新闻创新“失败”的比较研究

新闻研究重视成功而漠视失败,让失败成为新闻创新研究中的盲点,遮蔽了新闻业的“真问题”。本研究立足新闻创新的实践,采取比较分析的研究方法,对四个新闻创新遭遇困境、挫折与失败的典型案例进行深描,同时就新闻创新中存在的“自主造血”功能缺陷、法律与监管合规风险、跟风式的技术模仿、漠视原创内容生产、支撑性人才流失等问题进行分析,形成一个理解新闻创新困境与失败的框架。

Optical Neural Network Architecture for Deep Learning with Temporal Synthetic Dimension

The physical concept of synthetic dimensions has recently been introduced into optics.The fundamental physics and applications are not yet fully understood,and this report explores an approach to optical neural networks using synthetic dimension in time domain,by theoretically proposing to utilize a single resonator network,where the arrival times of optical pulses are interconnected to construct a temporal synthetic dimension.The set of pulses in each roundtrip therefore provides the sites in each layer in the optical neural network,and can be linearly transformed with splitters and delay lines,including the phase modulators,when pulses circulate inside the network.Such linear transformation can be arbitrarily controlled by applied modulation phases,which serve as the building block of the neural network together with a nonlinear component for pulses.We validate the functionality of the proposed optical neural network for the deep learning purpose with examples handwritten digit recognition and optical pulse train distribution classification problems.This proof of principle computational work explores the new concept of developing a photonics-based machine learning in a single ring network using synthetic dimensions,which allows flexibility and easiness of reconfiguration with complex functionality in achieving desired optical tasks.

Characterization methods for additive manufacturing

Additive manufacturing(AM),also generally known as 3D print-ing,is one of the most disruptive technologies that has been widely used in automobile,aerospace,biomedical,weapons,and other industrial fields.Compared with traditional manufacturing technologies,AM has many significant advantages,including rapid production,easy operation,less material waste and labor costs,high efficiency,and is easy to realize personalized design and fab-rication especially for complex components.

Residual stress evolution regularity in thermal barrier coatings under thermal shock loading

Residual stress evolution regularity in thermal barrier ceramic coatings(TBCs) under different cycles of thermal shock loading of 1 100℃ was investigated by the microscopic digital image correlation(DIC) and micro-Raman spectroscopy, respectively. The obtained results showed that, as the cycle number of the thermal shock loading increases, the evolution of the residual stress undergoes three distinct stages: a sharp increase, a gradual change, and a reduction.The extension stress near the TBC surface is fast transformed to compressive one through just one thermal cycle. After different thermal shock cycles with peak temperature of 1 100℃, phase transformation in TBC does not happen, whereas the generation, development, evolution of the thermally grown oxide(TGO) layer and micro-cracks are the main reasons causing the evolution regularity of the residual stress.

Research on synchronous measurement technique of temperature and deformation fields using multispectral camera with bilateral telecentric lens

The hot-section parts easily occur the creep-fatigued interaction under the condition of mechanicalthermal coupled load during the period of service, which may lead to the damage of the parts, and therefore, the measurement and characterization of thermal-deformed fields of the parts are important to understand its damage process. Aiming at relevant demand, the bilateral telecentric-multispectral imaging system was established, the research of synchronous measurement technique of the temperature and deformation fields was developed. On the one hand, the measurement technology for surface temperature of the object was developed using the two-color images captured by the multispectral camera with bilateral telecentric lens and combined with colorimetric method. On the other hand, the 2 D-DIC measurement technique of the multispectral camera was developed by conducting digital image correlation analysis using the blue light images before and after deformation, which can measure the high temperature deformation field of the object(the blue light images were filtered by multispectral camera).Results showed that the bilateral telecentric lens is used to replace the ordinary optical lens for imaging,which can effectively eliminate the distortion of the multispectral imaging system. Since the temperature measurement process of this measurement system is little affected by the emissivity of the object, therefore, it has excellent robustness. The thermal expansion coefficients of the nickel alloys are evaluated at the temperature ranges of 700–1000℃, indicating this system can achieve the synchronous and precise measurement of the temperature and deformation fields of the object.

Mechanical properties evaluation for thin film/substrate material systems

Thin film/substrate material systems have been widely used in various industries such as aerospace,automotive,marine and electronics.One example is thermal barrier coatings(TBCs):TBCs are extensively applied to metallic components on gas turbine engines in order to protect them from high and prolonged heat loads,and they play an essential role in the aircraft industry.Another example is laminated polymer matrix composites(PMCs),reinforced with fibers such as carbon,glass or aramid:These materials have been extensively employed in a variety of applications due to their superior properties and the improving ease and cost-effectiveness of fabricating them.The evaluation of mechanical properties for thin film/substrate material systems is imperative for more efficient use of these material systems and further improvements.

Microstructure design to improve the efficiency of thermal barrier coatings

The insulation effect of ceramic coating in a turbine blade is of great importance for the service of engine in the field of aviation industry. Fabricating microstructure in the thermal barrier coatings(TBCs) is considered to be able to enhance the thermal insulation effect. In this study, the traditional three-layer structure, containing ceramic top coat, bonding coat and substrate, is firstly simplified into a double-layer structure, where only ceramic layer and substrate are left, for analyzing the thermal insulation. Afterwards, the thermal insulation effect of the designed microstructure in the bonding coat of the three-layer structure is further studied. Column-like microstructures, filled with hollow ceramic microspheres in the interspace, are designed to improve the thermal insulation effect. The size parameters of the designed microstructure were optimized. The existence of the designed microstructure can significantly prolong the efficiency of thermal barrier coatings. The insulation temperature between the heating surface and lower surface of the substrate can exceed 300℃ and the thermal balance time has a big improvement of 240 s, more than 50%, than the traditional TBCs structure. Compared with the TBCs structure without microstructure, the designed microstructure can significantly improve the insulation temperature of more than 110℃.

Simulation and experimental analysis of melt pool evolution in laser engineered net shaping

In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.

Edge dislocation-induced strains break the limit of PtNi alloys in boosting Pt mass activity for efficient alkaline hydrogen evolution

Creating lattice defects and alloying to produce strain effect in Pt-based bimetallic alloys are both effective methods to optimize the crystal and electronic structure and improve the electrocatalytic performance.Unfortunately,the principles that govern the alkaline hydrogen evolution reaction(HER)performance remain unclear,which is detrimental to the rational design of efficient Pt-based electrocatalysts.Herein,PtNi alloys with different Pt/Ni ratios and edge dislocations were synthesized,and the effects of Pt/Ni composition and edge dislocations on the alkaline HER electrocatalytic activity of PtNi alloys were systematically studied.Combined experimental and theoretical investigations reveal that tuning Pt/Ni ratio results in only 1.1 times enhancements in Pt mass activity,whereas edge dislocations-induced extra tensile strain on Ni site and compressive strain on Pt site further boost the alkaline HER intrinsic activity at all Pt/Ni ratios.Impressively,the introduction of edge dislocations in PtNi alloys could break the limit of alloying in boosting Pt mass activity and result in up to 13.7-fold enhancement,in the case that Pt and Ni contents are nearly identical and thus edge dislocation density reaches the maximum.Fundamental mechanism studies demonstrate that the edge dislocation strategy could make a breakthrough in facilitating water dissociation kinetics of PtNi alloys.

低阶煤热解条件对高炉喷吹半焦燃烧性能及动力学特性的影响

采用热重分析法研究了不同热解条件下半焦的燃烧性能和动力学特征,利用Ozawa法求取动力学参数。结果表明,热解温度越低、保温时间越短时,半焦的燃烧性能越好;热解升温速率对半焦燃烧过程的反应程度影响不大;粒度越大,燃烧性能差异性越明显。热解温度对半焦燃烧性能影响较大,550℃是本研究中制备高燃烧反应性半焦的适宜热解温度。两种不同粒度原煤制得的半焦均随转化率增大,活化能减小。1~3 mm原煤在热解温度为550℃时所得半焦在燃烧过程中符合反应级数模型,化学反应为限制性环节,反应最概然机理函数为f(α)=(1–α)~2。

RECENT PROGRESS IN RESIDUAL STRESS MEASUREMENT TECHNIQUES

Residual stress measurement is of critical significance to in-service security and the reliability of engineering components,and has been an active area of scientific interest.This paper ofers a review of several prominent mechanical release methods for residual stress measurement and recent developments,focusing on the hole-drilling method combined with advanced optical sensing.Some promising trends for mechanical release methods are also analyzed.