An improved evaluation of the neutron background in the PandaX-Ⅱ experiment

In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively.     

Can (H2O) n (n = 1–2) as effective catalysts in the CH2OO + H2S reaction under tropospheric conditions?

The addition reaction of CH₂OO?+?H₂S → HSCH₂OOH without and with catalyst X (X?=?H₂O and (H₂O)₂) has been investigated by CCSD(T)-F12a/VTZ-F12//B3LYP/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling correction. When H₂O was introduced in the CH₂OO?+?H₂S reaction, it not only acts as a catalyst for producing HSCH₂OOH, but also plays as a reactant to forming HOCH₂OOH. The formation channel of HSCH₂OOH is more important than the formation channel of HOCH₂OOH with its calculated rate constant larger by 11.0–43.2 times within the temperature 280–320?K. Then, (H₂O)₂ catalysed CH₂OO?+?H₂S → HSCH₂OOH reaction has been taken into account with its rate lower 1.9–4.2 times than the reaction of CH₂OO?+?H₂S → HSCH₂OOH with water. Also, CH₂OO?+?H₂S with H₂O cannot compete with the CH₂OO?+?H₂S reaction without water. This is different from CH₂OO?+?(H₂O)₂ reaction, which is about 4 orders of magnitude larger than the rate constant for CH₂OO?+?H₂O reaction. Such discrepancy is possible because C(CH₂OO)···O(H₂O) interaction has been enhanced more obviously by H₂O as compared to that of C(CH₂OO)···O(H₂S) interaction.     

基于PLC 的中央空调制冷系统变频控制研究

针对现有中央空调系统能源消耗严重的现状,基于可编程逻辑控制器(Programmable Logic Controller,PLC)对中央空调系统进行变流量节能改造。分析改造后中央空调系统的结构组成和变频运行原理,并提出适用于冷冻水泵和冷却水泵的分段速温差控制和PID温差控制设计方案。控制硬件选用三菱FX3U系列PLC和台达VFD-EL变频器,软件选用GX Work2编程软件及力控组态软件。将控制方案进行实验验证,实验结果表明,所设计的两种控制策略不仅跟随系统末端负荷变化快速达到稳定运行状态,提高运行能效比,而且节能效果显著,节能率分别为40.2%和48.7%。     

碳纳米管的可控长度拾取及导电性分析

拾取指定长度的半导体性碳纳米管对大规模制造碳纳米管场效应管具有重要意义.本文提出了一种利用原子力显微镜探针和钨针对碳纳米管进行可控长度拾取的方法并进行了碳纳米管导电性分析.在扫描电子显微镜下搭建微纳操作系统,针对切割操作过程中原子力显微镜探针、钨针和碳纳米管的接触情况进行了力学建模和拾取长度误差分析.建立了单根金属性碳纳米管、单根半导体性碳纳米管及碳纳米管束与钨针接触的电路模型,推导了接入不同性质碳纳米管后电路的电流电压特性方程.使用原子力显微镜探针对碳纳米管的空间位姿进行调整,控制钨针对碳纳米管上目标位置进行通电切割,同时获取切割电路中的电流电压数据.实验结果表明,本文提出的方法能够有效控制所拾取碳纳米管的长度,增加碳纳米管与原子力显微镜探针的水平接触长度能够减小碳纳米管形变导致的拾取长度误差,建立的电流电压特性方程能够用于分析碳纳米管的导电性.     

Derivative temporal clustering analysis: detecting prolonged neuronal activity

Temporal clustering analysis (TCA) and independent component analysis (ICA) are promising data-driven techniques in functional magnetic resonance imaging (fMRI) experiments to obtain brain activation maps in conditions with unknown temporal information regarding the neuronal activity. Although comparable to ICA in detecting transient neuronal activities, TCA fails to detect prolonged plateau brain activations. To eliminate this pitfall, a novel derivative TCA (DTCA) method was introduced and its algorithms with different subtraction intervals were tested on simulated data with a pattern of prolonged plateau brain activation. It was found that the best performance of DTCA method in generating functional maps could be obtained if the subtraction interval is equal to or larger than the length of the rising time of the fMRI response. The DTCA method and its theoretical predication were further investigated and validated using in vivo fMRI data sets. By removing the limitations in the previous TCA, DTCA has shown its powerful capability in detecting prolonged plateau neuronal activities.     

Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

A widely and continuously tunable optical parametric generator (OPG) pumped by a 1064-nm acoustooptically Q-switched diode-end-pumped Nd:YAG laser based on MgO-doped periodically poled LiNbO3 crystal with a multigrating structure (29.2-30.4 μm) is reported.A broad continuous signal spectrum of 1513-1700 nm is obtained by changing the crystal grating periods from 29.2 to 30.4μm and by tuning the crystal temperature from 30 to 180 ℃ simultaneously.When the average pump power is 1.82 W with pulse duration of about 70 ns operating at a repetition rate of 10 kHz,the maximum signal output power of the periodically poled MgO-doped lithium niobate (PPMgLN) OPG is about 210 mW corresponding to the idler and total powers of 118.4 and 328.4 mW respectively.     

北斗用户机复杂电磁环境适应性试验评估方法

为精确评价北斗用户机复杂电磁环境适应能力, 在分析北斗用户机工作机理及易攻击性的基础上, 构建了北斗用户机面临的战场复杂电磁环境, 进行了电磁干扰对北斗用户机信号捕获、跟踪环节影响的仿真和评估方法研究, 得到了某型北斗用户机定位成功率和通信成功率与电磁环境复杂度的关系, 对北斗用户机的推广应用具有重要的借鉴意义。     

Prospect for Cosmological Parameter Estimation Using Future Hubble Parameter Measurements

We constrain cosmological parameters using only Hubble parameter data and quantify the impact of future Hubble parameter measurements on parameter estimation for the most typical dark energy models. We first constrain cosmological parameters using 52 current Hubble parameter data including the Hubble constant measurement from the Hubble Space Telescope. Then we simulate the baryon acoustic oscillation signals from WFIRST (Wide-Field Infrared Survey Telescope) covering the redshift range of z ∈[0.5,2] and the redshift drift data from E-ELT (European Extremely Large Telescope) in the redshift range of z ∈[2,5]. It is shown that solely using the current Hubble parameter data could give fairly good constraints on cosmological parameters. Compared to the current Hubble parameter data, with the WFIRST observation the H(z) constraints on dark energy would be improved slightly, while with the E-ELT observation the H(z) constraints on dark energy is enormously improved.     

Theoretical description of improving measurement accuracy for incoherence Mie Doppler wind lidar

For the nonlinearity of Fabry-Perot interferometer(FPI) transmission spectrum,the measurement uncertainty of incoherent Mie Doppler wind lidar based on it increases evidently with the increase of backscattering signal Doppler shift.A method of repeating the use of the approximate linear part of FPI transmission spectra for reducing the high uncertainty of a big Doppler shift is proposed.One of the ways of realizing this method is discussed in detail,in which the characteristics of FPI transmission spectrum changing with thickness and incident angle are utilized simultaneously.Under different atmosphere conditions,it has been proved theoretically that the range of measurement uncertainty drops to one-sixth while its minimum has no serious change.This method can be used not only to guide the new system design,but also as a new working way for the fabricated system.     

Coherent beam combination of adaptive fiber laser array with tilt-tip and phase-locking control

We present an experimental study on tilt-tip(TT) and phase-locking(PL) control in a coherent beam combination(CBC) system of adaptive fiber laser array.The TT control is performed using the adaptive fiber-optics collimator(AFOC),and the PL control is realized by the phase modulator(PM).Cascaded and simultaneous controls of TT and PL using stochastic parallel gradient descent(SPGD) algorithm are investigated in this paper.Two-fiber-laser-,four-fiber-laser-,and six-fiber-laser-arrays are employed to study the TT and PL control.In the cascaded control system,only one high-speed CMOS camera is used to collect beam data and a computer is used as the controller.In a simultaneous control system one high-speed CMOS camera and one photonic detector(PD) are employed,and a computer and a control circuit based on field programmable gate array(FPGA) are used as the controllers.Experimental results reveal that both cascaded and simultaneous controls of TT using AFOC and PL using PM in fiber laser array are feasible and effective.Cascaded control is more effective in static control situation and simultaneous control can be applied to the dynamic control system directly.The control signals of simultaneous PL and TT disturb each other obviously and TT and PL control may compete with each other,so the control effect is limited.