Design and optimization of fluid lubricated bearings operated with extreme working performances——a comprehensive review

Fluid lubricated bearings have been widely adopted as support components for high-end equipment in metrology,semiconductor devices,aviation,strategic defense,ultraprecision manufacturing,medical treatment,and power generation.In all these applications,the equipment must deliver extreme working performances such as ultraprecise movement,ultrahigh rotation speed,ultraheavy bearing loads,ultrahigh environmental temperatures,strong radiation resistance,and high vacuum operation,which have challenged the design and optimization of reliable fluid lubricated bearings.Breakthrough of any related bottlenecks will promote the development course of high-end equipment.To promote the advancement of high-end equipment,this paper reviews the design and optimization of fluid lubricated bearings operated at typical extreme working performances,targeting the realization of extreme working performances,current challenges and solutions,underlying deficiencies,and promising developmental directions.This paper can guide the selection of suitable fluid lubricated bearings and optimize their structures to meet their required working performances.

Improving the electrical performances of InSe transistors by interface engineering

InSe has emerged as a promising candidate for next-generation electronics due to its predicted ultrahigh electrical performance.However,the efficacy of the InSe transistor in meeting application requirements is hindered due to its sensitivity to interfaces.In this study,we have achieved notable enhancement in the electrical performance of InSe transistors through interface engineering.We engineered an InSe/h-BN heterostructure,effectively suppressing dielectric layer-induced scattering.Additionally,we successfully established excellent metal-semiconductor contacts using graphene ribbons as a buffer layer.Through a methodical approach to interface engineering,our graphene/InSe/h-BN transistor demonstrates impressive on-state current,field-effect mobility,and on/off ratio at room temperature,reaching values as high as 1.1 mA/μm,904 cm^(2)·V^(-1)·s^(-1),and>10~6,respectively.Theoretical computations corroborate that the graphene/InSe heterostructure shows significant interlayer charge transfer and weak interlayer interaction,contributing to the enhanced performance of InSe transistors.This research offers a comprehensive strategy to elevate the electrical performance of InSe transistors,paving the way for their utilization in future electronic applications.

Elliptical encirclement control capable of reinforcing performances for UAVs around a dynamic target

Most researches associated with target encircling control are focused on moving along a circular orbit under an ideal environment free from external disturbances.However,elliptical encirclement with a time-varying observation radius,may permit a more flexible and high-efficacy enclosing solution,whilst the non-orthogonal property between axial and tangential speed components,non-ignorable environmental perturbations,and strict assignment requirements empower elliptical encircling control to be more challenging,and the relevant investigations are still open.Following this line,an appointed-time elliptical encircling control rule capable of reinforcing circumnavigation performances is developed to enable Unmanned Aerial Vehicles(UAVs)to move along a specified elliptical path within a predetermined reaching time.The remarkable merits of the designed strategy are that the relative distance controlling error can be guaranteed to evolve within specified regions with a designer-specified convergence behavior.Meanwhile,wind perturbations can be online counteracted based on an unknown system dynamics estimator(USDE)with only one regulating parameter and high computational efficiency.Lyapunov tool demonstrates that all involved error variables are ultimately limited,and simulations are implemented to confirm the usability of the suggested control algorithm.

Ballistic performances of the hourglass lattice sandwich structures under high-velocity fragments

In this paper,the numerical simulation method is used to study the ballistic performances of hourglass lattice sandwich structures with the same mass under the vertical incidence of fragments.Attention is paid to elucidating the influences of rod cross-section dimensions,structure height,structure layer,and rod inclination angle on the deformation mode,ballistic performances,and ability to change the ballistic direction of fragments.The results show that the ballistic performances of hourglass lattice sandwich structures are mainly affected by their structural parameters.In this respect,structural parameters optimization of the hourglass lattice sandwich structures enable one to effectively improve their ballistic limit velocity and,consequently,ballistic performances.

Interfacial friction effects on sealing performances of elastomer packer

Elastomer sealing performance is of critical importance for downhole tools application including the use of fracturing(Frac)plugs during multi-stage hydraulic fracking.In practice sealing performances of such plugs are normally evaluated through pressure tests,and in numerical simulation studies,maximum contact stress,average contact stress and contact length data are used to determine sealing quality between a packer and casing.In previous studies,the impact of friction forces on sealing performance is often overlooked.This work aims to fill this knowledge gap in determining the influence of friction forces on elastomer packer sealing performances.We first determined the most appropriate constitutive hyperelastic model for the elastomers used in frac plug.Then we compared analytical calculation results with Finite Element Analysis simulation using a simplified tubular geometry and showed the significant influences on interfacial friction on elastomer packer stress distribution,deformation,and contact stress after setting.With the demonstration of validity of FEA method,we conducted systematic numerical simulation studies to show how the interfacial friction coefficients can affect the maximum contact stress,average contact stress,contact stress distribution,and maximum mises stress for an actual packer used in plug products.In addition,we also demonstrated how the groove in a packer can affect packer deformation and evolvement during setting with the consideration of interfacial stress.This study underscores the critical role that friction forces play in Frac plug performance and provides a new dimension for optimizing packer design by controlling interfacial interactions at the packer contact surfaces.

Aseismic performances of constrained damping lining structures made of rubber-sand-concrete

Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures.In this study,a constrained damping structure for underground tunnel lining,using a rubber-sand-concrete(RSC)as the aseismic material,is proposed.The aseismic performances of constrained damping structure were investigated by a series of hammer impact tests.The damping layer thickness and shape effects on the aseismic performance such as effective duration and acceleration amplitude of time-domain analysis,composite loss factor and damping ratio of the transfer function analysis,and total vibration level of octave spectrum analysis were discussed.The hammer impact tests revealed that the relationship between the aseismic performance and damping layer thickness was not linear,and that the hollow damping layer had a better aseismic performance than the flat damping layer one.The aseismic performances of constrained damping structure under different seismicity magnitudes and geological conditions were investigated.The effects of the peak ground acceleration(PGA)and tunnel overburden depth on the aseismic performances such as the maximum principal stress and equivalent plastic strain(PEEQ)were discussed.The numerical results show the constrained damping structure proposed in this paper has a good aseismic performance,with PGA in the range(0.2-1.2)g and tunnel overburden depth in the range of 0-300 m.

Physical-Rheological Properties and Performances of Rejuvenated(Styrene-Butadiene-Styrene)Asphalt with Polymerized-MDI and Aromatic Oil

Traditional asphalt rejuvenators,like aromatic oil(AO),are known to be effective in improving the low-temperature properties and fatigue performances of aged SBS(styrene-butadiene-styrene)modified asphalt(SBSMA)binders and mixtures.However,these rejuvenators inevitably compromise their high-temperature properties and deformation resistances because they dilute asphalt binder but do not fix the damaged structures of aged SBS.In this study,a highly-active chemical called polymerized 4,4-diphenylmethane diisocyanate(PMDI)was used to assist the traditional AO asphalt rejuvenator.The physical and rheological characteristics of rejuvenated SBSMA binders and the moisture-induced damage and rut deformation performances of corresponding mixtures were comparatively evaluated.The results showed that the increasing proportion of AO compromises the hightemperature property and hardness of aged SBSMA binder,and an appropriate amount of PMDI works to compensate such losses;3%rejuvenator at mass ratio of AO:PMDI=70:30 can have a rejuvenated SBSMA binder with a high-temperature performance similar to that of fresh binder,approximately at 71.4°C;the use of AO can help reduce the viscosity of PMDI rejuvenated SBSMA binder for improving its workability;PMDI can help improve the resistance of AO rejuvenated SBSMA binder to deformation,especially at elevated temperatures,through its chemical reactions with aged SBS;moisture induction can enhance the resistance to damage of rejuvenated mixtures containing AO/PMDI or only PMDI;and the rejuvenator with a mass ratio of AO:PMDI=70:30 can lead the rejuvenated mixture to meet the application requirement,with a rut depth of only 2.973 mm,although more PMDI can result in a higher resistance of rejuvenated mixtures to high-temperature deformation.

Fruit Powder of Tetrapleura tetraptera in Local Feed on Some Zootechnical Performances of Juveniles of Clarias gariepinus in Concrete Tank

This study focused on the supplementation of four-sided spice fruit powder (Tetrapleura tetraptera) on some zootechnical performances of juveniles of Clarias gariepinus and was carried out from February 14 to July 20 at the Massoma Fish Farm of Bojongo Mbeidi located in the Littoral Region, Department of Wouri, Douala IV district. The farm benefits from a climate favorable to aquaculture activity. For this purpose, five (5) treatments were tested including T0+ (imported feed), T0-, T0.3, T0.4, and T0.5 respectively for the treatments with 0% supplemented food;0.3%;0.4% and 0.5% of Tetrapleura tetraptera powder. A total of 450 Clarias gariepinus fry with an initial average weight of 7 ± 1.5 g, were distributed in happas of 0.49 m2 each placed in Triplicate in a completely randomized device. Four isoprotein foods with 38% crude protein were formulated to feed these fry at 7% of their biomass per day for 15 days then to their fullness until the end of the experiment. Intermediate fishing was carried out every fortnight. 75 days later, the results recorded show that the highest average survival rate (96.44% ± 3.5%) was recorded with the subjects fed feed supplemented with 0.4% T. tetraptera powder. The average weight (120.93 ± 67.20), weight gain (113.93 ± 67.20), specific growth rate (3.64 ± 0.79% g/d) and total lengths and standard (26.43 ± 1.9 and 23.66 ± 1.76) the highest were recorded with the T0+ treatment (imported feed). The highest conditioning factor K (2.14 ± 0.15) was recorded with the treatment supplemented with 0.4% T. tetraptera. The lowest conversion ratio (1.28) was recorded with the treatment fed with imported blue crown food (T0+). Furthermore, the lowest production cost was recorded with the treatment supplemented with 0.4% T. tetraptera. It appears from this study that the juveniles of C. gariepinus better value the feed substituted with 0.4% of the powder of four sides (Tetrapleura tetraptera).

Video Games and School Performances of Dakar High School Students

The triptych (Smartphones, Video games, adolescents) has imposed itself on the collective consciousness in the form of questioning to the point of becoming a social phenomenon. It thus raises concerns about the uses that adolescents make of it and the effects on their academic performance, which we proposed to study among middle school students from the Dakar academy inspection. Where appropriate, we used mixed methods with the collection techniques of questionnaire survey, semi-structured interviews respectively with middle school students, adults (parents, supervisors, teachers, etc.), participant observation and literature review. Concretely, before accessibility to video games, the middle school students were more idle and well-behaved, watched a lot of TV, played with their brothers and sisters or did household chores. The majority of young people had good, very good or excellent conduct and their averages were fair, fairly good or good. With access to a diverse digital environment, middle school students have passionately turned to video games. As a result, their learning time, concentration and submission to parental injunctions have declined significantly. This situation negatively affected their academic performance and encouraged bad behavior.

Enhanced Electrochemical Performances of Ni Doped Cr_(8)O_(21)Cathode Materials for Lithium-ion Batteries

Cathode materials,nickel doped Cr_(8)O_(21),were synthesized by a solid-state method.The effects of Ni doping on the electrochemical performances of Cr_(8)O_(21) were investigated.The experimental results show that the discharge capacities of the samples depend on the nickel contents,which increases firstly and then decreases with increasing Ni contents.Optimized Ni_(0.5)Cr_(7.5)O_(21)delivers a first capacity up to 392.6 m Ah·g^(-1)at 0.1C.In addition,Ni doped sample also demonstrates enhanced cycling stability and rate capability compared with that of the bare Cr_(8)O_(21).At 1 C,an initial discharge capacity of 348.7 m Ah·g^(-1)was achieved for Ni_(0.5)Cr_(7.5)O_(21),much higher than 271.4 m Ah·g^(-1)of the un-doped sample,with an increase of more than 28%.Electrochemical impedance spectroscopy results confirm that Ni doping reduces the growth of interface resistance and charge transfer resistance,which is conducive to the electrochemical kinetic behaviors during charge-discharge.

Bamboo Fiber Modified Asphalt Mixture Proportion Design and Road Performances Based on Response Surface Method

In order to comprehensively utilize the remaining bamboo residue of bamboo products,this paper presents a research on recycling the bamboo fibers from bamboo residue for improving the performance of the asphalt mixtures.First of all,the basic performance parameters of sinocalamus affinis fiber,phyllostachys pubescens fiber,green bamboo fiber were tested and analyzed,and the optimal content and length were put forward.Then,the mix ratio design of the bamboo fiber modified asphalt mixture was further designed through the response surface method,and was verified the rationality of the mix ratio.Finally,the mixture specimens were made according to the experimental design mix ratio,and the high temperature,low temperature performance and moisture susceptibility of the bamboo fiber modified mixtures asphalt were tested.The results showed that the high temperature performance,low temperature performance and moisture susceptibility of bamboo fiber modified asphalt mixtures were improved compared with the performance of SBS modified asphalt mixture.When the length of bamboo fiber is 7.25 mm and the content of 0.22%,the road performance of the asphalt mixture was optimal.Consequentially,the decomposition of bamboo residue into bamboo fiber and its application in asphalt pavement can improve the reuse of bamboo waste,with remarkable environmental benefits and great promotion value.

Influence of Erosion Induced by NaCl on the Mechanical Performances of Alkali-Activated Mineral Admixtures

In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated.The considered NaCl concentration is 3%.The effect of polypropylenefibers on the mechanical strengths is also examined.Scanning electron microscopy(SEM),thermogravimetry(TG)and X-ray diffraction(XRD)are selected to discern the mechanisms underpinning the NaCl-induced erosion.The obtained results indicate that the best results in terms of material resistance are obtained with admixtures containing 60%BFS and 40%FA in terms of mass ratio and 3%polypropylenefibers in terms of volume ratio.The maximum rates of decrease of theflexural,compressive and bonding strengths after 300 NaCl F-T cycles are 21.5%,20.3%and 22.6%,respec-tively.The corresponding rates of decrease due to NaCl D-W alternations are 28.1%,26.1%and 31.5%,respec-tively.The TG curves show that the alkali-activating activity of BFS is higher than that of FA.Moreover,in thefirst case,the microstructure of the hydration products is more compact.The results also show that NaCl F-T cycles lead to increasing cracks in the alkali-activated BFS.

Ultrasonic solidification mechanism and optimized application performances of ternary Mg_(71.5)Zn_(26.1)Y_(2.4) alloy

One dimensional(1D) and three dimensional(3D) ultrasound sources were applied to the solidification process of Mg_(71.5)Zn_(26.1)Y_(2.4) alloy.The acoustic spectra were in-situ measured, based on which the cavitation intensities and dynamic solidification mechanism were further investigated. With the increase of ultrasonic dimension and amplitude, the primary Mg_(3)Zn_(6)Y phase was significantly refined from petals to nearly pentagonal shape. The sound field measurements showed that the transient cavitation played a decisive role in generating a high local undercooling, which facilitated the formation of icosahedral clusters and promoted the nucleation of primary Mg_(3)Zn_(6)Y phase. The morphological transition of(α-Mg+Mg_(3)Zn_(6)Y) eutectic from lamellar to anomalous structure occurred under 3D ultrasonic condition. The stable cavitation took the main responsibility because the high pressure excited by nonlinearly oscillating bubbles induced the preferential nucleation of α-Mg phase rather than Mg_(3)Zn_(6)Y phase. As compared with its static values, the tensile strength and compression plasticity of this alloy were increased by the factors of 1.9 and 2.1, and its corrosion resistance was also improved with the corrosion current density decreased by one order of magnitude.

Experimental Study on the Resistance and Splash Performances of Water Collecting Devices for Mechanical Draft Cooling Towers

In recent years,water collecting systems,with the associated advantages of energy saving and noise reduction,have become the foundation for the development of a scheme to optimize the structure of cooling towers.To explore the feasibility of this approach for mechanical draft cooling towers,a small-scale experimental device has been built to study the resistance and splash performances of three U-type water collecting devices(WCDs)for different water flow rates and wind speeds.The experimental results show that within the considered ranges of wind speed and water flow rate,the pressure drop of the different WCDs can vary significantly.The resistance and local splash performances can also be remarkably different.Some recommendations about the most suitable system are provided.Moreover,a regression analysis of the experimental data is conducted,and the resulting fitting formulas for resistance and splash performance of WCD are reported.

Seed Priming Improves Enzymatic and Biochemical Performances of Rice During Seed Germination under Low and High Temperatures

As an abiotic stress,adverse germination temperatures cause serious disruptions in physiological and biochemical processes involved in seed germination.Using a factorial experiment,we examined the effects of different seed priming treatments on enzymatic and biochemical performances of rice seed germination under different temperatures.Each of the rice genotypes(Hashemi,Sadry-domsefid,IRON-70-7053-7 and NORIN-22)was primed with hydro-hardening,KCl,CaCl2 and ascorbic acid(AsA)and without a priming agent as a control at low(15℃),optimum(25℃)and high(35℃)germination temperatures.The results showed that the enzymatic and biochemical performances of all the rice genotypes were affected by the seed priming agents,especially under the low germination temperature.At 15℃,seed priming with AsA was found to be the best agent for the activities of amylase,α-amylase,catalase(CAT),peroxidase(POX),ascorbate peroxidase(APOX)and superoxide dismutase(SOD)as well as the content of soluble sugars in the NORIN-22 genotype,and for protease activity and soluble protein content in the IRON-70-7053-7 genotype.SOD at the low germination temperature and CAT,POX and protease at the optimum and high germination temperatures were the most important enzymes in occurrence of germination potential in terms of seedling length,vigor index,normal seedling rate and germination rate.Under the priming agents,the highest changes in normal seedling rate were observed at the low and optimum germination temperatures by AsA priming in the Hashemi and NORIN-22 genotypes,and at the high germination temperature under KCl priming in the Hashemi genotype.

Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.

Influence of specific speed on hydraulic performances and pressure fluctuations in mixed-flow pumps

A series of steady and unsteady numerical calculations of the internal flow in mixed-flow pumps with three different specific speeds were carried out based on the N-S equation coupled with the standard k-εturbulence model under different operating conditions to investigate the relationship between the impeller specific speed and the pump performance as well as pressure pulsations.Meanwhile,the pump performance and pressure pulsations inside the mixed-flow pump with three different specific speeds were also analyzed and compared with the corresponding test data.From the results,the averaged deviations between the predicted and tested head among different impellers are below 5%,and with respect to the equivalent impeller specific speeds of 280 and 260,the values are 4.30%and 3.69%,respectively.For all the impeller schemes,the best efficiency point of the mixed-flow pump is found at the flow rate of 1.2 Q_(d) and the higher head deviation occurs at lower flow rates.Especially,it can be found that the specific speed has a slight effect on the pressure fluctuation in the impellers.Eventually,it is determined that the pump performance curves calculated by numerical simu-lations have good agreement with the relevant experimental results,which verifies that the numerical methods used in the present study are accurate to a certain extent.Furthermore,the results also provide some references to the pressure pulsation analysis and the performance improvement of the mixed-flow pump design.

Spray Effect on the Thermal Performances of a Dry Cooling Tower

Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature.To study the spray effect on the thermal performance of natural draft dry cooling towers(NDDCTs),in this study 3-D numerical simulations of such a process have been conducted using Fluent 16.2(a two-way coupled Eulerian-Lagrangian approach).The considered NDDCT is 120 m high and only half system is simulated due to its structural symmetry.Three different spray strategies have been investigated at a typical crosswind speed of 4 m/s,which is the most frequent wind speed.The results have shown that:(1)The three implemented spray strategies can improve the thermal performance of the studied NDDCT with a vary-ing degree of success.In one case,the heat rejection rate can be increased by 35.2%,and the tower outlet water temperature can be decreased by 2.1℃ when compared with the no spray case;(2)To improve the thermal per-formance of the NDDCT using a small amount of water,the design of the spray pre-cooling system must include more nozzles on the windward and fewer or even no nozzles on the leeward sides of the NDDCT.

Improving electrochemical performances of LiFePO_4 /C cathode material via a novel three-layer electrode

As an improvement on the conventional two-layer electrode （active material layerlcurrent collector）, a novel sandwich-like three-layer electrode （conductive layerlactive material layertcurrent collector） for cathode material LiFePO4/C was introduced in order to improve its electrochemical performance. LiFePO4/C in the three-layer electrode exhibited superior rate capability in comparison with that in the two-layer electrode in accordance with charge-discharge examination. Cyclic voltammetry and electrochemical impedance spectroscopy indicated that Fe3＋/Fe2＋ redox couple for LiFePO4 in the three-layer electrode displayed faster kinetics, better reversibility and much lower charge transfer resistance than that in the two-layer electrode in electrochemical process. For three-layer electrode, the holes in the surface of active material layer were filled by smaller acetylene black grains, which formed electrical connections and provided more pathways to electron transport to/from LiFePO4/C particles exposed to the bulk electrolyte.

Modeling Photovoltaic Performances of BTBPD-PC61BM System via Density Functional Theory Calculations

Designing and fabricating high-performance photovoltaic devices have remained a major challenge in organic solar cell technologies. In this work, the photovoltaic performances of BTBPD-PC61BM system were theoretically investigated by means of density functional theory calculations coupled with the Marcus charge transfer model in order to seek novel photovoltaic systems. Moreover, the hole-transfer properties of BTBPD thin-film were also studied by an amorphous cell with 100 BTBPD molecules. Results revealed that the BTBPD- PC61BM system possessed a middle-sized open-circuit voltage of 0.70 V, large short-circuit current density of 16.874 mA/cm2, large fill factor of 0.846, and high power conversion effi- ciency of 10%. With the Marcus model, the charge-dissociation rate constant was predicted to be as fast as 3.079×10^13 s^-1 in the BTBPD-PC61BM interface, which was as 3-5 orders of magnitude large as the decay （radiative and non-radiative） rate constant （108-10^10 s^-1）, indicating very high charge-dissociation efficiency （-100%） in the BTBPD-PC61BM system. Furthermore, by the molecular dynamics simulation, the hole mobility for BTBPD thin-film was predicted to be as high as 3.970× 10^-3 cm^2V^-1s^-1, which can be attributed to its tight packing in solid state.