Wind-Vortex-Induced Vibrations of a Deepwater Jacket Pipe and Vibration Suppression Using a Nonlinear Energy Sink

The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position on the suppression effect.In this work,the wind-vortex-induced vibration of an elastic pipe of a deepwater jacket was studied,and vibrations were suppressed by using an NES.A van der Pol wake oscillator was used to simulate vortex-induced force,and the dynamic equation of the pipe considering the NES was established.The Galerkin method was applied to discretize the motion equation,and the vortex-induced vibration(VIV)of the pipe at reduced wind speeds was numerically analyzed.The novelty of this research is that particle swarm optimization was used to optimize the parameters of the NES to improve vibration suppression.The influence of the installation position,nonlinear stiffness,and damping parameters of the NES on vibration suppression was analyzed.Results showed that the optimized parameter combinations of the NES can effectively reduce wind-vortex-induced pipe vibration.The installation position of the NES had a significant effect on vibration suppression,and the midpoint of the pipe was the optimal NES installation position.An increase in stiffness or a 10% decrease in damping may cause vibration suppression failure.The results of this study provide some guidance for VIV suppression in deepwater jacket pipes.

Suppression effect of jet flow on pulsating pressure of cavity using scale-adaptive simulation model

The suppression of the aerodynamic noise in the cavity has a great significance to solve relevant puzzles of weapon bays. Acoustic field of the standard cavity model is simulated by using the computational fluid dynamics technology based on scale-adaptive simulation （SAS） model. The results obtained by the proposed method in this paper show reasonable agreement with experiments. On the basis of this, effect of different jet flow rates on the time-averaged variables, turbulent kinetic energy, root mean square （RMS） of sound pressure, sound sources distribution and the pulsating pressure distribution in the cavity is studied. The analysis shows that the jet flow has great influence on the cavity flow field and the distribution of pulsating pressure RMS by changing the morphology of the shear layer. The most obvious of these measures is spout4 configuration, the influence mainly in the form of reducing the pulsating pressure of the whole cavity and changing the sound pressure level in the far field. The results show that different jet flow rates have different control effects on pulsating pressure in the cavity and sound pressure level in the far field. Furthermore, the jet flow rates and the suppression effect on the pulsating pressure have no linear relation.

Advanced preparation and application of bimetallic materials in lithium-sulfur batteries:A review

Lithium-sulfur(Li-S)batteries are considered highly promising as next-generation energy storage systems due to high theoretical capacity(2600 Wh kg^(-1))and energy density(1675 mA h g^(-1))as well as the abundant natural reserves,low cost of elemental sulfur,and environmentally friendly properties.However,several challenges impede its commercialization including low conductivity of sulfur itself,the severe“shuttle effect”caused by lithium polysulfides(LiPSs)during charge–discharge processes,volume expansion effects and sluggish reaction kinetics.As a solution,polar metal particles and their compounds have been introduced as the main hosts for sulfur cathode due to their robust catalytic activity and adsorption capability,effectively suppressing the“shuttle effect”of Li PSs.Bimetallic alloys and their compounds with multi-functional properties exhibit remarkable electrochemical performance more readily when compared to single-metal materials.Well-designed bimetallic materials demonstrate larger specific surface areas and richer active sites,enabling simultaneous high adsorption capability and strong catalytic properties.The synergistic effect of the“adsorption-catalysis”sites accelerates the adsorptiondiffusion-conversion process of Li PSs,ultimately achieving a long-lasting Li-S battery.Herein,the latest progress and performance of bimetallic materials in cathodes,separators,and interlayers of Li-S batteries are systematically reviewed.Firstly,the principles and challenges of Li-S batteries are briefly analyzed.Then,various mechanisms for suppressing“shuttle effects”of Li PSs are emphasized at the microscale.Subsequently,the performance parameters of various bimetallic materials are comprehensively summarized,and some improvement strategies are proposed based on these findings.Finally,the future prospects of bimetallic materials are discussed,with the hope of providing profound insights for the rational design and manufacturing of high-performance bimetallic materials for LSBs.

Effect of oxygen on regulation of properties of moderately boron-doped diamond films

Regulation of oxygen on properties of moderately boron-doped diamond films is fully investigated.Results show that,with adding a small amount of oxygen(oxygen-to-carbon ratio<5.0%),the crystal quality of diamond is improved,and a suppression effect of residual nitrogen is observed.With increasing ratio of O/C from 2.5%to 20.0%,the hole concentration is firstly increased then reduced.This change of hole concentration is also explained.Moreover,the results of Hall effect measurement with temperatures from 300 K to 825 K show that,with adding a small amount of oxygen,boron and oxygen complex structures(especially B_(3)O and B_(4)O)are formed and exhibit as shallow donor in diamond,which results in increase of donor concentration.With further increase of ratio of O/C,the inhibitory behaviors of oxygen on boron leads to decrease of acceptor concentration(the optical emission spectroscopy has shown that it is decreased with ratio of O/C more than 10.0%).This work demonstrates that oxygen-doping induced increasement of the crystalline and surface quality could be restored by the co-doping with oxygen.The technique could achieve boron-doped diamond films with both high quality and acceptable hole concentration,which is applicable to electronic level of usage.

Inhibiting effect of tungstic compounds on glucose hydrogenation over Ru/C catalyst

The effect of acid component including various conventional acids and tungstic compounds on glucose hydrogenation over a series of binary catalyst system containing Ru/C catalyst was investigated. The results showed that HC1, H2SO4, H3BO3, H3PO4, and HNO3 had negligible effect, while all the tungstic compounds imposed inhibiting effects on the hydrogenation of glucose over Ru/C catalyst, and the suppressing effect followed the order of H2WO4〉HPW〉WO3〉AMT〉HSiW. This order is the same as the order of ethylene glycol （EG） yields in the one-pot conversion of glucose to EG, suggesting the important role of competition between glucose hydrogenation and retro-aldol condensation in controlling the selectivity of EG.

Suppressing Effects of Ag Wetting Layer on Surface Conduction of Er Silicide/Si(001) Nanocontacts

Current-voltage electrical characteristics of Er silicide/Si（001） nanocontacts are measured in situ in a scanning tunneling microscopy system. Introduced as a new technique to suppress surface leakage conduction on Si（001）,a silver wetting layer is evaporated onto the substrate surface kept at room temperature with Er Si2 nanoislands already existing. The effects of the silver layer on the current-voltage characteristics of nanocontacts are discussed.Our experimental results reveal that the silver layer at coverage of 0.4–0.7 monolayer can suppress effectively the current contribution from the surface conduction path. After the surface leakage path of nanocontacts is obstructed, the ideality factor and the Schottky barrier height are determined using the thermionic emission theory, about 2 and 0.5 eV, respectively. The approach adopted here could shed light on the intrinsic transport properties of metal-semiconductor nanocontacts.

Suppressive effect of dexamethasone on the neutrophil expression of CD18 in rats with radiation induced brain edema

BACKGROUND： Stereo-tactic radiation therapy （SRT） is widely used to treat intracranial diseases, but some patients suffered from radiation induced brain edema after SRT. Once radiation induced brain edema occurs, the treatment is quite difficult, and it always leads to a poor outcome. Dexamethasone has certain therapeutic effect on traumatic brain edema, but the biological mechanism is still unclear. OBJECTIVE ： To observe the effect of dexamethasone on the neutrophil expression of CD18.DESIGN ： A randomized control observation.SETTING： Changhai Hospital of the Second Military Medical University of Chinese PLA. MATERIALS ： The experiment was carried out in Changhai Hospital of the Second Military Medical University of Chinese PLA from January 1999 to December 1999. Twenty SD rats （male and female each in half） weighing （250±50） g were used. METHODS： Twenty SD rats were divided into four groups at random. ① Blank control group （n=5）： The rats were not treated without dexamethasone or irradiation;② Irradiation group （n=5）： The rats were given irradiation but no dexamethasone treatment; ③ Irradiation＋1 mg/kg dexamethasone group （n=5）; The rats were treated with irradiation and dexamethasone of 1 mg/kg; ④Irradiation＋5 mg/kg dexamethasone group （n=5）： The rats were treated with irradiation and dexamethasone of 5 mg/kg. The heads of the rats were irradiated with 10 MeV X-ray （30 Gy）, and brain tissue was removed after 2 weeks to observe the pathological changes. Blood samples were taken from the carotid artery, gradient centrifugation was used, and neutrophile layer was obtained, the level of neutrophile expression of CD18 mRNA and quantity of membrane proteins in blood were detected with Northern blot and flow cytometry respectively. MAIN OUTCOME MEASURES： ① Blood cell count; ② Pathological results; ③ level of neutrophile expression of CD18 mRNA and quantity of membrane proteins. RESULTS ： All the 20 SD rats were involved in the analysis of results without deletion. At 2 weeks after irradiation, obvious cell injury could be observed under light microscope. The level of neutrophile expression of CD18 mRNA and quantity of membrane proteins in blood were obviously increased, but the severity of cell injury was relieved in the irradiation＋1 and 5 mg/kg dexamethasone groups, and the CD18 expression was markedly suppressed （P 〈 0.05）, and the suppression was more obvious in the irradiation＋5 mg/kg dexamethasone group than in the irradiation＋1 mg/kg dexamethasone group （P 〈 0.01 ）. CONCLUSION： Dexamethasone can reduce the radiation induced brain edema by inhibiting the expression of CD18.

A review on electronically conducting polymers for lithium-sulfur battery and lithium-selenium battery:Progress and prospects

Lithium-sulfur(Li-S) batteries and lithium-selenium(Li-Se) batteries,as environmental protection energy storage systems with outstanding theoretical specific capacities and high energy densities,have become the hotspots of current researches.Besides,elemental S(Se) raw materials are widely sourced and their production costs are both low,which make them considered one of the new generations of high energy density electrochemical energy storage systems with the most potential for development.However,poor conductivity of elemental S/Se and the notorious "shuttle effect" of lithium polysulfides(polyselenides) severely hinder the commercialization of Li-S/Se batteries.Thanks to the excellent electrical conductivity and strong absorption of lithium polysulfide(polyselenide) about electronically conducting polymer,some of the above thorny problems have been effectively alleviated.The review presents the fundamental studies and current development trends of common electronically conducting polymers in various components of Li-S/Se batteries,which involves polyaniline(PANI) polypyrrole(PPy),and polythiophene(PTh) with its derivatives,e.g.polyethoxythiophene(PEDOT) and poly(3,4-ethylene dioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS).Finally,the review not only summarizes the research directions and challenges facing the application of electronically conducting polymers,but also looks forward to the development prospects of them,which will provide a way for the practical use of electronically conducting polymers in Li-S/Se batteries with outstanding electrochemical properties in the short run.

The Relationship between College Graduate’s Dual Self-Consciousness and Job Search Clarity: The Mediating Role of Perceived Stress

The aim of the study was to explore the relationship between college graduates’dual self-consciousness,job search clarity and perceived stress,and reveal the mediating role of perceived stress between dual self-consciousness and job search clarity.In this study,467 college graduates were investigated using the Dual Self-Consciousness Scale,Job Search Clarity Scale,and Perceived Stress Scale.After controlling for gender,age,and region,the results revealed that:(1)private self-consciousness has a significant positive predictive effect on job search clarity;(2)perceived stress has a significant negative predictive effect on job search clarity;(3)perceived stress plays partial mediation effects between private self-consciousness and job search clarity;(4)perceived stress plays complete mediation effects between public self-consciousness and job search clarity;(5)perceived stress has suppressing effects between public self-consciousness and job search clarity.

A current-mode DAC unit circuit with smooth transition

The digital-to-analogue converter （DAC） plays a significant role in modern electronic systems, and current-mode DACs are widely used due to their excellent properties. However, the non-ideal transition at switching instants of the unit circuit will directly affect the performance of the current-mode DAC. The parasitic effects resulting in non-ideal transition are analyzed in this paper. A simple structure unit circuit is proposed to diminish the non-ideal transition. The simulation results show that the parasitic effects are suppressed effectively, and a smoother output transition is achieved. The feasibility of the proposed current-mode DAC unit circuit is verified by the application in a frequency jitter circuit.