水平分置海底混响信号的空间相关特性研究

海洋混响是影响声呐性能的主要因素之一,同时也包含了大量的海洋环境信息,因此对海洋混响的研究就显得尤为重要。本文依据海底散射系数的空间相关半径来划分散射单元,给出一种水平分置多阵元接收海底混响信号的仿真模型,重点分析了混响信号的空间相关特性。从理论上得出水平分置海底混响信号的空间相关特性符合sinc(x)函数衰减规律;根据仿真信号分析得出,混响信号的空间相关性随海底散射系数相关半径和发射信号脉宽增大而减小。

Heat Transfer Analysis of Sterilization of Canned Milk Using Computational Fluid Dynamics Simulations

A uniform and effective heat distribution inside the canned milk is very crucial for achieving effective sterilization. It is extremely difficult to establish the temperature profile inside the canned milk during continuous industrial scale operation. Computational fluid dynamics （CFD） simulation can be a useful tool to determine the temperature distribution of the fluid inside the can during the sterilization process. A CFD model was developed for the sterilization of canned milk at 121 ~C. The simulation results were validated with the experimental measurements of temperatures. The formation and movement of slowest heating zone （SHZ） during the sterilization process was tracked. Moreover, effect of can position （vertical and horizontal） during processing on milk temperature distribution inside the can was also investigated. Higher Grashof and Rayleigh numbers were obtained for vertical positioning of can compared to horizontal can processing. Further, effectiveness of the process was calculated based on F-value and these results reinforced the positive effect of horizontal position of can during the sterilization process.

Geant4 Comparative Study of Affecting Different Parameters on Optical Photons Related to the Plastic Scintillation Detector

In this research, different parameters of plastic scintillator detector were investigated by Geant4 simulation toolkit. These parameters consisted of radius, length and position of PMT as well as surface reflective type and finish options. Furthermore, response time distributions of two organic plastic materials were studied. The results indicated that collecting optical photons has a linear relationship with PMT radius head. Also, the vertical location of PMT has a non-linear relationship with the optical photons collection. However, the collection decreased by increasing PMT length or moving PMT head horizontal position. The response functions of two plastic scintillator materials were in good agreement with experimental published results. Also, Geant4 radiation transport code can simulate incident radiation photon and predict subsequent events to the PMT head very well. The results indicated that BC-404 has faster scintillation properties versus BC-400 organic scintillator materials. Comparison between Geant4 outputs illustrates that the best reflector material and surface finish type for optical photons is ground TiO2.

A Method for Node Fault Detection in Wireless Sensor Networks

To reduce excessive computing and communication loads of traditional fault detection methods,a neighbor-data analysis based node fault detection method is proposed.First,historical data is analyzed to confirm the confidence level of sensor nodes.Then a node's reading data is compared with neighbor nodes' which are of good confidence level.Decision can be made whether this node is a failure or not.Simulation shows this method has good effect on fault detection accuracy and transient fault tolerance,and never transfers communication and computing overloading to sensor nodes.

Spectrum Response Estimation for Deep-Water Floating Platforms via Retardation Function Representation

The key concept of spectrum response estimation with commercial software,such as the SESAM software tool,typically includes two main steps:finding a suitable loading spectrum and computing the response amplitude operators(RAOs) subjected to a frequency-specified wave component.In this paper,we propose a nontraditional spectrum response estimation method that uses a numerical representation of the retardation functions.Based on estimated added mass and damping matrices of the structure,we decompose and replace the convolution terms with a series of poles and corresponding residues in the Laplace domain.Then,we estimate the power density corresponding to each frequency component using the improved periodogram method.The advantage of this approach is that the frequency-dependent motion equations in the time domain can be transformed into the Laplace domain without requiring Laplace-domain expressions for the added mass and damping.To validate the proposed method,we use a numerical semi-submerged pontoon from the SESAM.The numerical results show that the responses of the proposed method match well with those obtained from the traditional method.Furthermore,the estimated spectrum also matches well,which indicates its potential application to deep-water floating structures.

Statistical Analysis of the Relation Between Inflation and Unemployment in Democratic States Using Spearman＇s Correlation Coefficient With Application in Albania

The main purpose of the present study is to investigate the relation between inflation rate and unemployment rate in contemporary democratic states, using Spearman＇s correlation coefficient. We apply this method in Albania during the period from January 2005 to December 2014. Some results of the study include： （1） The Central Limit Theorem （CLT） is not applicable for the quarterly inflation rate as well as for quarterly unemployment rate in Albania during the period from January 2005 to December 2014 at the confidence level of 99.99%. The official data for inflation and unemployment contradict the CLT at a very high confidence level of 99.99%; （2） The inflation process in Albania during the period from January 2005 to December 2014 is an unfair game at the confidence level of 99.2%; （3） The unemployment process in Albania during the period from January 2005 to December 2014 is an unfair game at the confidence level of 99.99%; （4） The inflation and unemployment in Albania during the period from January 2005 to December 2014 are statistically dependent at the 96% confidence level; （5） Spearman＇s correlation coefficient = 0.387 indicates a weak positive correlation between inflation and unemployment in Albania during the specified period; and （6） The official data for inflation and unemployment in Albania during the period from January 2005 to December 2014 are consistent with Friedman＇s hypothesis.

Fluorocarbon paint on Daya Bay antineutrino detectors

The aim of the Daya Bay reactor antineutrino experiment is to determine the neutrino mixing angle 813 with a sensitivity of 0.01 or better at 90% confidence level. In order to improve the position resolution of both the positron interaction and the neu- tron capture, the inside of the antineutrino detectors should be as unreflecting as possible. A black matt fluorocarbon paint is coated on the inner surface of the detectors made of 304L stainless steel to meet the physical requirement. This paint is com- patible with mineral oil, has low radioactivity, is easy to spray and fast curing at normal temperatures. The coating has excel- lent performance such as good adhesive force, uniformity, compact, scratch and wear resistance, and so on. It is the first appli- cation of such paint to large physical devices.