In this paper, accurate trajectory tracking problem of a surface vehicle disturbed by complex marine environments is solved by creating a finite-time control (FTC) scheme whereby the nonsingular fast ...terminal sliding mode (NFTSM) and finite-time disturbance observer (FDO) techniques are deployed. Salient features are as follows. By devising an FDO, complex disturbances arising from marine environments can be exactly identified within a short time, in conjunction with the defined NFTSM manifold, and thereby contributing to exact trajectory tracking. Finite-time disturbance observation is completely decoupled from the nominal FTC scheme, and achieves stronger disturbance rejection and faster transient response, simultaneously. Both disturbance observation and trajectory tracking errors can exactly reach to zero in a finite time. Simulation results and comparisons are comprehensively conducted on CyberShip II and demonstrate remarkable superiority of the FTC scheme.
In this brief, a finite-time unknown observer-based interactive trajectory tracking control (FUO-ITTC) scheme is created for an asymmetric underactuated surface vehicle (AUSV). In lieu of a selfish ...trajectory which might be essentially inaccessible for an AUSV, the philosophy of an interactive trajectory, which features freely prescribed surge and yaw dynamics, and sway interactions with cross-tracking dynamics, is innovatively established for the first time, and thereby contributing to a family of uniformly trackable trajectories which completely remove persistent-excitation constraints on the desired yaw rate. By defining a composite coordinate transformation (CCT), interactive trajectory tracking error dynamics are formulated in a cascade structure with finite-time vanishing residuals. By virtue of the CCT-based cascade structure, FUO-based surge and yaw controllers are separately synthesized with an interaction law. The entire FUO-ITTC closed-loop system stability is guaranteed by combining the Lyapunov approach with cascade analysis, which in turn rigorously proves that both kinematic and dynamic tracking errors globally asymptotically converge to zero. Comprehensive experiments and comparisons are conducted on a benchmark AUSV and demonstrate the remarkable performance of the proposed FUO-ITTC scheme in terms of both transient and steady-state tracking accuracy.
A novel adaptive fuzzy control scheme is designed in this article for a class of stochastic nonstrict feedback nonlinear systems with output constraint and unknown control coefficients. A reduced ...adaptive fuzzy system is proposed to approximate the unknown function which contains all state variables of the whole system and ensures that the backstepping design method works normally for nonstrict feedback nonlinear systems. With the use of this reduced adaptive fuzzy control method and a combination of Barrier Lyapunov Function control design and Nussbaum gain technique, a novel adaptive fuzzy controller is proposed to guarantee that the output tracking error always meets the given constraint requirement in a sense of probability and the resulting closed-loop states are bounded in probability. Finally, an example is presented to confirm the effectiveness of the designed method.
In this paper, a challenging problem of full-state regulation control (FSRC) for an asymmetric underactuated surface vehicle (AUSV) suffering from disturbances is solved. The FSRC objective is ...divided into two subtasks, i.e., reaching trajectory (RT) guidance and tracking controller synthesis with underactuation and disturbances. The RT guidance is achieved by devising a circular orbit (CO) accurately passing through the desired full-state waypoint (FWP). Using a series of coordinate transformations, tracking error dynamics are shaped in a translation-rotation cascade form with respect to the CO-center frame. Using finite-time approach, lumped disturbances are accurately estimated by exact observers, which facilitate synthesizing surge and yaw controllers. By creating a new coordinate, translation subsystem is converted to a lower-triangular form. Combining with backstepping technique, cascade analysis and Lypunov approach, translation and rotation controllers are derived systematically, and render the entire closed-loop FSRC system globally asymptotically stable. Hence, the AUSV is regulated to the desired FWP. Simulation studies on a benchmark AUSV are conducted to demonstrate remarkable performance.
Thiacalix4arenes as a family of promising ligands have been widely used to construct polynuclear metal clusters, but scarcely employed in silver nanoclusters. Herein, an anion-templated Ag
...nanocluster (SD/Ag88a) built from p-tert-butylthiacalix4arene (H
TC4A) is reported. Single-crystal X-ray diffraction reveals that C
-symmetric SD/Ag88a resembles a metal-organic super calix comprised of eight TC4A
as walls and 88 silver atoms as base, which can be deconstructed to eight CrO
@Ag
(TC4A)(EtS)
(OAc) secondary building units arranged in an annulus encircling a CrO
in the center. Local and global anion template effects from chromates are individually manifested in SD/Ag88a. The solution stability and hierarchical assembly mechanism of SD/Ag88a are studied by using electrospray mass spectrometry. The Ag
nanocluster represents the highest nuclearity metal cluster capped by TC4A
. This work not only exemplify the specific macrocyclic effects of TC4A
in the construction of silver nanocluster but also realize the shape heredity of TC4A
to overall silver super calix.
This paper focuses on the design of a reduced adaptive fuzzy tracking controller for a class of high-order stochastic nonstrict feedback nonlinear systems with full-state constraints. In the proposed ...approach, reduced fuzzy systems are used to approximate uncertain functions which involve all state variables and a high-order tan-type barrier Lyapunov function (BLF) is considered to deal with full-state constraints of the controlled system. With this BLF and a combination of the reduced fuzzy control and adding a power integrator, a novel control scheme is constructed to ensure that tracking error is within a very small range of the origin almost surely, meanwhile, the constraints on the system states are not breached almost surely during the operation. Two examples are proposed to show the effectiveness of the design scheme.
Although great achievements have been made in the synthesis of giant lanthanide clusters, novel structural models are still scarce. Herein, we report a giant lanthanide cluster Dy76, constructed from ...Dy3(μ3‐OH)4 and Dy5(μ4‐O)(μ3‐OH)8 building blocks. As the largest known Dy cluster, the structure of Dy76 can be seen as arising from the fusion of two Dy48 clusters; these clusters can be isolated under various synthetic conditions and were characterized by single‐crystal X‐ray diffraction. This new, fused structural model of the pillar motif has not been found in Ln clusters. Furthermore, the successful conversion of Dy76 back into Dy48 in a retrosynthetic manner supports the proposed fusion formation mechanism of Dy76. Electrospray ionization mass spectrometry (ESI‐MS) analysis suggests that the metal cluster skeleton of Dy76 shows good stability in various solvents. This work not only reveals a new structural type of Ln clusters but also provides insight into the novel fusion assembly process.
We go together: Two dysprosium clusters with 48 and 76 metal atoms, respectively, were generated under solvothermal conditions by using 3‐furancarboxylic acid. The bi‐nanopillar Dy76 was formed by the fusion of two Dy48 nanopillars.
Cross‐electrophile coupling has emerged as a promising tool for molecular synthesis; however, current studies have focused mainly on forging C−C bonds. We report a cross‐electrophile C−Ge coupling ...reaction and thereby demonstrate the possibility of constructing organogermanes from carbon electrophiles and chlorogermanes. The reaction proceeds under mild conditions and offers access to both aryl and alkenyl germanes. Electron‐rich, electron‐poor, and ortho‐/meta‐/para‐substituted (hetero)aryl electrophiles, as well as cyclic and acyclic alkenyl electrophiles, were coupled. Gram‐scale reaction, incorporation of the ‐GeR3 moiety into complex biologically active molecules, and derivatization of formed organogermanes are demonstrated.
A new C−Ge bond‐forming framework was established, which bridges a gap between a recently developed mild coupling technique and organogermane chemistry. The method provides a mild approach for the synthesis of both aryl and alkenyl germanes, with improved molecular diversity and structural complexity, using readily available carbon electrophiles and chlorogermanes as starting materials.
The structural transformation of high-nuclearity silver clusters from one to another induced by specific stimuli is of scientific significance in terms of both cluster synthesis and reactivity. ...Herein, we report two silver-thiolate clusters, Mo
O
@Ag
and Mo
O
@Ag
, which are templated by isopolymolybdates inside and covered by
PrS
and PhCOO
ligands on the surfaces. Amazingly, the Mo
O
@Ag
can be transformed from Mo
O
@Ag
by adding PhCOOH which increases the degree of condensation of molybdates template from Mo
O
to Mo
O
, then enlarging the outer silver shell from Ag
to Ag
. The evolution of solution species revealed by time-dependent electrospray ionization mass spectrometry (ESI-MS) suggests a breakage-growth-reassembly (BGR) transformation mechanism. These results not only provide a combined assembly strategy (anion-template + induced transformation) for the synthesis of silver-thiolate clusters but also help us to better understand the complex transformation process underpinning the assembly system.
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