Material transfer behavior of AgTiB_2 contact under different contact forces and electrode gaps

To disclose the effect of contact force and electrode gap on the material transfer behavior of Ag-based contact material, arc-erosion tests of the Ag-4wt.%TiB2 contact material were performed for 5000 operations at 24 V/16 A under resistive load on an electric contact material testing system. The arc energy and arc duration were investigated, the surface morphologies of eroded anode and cathode were characterized, the mass changes after arc-erosion tests were determined, and the material transfer behavior was discussed as well. The results show that contact force has a significant effect on the arc energy, arc duration and erosion morphology, but has no impact on the material transfer mode. However, electrode gap not only influences the arc energy, arc duration and surface morphology, but also changes the material transfer mode. At 1 mm, the material transfers from anode to cathode. Nevertheless, an opposite mode presents at 4 mm, which is from cathode to anode.

Numerical investigation on freeze-drying of aqueous material frozen with pre-built pores

Freeze-drying of the initially porous frozen material with pre-built pores from liquid material was found experimentally to save drying time by over 30% with an initial saturation being 0.28 compared with the conventional operation with the initial saturation being 1, using mannitol as the solid material. In order to understand the mass and heat transfer phenomena of this novel process, a two-dimensional mathematical model of coupled mass and heat transfer was derived with reference to the cylindrical coordinate system. Three adsorption–desorption equilibrium relationships between the vapour pressure and saturation value namely, power-law, Redhead's style and Kelvin's style equation, were tested. Kelvin's style in exponential form of adsorption equilibrium relation gave an excellent agreement between the model prediction and experimental measurement when the equation parameter, γ, of 5000 was applied. Analyses of temperature and ice saturation profiles show that additional heat needs to be supplied to increase the sample temperature in order to promote the desorption process. Simulation also shows that there is a threshold initial porosity after which the drying time decreased with the increase in the initial porosity. Enhanced freeze-drying is expected to be achieved by simultaneously enhancing mass and heat transfer of the process.

Study of the Material Transfer Characteristics and Surface Morphology Due to Arc Erosion of PtIr Contact Materials

By means of breaking tests on PtIr contact materials via a JF04C contact material testing machine, it was attempted to elucidate the characteristics of the various surface morphology and material transfer after the arc erosion process caused by break arc. The material transfer characteristics appeared in the experiments were concluded and analyzed. Meanwhile, the morphology of the anode and cathode surface were observed and analyzed by SEM.

High-temperature acoustic properties of porous titanium fiber metal materials

The high-temperature acoustic absorption performance of porous titanium fiber material was investigated in terms of sample thickness, porosity, temperature, air-cavity thickness and double-layer structure arrangement. The effects on absorption coefficient were systematically assessed. The results show that the sound absorption performance is improved by increasing the sample porosity and/or thickness, and/or increasing the air-cavity thickness. Meanwhile, increasing the temperature gives better acoustic absorption performance in the low frequency range but also lowers the performance in the high frequency range, while double-layer structure enables better acoustic absorption performance.

Design of transfer device for magnetic thin sheet material

In order to realize the processing and retrieval of magnetic thin sheet materials in industrial production, this paper proposed a kind of transfer device for magnetic thin sheet raw material, which uses rodless cylinders as the main motive device and the programmable logic controller （PLC） to achieve the required functions, and applies the finite element analysis method to analyze its main components in the end of the design.

Evaporation Erosion During the Relay Contact Breaking Process Based on a Simplified Arc Model

Evaporation erosion of the contacts is one of the fundamental failure mechanisms for relays. In this paper, the evaporation erosion characteristics are investigated for the copper contact pair breaking a resistive direct current （dc） 30 V/10 A circuit in the air. Molten pool simulation of the contacts is coupled with the gas dynamics to calculate the evaporation rate. A simplified arc model is constructed to obtain the contact voltage and current variations with time for the prediction of the current density and the heat flux distributions flowing from the arc into the contacts. The evaporation rate and mass variations with time during the breaking process are presented. Experiments are carried out to verify the simulation results.

Impacts of the retinal environment and photoreceptor type on functional regeneration

Retinal regeneration is a promising central nervous system（CNS） target amongst the various stem cell therapy pursuits,due to its accessibility for manipulation and its disposition towards longitudinal monitoring of treatment safety and efficacy.We offer our perspective on current hurdles towards functional regeneration of cone photoreceptors.Cones are key：For patients suffering vision loss,cone photoreceptors are a required cellular component to restoring daytime vision,colour vision,and high acuity vision.The challenges of regenerating cones contrast with logistic challenges of regenerating rod photoreceptors,which underlines the importance of evaluating context in degeneration and regeneration studies.Foundational research is required to delineate the factors required to generate a diversity of cones in the human macula,and to coax both remaining and newly regenerating cones to rewire towards restoring daytime colour vision.A complex interplay between cell-intrinsic factors and the retinal environment determine both the specification of cone fates and the synaptic plasticity enabling their functional integration.Recent revelations that cellular materials are transferred amongst photoreceptor progenitors further emphasize the critical role of neighbouring cells in directing stem cell fates.From our vantage point,translation of stem cell therapies to restore the cone-rich human macula must be borne upon foundational research in cone-rich retinas.Research frameworks centered on patient outcomes should prioritize animal models and functional outputs that enable and report functional restoration of cone-mediated vision.

Evolution of surfaces and mechanisms of contact electrification between metals and polymers

Contact electrification(CE)is a pretty common phenomenon,but still is poorly understood.The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity.In this paper,the CE between metals and polymers is systematically studied,which shows the evolution of surfaces is accompanied by variations of CE outputs.The variations of CE charge quantity are closely related to the creep and deformation of the polymer and metal surfaces.Then the relationship between CE and polymer structures is put forward,which is essentially determined by the electronegativity of elements and the functional groups in the polymers.The effects of load and contact frequency on the CE process and outputs are also investigated,indicating the increase of CE charge quantity with load and frequency.Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer,both of which are believed to have an influence on each other.The findings advance our understanding of the mechanism of CE between metal and polymers,and provides insights into the performance of CE-based application in various conditions,which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.

The progression of clinical trials in Indonesia:an observational study of records from clinical trial registries databases

Objective:This report presents an overview on the progress of clinical trials in Indonesia based on database assessment from clinical trial registries.Methods:Study records that were registered up to December 26,2018,were extracted from three clinical trial registries(ClinicalTrials.gov,ISRCTN registry,and EudraCT)and a clinical trial register(WHO International Clinical Trials Registry Platform(ICTRP))with the keyword“Indonesia”.A total of 505 records comprised of 402 interventional studies and 103 observational studies were found and analyzed.Results:The top five noncommunicable diseases(NCDs)studied were cancers,diabetes,cardiac diseases,hypertension,and gastrointestinal diseases,while the top five infectious diseases(IDs)were malaria,tuberculosis,vaccines for IDs,HIV,and dengue.Remarkably,the proportion of regional studies(within Indonesia only)was higher than that of multiregional studies(including areas outside of Indonesia)in general.This trend became most apparent after the issuance of national regulations on Material Transfer Agreements(MTA)and other rules.Upon closer scrutiny,regional clinical trials and multiregional clinical trials(MRCTs)in Indonesia differed in terms of sponsorship,target population and size,interventions,and study phases.Conclusions:The total number of clinical trials in Indonesia is increasing and is mainly attributed to the growing number of regional clinical trials sponsored from within the country.Interrelated factors have shaped the characteristics of these as compared to the dwindling number of MRCTs.Establishment of a national level of management is an option that can better facilitate both MRCTs as well as regional clinical trials,to better address the national health issues,and to cope with the regulations.

Wear and Contact Temperature on Steel Surface in Linear Dry Friction Contact with Polimers with SGF

In this paper, we tried to present a qualitative correlation, based on extensive experimental trials between the value and the evolution of the friction coefficient, wear and contact temperature in the case of linear dry contact, thermoplastic material reinforced with SGF （short glass fibres） and various steel surfaces. We tried, believing successfully, the graphic illustration of the evolution of the steel surface wear and of the contact temperature, depending on the friction coefficient. It was analyzed in detail the influence of the normal load and sliding speed, but also of the metallic surface roughness on the friction coefficient.

A holistic perspective on Earth system science

Earth system can be categorized into three parts, solid Earth system, surface Earth system, and Sun-Earth space system. These three subsystems not only have mutual transmission and coupling relationships in both energy and matter but also involve multiple scales from microscopic to macroscopic. Earth system science is characterized by its globality and unity with a holistic view and a systematic view at multiple scales in both space and time. It focuses not only on the physical, chemical and biological interactions between various geospheres but also on the properties, behaviors, processes, and mechanisms of the entire Earth and its spheres. Although significant progress has been made in the study of internal disciplines of these three subsystems,there is still insufficient understanding of their overall behavior and interactions between individuals, thus facing challenges of different types and levels. The solid Earth system is composed of the crust, mantle, and core. Existing observational techniques struggle to penetrate deep into the mantle, making direct observation and data acquisition difficult;the extreme environments within Earth, such as high temperature, high pressure, and strong magnetic fields, also pose great challenges to observational equipment and scientific experiments. The surface Earth system is an open complex mega-system, in which there are complex interactions and feedback mechanisms among its geospheres(such as atmosphere, hydrosphere, biosphere, pedosphere and lithosphere), leading to difficulties in understanding of its overall behavior and long-term evolution. Biological activities have become increasingly significant in affecting the surface Earth system. The coupling between the internal and external Earth systems becomes more complex. Distinguishing and quantifying the impacts of Earth spherical interactions and biological activities on the surface Earth system is a major challenge. The Sun-Earth space system involves multiple physical processes such as solar activity, Earth's magnetic field, atmosphere, and space weather. Solar activity significantly affects the Earth's space environment, but existing observational and reconstruction methods and prediction models still lack precision and timeliness.Thus it is important to improve the prediction capability of solar activity and reduce the impact of space weather disasters. How to cross different scales and establish coupled models of multiple physical processes is a significant challenge in the study of the Sun-Earth space system. Because the various processes and phenomena within and between these three Earth subsystems often span multiple scales in both space and time and exhibit strong nonlinear characteristics, understanding their behaviors and processes becomes complex and variable, posing great challenges for theoretical modelling and numerical simulation. Therefore,the study of Earth system science requires in-depth interdisciplinary integration to jointly reveal the basic laws and operating mechanisms of Earth system.

High-Speed Rubbing Behavior of Abrasive Coating Coated on Titanium Alloy Blade Tips

In aero-engines, abrasive coatings are typically utilized to protect the blade tip from excessive wear caused by the harder abradable sealing coating and thereby improve the sealing performance of engines. Therefore, a Ni/cBN abrasive coating was prepared on titanium alloy using electrodeposition. The high-speed rubbing tests with a linear velocity of 350 m/s and different incursion rates were performed to investigate the effect of the Ni/cBN abrasive coating on the wear behavior against NiCrAl/diatomite seal coating. Results showed that melting wear and adhesive transfer occurred on the bare blades, causing the bare blade to suffer excessive wear. While the Ni/cBN abrasive coating exhibited superior wear resistance and cutting performance. The cBN grits pullout, the abrasion of Ni matrix and transfer of seal coating to the cBN grits were the main wear mechanism of the Ni/cBN abrasive coating. Additionally, it was found that the relationship between the incursion rate and high-speed rubbing behavior is quite different for the bare blade and Ni/cBN coating. The reason for the difference in wear behavior of bare blade and Ni/cBN coating at different incursion rates was discussed in detail.

Effect of Temperature on Material Transfer Behavior at Different Stages of Friction Stir Welded 7075-T6 Aluminum Alloy

In this work, the morphologies of weld of 7075-T6 aluminum alloy via friction stir welding （FSW） were analyzed by optical microscopy, the temperature field was attained by numerical simulation, and the effect of temperature on material transfer behavior in the thermal-mechanical affected zone （TMAZ） at different stages was mainly investigated. The FSW process consists of three stages. It is very interesting to find that the maximum transfer displacement of material appears at the final stage of welding process, then at the stable stage and at the initial stage, which results from the difference of peak temperatures at different stages. At any stage, the material in TMAZ near the surface of weld transfers downwards, the material in the middle of weld moves upwards and the material near the bottom of weld hardly moves. In any cross section of weld, the largest transfer displacement of material appears in the middle of weld. The increase of rotational velocity and the decrease of welding speed are both beneficial to the transfer displacement of material in the middle of weld.

Boosting efficiency and stability of perovskite solar cells with nickel phthalocyanine as a low-cost hole transporting layer material

The efficiency of perovskite solar cells（PSCs） has increased from around 4% to over 22% following a few years of intensive investigation. For most PSCs, organic materials such as 2,2＇,7,7＇-tetrakis（N,Npdimethoxyphenylamino）-9,9＇-spirobifluorene（spiro-OMeTAD） are used as the hole transporting materials（HTMs）, which are thermally and chemically unstable and also expensive. Here, we explored nickel phthalocyanine（NiPc） as a stable and cost-effective HTM to replace the conventionally used spiroOMeTAD. Because of its high carrier mobility and proper band alignments, we achieved a PCE of 12.1% on NiPc based planar device with short-circuit current density（Jsc） of 17.64 mAcm（-2）, open circuit voltage（Voc） of 0.94 V, and fill factor（FF） of 73%, outperforming the planar device based on copper phthalocyanine（CuPc） that is an outstanding representative of metal phthalocyanines（MPcs） reported. Moreover,the device with NiPc shows much improved stability compared to that based on the conventional spiroOMeTAD as a result of NiPc＇s high stability. Photoluminescence（PL） and Impedance spectroscopy analysis results show that thermally deposited NiPc has good hole-extraction ability. Our results suggest that NiPc is a promising HTM for the large area, low cost and stable PSCs.

Thermoacoustic theory of graphene films considering heat transfer of substrate materials

Based on thermoacoustic theory, a coupled thermal-mechanical model for graphene films is established, and the analytical solutions for thermal-acoustic radiation from a graphene thin film are obtained. The sound pressure of the graphene film generator on different substrates is measured, and the measurement data is compared with the theoretical results. The frequency response from the experimental results is consistent with the theoretical ones, while the measured values are slightly lower than the theoretical ones. Therefore, the accuracy of the proposed theoretical model is verified. It is shown that thermal-acoustic radiation from a graphene thin film reveals a wide frequency response. The sound pressure level increases with the frequency in the low frequency range, while the sound pressure varies smoothly with frequency in the high frequency range. Thus it can be used as excellent thermal generator. When the thermal effusivity of the substrate is smaller, then the sound pressure of grapheme films will be higher. Furthermore, the sound pressure decreases with the increase of heat capacity per unit area of grapheme films. Results will contribute to the mechanism of graphene films generator and its applications in the design of loudspeaker and other related areas.

High temperature tribological behaviour of PVD coated tool steel and aluminium under dry and lubricated conditions

Aluminium alloys are commonly used as lightweight materials in the automotive industry.This non-ferrous family of metallic alloys offers a high versatility of properties and designs.To reduce weight and improve safety,high strength-to-weight ratio alloys(e.g.6XXX and 7XXX),are increasingly implemented in vehicles.However,these alloys exhibit low formability and experience considerable springback during cold forming,and are therefore hot formed.During forming,severe adhesion(i.e.galling)of aluminium onto the die surface takes place.This phenomenon has a detrimental effect on the surface properties,geometrical tolerances of the formed parts and maintenance of the dies.The effect of surface engineering as well as lubricant chemistry on galling has not been sufficiently investigated.Diamond-like carbon(DLC)and CrN physical vapour deposition(PVD)coated steel have been studied to reduce aluminium transfer.However,the interaction between lubricants and PVD coatings during hot forming of aluminium alloys is not yet fully understood.The present study thus aims to characterise the high temperature tribological behaviour of selected PVD coatings and lubricants during sliding against aluminium alloy.The objectives are to first select promising lubricant-coating combinations and then to study their tribological response in a high-temperature reciprocating friction and wear tester.Dry and lubricated tests were carried out at 300℃ using a commercial polymer lubricant.Tests using DLC,CrN,CrTiN,and CrAIN coated tool steel were compared to uncoated tool steel reference tests.The initial and worn test specimen surfaces were analysed with a 3-dimensional(3D)optical profiler,scanning electron microscope(SEM)and energy dispersive X-ray spectroscope(EDS)as to understand the wear mechanisms.The results showed formation of tribolayers in the contact zone,reducing both friction and wear.The stability of these layers highly depends on both the coatings'roughness and chemical affinity towards aluminium.The DLC and CrN coatings combined with the polymer lubricant were the most effective in reducing aluminium transfer.

Computational fluid dynamics simulation of friction stir welding:A comparative study on different frictional boundary conditions

Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.

A qualitative correlation between friction coefficient and steel surface wear in linear dry sliding contact to polymers with SGF

In this paper we tried to present a qualitative correlation,based on extensive experimental determinations between the value and the evolution of the friction coefficient,wear,and contact temperature,in the case of linear dry contact,for thermoplastic material reinforced with short glass fibers(SGF)and various steel surfaces.The aim was to highlight the evolution of the wear process depending on the evolution of the friction coefficient.As a result,it was possible to graphically illustrate the evolution of the friction coefficient and the change of the wear process,emphasizing the abrasive,adhesive and corrosive wear.The evolution of the plastic material transfer function of the contact temperature,namely of the power lost by friction(product between the contact pressure and sliding speed,p and v)was aimed and it was highlighted.It has been demonstrated that in the case of a 30%SGF content it can reach and even exceed contact temperatures very close to the flow limit of the plastic material.We tried,believing successfully,the graphic illustration of the evolution of the steel surface wear and of the contact temperature,depending on the friction coefficient.The influence of the normal load and sliding speed was evaluated in detail,but also the influence of the metallic surface roughness on the friction coefficient was discussed.