The present work investigates the pressure fluctuation intensity and vortex characteristic of a mixed flow pump as turbine at pump mode with a tip clearance. The tip clearance between the blade tip ...and shroud can induce tip leakage flow and interact with main flow, which causes the unstable flow structure and complex vortex in the passage. The external characteristics of experimental results and numerical simulations are in agreement. With tip clearance increasing, the head and efficiency of pump decrease by 10.8% and 6.26%, respectively. The distribution of pressure fluctuation intensity is presented as a triangular shape under design flow rate. Results show that the tip leakage vortex (TLV) can be divided into four categories, namely, primary TLV, secondary TLV, entangled TLV, and dispersed TLV. The flow rate has a significant influence on the TLV structure and trajectory, and the starting point of the primary TLV shifts to approximately 20% of the blade chord at large flow rate. The relative vorticity transport equation is introduced to analyze the vortex derivation by using the relative vortex stretching, Coriolis force and viscous diffusion.
•Pressure fluctuation intensity presents to be a triangular shape.•Tip leakage vortex (TLV) can be divided into four categories.•Primary TLV, secondary TLV, entangled TLV and dispersed TLV.•Relative vorticity transport equation is used for the vortex derivation.•Relative vortex stretching item, Coriolis force item and viscous diffusion item.
Transient cavitating flows of a mixedflow PAT (pump as turbine) at pump mode are investigated experimentally and numerically. Radial force on principal axis is recorded and compared between pump with ...symmetrical and unsymmetrical tip clearance. Numerical simulation with improved cavitation model by modifying the vapor pressure is conducted, and the simulation results agree well with the experiments. Tip clearance has great influence on pump cavitation performance. The pump energy performance will deteriorate with tip clearance increasing. In addition, in comparison with the symmetrical tip clearance, the unsymmetrical tip clearance makes the pump cavitation performance worse. As the cavitation develops, the unsymmetrical tip clearance simultaneously influences the magnitude and direction of radial force, while the symmetrical tip clearance only influences the magnitude of radial force. The dominant frequencies of radial force of symmetrical and unsymmetrical tip clearances are related to the blade number and guide vane number, respectively. The maximum amplitude of force fluctuation for unsymmetrical tip clearance is 7 times that for symmetrical tip clearance.
•Cavitation performance and radial force of a mixed flow pump.•Symmetrical and unsymmetrical tip clearances.•Dominant frequencies are related to blade and vane number.•Maximum amplitudes of radial force fluctuations are different.
Bacterial infection and lack of bone tissue integration are two major concerns of orthopedic implants. In addition, osteoinductivity often decreases and toxicity may arise when antibacterial agents ...are introduced to increase the antibacterial ability. Here hybrid ZnO/polydopamine (PDA)/arginine-glycine-aspartic acid-cysteine (RGDC) nanorod (NR) arrays are designed and prepared on titanium (Ti) implants to not only enhance the osteoinductivity but also effectively kill bacteria simultaneously, which are ascribed to the selective physical puncture and the biofunctionalization of ZnO/PDA/RGDC nanorods during the competition between bacteria and osteoblasts. That is, owing to the much larger size of osteoblasts than bacteria, the hybrid NRs can puncture bacteria but not damage osteoblasts. Meanwhile, the cytocompatibility can be enhanced through the suppression of both reactive oxygen species and higher Zn2+ concentration by the covering of PDA and RGDC. The in vitro results confirm the selective puncture of the bacterial membrane and the better osteoinductivity. In vivo tests also show much higher antibacterial efficacy of the hybrid NRs with far less amounts of lobulated neutrophils and adherent bacteria in the surrounding tissues. In addition, the hybrid NRs also accelerate formation of new bone tissues (20.1% higher than pure Ti) and osteointegration between implants and newly formed tissues (32.0% higher than pure Ti) even in the presence of injected bacteria. This work provides a surface strategy for designing implants with desirable ability of osseointegration and infection prevention simultaneously, which will exhibit tremendous clinical potential in orthopedic and dental applications.
The application of photothermal therapy to treat bacterial infections remains a challenge, as the high temperatures required for bacterial elimination can damage healthy tissues. Here, we develop an ...exogenous antibacterial agent consisting of zinc-doped Prussian blue (ZnPB) that kills methicillin-resistant Staphylococcus aureus in vitro and in a rat model of cutaneous wound infection. Local heat triggered by the photothermal effect accelerates the release and penetration of ions into the bacteria, resulting in alteration of intracellular metabolic pathways and bacterial killing without systemic toxicity. ZnPB treatment leads to the upregulation of genes involved in tissue remodeling, promotes collagen deposition and enhances wound repair. The efficient photothermal conversion of ZnPB allows the use of relatively few doses and low laser flux, making the platform a potential alternative to current antibiotic therapies against bacterial wound infections.
Bone‐implant‐associated infections are common after orthopedic surgery due to impaired host immune response around the implants. In particular, when a biofilm develops, the immune system and ...antibiotic treatment find it difficult to eradicate, which sometimes requires a second operation to replace the infected implants. Most strategies have been designed to prevent biofilms from forming on the surface of bone implants, but these strategies cannot eliminate the biofilm when it has been established in vivo. To address this issue, a nonsurgical, noninvasive treatment for biofilm infection must be developed. Herein, a red‐phosphorus–IR780–arginine–glycine–aspartic‐acid–cysteine coating on titanium bone implants is prepared. The red phosphorus has great biocompatibility and exhibits efficient photothermal ability. The temperature sensitivity of Staphylococcus aureus biofilm is enhanced in the presence of singlet oxygen (1O2) produced by IR780. Without damaging the normal tissue, the biofilm can be eradicated through a safe near‐infrared (808 nm) photothermal therapy at 50 °C in vitro and in vivo. This approach reaches an antibacterial efficiency of 96.2% in vivo with 10 min of irradiation at 50 °C. Meanwhile, arginine–glycine–aspartic‐acid–cysteine decorated on the surface of the implant can improve the cell adhesion, proliferation, and osteogenic differentiation.
A red‐phosphorus–IR780–arginine–glycine–aspartic‐acid–cysteine film with photothermal and photodynamic properties is prepared on a bone implant. The susceptibility of bacteria to heat is enhanced in the presence of 1O2. This study presents a practicable and noninvasive strategy for rapid in situ biofilm eradication on bone implants in vivo under near‐infrared irradiation.
As an active defense technique to change asymmetry in cyberattack-defense confrontation, moving target defense research has become one of the hot spots. In order to gain better understanding of ...moving target defense, background knowledge and inspiration are expounded at first. Based on it, the concept of moving target defense is analyzed. Secondly, literature analysis method is adopted to explain the design principles and system architecture of moving target defense. In addition, some relevant key techniques are introduced from the aspects of strategy generation, shuffling implementation, and performance evaluation. After that, the applications of moving target defense in different network architectures are illustrated. Finally, existing problems and future trend in this field are elaborated so as to provide a basis for further study.
In order to overcome severe capacity fading of LiMn2O4 cathode lithium-ion battery, tris(trimethylsilyl) borate (TMSB) is used as an electrolyte additive. With 0.5 wt% TMSB addition into the ...electrolyte (EC/DMC with 1 M LiPF6), the capacity retention is significantly improved at both room temperature and 55 °C. The effects of the TMSB on the LiMn2O4 electrode are investigated via a combination of cyclability, capacity retention of high temperature storage, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Based on these results, it is suggested that the improved cyclability of the cells containing the TMSB additive is mainly originated from the participation in the formation of solid electrolyte interface (SEI) on the surface of electrode, the dissolution of LiF out of the SEI and the enhancement of cyclability of Li anode.
► TMSB used as additive to improve cyclability of LiMn2O4 cathode lithium-ion battery. ► The lithium-ion battery containing TMSB shows excellent capacity retention at 55 °C. ► TMSB participated in the formation of SEI on the surface of electrode. ► Enhancement of cyclability of Li anode by TMSB additive.
Large petroleum resources in deep sea, and huge market demands for petroleum need advanced petroleum extraction technology. The multiphase pump, which can simultaneously transport oil and gas with ...considerable efficiency, has been a crucial technology in petroleum extraction. A numerical approach with mesh generation and a Navier-Stokes equation solution is employed to evaluate the effects of gas volume fraction on energy performance and pressure fluctuations of a multiphase pump. Good agreement of experimental and calculation results indicates that the numerical approach can accurately simulate the multiphase flow in pumps. The pressure rise of a pump decreases with the increasing of flow rate, and the pump efficiency decreases with the increasing of GVF (the ratio of the gas volume to the whole volume). Results show that the dominant frequencies of pressure fluctuation in the impeller and diffuser are eleven and three times those of the impeller rotational frequency, respectively. Due to the larger density of water and centrifugal forces, the water aggregates to the shroud and the gas gathers to the hub, which renders the distribution of GVF in the pump uneven. A vortex develops at the blade suction side, near the leading edge, induced by the leakage flow, and further affects the pressure fluctuation in the impeller. The obvious vortex in the diffuser indicates that the design of the divergence angle of the diffuser is not optimal, which induces flow separation due to large diffusion ratio. A uniform flow pattern in the impeller indicates good hydraulic performance of the pump.
Periprosthetic infection is considered the main cause of implant failure, which is expected to be solved by fabricating an antibacterial coating on the surface of the implant. Nevertheless, systemic ...antibiotic treatment still represents the mainstream method for preventing infection, and few antibacterial coatings are applied clinically. This is because the externally introduced traditional antibacterial coatings suffer from the risk of invalidation and tissue toxicity induced by the consumption of antibacterial agents, degradation, and shedding. In this work, we proposed a rapid photo-sonotherapy by creating an oxygen deficiency on a titanium (Ti) implant through sulfur (S)-doping (Ti–S–TiO2–x ), which endowed the implants with great sonodynamic and photothermal ability. Without introducing an external antibacterial coating, it reached a high antibacterial efficiency of 99.995% against Staphylococcus aureus under 15 min near-infrared light and ultrasound treatments. Furthermore, bone infection was successfully treated after combination treatments, and improved osseointegration was observed. Importantly, the S-doped Ti implant immersed in water for 6 months showed an unchanged structure and properties, suggesting that the Ti implant with intrinsic modification showed stable antibacterial performance under exogenous stimuli with a high antibacterial performance in vivo. This photo-sonotherapy based on sulfur doping is also promising for cancer therapy with biosafety.
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