摘要：In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.

摘要：With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train head design. Given that the aerodynamic drag is a significant factor that restrains train speed and energy conservation, reducing the aerodynamic drag is thus an important consideration of the high-speed train head design. However, the reduction of the aerodynamic drag may increase other aerodynamic forces (moments), possibly deteriorating the operational safety of the train. The multi-objective optimization design method of the high-speed train head was proposed in this paper, and the aerodynamic drag and load reduction factor were set to be optimization objectives. The automatic multi-objective optimization design of the high-speed train head can be achieved by integrating a series of procedures into the multi-objective optimization algorithm, such as the establishment of 3D parametric model, the aerodynamic mesh generation, the calculation of the flow field around the train, and the vehicle system dynamics. The correlation between the optimization objectives and optimization variables was analyzed to obtain the most important optimization variables, and a further analysis of the nonlinear relationship between the key optimization variables and the optimization objectives was obtained. After optimization, the aerodynamic drag of optimized train was reduced by up to 4.15%, and the load reduction factor was reduced by up to 1.72%.

摘要：Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen ***-exchange membrane water electrolyzers(PEMWEs)are promising devices for hydrogen production,given their high efficiency,rapid responsiveness,and *** plates account for a relatively high percentage of the total cost and weight compared with other components of ***,optimization of their design may accelerate the promotion of *** paper reviews the advances in materials and flow-field design for bipolar ***,the working conditions of proton-exchange membrane fuel cells(PEMFCs)and PEMWEs are compared,including reaction direction,operating temperature,pressure,input/output,and ***,the current research status of bipolar-plate substrates and surface coatings is summarized,and some typical channel-rib flow fields and porous flow fields are ***,the effects of materials on mass and heat transfer and the possibility of reducing corrosion by improving the flow field structure are ***,this review discusses the potential directions of the development of bipolar-plate design,including material fabrication,flow-field geometry optimization using threedimensional printing,and surface-coating composition optimization based on computational materials science.

摘要：Hypoxia is a typical feature of the tumor microenvironment,one of the most critical factors affecting cell behavior and tumor ***,the lack of tumor models able to precisely emulate natural brain tumor tissue has impeded the study of the effects of hypoxia on the progression and growth of tumor *** study reports a three-dimensional(3D)brain tumor model obtained by encapsulating U87MG(U87)cells in a hydrogel containing type I *** also documents the effect of various oxygen concentrations(1%,7%,and 21%)in the culture environment on U87 cell morphology,proliferation,viability,cell cycle,apoptosis rate,and ***,it compares two-dimensional(2D)and 3D *** comparison purposes,cells cultured in flat culture dishes were used as the control(2D model).Cells cultured in the 3D model proliferated more slowly but had a higher apoptosis rate and proportion of cells in the resting phase(G0 phase)/gap I phase(G1 phase)than those cultured in the 2D ***,the two models yielded significantly different cell ***,hypoxia(e.g.,1%O2)affected cell morphology,slowed cell growth,reduced cell viability,and increased the apoptosis rate in the 3D *** results indicate that the constructed 3D model is effective for investigating the effects of biological and chemical factors on cell morphology and function,and can be more representative of the tumor microenvironment than 2D culture *** developed 3D glioblastoma tumor model is equally applicable to other studies in pharmacology and pathology.

摘要：The range of memory impairments associated with Alzheimer's disease(AD) has been a focus for psychological and clinical researchers for many *** addition to investigations of AD patients' veridical memory using traditional recognition memory tasks,a number of recent studies have focused on false memories to reveal the underlying causes of memory impairment in *** comparing illusory memories between AD patients and healthy older people have revealed various differences in memory deficits between the development of AD and the typical aging ***,we review 3 types of memory illusions tested in AD patients:associative memory illusions,fluency-based false memories and source memory *** comparing AD patients with healthy older adults,we sought to analyze the mechanisms underlying AD-related memory impairments at different stages of memory processing,including encoding,retrieval and *** comparison revealed that AD patients exhibit an impaired ability to establish and utilize gist representations at the encoding stage and impairments in processing on the basis of familiarity and recollection at the retrieval ***,patients with AD have access to less information when making memory *** a result,they become more susceptible to the effects of item fluency,which can be manipulated during the retrieval ***,with impaired source memory monitoring abilities,the capacity of AD patients to suppress memory illusions is *** on these findings,we propose that the study of false memories constitute a critical tool for elucidating the memory impairments involved in *** explorations of these memory impairments will have practical significance for the diagnosis and treatment of AD in the future.

摘要：A method of designing an E-plane power combiner composed of two quarter-arc bent rectangular waveguides is proposed for sub-THz and THz waves. The quarter-arc bent-waveguide power combiner has a simple geometry which is easy to design and fabricate. By HFSS codes, the physical mechanism and performance of the power combiner are analyzed, and the relationship between the output characteristics and the structure/operating parameters is given. Simulation results show that our power combiner is suitable for the combining of two equalpower and reversed-phase signals, the bandwidth of the combiner is wide and can be adjusted by the radius of the quarter-arc, and the isolation performance of the combiner can be improved by adding thin film resistive septa at the junction of two quarter-arc bent waveguides. Meanwhile, an approximate method based on the analytic geometrical analysis is given to design this power combiner for different frequency bands.

摘要：Corrosion in complex coupling environments is an important issue in corrosion field, because it is difficult to take into account a large number of environment factors and their interactions. Design of Experiment(DOE) can present a methodology to deal with this difficulty, although DOE is not commonly spread in corrosion field. Thus, modeling corrosion of Ni-Cr-Mo-V steel in deep sea environment was performed in order to provide example demonstrating the advantage of DOE. In addition, an artificial neural network mapping using back-propagation method was developed for Ni-Cr-Mo-V steel such that the ANN model can be used to predict polarization curves under different complex sea environments without experimentation. Furthermore, roles of environment factors on corrosion of Ni-Cr-Mo-V steel in deep sea environment were discussed.

摘要：Backfill hydraulic support is the key equipment in achieving coal mining and solid backfilling simultaneously in solid backfill mining *** on the summary and analysis of main types,basic structural properties and filed application of backfill hydraulic support,this work has firstly proposed the basic principle of backfill hydraulic support optimization design and provided the method of optimal design of key structural components,like four-bar linkage,rear canopy and tamping structure;the method is further elaborated as changing hinging position of upper bar to optimize four-bar linkage,by lengthening or shortening the rear canopy to optimize length ratio of canopy;and by changing length and hinging position of tamping structure as well as suspension height of backfill scrape conveyor to realize optimization of tamping *** this basis,the process of optimal design of backfill hydraulic support is *** optimal design case of ZC5200/14.5/30 six columns-four bar linkage used in 7203 W workface of Zhaizhen Coal Mine shows that the backfill properties like horizontal roof gap,vertical horizontal gap,tamping angle and tamping head gap are improved obviously through optimizing four-bar linkage,canopy length and tamping structure according to the optimal design method proposed in this work.

摘要：This paper proposes a new approach to mial function of transmission error （TE） for spiral design and implement a seventh-order polyno- bevel gears with an aim to reduce the running vibration and noise of gear drive and improve the loaded distribution of the tooth. Based on the constraint conditions of predesigned seventh-order polynomial function curve and the theory of linear algebra, the polynomial coefficients of the seventh-order polynomial function of transmission error can be obtained. By applying a method named reverse tooth contact analysis, the modified roll coefficients as well as parts of machine-tool settings for the face-milling of spiral bevel gears can be individually determined. Therefore, a predesigned seventh-order polynomial function of transmission error for spiral bevel gears can be obtained by the modified roll with high-order coef- ficients, and comparisons of the seventh-order polynomial and parabolic functions of transmission error are also performed. The achievement of spiral bevel gears with the seventh-order function of transmission error can be accomplished on a universal Cartesian-type hypoid gear generator or a numerically controlled cradle-style hypoid gear generator due to its simple generating motion of axes of the cradle and the work piece. The results of a numerical example show that the bending stresses of the tooth of seventh-order are less than those of a parabolic one, while the contact stresses remain almost eouivalent.

摘要：Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of great importance to develop means to suppress these undesirable *** paper proposes a new idea for designing a tunable mass damper(TMD) to reduce vibrations in milling of cylindrical parts. Frequency response function(FRF) of the milling system is derived to comprehensively reveal the influence of both the dynamic response of the machine tools and the TMD. Critical axial depth of cut, which is usually used to characterize the process stability, is formulated by considering the FRFs of both the milling system itself and the TMD. Maximization of critical axial depth of cut is taken as objective function, while kernel dynamic parameters of TMD,which are involved in the derived expression of critical axial depth of cut, are extracted as designable variables. Optimization procedure is carried out to adjust the parameters of TMD by using sequential quadratic programming algorithm. A series of experiments with a designed passive TMD validate that the design has a good performance in reducing vibrations and improving stability of milling process.