Dynamic Characteristics of Single-frequency Signal after Modulated by Feedback Control System

In order to study the dynamic characteristics of the single-frequency signal through the nonlinear control system, the system control mode, the outer excitation patterns of the model and the amplitude are investigated by using the methods of the nonlinear dynamical analysis. The time-domain diagram, power spectrum, phase diagram and the largest Lyapunov exponent obtained from the process of the signal propagate through different control module are given. The researches on different control systems demonstrate that： after single-frequency signal goes through the nonlinear controller, it is still non-chaotic although the output contains more frequency components; but with the feedback and the external perturbation, the output is a continuous broadband spectrum and the result shows that there is chaos. The energy of the input signal reduces with some appropriate parameters. Therefore, the control system of the nonlinear feedback is a good way to broaden the spectrum of output with inputting a single-frequency signal.     

Effect of gas tightness-controlled compartment system on quality keeping of fresh produce stored in household refrigerator

Refrigerator chill compartments with volumes of 22-L were fabricated, which had different gas tightness properties to gas or water vapor, ranging from 1,770 to 107,000 mL/hr·m²·atm in CO₂ permeance at 25°C. Those compartments were filled with prepared fresh vegetables, and then their ability to preserve the quality at 3°C for 14 days was compared. The internal atmosphere and humidity were monitored together with the stored produce quality. The air-tight compartment with the lowest permeance created an atmosphere slightly different from air (CO₂ 0.8–1.6%; O₂ 19.7–20.4%), while the other ones had atmospheres of normal air. The relative humidity of the compartments ranged from 52 to 97%. Two air-tight compartments, maintaining a relative humidity mostly higher than 95%, preserved the produce better than the conventional open type one, with reduced weight loss and better retentions of ascorbic acid and chlorophyll.     

考虑地墙渗漏影响的地铁基坑安全性状研究

在饱和含水软土层开挖基坑,地下水已成为影响基坑安全的最重要因素之一。对于地铁基坑,一般都会采取基坑降水等措施,但其地下连续墙施工质量的优劣直接影响了地下水对基坑的危害程度,结合已有的文献和工程资料,在分析地下连续墙渗漏对墙周地下水影响的基础上,根据基坑降水计算方法,从理论角度考虑地下连续墙渗漏时基坑的安全评判,并根据实际工程案例分析文中所提出评判方法的适用性,希望工程建设者们在施工中注意相应的问题,避免不必要的险情发生。