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A highly stable new monoelemental 2D boron structure inspired by MXenes is discovered and is promising for various energy applications such as high-capacity anodes.

High-performance flexible perovskite solar cells based on a citric acid modified transparent conductive substrate of silver nanowires semi-embedded in colorless polyimide.

_ Low-speed two-stroke diesel engines are widely employed in the marine industry, especially in tanks, owing to their advantages of fuel economy and reliability. However, with the emerging ultra-long-stroke trend, existing scavenging models, which are based on the configuration of cylinders with short strokes, are no longer applicable. In this study, we investigate the flow field and residual exhaust gas distribution in a cylinder using particle image velocimetry and computational fluid dynamics (CFD) simulations. The result shows a strong Burgers vortex structure upstream of the scavenger flow and dissipates gradually as it moves downstream. Furthermore, the scavenging process comprises three processes according to the detailed CFD analysis: displacement, mixing scavenging, and short circuit. Inspired by the results, a tailored empirical model of ultra-long-stroke uniflow scavenging comprising three sub-models is proposed. Specifically, a logarithmic relationship between the concentration level and scavenging deliver ratio is proposed to describe the mixing scavenging process. Finally, the model was validated against CFD results. The results demonstrate that the discrepancy in the scavenging efficiency curve predicted by this model and CFD is less than 1%, thereby demonstrating model reliability. Introduction Owing to the advantages of a large power range, high thermal efficiency, low fuel consumption rate, and good reliability, marine low-speed engines are widely used to provide power to civil ships (Heywood 1999). The market for low-speed engines is vast and is improving the performance of low-speed engines through research has great economic and environmental significance (Woodyard 2004). To meet the requirements of ship owners for lower fuel consumption and the IMO’s regulation of halving the greenhouse gas emissions of newly built ships, the ultra-long stroke of low-speed engines has become a trend (Lamas & Vidal 2012). With an ultralong stroke, the combustion speed of low-quality fuel oil is slow, and an ultra-long-stroke cylinder can prolong the expansion process, improve the combustion process, and reduce the fuel consumption rate (Fenghua 2014). The ultra-long-stroke diesel engine further creates fuel savings of 3.5–7% based on the original low fuel consumption. Previously, ultra-long strokes could not be achieved, limited by materials and manufacturing processes. However, in recent years, with the advancement of materials and processes, ultra-long strokes have been widely adopted as they have demonstrated superior competitiveness.

Diamond is an ultrawide bandgap semiconductor with excellent electronic and photonic properties, which has great potential applications in microelectronic and optoelectronic devices. As an allotrope of diamond, graphene also has many fantastic properties like diamond, which caught much attention in combing them together. In this work, a direct sp3-to-sp2 conversion method was proposed to fabricate graphene layers on single crystal diamond by thermal treatment with Ni film catalyst. By optimizing the conversing conditions, a thin graphene layer with low sheet resistance was obtained on diamond. Based on this, an all-carbon sandwich structural graphene-diamond-graphene (GDG) detector was fabricated, which shows low dark current of 0.45 nA at 0.5 V μm−1 applied electric field. The maximum sensitivity of this detector is obtained when the incident X-ray is 12 keV, with the value of 2.88 × 10−8 C Gy−1. Moreover, the rise time and delay time of the GDG detector is about 1.2 and 22.8 ns, respectively, which are very close to that of diamond detector with Ti/Au electrode. The realization of the direct in-situ sp3-to-sp2 conversion on diamond shows a promising approach for fabricating diamond-based all-carbon electronic devices.

The Nb2CTx prepared by hydrothermal-assisted in-situ HF generation etching was investigated in terms of its gas sensor performance. The Nb2CTx was obtained by mixing Nb2AlC with pure water, hydrochloric acid, and fluoride (LiF or NH4F) and then hydrothermally treated at 180 °C for 24 h. This in-situ HF generation etching by hydrothermal treatment was more efficient and safer in the synthesis of the Nb2CTx than the direct HF etching. The Nb2CTx etched with LiF had relatively wide interlayer spacing because the hydration radius of Li+ was larger than that of NH4+. The results also suggest that Nb2O5 is formed during the synthesis process. These results suggest that interlayer spacing, surface termination, and secondary phases formation can be controlled by the etchant, and that hydrothermal treatment extended the applicability of insoluble etchants. The Nb2CTx synthesized with LiF was evaluated as a gas sensor at room temperature in air in the presence of designated concentrations of 6 different gases, which exhibited good sensitivity and repeatability and fast recovery time, except for NH3. Hydrothermal-assisted etching contributed to providing sufficient interlayer spacing for the gas response without an exfoliation process.

An offshore wind power medium-voltage direct-current (MVDC) transmission system based on distributed diode rectifiers (DRs) is proposed to realize the DC transmission of offshore wind power and eliminate offshore platforms. A coordinated control strategy between wind turbines (WTs) is proposed to greatly reduce the transmission voltage ripple and current ripple for this system. A small-signal state-space model for the WT line-side converter control system is established. The less damped terms in the control system are found through system eigenvalues, and the stabilization control method is further proposed. A joint control strategy between the onshore converter station and offshore WTs is proposed to achieve system fault ride-through. This strategy can quickly transmit the onshore AC grids fault information to each WT and consume unbalanced power by the dc choppers inside WTs. The simulation results in PSCAD verify the effectiveness of the proposed control strategy.

Cactus spines have inspired a wide range of micro- and nano-structures that cause droplets to move spontaneously and directionally. The conical shape and the surface wettability gradient are two typical characteristics in such systems. The cross section of the existing conical fibers is usually assumed to be an ideal circle. In fact, microridges are observed on the spine surface of the cactus, and the function is not yet fully understood. The present work thus focuses on how microridges affect droplet self-transport. Structures mimicking microridges are first investigated by constructing pyramidal cross sections with concave or convex lateral faces. The dissipative particle dynamics method is then employed to numerically investigate and theoretically analyze the dynamic behaviors of droplets on these conical fibers with different cross sections. The results show that the microridges reduce the base radius and the contact area of the droplet, thereby increasing the driving force and reducing the friction force. Moreover, by mimicking the microridges structure, we propose a conical fiber with a triple concave cross section, which increases the droplet velocity and the distance traveled over the traditional circular fiber. This work reveals the role of the microridges in the droplet self-transport, which opens up new prospects for the manufacture of fiber systems for microfluidics and liquid manipulation.

Cytokinesis is required for faithful division of cytoplasmic components and duplicated nuclei into two daughter cells. However, its underlying mechanism remains elusive. Here, we show that an Hsp90 co-chaperone NudC-like protein 2 (NudCL2) regulates cytokinesis by stabilizing regulator of chromosome condensation 2 (RCC2) in mammalian cells. NudCL2 co-localizes with RCC2 at the midbody and is required for RCC2 stabilization. Either NudCL2 knockout (KO) or RCC2 depletion causes similar phenotypes, including cytokinesis failure, midbody disorganization, and multinucleation. Ectopic expression of RCC2 effectively reverses the cytokinesis defect induced by NudCL2 KO. Furthermore, Hsp90 is also found to co-localize with NudCL2 at the midbody and is involved in NudCL2-mediated RCC2 stability and cytokinesis. Interestingly, our results reveal that the mRNA and newly synthesized peptides of RCC2 accumulate at the midbody. Loss of NudCL2 decreases the nascent RCC2, but not RCC2 mRNA, at the midbody. Taken together, our data provide a previously undescribed mechanism showing that NudCL2/Hsp90/RCC2 pathway is essential for cytokinesis at the midbody.

Two-stage turbocharging becomes prevailing in internal combustion engines due to its advantage of flexibility of boosting for the variation of operational conditions. Two turbochargers are closely coupled by engine manifolds in the system especially under the requirement of compactness. This paper studies the influence of the interaction of two turbines in a two-stage turbocharging system on the performance. Results show that the performance of low-pressure turbine is highly sensitive to the stage interaction. Specifically, compared with the cases without interaction, the efficiency of low-pressure turbine increases maximumly by 2.8% when the bypass valve is closed, but reduces drastically by 7.5% when the valve is open. Detailed flow analysis shows that the combined results of swirling flow from the high-pressure turbine and the Dean vortex caused by the manifold elbow result in the alleviation of entropy generation in the turbine rotor. However, when the bypass valve is open, interaction of the swirling flow with the injected bypass flow results in strong secondary flow in the volute and distorted inlet flow condition for the rotor, leading to the enhancement of entropy generation in low-pressure turbine. The study provides valuable insights into turbine performance in a two-stage turbocharging system, which can be used for the modeling and optimization of multi-stage turbocharging systems.

Stretchable and transparent electrodes (STEs) are indispensable components in numerous emerging applications such as optoelectrical devices and wearable devices used in health monitoring, human-machine interaction, and artificial intelligence. However, STEs have limitations in conductivity, robustness, and transmittance owing to the exposure of the substrate and fatigue deformation of nanomaterials under strain. In this study, an STE consisting of conductive materials embedded in in situ self-cracking strain-spread channels by wettability self-assembly is fabricated. Finite element analysis is used to simulate the crevice growth using the representative unit cell network and strain deformation using a random network. The embedded conductive materials are partly protected by the strain-opening crevice channel, and network dissociation is avoided under stretching, showing a maximum strain of 125%, a transmittance of approximately 89.66% (excluding the substrate) with a square resistance of 9.8 Ω sq-1, and high stability in an environment with high temperature and moisture. The wettability self-assembly coating process is verified and expanded to several kinds of hydrophilic inks and hydrophobic coating materials. The fabricated STE can be employed as a strain sensor in motion sensing, vital sign and posture feedback, and mimicking bioelectronic spiderweb with spatial gravity induction.

Developing advanced thermal interface materials (TIMs) to bridge heat-generating chip and heat sink for constructing an efficient heat transfer interface is the key technology to solve the thermal management issue of high-power semiconductor devices. Based on the ultra-high basal-plane thermal conductivity, graphene is an ideal candidate for preparing high-performance TIMs, preferably to form a vertically aligned structure so that the basal-plane of graphene is consistent with the heat transfer direction of TIM. However, the actual interfacial heat transfer efficiency of currently reported vertically aligned graphene TIMs is far from satisfactory. In addition to the fact that the thermal conductivity of the vertically aligned TIMs can be further improved, another critical factor is the limited actual contact area leading to relatively high contact thermal resistance (20–30 K mm2 W−1) of the “solid–solid” mating interface formed by the vertical graphene and the rough chip/heat sink. To solve this common problem faced by vertically aligned graphene, in this work, we combined mechanical orientation and surface modification strategy to construct a three-tiered TIM composed of mainly vertically aligned graphene in the middle and micrometer-thick liquid metal as a cap layer on upper and lower surfaces. Based on rational graphene orientation regulation in the middle tier, the resultant graphene-based TIM exhibited an ultra-high thermal conductivity of 176 W m−1 K−1. Additionally, we demonstrated that the liquid metal cap layer in contact with the chip/heat sink forms a “liquid–solid” mating interface, significantly increasing the effective heat transfer area and giving a low contact thermal conductivity of 4–6 K mm2 W−1 under packaging conditions. This finding provides valuable guidance for the design of high-performance TIMs based on two-dimensional materials and improves the possibility of their practical application in electronic thermal management.

Turbocharging is the key technique to improve engine-specific power and reduce CO2 emissions of a piston-driven engine. Repeated actions of engine pistons and valves give rise to engine pulsations resulting in intensive unsteady flow in the turbines. Understanding the pulsation effects on a turbine that is steady-flow designed is crucially important for performance enhancement. The present work derives an equation that is capable of evaluating the pulsation effects on the volute-outlet flow angle. Based on the equation, a reduced order model (1-D) is proposed and applied to a single-entry mixed flow turbine. By comparing to 3-D unsteady computational fluid dynamics (CFD), the ability and accuracy of the 1-D model on predicting the unsteady volute-outlet flow angle is verified. The effects of the unsteady flow angle on the turbine performance are further investigated by comparing unsteady and quasi-steady flow field characteristics given by 3-D CFD. The present work unveils the volute unsteady behaviour and explains the unsteady coupling mechanism between the volute and the rotor. The findings can lead to improvement of turbine design methodology under pulsating flow conditions.

The unsteady response of a turbine exposed to pulsatile incoming flow is studied via the analytical model in this article. First, the response of output torque of the turbine to pulsatile condition is theoretically studied and a correlation of the torque response is deduced. The results confirm that the fluctuations of the torque are proportional to the fluctuations of velocity at the rotor inlet. Next, the unsteady response of turbine system is modeled by the method of transfer matrixes of quasi-2D flow elements connected in sequence. The correlations of swallowing capacity and output torque with the imposed pulsatile inlet pressure are obtained via the models. The results prove that the unsteadiness of turbine performance is proportionally enhanced by the pulse magnitude and the acoustic throttle slope in swallowing capacity curve. In particular, the unsteadiness increases first, but then reduces as the Strouhal number increases. The strongest unsteady performance is achieved when the resonance of the system happens at the Strouhal number as 1. Furthermore, the model proves that the total torque deviation of the turbine is proportional to the mass accumulation in a pulse period. This justifies the validity of the widely used assumption of the mass accumulation as an indicator of turbine performance unsteadiness. Finally, the results of the theoretical model are validated against the 1D gas-dynamic simulation via in-house developed code.

This research aims to propose a method to achieve the maximum altitude adaptability of turbocharged diesel engines with the optimum fuel consumption. Firstly, engine performance at different altitudes is studied by experimental method. It is found that the engine power recovery is restricted by three constraints, which are cylinder pressure, exhaust temperature and boosting pressure ratio. Following that, the influence of turbocharging system and fuel injection on the three constraints is studied via experimentally validated numerical model. A power-recovery-zone bounded by the three constraints is proposed, inside which engine power can be fully recovered. The altitude adaptability of the engine is discussed in details via this zone. Further analysis finds that the boosting pressure and the maximum pressure ratio are the key factors to the constraints. A new methodology which can achieve the maximum altitude with the optimum fuel consumption is proposed based the concept of the zone. Finally, the methodology is applied in the engine with three types of turbocharging systems to quantitatively compare their altitude adaptability. Results prove that the altitude adaptability of the engine is notably improved by adapting the proposed method, especially for the two stage turbocharging system.

As vehicle turbochargers are developed toward higher performance and lower turbo lag, high cycle fatigue (HCF) of radial turbine blades is becoming increasingly common which greatly threatens the reliability of turbochargers. Tip leakage vortex is one of potential sources of blade excitation and it’s profoundly influenced by blade tip clearance. This paper studies the influence of tip clearance distribution on blade excitation of a vaneless radial turbine via experimentally validated one-way fluid-structure interaction (FSI) numerical method. The results suggest that blade vibration response is significantly influenced by tip clearance distribution in the meridional direction. Generalized energy method is proposed to determine the key factors for blade excitation. The results manifest that complex distributions of harmonic pressure amplitude on the blade dominate blade vibration response. Detailed flow field analysis is carried out to further investigate the mechanism of blade excitation. The results show that distributions of harmonic pressure amplitude on pressure surface (PS) and suction surface (SS) are both dominated by tip leakage vortex, whereas the roles that tip leakage vortex plays are quite different. Specifically, tip leakage vortex influences harmonic pressure amplitude on SS directly because of short distance between vortex core and SS, whereas it influences harmonic pressure amplitude on PS indirectly by interfering the evolution of passage vortex. This research can guide new designs for durable vaneless radial turbines without sacrificing aerodynamic performance.

The turbocharged piston-driven engines are widely used in high altitude long endurance unmanned aerial vehicles (HALE UAVs). Repeated actions of engine pistons and valves give rise to engine pulsations resulting in intensive unsteady flows in the turbocharger. One-dimensional (1-D) modeling, which is computationally effective, plays a crucial role in evaluating turbocharger performance and conducting turbocharger-engine matching under pulsating conditions. The present work introduces a newly developed 1-D software (TURBODYNA) for the sake of improving traditional 1-D modeling's accuracy and generality. The advantages and capabilities of TURBODYNA are illustrated by applying it to three different and typical sorts of turbocharger applications: the single-entry turbine, the twin-entry turbine, and the centrifugal compressor. The unsteady testing conditions include high frequent pressure pulses for the single-entry turbine, out-of-phase pressure pulses for the twin-entry turbine, and rotating stall and surge for the centrifugal compressor. Results show that, by contrast to traditional 1-D modelings, the current 1-D modeling has achieved exceptional improvements in both accuracy and applicability. The novel and powerful tool provides a solid framework for assessing turbocharger unsteady performances and addressing turbocharger-engine matching.

The terahertz stealth and shielding performance of a new type of two-dimensional material, borophene, has been studied theoretically and experimentally. Studies have shown that borophene materials have good terahertz stealth and shielding properties. First-principles calculations show that compared with single-layer borophene, few-layer borophene has good terahertz stealth and shielding performance in the range of 0.1~2.7 THz. In the range of 2~4 layers, the terahertz stealth and shielding performance of few-layer borophene increases with the increase of the number of layers. The finite element simulation calculation results also confirmed this point. Using the few-layer borophene prepared by our research group as a raw material, a PDMS composite was prepared to verify the terahertz stealth and shielding performance of the few-layer borophene. In the ultra-wide frequency range of 0.1~2.7 THz, the electromagnetic shielding effectiveness (EMI SE) of the PDMS material mixed with few-layer borophene can reach 50 dB, and the reflection loss (RL) can reach 35 dB. With the concentration of few-layer borophene increasing, the terahertz stealth and shielding effectiveness of the material is enhanced. In addition, the simultaneous mixing of few-layer borophene and few-layer graphene will make the material exhibit better terahertz stealth and shielding performance compared with mixing separately.

A new two-dimensional material B

The main purpose of this investigation is to study the dynamic characteristics of shut-in and restart process in reservoirs with high water cut and strong vertical heterogeneity. The physical model, which includes three layers with low, medium, and high-permeability from top to bottom, was made according to the similarity law. Water drive test, the first restart test, and the second restart test were conducted, respectively. Water cut, oil recovery, and saturation distribution of the remaining oil were obtained during the tests. On this basis, mechanisms of shut-in and restart process of the reservoir were analyzed. It is concluded that appropriate developing plan such as layering mining and cyclic waterflooding should be implemented for developing strong heterogeneity reservoirs. The shut-in and restart tests showed that closing the water-flooded layer is beneficial for enlarging the sweep volume. Besides, water cut of 98% does not mean the economic limits of waterflooding. Under the effect of capillary force and gravitational differentiation, oil and water will redistribute in the formation. The redistribution of the oil and water, the fluctuation of the pressure difference, and the rebuild of the flow path, which produce parts of the bypassed oil, are the main mechanisms of the recovery enhancement by shut-in and restart operation. It should be noted that the shut-in and restart process indeed prolongs the waterflooding development. However, simply replying on the oil and water distribution under static conditions cannot greatly enhance the oil recovery.

As an ultra-wide bandgap semiconductor, hexagonal boron nitride (h-BN) has drawn great attention in solar-blind photodetection owing to its wide bandgap and high thermal conductivity. In this work, a metal-semiconductor-metal structural two-dimensional h-BN photodetector was fabricated by using mechanically exfoliated h-BN flakes. The device achieved an ultra-low dark current (16.4 fA), high rejection ratio (R 205nm/R 280nm = 235) and high detectivity up to 1.28 × 1011 Jones at room temperature. Moreover, due to the wide bandgap and high thermal conductivity, the h-BN photodetector showed good thermal stability up to 300 °C, which is hard to realize for common semiconductor materials. The high detectivity and thermal stability of h-BN photodetector in this work showed the potential applications of h-BN photodetectors working in solar-blind region at high temperature.

This paper investigates the stability problem of sliding mode controlled buck converters affected by unmodelled dynamics of circuit elements and Hall sensor. The parasitic resistors of all elements are contained in the modelling of buck converters. Different from the traditional sliding mode approach based on the nominal model, the circuit parasitic parameters are directly included in the controller design and stability analysis, which divide the regulation region located in the right half axis into four sub‐ranges. It is more accurate and has no need of extra compensator. For Hall sensor, singular perturbation theory is adopted for modelling and analysing, giving a stable condition concerning its dynamic and static parameters. Finally, the influence of the two types of unmodelled dynamics on the whole closed‐loop system is investigated by constructing an equivalent model, giving a more strict stability condition. Simulations and experiments are presented to illustrate the non‐negligible influence of these unmodelled dynamics.

Centrifugal compressor is exposed to pulsating backpressure due to the movement of intake valves in internal combustion engine. The performance of compressor deviates from the steady performance map, which affects the matching between turbocharger and engine. The behavior of compressor system at pulsation conditions are investigated via an in-house developed 1D unsteady code validated by experimental results. The influence of pulse frequency, magnitude and compressor characteristic curve on the compressor transient responses, including filling-emptying effect and wave dynamics, are analyzed. Results show that the strength of wave dynamics grows stronger with the increasing of pulse frequency, while the strength of filling-emptying effect increases first then decreases. The rise of pulse magnitude results in an almost linearly increasing of filling-emptying effect, while it can hardly affect the wave dynamics. Furthermore, the influence of pulsation magnitude and frequency represents the influence of local pressure gradient, and a correlation as quadratic curve can be evaluated between the pressure gradient and compressor unsteadiness. On the other hand, the influence of operating point, including the average mass flow rate and the slope of characteristic curve, is confirmed to be evidently smaller, comparing to the influence of pulsation frequency and magnitude. This study is helpful to estimate the behavior of compressor and the discrepancy of performance when operating at unsteady environment or matched with engine.

Lithium-rich layered oxide cathodes have an advantage of high energy density. However, continuous capacity fading and voltage hysteresis have largely restricted their practical application. In this work, we investigated in depth the voltage-fading mechanism of Li-rich materials by in situ Raman spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy, and high-resolution transmission electron microscopy (HRTEM). It has been found that the chemical and structural evolution of a Li1.2Ni0.15Co0.1Mn0.55O2 cathode is quasi-reversible in a whole charge–discharge cycle. The structural evolution is evidently irreversible upon long-term cycling, resulting in the dissolution of cations from the lattices and structural collapse, which in turn leads to undesirable voltage fading. This finding is important for a better understanding of the redox reaction mechanisms of high-capacity Li-rich cathodes.

The performance of the SCO2 centrifugal compressor is the key component influencing the efficiency and stability of the whole Close-Bryton cycle system. It is important to understand the loss mechanism inside the compressor to guide the design and performance optimization of the compressor. However, the physical properties of SCO2 are strongly nonlinear near the critical point, and the internal flow of the compressor is highly coupled with its properties, which inevitably profoundly influences the loss generation in the device. In this paper, the loss mechanism of SCO2 compressor is investigated comprehensively based on numerical method compared with experimental data. CO2 real gas model embodied in RANS model are used for the study. Firstly, grid independence and influence of the resolution of real gas properties tables are discussed. The numerical simulation results are in good agreement with the experimental data of Sandia SCO2 compressor. Secondly, the distribution of the loss of the compressor are evaluated by means of local entropy generation at different mass flow rates. In particular, a direction comparison between the cases with real gas properties and the constant properties is carried out for manifesting of the influence by real gas properties. The results manifest that the loss of the case with constant properties is profoundly higher than that of the real gas properties, especially at small flow rate. Detailed flow field is compared to understand the influence of the properties. It is shown that the tip leakage flow is evidently decreased with the real gas properties and results in a much more uniform flow distribution throughout the impeller. The decrease in static temperature and pressure due to the acceleration of SCO2 at the tip of the main blade causes an increase in fluid density, reducing the tip leakage and secondary flow. Moreover, the influence on the flow in the impeller results in smaller incidence angle near hub side for the case with real gas properties, thus the separation on the suction surface which happens in the case with constant properties is alleviated. Therefore, the loss in both the impeller and diffuser is significantly reduced by the real gas properties.

High cycle fatigue (HCF) is the most common form of blade failure in nozzleless radial turbines. Current studies related to blade vibration alleviation focus on redesign of blade and volute geometries. These methods have the drawbacks of long period, performance sacrifice and poor universality. This paper investigates a novel flow control method for blade vibration alleviation based on casing treatment. Fluid-structure interaction (FSI) numerical method validated by experiments is employed. Inspired by the generalized force method, the aerodynamic excitation force caused by volute can be offset by introducing additional excitation force artificially. Axial grooves are designed on the casing in the vicinity of blade trailing edge to achieve this target. Firstly, the influence of relative position of volute tongue and grooves on blade excitation is investigated. It’s found that the vibration amplitude is evidently reduced by maximizing the distance between the tongue and the adjacent groove. Generalized force analysis and flow field analysis reveal that the excitation effects caused by volute and casing treatment cancel each other out in this relative location. Next, the influence of configuration parameters of grooves on blade excitation is investigated. Two of the parameters only influence the length of generalized force caused by grooves rather than the phase, which greatly facilitates the design of casing treatment to achieve minimum vibration response. Finally, the effect of optimum design of casing treatment under various working conditions is investigated. The optimum design has good effect at high pressure ratio, which is going to be further optimized to improve its adaptability.

Fourier ptychography imaging is a powerful phase retrieval method that can be used to realize super-resolution. In this study, we establish a mathematical model of long-distance camera scanning based on reflective Fourier ptychography imaging. In order to guarantee the effective recovery of a high-resolution image in the experiment, we analyze the influence of laser coherence in different modes and the surface properties of diverse materials for diffused targets. For the analysis, we choose a single-mode fiber laser as the illumination source and metal materials with high diffused reflectivity as the experimental targets to ensure the validity of the experimental results. Based on the above, we emulate camera scanning with a single camera attached to an X-Y translation stage, and an experimental system with a working distance of 3310 mm is used as an example to image a fifty-cent coin. We also perform speckle analysis for rough targets and calculate the average speckle size using a normalized autocorrelation function in different positions. The method of calculating the average speckle size for everyday objects provides the premise for subsequent research on image quality evaluation; meanwhile, the coherence of the light field and the targets with high reflectivity under this experiment provide an application direction for the further development of the technique, such as computer vision, surveillance and remote sensing.

Aerodynamic interaction of rotor with stator is the primary cause of high cycle fatigue of radial turbine blade. However, few studies have been carried out on aerodynamic interaction in nozzleless radial turbines. This paper studies aerodynamic interaction in a nozzleless radial turbine via the experimentally validated numerical method. The results suggest that several flow phenomena are related to blade excitation. First, when the blade sweeps by the volute tongue, the tongue wake induces a strong separation vortex at the blade leading edge and interacts with it. As the tongue wake migrates downstream, it deforms into a triangular shape across the rotor passage. Second, the potential field of the volute leads to drastic fluctuations of blade load as well as tip leakage flow. Importantly, the tongue wake interacts with the tip leakage vortex in the vicinity of blade trailing edge. This phenomenon results in strong disturbance to pressure fluctuations on suction surface at low pressure ratio, and the frequency of disturbance is roughly one order higher than that of potential field. However, its influence can be neglected at high pressure ratio. Furthermore, the details of vortex evolution in the rotor passage are discussed via the time-space contour plots of pressure difference. Various behaviors including propagation speed, direction, and strength can be well manifested by this method. Finally, the strong influence of unsteady interaction on blade excitation in the nozzleless turbine is confirmed by a direct comparison of blade loads in unsteady conditions with that in quasi-steady conditions.

Borophene has been predicted to be a potential anode material of lithium-ion batteries because of its high specific capacity, high mechanical strength, and low diffusion barrier. However, borophene...

It is a great challenge to prepare non-noble metal electrocatalysts toward hydrogen evolution reaction (HER) with large current density. Synergistic electronic and morphological structures of the catalyst have been considered as an effective method to improve the catalytic performance, due to the enhanced intrinsic activity and enlarged accessible active sites. Herein, we present novel ternary Co1−xVxP nano-needle arrays with modulated electronic and morphological structures as an electrocatalyst for highly efficient HER in alkaline solution. The NF@Co1−xVxP catalyst shows a remarkable catalytic ability with low overpotentials of 46 and 226 mV at current densities of 10 and 400 mA cm−2, respectively, as well as a small Tafel slope and superior stability. Combining the experimental and computational study, the excellent catalytic performance was attributed to the improved physical and chemical properties (conductivity and surface activity), large active surface area, and fast reaction kinetics. Furthermore, the assembled Co-V based electrolyzer (NF@Co1−xVx-HNNs(+)||NF@Co1−xVxP(−)) delivers small full-cell voltages of 1.58, 1.75, and 1.92 V at 10, 100, and 300 mA cm−2, respectively. Our findings provide a systematic understanding on the V-incorporation strategy to promote highly efficient ternary electrocatalysts via synergistic control of morphology and electronic structures.

PurposeThe results showed that the use of a magnetic marker could relatively accurately reflect the fracture pattern inside the rock-like material (RLM).Design/methodology/approachThis study investigated the internal structure and fracture pattern of a fractured RLM. Magnetized iron oxide powder, which was used as a magnetic marker, was mixed with water and glue to form a magnetic slurry, which was subsequently injected into a fractured RLM. After the magnetic slurry completely filled the cracks inside the RLM and became cemented, the distribution and magnitude of the magnetic field inside the RLM were determined using a three-dimensional (3D) magnetic field imaging system.FindingsA model for determining the magnetic field strength was developed using MATLAB.Originality/valueThis model of 3D magnetic will further be used as a finite element tool to simulate and image cracks inside the rock.

In the present research, a glycosyl cross-linking coordination chelate flame retardant was designed to enhance durable flame retardancy of cotton fabrics. It was a halogen-free, non-formaldehyde boron acid and phytic acid ammonium salt synergistic flame-retardant system. The flame retardancy and durability of flame retardants prepared by different saccharides were investigated. Results showed that raffinose was the best cross-linking reagent compared with the other monosaccharides and oligosaccharides. The raffinose as cross-linking reagent prepared glycosyl cross-linking boron acid and ammonium salt of phytic acid flame retardant (r-GBAP) (100 g/L) can obtain the shortest char length of 56 mm and the largest limiting oxygen index (LOI) value of 37.4%. A lower r-GBAP concentration can get good flame retardancy, due to adopt the three curing cycles process. FTIR, XPS, LOI, TG and SEM testing and characterization techniques were used to analyze and research the flame retardancy, durability, thermal oxidation stability and flame-retardant mechanisms of r-GBAP and the treated cotton fibers.

High-performance nanomaterial catalysts for hydrogen evolution reaction via electrochemical water splitting are significant to the development of hydrogen energy. In this work, we report a robust and highly active catalyst fabricated through direct electrochemical deposition of Pt nanodendrites at the surface of activated carbon (Pt NDs). Owing to the large electrochemically active area and the exposed (111) facet of Pt, Pt NDs exhibits outstanding activity towards hydrogen evolution reaction with a low requiring overpotential of 0.027 V at 10 mA/cm2 and Tafel slope of ≈ 22 mV/dec in acidic media. In addition, the hydrogen yield of Pt NDs is 30%–45% larger than that of commercial Pt/C at the same Pt loadings. Moreover, Pt NDs exhibits excellent long-term durability whose hydrogen production efficiency remains unchanged after six-hour hydrogen production, while the efficiency of commercial Pt/C catalyst decayed 9% under the same circumstance. Considering the superiority of catalytic activity and stability, this Pt NDs present great potentiality towards practical hydrogen production application.

A halogen-free, non-formaldehyde and eco-friendly bio-based synergistic flame retardant containing phosphorus–boron–nitrogen elements were synthesized and applied on cotton fabrics. Three curing cycles in cotton finishing process were employed. Samples treated with 30 g/L PBN solutions revealed the best result, while high concentrations did not gain more weight increase nor improved performance on the products. The SEM morphologies suggested penetration of ammonium phytate groups to the inner space and floatation of boron-containing groups on the surfaces of the cotton fibers. FTIR and XPS analyses indicated that after 50 laundering cycles, the boron can still stay on the surface of the treated cotton fibers. The LOI value of 30 g/L PBN finished cotton fabrics reached 45.0% and remained at 37.6% after 50 LCs. The char length of the treated cotton sample was 63 mm, whereas the control sample was 300 mm. The TG analysis in N2 demonstrated that the decomposition temperature of the treated fabric slightly decreased, while the thermal oxidation stability was significantly improved. Cone calorimetry analysis showed that the peak heat release rate, total heat release, and effective heat combustion of the treated samples were substantially reduced compared with the control sample at 50 kW/m2. LOI, TG, vertical burning and cone calorimetry showed that the PBN treated samples had good flame retardancy and thermal stability.