of the graphene layer, as revealed by first‐principles calculations. This work considers a dynamic charge interaction among water, graphene, and the substrate, highlighting the crucial role of the underlying substrate in the electricity‐generating process, which will greatly enhance understanding of the flow‐induced voltage and push the graphene‐water nanogenerator close to practical applications.
Through introducing piezoelectric template beneath graphene, moving droplets of deionized water along the graphene surface can induce an electric potential. This electricity is suggested to be a result of a dynamic charge interaction among water, graphene, and the piezoelectric substrate, which highlights the crucial role of the underlying substrate in the electricity generating process.
China is becoming an aging society. The emotional health of the elderly is gaining importance. Social trust is an important factor affecting emotional health, but existing studies have rarely ...considered the various effects of different types of social trust on rural elderly emotional health. Few studies have analysed the role of subjective well-being and subjective social status in the relationship between social trust and elderly emotional health.
Using the data of the China Labor-force Dynamics Survey 2016 (CLDS 2016) and regression models, this study selected 2084 rural respondents aged 60 years and above to analyse the impact of social trust on their emotional health. Social trust was divided into three categories: trust in family members, trust in friends, and trust in neighbours. This study also examined the mediating and moderating effects of subjective well-being and subjective social status on the relationship between social trust and emotional health.
Trust in family members was significantly and positively associated with emotional health (coefficient = 0.194, P < 0.01) and subjective well-being (coefficient = 0.177, P < 0.01). Trust in friends was significantly and positively associated with emotional health and subjective well-being (coefficient = 0.097, P < 0.01; coefficient = 0.174, P < 0.01, respectively). Trust in neighbours was significantly and positively associated with emotional health and subjective well-being (coefficient = 0.088, P < 0.01; coefficient = 0.177, P < 0.01; respectively). Subjective well-being effectively reduced the impact of social trust in family, friends, and neighbours on the emotional health of the elderly by 0.023, 0.022, and 0.023, respectively. Trust in friends and neighbours significantly and positively affected respondents' subjective social status (coefficient = 0.120, P < 0.05; coefficient = 0.090, P < 0.10; respectively). Subjective social status effectively reduced the impact of social trust in friends and neighbours on the emotional health of the elderly both by 0.004. The positive relationship between trust in family members and emotional health is weakened by subjective well-being.
Social trust, especially family relationships, play an important role in maintaining the emotional health of the rural elderly. In response to population ageing, more social policies must be introduced to care for the rural elderly and help them lead a happy and satisfactory life.
Delay tolerant networks (DTNs) is a network evolved from mobile networks. Differing from the traditional network, which has a stable end‐to‐end transmission path, DTNs are sparse and intermittently ...connected mobile ad hoc network, which are widely used in harsh environments, such as battlefields, seabed, space communication networks, and so on. In DTNs, intermittent connectivity, partitioned network, long delays and node mobility characteristics make the network fail to communicate frequently, therefore, how to successfully forward the message is of extreme importance. Up to now, almost all the traditional models in DTNs use the store‐carry‐forward method. This paper proposes a novel clustered DTN routing model based on sensing node relationship strength. The routing mechanism takes advantage of the number of other nodes encountered by the nodes in the process of movement and the changes in the number of nodes to calculate the strength of the relationship between nodes, and clusters DTN routing according to the strength of the relationship between nodes. Moreover, the relationship between nodes in a cluster and other clusters is used to transmit messages between clusters, and messages are transmitted within clusters according to the strength of the relationship between nodes. Simulation results show that the routing mechanism not only increases the success rate of message transmission, but also reduces the transmission delay of messages and improves network performance.
A novel clustered delay tolerant networks (DTN) routing model based on sensing node relationship strength are proposed. The routing mechanism takes advantage of the number of other nodes encountered by the nodes in the process of movement and the changes in the number of nodes to calculate the strength of the relationship between nodes, and clusters DTN routing according to the strength of the relationship between nodes. Moreover, the relationship between nodes in a cluster and other clusters is used to transmit messages between clusters, and messages are transmitted within clusters according to the strength of the relationship between nodes. Simulation results show that the routing mechanism not only increases the success rate of message transmission, but also reduces the transmission delay of messages and improves network performance.
PDF
