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The lightweight structure design is a crucial consideration in the industrial field. Unlike passive structures that rely solely on material stiffness to resist external loads, active structures achieve lightweighting by active change of the internal force-driven deformation. An explicit topology optimization method was introduced for piezoelectric multi-material active structures with the moving morphable components (MMC) method. The proposed method minimizes the total mass of the active structure by simultaneously optimizing the structure topology and the distribution of piezoelectric actuators while satisfying the displacement constraints. To optimize the polarization characteristics for adaptive piezoelectric actuation under complex loading conditions, 3 independent sets of MMCs were utilized. These components describe the distributions of elastic and piezoelectric materials as well as the corresponding polarization characteristics, resulting in a composite active structure with explicit geometric descriptions. Numerical examples demonstrate that, compared to passive structures, multi-material active structures based on piezoelectric actuation can realize structural lightweighting more efficiently. [ABSTRACT FROM AUTHOR]

A multi-material active structure is a mechanical system made of passive and active materials with the ability to alter its configuration, form, or properties in response to changes in the environment. Active structures have been investigated to design lightweight structures and structures with the ability to “smartly” alter their shapes and/or internal forces. Recently, the potential of active structures to reduce environmental impact, i.e., reduce energy consumption and greenhouse gas (GHG) emissions, has been investigated. It has been verified that, compared to passive structures, active structures can not only use less material but also consume less energy and cause less GHG emissions during their service life, and thus have a significant potential to be applied as environment-friendly mechanical structures. This study aims to develop a general topology optimization (TO) approach to design novel multi-material active structural systems to reduce environmental impact. The approach is based on the density-based TO scheme. Passive and active materials are considered in the TO process and are required to be optimally distributed according to the optimization objective and constraints. The energy consumption or GHG emissions caused by the structure during its service life are treated as the objective function to be minimized under multiple displacement requirements. Typical examples are carried out to verify the developed approach. Results show that the topology optimized active structures may not only achieve significant weight savings but also less energy consumption and GHG emissions compared to equivalent topology optimized passive structures, which indicates that the developed approach has the potential to be applied to design novel structural systems with lighter weight, larger span, and with less environmental impact compared to conventional passive structural systems. [ABSTRACT FROM AUTHOR]

Dual‐atom catalysts (DACs) have been a new frontier in heterogeneous catalysis due to their unique intrinsic properties. The synergy between dual atoms provides flexible active sites, promising to enhance performance and even catalyze more complex reactions. However, precisely regulating active site structure and uncovering dual‐atom metal interaction remain grand challenges. In this review, we clarify the significance of the inter‐metal interaction of DACs based on the understanding of active center structures. Three diatomic configurations are elaborated, including isolated dual single‐atom, N/O‐bridged dual‐atom, and direct dual‐metal bonding interaction. Subsequently, the up‐to‐date progress in heterogeneous oxidation reactions, hydrogenation/dehydrogenation reactions, electrocatalytic reactions, and photocatalytic reactions are summarized. The structure‐activity relationship between DACs and catalytic performance is then discussed at an atomic level. Finally, the challenges and future directions to engineer the structure of DACs are discussed. This review will offer new prospects for the rational design of efficient DACs toward heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

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Metal‐exchanged zeolites are well‐known propane dehydrogenation (PDH) catalysts; however, the structure of the active species remains unresolved. In this review, existing PDH catalysts are first surveyed, and then the current understanding of metal‐exchanged zeolite catalysts is described in detail. The case of Ga/H‐ZSM‐5 is employed to showcase that advances in the understanding of structure–activity relations are often accompanied by technological or conceptional breakthroughs. The understanding of Ga speciation at PDH conditions has evolved owing to the advent of in situ/operando characterizations and to the realization that the local coordination environment of Ga species afforded by the zeolite support has a decisive impact on the active site structure. In situ/operando quantitative characterization of catalysts, rigorous determination of intrinsic reaction rates, and predictive computational modeling are all significant in identifying the most active structure in these complex systems. The reaction mechanism could be both intricately related to and nearly independent of the details of the assumed active structure, as in the two main proposed PDH mechanisms on Ga/H‐ZSM‐5, that is, the carbenium mechanism and the alkyl mechanism. Perspectives on potential approaches to further elucidate the active structure of metal‐exchanged zeolite catalysts and reaction mechanisms are discussed in the final section. [ABSTRACT FROM AUTHOR]

Abstract Metal‐exchanged zeolites are well‐known propane dehydrogenation (PDH) catalysts; however, the structure of the active species remains unresolved. In this review, existing PDH catalysts are first surveyed, and then the current understanding of metal‐exchanged zeolite catalysts is described in detail. The case of Ga/H‐ZSM‐5 is employed to showcase that advances in the understanding of structure–activity relations are often accompanied by technological or conceptional breakthroughs. The understanding of Ga speciation at PDH conditions has evolved owing to the advent of in situ/operando characterizations and to the realization that the local coordination environment of Ga species afforded by the zeolite support has a decisive impact on the active site structure. In situ/operando quantitative characterization of catalysts, rigorous determination of intrinsic reaction rates, and predictive computational modeling are all significant in identifying the most active structure in these complex systems. The reaction mechanism could be both intricately related to and nearly independent of the details of the assumed active structure, as in the two main proposed PDH mechanisms on Ga/H‐ZSM‐5, that is, the carbenium mechanism and the alkyl mechanism. Perspectives on potential approaches to further elucidate the active structure of metal‐exchanged zeolite catalysts and reaction mechanisms are discussed in the final section.

Copyright of Acta Geoscientica Sinica is the property of Acta Geoscientica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The emission behaviors of HMWG during coal oxidation and pyrolysis were studied. • The yields of HMWG generated from coal oxidation and pyrolysis were calculated. • The evolution of microstructure during coal oxidation and pyrolysis was studied. • The formation mechanism of HMWGs during CSC was proposed. Higher-molecular-weight gases (HMWGs), which have not received much attention, also contain invaluable information about the coal spontaneous combustion (CSC) development process. In order to investigate the formation mechanism of HMWG, the emission behaviors of HMWG from coal oxidation and pyrolysis experiments were compared, and FTIR and ESR were used to analyze the microstructural evolution of the coal sample. The results show that the volume fractions of most HMWGs increased regularly with increasing temperature. The contribution of the pyrolysis process to the yield of most hydrocarbon HMWGs was close to 100 %, while it was below 89 % for C 4 ∼ C 6 n-alkanes and benzene and less than 10 % for acetaldehyde and acetone. The decomposition of active structures could produce free radicals, the concentration of which increases with increasing temperature. The formation mechanism of HMWGs was proposed based on the experimental results: HMWGs came from both the thermal reaction and the coal-oxygen reaction process. The thermal reaction process would release the majority of hydrocarbon HMWGs from room temperature. Some active structures began participating in the coal-oxygen reactions to produce oxygen-containing HMWGs at 90 ℃. After reaching 170 ℃, the coal-oxygen reactions were further intensified to release minority n-alkanes, benzene, and small amounts of C 4 olefins. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • The CO oxidation catalyzed by various CuO-CeO 2 interfacial sites involves a typical Mars-van Krevelen mechanism. • The CuO-CeO 2 interfaces in the CeO 2 -CuO/c-Cu 2 O (cubes) nanocomposites are more intrinsically active at CeO 2 loadings no less than 0.75 wt%. • The higher activity is relevant to lower coordinated oxygen ions and thus better CO reactivity for the CeO 2 -CuO/c-Cu 2 O nanocomposites. • The active oxygen species on CuO-CeO 2 interface in catalyzing CO oxidation should come from CuO rather than CeO 2. • A highly active 13.2 %CeO 2 -CuO/c-Cu 2 O(s) (small) catalyst with high density of active sites for CO oxidation is realized on fine Cu 2 O cubes. Several CeO 2 -CuO/Cu 2 O nanocomposites with different CuO structures were used to identify the structure sensitivity of CuO in the CeO 2 -CuO/Cu 2 O catalyzed CO oxidation. The CO oxidation catalyzed by various CuO-CeO 2 interfacial sites involves a typical Mars-van Krevelen mechanism, in which the CuO-CeO 2 interfaces in the CeO 2 -CuO/c-Cu 2 O (cubes) nanocomposites are more intrinsically active, exhibiting ca. 15 kJ mol−1 lower activation energy than those in the CeO 2 -CuO/o-Cu 2 O (octahedra) and CeO 2 -CuO/d-Cu 2 O (rhombic dodecahedra) nanocomposites at CeO 2 loadings no less than 0.75 wt%. The higher activity is relevant to lower coordinated oxygen ions on CuO/c-Cu 2 O surface and thus better CO reactivity for the CeO 2 -CuO/c-Cu 2 O nanocomposites, which therefore indicates that the active oxygen species on CuO-CeO 2 interface should come from CuO rather than CeO 2. Moreover, a highly active 13.2 %CeO 2 -CuO/c-Cu 2 O(s) catalyst for CO oxidation is realized on fine Cu 2 O cubes, which thus has high density of active sites. [ABSTRACT FROM AUTHOR]

We consider a quasi-static fluid–structure interaction problem where the fluid is modeled by the Stokes equations and the structure is an active elastic material. More precisely, the displacement of the structure satisfies the equations of elasticity with an additional active stress, which models the presence of internal biological motors in the structure. Under smallness assumptions on the data, we prove the existence of a solution for this strongly coupled system. [ABSTRACT FROM AUTHOR]

Nonlinear dynamics of a rotating flexible slender beam with embedded active elements is studied in the paper. Mathematical model of the structure considers possible moderate oscillations thus the motion is governed by the extended Euler–Bernoulli model that incorporates a nonlinear curvature and coupled transversal–longitudinal deformations. The Hamilton's principle of least action is applied to derive a system of nonlinear coupled partial differential equations (PDEs) of motion. The embedded active elements are used to control or reduce beam oscillations for various dynamical conditions and rotational speed range. The control inputs generated by active elements are represented in boundary conditions as non-homogenous terms. Classical linear proportional (P) control and nonlinear cubic (C) control as well as mixed ( P - C ) control strategies with time delay are analyzed for vibration reduction. Dynamics of the complete system with time delay is determined analytically solving directly the PDEs by the multiple timescale method. Natural and forced vibrations around the first and the second mode resonances demonstrating hardening and softening phenomena are studied. An impact of time delay linear and nonlinear control methods on vibration reduction for different angular speeds is presented. [ABSTRACT FROM AUTHOR]

CuOx/TiO2 nanocatalysts (x=0 or 1) with ∼11 % wt. Cu loading employing TiO2 nanocrystals with various morphologies predominantly exposing {001}, {100}, and {101} facets as supports have been synthesized as catalysts for CO oxidation with excess of O2 (oxidative atmosphere) and water gas shift (WGS) reaction (reductive atmosphere). Strong TiO2 morphology effects were observed. The strongest Cu2O−TiO2 interaction was observed in CuO−TiO2{001} nanocatalyst, while the strongest Cu‐TiO2 interaction occurred in Cu‐TiO2{100} nanocatalyst. Catalytic activities of various CuO/TiO2 nanocatalysts in CO oxidation and of various Cu/TiO2 nanocatalysts in WGS reaction follow the same order of CuOx/TiO2{100}>CuOx/TiO2{101}>CuOx/TiO2{001}, and all CuO/TiO2 nanocatalysts are stable in CO oxidation but all Cu/TiO2 nanocatalysts suffer from serious deactivation in WGS reaction. The active structure of CuO/TiO2 nanocatalysts in CO oxidation was found to be the CuO species, while the active structure of Cu/TiO2 nanocatalysts in WGS reaction to be the Cu‐TiO2 interface which is relevant to the Cu‐TiO2 interaction. The supported Cu nanoparticles in Cu/TiO2 nanocatalysts tend to agglomerate at high temperatures in 5 %CO/Ar atmosphere, responsible for the deactivation in WGS reaction. These results not only demonstrate the morphology‐dependent CuOx‐TiO2 interaction in CuOx/TiO2 nanocatalysts, but also reveal reaction‐dependent active structures of CuOx/TiO2 nanocatalysts. [ABSTRACT FROM AUTHOR]

Previous studies have identified a seismic gap that has not witnessed any surface rupture earthquakes in the last 200–500 years located in the central sub-Himalaya (i.e., area around Chitwan intermontane valley). A higher rate of convergence in these parts poses a great threat of a surface rupturing earthquake in future. Recent analysis of the 2015 Gorkha earthquake to the north of this region suggests that it failed to rupture the surface; moreover, the stress is suggested to have transferred towards south. Therefore, the Chitwan intermontane valley - located in the sub-Himalaya of the central Himalayan seismic gap - is investigated in this study to identify the active structures. The longitudinal profile of a river considered to be one of the important geomorphic markers is used in this study for the identification of the active structures. The Hack profile and Stream-Length gradient index (SL index) is used to identify the anomalous segments of the rivers; these anomalous reaches are verified in the field for the presence of structures. Geomorphology of the region also supports the presence of active reverse faults in the valley. Abrupt break in the continuity of the geomorphic units and its correlation with the knick points and high SL index values indicate presence of around nine active structures in the Chitwan intermontane valley. Six new structures viz., Jharahi Thrust (JHT). Belani Thrust (BT), West Chitwan Thrust (WCT), Danda Thrust (DT), Central Churia Thrust 2 (CCT 2) and Shaktikhor Thrust (ST) have been identified in this study; whereas, three previously mapped structures viz., Main Boundary Thrust (MBT), Barakot Fault (BKF) and Central Churia Thrust (CCT) are also found to be active during the Quaternary/Holocene. Most of the newly identified structures appear to be splays of either the MBT or the CCT. These structures have displaced Quaternary landforms within the valley and are potentially active. The structures can get re-activated during large magnitude earthquake events in future. [ABSTRACT FROM AUTHOR]

The current study is a short follow-up to our most recent work (Stylianou et al., 2016), where among other things we have presented an effective criterion suitable for distinguishing large-scale coherent structures with low turbulent kinetic energy content (i.e.  inactive structures ) from their high energy counterparts (i.e.  active structures ). This criterion is based on the instantaneous values of the one-point turbulence Structure Tensors (Kassinos et al., 2001), which are effective in quantifying the different aspects of the coherent structures of turbulence. Same as in our previous work, here we perform Direct Numerical Simulation (DNS) of a fully developed turbulent pipe flow at bulk Reynolds number R e b = 5300 . Using simulation results, we accentuate the ability of this criterion to identify large-scale coherent structures and to differentiate between low energy and high energy content. Furthermore, based on this criterion we perform conditional averaging during the collection of statistics, which allows us to examine the contribution of the active and inactive structures to various large-scale and small-scale statistical quantities. Our results reveal that the characteristic trends in the turbulence statistics associated with the law of the wall , arise primarily due to contributions from the inactive structures. Moreover, in the log-law region both active and inactive structures contribute equally to the turbulence statistics. [ABSTRACT FROM AUTHOR]

Piezoelectric composite laminates are a powerful material system that offers vast options to improve structural behavior. Successful design of piezoelectric adaptive structures and testing of control laws call for highly accurate, reliable and numerically efficient numerical tools. This paper puts focus onto linear and geometrically nonlinear static and dynamic analysis of smart structures made of such a material system. For this purpose, highly efficient linear 3-node and 4-node finite shell elements are proposed. Both elements employ the Mindlin-Reissner kinematics. The shear locking effect is treated by the discrete shear gap (DSG) technique with the 3-node element and by the assumed natural strain (ANS) approach with the 4-node element. Geometrically nonlinear effects are considered using the co-rotational approach. Static and dynamic examples involving actuator and sensor function of piezoelectric layers are considered. [ABSTRACT FROM AUTHOR]

The active approach is nowadays well developed and widely used for various kinds of structures for vibration control or compensation. However, it makes the structure more complex than a passive structure. In this study, active and passive beam structures with the same designed size are compared with regard to uncertainty analysis of the system. The purpose of the comparison is to find a comprehensive way to decide whether an active or a passive approach should be used in the structural design phase. An active beam structure used in this study is a beam structure with one sensor, one actuator, and one controller. The controller is designed to reduce the structural vibration. An active beam structure with a properly designed controller can reduce the structural vibration without changing the structure’s physical dimensions. In contrast, a passive approach can also reduce the structural vibration without additional electric energy for active components, e.g., by changing the material. The comparison of the active and the passive beam structure is based on a beam structure with the same boundary conditions. It is well known that after manufacture and assembly the input parameters of the structure do not exactly correspond to the designed values. Therefore, the input parameters are assumed to be normally or uniformly distributed according to the manufacture tolerance class. They are varied according to the Monte Carlo method to compare the vibration reduction ability of the active and the passive approaches. Finally, uncertainty analysis supports the decision if an active or a passive approach should be used in the structural design phase. [ABSTRACT FROM AUTHOR]

The structural transition in micrometer-sized liquid crystal bubbles (LCBs) derived from rod-like cellulose nanocrystals (CNCs) was studied. The CNC-based LCBs were suspended in nematic or chiral nematic liquid-crystalline CNCs, which generated topological defects and distinct birefringent textures around them. The ordering and structure of the LCBs shifted from a nematic to chiral nematic arrangement as water evaporation progressed. These packed LCBs exhibited a specific photonic cross-communication property that is due to a combination of Bragg reflection and bubble curvature and size. [ABSTRACT FROM AUTHOR]

Results of the linear closed form solution of an active or adaptive tensegrity unit, as well as its numerical analysis using finite element method are presented in the paper. The shape of the unit is an octahedral cell with a square base and it is formed by thirteen members (four bottom and four top cables, four edge struts and one central strut). The central strut is designed as an actuator that allows for an adjustment of the shape of the unit which leads to changes of tensile forces in the cables. Due to the diagonal symmetry of the 3D tensegrity unit the closed-form analysis is based on the 2D solution of the equivalent planar biconvex cable system with one central strut under a vertical point load.

Pole assignment is one of the central problems in most control systems designs. In relation to low-authority active flexible structural systems where robustness is difficult to achieve primarily due to many closely-spaced low-frequency lightly damped modes, pole-placement techniques are commonly used to design constant gain collocated controllers that will ensure that the transient phenomenon of the structure dies down sufficiently fast. In this paper, the active control of flexible structures is presented for collocated control design using a modified pole-placement approach that reduces the control efforts significantly. The effectiveness of employing the proposed approach is demonstrated using tensegrity structures. [ABSTRACT FROM AUTHOR]

To stop the light group velocity by metamaterial waveguides, for applying in several usages is the matter of attention in recent years. The new researches work on compensating losses in metamaterial waveguides with non-zero loss on metamaterial articles. In the present study, a structure of five layers is suggested, in which the side thickness of metamaterial core is variable but the central thickness is constant. In a part of center there located an active ZnO/Au in cladding layer; By pumping a proper magnitude of external optical field with specific wavelength, different from internal optic wavelength to it, there appears a non-linear optical effect. Theoretical and numerical analysis results show that in the mentioned part losses of the waveguide are compensated and exactly equal to the time of the pump pulse, light group velocity will be zero. [ABSTRACT FROM AUTHOR]

Abstract: A fast prototyping method for the active vibration control system of 3D mechanical structures is presented in the paper. To control such system piezo-stack actuators were used. The subsequent steps of the prototyping procedure are explained for the bar structure as an example. The Finite Element Modeling (FEM) approach was used to find the quasi-optimal location of piezo-stacks in the structure. Next, the structure with inbuilt piezo-actuators was designed and tested in the laboratory. The more accurate mathematical model of the structure dynamics was obtained as a result of the identification procedure. The mathematical model was reduced and decoupled to change the Two Input Two Output (TITO) system into two Single Input Single Output (SISO) systems. Such approach allowed us to design simple control laws with the aid of the computer simulation procedure. In the last chapter the tests on the laboratory stand of the active vibration control system with local Proportional-Derivative (PD) controllers are described. Experimental results have proved that these PD controllers work good increasing the damping level. Additional damping causes an excellent vibration reduction of the whole mechanical structure. [Copyright &y& Elsevier]

Abstract: Results of the linear closed form solution of an active or adaptive tensegrity unit, as well as its numerical analysis using finite element method are presented. The shape of the unit is an octahedral cell and it is formed by thirteen members (eight cables, four edge struts and one central strut). The central strut is designed as an actuator that allows for an adjustment of the shape of the unit which leads to changes of tensile forces in the cables. Since the unit is diagonally symmetrical, it may be simply solved as planar biconvex cable system with one central strut. [Copyright &y& Elsevier]

Abstract: Ag/CeO2 catalysts employing CeO2 nanocubes (c-CeO2) and nanorods (r-CeO2) as the support were prepared by conventional incipient wetness impregnation followed by calcination at 500°C in air. Their structures have been characterized in detail and their catalytic activities in CO oxidation have also been tested. c-CeO2 and r-CeO2 nanocrystals exhibit different concentrations and structures of oxygen vacancies. The silver-r-CeO2 interaction is stronger than the silver-c-CeO2 interaction. Fine Ag nanoparticles form in 1%-Ag/c-CeO2 and grow in size in 3%-Ag/c-CeO2; however, positively charged clusters dominate in 1%-Ag/r-CeO2, and fine Ag nanoparticles dominate in 3%-Ag/r-CeO2. Supported Ag nanoparticles are much more capable of creating oxygen vacancies in CeO2 than supported positively charged clusters. More oxygen vacancies form in Ag/c-CeO2 than in Ag/r-CeO2. The average charge density of oxygen vacancies and the ratio between large oxygen vacancy clusters and small vacancies in CeO2 nanocrystals are enhanced when loaded with positively charged clusters but reduced when loaded with Ag nanoparticles. Ag nanoparticles greatly promote the reduction and catalytic activity in CO oxidation of CeO2 nanocrystals but positively charged clusters do not. These results demonstrate the concept that the interplay between oxygen vacancies and Ag–CeO2 interaction controls the structures of silver and CeO2 in Ag/CeO2 catalysts and thus their surface reactivity and catalytic activity, deepening the fundamental understanding of metal/CeO2 catalysts. These results also reveal that the interplay between oxygen vacancies and Ag–CeO2 interaction in Ag/CeO2 catalysts depends on the shape of CeO2 support, opening up a new strategy for the design of efficient and economic metal/CeO2 catalysts by engineering the shape of CeO2 support. [Copyright &y& Elsevier]