Improving Humidity Sensing of Black Phosphorus Nanosheets by Co-Doping Benzyl Viologen and Au Nanoparticles

Black phosphorus (BP) is a two-dimensional and layered elemental semiconductor that is very sensitive to the subtle fluctuation of relative humidity (RH). However, the practical application of BP material was undesirably plagued by the irreversible degradation under moisture/oxygen atmospheres. To circumvent this limitation, here we prepared BP co-doped with benzyl viologen (BV) and Au nanoparticles as the sensing layer and explored the humidity-sensing performance at room temperature (20 oC). Unlike BP (BP-BV) counterparts, BP-Au (BP-BV-Au) sensors demonstrated unvaried response polarity with increasing RH. And BV introduction improved the recovery characteristics. Additionally, the ternary BP-BV-Au sensors delivered decent selectivity and negligible hysteresis. On the one hand, the in situ reduction of Au nanoparticles consumed lone electron pairs within BP, suppressed the interaction with ambient moisture/oxygen, and improved the operation stability and recovery. On the other hand, hydrophobic BV as the protection layer further hindered water attachment. This co-doping behavior reduced the hole density and ensured the predominant interaction between low-energy sorption sites within BP and water molecules, thus leading to a larger resistance modulation (i.e., stronger response) and quicker reaction kinetics. This work offered a feasible method to propel the practical application and enriched the sensing mechanisms of BP-based humidity sensors.

MLCOR Model for Suppressing the Cascade of Edge Failures in Complex Network

As a decisive parameter of network robustness and network economy, the capacity of network edges can directly affect the operation stability and the construction cost of the network. This paper proposes a multilevel load–capacity optimal relationship (MLCOR) model that can substantially improve the network economy on the premise of network safety. The model is verified in artificially created networks including free-scale networks, small-world networks, and in the real network structure of the Shanghai Metro network as well. By numerical simulation, it is revealed that under the premise of ensuring the stability of the network from the destruction caused by initial internal or external damage on edge, the MLCOR model can effectively reduce the cost of the entire network compared to the other two linear load–capacity models regardless of what extent of the destruction that the network edges suffer initially. It is also proved that there exists an optimal tunable parameter and the corresponding optimal network cost for any BA and NW network topology, which can provide the reference for setting reasonable capacities for network edges in a real network at the stage of network planning and construction, promoting security and stability of network operation.

Influence of Controller’s Parameters on Static Bifurcation of Magnetic-Liquid Double Suspension Bearing

Magnetic-Liquid Double Suspension Bearing (MLDSB) is composed of an electromagnetic supporting and a hydrostatic supporting system. Due to greater supporting capacity and static stiffness, it is appropriate for occasions of middle speed, overloading, and frequent starting. Because of the complicated structure of the supporting system, the probability and degree of static bifurcation of MLDSB can be increased by the coupling of hydrostatic force and electromagnetism force, and then the supporting capacity and operation stability are reduced. As the key part of MLDSB, the controller makes an important impact on its supporting capacity, operation stability, and reliability. Firstly, the mathematical model of MLDSB is established in the paper. Secondly, the static bifurcation point of MLDSB is determined, and the influence of parameters of the controller on singular point characteristics is analyzed. Finally, the influence of parameters of the controller on phase trajectories and basin of attraction is analyzed. The result showed that the pitchfork bifurcation will occur as proportional feedback coefficient Kp increases, and the static bifurcation point is Kp = −60.55. When Kp < −60.55, the supporting system only has one stable node (0, 0). When Kp > −60.55, the supporting system has one unstable saddle (0, 0) and two stable non-null focuses or nodes. The shape of the basin of attraction changed greatly as Kp increases from −60.55 to 30, while the outline of the basin of attraction is basically fixed as Kp increases from 30 to 80. Differential feedback coefficient Kd has no effect on the static bifurcation of MLDSB. The rotor phase trajectory obtained from theoretical simulation and experimental tests are basically consistent, and the error is due to the leakage and damping effect of the hydrostatic system within the allowable range of the engineering. The research in the paper can provide theoretical reference for static bifurcation analysis of MLDSB.

The Temporal-Spatial Features of Pressure Pulsation in the Diffusers of a Large-Scale Vaned-Voluted Centrifugal Pump

A large-scale, vaned-voluted centrifugal pump can be applied as the key component in water-transfer projects. Pressure pulsation will be an important factor in affecting the operation stability. This paper researches the propagation and spatial distribution law of blade passing frequency (BPF) and its harmonics on the design condition by numerical simulation. Experimental and numerical monitoring is conducted for pressure pulsation on four discrete points in the vaneless region, which shows that the BPF is dominant. The pulsation tracking network (PTN) is applied to research propagation law and spatial distribution law. It provides a reference for frequency domain information and visualization vaned diffuser. The amplitude of BPF and its harmonics decays rapidly in the vaneless region. BPF and BPF’s harmonics influence each other. BPF has local enhancement in the vaneless region when its harmonics attenuate. In the vaned diffuser, the pulsation amplitude of BPF attenuates rapidly, but the local high-pressure pulsation amplitude can be found on the vane blade concave side because of obstruction and accumulation of the vaned diffuser. In the volute, the pulsation amplitude of BPF is low with the decelerating attenuation. This study provides an effective method for understanding the pressure pulsation law in turbomachinery and other engineering flow cases.

Increasing the operation stability of the electron accelerator based on ion-electron emission

This paper presents the results of studying the stability of the plasma emitter of an electron accelerator based on ion-electron emission during the transition from self-sustained continuous to self-sustained frequency (up to 50 kHz) repetitively pulsed generation of an auxiliary glow discharge with a hollow cathode with an area of 20.8×103 cm2 The experimental dependences of the probability of the appearance of cathode spots on the walls of a hollow cathode per unit time on the operating modes of the plasma emitter (pressure and type of working gas, amplitude of the auxiliary discharge current) are presented.

Design and multi-objective optimization of magnetorheological damper considering vehicle riding comfort and operation stability

Mostly, magnetorheological (MR) dampers were optimized based on individual performance, without considering the influence of structure parameters change on vehicle performance. Therefore, a multi-objective optimization scheme of MR damper based on vehicle dynamics model was proposed. The finite element method was used to analyze magnetic flux density distribution in tapered damping channel under different structure parameters. Furthermore, the damping force expression of the tapered flow mode MR damper was derived, and the damping force was introduced into the vehicle dynamics model. In order to improve the ride comfort and operation stability of the vehicle, a collaborative optimization platform combining magnetic circuit finite element analysis and vehicle dynamics model was established. Based on this platform, the optimal design variables were determined by comfort and stability sensitivity analysis. The time domain optimization objective and frequency domain optimization objective are proposed simultaneously to overcome the lack of time domain optimization objective. The results show that compared with the time domain optimization and the initial design, the suspension dynamic deflection, tire dynamic load and vehicle body vertical acceleration are decreased after the time-frequency optimization. At the same time, in the frequency domain, the amplitude of vibration acceleration in each working condition is significantly reduced.

Optoelectrical Operation Stability of Broadband PureGaB Ge-on-Si Photodiodes with Anomalous Al-Mediated Sidewall Contacting

An anomalous aluminum-mediated material transport process was investigated in sets of Ge-on-Si photodiodes with broadband optoelectrical characteristics measured at wavelengths from 255 nm to 1550 nm. The diodes had “PureGaB” anode regions fabricated by depositing a Ga wetting layer capped with an 11-nm-thick B-layer on 0.5 µm-thick Ge islands grown on Si. The Al metallization was able to reach the Ge-Si interface through ~ 0.1-µm-wide holes inadvertently etched along the perimeter of the Ge-islands, and then traveled along the Ge-Si interface, displacing and recrystallizing Ge and Si. The rest of the Ge surface was protected from the Al contact metallization by the B-layer. For diodes that had received the standard 400°C Al alloying step, the responsivity was near-theoretical at 406 nm and 670 nm, but, at 1310 nm and 1550 nm, the proximity of Ge-Si interfacial defects caused significant attenuation. Extra annealing at 400°C or 500°C enhanced the formation of Si pits that were filled with modified Ge crystals alloyed with Si and p-doped with Al. All these diodes maintained low dark currents, below 50 µA/cm2 at 2 V reverse bias, but the responsivity was degraded, particularly for the long wavelengths. On the other hand, neither responsivity nor degradation of current–voltage (I–V) characteristics was observed for prolonged exposure to normal operating temperatures up to 100°C. Since the direct Al contacting of the Ge sidewalls does not degrade the dark current, for large diodes it could be a low-cost method of obtaining low contact resistance to an anode with p-type sidewall passivation and high fill-factor.