Simulations of a DC non-transferred arc plasma torch operating with argon–hydrogen have been performed by using a three-dimensional model. An artificially high electrical conductivity layer is ...employed to allow the current passing through the low temperature region near the anode wall. A new way by using two equations to describe the current density distribution is developed. Besides, a new method for determining the location of the arc-root attachment is proposed, in which the minimum total heat transfer rate through the anode wall is considered as the criterion for the lowest energy loss. Based on this criterion, the real arc core radius and length are predicted. Moreover, the influences of arc current and mass flow rate on the plasma arc characteristics are also investigated. The results obtained show that the location of the arc-root attachment predicted by the minimum total heat transfer rate principle is in good agreement with the previous work and the experimental data. Additionally, it is found that arc length can be reduced by increasing current or decreasing flow rate. Also, higher current and flow rate lead to higher temperature and velocity inside the plasma torch.
Several soft tissues residing in the living body have excellent hydration lubrication properties and can provide effective protection during relative motion. In order to apply this advantage of soft ...matters in practical applications and try to avoid its disadvantage, such as swelling and weakening in water, a design strategy of a soft/hard double network (DN) hydrogel microsphere modified ultrahigh molecular weight polyethylene (UHMWPE) composite is proposed in this study. A series of microspheres of urea-formaldehyde (UF), polyacrylamide (PAAm) hydrogel, UF/PAAm double network, and their composites were prepared. The mechanical properties, swelling, wettability, friction properties, and the lubrication mechanisms of the composites were investigated. The results show that DN microspheres can have an excellent stability and provide hydration lubrication. The performance of 75 DN-1 composite was superior to others. This finding will provide a novel strategy for the development of water-lubricated materials and have wide application in engineering fields.
Abstract
The rotational angular velocity of fragments under the driver of explosive products makes the fragments constantly flip during the trajectory, which has a huge effect on the velocity decay ...of the fragments. In order to more accurately calculate the residual velocity of the fragments during flight, it is necessary to study the rotational angular velocity of the fragments. Based on the paper target system, an experimental method for measuring the angular velocity of fragments is proposed. By using ANSYS/LSDYNA finite element software, the rotational angular velocity of preformed fragments under explosion is studied. A new meshing method is proposed to simulate the driven process of the explosive products on the fragments more accurately. The experimental results and the numerical simulation results are considered to be consistent within the margin of error. And at last, the distribution of fragment is studied base on numerical simulation. The research results provide a foundation for studying the trajectory of preformed fragments after explosive driven.
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•PdRu alloy nanoparticles of solid solution in atomic scale were prepared in the range of 6.0–16.6 nm.•Elemental mapping and X-ray diffraction provide strong evidence for the solid ...solution in atomic scale.•The valence bandwidth of PdRu alloy nanoparticles increased with the increase of the size of the nanoparticles.•The catalytic activity of PdRu/CNT alloy nanoparticles towards electrochemical strongly depend on the size of the nanoparticles and showed volcano-shape dependence.
It has been challenging to synthesize palladium (Pd) and ruthenium (Ru) alloy nanoparticles of solid solution in atomic scale, thus preventing us to study the size effect on the catalytic activity. Here we reported the synthesis of PdRu alloy nanoparticles through polyol reduction method, with the size from 6.0 to 16.6 nm. Elemental mapping indicated that Pd and Ru with 1:1 ratio are evenly distributed over the alloy nanoparticles. XRD of PdRu alloy nanoparticles displayed the characteristic diffraction patterns of face centered cubic (fcc) of Pd and invariable inter plane distance of (1 1 1). The band width of valence state increased from 5.7 to 6.2 eV when the diameter of the nanoparticles increased from 6.0 to 16.6 nm. The size effect of PdRu alloys towards electrooxidation of formic acid was examined on the support of CNT. PdRu alloy nanoparticles with diameter of 15.6 nm performed best among all the samples, 5.7 times higher than that of commercial Pd/C with formic acid. PdRu alloy nanoparticles also demonstrated optimum catalytic activity towards methanol oxidation in alkaline medium solution and the best performance was achieved by PdRu alloy nanoparticles with diameter of 15.6 nm, which was 2.5 times that of Pd/C. A volcano shape dependence of catalytic activity towards both formic acid and methanol oxidation on the size of PdRu alloy nanoparticles was observed. This work provided a vial strategy for the size-controlled synthesis of alloy nanoparticles of solid solution in atomic scale, especially for those elements that are immiscible, unraveled the size effect on the electronic structure and catalytic activity on metal nanoparticles and may shed light on the optimization of alloy noble metal nanoparticles.
Water-lubrication bearings are critical components in ship operation. However, studies on their maintenance and failure detection are highly limited. The use of sensors to continually monitor the ...working operation of bearings is a potential approach to solve this problem, which is collectively called intelligent bearings. In this literature review, the recent progress of electrical resistance strain gauges, Fiber Bragg grating, triboelectric nanogenerators, piezoelectric nanogenerators, and thermoelectric sensors for in-situ monitoring is summarized. Future research and design concepts on intelligent water-lubrication bearings are also comprehensively discussed. The findings show that the accident risks, lubrication condition, and remaining life of water-lubricated bearings can be evaluated with the surface temperature, coefficient of friction, and wear volume monitoring. The research work on intelligent water-lubricated bearings is committed to promoting the development of green, electrified, and intelligent technologies for ship propulsion systems, which have important theoretical significance and application value.
Abstract
Since the quantum concept of parity-time (PT) symmetry has been introduced into the conventional inductor–capacitor resonance, strategies based on exceptional points (EP) based strategies ...redefine our understanding of sensitivity limitation. This considerable enhancement of sensitivity originated in exploration of the non-Hermitian physics in photonics, acoustics and electronics, which exhibits a substantial application to the miniaturization of implanted electronic sensors in medicine field. By continuously accessing the EP, the spectral response of reader ∆
ω
follows a dependency of Δ
ω
∼
κ
2/3
to a weakly coupling rate (|
κ
| ≈ 0), which may approach the theoretical limit of sensitivity in a second-order EP system. In this paper, we experimentally demonstrate a high-order (higher than second-order) PT symmetric system for weak coupling detection, in which a third-order EP can be employed to fulfill the sensitivity of Δ
ω
∼
κ
1/2
. Particularly, we introduce the incoming wave as an effective gain to balance the loss and obtain a pair of purely real eigenfrequencies. There are absence of imaginary parts despite corresponding real parts shifts dramatically by using a neutral resonator, without a broadening of the reflection spectrum so that maintaining a high resolution on the sensitivity. This work may reveal the physical mechanics of a small perturbation at a high-order EP and promote applications in implanted medicine devices.
Ultra-high molecular weight polyethylene (UHMWPE) has great potential in the field of water-lubricated bearings. However, water-lubricated bearing made of pure UHMWPE produce significant heat and ...undergo physical damage under low speed and heavy load conditions. These performance issues can be improved by reinforcement with fibers that have excellent complementary properties to UHMWPE. Polyester fibers (PETFs) have high compressive strength and wear resistance, and corresponding oriented-fiber-reinforced-composites (OFRCs) wherein PETF acts as reinforcement show even better mechanical and tribological properties. In this study, the influence of PETF density on UHMWPE was investigated by systematic testing of different OFRCs. The results show that the optimal fiber density of composites with PETF oriented along the axial direction was between 1.1 wt% and 2.2 wt%, and that for heavy loads, performance deteriorated with increasing fiber density. Compared with UHMWPE, OFRCs with the optimal fiber density obtained from this study reduced friction coefficient by up to 25.93 % and wear volume by 22.67 %, respectively. Considering the low cost, high durability, and relatively low content (<2.2 wt%) necessary for enhanced properties, reinforcement with oriented PETF is a viable approach to enhance water lubrication performance of UHMWPE.
The low-frequency vibration and radiation performance of a locally resonant (LR) plate with periodic multiple resonators is studied in this paper, with both infinite and finite structure properties ...examined. For the finite cases, taking the LR plate attached with two periodic arrays of resonators as an example, the forced vibration response and the radiation efficiency are theoretically derived by adopting a general model with elastic boundary conditions. Through a comparison with the band structures calculated by the plane-wave-expansion method, it shows that the band gaps in the infinite LR plate are in good agreement with the vibration-attenuation bands in the finite LR plate, no matter what boundary conditions are applied to the latter. In contrast to the vibration reduction in the band gaps, the radiation efficiency of the finite LR plate is sharply increased in the band-gap frequency ranges. Furthermore, the acoustic power radiated from the finite LR plate can be seriously affected by its boundary conditions. For the LR plate with greater constraints, the acoustic power is reduced in the band-gap frequency ranges, while that from the one with fully free boundary conditions is increased. When further considering the damping loss factors of the resonators, the attenuation performance can be improved for both the vibration and radiation of the LR plate.
In order to suppress the transverse vibration of a plate, a quasi-zero-stiffness (QZS) resonator with tunable ultralow frequency bandgaps was introduced and analyzed. The resonator was designed by ...introducing the quasi-zero-stiffness systems into mass-in-mass resonators. The plane wave expansion method was employed to derive the bandgap characteristics of the locally resonant (LR) plate with QZS resonators, and corresponding simulations were carried out by finite element method (FEM). The results show that an LR plate with a QZS resonator can provide two bandgaps, and the ranges of the bandgaps agree well with the vibration attenuation bands calculated by FEM. Owing to the introduction of the QZS system, the bandgaps can be easily transferred to a lower frequency or even an ultralow frequency. The damping of the QZS resonators can effectively broaden the vibration attenuation bands. In addition, the differentiated design of the bandgap frequencies can be realized to obtain broadband low-frequency transverse wave suppression performance. Finally, a mechanical structure design scheme was proposed in order to achieve flexible adjustment of the bandgap frequency, which significantly increases the engineering applicability of QZS resonators.
It is widely believed that effective prediction of wastewater treatment results (WTR) is conducive to precise control of aeration amount in the wastewater treatment process (WTP). Conventional ...biochemical mechanism-driven approaches are highly dependent on complicated and redundant model parameters, resulting in low efficiency. Besides, sharp increase in business volume of wastewater treatment requires automatic operation technologies for this purpose. Under this background, researchers started to introduce the idea of data mining to model the WTP, in order to automatically predict WTR given inlet conditions and aeration amount. However, existing data-driven approaches for this purpose focus on modelling of the WTP at independent timestamps, neglecting sequential characteristics of timestamps during the long-term treatment process. To tackle the challenge, in this paper, a novel prediction and control framework through combination of convolutional neural network (CNN) and recurrent neural network (RNN) is proposed for prediction of the WTR. Firstly, the CNN model is utilized to automatically extract the local features of each independent timestamp in the WTP and make them encoded. Next, the RNN model is employed to represent global sequential features of the WTP on the basis of local feature encoding. Finally, we conduct a large number of experiments to verify efficiency and stability of the proposed prediction framework.
This work proposes a novel data-driven mechanism for prediction of wastewater treatment results through mixture of two neural network models.
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