0Cr18Ni9不锈钢焊接温度场的数值仿真

基于有限元软件SYSWELD对不锈钢0Cr18Ni9平板TIG焊的温度场进行三维动态模拟,得出了瞬态温度场分布图和特征点的热循环曲线,同时也得出了焊缝上任一点的温度变化与相变的关系.与文献资料比较表明,所建立的数值模拟仿真模型可以较好的模拟焊接温度场,为研究焊接过程中的应力应变和减少焊接应力与变形提供了参考依据.     

Phylogenetic relationships and divergence times of the family Araucariaceae based on the DNA sequences of eight genes

Araucariaceae is one of the most primitive families of the living conifers, and its phylogenetic relationships and divergence times are critically important issues. The DNA sequences of 8 genes, i.e., nuclear ribosomal 18S and 26S rRNA, chloroplast 16S rRNA, rbcL, matK and rps4, and mitochondrial coxl and atpl, obtained from this study and GenBank were used for constructing the molecular phylogenetic trees of Araucariaceae, indicating that the phyiogenetic relationships among the three genera of this family should be （（Wollemia, Agathis）, Araucaria）. On the basis of the fossil calibrations of Wollemia and the two tribes Araucaria and Eutacta of the genus Araucaria, the divergence time of Araucariaceae was estimated to be （308± 53） million years ago, that is, the origin of the family was in the Late Carboniferous rather than Triassic as a traditional view. With the same gene combination, the diver- gence times of the genera Araucaria and Agathis were （246 ± 47） and （61 ±15） Ma, respectively. Statis- tical analyses on the phylogenetic trees generated by using different genes and comparisons of the divergence times estimated by using those genes suggested that the chloroplast matK and rps4 genes are most suitable for investigating the phylogenetic relationships and divergence times of the family Araucariaceae.     

Climatic significance of δ18O records from precipitation on the western Tibetan Plateau

Analysis of daily precipitation samples for stable oxygen isotopes （δ^18O） collected at the Shiquanhe and Gerze （Gaize, Gertse） stations in the Ngari （Ali） region on the western Tibetan Plateau indicates that air temperature affects the δ^18O variations in precipitation at these stations. In summer, Shiquanhe and Gerze show strongly similar trends in precipitation δ^18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ^18O values in precipitation during the active monsoon period, resulting from the southwest monsoon （the summer phase of the Indian monsoon）. However, during the break monsoon period （during the summer rainy season, when the monsoon circulation is disrupted）, δ^18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ^18O strengthen during the non-monsoon period （January--June, and October--December） due to continental air masses and the westerlies. In addition, evaporation also influences the δ^18O variations in precipitation. The observed temporal and spatial variations of δ^18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.     

基于DS18B20的数字式测温计设计

讨论了用C8051F320单片机和DS18B20单总线数字测温传感器,来设计数字式测温计的方法.完全利用单总线技术线路简单、硬件开销少、成本低廉、软件设计简单的优点,较好地解决了传统测温仪器普遍存在的携带不便、易损坏、易受腐蚀、易受电磁干扰等不足.可应用于对温度测量要求高可靠度、高精度、高智能化的HVAC环境控制等领域.     

基于单总线协议的多点测温技术及应用

为了对幼苗培养室的温度实施检测,本文采用C8051F020单片机和数字式温度传感器DS18B20,设计了分布式的多点温度测量和报警系统,使用总线驱动芯片74LS245驱动DS18B20,提高了驱动能力,延长了传输距离,增强了系统的可靠性,并根据DS18B20的单总线协议编写了软件.实践表明,该系统工作稳定,操作方便,温度测量误差为±0.5℃,实现了对多点温度的测量和报警,满足了系统设计要求.     

基于PC串口的多点测温系统

介绍一种基于PC串口通讯的简易测温系统,该系统由数字温度传感器DS18B20,通过单总线方式连接组成测温网络;PC机通过串口协议对单片机进行控制,实现测温.PC机可视化程序可以进行添加、删除、修改测温点;对测温点添加备注位置信息;循环测温并实时越限报警,显示各测温点的温度曲线;系统人机界面友好,实际效果好.     

基于嵌入式和DS18B20的温度采集系统

利用MCU、温度传感器、Flash芯片和USB控制芯片设计一个基于嵌入式USBX机的温度采集系统．该系统能将采集到的温度数据存储在自己的Flash芯片中,能将数据通过USB接口存储到USB移动存储设备中,同时还能够作为PC机的一个外设,通过USB接口连接到PC机上,直接在PC软件上进行温度数据的分析和处理．重点论述了温度采集系统的设计与实现．     

基于AT89C52的多功能实时时钟

本文旨在利用单片机AT89C52和DS12C887时钟芯片实现多功能实时时钟。采用DS18820作为温度传感器,可同时显示时间、日历、温度等信息。同时采用红外遥控技术实现远距离调整时间,方便快捷。     

基于单片机STC89C52的LED数码管温度显示及报警器的实现

随着时代的进步和发展,单片机技术已经普及到我们生活,工作,科研,各个领域,已经成为一种比较成熟的技术,本文将介绍一种基于单片机控制的数字温度计,本温度计属于多功能温度计,可以设置上下报警温度,当温度不在设置范围内时,可以报警。     

Geochemical characteristics and applications of 18a (H)-neohopanes and 17a (H)-diahopanes

Distributions and geochemical significances of 18α(H)-neohopanes and of 17α(H)-diahopanes in oils from west Xialiaohe depression of the Bohai Bay Basin have been studied. Relative abundance of 18α(H)-neohopanes and of 17α(H)-diahopanes can be effectively used as maturity parameters, in a range of medium-high mature stage, based on consideration on sedimentary-organic facies of source rocks. With a dual geochemical significance of maturity and sedimentary-organic facies, neohopane and diahopane parameters can be well used in oil-source correlation and in petroleum population division. Formation, primary concentration and preservation of precursors of rearranged hopanes are closely related to depositional conditions such as Eh-pH and clays content. A series of probable diahopanes (series D) was detected in the oils, which exhibits a similar distribution pattern and geochemical behavior as that of 17α(H)-diahopanes (series B).