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BackgroundThe silicon drift detector (SDD) has been widely used in space exploration in recent years. The SDD has outstanding energy resolution, but its time resolution is not very satisfactory. The charge packet generated by the interaction between the incident photon and the detector takes some time to drift to anode. The drift time depends on the distance between the interaction position and the anode, and usually can't be measured directly. Therefore, the uncertainty of drift time is the main factor that affects the time resolution of the SDD system.PurposeThis study aims to propose a method called pulse amplitude ratio to measure the drift time so as to improve the time resolution of the SDD system.MethodsThe correspondence between the drift time and the rise time of the output signal of the charge sensitive amplifier (CSA) was made use of. The rise time was measured by the pulse amplitude ratio of triangular and trapezoidal shaping, hence the drift time was obtained by measuring the pulse amplitude ratio. Matlab/Simulink module and Xilinx module of system generator were used to build the system for simulation of the readout chain for pulse amplitude ratio measurement. The relationship between pulse amplitude ratio and CSA output signal, and the influence of SDD and CSA electronic noise on pulse amplitude ratio were investigated in details.ResultsSimulation results show that the pulse amplitude ratio of the shaping network only depends on the rise time, and the electronic noise of SDD and CSA can cause the measurement error.ConclusionsThe influence of electronic noise of SDD can be reduced by using optimized parameters of the shaping network, and the accuracy of the corrected arrival time can be improved by about one order of magnitude.

To meet the application requirements of airport pavement with high permeability, three kinds of continuous gradations with void ratios of 25%, 30% and 35% respectively were designed for gravel and gravel with sand, as well as three kinds of single-grain gradations with the size of 2.36~9.5 mm, 9.5~26.5 mm and 26.5~37.5 mm respectively for gravel. The bulk density and apparent density of gravel with different gradations were tested for calculating the loose paving coefficient and void ratio. The mechanisms of the effect of gradation on the above properties were analyzed. The results show that:with the increase of the content of sand and gravel with the size less than 9.5 mm, the loose paving coefficient first increased and then decreased. The gradation effect for gravel with smaller size was better than that for gravel with larger size. The void ratio of gravel mainly depended on the gradation. Suggesting that making the content of gravel with size less than 9.5 mm at about 35% and sand no more than 18% to effectively improve the compaction effect and mechanical structure of graded gravel. Suggesting that the value of n should be 1.009 and 1.221 respectively when the gradation of gravel with void ratios of 25% and 30% was designed by Taibo formula. [ABSTRACT FROM AUTHOR]

For testing ventilation rate, a reusable control sample was designed for cigarette test station. The control sample was composed of a wrapper layer of elastic material and a filler layer of porous material. The critical flow tubes used for draw resistance and ventilation rate testing were adopted to simulate the draw resistance and ventilation rate of cigarette. A quality control chart was used to monitor the testing process and effectively identify the problems in the testing process. The performance and applicability of the control sample were assessed and the effects in major application scenarios were analyzed. The results showed that: 1) The simulative testing of all cigarette physical indexes, including weight, circumference, draw resistance, hardness, length and ventilation rate, were realized. 2) The consistency and uniformity of the control sample was significantly better than those of cigarette. The coefficient of variation of all indexes was obviously lower than that of cigarette, that of hardness was lower than 2% and that of the other indexes was lower than 1%. The variation range of draw resistance was 9 Pa and that of ventilation rate was 1.7% during five successive years, and the means and standard deviations of the other indexes did not change basically. It suggested that designed control sample might be adaptable to cigarette test stations of different types. 3) The control sample performed very well in inter-laboratory collaborative testing, testing process monitoring, the repeatability and reproducibility evaluation of standard measurement methods and measurement auditing, it guaranteed the effectiveness and comparability of test results. [ABSTRACT FROM AUTHOR]

Chemometrics method was used to solve the problem of automatic selecting model for the detailed hydrocarbon analysis (DHA) of gasoline samples by gas chromatography/ flame ionization detection (GC/FID). The 29 peaks in GC/FID DHA chromatogram and their amounts were selected as the discriminating parameters to establish the five pattern models for different gasoline samples, such as fluid catalytic cracking (FCC) gasoline, coking gasoline, straight run gasoline, reformed gasoline, and alkylation gasoline. The principle component analysis (PCA) and Soft Independent Modeling of Class Analogies (SIMCA) were used to classify the gasoline samples and to identify the unknown samples according to the above pattern models. One hundred gasoline samples, derived from known resources, were employed to validate the reliability of the sample identity technique. With the help of the pattern identity method referred here, the automation of GC/FID DHA method becomes possible.

A method to establish octane number prediction model based on detailed hydrocarbon analysis (DHA) data is presented. The techniques of fuzzy-clustering and the Euclidian distance are employed to select the samples needed in pattern establishment. One hundred and fifty gasoline samples and an amount of 140 characteristic components in the DHA chromatogram of each sample are used for the fuzzy-clustering research. It is found that the 3 - 10 samples, which have the nearest Euclidian distance ( < 1.5) to the prediction sample in the same cluster, are enough to build the octane number prediction model. The experimental results proved that the model obtained according to the above method has more predictable accuracy, wider application range and higher data resource utility compared with the current prediction method.