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排序方式: 共有746条查询结果,搜索用时 31 毫秒
31.
Pitiporn Manokhoon 《International Journal of Green Energy》2020,17(13):864-871
ABSTRACT Sodium hydroxide is ideal in removing lignin from lignocellulosic materials at an effective operational cost. Two-stage NaOH pretreatment was employed herein to investigate lignin and hemicellulose removal and understand the morphology of Napier grass (Pakchong 1) (Pennisetum purpureum), which is considered lignocellulosic due to its high carbohydrate content. NaOH was used at different concentrations (0, 1, 2, 3, and 4 wt.%) and presoak times (1, 2, 3, and 4 h). The results demonstrated that 3 wt.% NaOH at 121°C without presoak resulted in 83.5% lignin removal, with a cellulose to lignin ratio of 3.0. Moreover, the treated samples showed cracking and irregular patterns at optimal conditions. 相似文献
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Given that the gold market and the crude oil market are the main representatives of the large commodity markets, it is of crucial practical significance to analyze their cointegration relationship and causality, and investigate their respective contribution, from the perspective of price discovery, to the common price trend so as to interpret the dynamics of the whole large commodity market and forecast the fluctuation of crude oil and gold prices. 相似文献
34.
This paper models the monthly price volatilities of four precious metals (gold, silver, platinum and palladium prices) and investigates the macroeconomic determinants (business cycle, monetary environment and financial market sentiment) of these volatilities. Gold volatility is shown to be explained by monetary variables, but this is not true for silver. Overall, there is limited evidence that the same macroeconomic factors jointly influence the volatility processes of the four precious metal price series, although there is evidence of volatility feedback between the precious metals. These results are consistent with the view that precious metals are too distinct to be considered a single asset class, or represented by a single index. This finding is of importance for portfolio managers and investors. 相似文献
35.
The study of extreme values and prediction of ozone data is an important topic of research when dealing with environmental problems. Classical extreme value theory is usually used in air-pollution studies. It consists in fitting a parametric generalised extreme value (GEV) distribution to a data set of extreme values, and using the estimated distribution to compute return levels and other quantities of interest. Here, we propose to estimate these values using nonparametric functional data methods. Functional data analysis is a relatively new statistical methodology that generally deals with data consisting of curves or multi-dimensional variables. In this paper, we use this technique, jointly with nonparametric curve estimation, to provide alternatives to the usual parametric statistical tools. The nonparametric estimators are applied to real samples of maximum ozone values obtained from several monitoring stations belonging to the Automatic Urban and Rural Network (AURN) in the UK. The results show that nonparametric estimators work satisfactorily, outperforming the behaviour of classical parametric estimators. Functional data analysis is also used to predict stratospheric ozone concentrations. We show an application, using the data set of mean monthly ozone concentrations in Arosa, Switzerland, and the results are compared with those obtained by classical time series (ARIMA) analysis. 相似文献
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NaCl和KCl对厌氧污泥抑制的动力学研究 总被引:2,自引:0,他引:2
在厌氧颗粒污泥和厌氧絮状污泥系统中,进行盐质量浓度(NaCl或KCl质量浓度,下同)对厌氧污泥抑制动力学的研究,得到不同拟合的COD降解动力学方程及参数.实验结果表明:当盐质量浓度为10~30 g/L时,KCl对厌氧污泥的COD比降解速率的抑制程度大于NaCl;当盐质量浓度由0 g/L增至10 g/L时,半速率常数逐渐增加;当盐质量浓度由10 g/L增至30 g/L时,半速率常数逐渐减小;在厌氧污泥系统中,NaCl抑制作用下的盐抑制常数高于KCl,且颗粒污泥的盐抑制常数高于絮状污泥. 相似文献
38.
介绍了基于智能卡读写模块ZL G500的门禁系统设计原理与方法,主要分析了该智能卡门禁系统中的数据存储与传输模块、系统主模块和时钟模块等重要组成模块的工作原理,同时给出了ZL G500与MCU的硬件接口及部分软件代码.本系统经过实际运行,具有稳定可靠、操作简便等特点. 相似文献
39.
介绍一种基于Linux的嵌入式操作系统和CDMA 1X无线数据业务的图像监控系统方案.系统以LvRLinux操作系统为软件平台,以ARM9微处理器AT91RM9200为硬件平台,采用MPEG-4的专用编码芯片G07007SB对采集到的视频信号进行压缩编码.然后生成MPEG-4视频流.AT91RM9200将视频流进行处理、缓存后通过串口发送到CDMA 1X无线模块,通过CDMA 1X业务将图像数据发送到远端服务器.远端服务器具有固定的实IP地址.远端服务器通过SOCK2ET接收图像数据并进行解码显示,还可以通过发送控制信号实现对下位机的控制. 相似文献
40.
Lumei Wang Weihong Ye Shanshan Zhou Kunde Lin Meirong Zhao Weiping Liu 《Journal of environmental science and health. Part. B》2013,48(1):38-43
The acute and chronic toxicity of monocrotophos (MCP), the binary joint toxicity of MCP and bifenthrin (BF), and sodium dodecyl benzene sulfonate (SDBS) to Daphnia magna (D. magna) was evaluated. The 24 h-median effective concentration (24 h-EC50) and 48 h-median lethal concentration (48 h-LC50) of MCP towards D. magna were 161 and 388 μ g/L, respectively. In addition, the lowest-observed effective concentration (LOEC) and non-observed effective concentration (NOEC) of MCP to D. magna were 10 and 5 μ g/L, respectively. Furthermore, the chronic value (ChV) of MCP against D. magna was 7 μ g/L and the acute chronic ratio (ACR) was 55. The number of offspring per female and the intrinsic rate of natural increase (r) were identified as the parameters that were most sensitive to MCP. In addition, toxic unit (TU) analysis was employed to evaluate the joint toxicities. The calculated TUmix values of binary equitoxic mixtures of MCP + BF and MCP + SDBS were 1.47 and 1.63, respectively, which suggests that both equitoxic mixtures exert a limited antagonistic effect. The results of this study revealed that the toxic threshold of MCP towards D. magna is higher than its reported highest residue (4 μ g/L) in the ordinary aquatic environment, and that concurrent exposure to BF or SDBS may exert a slight antagonistic effect. 相似文献