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Spinel Li4Ti5O12 hollow nanospheres self-assembled with lamellar nanocrystallites, prepared by employing colloid carbon spheres as templates, exhibit excellent capacity retention.

Since the reform and opening up, export trade has made great contribution to China ' s economic growth. Facing the complex and changeable international situation, how to continue to play the role of export in promoting China 's economic growth. By analyzing the risks faced by China 's export trade and exploring the mechanism of export credit insurance, this paper draws the following conclusions: export credit insurance provides help to export enterprises in terms of loss compensation, financing support and risk management, reduces the risks faced in foreign trade, and then effectively stimulates trade exports and promotes economic growth.

Polymer gears have shown potential in power transmission by their comprehensive mechanical properties. One of the significant concerns with expanding their applications is the deficiency of reliability evaluation methods considering small data set circumstances. This work conducts a fair number of polyoxymethylene (POM) gear durability tests with adjustable loading and lubrication conditions via a gear durability test rig. A novel machine learning-based reliability model is developed to evaluate contact fatigue reliability for the POM gears with such a data set. Results reveal that the model predicts reasonable POM gear contact fatigue curves of reliability–stress–number of cycles with 2.0% relative error and 18.8% reduction of test specimens compared with the large sample data case. In contrast to grease lubrication, the oil-lubricated POM gear contact fatigue strength improves by 10.4% from 52.1 to 57.6 MPa.

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through water decomposition are feasible methods to produce green and clean energy. Herein, we report a facile two-step strategy for the preparation of non-noble metal defect-rich nanosheets by an electrochemical process at room temperature. First-principle calculations are used to study the bifunctional catalytic reaction mechanism of defect engineering in transition-metal dichalcogenides (TMDs); from the first-principle calculations, we predicted that the rich S vacancies on the nanosheet promoted electron transfer and reduced the energy barrier of electrocatalysis. As a substantiation, we conducted HER/OER electrochemical characterizations and found that the defect-rich atomic-thick tantalum sulfide is a kind of dual-function electrocatalyst with enhanced comprehensive properties of Tafel slope (39 mV/dec for HER, 38 mV/dec for OER) and low overpotential (0.099 V for HER, 0.153 V for OER) in acidic and alkaline environments, respectively. Likewise, the defect-rich catalysts exhibit high stability in acidic and alkaline solutions, which have potential applications as electrocatalysts for the large-scale production of hydrogen and oxygen.

Applications of polymer gears have been gradually expanding from motion transmission to power transmission fields. Design of new gear teeth profiles plays a crucial role in meeting the requirement of replacing metallic gears with polymer ones. This work develops a computational framework consisting of tooth profile generation and fatigue life prediction of S-shaped and involute POM gears. The contact and bending fatigue performances of S-shaped and involute POM gears under oil lubrication are comparatively studied. It is found that the S-shaped profile reduces the tooth root stress by 25% and significantly improves the bending fatigue life by 10 times compared with the involute profile, especially under medium or high loading levels. Furthermore, the S-shaped gear with a single circular-filleted root curve benefits a 20% reduction of tooth root stress and a 30% increase in bending fatigue life compared to a double circular-filleted root curve S-shaped gear.

Polyketone (PK) is an environmentally friendly engineering plastic with good wear resistance and shows potential in gear applications. In this work, the durability of PK gears under various lubrication conditions was investigated via a power opened gear durability test rig and compared with polyformaldehyde (POM) gears. Experimental results show that PK gears under oil lubrication and grease lubrication represent the same failure mode at the same torque. The contact fatigue life of oil-lubricated PK gear was higher than that under grease lubrication but slightly lower than POM gear under the same conditions.

This study presents the results of detailed wear process examination on polyformaldehyde gears under both dry and lubricated conditions. A multi-purpose durability test rig was employed to study the wear performance of polyformaldehyde gear pairs. The wear behaviors of polyformaldehyde gears under dry and oil-lubricated operating conditions were characterized via measurements of gear tooth surface micro-topography and tooth profile deviation. Under the dry running condition, a hump and a gully appear on the tooth surface in the pitch line area of the driving gear and the driven wheel, respectively. The largest amount of wear was observed around the tooth root of the driving gear. However, the gear tooth wear pattern with lubrication is different from that under the dry running condition.

An experimental investigation is conducted to identify the failure modes of the lubricated PEEK gears under different loading conditions through the enclosed power flow test rig, supplemented with the measurements on wear, vibration and the surface micro-topography. The FZG C type gear pair is selected while the mating driving gear is chosen with the material of C45. Experimental results reveal that the pitting-induced tooth breakage occurs under light and moderate loading conditions, while the tooth root breakage dominates under heavy duty loading conditions. The measurement of the wear and the tooth surface micro-topography help to identify that the micro-pits near the pitch line lead to the final tooth breakage under moderate loading conditions. Meanwhile, the insufficiency of the bending strength under heavy loading conditions is the cause of the tooth root fracture.

Micro LED has a wide range of application prospects due to the advantages of high brightness, high contrast and long life. In this paper, square shape Micro LED with the side length of 30-100μm and corresponding circular shape Micro LED were designed and fabricated. The electrical, optical and thermal characteristics of micro LEDs with the same light-emitting area and different chip shapes are comparatively studied. The results show that the forward voltage and series resistance of square and circular Micro LEDs are approximately. The change of chip shape does not affect the luminous flux. The radiant flux of square and circular Micro LED is approximately at low current density. However, at a higher current density, the radiation flux of the square Micro LED with a size of 60μm or more is larger than that of the circular Micro LED, and the peak radiant fluxes of 80μm, 100μm are 7.4%, 3.3% higher than that of the circular chip. This is because the side area of the square chip is about 12.8% larger than that of the circular chip, resulting in more photons overlapping from the side surface. The measured temperature coefficient and the junction temperature at 20mA of square and circular chips are also approximately.

Gallium nitride (GAN) based power light emitting diode (LED) has the advantages of energy saving, environmental protection, long life and so on. It has a wide range of application prospects in the fields of lighting and display. Although its performance has been improved in recent years and the products are becoming mature, the new LED structure will still bring new reliability problems. Therefore, it is of great significance to carry out photoelectric performance test and accelerated aging life test, and analyze its reliability and failure mechanism. In this paper, the initial photoelectric parameters of 1W GaN based blue LED with or without current blocking layer (CBL) are tested. The two kinds of LEDs are divided into four groups named A1, A2, B1 and B2 for accelerated life aging test. The devices selected by A1 and A2 are LED with CBL; the devices selected by B1 and B2 are LED without CBL. The accelerated life test of A1 and B1 devices is conducted at 700mA/25°C, and the accelerated life test of A2 and B2 devices is conducted at 900mA/25°C. During the experiment, the interval time of photoelectric parameter measurement is determined according to the actual situation of the experiment and the measurement of photoelectric parameters such as luminous flux, luminous efficiency and forward voltage, etc. is completed. The results showed that the luminous flux attenuation of the blue LED with CBL under 700mA and 900mA working current was 5% and 1.76% smaller than that of the blue LED without CBL structure. The LED with CBL structure has slower attenuation and better device performance. The forward voltage of the device increases with the increase of the aging time. The reason is that the ohmic contact resistance of the p-type layer increases due to the influence of large current and higher junction temperature, and the degradation of the packaging material also causes the series resistance to increase. Finally, the actual life of the device when it meets the L50 standard under normal current is deduced according to the inverse power law model. LEDs with or without CBL structure are 93555h and 40881h, respectively. LEDs with CBL structure have longer life and higher reliability.

The application of polymer gears in power transmission has been considered recently due to their advantages over metal gears, e.g., lighter weights and lower costs. Much further research work needs to be carried out to understand their wear mechanisms and to establish their design methods. This paper aims to investigate the wear and failure behavior of the poly-ether-ether-ketone (PEEK) gear against the steel gear under oil jet lubrication through the durability test with the standard FZG test rig. The service life and wear loss of PEEK gears were experimentally recorded under different moderate loading conditions ranging from the output torque of 10–20 Nm with a fixed input rotational speed of 1000 rpm. Moreover, the tooth surface morphologies and the wear loss of PEEK gears under different running stages were investigated. The experimental measurements reveal that there is a critical load magnitude for the transition of wear performance. With a load above 15 Nm, the PEEK gear wear rate increases rapidly, leading to a quick breakage failure, whereas the gear wear rate with a torque below 15 Nm is much lower. All tested PEEK gears finally failed with a pitting-induced tooth breakage mode under moderate loading conditions.

GaN-based blue light-emitting diodes (LEDs) with patterned SiO 2 passivation layer and discontinuous current block layer (CBL) has been proposed and fabricated. The patterned SiO 2 passivation layer is inserted between Indium tin oxide (ITO) and P/N electrodes, and has a series of windows under the P and N electrodes, it can not only isolate the N electrode from the sidewall to prevent leakage, but also can re-contact the P electrode with ITO to form discontinuous P electrode structure and current injection. For the etching of active region, we use the method that partially etched to form a discontinuous N-GaN mesa, which can reduce the loss of the active area and improve the light emission intensity of the LEDs. It can be called discontinuous N-electrode structure. In addition, the discontinuous CBL deposited between P-GaN and ITO can increase the light extract efficiency from the active region under the P electrode compared to the conventional LED structure. As a result, at an injection current of 150mA, the light output power of the LED with patterned SiO 2 passivation layer and discontinuous CBL was 7.06% higher than that of conventional structure LED. What’s more, at 50mA, the LED with the patterned SiO 2 passivation layer and discontinuous CBL structure shows the lower forward voltage of 3.29V compared with the conventional LED of 3.41V.

Novel butterfly-like CaTiO

Acetal gears are the most widely applied type among these polymer gears. Acetal gears may suffer from many failure forms such as severe wear, tooth breakage or tooth surface cracks depending on the loading conditions and the lubrication and temperature environment. The contact fatigue performance of acetal gear relates to many factors including temperature and load, however, their influences on the mechanical properties and fatigue parameters of the acetal material are still not fully understood. In this work, the thermo-elastic-plastic constitutive equations are derived to describe the acetal material behavior during gear meshing process, and the modified Brown-Miller multi-axial fatigue criterion is proposed to estimate the polymer gear contact fatigue life. Durability tests of acetal gear against steel gear are conducted based upon a developed test rig. Results reveal that the temperature rise could significantly reduce the contact pressure of acetal gear due to the decay of the modulus, but still jeopardize the fatigue life on tooth flank because the fatigue properties are also affected by the temperature rise. The predicted location of fatigue failure zone on the tooth and the lifespan agree well with experimental observation.

Polymer gears manufactured with injection molding have been widely used in many industries, but the unavoidable injection molding lunker defects limit the loading capacity and the further use of polymer gears in power transmissions. In this work, injection molding lunker defects are detected by X-ray CT and a polymer gear fatigue model with lunker defect is established considering the thermal-elastic-plastic constitutive material behavior. Durability tests are also conducted, and the fatigue lives correspond well with simulation results. Results reveal that the lunker defect jeopardizes the loading capacity of tooth root under medium or heavy loading conditions, while the tooth flank failure is significantly influenced by the loading condition.

Novel butterfly-like CaTiO3 dendrites dominantly bounded by {101} facets have been synthesized via a conventional hydrothermal by using tetramethylammonium hydroxide (TMAH) as a mineralizer and surface modifier. The wing-branches of the butterfly-like CaTiO3 dendrites are composed of primary block tetragonal plates with dominant {101} facets overlapping and ranking around the stem of 〈131〉 directions in the same plane belonging to the group of {101}. With the basis of the experimental results and the lattice structure, a possible formation mechanism of the butterfly-like CaTiO3 dendrites has been discussed and proposed. The preferential adsorption of the organic [Formula: see text] ions released by the ionization of TMAH on {101} planes suppresses the deposition of the calcium titanate species on {101} planes, which induces the formation of the primary block tetragonal plates and their overlapping as well as ranking around 〈131〉 direction along {101} planes, resulting in the butterfly-like CaTiO3 dendrites bounded with {101} facets. The investigation on the degradation of rhodamine-B demonstrates, due to the dominant exposition of the {101} facets, the butterfly-like CaTiO3 dendrites display superior photocatalytic activity of more than four time that of CaTiO3 microcuboids bounded with smart {101} and (010) facets.

This paper introduces a modular multilevel converter (MMC) sub-module topology and analyses several major component failure characteristics of the sub-modules. Sub-modules using a hot reservation redundancy fault-tolerant control strategies for solving sub-module fault. For MMC redundancy policy problems caused by the asymmetric operating state and the DC current disturbances, two ways are presented to solve the problem of asymmetric redundancy result - the energy balance control arm of bridge and added to the base frequency resonant controller. In addition, a 21-level MMC-HVDC system based on PSCAD/EMTDC software was established and simulation results demonstrated the effectiveness of the two control strategies.