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931.
932.
933.
Time measurement plays a crucial role for the purpose of particle identification in high energy physics experiments. With increasingly demanding physics goals and the development of electronics, modern time measurement systems need to meet the requirement of excellent resolution specification as well as high integrity. Based on Field Programmable Gate Arrays(FPGAs), FPGA time-to-digital converters(TDCs) have become one of the most mature and prominent time measurement methods in recent years. For correcting the time-walk effect caused by leading timing, a time-over-threshold(TOT) measurement should be added to the FPGA TDC. TOT can be obtained by measuring the interval between the signal leading and trailing edges. Unfortunately, a traditional TDC can recognize only one kind of signal edge, the leading or the trailing. Generally, to measure the interval, two TDC channels need to be used at the same time, one for leading, the other for trailing. However, this method unavoidably increases the amount of FPGA resources used and reduces the TDC's integrity.This paper presents one method of TOT measurement implemented in a Xilinx Virtex-5 FPGA. In this method,TOT measurement can be achieved using only one TDC input channel. The consumed resources and time resolution can both be guaranteed. Testing shows that this TDC can achieve resolution better than 15 ps for leading edge measurement and 37 ps for TOT measurement. Furthermore, the TDC measurement dead time is about two clock cycles, which makes it good for applications with higher physics event rates. 相似文献
934.
近些年海量恒星光谱数据的获取使得恒星三个基本参数(表面有效温度Teff,表面重力log g,金属丰度[Fe/H])的自动测量方法研究成为一个重要的研究课题,相应对恒星大气物理参数测量的研究将对科学家研究宇宙演化等重大科学问题具有重要的意义。但是目前国内外针对此问题所做的研究并不是很广泛深入,且已有的一些方法还不能够完全准确地估计出恒星的大气物理参数。因此本文研究了一种基于质量估计的恒星大气物理参数自动测量方法,该方法计算量比较小,其主要思想是首先建立一些质量分布,将原始光谱数据经过质量估计算法映射到新的质量空间,然后在质量空间利用支持向量机回归对恒星的三个基本物理参数进行估计。在实验中,从SDSS-DR8光谱数据库中选择部分实测光谱数据来进行训练和测试,并将该方法预测出的参数结果与SSPP给出的参数值进行了对比,取得了比较理想的结果。实验结果表明, 该研究方法的准确率更高,预测结果更稳定,训练所用的时间短,在恒星大气物理参数自动测量上是行得通的,可以有效地测量恒星的大气物理参数。 相似文献
935.
采用综合物性测量系统(PPMS)的热容测量模块在1.9-300 K温度区间内对两种药物中间体(尿嘧啶和5-溴尿嘧啶)的低温热容进行了测量与研究. 结果表明, 在测量温区内两种化合物的低温热容随温度的上升而逐步增加, 无任何热异常现象产生; 在相同温度下, 5-溴尿嘧啶的热容数值始终高于尿嘧啶. 利用低温热容理论模型对热容数据进行了拟合, 并计算得到了0-300 K温区的摩尔熵变、焓变等热力学函数. 此外, 通过热容拟合数据计算得到的尿嘧啶和5-溴尿嘧啶在298.15 K的标准摩尔规定熵分别为(132.48±1.32)和(165.39±1.65) J·K-1·mol-1. 相似文献
936.
大气硝基(NO3)自由基和五氧化二氮(N2O5)是对流层大气化学反应的核心物种,对于理解大气氧化性、二次有机气溶胶生成、活性卤素化学和全球硫素循环等对流层大气化学研究的关键问题具有重要意义。大气NO3自由基和N2O反应活性高、大气寿命短、浓度低,其定量分析非常具有挑战性。本文总结了大气NO3自由基与N2O5的实地测量方法,并对差分光学吸收光谱(DOAS)、腔衰荡光谱(CRDS)、腔增强光谱(CEAS)、激光诱导荧光光谱(LIF)、电子顺磁共振谱(MIESR)和化学离子化质谱(CIMS)等六类技术方法的准确度、精确度、时间分辨率、测量干扰、标定方法和系统稳定性等方面进行了系统比较。综合分析认为吸收光谱法是对流层NO3自由基与N2O5测量技术的发展方向,其中近期发展起来的腔技术(CRDS和CEAS)显示出较好的应用潜力。但是我国实际大气环境中普遍存在高浓度的颗粒物污染,如何在高颗粒物条件下实现NO3自由基与N2O5的精密准确测量具有挑战性。本文进一步归纳了NO3自由基与N2O5在城市、森林、自由大气和海洋海岸等典型大气环境条件下的浓度水平和主要科学发现,探讨了一些亟待解决的问题和可能的重点研究方向。 相似文献
937.
The heat capacities of D-galactose and galactitol were measured on a quantum design physical property measurement system(PPMS) over a temperature range of 1.9―300 K, and the experimental data were fitted to a function of T using a series of theoretical and empirical models in appropriate temperature ranges. The fit results were used to calculate thermodynamic function values,Cp,mθ,Δ0TSmθ, and Δ0THmθfrom 0 K to 300 K. The standard molar heat capacity, entropy and enthalpy values of D-galactose and galactitol at 298.15 K and 0.1 MPa were determined to be Cp,mθ =(227.96±2.28) and (239.50±2.40) J·K-1·mol-1,Smθ= (211.22±2.11) and (230.82±2.30) J·K-1·mol-1 and = Hmθ (33.95±0.34) and (36.57± 0.37) kJ/mol, respectively. 相似文献
938.
吕德斯效应是多种金属和合金材料由于屈服阶段的不均匀变形而在材料表面产生条带状褶皱的现象,它会使冲压件表面质量降低. 为了防止它的出现,对吕德斯效应进行研究变得非常重要. 采用小视场(15mm×15 mm)下三维数字图像相关方法对小尺寸低碳钢试件在单轴拉伸载荷作用下的变形场进行测量,实际观测了小尺寸试件的吕德斯效应,结合理论模型解释了其形成机理,并分析了吕德斯带传播过程中应变及应变率的变化规律.实验研究表明,运用三维数字图像相关方法测量试件表面变形场,实现了对小尺寸低碳钢试件的吕德斯带演化过程以及颈缩、断裂等细观力学行为的观测,该方法是研究材料变形细观机理的一种有效测量手段. 相似文献
939.
Ning Zhang Zhongquan Zheng Steven Eckels Venkata B. Nadella Xiaoyang Sun 《Particle & Particle Systems Characterization》2009,26(4):199-209
We inject a large number of newly created nano‐particle aggregates into a chamber for the purpose of removing harmful contents in an indoor environment. This study is to experimentally and numerically investigate transient response of particle distributions to particle injections. A room‐sized chamber of 4 m × 2.1 m × 2.4 m is connected to a specially designed particle‐injection system, with two Optical Particle Counters used to simultaneously measure particle‐number densities with the size range from 0.3 μm to 10 μm at the inlet and in the chamber. A velocity probe measures the flow that is up to 1 m/s. An Euler‐type particulate‐phase‐transport model is developed and validated by comparing with experimental data. The study shows that the transient behavior of particle distributions is determined by many factors, including particle size, particle settling speed, sampling location, and velocity distribution. Particle number densities decrease in time more quickly for large particles than for small particles, and locations farther downstream in the chamber correlate more weakly with the inlet injection. 相似文献
940.
Study on autonomous navigation based on pulsar timing model 总被引:1,自引:0,他引:1
The basic principle of pulsar timing model was introduced, and the general relativistic corrections were analyzed when pulse
time of arrival (TOA) was transferred to coordinate TOA at the Solar System Barycentre. Based on the shifting, an iterative
method of autonomous position determination for spacecraft was developed. Accordingly, the linear form of the position offset
equation was evolved. Using the initial estimated value of spacecraft’s position as the input of pulsar timing equation, through
calculation of the offset between measured or transferred and predicted TOA, the position offset can be solved by Least Squares.
At last, the main error sources including modeling error and parameters error were discussed.
Supported by the National Defence Laboratory Foundation of China (Grant No. 9140C3601010901) and Science Foundation of Shaanxi
Province (Grant No. 2007F12) and the Technology Specialism Foundation of Shaanxi Education Department of Shaanxi Province
(Grant No. 07JK332), and the Innovative Research Plan of Xi’an University of Technology (Grant No. 105-210714) 相似文献