Machine Learning-Based Predictions on the Self-Heating Characteristics of Nanocomposites with Hybrid Fillers

A machine learning-based prediction of the self-heating characteristics and the negative temperature coefficient (NTC) effect detection of nanocomposites incorporating carbon nanotube (CNT) and carbon fiber (CF) is proposed. The CNT content was fixed at 4.0 wt.%, and CFs having three different lengths (0.1, 3 and 6 mm) at dosage of 1.0 wt.% were added to fabricate the specimens. The self-heating properties of the specimens were evaluated via self-heating tests. Based on the experiment results, two types of artificial neural network (ANN) models were constructed to predict the surface temperature and electrical resistance, and to detect a severe NTC effect. The present predictions were compared with experimental values to verify the applicability of the proposed ANN models. The ANN model for data prediction was able to predict the surface temperature and electrical resistance closely, with corresponding R-squared value of 0.91 and 0.97, respectively. The ANN model for data detection could detect the severe NTC effect occurred in the nanocomposites under the self-heating condition, as evidenced by the accuracy and sensitivity values exceeding 0.7 in all criteria.     

Electrothermal Tristability Causes Sudden Burn-In Phenomena in Organic LEDs

Organic light-emitting diodes (OLEDs) have been established as a mature display pixel technology. While introducing the same technology in a large-area form factor to general lighting and signage applications, some key questions remain unanswered. Under high-brightness conditions, OLED panels were reported to exhibit nonlinear electrothermal behavior causing lateral brightness inhomogeneities and even regions of switched-back luminance. Also, the physical understanding of sudden device failure and burn-ins is still rudimentary. A safe and stable operation of lighting tiles, therefore, requires an in-depth understanding of these physical phenomena. Here, it is shown that the electrothermal treatment of thin-film devices allows grasping the underlying physics. Configurations of OLEDs with different lateral dimensions are studied as a role model and it is reported that devices exceeding a certain panel size develop three stable, self heating-induced operating branches. Switching between them causes the sudden formation of dark spots in devices without any preexisting inhomogeneities. A current-stabilized operation mode is commonly used in the lighting industry, as it ensures degradation-induced voltage adjustments. Here, it is demonstrated that a tristable operation always leads to destructive switching, independent of applying constant currents or voltages. With this new understanding of the effects at high operation brightness, it will be possible to adjust driving schemes accordingly, design more resilient system integrations, and develop additional failure mitigation strategies.     

自加热茄汁酥肉加工工艺的研究

采用猪后腿肉为原料,以水分含量、剪切力、质构和感官评分为考察指标,研究挂糊组分、初炸温度、初炸时间、复炸温度和复炸时间等因素对自加热茄汁酥肉品质的影响规律.在单因素试验的基础上,采用L9(34)正交试验对自加热茄汁酥肉的工艺进行优化.结果 表明,挂糊组分对剪切力、硬度、咀嚼性影响显著(P＜0.05),初炸温度对硬度、内...     

Optimized power simulation of AlGaN/GaN HEMT for continuous wave and pulse applications

An optimized modeling method of 8 × 100 μm AlGaN/GaN-based high electron mobility transistor (HEMT) for accurate continuous wave (CW) and pulsed power simulations is proposed. Since the self-heating effect can occur during the continuous operation, the power gain from the continuous operation significantly decreases when compared to a pulsed power operation. This paper extracts power performances of different device models from different quiescent biases of pulsed current-voltage (I-V) measurements and compared them in order to determine the most suitable device model for CW and pulse RF microwave power amplifier design. The simulated output power and gain results of the models at V_gs = -3.5 V, V_ds = 30 V with a frequency of 9.6 GHz are presented.     

Investigation of wood pellets self-heating kinetics and thermal runaway phenomena using lab scale experiments

The phenomena of spontaneous combustion and thermal runaway in wood pellets storage were investigated using lab-scale experiments in the temperature range of 100–200 °C. The critical temperatures were determined for four sizes of reactors. The kinetic parameters of the self-heating were determined using three methods, the Frank-Kamenetskii's method, crossing point method, and numerical curve fitting method. Mean values of activation energy (E) of 78.7 ±0.8 kJ/mol and self-heating rate constant (∆ _rhA) of (4.22 ±2.5) × 10 ⁶ kJ/(kg s) were obtained for four type of wood pellets (made from whitewood) samples from different pellet producers in British Columbia. Finally, a two-dimensional numerical model was developed to predict the temperature development during self-heating and the critical temperature for known sizes of reactors.     

激光测距仪的脉冲电流供电温度控制系统

激光测距系统中的发射器件和接收器件具有温敏特性且均为小功率器件,精密测温电路采用Pt电阻时,Pt电阻的自热效应影响测温精度.为减小自热效应产生的测温误差,在分析Pt电阻测温误差产生机理的基础上,提出了一种新的脉冲电流供电方案,建立了脉冲电流供电电路及其自热升温过程的数学模型,给出了脉冲宽度和热量积累的关系,并通过合理控制脉冲宽度大大减小了自热效应引起的测温误差.使用高阶正交多项式拟合法对Pt电阻的非线性进行了补偿,给出了该系统温度测量模块测量数据与一级标准铂电阻温度值的比较实验,在不同的温度点,该温度测量系统的最大误差为0.000 6 ℃.系统稳定性测试结果表明,该系统在0～15 ℃时,各温度点控制稳定度均优于0.005 ℃,满足高精度激光测距的需要.     

激光测距仪中基于脉冲电流供电的高精度温度控制系统

半导体激光器及雪崩光电二极管作为激光测距仪中发射和接收系统中的关键器件,温度对其性能的影响限制激光测距仪的测量精度。而且二者均为小功率器件,精密测温电路中采用Pt电阻测温时,Pt电阻的自热效应产生的测温误差不能忽略。基于此,在对Pt电阻测温的误差产生机理做详细分析的基础上,提出了一种新的脉冲电流供电的方案,建立了脉冲电流供电电路及其自热升温过程的数学模型,给出了脉冲宽度和热量积累的关系,通过合理控制脉冲宽度大大减小了自热效应引起的测温误差;使用高阶正交多项式拟合的方法对Pt电阻的非线性进行了补偿,给出了该系统温度测量模块测量数据与一级标准铂电阻温度值的比较实验,在不同的温度点,该温度测量系统的最大误差为 0.0006度。系统稳定性测试结果表明,该系统在0度到15度 的温度范围内各温度点控制稳定度均优于±0.005度 。     

Phenomenological characteristics of cool-flame oxidation of cyclohexane

The phenomenological characteristics of cool flames of cyclohexane are studied. It is shown that cyclohexane flames arise at lower temperatures (beginning at T ≈ 230°C) and lower pressures (lower than 10 torr at T = 290°C) than alkane and alkene flames. The temperature dependence of the lower pressure limit of the cool flame is determined. It is established that, depending on the conditions (p, T, and C₆H₁₂/O₂ ratio), cool-flame ignition is characterized by a rise and drop of the temperature ΔT or by several peaks imposed on each other. The dependence of the cool-flame structure (for ΔT) on the oxygen content in the reaction mixture is studied. It is shown that the cool flame resulting from cyclohexane oxidation is accompanied by ring opening and formation of products with a smaller number of carbon atoms. It is established that cool flames of cyclohexane are characterized by a negative temperature coefficient. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 26–28, January–February, 2008.     

轻烃三一段纯氧转化制甲醇合成气的自然增碳研究

为达到甲醇合成的化学当量比,采用三一段纯氧自热转化工艺,即原料气分3路进行换热蒸汽转化、外热蒸汽转化和直入二段炉的蒸汽转化串纯氧自热转化方法,实现自然增碳的目的。对比了天然气制甲醇一段法与三一段纯氧转化法工艺的基本原理和工艺流程;分析了国外天然气二段转化合成甲醇的主要技术参数;从工艺特征、转化流程、设备组合等方面论述了三一段纯氧转化制甲醇合成气的设计技术、消耗指标、投资及成本。结果表明,按甲醇售价2 500元/t计,投产后约2年即可收回投资。     

GaAsMESFET准二维动态大信号模型

本文运用电荷控制分析方法,提出了GaAs MESFET以电荷源为基本组成元件的大信号非线性动态模型.该模型在解决了电荷不守恒问题以及DC与RF电流不一致性问题的同时,结合器件的温度特性与自升温效应,实现了GaAs MESFET的准二维大信号动态分析.