Numerical Simulation of Maximum Spreading of an Impacting Ferrofluid Droplet under a Vertical Magnetic Field.

Theoretical modeling is proposed to predict the maximum spreading of water-based ferrofluid droplets impacting upon dry surfaces influenced by a vertical magnetic field. Constructed on the principle of energy balance, this model demonstrates excellent agreement with numerical findings across various impact velocities, contact angles, and magnetic strengths. Notably, as magnetic field strength escalates, magnetic forces prevail over viscous and capillary forces, exerting a significant influence on spreading dynamics and diminishing the maximum spreading diameter of ferrofluid droplets if the impacting shape is spherical. However, for freely falling droplets, the shape becomes prolate before impacting and the promoted surface energy balances the magnetic inhibitory effect on droplet spreading, thus resulting in an almost unchanged maximum spreading diameter. By postulating complete conversion of initial kinetic energy into magnetic energy, a scaling law is derived for maximum spreading diameter under extremely high magnetic fields. Further interpolation with viscous dissipation and capillary effects enables universal rescaling under diverse impact conditions. Through comparison with numerical outcomes, the validity of our theoretical model is affirmed, establishing a balanced formula between distinct energy components for predicting maximum spreading diameter of ferrofluid droplets accurately.

Atomic layer deposition (ALD)-constructed TaS2nanoflakes for cancer-related nucleolin detection.

Sensitive detection of nucleolin (NCL) is of great significance for the early diagnosis of cancer. In this work, as a new type of two-dimensional (2D) transition metal dichalcogenides (TMDCs), TaS2nanoflakes (NFs) were precisely constructed by atomic layer deposition (ALD) on carbon fiber paper (CFP) with high specific surface area.In situobservation showed that the nucleation and growth of TaS2nanoflakes were precisely controlled by the number of ALD cycles, thereby regulating their electrochemical properties. The electrochemical performance of TaS2NFs was observed in depth, and compared with that of traditional 2D TMDCs. Due to the high surface area and conductivity, anodic/cathodic current of ∼1570µA of TaS2NFs/CFP can be obtained. Subsequently, an electrochemical biosensor based on ALD-constructed TaS2NFs/CFP for cancer-related NCL detection was fabricated. Due to the excellent electrochemical performance of TaS2NFs/CFP, ultrasensitive detection of NCL in the linear range of 0.1 pM-10 nM with a detection limit of 0.034 pM was achieved.

Application of the Lamb Wave Mode of Acoustic Emission for Monitoring Impact Damage in Plate Structures.

The impact acoustic emission (AE) of plate structures is a transient stress wave generated by local materials under impact force that contains the state information of the impacted area. If the impact causes damage, the AE from material damage will be superimposed on the impact AE. Therefore, this paper details the direct extraction of damage-induced AEs from impact AEs for the health monitoring of plate structures. The damage-induced AE was analysed based on various aspects, including the cut-off range and propagation speed characteristics of the Lamb wave mode, the correlation between the force direction and the Lamb wave mode, and the impact damage process. According to these features, the damage-induced AE wave packets were extracted and verified via impact tests on epoxy glass fibreboards. The results demonstrated the feasibility of the proposed method for determining whether an impact causes damage via the direct extraction of the damage-induced AE from the impact AE.

Nanocrystalline NiSe2/MoS2 heterostructures for electrochemical hydrogen evolution reaction.

Although it suffers from a heavy dependence on the noble platinum catalyst, the electrochemical hydrogen evolution reaction (HER) is one of the most promising methods for the production of hydrogen. After numerous efforts, it is found that MoS2-based heterostructure may replace platinum as the electrochemical HER catalyst. In this work, the nanocrystalline NiSe2/MoS2 heterostructures were successfully prepared on the carbon fiber paper (CFP) substrate through electrochemical deposition and hydrothermal process. According to a series of electrochemical HER tests and a comparison with other MoS2-based heterostructure catalysts, the CFP/NiSe2/MoS2 catalyst with an overpotential η 10 of 143 mV and a Tafel slope of 45 mV dec-1 exhibited an excellent electrochemical HER catalytic performance and durability. In addition, CFP/NiSe2/MoS2 catalyst was treated by plasma to further improve the catalytic performance of the catalyst.

Analysis and Optimization of a Microgripper Driven by Linear Ultrasonic Motors.

This paper presents the vibration response analysis and optimal structural design of a microgripper driven by linear ultrasonic motors (LUMs) dedicated to improving end-point positioning accuracy. Based on structural vibration theory, a parametric vibration response model of the microgripper finger was established, and the relative sensitivities of the structural and material parameters that affect the vibration amplitude of the fingertip were calculated within the structural and material constraints. Then, according to the sensitivity calculation results, a multidimensional constrained nonlinear optimization model was constructed to suppress the vibration of the end-effector. The improved internal penalty function method combined with Newton iteration was adopted to obtain the optimal structural parameters. Finally, the vibration experimental results show that the vibration amplitude of the initial microgripper fingertip is 16.31 µm, and the value measured after optimization was 2.49 µm, exhibiting a reduction of 84.7%. Therefore, the proposed optimal design method can effectively restrain the vibration of the microgripper end-effector and improve manipulation stability.

Constructing NiSe2@MoS2 nano-heterostructures on a carbon fiber paper for electrocatalytic oxygen evolution.

Although MoS2 has shown its potential as an electro-catalyst for the oxygen evolution reaction (OER), its research is still insufficient. In this study, as a novel MoS2-based heterostructure electro-catalyst for OER, namely NiSe2@MoS2 nano-heterostructure, was constructed on a carbon fiber paper (CFP) substrate by a simple approach, which includes electrochemical deposition of NiSe2 film and hydrothermal processing of MoS2 film. In addition to a series of observations on the material structure, electrocatalytic OER performance of NiSe2@MoS2 was fully evaluated and further compared with other MoS2-based OER electro-catalysts. It exhibits an outstanding catalytic performance with an overpotential η 10 of 267 mV and a Tafel slope of 85 mV dec-1. Only 6% loss of current density before and after 10 h indicates its excellent durability. The results indicate that the obtained NiSe2@MoS2 is an excellent OER electro-catalyst and worth exploring as a substitute for noble metal-based materials.

Single Transition Metal Atom Bound to the Unconventional Phase of the MoS2 Monolayer for Catalytic Oxygen Reduction Reaction: A First-Principles Study.

Supported single-atom catalysts (SACs) have received a lot of attention due to their super-high atom utilization and outstanding catalytic performance. However, the instability of the supported transition-metal (TM) atoms hampers their widespread applications. Exploration of an appropriate substrate to stabilize the supported single atom is crucial for the future implementation of SACs. In recent years, two-dimensional materials have been proposed as possible substrates due to their large specific surface areas, but their chemically inert surfaces are difficult to stabilize TM atoms without defecting or doping. Herein, by means of systematic first-principles calculations, we demonstrate that the defect-free MoS2 monolayer in the unconventional phase (1T') can effectively immobilize single TM atoms owing to its unique electrophilic property as compared to the conventional 2H phase. As a prototype probe, we investigated oxygen reduction reaction (ORR) catalyzed by a total of 21 single TM atoms stabilized on 1T'-MoS2 and successfully screened out two candidates, Cu and Pd@1T'-MoS2, which have a low overpotential of 0.41 and 0.32 V respectively, outperforming most of the previously reported ORR catalysts. Furthermore, we reveal that the adsorption energy of the ORR intermediate, *OH, provides an excellent descriptor to assess the ORR activity, which is further determined by the d-band center of the supported TM adatoms, thus being a great advantage for future design of stable and high-performance SACs.

Reduced-order observer-based saturated finite-time stabilization of high-order feedforward nonlinear systems by output feedback.

This paper is concerned with the problem of global finite-time stabilization by output feedback for a class of feedforward (upper-triangular) nonlinear systems in p-normal form. Remarkably, both the high order powers and the saturated input are involved in the system under consideration, that renders the existing output feedback control methods are inapplicable. Based on the finite-time stability theorem, and by skillfully using the homogeneous domination approach and the nested saturation technique, a reduced order observer-based saturated finite-time output feedback control scheme is successfully developed. With choosing appropriate design parameters, the proposed controller ensures that the states of the closed-loop system are regulated to zero in a finite time without violation of the input constraint. Finally, two simulation examples are provided to demonstrate the effectiveness of the proposed method.