仿生纳米复合膜透CO_2性能及应用研究

优化仿生纳米复合膜透CO2性,并将其应用于草莓保鲜实验。结果表明,仿生纳米复合膜最佳配方为:壳聚糖含量2 g,纳米SiO2含量0.07 g,冰乙酸含量1.4 mL,且透CO2量达到最低为0.0909 g/d;优化膜处理的草莓低温4℃下贮藏11天后,腐烂指数比空白组降低了23.9%。这证明,优化膜处理可有效延长草莓低温下的贮藏保鲜时间。     

Dynamic performance of vehicle in high-speed freight EMU equipped with four double-axle bogies

Size and weight limitations mean that ordinary railway vehicles with two double-axle bogies cannot deliver some extremely heavy cargo and products. Thus, a newly designed high-speed freight electric multiple unit(EMU) equipped with two bogie groups each with two double-axle bogies connected by a transition frame is an alternative means of transporting heavy products because of its greater load capacity. However, because it is still in the design stage, its dynamic performance is yet to be researched, something that is urgently required because of the more-complicated structure and more-intensive wheel-rail interactions than those of traditional high-speed railway vehicles. Therefore, to reveal the dynamic performance, this study establishes a three-dimensional dynamic model of a trailer vehicle in a high-speed freight EMU equipped with four double-axle bogies based on the classical theory of vehicle-track coupled dynamics. In this dynamic model, the vertical, horizontal, rolling,pitching, and yaw motions of the major components excited by random irregularities in the track geometry are considered fully.The results indicate that the derailment coefficient and stability index of this vehicle are both at excellent levels for the simulated conditions. The wheel unloading ratio appears to be larger but still within the safety range when the vehicle runs in a straight line,but it is close to or can even exceed the limit value when the vehicle runs at 400 km/h on a specified curved line.     

Mesh stiffness evaluation of an internal spur gear pair with tooth profile shift

Tooth profile shift will change the thickness of gear teeth and a part of geometrical parameters of a gear pair, thus influencing its mesh stiffness and consequently the dynamic performances. In this paper, an analytical mesh stiffness calculation model for an internal gear pair in mesh considering the tooth profile shift is developed based on the potential energy principle. Geometrical representations of the tooth profile shift are firstly derived, and then fitted into the analytical tooth stiffness model of gears. This model could supply a convenient way for mesh stiffness calculation of profile shifted spur gears. Then, simulation studies are conducted based on the developed model to demonstrate the effects of tooth profile shift coefficient on the tooth compliances and the mesh stiffness of the internal spur gear pair. The results show that tooth profile shift has an obvious influence on the mean value, amplitude variation and phase of the mesh stiffness, from which it can be predicted that the dynamic response of an internal gear transmission system will be affected by the tooth profile shift.     

The uplifting and denudation of main Huangshan Mountains,Anhui Province,China

The Huangshan Mountain Geopark is an important geological landmark and tourist attraction.In this paper,we apply fission track dating to examine the uplift and exhumation processes that created the Huangshan Mountains and provide a timeline for their development.In addition to being an important scientific contribution,this information can be used on guided tours and to promote tourism.The results of eight apatite fission-track analyses suggest three age groups:56,45-30,and 15 Ma.These age groups are relate...     

Effect of the drive system on locomotive dynamic characteristics using different dynamics models

Based on the theory of vehicle-track coupled dynamics and gear system dynamics, a locomotive-track coupled spatial dynamics model is established by considering the dynamic effects of the gear transmission system. The vibration responses of a locomotive's major components are then simulated using three locomotive-track models, namely the proposed dynamics model with the gear transmissions, a locomotive-track coupled dynamics model that considers the traction motor, and the classical Zhai's model. The locomotive dynamic responses of the three models are extracted and compared to reveal discrepancies between them so as to explore the dynamic effects of the power transmission system and clarify potential applications of these models. The results indicate that the dynamic effects of the gear transmissions have a negligible influence on the lateral vibrations of the locomotive components. However, they have obvious effects on the vertical and longitudinal vibrations of the wheelset and the traction motor. Another advantage of the locomotive dynamics model that considers the dynamic effects of the gear transmissions is that the dynamic performance of the drive system can be assessed in the vehicle vibration environment. This study provides theoretical references that can assist researchers in choosing the most appropriate locomotive dynamics model according to their specific research purpose.     

模／数转换器和数／模转换器工作原理分析

随着数字技术的发展，在电视节目制作的前期和后期越来越多地采用数字音视频系统。考虑到现在处在从模拟向数字的过渡时期，还必需使用一些模拟视频源，这就需要将模拟信号转换为数字信号，才能送到数字系统中去；为了播出或监看等需要，又需要将数字信号转换为模拟信号。可以说模／数转换器（ADC）和数／模转换器（DAC）是联结模拟世界与数字世界的桥梁，     

水的汽液相平衡及径向分布的分子模拟研究

采用J．R．Errington等提出的固定点电荷水分子新模型,分别以Buckingham Exp-5势能结合哥伦布势能模型计算分子间的短程作用及Ewald Summation方法计算电荷间的长程作用,采用恒NVT吉布斯系综Monte Carlo模拟方法模拟了水在300K～600K下的汽液相平衡,并采用经典的恒NVT系综Monte Carlo模拟方法模拟了水在温度T=300K,ρ=1．0g／cm^3下的原子对径向分布函数。模拟结果与文献中的实验值吻合良好。本文工作为推广至更复杂水溶液体系的模拟打下了良好的基础。