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The frequent replacement of worn rails on tracks brings an immense economic burden on the railroad industry, and also causes significant interruptions to railroad operation. Restoration of worn rails via laser powder deposition (LPD) can considerably reduce the associated maintenance costs. This study was focused on the use of LPD to repair the worn profile of a standard U.S. rail. The microstructure of the 304L stainless steel deposits with a minimum hardness of 85 HRB was composed of austenite, δ-ferrite, and sigma. Micropores were dispersed throughout the deposit, and microcracks were found at the rail-deposition interface. The pearlitic rail substrate showed a moderate hardness of 94 HRB. The fine-grain, pearlitic-ferritic heat affected zone had the maximum hardness of 96 HRB, which was still below the minimum required hardness of 97 HRB for a typical rail. To increase the hardness to or above 97 HRB and to mitigate the microstructural defects, the as-repaired rail went through a heat treatment process. The average hardness of the as-treated rail was increased significantly, i.e., to 103 HRB. Besides, the porous and coarse-grain deposition materials were transformed into an impermeable and fine-grain microstructure. However, heat treatment intensified the microcracks at the rail-deposition interface and also led to the formation of martensite and augmentation of the micropores in the parent rail. Isolation of the base rail during heat treatment and preheating were suggested as solutions for the problematic results. The LPD process ultimately was found to be a promising technique for repairing rails.

Pantograph-catenary system is a key component of high-speed railway. Under high speed and strong current operation conditions, the surface roughness of the sliding electrical contact between contact wire and slide changes continuously. It will cause the fluctuation of contact resistance and lower the electrical contact property of the system. Therefore, it is of great significance to study the relationships between the contact resistance and surface roughness characteristics. In this paper, lots of current-carrying friction experiments were carried out under different contact pressure, contact current and sliding speed conditions. A roughness tester was used to measure the roughness of the contact surface after experiment. Four characteristic parameters were proposed to describe the roughness. They are the root mean square and the maximum peak height of the rough surface, the peak count and the curvature radius of asperity respectively. The function relationships between these characteristic parameters and experimental conditions were obtained and discussed. On the basis of Greenwood-Williamson contact model, a new mathematical model of contact resistance in pantograph-catenary system considering rough surface characteristics were established and verified. It can be used to further study the current conduction mechanism of sliding electrical contact in pantograph-catenary system and evaluate the electrical contact performance.

SnS2 with atomic thickness has attracted extensive attention in the field of photocatalysis due to its special physicochemical properties, suitable band gap, low cost and low environmental toxicity. However, the application of SnS2 in the field of optoelectronics is restricted by its low photocatalytic efficiency and carrier mobility. In this study, vacancy and transition metal atoms are introduced into SnS2 monolayer to modulate its physicochemical properties. Meanwhile, the SnS2 monolayer modified by vacancy and transition metal atoms is combined with graphene to form a heterostructure, which promotes the separation of photogenerated electron hole pairs. The results of theoretical calculation show that SnS2/graphene heterojunction can promote the separation of photogenerated carriers in intrinsic monolayer SnS2, improve the photocatalytic efficiency and carrier mobility. The modification of Sn vacancy and Fe, Co atoms not only expands the visible light response range of SnS2/graphene heterojunction, but also introduces magnetism, which is expected to be applied in spin optoelectronic materials. In this work, defects, doping and heterojunction assembly are rationally integrated, which provides a new idea for the design and development of spin optoelectronic devices based on monolayer SnS2.

Magnesium alloy sheets have an increasing proportion of applications in automobiles due to their high specific strength. The usability of traditional welding processes and mechanical joining processes is restricted by the characteristic of magnesium alloy sheets. In order to improve the plasticity of magnesium alloy sheets and realize the reliable joining of magnesium alloy sheets with dissimilar sheets, researchers have conducted a lot of research. In this paper, the existing joining processes of friction stir spot welding, friction stir blind riveting, hybrid self-piercing riveting, and friction self-piercing riveting for magnesium alloy sheets are reviewed; the latest advances of joining process are introduced; and the principle, development, advantages, and shortcomings of each process for improving the plasticity of magnesium alloy sheets are systematically described. Several unaddressed issues in the joining of magnesium alloy sheets are identified. The hybrid of mechanical and solid-state joining processes will be a trend in future development.

Utilization of laser powder deposition (LPD) as an innovative repair tool for damaged steel components is increasingly growing in recent years. This paper investigates repairing a standard US light rail using LPD. No study has focused on repairing standard US rails thus far. Besides, this is the first time that a three-dimensional finite element model is developed where element-birth-and-kill technique is employed to study thermal-kinetic-mechanical evolutions during the LPD rail repair process. Exploration of hardness versus microstructure yielded a reverse correlation between hardness level and austenite volume fraction. The maximum hardness was found near rail-deposition interface with the minimum austenite concentration, while the topmost deposition layer with the highest austenite concentration showed the minimum hardness. Longitudinal residual stresses at the rail-deposition interface were significantly more than that of transversal and normal. Comparing the residual stress against deposition material yield strength showed a slight exceedance (~5%) of transversal stress from the maximum limit, no exceedance for normal stress, but an extreme exceedance of 50% for longitudinal stress. This fact suggested a high risk of cracking along longitudinal direction at the rail-deposition interface, while there existed only a minor risk of transversal cracking and almost no chance of layer delamination. The simulated results were compared against experimental results obtained via optical and scanning electron microscopy, hardness test, and X-ray diffraction stress measurement, where a maximum deviation of 10% proved the model accuracy. The validated model in this study would be a great backbone for future studies on different process parameters to increase hardness and reduce stress in an LPD repaired rail.

Hydrogel based scaffolds with the ability of on-demand drug delivery gained increasing interests for localized cancer therapy and tissue engineering application. However, most drug-loaded hydrogels are generally not suitable for long-term drug delivery, because of the uncontrolled diffusion of drugs from the swollen hydrogels. Therefore, in this study, a core/shell fiber scaffold was fabricated by coating a homogeneous layer of polycaprolactone (PCL) on the 3D printed alginate-gelatin hydrogel scaffolds. The PCL coatings could reduce the free diffusion of drugs from the core gels. Subsequently, polydopamine (PDA) was coated on the Gel/PCL core/shell scaffolds, endowing the scaffolds with great photothermal effects. Thus, near-infrared (NIR) laser triggered on-demand drug release was realized in this system due to the thermally induced sol-gel transition of the core gels. The released drugs (doxorubicin) and photothermal therapy could effectively prohibit or ablate tumor in vitro and in vivo. Additionally, the Gel/PCL/PDA core/shell scaffold could serve as platform for promoting wound healing. Therefore, the reported Gel/PCL/PDA core/shell scaffolds have the potential for application in localized cancer therapy and tissue regeneration. Especially for those cancer patients suffering surgical resection, the scaffolds could be implanted in the resection site to kill the residual or recurrent cancer cells, as well as to repair the tissue defects caused by surgery. STATEMENT OF SIGNIFICANCE: This paper reported a facile strategy to realize stimuli-triggered on demand drug release in vitro and in vivo. Polycaprolactone (PCL) and polydopamine were sequentially deposited on the surface of 3D printed drug-loaded alginate/gelatin scaffold. PCL encapsulation could effectively reduce the free diffusion of drugs from the core hydrogel, achieving sustained drug release. Polydopamine with good photothermal effects endowed the scaffold with stimuli-triggered drug release in response to near-infrared (NIR) laser irradiation. This scaffold could be applied for localized cancer therapy and tissue regeneration. Especially for those cancer patients suffering surgical resection, the scaffolds could be implanted in the resection site to kill the residual or recurrent cancer cells, as well as to repair the tissue defects caused by surgery.

Researches on environmentally friendly semiconductor photocatalysts for efficient photocatalytic hydrogen evolution have important practical significance. Here, using first-principles calculations, the CeO2(111)/hBN heterojunction was conceived. The influence of the interface effect on the structural, electronic and optical properties of the heterojunction was investigated in detail. The band gap of the heterojunction is smaller than the two individual components and forms a type-II heterojunction, improving the photocatalytic activity. Furthermore, by doping two C atoms, the band gap of heterojunction was further narrowed. Both the oxidation and reduction potential of CeO2(111)/hBN heterojunction meet the requirements of water splitting and has certain advantages over other photocatalysts in the ability for photocatalytic hydrogen evolution. The study revealed the possible mechanism of CeO2(111) and hBN monolayers compositing to facilitate photocatalysis and hydrogen evolution ability, which may provide a possible reference direction for the practical design of more high-quality semiconductor photocatalysts.

This work presents a nonlinear finite element method to simulate the macroscopic mechanical responses and the effects of martensite plasticity in a shape memory alloy (SMA) structure. A linear relationship formulation is adopted to express the influence of martensite plasticity on the inverse martensitic phase transition of SMA material. Incorporating with a trigonometric-type phase transition evolution law and an exponential-type plastic flow evolution law, an incremental mechanical model with two internal variables is supposed based on the macroscopic experimental phenomena. A nonlinear finite element equation is formulated and solved by the principle of virtual displacement and Newton-Raphson method respectively. By employing the proposed nonlinear finite element method, the uniform tensile bar and three-point bending beam are simulated and analyzed. Results illustrate that the presented nonlinear finite element method is suitable to act as an effective computational tool for the wide applications based on the SMA material considering the effects of martensite plasticity because all material constants related to the method can be obtained from macroscopic experiments.

The fracture behavior in stiff-thin-film-on-soft-substrate structures (STFSS) differs significantly from that in bulk materials, and has thus become a hot spot in solid mechanics and materials. Traditional research on the fracture mechanics in STFSS mostly focuses on the mechanical behavior under uniaxial stress state. However, in actual applications, STFSS is subjected to biaxial loading. In response to this lack of research, the present work examined the fracture behavior in STFSS under biaxial stress state by using a self-developed biaxial tension rig. Specially designed and fabricated STFSS specimens with prefab cracks along desirable directions were employed. The influence of the biaxial loading ratio and the prefab cracks on STFSS fracture behavior has been analyzed and discussed both theoretically and experimentally. The experimental results agree well with the theoretical model, which validates the feasibility of the current investigation for STFSS.

In order to be used as matrix of lubricating material, epoxy resin needs to be modified to enhance its tribological properties. In this study, polyetheramine-functionalized graphene oxide was used to prepare epoxy composite. The mechanical properties, thermal properties and friction properties of composite materials with different types and contents of fillers were studied. 0.2 wt% polyetheramine-functionalized graphene oxide/epoxy composite exhibited the best tribological performance, that is, friction coefficient decreased by 54% and wear rate dropped by 94% compared with pure resin. The wear rate was reduced by 67%–94% in a wide content range (from 0.1 wt% to 0.4 wt%). Simultaneously, modified GO also enhanced thermal stability, and mechanical properties, including tensile strength, Young's modulus, elongation at break and microhardness due to enhanced dispersity and interface interaction in matrix. The excellent lubrication and anti-wear properties was attribute to the benign interaction of the composite and transfer film. It was further proved that polyetheramine modified graphene could improve the tribological properties of epoxy resin under heavy load and high slipping speed. The results showed a prospect to the practical applications of graphene and solve wear-related mechanical failures of epoxy resin.

The Mn-doped MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by the melt quenching technique. The effect of MnO on the crystallization, microstructure, and properties of MAS was discussed. XRD results showed that MnO promotes the phase transformation from indialite to Mg0.6Al1.2Si1.8O6 and enstatite. Crystallization kinetics suggested that MnO inhibits the precipitation of indialite. Both the crystallization index and SEM photographs proved that the bulk crystallization plays an important role in the Mn-doped MAS system. EDS analyses indicated that the large grain corresponds to Mg0.6Al1.2Si1.8O6 and the small grain corresponds to the magnesium-rich phase. Due to the addition of 0.5 wt% MnO, the flexural strength was enhanced from 146 to 247 MPa, and the coefficient of thermal expansion was increased from 3.52 × 10−6/°C to 5.41 × 10−6/°C. • Mn-modified MAS glass-ceramic with high flexural strength and low thermal expansion was developed. • Small addition of MnO markedly improved the flexural strength and Young’s modulus. • The relation between CTE values and crystal phases was revealed. • Crystallization kinetics suggested that MnO inhibited the precipitation of indialite.

A study on the resistance of rigid projectiles penetrating into semi-infinite concrete targets is performed in this paper. Experimental data are analyzed to examine the penetration resistance during various stages of the penetration process. A numerical tool using AUTODYN hydrocode is applied in the study. The numerical results on both deceleration-time history and depth of penetration of projectiles are in good agreement with experimental data, which demonstrate the feasibility of the numerical model in these conditions. Based on the numerical model with a two-staged pre-drilled hole, the rigid projectile penetration in tunneling stage is studied for concrete targets with different strengths in a wide range of impact velocities. The results show that the penetration in tunnel stage can be divided into two different cases in terms of initial impact velocity. In the first case, when the impact velocity is approximately less than 600 m/s, the deceleration depends on initial impact velocity. In the second case, when the impact velocity is greater than 600 m/s, the effect of target inertia becomes apparent, which agrees with commonly used concrete penetration resistance equations based on cavity expansion model. A two-staged pre-drilled hole model was developed and the results show that the depth of entrance stage tends to decrease with the increase of impact velocity. The influence of the inertial term at low velocity range (approximately close to 600 m/s) is inconspicuous. With further increase of the penetration velocity, the effect of the target inertia becomes apparent as proposed by Forrestal. The effect of mass abrasion of projectiles, entrance phase and strain effect of concrete materials on the tendency of deceleration was clarified.

Hybrid bonded/bolted (HBB) joint has been widely used in engineering practice because it can overcome the potential weakness of pure bonded and pure bolted joints. However, studies on HBB joint are still at the initial stage. In this paper, tensile properties of a composite–metal single-lap HBB joint was investigated experimentally. And a detailed finite element model (FEM) was established to simulate the tensile behavior of the joint. The model was verified by the experimental results. Then the damage propagation and load transfer mechanism were explored based on the FEM. The results show that the HBB joint can provide multi-load transmission paths and resist damage propagation in the adhesive. The HBB joint has higher strength and energy absorption capacity than the pure bonded joint. And the HBB joint has greater initial damage load and tensile stiffness than pure bolted joint. Adhesive fillets can obviously improve the tensile performances of the HBB joint. Lateral stiffness of the joint boundary and testing machine show obvious effects on tensile performances of single-lap hybrid joints.

The cross-sectional morphology of GaAs/Si3N4/SiO2 composite wafer after He+ implantation has been systematically observed. Experiment sample is prepared by focused ion beam system to meet the observation requirements of transmission electron microscope. The results show that implantation of 300 keV, 5 × 1016/cm2 He+ gives rise to formation of bubbles and dislocations in GaAs material, but no cracks are observed. In addition, after annealing, interface separation and micro-gap appear at the interface between GaAs layer and Si3N4 layer. Finally, the mechanisms of bond fracture and blisters formation at the interface are explained by density function theory calculation.

Local delivery of drugs, proteins and living cells with on demand release manner using porous scaffolds has been widely used in the field of tissue engineering and cancer therapies. Drugs directly loaded in the porous scaffolds, are generally prone to free diffuse especially for long term incubation. Herein, in this study, hollow fiber alginate/iron oxide nanoparticles scaffolds were prepared by coaxial 3D printing with drugs, protein or living cells encapsulating in the core part (low concentration of alginate gels). Magnetically-driven on demand release was realized by extruding the loaded drugs, proteins and cells from the core part of the hollow fibers due to the deformation of the scaffolds under magnetic field. Additionally, the hollow fibers could sever as diffusion barriers to reduce uncontrolled diffusion of drugs, proteins and cells from scaffolds in the conditions of no required stimulation. The factors influencing the deformation of the scaffolds, as well as the release behavior were investigated. The data indicated that the scaffolds prepared by 10 wt% of alginate with 13% of iron oxide nanoparticles after crosslinking using 0.1 M CaCl2 solution for 10 s showed repeated on demand release capability in vitro and in vivo under intermittently magnetic stimulation. Thus, this 3D printed alginate/iron oxide nanoparticles hollow scaffolds with on demand controlled delivery capability may prove useful for tissue engineering and disease therapies.

Bi is an attractive catalyst towards the electrochemical reduction of CO2 to formate. In this work, nanoporous bismuth was prepared by dealloying Mg3Bi2 with tartaric acid (TA) solution, and the size of the primary Bi nanoparticles was adjusted according to the concentration of TA. When the concentration of TA increased from 2 wt% to 20 wt%, the particle size of Bi increased from about 70 nm to 400 nm. The synthesized nanoporous Bi samples were investigated as electrocatalysts for the reduction of CO2 in KHCO3 electrolyte, and it was found that the smaller the particle size, the higher the catalytic activity. However, nanoporous Bi comprising 70 nm particles suffered from mass transfer difficulty and sintering during the reaction, whereas the 100 nm nanoporous Bi delivered both a high formate formation current and faradaic efficiency (FE) (16 mA cm−2, FE > 90% at −0.88 V vs. RHE) and showed excellent durability.

Hollow-core negative-curvature fibres have been the focus of current research, but how to reduce the loss of hollow-core negative-curvature fibres is a serious problem. This paper proposes a new structure of hollow-core negative-curvature fibres, that is numerically simulated using the finite-element method, and compared with the simulation results of hollow-core conjoined-tube negative curvature fibres (CTNCFs) and hollow-core nested anti-resonant nodeless fibres (NANFs). The results show that, the LP01 mode loss can reach 0.003694 dB/km with a transmission wavelength of 1.06 μm, the LP11 mode loss can be as low as 0.28423 dB/km, and the bending loss is 0.4405 dB/km with a bending radius of 5 cm and a transmission wavelength of 1.06 μm. The loss is reduced by an order of magnitude compared to CTNCFs and NANFs.

Simultaneous measurement of the substrate/film thickness and film conductivity in a thin metal film/substrate structure is still challenging. In this article, we propose a method for the measurement based on a terahertz time-domain spectroscopy system by combining time-domain and frequency-domain analysis, in which an error function is established, whereas quasi-Newton algorithm is employed. The advantage of the proposed method is that neither the substrate thickness nor the terahertz transmission of the bare substrate is prerequisite before the measurement. The feasibility of the method is validated by our experimental conclusion that agrees well with the theoretical model.

Two benzothiadiazole (BT) small molecule donors (namely D1 and D2) were designed and synthesized. We studied their photovoltaics properties and filed effect properties. It is found that the best power conversion efficiency (PCE) of the organic solar cells (OSCs) was 6.87% based on the D2: IDIC-4F (the donor/acceptor(D/A) ratio is 1:1). In contrast, the device of D1: IDIC-4F (the D/A ratio is 1:1) only shows PCE value of 2.41%. This is because that the crystallization property of the material is improved by the changing of side chain group, which is beneficial to the improvement of the morphology of the donor material. Moreover, the introduction of side chain greatly improves the external quantum efficiency (EQE) of D2 based solar cell. Also, we fabricated the organic field effect transistors (OFETs) with D1 and D2 as semiconductor layer, and n-octadecylphosphonic acid (ODPA) as self-assembled monolayers (SAMs), as a result, the hole motilities of the devices are ${1.21}\times {10} ^{-{2}}$ cm $^{{2}}\text{v}^{-{1}}\text{s}^{-{1}}$ for D1 and ${1.25}\times {10} ^{-{2}}$ cm $^{{2}}\text{v}^{-{1}}\text{s}^{-{1}}$ for D2, respectively.

The electronic and transport properties of borophene/phosphorene heterojunctions are systematically investigated by first-principles calculations. The geometrical structures and electronic band structures of monolayer borophene, monolayer phosphorene and heterojunctions with different distances between layers are analysed. The calculated results show that the band gap can be adjusted by tuning the distance between heterostructure layers. Then the transport properties of the heterojunction with different electrodes are also studied. It can be found that the selected different electrodes have significant effect on the transport property of the heterojunction. Interestingly, when the heterostructure is selected as the electrode, the heterostructure with an interlayer distance of 2.65 Å showed the best transport performance. It is hoped that this paper may provide useful insights for the design of nanoelectronic devices based on borophene/phosphorene heterojunctions.

Photocontrolled therapeutic release holds great promise due to its versatile manipulability, superb spatiotemporal precision and minimal tissue invasiveness in biomedical purposes. However, most of light-responsive platforms thus far have relied on UV or visible light which substantially limit the potential applicability in living animals. In recent decades, near-infrared (NIR) light-mediated theranostic upconversion nanocomposites (UCNCs) that integrate conventional UV/Vis-sensitive materials and classic lanthanide-doped upconversion nanoparticles (UCNPs) have significantly promoted the development of deep-tissue photoreleasable therapeutics in vivo. Herein, we seek to review current NIR upconversion triggered photorelease techniques and their diverse applications in the biological regulation, as well as diseases therapy. In addition, the future perspectives and challenges for advancing UCNCs based NIR photoreleasable nanotherapeutics into clinical translations are proposed. Agency for Science, Technology and Research (A*STAR) Nanyang Technological University B.X. acknowledges the financial supports from NTU-AIT-MUV NAM/16001, Tier 1 RG5/18 (S), SSIJRI (203-A018003), MOE 2017-T2- 2-110, A*Star SERC A1983c0028 (M4070319), SPMS-M4082042.110 awarded in Nanyang Technological University (NTU), Singapore and National Natural Science Foundation of China (NSFC) (No. 51929201), China.

The ferroelectric thin film such as BaSrTiO3 (BST), exhibiting great tunable characteristics, is a hot spot in photonic devices for both microwave and terahertz frequencies. This report presents a ...

Herein, we report on the effect of a high gravity field on metal-free catalytic reduction, taking the nitrobenzene (NB) reduction and methylene blue (MB) degradation as model reactions in a high-gravity rotating tube reactor packed with three-dimensional (3D) nitrogen-doped graphene foam (NGF) as a metal-free catalyst. The apparent rate constant (kapp) of the metal-free catalytic reduction of NB in the rotating tube reactor under a high gravity level of 6484g (g = 9.81 m·s−2) was six times greater than that in a conventional stirred reactor (STR) under gravity. Computational fluid dynamics (CFD) simulations indicated that the improvement of the catalytic efficiency was attributed to the much higher turbulent kinetic energy and faster surface renewal rate in the high-gravity tube reactor in comparison with those in a conventional STR. The structure of the 3D metal-free catalysts was stable during the reaction process under a high gravity field, as confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectra. In the other model reaction, the rate of MB degradation also increased as the high gravity level increased gradually, which aligns with the result for the NB catalytic reduction system. These results demonstrate the potential to use a high-gravity rotating packed tube reactor for the process intensification of metal-free catalytic reduction reactions.

The investigation of the dynamic compressive properties and failure process of ceramics can broaden their applications under extreme conditions. In this study, the online dynamic deformation and failure processof silicon carbide (SiC) ceramic were directly observed in the split-Hopkinson pressure test by high speed photography. The failure strength of the silicon carbide has been quantified as a function of strain rate. There appears to be a critical value (a transition strain rate), above which the strain rate dependency becomes significant. The failure in the dynamic test is an outcome of the concurrent incline major crack and longitudinal micro-cracks. Scanning electronic microscopy (SEM) observation of the dynamic fragments shows that the transgranular fracture dominates the failure process. High-resolution transmission electron microscopy (HRTEM) observation of the post-collected fragments indicates that the local shear stress causes the nucleation of dislocations responsible for the macroscopic inelastic deformation behavior.

It remains a challenge for graphene to reach its full potential as a lubricant and wear-resistant material in thermosetting resin composites. In this study, the mechanical properties and friction properties of amino-treated graphene-filled epoxy composites, which were influenced by the conditions for the modification of graphene and filler content, were investigated. The mechanical properties were measured by tensile examination and the tribological properties were determined using a ball-on-disk tribometer. The results showed that the composite filled with amino-treated graphene for a short reaction time exhibited the best tribological behavior, where the friction coefficient was 57.9% lower than that of the pure resin and the wear rate was 92.2% less than that of the neat resin. Simultaneously, this amino-treated graphene also resulted in enhanced mechanical properties and Tg in the nanocomposite, implying its good crosslinking network and strong interface strength. The wear track analysis demonstrated that the excellent wear resistance was induced by its improved toughness, which restrained the crack propagation of fatigue wear and decreased the size of debris, promoting the formation of a transfer film, and thus protecting the contact surface. The tribological properties also varied with the concentration of the nanofiller, which showed the best performance at 0.2 wt%. Through the optimization of the modification conditions and concentration, this work highlights a promising strategy for the application of graphene-related materials in the field of tribology.

The design of molecular rotors that can rotate at ultrahigh speeds is important for the development of artificial molecular machines. Based on theoretical calculations, we demonstrate that two kinds of carbon nano-rings, i.e. [n]cycloparaphenylenes ([n]CPP) and cyclo[18]carbon (C18), can form an ultrafast ring-in-ring nano-rotor through π–π interaction. As a high-symmetry and low-barrier rotator, the rotational frequency of C18 in [11]CPP is close to the THz regime. At low temperatures, the motion of the [11]CPP:C18 system is purely rotational. As temperature increases, precession movements start to be observed and the motion resembles the behaviour of a gyroscope. The [11]CPP:C18 rotor can serve as a building block for bottom-up construction of more complex molecular machines.

Electrochromic devices (ECDs) have emerged as a unique class of optoelectronic devices for the development of smart windows. However, current ECDs typically suffer from low coloration efficiency (CE) and high energy consumption, which have thus hindered their practical applications, especially as components in solar-powered EC windows. Here, the high-performance ECDs with a fully crystalline viologen-immobilized 2D polymer (V2DP) thin film as the color-switching layer is demonstrated. The high density of vertically oriented pore channels (pore size approximate to 4.5 nm; pore density approximate to 5.8 x 1016 m-2) in the synthetic V2DP film enables high utilization of redox-active viologen moieties and benefits for Li+ ion diffusion/transport. As a result, the as-fabricated ECDs achieve a rapid switching speed (coloration, 2.8 s; bleaching, 1.2 s), and a high CE (989 cm2 C-1, and low energy consumption (21.1 µW cm-2). Moreover, it is managed to fabricate transmission-tunable, self-sustainable EC window prototypes by vertically integrating the V2DP ECDs with transparent solar cells. This work sheds light on designing electroactive 2D polymers with molecular precision for optoelectronics and paves a practical route toward developing self-powered EC windows to offset the electricity consumption of buildings.

This paper focus on the mechanical and martensitic transformation behaviors of axially functionally graded shape memory alloy (AFG SMA) beams. It is taken into consideration that material properties, such as austenitic elastic modulus, martensitic elastic modulus, critical transformation stresses and maximum transformation strain vary continuously along the longitudinal direction. According to the simplified linear SMA constitutive equations and Bernoulli-Euler beam theory, the formulations of stress, strain, martensitic volume fraction and governing equations of the deflection, height and length of transformed layers are derived. Employing the Galerkin’s weighted residual method, the governing differential equation of the deflection is solved. As an example, the bending behaviors of an AFG SMA cantilever beam subjected to an end concentrated load are numerically analyzed using the developed model. Results show that the mechanical and martensitic transformation behaviors of the AFG SMA beam are complex after the martensitic transformation of SMA occurs. The influences of FG parameter on the mechanical behaviors and geometrical shape of transformed regions are obvious, and should be considered in the design and analysis of AFG SMA beams in the related regions.

In order to analyze the making arc characteristics of AgSnO2 contact, experiments were carried out with a self-developed experimental equipment. It was found that contact resistance had no obvious change with the increase of the number of experiments.In the later stage of the experiment, the contact bounces occurred during the contact closing process, which not only prolonged the making arc duration, but also increased making arc energy. When the contact was eroded to a certain extent by arc, making welding occurs.

Synchronous tuning can extend the mode-hop-free (MHF) tuning range of external-cavity diode lasers (ECDLs) without antireflection coating. However, due to nonlinearities in the internal and external cavities of ECDLs, the synchronous tuning ratio is not constant, causing detuning, which limits the MHF tuning range. To solve the nonlinearity mismatch between the two cavities, the nonlinearity of the internal cavity is identified and a correction model for the both cavities based on a mapping method is established. Further, the zero-vibration-derivative (ZVD) method is applied to optimize the dynamic response of the system. Experimental results show that MHF tuning in the full scanning period is achieved, and the optical frequency shows good linearity.

In this paper, a pragmatic technique has been developed to evaluate the erosion-corrosion behavior of three kinds of ZrN coatings (i.e., monolayer, multilayer, and gradient layers) which were deposited on AISI 420 martensitic stainless steel using an ion-assisted deposition technology. Among them, the monolayer coating refers to the coating with no change in composition and structure, the multilayer coating refers to the coating with alternating change of Zr/ZrN, and the gradient coating refers to the ZrN coating by increasing N2 partial pressure gradually. The morphology, composition, and microhardness of these ZrN coatings were examined by means of integrating the scanning electron microscopy (SEM), X-ray diffraction (XRD), and Knoop hardness measurements, while anodic polarization tests and salt fog spray tests in a simulated industrial environment have been performed to evaluate and identify the corrosion mechanisms of these coatings. The surface microhardness and corrosion resistance of the AISI420 martensitic stainless steel is found to be significantly improved by depositing the ion-assisted deposition ZrN coatings. The study indicates that the erosion-corrosion behavior in the slurry is the result of the synergistic effect of small-angle erosion and acid solution corrosion. Three ZrN coatings hinder the slurry erosion-corrosion behavior from two aspects (i.e., erosion resistance of small-angle particles as well as corrosion resistance of the substrate), thereby significantly improving the erosion-corrosion resistance of AISI 420 stainless steel. In addition, the ZrN gradient coatings show a much better erosion-corrosion resistance than that of the monolayer/multilayer ZrN coating because they have excellent crack resistance, bearing capacity, and electrochemical performance.

Single-mode waveguide devices are necessary in photonic integrated circuits. Previous studies on the single-mode conditions (SMCs) of the thin film lithium niobate (TFLN) either only focus on wire waveguide, or lack comprehensive discussions on the influence of the rib waveguide with different cross-section area at a certain height. In this paper, a systematical study on the SMCs of rib waveguide based on TFLN is carried out by using finite difference method (FDM). By comparing the effective refractive index between the first-order mode in the central rib region and the fundamental mode in the slab waveguide, and the fraction of the mode power flux between the TFLN rib region and the whole waveguide region, the SMCs in the central rib region are analyzed in terms of geometric parameters of the TFLN rib waveguide. The simulation results suggest that no single equation could meet the SMCs of different waveguide structures simultaneously in a small TFLN with the height no more than 900 nm. Ultimately, new approximate expressions as functions of rib-waveguide width and etching depth are proposed to precisely describe the single-mode condition at these dimensions.

Stimulated Brillouin scattering (SBS) lasers based on silicon waveguides with large SBS gain, have been widely used in frequency tunable laser emission, mode-locked pulse laser, low-noise oscillator, optical gyroscope, and other fields. However, current SBS lasers still need long waveguide lengths to realize Brillouin laser output, which increases the waveguide losses and is not conductive to be integrated. In this paper, we propose a silicon ring waveguide, in order to tune the frequency of the phonon field of SBS laser based on the silicon substrate of the ring cavity. The simulation results exhibit that the tailorable forward SBS effect is realized in the silicon-based optical waveguide with a large SBS gain up to 1.90 W-1m-1. Particularly, with the mutual restraint between photoelastic and moving boundary effects, the tunable phonon frequencies emitting from 1 to 15 GHz are realized through the conversion among higher order modes by modifying the widths of the ring cavity. Therefore, this silicon waveguide based on ring cavity will provide a new technical scheme for designing tunable SBS lasers by tuning the ring widths. In addition, this enhanced and broadband acoustic radiation will pave the way for hybrid integration in silicon-based optical waveguide, micro-electromechanical system, and CMOS signal processing technology.

Stimulated Brillouin scattering (SBS) lasers based on silicon waveguides with large SBS gain have been widely used in frequency tunable laser emissions, mode-locked pulse lasers, low-noise oscillators, optical gyroscopes and other fields. However, among SBS lasers, the realization of Brillouin laser output often requires a longer waveguide length, which not only increases waveguide loss but also increase the size of the device. As a new medium, lithium niobate has been fabricated into a new type of hybrid structure. Meanwhile, the width of a suspended waveguide is adjusted to tune the phonon frequency of an SBS laser based on lithium niobate substrate. Simulation results show that the tunable forward SBS effect is realized in a lithium niobate-suspended optical waveguide, showing a larger forward stimulated Brillouin scattering gain of 0.31 W−1m−1. The tunable phonon frequency ranges from 1 to 15 GHz. Therefore, utilizing the photon–phonon conversion effect, the waveguide system with LiNbO3 will pave a new way forward with better integration.

The application of cement based materials in engineering requires the understanding of their characteristics and subsequent deformation and fracture process of C-S-H gel in service. In this work, three types of amine molecules including TEPA, PAM and TEA were intercalated unsaturatedly into C–S–H gel successfully. Systematical analysis was performed on the structures and properties on both C–S–H gel and corresponding amine molecules / C–S–H gel. It was found that unsaturated intercalation of amine molecules into C–S–H gel plays a key role in the geometry and therein density of nanocomposites. Subsequently, radial distribution function (RDF), time correlated function (TCF) and mean square displacement (MSD) were applied to characterize the structure and dynamic information of the as-generated nanocomposites, demonstrating the occurance of interaction between amine molecules with Ca–Si layer and acceleration of water diffusion by unsaturated intercalation of amine molecules into the interlayer region in C–S–H gel. Finally, deformation and fracture process of C–S–H gel and amine molecules / C–S–H gel under uniaxial tensile loads were displayed by molecular dynamics simulation. It was indicated that Young’s modulus of nanocomposites demonstrates a strain softening nature, indicating a visco-elastic behavior. The breakage of Ca–O bonds and hydrogen bonds dominates the fracture of C–S–H gel. Weak interaction for TEPA / C–S–H gel or TEA / C–S–H gel leads to a decreased tensile strength. Local stress concentration in other interlayer region governs the deformation and fracture process in spite of the formation of strong interaction between double bonded polar oxygen atoms in PAM molecules and Ca atoms in C–S–H gel.

It is significant to numerically investigate thermo-mechanical behaviors of shape memory alloy (SMA) structures undergoing large and uneven deformation for they are used in many engineering fields to meet special requirements. To solve the problems of convergence in the numerical simulation on thermo-mechanical behaviors of SMA structures by universal finite element software. This work suppose a finite element method to simulate the super-elasticity and shape memory effect in the SMA structure undergoing large and uneven deformation. Two scalars, named by phase-transition modulus and equivalent stiffness, are defined to make it easy to establish and implement the finite element method for a SMA structure. An incremental constitutive equation is developed to formulate the relationship of stress, strain and temperature in a SMA material based on phase-transition modulus and equivalent stiffness. A phase-transition modulus equation is derived to describe the relationship of phase-transition modulus, stress and temperature in a SMA material during the processes of martensitic phase transition and martensitic inverse phase transition. A finite element equation is established to express the incremental relationship of nodal displacement, external force and temperature change in a finite element discrete structure of SMA. The incremental constitutive equation, phase-transition modulus equation and finite element equation compose the supposed finite element method which simulate the thermo-mechanical behaviors of a SMA structure. Two SMA structures, which undergo large and uneven deformation, are numerically simulated by the supposed finite element method. Results of numerical simulation show that the supposed finite element method can effectively simulate the super-elasticity and shape memory effect of a SMA structure undergoing large and uneven deformation, and is suitable to act as an effective computational tool for the wide applications based on the SMA materials.

Based on dynamic three-point bending tests, the dynamic notch toughness ( $$ K_{\text{Q}}^{\text{d}} $$ ) of Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit 1) bulk metallic glass (BMG) was found to be sensitive to stress intensity factor rate ( $$ \dot{K}_{\text{Q}}^{\text{d}} $$ ), which varied from 5.21 to 31.90 MPa m1/2. The number of shear bands (Ns) in the notch tip plastic zone was quantitatively analyzed. The phenomenon wherein Ns decreased with increasing loading rate was explained based on the theory of the shear transformation zone and the softening mechanism. Then, power law relationships were established among Ns, $$ K_{\text{Q}}^{\text{d}} $$ and $$ \dot{K}_{\text{Q}}^{\text{d}} $$ . The results showed that shear bands can affect $$ K_{\text{Q}}^{\text{d}} $$ and $$ \dot{K}_{\text{Q}}^{\text{d}} $$ and act as a bridge connecting $$ K_{\text{Q}}^{\text{d}} $$ and $$ \dot{K}_{\text{Q}}^{\text{d}} $$ . The sensitivity of $$ K_{\text{Q}}^{\text{d}} $$ to $$ \dot{K}_{\text{Q}}^{\text{d}} $$ in BMGs can be well explained by the variation of Ns with loading rate.

In this paper, a novel sonogel was prepared based on the modified h-BN nanosheet (BTO) and PAO10. The rheological investigations demonstrate that the sonication induced gel is pseudoplastic fluid with yield strength and shear thinning property. The tribological tests show that of sonogel exhibits reliable lubricating performances even under the high load of 800 N and high temperature of 180 °C. The lubricating mechanism was discussed based on surface analyzations. The work indicates that the BTO gelator not only could alter the rheological behavior of PAO10, but also remarkably improve the tribological performances, especially under the harsh conditions.

To satisfy the requirement of a chip package, Nd2O3 addition was adopted to improve the thermal, mechanical, and dielectric properties of CaO-B2O3-SiO2 (CBS) glass–ceramics. The reduction of activation energy from 165.86 to 114.73 kJ/mol indicated that Nd2O3 doping promoted the sintering process of CBS glass–ceramics. X-ray diffraction analysis showed that an appropriate amount of Nd2O3 additive improved the crystallization of the CBS system, while suppressing the formation of cristobalite. The amount of Nd2O3 significantly affected the mechanical properties and thermal expansion curves. The dielectric properties, however, were not observably affected by Nd2O3. In general, 0.5% Nd2O3 doped CBS glass–ceramics showed good properties: α = 11.32 × 10−6/°C, σ = 203.3 MPa, φ = 76.2 GPa, er = 5.36, and tanδ = 9.9 × 10−4.

In this paper, we have investigated the magnetism and transport properties of borophene nanoribbons by using the first-principles calculations based on density functional theory. It can be seen that the hydrogenated borophene nanoribbons are more stable than the bare borophene nanoribbons. The magnetism of borophene nanoribbon can be modulated by the edge’s hydrogenated. Interestingly, with regard to the hydrogenated armchair borophene nanoribbons, the current increases with the increase of bias voltage when V ≤ 1.0 V, and then the current decreases with the increase of bias voltage when V > 1.0 V, namely, it appears negative differential resistance effect. It is hoped that borophene may be useful for the design and application of spintronic devices.

Rare earth oxychlorides were investigated for the first time as precursors to prepare rare earth alloys through solid cathode electrolysis in molten CaCl2, and to demonstrate this approach the electrochemical reduction of a LaOCl and NiO mixture to LaNi5 was performed. It was found that LaOCl is a good solid precursor of La because it neither absorbs water from the air nor reacts with the molten electrolyte. The electrode process consists of two simple and rapid steps: the reduction of NiO to Ni, followed by the reduction of LaOCl on the formed Ni, generating LaNi5. Moreover, as most of the rare earth elements have similar physicochemical properties and their oxychlorides are easily available, our findings may promise a general route for the preparation of rare earth alloys. Keywords: Solid-state electrochemistry, Rare earth oxychlorides, LaNi5, Molten salts, Electrolysis

Pb-doped copper nitride (Cu3N:Pb) films were prepared on monocrystalline silicon through reactive magnetron sputtering by using high-purity Cu and Pb as targets. The surface morphology, microstructure, and electrical parameters of the Cu3N:Pb films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and Hall effect analyses. The Cu3N:Pb films possess typical anti-ReO3 structure. The ratio of Cu to N in the films is slightly higher than 3:1. After Pb doping, the carrier concentration of the films changes greatly, but its carrier mobility does not remarkably change. This finding could be due to the Fermi level and the effective barrier change when the carrier concentration in the films changes. Overall, a film material with good electrical properties can be obtained by reasonably adjusting lead content in the Cu3N:Pb films.

Nanoporous Ag-Sn was prepared by direct electroreduction of a codeposited AgCl-SnO2 mixture in 0.1 M HCl, and evaluated as an electrode catalyst for the reduction of CO2 in 0.5 M KHCO3. A volcano-type correlation between selectivity for the formate product and the atomic ratio of Ag to Sn in the nanoporous catalysts was revealed. It was found that the bimetallic catalyst with a Ag:Sn ratio of 3:2, mainly composed of the Ag4Sn alloy, showed excellent catalytic performance for the conversion of CO2 to formate. This catalyst delivered a current of about 10 mA cm−2 with a high formate faradaic efficiency of about 85% at −0.8 V vs. the reversible hydrogen electrode. Moreover, the catalytic activity remained reasonably stable during a 13.5-hour electrolysis. Keywords: Ag-Sn bimetals, Solid electroreduction, Electrocatalysis, Carbon dioxide, Formate

The application of cellular structure for energy dissipation requires the investigation on the deformation and failure process of the foam under dynamic loading. In this study, the split-Hopkinson pressure bar technique with high speed video camera was used to directly observe the dynamic deformation in quasi-closed-cell aluminum foam fabricated by an in-house direct foaming methodology. The characterization of cellular structure was first performed on the developed aluminum foam, indicating that the cell size follows a log-normal distribution. The measurements revealed that the deformation mode varies with the strain rate. After that an experimentally validated X-ray micro-computed tomography based 3D finite element model of the as-fabricated specimen was established to predict the stress distribution and deformation history under impact loading, and correlated to the experimental observations to explore the deformation mechanisms. It was found that shear band is formed after peak stress. The dynamic deformation and failure process of the quasi-closed-cell aluminum foam result from the coexistence of cell wall bending and buckling, cell collapse and shear traction induced tearing breakage.

The contact problem of spherical indentation on the anisotropic elastic half-space is considered based on an experimental method in this work. The mechanical anisotropy is simulated by uniaxially stretching isotropic material made of silica gel. A special optical system is adopted to capture the contact images during indentation tests. The experimental results further prove the reasonability of the assumption that the contact area of spherical indentation on the anisotropic half-space is elliptical. And the results also show that the direction of strengthening by the uniaxial tension is consistent with the minor axis of the elliptical contact area. Such results validate the associated theory. Besides, the error analysis is made to examine the reliability of the fitting results, where the relative errors are less than 0.8% under the influence of given drawbacks. The indentation modulus can be determined through experimental data. Results show that the indentation modulus monotonically increases with the increase of the prestrain value. In the case of isotropy, the initial elastic modulus is determined under the assumption of incompressibility. The result by indentation test is in a good agreement with that by uniaxial tensile test.

A modified mixed mode fracture criterion, called generalized maximum energy release rate criterion, is proposed to predict the fracture initiation angles and estimate the fracture resistances in brittle and quasi-brittle materials under mixed mode loading. With this generalized maximum energy release rate criterion, the energy release rate around the crack tip is calculated by considering the contributions from both singular stress terms and T-stress. Experimental data, extracted from prior literatures for central cracked Brazilian disk, cracked semi-circular bend and edge-crack triangular specimens, are used to validate the modified criterion and evaluate the accuracy of the prediction obtained from this modified criterion. Results show that the T-stress plays a remarkable role in the mixed mode I/II fracture analysis when the energy-based criterion is employed. In addition, it is shown that the modified criterion can well predict the mixed mode I/II fracture behaviors of brittle and quasi-brittle materials.