Search

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Magnetic fluid sealing (MFS) is one of the most advanced applications of magnetic fluids (MF). To improve the pressure resistance of the traditional MFS with a large gap, this paper proposes a large-gap divergent embedded magnetic fluid seal (DEMFS) structure with radial and axial sealing capabilities. Through the simulation analysis of the radial and axial seal gaps (0.5–0.8 mm) and the number of radial and axial pole teeth (PT), the theoretical pressure resistance was obtained. A large-gap DEMFS test bench was built to experimentally verify the simulation results, and the effects of the MF volume and shaft speed on the pressure resistance of the sealing device were also experimentally investigated and compared with the theoretical pressure resistance of the traditional MFS structure. The numerical simulation and experimental results that the experimental values of the DEMFS are in good agreement with the theoretical values. When the MF injection volume was 2.5 ml, the pressure resistance reached the maximum and tended to be stable. With the change in the size of the seal gap and the number of PT, the variation trend of the pressure resistance of the DEMFS was different from that of the traditional MFS. When the shaft speed was low, the low speed had almost no effect on the pressure resistance of the DEMFS. The axial seal gap and axial PT were beneficial to the sealing effect. [ABSTRACT FROM AUTHOR]

Due to the limitations in autogenous nerve grafting or Schwann cell transplantation, large gap peripheral nerve injuries require a bridging strategy supported by nerve conduit. Cell based therapies provide a novel treatment for peripheral nerve injuries. In this study, we first experimented an optimal scaffold material synthesis protocol, from where we selected the 10% GFD formula (10% GelMA hydrogel, recombinant human basic fibroblast growth factor and dental pulp stem cells (DPSCs)) to fill a cellulose/soy protein isolate composite membrane (CSM) tube to construct a third generation of nerve regeneration conduit, CSM-GFD. Then this CSM-GFD conduit was applied to repair a 15-mm long defect of sciatic nerve in a rat model. After 12 week post implant surgery, at histologic level, we found CSM-GFD conduit could regenerate nerve tissue like neuron and Schwann like nerve cells and myelinated nerve fibers. At physical level, CSM-GFD achieved functional recovery assessed by a sciatic functional index study. In both levels, CSM-GFD performed like what gold standard, the nerve autograft, could do. Further, we unveiled that almost all newly formed nerve tissue at defect site was originated from the direct differentiation of exogeneous DPSCs in CSM-GFD. In conclusion, we claimed that this third-generation nerve regeneration conduit, CSM-GFD, could be a promising tissue engineering approach to replace the conventional nerve autograft to treat the large gap defect in peripheral nerve injuries.

In order to improve the pressure capability of the ferrofluid seal under the condition of large sealing gap, a diverging stepped ferrofluid seal with a large gap and two magnetic sources was designed. The magnetic field distributions in the gap of the ferrofluid seal were calculated by finite element method. The effects of the pole teeth number, the height of the pole teeth and the sealing gap on the pressure capabilities of the diverging stepped ferrofluid seal are studied and compared with ordinary ferrofluid seal. The results show that the change of the radial pole teeth number has little effect on the pressure capability of the stepped ferrofluid seal. The pressure capability of stepped ferrofluid seal decreases with the increase of the axial pole teeth number. The pressure capability of the stepped ferrofluid seals reach maximum when the radial and axial pole teeth height is 0.6 mm. The pressure capability of stepped ferrofluid seal decreases as the radial sealing gap increases. The pressure capability of stepped ferrofluid seal decreases firstly and then increases with the increase of the axial sealing gap. Comparing with ordinary ferrofluid seal, the stepped ferrofluid seal has better pressure capability. [ABSTRACT FROM AUTHOR]

The diverging stepped magnetic fluid seal based on stepped labyrinth seal was an effective method to improve the capability of usual magnetic fluid seal with large gap. Pressure theory of the diverging stepped magnetic fluid seal was presented and a diverging magnetic fluid sealing with two magnetic sources was designed. The leakage location hypothesis in the diverging stepped magnetic fluid seal has been made. The magnetic field distributions in the radial and axial sealing gaps have been calculated by means of the finite element method of magnetic field and its maximum sealing capabilities have been calculated based on its pressure theory. The effects of radial and axial sealing gaps on the diverging stepped magnetic fluid seal have been obtained. The numerical and experimental results were analyzed and discussed. The results show that the theoretical pressure-resistant capabilities of the diverging stepped magnetic fluid seal with two magnetic sources agree well with its experimental pressure-resistant capabilities. The leakage path in the axial sealing gap located at its center position and the leakage path in the radial sealing gap located in the vicinity of the shaft. [ABSTRACT FROM AUTHOR]

To solve the problem of low pressure resistance of the conventional ferrofluid seal (FFS) under the condition of single magnetic source with large gap, which is difficult to meet the demand of vacuum sealing, the convergent FFS with stepped pole piece structure was designed. The designed structure is also compared with the conventional FFS structure. The effects of radial and axial sealing gaps (SGs), number of steps, step height on the pressure resistance and self-repairing ability of the seal were experimentally investigated. The results show that the new FFS structure can withstand 1 atm when the number of steps is 4 and the radial SG is 0.4 mm, which can provide a reference for vacuum sealing. The innovative FFS has a maximum pressure resistance 23 times higher than the conventional FFS for the same size. The self-repairing ability of the seal is negatively correlated with the radial and axial SG, the number of steps, and the height of the steps. The results of this study are important for the design of the FFS structure with single magnetic source that meets the requirements of a vacuum environment. • The ferrofluid seal with the stepped pole piece is designed. • The maximum pressure resistance of the new ferrofluid seal is 23 times higher than the conventional ferrofluid seal under the same size. • The purpose of this study is to provide a reference for the design of vacuum seals that can withstand 1 atm. [ABSTRACT FROM AUTHOR]

The application of traditional electrode materials for high-performance capacitive deionization (CDI) has been persistently limited by their low charge-storage capacities and slow salt removal rates. In order to improve the electrochemical performance, cobalt‑vanadium coated porous carbon gradient hollow spheres (Co 3 V 2 O 8 @C) with large internal spacing, and high pore structure was prepared in this paper to improve the ion mobility. The structure with the following characteristics: (1) Co 3 V 2 O 8 @C with a reversible ionic insertion/de-insertion and good electrical conductivity; (2) the increased lattice spacing effectively mitigates volume expansion during prolonged cycling; (3) it increases the utilization rate of the active center inside the electrode material and shows high electrochemical adsorption capacity by being applied to capacitive deionization. When applied to CDI, Co 3 V 2 O 8 @C has top CDI performance compared to the currently reported cobalt-based electrode materials. The holding capacities for different ions (Cl−, SO 4 2−, NO 3 −, and Na+) were 160, 161, 244, and 69 mg·g−1 with good cycling stability after 100 h. Our research provides a reasonable pathway for building the structure of high-capacity cobalt-based electrodes and further promoting the development of high-performance CDI electrode materials. [Display omitted] • Increased internal structure spacing enhances the utilization of active centers of electrode materials. • Demonstrates high electrochemical adsorption capacity in capacitive deionization applications. • The increased spacing effectively mitigates volume expansion during prolonged cycling. • Stability degradation during long cycles influenced by material morphology changes. [ABSTRACT FROM AUTHOR]

MXenes are a large family of two-dimensional (2D) early transition metal carbides that have shown great potential for a host of applications ranging from electrodes in supercapacitors and batteries to sensors to reinforcements in polymers. Here, on the basis of first-principles calculations, we predict that Mo2MC2O2 (M = Ti, Zr, or Hf), belonging to a recently discovered new class of MXenes with double transition metal elements in an ordered structure, are robust quantum spin Hall (QSH) insulators. A tight-binding (TB) model based on the dz²-, dxy-, and dx²-y²-orbital basis in a triangular lattice is also constructed to describe the QSH states in Mo2MC2O2. It shows that the atomic spin-orbit coupling (SOC) strength of M totally contributes to the topological gap at the Γ point, a useful feature advantageous over the usual cases where the topological gap is much smaller than the atomic SOC strength based on the classic Kane-Mele (KM) or Bernevig-Hughes-Zhang (BHZ) model. Consequently, Mo2MC2O2 show sizable gaps from 0.1 to 0.2 eV with different M atoms, sufficiently large for realizing room-temperature QSH effects. Another advantage of Mo2MC2O2 MXenes lies in their oxygen-covered surfaces which make them antioxidative and stable upon exposure to air. [ABSTRACT FROM AUTHOR]

To improve the pressure capacity of the magnetic fluid seal with a large sealing gap, a new type of stepped magnetic fluid seals was firstly proposed based on magnetic fluid seal with multiple magnetic sources or stepped labyrinth seals. A universal magnetic fluid seal with two permanent magnets and a diverging stepped magnetic fluid seal have been investigated by experimental methods. The experimental results of the both sealing structures have been compared and analyzed. The results indicate that the diverging stepped magnetic fluid seal shows good performance compared to the universal magnetic fluid seal without stepping structure and it is an effective method to improve magnetic fluid sealing capacity with a large gap. [ABSTRACT FROM AUTHOR]

In some special applications, especially in the military industry, a magnetic liquid sealing technique is needed to solve the problem of leakage in the large gap. To improve and verify the pressure capability of magnetic liquid seal with large gaps, a magnetic liquid sealing structure with multiple magnetic sources is designed. The sealing capability and self-healing capability of magnetic liquid seal with multiple magnetic sources with 0.4 mm, 0.5 mm, 0.6 mm and 0.7 mm gaps are investigated by using experimental methods. The relations between the experimental results of magnetic liquid seal with multiple magnetic source and the theoretical results of magnetic liquid seal with single magnetic source are analyzed. The results show that the sealing capability and self-healing capability of magnetic liquid seal with multiple magnetic source decrease with the increase in gap height; the pressure capabilities of magnetic liquid seal with multiple magnetic source are 4. 7 , 3. 8 , 2. 8 and 2. 5 times of that of a magnetic liquid seal with single magnetic source for four different sealing gaps. In addition, the magnetic liquid seals with large gaps and multiple magnetic sources have good self-healing capabilities. [ABSTRACT FROM AUTHOR]

Abstract: Centrifugal instability of Bingham fluids is investigated in Taylor–Dean flow when the gap size is large compared to the cylinders radii. To determine conditions for the onset of instability, an infinitesimal axisymmetric disturbance was introduced to the basic flow and its evolution in time was monitored using a normal-mode linear stability analysis. To avoid the problem with the stress discontinuity at the location of the yield surface(s), use was made of the Papanastasiou’s regularized variation of the Bingham model in order to obtain the basic flow velocity profiles. An eigenvalue problem was obtained for the exact Bingham fluid which was solved numerically using the collocation method. A plot of the neutral instability curve at different Bingham numbers suggests that the yield stress can have a stabilizing or destabilizing effect on Taylor–Dean flow depending on the sign and magnitude of the pressure gradient, and also on the sense of rotation of the two cylinders with respect to each other. [Copyright &y& Elsevier]

Abstract: The electronic properties of both Sc x Ga1−x As and Sc x Ga1−x N ternary alloy and superlattice systems are investigated within the first-principles full-potential linear muffin-tin orbitals method (FPLMTO) in its atomic sphere approximation (ASA) using the technique of empty spheres, which allows an accurate treatment of the interstitial regions. The phase transition from the rocksalt (B1) to the zinc blende (B3) structure is investigated and the possibility of zinc blende/zinc blende GaN/Sc x Ga1−x N and GaAs/Sc x Ga1−x As superlattices is expected. Wide and direct gaps are found to be possible in these systems, predicting them as good candidates for optoelectronic applications. [Copyright &y& Elsevier]

• Magnetic fluid seal device designed to test pressure resistance and durability. • Enhanced MFS sealing performance in large gap sealing structure. • Durability of dynamic seal decreases as rotating speed increases. • Increase in clearance decreases the durability. • Proposed structure has better critical sealing pressure than traditional structure. Magnetic fluid seals (MFSs) have been widely used as a gas seal because of its advantages such as low wear, zero leakage, and long service life. However, the MFS is generally unstable due to structural- and material-related challenges in a liquid environment. To improve the pressure resistance and durability of the sealing liquid, we proposed an improved structure, where the annular pole component is designed as a radially magnetized annular permanent magnet. Furthermore, the structural parameters are optimized to maximize the magnetic induction intensity in the sealing gap. An MFS test device was simultaneously designed, according to the optimized results, to test the pressure resistance and durability under static and dynamic conditions. The results show that the pressure resistance and durability of the improved MFS structure is better than those of the traditional structures, specifically for a large gap structure. Furthermore, in a static seal, the sealing performance depends on the magnetic fluid magnetic saturation rather than other physical parameters, while in dynamic sealing, although magnetic saturation is a primary factor, the viscosity of the magnetic fluid also affects the sealing performance. Furthermore, the high-viscosity magnetic fluid had a higher critical pressure, while the low-viscosity magnetic fluid improved the durability of the seal. This result provides a reference for designing a magnetic fluid sealing device in a liquid environment. [ABSTRACT FROM AUTHOR]

Abstract: This is the second part of the study of soil–structure interaction (SSI) and ground motion spatial variation effects on bridge pounding responses. The first part [Chouw N, Hao H. Significance of SSI and non-uniform near-fault ground motions in bridge response I: Effect on response with conventional girder gap. J Eng Struct. [in press]] concentrated on studying the responses of bridges with a traditional expansion joint between adjacent girders. The main objective of this second paper is to investigate the influence of spatial variation of ground motions and SSI on the minimum total gap that a modular expansion joint system (MEJS) between two bridge frames must have to prevent any pounding between the adjoined girders. This minimum total gap is critical in a MEJS design because it ensures intact expansion joint and adjacent girders. Additional investigations of pounding response with a large total gap of a MEJS are performed to study the characteristics of pounding responses when collision does occur e.g. due to unintended underestimation of the ground excitation magnitude, which may be different from the pounding responses between bridge girders with a small gap of a conventional expansion joint. The spatially varying ground excitations are simulated stochastically based on an empirical near-source response spectrum and an empirical coherency loss function. The investigation reveals that neglecting spatial variation of ground motions and SSI can significantly underestimate the total gap of a MEJS required to avoid pounding between the adjacent bridge girders. The results also show that pounding between girders with a large gap of a MEJS in general causes stronger impact forces. Compared with the results reported in the first part of this study, using a MEJS with a large gap is likely to completely preclude bridge girder pounding, and consequently to prevent local damage at the girder ends. However, a large girder movement results in large bending moment in bridge piers, which compensates the advantages of using MEJS in bridges to resist earthquake loading. [Copyright &y& Elsevier]

To solve the problems of bus bunching and large gaps, this study combines bus holding and speed adjusting to alleviate them respectively considering the characteristics of passenger's perceived waiting time. The difference between passenger's perceived waiting time at stops and actual time is described quantitatively through the expected waiting time of passengers. Bus holding based on a threshold method is implemented at any stops for bunching buses, and speed adjusting based on a Markovian decision model is implemented at limited stops for lagging buses. Simulations based on real data of a bus route show that the integrated control strategy is able to improve the service reliability and to decrease passengers' perceived waiting time at stops. Several insights have been uncovered through performance analysis: (1) The increase of holding control strength results in improvement of the headway regularity, and leads to a greater perceived waiting time though; (2) Compared to traveling freely, suitable speed guidance will not slow down the average cruising speed in the trip; (3) The scale of passenger demand and through passengers are the two key factors influencing whether a stop should be selected as a speed-adjusting control point. [ABSTRACT FROM AUTHOR]

Due to the limitations in autogenous nerve grafting or Schwann cell transplantation, large gap peripheral nerve injuries require a bridging strategy supported by nerve conduit. Cell based therapies provide a novel treatment for peripheral nerve injuries. In this study, we first experimented an optimal scaffold material synthesis protocol, from where we selected the 10% GFD formula (10% GelMA hydrogel, recombinant human basic fibroblast growth factor and dental pulp stem cells (DPSCs)) to fill a cellulose/soy protein isolate composite membrane (CSM) tube to construct a third generation of nerve regeneration conduit, CSM-GFD. Then this CSM-GFD conduit was applied to repair a 15-mm long defect of sciatic nerve in a rat model. After 12 week post implant surgery, at histologic level, we found CSM-GFD conduit could regenerate nerve tissue like neuron and Schwann like nerve cells and myelinated nerve fibers. At physical level, CSM-GFD achieved functional recovery assessed by a sciatic functional index study. In both levels, CSM-GFD performed like what gold standard, the nerve autograft, could do. Further, we unveiled that almost all newly formed nerve tissue at defect site was originated from the direct differentiation of exogeneous DPSCs in CSM-GFD. In conclusion, we claimed that this third-generation nerve regeneration conduit, CSM-GFD, could be a promising tissue engineering approach to replace the conventional nerve autograft to treat the large gap defect in peripheral nerve injuries., Competing Interests: The authors declare that there is no known conflict of interest that could influence the findings reported in this paper, neither at personal nor at organizational level., (© 2020 [The Author/The Authors].)

MXenes are a large family of two-dimensional (2D) early transition metal carbides that have shown great potential for a host of applications ranging from electrodes in supercapacitors and batteries to sensors to reinforcements in polymers. Here, on the basis of first-principles calculations, we predict that Mo 2 MC 2 O 2 (M = Ti, Zr, or Hf), belonging to a recently discovered new class of MXenes with double transition metal elements in an ordered structure, are robust quantum spin Hall (QSH) insulators. A tight-binding (TB) model based on the d z 2 -, d xy -, and d x 2 -y 2 -orbital basis in a triangular lattice is also constructed to describe the QSH states in Mo 2 MC 2 O 2 . It shows that the atomic spin-orbit coupling (SOC) strength of M totally contributes to the topological gap at the Γ point, a useful feature advantageous over the usual cases where the topological gap is much smaller than the atomic SOC strength based on the classic Kane-Mele (KM) or Bernevig-Hughes-Zhang (BHZ) model. Consequently, Mo 2 MC 2 O 2 show sizable gaps from 0.1 to 0.2 eV with different M atoms, sufficiently large for realizing room-temperature QSH effects. Another advantage of Mo 2 MC 2 O 2 MXenes lies in their oxygen-covered surfaces which make them antioxidative and stable upon exposure to air.

The quantum spin Hall (QSH) effect predicted in silicene has raised exciting prospects of new device applications compatible with current microelectronic technology. Efforts to explore this novel phenomenon, however, have been impeded by fundamental challenges imposed by silicene's small topologically nontrivial band gap and fragile electronic properties susceptible to environmental degradation effects. Here we propose a strategy to circumvent these challenges by encapsulating silicene between transition-metal dichalcogenides (TMDCs) layers. First-principles calculations show that such encapsulated silicene exhibit a two-orders-of-magnitude enhancement in its nontrivial band gap, which is driven by the strong spin-orbit coupling effect in TMDCs via the proximity effect. Moreover, the cladding TMDCs layers also shield silicene from environmental gases that are detrimental to the QSH state in free-standing silicene. The encapsulated silicene represents a novel two-dimensional topological insulator with a robust nontrivial band gap suitable for room-temperature applications, which has significant implications for innovative QSH device design and fabrication.