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Atomically precise metal nanoclusters (NCs) are judiciously stabilized as simultaneous charge relay mediators and photosensitizers for photocatalytic organic transformation.

Precisely modulating the spatial charge migration/separation constitutes the central issue in dictating the solar conversion efficiency of photoelectrochemical (PEC) cells, whereas it still remains a grand challenge. Here, we conceptually demonstrate the construction of hierarchically ordered metal oxide (MO)/transition-metal chalcogenide quantum dots (TMC QDs) multilayered heterostructured photoanodes, that is, MO/[TMC QDs(+)/TMC QDs(-)]

Photocatalytic selective organic transformation represents an emerging avenue for artificial photosynthesis toward renewable solar energy conversion. However, solar-to-chemical conversion efficiency in photocatalysis is largely hampered by the sluggish charge transfer kinetic and difficulty in precise control over the charge migration pathway. Herein, we demonstrate conceptually new metal–insulator–semiconductor (MIS) electron tunneling photosystems to finely modulate the directional charge flow for photoredox selective organic transformation. The ultrathin insulating organic ligands layers capped on the surfaces of metal nanocrystals (NYs) and transition metal chalcogenides quantum dots (TMCs QDs) mutually function as precise directing-mediums to stimulate spontaneous electrostatic self-assembly between the tailor-made oppositely charged metal NYs and TMCs QDs for constructing metal (Au, Pd) NYs/TMCs (CdSe, CdS) QDs heterostructured electron tunneling photosystems. The electrons photoexcited from TMCs QDs can be efficaciously extracted and tunneled to metal NYs across the intermediate insulating hierarchical ligands layers to participate in the photoredox catalysis. The metal NYs-insulating ligands-TMCs QDs photosystems can efficiently mediate the minority carrier transport across the intermediate insulating ligand layers with minimal recombination, thereby resulting in the significantly enhanced net efficiency of multifarious photoactivities toward selective organic transformation including anaerobic photoreduction of nitroaromatics to amino derivatives and selective photo-oxidation of aromatic alcohols to aldehydes under visible light irradiation. The ligand-triggered electron tunneling effect has been evidence to be universal. Our work would inspire ongoing interest in exploring diverse organic ligands-based charge tunneling photosystems and provide a valuable roadmap for substantial solar energy conversion.

Transition metal chalcogenide quantum dots (TMCs QDs) constitute a crucial sector of semiconductors on account of large absorption coefficient for light harvesting, peculiar quantum confinement effect, and abundant active sites stemming from ultra-small size. However, elaborate and tunable modulation of anisotropic photoinduced charge carriers over TMCs QDs represents an enduring challenge in terms of sluggish charge transfer kinetic and ultra-short charge lifetime compared with nanoparticulate counterparts, thereby rendering maneuvering charge transfer of TMCs QDs a tough issue. We herein conceptually unlock the unanticipated charge transport capability of solid-state non-conductive poly(diallyl dimethylammonium chloride) (PDDA) for constructing cascade charge transfer pathway over self-assembled wide bandgap semiconductors (WBS)/PDDA/TMCs QDs multilayered heterostructures, by which unidirectional and accelerated electron transfer from TMCs QDs to WBS support mediums was spontaneously activated, markedly boosting the charge separation/migration efficiency. The integrated roles of such ultrathin insulating PDDA intermediate layer as simultaneous surface charge modifying agent and interfacial charge transfer mediator have been evidenced to be universal. The unexpected electron-withdrawing capability of ultrathin PDDA layer endows WBS (SnO 2, TiO2)@PDDA@TMCs (CdSe, CdS) QDs heterostructures with significantly enhanced net efficiency of photoactivities toward selective anaerobic reduction of nitroaromatics to amino derivatives under visible light irradiation. Our work would feature a promising scope for rational design of multifarious novel insulating polymers-based photosystems for solar energy conversion.

The novel protein MclX (mother cell lysis X) in Bacillus thuringiensis subsp. kurstaki strain HD73 (B. thuringiensis HD73) was characterized in this work. MclX has no known domain and its gene deletion in HD73 resulted in Cry1Ac encapsulation in the mother cell and did not influence Cry1Ac protein production or insecticidal activity. In vitro cell wall hydrolysis experiments showed that MclX cannot hydrolyze the cell wall. In mclX deletion mutants, the expression of cwlC (which encodes a key cell wall hydrolase) was significantly decreased, as shown by the β-galactosidase activity assay. MclX cannot directly bind to the cwlC promoter, based on the electrophoretic mobility shift assay (EMSA). The cwlC was reported to be regulated by σK and GerE. However, the transcriptional activities of sigK and gerE showed no difference between HD73 and the mclX deletion mutant. It is indicated that MclX influenced cwlC expression independently of σK or GerE, through a new pathway to regulate cwlC expression. mclX deletion could be a new approach for insecticidal protein encapsulation in Bacillus thuringiensis.

For the large high-temperature structure with multiple points of support, the support keys are not only subjected to the self-weight of the structure, but also to the static and dynamic loads in the assembly environment; on the other hand, the nonuniform temperature distribution forms different degrees of thermal stresses on the structure, while the thermal expansion effect has a significant impact on the assembly state of the support keys and the supports. As an over-constrained system, if the extreme assembly relationship between the bearing key and the support occurs, such as jamming, it will further deteriorate the pre-stress condition of the support system and seriously threaten the safety of the structure. Restricted by the size of the structure and test conditions, the scaled model is considered instead of the full-sized structure for dynamics analysis and experimental study to evaluate the safety and reliability of the support system under thermal environment. In this paper, the force state of the bearing system under operation is analyzed by combining numerical simulation and scaled model tests, the possible jamming risk during the application of the bearing is predicted and the corresponding plan is formulated. The effectiveness of the plan is verified by optimizing the clearance factor of the scaled model, which provides a reference for the safe design of multi-point support structures under thermal environment.

Conjugated polymers are deemed as conductive carrier mediators for engendering the π electrons along the molecular framework, while the role of nonconjugated insulated polymers has been generally overlooked without the capability to participate in the solar-powered oxidation-reduction kinetics and charge-transfer process. Alternatively, considering the ultrashort charge lifetime and significant deficiency of metal nanocluster (NC)-based photosystems, the fine tuning of charge migration over atomically precise ultrasmall metal NCs as novel light-harvesting antennas has so far not yet been unleashed. Here, we unlock the charge-transfer capability of a nonconjugated polymer to modulate the charge flow over metal NCs (Au

Most research about using piezoelectric stacks to suppress vibration of mechanical structures didn’t involve the similarity problem for the piezoelectric stacks. The goal of this paper is to investigate the dynamic similarity between a prototype piezo stack and a scaled up or down piezo stack, whilst discussing the feasibility of predicting the vibration of prototype structure which use the piezoelectric stacks for vibration control. To illustrate this problem concisely, a single-DOF system consists of a proof mass and a piezo stack shunted with a series RL circuit is considered. Firstly, the governing equation of such piezo-electromechanical system in frequency domain is derived. Next the dynamic similarity of prototype and model stack is analyzed by similitude theory. After that the scaling laws are derived. Finally, a numerical simulation and relative error analysis are given to demonstrate the scaling laws.

Transition metal chalcogenide quantum dots (TMC QDs) represent promising light-harvesting antennas because of their fascinating physicochemical properties including quantum confinement effect and suitable energy band structures. However, TMC QDs generally suffer from poor photoactivities and photostability due to deficiency of active sites and ultrafast recombination rate of photoinduced charge carriers. Here, we demonstrate how to rationally arouse the charge transfer kinetic of TMC QDs by close monolayered graphene (GR) encapsulation via a ligand-dominated layer-by-layer (LbL) assembly utilizing oppositely charged TMC QDs and GR nanosheets as the building blocks. The assembly units were spontaneously and intimately integrated in an alternate integration mode, thereby resulting in the multilayered three-dimensional (3D) TMC QDs/GR ensembles. It was unveiled that multifarious photoactivities of TMC QDs/GR nanocomposites toward versatile photoredox organic catalysis including photocatalytic aromatic alcohols oxidation to aldehydes and nitroaromatics reduction to amino derivatives under visible light irradiation are conspicuously boosted because of spatially multilayered monolayered GR encapsulation which are superior to those of TMC QDs counterparts. The substantially enhanced photoactivities of TMC QDs/GR nanocomposites arise from reasons including improved light absorption and enhanced charge separation efficacy because of GR encapsulation together with unique stacking mode between TMC QDs and GR endowed by LbL assembly. Our work would provide a promising and efficacious route to smartly accelerate the charge transfer kinetic of TMC QDs for solar energy conversion.

Atomically precise metal nanoclusters (NCs)-based photocatalytic systems have garnered enormous attention owing to the fascinating merits including unique physicochemical properties, quantum confin...

Directional and high-efficiency charge transport to the target active sites of photocatalyst is central to boost the solar energy conversion but is retarded by the sluggish charge transfer kinetics and deficiency of active sites. Here, we report the elaborate design of cascade unidirectional charge transfer channel over spatially multilayered CdS@CdTe@MoS2 dual core-shell ternary heterostructures by partial transformation of CdS to CdTe interim layer followed by seamless encapsulation with an ultrathin MoS2 layer. The suitable energy-level alignment and unique coaxial multilayered assembly mode among the building blocks accelerate the interfacial charge separation and transport, endowing the CdS@CdTe@MoS2 heterostructures with conspicuously enhanced visible-light-driven photocatalytic hydrogen generation performances along with good photostability. The integrated roles of ultrathin CdTe intermediate layer in passivating the defect sites of CdS NWs framework, mediating the unidirectional charge transfer cascade and prolonging the charge lifetime, were ascertained. Besides, the crucial role of the outermost MoS2 layer as the metal-free cocatalyst in enriching the surface active sites for hydrogen evolution was also determined. Our work would provide new alternatives for finely tuning the charge flow toward promising solar-to-hydrogen conversion efficiency.

Finely tuning the charge transfer constitutes a central challenge in photocatalysis, yet exquisite control of the directional charge transfer to the target reactive sites is hindered by the rapid charge recombination. Herein, dual separated charge transport channels were fabricated in a one-dimensional transition-metal chalcogenide (TMC)-based system via an elaborate layer-by-layer (LbL) self-assembly approach, for which oppositely charged metal-ion-coordinated branched polyethylenimine (BPEI) and MoS2 quantum dots (QDs) were alternately integrated to fabricate the multilayered TMC@(BPEI/MoS2 QDs)n heterostructures with controllable interfaces. Photocatalytic hydrogen generation performances of such ternary heterostructures under visible light irradiation were evaluated, which unravels that the BPEI layer not only behaves as "molecule glue" to enable the electrostatic LbL assembly with MoS2 QDs in an alternate stacking fashion on the TMC frameworks but also acts as a unidirectional hole-transfer channel. More significantly, transition-metal ions (Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) coordinated on the outmost BPEI layer are able to function as interfacial electron transfer mediators for accelerating the interfacial cascade electron transport efficiency. These simultaneously constructed dual high-speed electron and hole-transfer channels are beneficial for boosting the charge separation and enhancing the photocatalytic hydrogen evolution performances.

Graphene oxide (GO)/Ag3PO4/Ni composite film electrodes were prepared by composite electrodeposition using a mixture of ammonium phosphate and GO aqueous suspension as the electrolyte. The morphology, crystallinity, and optical characteristics of the composite films were analyzed. The photoelectrocatalytic (PEC) degradation activity of the film electrodes towards rhodamine B (RhB) was determined by applying an anodic bias under visible-light irradiation. The PEC mechanism of the GO/Ag3PO4/Ni film electrodes was explored by investigating the photo-generated charge behavior and the active species of the PEC reaction. The results showed that the GO/Ag3PO4/Ni composite films prepared by the optimum process consisted of GO coated on Ag3PO4 nanospheres with a diameter of about 100 nm. Under the optimum anodic bias, their PEC degradation efficiency toward RhB was 1.74 times that of an Ag3PO4/Ni film and 4.47 times higher than their photocatalytic (PC) efficiency without an applied bias. Importantly, the GO/Ag3PO4/Ni composite films exhibited an obvious photoelectric synergistic effect and excellent PEC stability; at an anodic bias of 0.1 V, its their PEC stability was about twice their PC stability. The excellent charge conduction properties of GO and its ability to separate photogenerated electrons and holes more effectively under an anode bias and with an increase in the concentration of ˙RhB+ were the main reasons for the high PEC activity of the composite films.

Precise tuning of photoinduced charge separation and transport has been an enduringly central issue in photocatalysis but has met with limited success. In particular, the controllable, accurate and simultaneous modulation on the charge (electrons/holes) transfer pathway in photocatalytic selective organic transformations has not yet been achieved. Herein, as a proof-of-principle demonstration, we report the fine tuning of charge separation/migration by smartly constructing spatially separated charge transport channels over diverse metal/transition metal chalcogenide [(M/TMC), M = Au, Ag, Pd, TMCs = ZnIn2S4, CdIn2S4, In2S3, and CdS] heterostructure photosystems, which were elaborately crafted by an efficient surface ligand-triggered electrostatic self-assembly. Accordingly, tailor-made positively charged branched poly(ethylene imine) (bPEI)-capped metal nanocrystals (NCs) were controllably and uniformly anchored on the two-dimensional (2D) TMC nanosheet (NS) framework, resulting in well-defined metal/TMC heterostructures. We found that electrons photoexcited over TMC NSs could be spontaneously, smoothly and unidirectionally migrated to closely integrated metal@bPEI NCs, wherein the metal core acts as a Schottky-type electron-trapping reservoir and bPEI ligand as a hole transfer mediator, synergistically affording spatially separated charge transfer channels and expediting the charge separation/transfer efficiency. Benefiting from these merits, the self-assembled M/TMC heterostructures exhibited conspicuously boosted photoactivities in the visible light-driven selective organic transformation toward the anaerobic reduction of aromatic nitro compounds to amino derivatives, which are superior to pristine TMCs and M/TMCs without ligand encapsulation. More significantly, the self-assembly strategy and charge modulation concept are universal for diverse metal NCs and TMCs. Thus, our study provides a general and effective protocol to construct a host of metal/TMC heterostructures and stimulates new inspiration for modulating tunable charge separation/migration for substantial solar energy conversion.

Unidirectional and smooth charge transfer to the reactive sites plays an imperative role in boosting the solar-to-hydrogen conversion efficiency of photoelectrochemical (PEC) cells but suffers from sluggish charge transfer kinetics. Herein, as a proof-of-concept demonstration, high-speed spatially separated electron and hole transfer channels were simultaneously constructed in an integrated multilayered heterostructured photoanode via an efficient electrostatic layer-by-layer (LbL) assembly strategy, wherein a tailor-made positively charged polymer of branched polyethylenimine (BPEI) and negatively charged MoS2 quantum dot (QD) building blocks were intimately and alternately integrated on the hierarchically ordered TiO2 nanotube array (TNTA) framework in a unique “face-to-face” stacking fashion. The periodically alternately stacked ultra-thin BPEI layer in the ternary multilayered photoanode serves as a directional hole transport channel and the MoS2 QD layer functions as a cascade electron transfer channel, which synergistically contribute to the considerably enhanced separation and prolonged lifetime of charge carriers, endowing the multilayered TNTAs/(BPEI–MoS2 QDs)n photoanodes with markedly enhanced PEC water dissociation performances with respect to the single and binary counterparts under simulated solar light irradiation. Moreover, the essential role of the assembly unit was clarified. Our work would afford a new frontier to intelligently mediate the photoinduced charge flow by rationally constructing the unidirectional charge transport channels in semiconductor-based photoelectrodes for solar energy conversion.

Modulating photo-induced charge separation/transfer constitutes a central challenge in heterogeneous photocatalysis. Despite advancements in this area, finely tuning directional electron migration without involving conventional co-catalysts [e.g., metal nanocrystals and transition metal dichalcogenides (TMDs)] for boosted photoredox catalysis has not yet been explored. Herein, we report the exquisite design of a novel and general macromolecule-modulated photoredox selective organic transformation system, wherein an ultrathin macromolecular poly(diallyldimethylammonium chloride) (PDDA) layer was integrated at the interface of wide-band-gap (WBG) and narrow-band-gap (NBG) semiconductors to construct heterostructured photocatalysts. The ultra-thin PDDA interim layer expedites interfacial unidirectional electron transfer from the NBG to WBG semiconductor, resulting in a cascade electron transfer channel. The favorable energy level alignment among the building blocks, intimate interfacial integration and multilayered nanoarchitecture endow the WBG@PDDA@NBG heterostructures with substantially enhanced and versatile photoredox performance toward the selective oxidation of aromatic alcohols to aldehydes and the anaerobic reduction of nitroaromatics to amino compounds under visible light irradiation. This can be ascribed to the crucial role of the ultrathin intermediate PDDA layer as a highly efficient metal and TMD-free charge transfer mediator, relaying the electrons from the NBG to WBG semiconductor and slowing charge recombination. Our work could open up new frontiers to exploit diverse metal and TMD-free photocatalytic systems and provide a first insight into the fine tuning of charge transport utilizing non-conductive ionic polymers for solar energy conversion.

Z-Scheme artificial photosystems, resembling the natural photosynthesis procedure, circumvent the disadvantage of a single-ingredient photosystem and hold fascinating prospects for solar energy conversion. Despite the advancements, bottom-up elaborate design of composite heterostructured Z-scheme photosystems by flexible interface engineering for photoredox organic transformation has been poorly investigated. We herein report the construction of a metal-based Z-scheme photoredox system via a progressive self-assembly strategy integrated with a facile photo-deposition. Tailor-made hierarchically branched ligand-capped Pd nanocrystals (NCs) sandwiched in-between a WO3 nanorod (NR) core and CdS shell are harnessed as the charge transport modulator to regulate the interfacial oxidation–reduction kinetics for boosted Z-scheme photocatalysis. The intermediate Pd NCs as Schottky-type electron flow mediators considerably accelerate the unidirectional Z-scheme charge motion rate, endowing multilayered WO3@Pd@CdS core–shell heterostructures with significantly boosted net efficiency of photoactivities toward anaerobic selective nitroaromatic reduction to amino derivatives and aromatic alcohol oxidation to aldehydes under visible light illumination. The predominant active species produced in the versatile photocatalytic selective organic transformation were explored and photocatalytic mechanisms were thus ascertained. Our endeavor could offer a promising route for smartly crafting diverse heterostructured Z-scheme photoredox systems for solar energy conversion.

Bacillus thuringiensis is a bacterium capable of differentiating into a spore, a dormant and highly resistant cellular form. During the sporulation process, this bacterium produces insecticidal toxins in the form of a crystal inclusion, usually in the sporulating cell. We previously reported that the B. thuringiensis LM1212 strain can differentiate into two distinct subpopulations of sporeformers and crystal producers and that this division-of-labor phenotype provides the bacterium with a fitness advantage in competition with a typical B. thuringiensis strain. The transcription factor CpcR was characterized as the regulator responsible for this phenotype. Here, we examined how CpcR interacts with the sporulation network to control the cell differentiation. We found that the sporulation process was inhibited prior to polar septum formation and that Spo0A activity was impaired in the presence of cpcR in strain LM1212. Using bioinformatics and genetic tools, we identified a gene positively controlled by CpcR encoding a putative phosphatase of the Spo0E family known to specifically dephosphorylate phosphorylated Spo0A (Spo0A-P). We showed that this protein (called Spo0E1) is a negative regulator of sporulation and that variations in spo0E1 expression can modulate the production of spores. Using fluorescent reporters to follow gene expression at the single-cell level, we correlated expression of cpcR and sporulation genes to the formation of the two differentiated subpopulations. IMPORTANCE Formation of spores is a paradigm for study of cell differentiation in prokaryotes. Sporulation initiation is governed by a gradual increase in the level and activity of the master regulator Spo0A. Spo0A is usually indirectly phosphorylated by a multicomponent phosphorelay, and modulation of this phosphorelay system is a critical aspect of Bacillus physiology. Though we know that this phosphorelay system is usually affected by two negative regulatory mechanisms, i.e., rap genes and spo0E family genes, the regulatory mechanisms controlling the transcription of these genes are poorly understood. Here, we report that the transcription factor CpcR positively regulates a spo0E family gene and that variations in spo0E expression can modulate the production of spores in B. thuringiensis. This work emphasizes the diversity in modes of sporulation and illustrates the diversity in the strategies employed by bacteria to control this differentiation pathway and ensure their survival.

Interfacial charge transfer and separation are both critical to the solar energy conversion efficiency, whereas it remains an enduring challenge. This work demonstrates the synergetic enhancement of interfacial charge transfer efficiency and bulk charge separation by depositing p-type Co3O4 cocatalyst onto n-type TiO2 nanotube arrays (TNTAs) that are uniformly coated with an ultrathin carbon layer, forming a p − n Co3O4/TNTAs heterojunction. Being highly dispersed on the surface of photoanodes, Co3O4 quantum dots retard forming charge recombination centers at the photoanode/cocatalyst interface, which facilitates hole transport. Simultaneously, ultrathin intermediate carbon layer boosts interfacial electron transfer kinetics, resulting in effective spatial charge separation and considerably improved photoelectrochemical (PEC) water splitting performances.

Sporulation is an important part of the life cycle of Bacillus thuringiensis and the basis for the production of parasporal crystals. This study identifies and characterizes two homologous spoVS genes (spoVS1 and spoVS2) in B. thuringiensis, both of whose expression is dependent on the σH factor. The disruption of spoVS1 and spoVS2 resulted in defective B. thuringiensis sporulation. Similar to Bacillus subtilis, B. thuringiensis strain HD(ΔspoVS1) mutants showed delayed formation of the polar septa, decreased sporulation efficiency, and blocked spore release. Different from B. subtilis, B. thuringiensis HD(ΔspoVS1) mutants had disporic septa and failed to complete engulfment in some cells. Moreover, HD(ΔspoVS2) mutants had delayed spore release. The effect of spoVS1 deletion on polar septum delay and sporulation efficiency could be compensated by spoVS2. β-Galactosidase activity analysis showed that the expression of pro-sigE and spoIIE decreased to different degrees in the HD(ΔspoVS1) and HD(ΔspoVS2) mutants. The different effects of the two mutations on the expression of sporulation genes led to decreases in Cry1Ac production of different levels. IMPORTANCE There is only one spoVS gene in B. subtilis, and its effects on sporulation have been reported. In this study, two homologous spoVS genes were found and identified in B. thuringiensis. The different effects on sporulation and parasporal crystal protein production in B. thuringiensis and their relationship were investigated. We found that these two homologous spoVS genes are highly conserved in the Bacillus cereus group, and therefore, the functional characterization of SpoVS is helpful to better understand the sporulation processes of members of the Bacillus cereus group.

Glutathione-protected Aux nanoclusters uniformly and intimately embedded at the interface of CdSe QDs and graphene were in situ self-transformed to Au nanocrystals (NCs) via a facile thermal reduction strategy. The inlaid Au NPs substantially accelerate the interfacial directional charge transfer toward multifarious photoreduction catalysis under visible light irradiation.

Recent years have witnessed an explosive investigation on the construction of graphene (GR)–semiconductor composite photocatalysts, but the specific correlation of the interface integration mode between GR and a semiconductor with the interfacial charge transfer characteristics is yet to be clearly clarified. To this end, a facile, green and surface linker-triggered self-assembly has been designed to construct GR-encapsulated antimony sulfide nanorod (Sb2S3 NRs–GR) ensembles, wherein tartaric acid-capped intrinsically negatively charged Sb2S3 NRs and surface-modified positively charged GR nanosheets were utilized as the building blocks. It was unveiled that the exquisitely designed interface configuration afforded by the intimate encapsulation of Sb2S3 NRs with GR via an electrostatic/hydrogen interaction is beneficial for fully harnessing the structural merits of GR in boosting light absorption, increasing the specific surface area and accelerating the interfacial electron transfer kinetics. Thus, the lifetimes of the photogenerated charge carriers were synergistically prolonged over Sb2S3, resulting in the considerably enhanced visible-light-responsive photoredox performances of the Sb2S3–GR nanocomposites toward the photoreduction of heavy metal ions and mineralization of organic pollutants compared with the blank Sb2S3 and nanocomposite counterpart without a finely tuned interface. More importantly, the crucial role of interface configuration between GR and the Sb2S3 NRs in dictating the interfacial charge transfer efficiency was substantiated. In addition, the predominant active species in the photoredox catalysis were determined and the corresponding photocatalytic mechanism was elucidated. Our work sheds light on mediating the interfacial charge transfer via rational interface configuration modulation toward substantial solar energy conversion.

Recent years have witnessed a rise in the construction of transition metal chalcogenide (TMS)-based heterostructured photocatalysts in terms of their excellent light absorption and suitable energy level alignment. Nevertheless, controllable modulation of photoinduced charge separation/transfer toward target active sites for photoredox catalysis still constitutes an enduringly challenging issue. Herein, tailor-made negatively charged mercaptoacetic acid (MAA)-capped CdX@MAA (X = Se, Te, S) quantum dot (QD) and positively charged ultra-thin branched poly-ethyleneimine (BPEI) layer building blocks were alternately assembled on the hierarchically ordered TiO2 nanotube array (NP-TNTA) framework for general electrostatic layer-by-layer (LbL) assembly of spatially multilayered NP-TNTAs/(BPEI/CdX QDs)n (X = Se, Te, S) photoanodes. The ultra-thin BPEI polymer layer integrated in-between the interface of CdX QDs functions as a cascade hole transfer channel for efficiently extracting the holes photoexcited over neighboring CdX QD layers, and simultaneously, alternately deposited CdX QD layers serve as an efficacious photosensitizer for constructing directional electron flow channels. The unique integration mode and intimate interfacial interaction endowed by LbL assembly render the well-defined NP-TNTAs/(BPEI/CdX QDs)n multilayered heterostructures a high-efficiency photoanode toward photoelectrochemical (PEC) water splitting under both simulated solar and visible light irradiation, greatly outperforming the single and binary counterparts on account of in situ generation of two spatially separated charge transfer channels, ultimately synergistically boosting the separation efficiency and prolonging the lifetime of charge carriers. Our work would open up new frontiers for strategically mediating the interfacial charge transfer and advancing rational construction of heterostructured photocatalysts for solar energy conversion.

Metal oxides (MOs)-based photoelectrochemical (PEC) cell, as an environmentally friendly and sustainable technique to convert solar energy to chemical energy, has been attracting enduring interest in the past few decades. However, sluggish charge transport dynamics, tough vectorial controllable charge migration route, and confined light absorption of MOs retard the solar energy conversion efficiencies of MOs-based photoelectrodes. Apart from MOs, transition metal chalcogenides (TMCs) photoanodes directly growing on the conductive substrate for PEC water splitting have been so far rarely reported albeit their generic merits of large absorption coefficient, suitable energy level alignment, and abundant active sites. Herein, we conceptually demonstrate the tunable construction of homogeneous TMCs heterostructured photoanodes (In2S3-CdIn2S4, In2S3-ZnIn2S4) by a facile, easily accessible, simple yet efficient cation exchange strategy at ambient conditions. The thus-designed TMCs composite photoanodes demonstrate significantly enhanced PEC water splitting performances relative to the pristine counterparts under both visible and simulated solar light irradiation, which is predominantly attributed to the markedly improved interfacial charge transfer/separation afforded by the favorable energy level configuration between the TMCs substrate and newly formed TMCs phase. We additionally ascertain that such ion exchange approach is universal for crafting other TMCs-based hybrid photoanodes. Our work is expected to provide an emerging avenue to craft a large variety of TMCs-based heterostructured photoanodes for solar energy conversion.

Atomically precise metal nanoclusters (NCs) have recently been unleashed as novel photosensitizers but inevitably suffer from light-induced self-transformation to metal nanocrystals (NYs), leading to substantially reduced photoredox activities. Herein, we conceptually demonstrate how to manipulate the intrinsic instability of metal NCs for smartly crafting long-range cascade charge transfer chain assisted by an ultrathin poly(dialyldimethylammonium chloride) (PDDA) layer that was intercalated at the interface of metal NCs and semiconductor. The unidirectional electron flow endowed by Schottky-type self-transformed metal NYs and unexpected electron-withdrawing capability of PDDA layer concurrently foster the charge transfer cascade, resulting in the markedly enhanced net efficiency of photocatalytic hydrogen evolution performances under visible light irradiation. Our work opens new frontiers for judiciously harnessing the inherent detrimental instability of metal NCs for boosted charge transfer toward solar-to-hydrogen conversion.

Modern vehicles are no longer merely mechanical systems but are monitored and controlled by various electronic systems. Safety-critical systems of connected vehicles become vulnerable to cyberattacks because of increasing interconnection. At present, the security risk analysis of connected vehicles is mainly based on qualitative methods, while these methods are usually subjective and lack consideration for functional safety. In order to solve this problem, we propose in this paper a security risk analysis framework for connected vehicles based on formal methods. Firstly, we introduce the electronic and electrical architecture of the connected vehicle and analyze the attack surfaces of the in-vehicle safety-critical systems from three levels of sensors, in-vehicle networks, and controllers. Secondly, we propose a method to model the target of evaluation (i.e., in-vehicle safety-critical system) as a Markov decision process and use probabilistic computation tree logic to formally describe its security properties. Then, a probabilistic model checker PRISM is used to analyze the security risk of target systems quantitatively according to security properties. Finally, we apply the proposed approach to analyze and compare the security risks of the collision warning system under a distributed and centralized electrical and electronic architecture. In addition, from a practical point of view, we propose a Markov model generation method based on a SysML activity diagram, which can simplify our modeling process. The evaluation results show that we can have a quantitative understanding of the security risks at the system level in the early stage of system design.

Modulation of photoinduced charge separation/migration and construction of controllable charge transfer pathway over photoelectrodes have been attracting enduring interest in semiconductor-based photoelectrochemical (PEC) cells but suffer from sluggish charge transport kinetics. Here, we report a general approach to fabricate NP-TNTAs/(TMCs QDs/PSS)n (X = Te, Se, S) photoanodes via a facile and green electrostatic layer-by-layer (LbL) self-assembly strategy, for which transition-metal chalcogenides quantum dots (TMCs QDs) [CdX (X = Se, Te, S)] and poly(sodium 4-styrenesulfonate) (PSS) were periodically deposited on the nanoporous TiO2 nanotube arrays (NP-TNTAs) via substantial electrostatic force, resulting in the continuous charge transfer pathway. NP-TNTAs/(TMCs QDs/PSS)n photoanodes demonstrate significantly enhanced solar-driven photoelectrochemical (PEC) water oxidation activities, relative to NP-TNTAs and TMCs QDs under visible and simulated sunlight irradiation, predominantly because of the suitable energy level configuration between NP-TNTAs and TMCs QDs, unique integration mode, and high-speed interfacial charge separation rate endowed by LbL assembly. The ultrathin PSS intermediate layer functions as "molecule glue" for pinpoint and uniform self-assembly of TMCs QDs on the framework of NP-TNTAs and photosensitization effect of TMCs QDs triggers the unidirectional charge transfer cascade, synergistically boosting the charge separation/transfer efficiency. Our work offers an efficacious approach to craft multilayered photoelectrodes and spur further interest in finely tuning the spatial charge flow in PEC cell for solar-to-hydrogen conversion.

Three-dimensional vanadium nitride porous nanoribbons/graphene composite with hierarchical porosity was prepared and investigated as the electrode material for supercapacitors. Morphology characterization of vanadium nitride porous nanoribbons/graphene composite indicates that vanadium nitride porous nanoribbons incorporate with graphene nanosheets to from a stable three-dimensional architecture with hierarchical porosity. This unique three-dimensional architecture and the combining effect of vanadium nitride porous nanoribbons and graphene nanosheets network make vanadium nitride porous nanoribbons/graphene composite a high-performance electrode material for supercapacitors. At a current density of 0.3 A g−1, vanadium nitride porous nanoribbons/graphene electrode displays a specific capacitance of 164.4 F g−1, which is much higher than that of pure vanadium nitride electrode. In addition, vanadium nitride porous nanoribbons/graphene composite shows high capacitance retention rate (82% capacitance retention at the current density up to 10 A g−1) and good long-term cycling stability (97.5% capacitance retention over 2500 cycles).

Hierarchical nanostructured polypyrrole (HNPPy) of spherical polypyrrole (PPy) nanoparticles anchored on the surface of PPy nanofiber network is prepared by a facile process and incorporated into dye-sensitized solar cells (DSCs) as Pt-free counter electrode. This unique hierarchical nanostructure can provide the fast electron-transport pathway and abundant electrocatalytic active sites simultaneously. Electrochemical impedance spectroscopy analysis demonstrates that the electrocatalytic activity of HNPPy electrode for the I3− reduction is higher than that of PPy nanoparticles (PPyNPs) electrode and comparable to that of Pt electrode. As a consequence, the DSC fabricated with HNPPy counter electrode achieves a high conversion efficiency of 6.78%, which is close to the efficiency using Pt counter electrode.

Three-dimensional (3D) porous vanadium nitride nanoribbon aerogels (PVNNRAs) are prepared by hydrothermal synthesis and subsequent nitridation in ammonia/argon atmosphere and investigated as Pt-free counter electrode in dye-sensitized solar cells (DSCs). 3D porous nanoribbon aerogel can simultaneously offer more electrocatalytic active sites, a fast electron-transport pathway, and a favorable electrolyte diffusion channel, which endows the PVNNRA electrode with high electrocatalytic activity for the reduction of I 3 − . Under full-sun illumination (AM 1.5, 100 mW cm −2 ), the DSC fabricated with PVNNRA counter electrode achieves a conversion efficiency of 7.05%, which is comparable to that of DSCs fabricated with Pt counter electrode. In addition, the PVNNRA electrode exhibits good stability in I − /I 3 − redox electrolyte. Thus, 3D PVNNRAs can be considered as a cost-effective alternative to Pt as the counter electrode of DSCs.

Nitrogen-doped porous carbon nanorods (N-PCNRs) with high accessible surface area are prepared by carbonization of polyaniline (PANI) nanorods and subsequent chemical activation, and explored as the counter electrode in dye-sensitized solar cells (DSCs). SEM and TEM images demonstrate that the nanorod morphology of PANI is preserved after pre-carbonization and chemical activation treatment. The unique combination of the porosity with high accessible surface area, nitrogen doping, and nanorod structure endows the N-PCNR electrode with an excellent electrocatalytic activity for the I3- reduction, which is illuminated by the electrochemical measurements. Under simulated AM 1.5 illumination (100 mW cm−2), the DSC based on N-PCNR counter electrode achieves a conversion efficiency of 7.01%, which is nearly close to that of the cell based on Pt counter electrode (7.25%).

Porous vanadium nitride nanoribbon aerogel (PVNNRA) was prepared by hydrothermal reaction at 180°C and subsequent ammonia treatment at 550°C using NH4VO3 as the precursor. The electrochemical properties of PVNNRA were discussed. SEM and TEM images demonstrated that as-prepared vanadium nitride showed a porous nanoribbon morphology with the width of 100–400 nm and the pore size of 10–20 nm. The analysis of electrochemical impedance spectroscopy indicated that the charge-transfer resistance of PVNNRA electrode was 1.36 Ω cm2, indicating a high electrocatalytic activity for I3− reduction. The dye-sensitized solar cell fabricated with PVNNRA counter electrode achieved a conversion efficiency of 7.05%, which is closed to that of the cell fabricated with Pt counter electrode. The results of cyclic voltammetry and galvanostatic charge/discharge tests demonstrated that PVNNRA has a good capacitive performance. At the current density of 0.5 A/g, PVNNRA exhibited a specific capacitance of 292.2 F/g in 2 mol/L KOH aqueous solution. Therefore, as-prepared PVNNRA can be considered as an effective electrode material for application in dye-sensitized solar cells and supercapacitors

A new approach for time-varying (TV) modal parameters identification is proposed in this research. In the identification process, the entire signal is divided into successive short time windows, where the structure response under white noise excitation is transformed into modal coordinates by the Independent Component Analysis (ICA) method. The decoupled time-varying Auto-Regressive Moving-Average (ARMA) model based on the new assumption of “short-time linearly varying” (STLV) is established with the extracted modal coordinates. The TV parameters can be obtained by solving a nonlinear least squares problem. The main motivation of the proposed approach is to simplify the model and reduce the computational difficulty. The effectiveness and accuracy are validated via both the numerical example and experiment.

Edge-nitrogenated graphene nanoplatelets (ENGNPs) with high surface area were prepared through a simple and eco-friendly mechanochemical pin-grinding process using the flake graphite as the precursors in the presence of nitrogen and investigated as the electrode materials for supercapacitors. Nitrogen adsorption, SEM, and XPS analysis indicated that the mechanochemical pin-grinding process can effectively delaminates the pristine graphite into graphene nanoplatelets and generates the activated carbon sites that can directly react with nitrogen at the broken edge of graphite framework, leading to ENGNPs with excellent capacitive performance. Electrochemical measurements indicate that the as-prepared ENGNPs exhibits a high specific capacitance of 202.8 F g −1 in 1 M H 2 SO 4 aqueous electrolyte at the current density of 0.3 A g −1 , meanwhile maintaining a good capacitance retention capability. The excellent capacitive performance of ENGNPs can be attributed to the combined effect of high surface area, edge-nitrogenated structure, and undamaged basal plane.

The composites of g-C 3 N 4 and conductive carbon black (CCB) were prepared by a simple ball-milling process and explored as the counter electrode for dye-sensitized solar cells (DSCs). The enhanced electrocatalytic activity for I 3 − reduction can be demonstrated when CCB was incorporated into g-C 3 N 4 . The charge-transfer resistance of g-C 3 N 4 /CCB (1:1, mass ratio) composite electrode was 2.4 Ω cm 2 , which is much lower than those of the individual g-C 3 N 4 and CCB electrodes, indicating predominant synergistic effect of g-C 3 N 4 and CCB in electrocatalytic activity. Under illumination of 100 mW cm −2 , the DSC with g-C 3 N 4 /CCB (1:1) composite counter electrode achieved a conversion efficiency of 5.09%, which is comparable to that of the cell with Pt counter electrode.

To simulate three-dimensional glaze ice accretion on a typical aircraft surface, the model of water film flow and ice accretion on a curved surface based on two coupled partial differential equations proposed by Myers et al. is extended in nonorthogonal curvilinear coordinates. Then, the governing equation for water film flow coupling with a Stefan model for glaze icing is built up. An efficient implicit–explicit numerical method is proposed for solving the governing equations. The glaze ice computations on two-dimensional airfoils and three-dimensional typical geometries in in-flight icing conditions are completely accomplished. Validation results of two-dimensional calculation cases with experimental ice shapes are presented. Three-dimensional simulations of glaze ice accretion on a sphere and a swept wing are successfully carried out and compared with ice profiles from icing tunnel tests and simulations based on the classical Messinger model.

A graphitic carbon nitride (g-C3N4)/multiwalled carbon nanotubes (MWCNT) composite is prepared by a combination of refluxing process and heating polymerization and investigated as the counter electrode in dye-sensitized solar cells. SEM and TEM studies indicate that MWCNT is very well incorporated and attached to g-C3N4. Electrochemical impedance spectroscopy demonstrates that the charge-transfer resistance of g-C3N4/MWCNT composite electrode is 2.1 Ω cm2, which is much lower than those of the individual g-C3N4 and MWCNT electrodes. This enhanced electrocatalytic activity is beneficial for improving the photovoltaic performance of dye-sensitized solar cells. Under illumination of 100 mW cm−2, the dye-sensitized solar cell based on g-C3N4/MWCNT counter electrode achieves a conversion efficiency of 6.34%, which is comparable to that of the cell based on Pt counter electrode.

Edge-nitrogenated graphene nanoplatelets (ENGNPs) are prepared by a simple and eco-friendly mechanochemical pin-grinding process using flake graphite as the precursor in the presence of nitrogen and investigated as the counter electrodes of dye-sensitized solar cells (DSCs). SEM images and nitrogen adsorption analysis indicate an effective and spontaneous delamination of the pristine graphite into small graphene nanoplatelets by a mechanochemical pin-grinding process. The mechanochemical cracking of the graphitic C-C bond generates activated carbon sites that react directly with nitrogen at the broken edges. The resultant ENGNPs are deposited on a fluorine-doped tin oxide (FTO) substrate by spray coating, and their electrocatalytic activities are investigated systemically in the I(-)/I3(-) redox electrolyte. Electrochemical measurements show that the ENGNP electrode possesses excellent electrocatalytic activity for the redox reaction of I(-)/I3(-) as evidenced by the low charge-transfer resistance at the interface of the electrode and electrolyte. Under 100 mW cm(-2) illumination, the DSC with the optimized ENGNP counter electrode achieves a conversion efficiency of 7.69%, which is comparable to that of the device with Pt counter electrode.

In numerous engineering structures with local nonlinearities, the nonlinear effects are usually localized and most parts of the structures behave linearly. Considering this, a reduced-order modelling technique for generally damped systems with localized nonlinearities is proposed. Firstly, the linear parts with non-proportional damping of the system is separated to form one component, which can be formulated in state space and transformed into the modal coordinates using its linear vibration complex modes. The residual flexibility matrix, which can be formulated by using a set of equivalent higher-order complex modes, has been developed to improve the accuracy by capturing the effects of the neglected higher-order complex modes. Secondly, the rest regions of the system form another component behaving nonlinearly, which is kept in its original form to adopt the entire set of nonlinear terms. Next, the second-order differential synthesis equation can be obtained by using compatibility conditions at the junctions. In order to calculate dynamic response of the system, the aforementioned synthesis equation needs to transform into the first-order differential equation because of the singularity of the equivalent mass matrix. Finally, two numerical examples are given to illustrate the effectiveness and the efficiency of the presented method.

A new identification approach based on a new assumption of “short time linear varying” is proposed for nonlinear time-varying (NTV) dynamic systems. In the identification procedure, the whole period is divided into a series of shifting windows. In each window, the NTV system model, which is known a priori, can be represented by regression equations and all the time-varying (TV) coefficients are determined by a least squares (LS) algorithm. The proposed approach has better identification precision than the traditional assumption of “short time invariant”. To enhance the robustness and stability, the problem of parameter identification is solved by means of constrained optimization in the global identification strategy when the noise level increases. The validity and accuracy are verified by applying the method to a single degree of freedom (SDOF) numerical example, and a qualitative analysis on the selection of the window size is carried out in this research.