Spatiotemporal characteristics and driving mechanism of the coupling coordination degree of urbanization and ecological environment in Kazakhstan

Journal of Geographical Sciences - When viewed against the backdrop of globalization and the Belt and Road Initiative (BRI), Central Asia has ushered in new development opportunities. However,...     

基于地理探测器下的川西高原地表温度空间格局及影响因子分析——以西昌市为例

以西昌市为例,选取2010年和2015年 Landsat系列遥感影像,在“3S”技术的支持下,采用监督分类中的最大似然法,并结合Google Earth高分辨率影像和GPS野外实地验证数据获取西昌市2010年和2015年土地利用信息;再利用大气校正法反演获得西昌市2010年和2015年地表温度,并对反演结果中的高温异常区进行实地调研验证;最后,采用地理探测器定量分析了坡度、总辐射、坡向、海拔、年均降水量、年均气温、植被类型、土壤类型以及土地利用类型9个影响因子对地表温度影响的解释力。结果表明：（1）地表温度空间分布存在显著差异。（2）影响因子对地表温度的影响存在差异,其中海拔和年均气温对地表温度的影响较大,而总辐射影响最小。（3）不存在单一因素或是单一性质的因素影响地表温度。不同影响因子之间存在交互作用,对地表温度的影响是相互增强或非线性增强的。（4）部分影响因子对地表温度具有显著性差异影响,并且地表温度均值最大时,对应着影响因子不同的范围或类型。     

Differentiation of bulk and surface events in p-type point-contact germanium detectors for light WIMP searches

The p-type point-contact germanium detectors are novel techniques offering kg-scale radiation sensors with sub-keV sensitivities. They have been used for light dark matter WIMPs searches and may have potential applications in neutrino physics. There are, however, anomalous surface behaviour which needs to be characterized and understood. We describe the methods and results of a research program whose goals are to identify the bulk and surface events via software pulse shape analysis techniques, and to devise calibration schemes to evaluate the selection efficiency factors. Efficiencies-corrected background spectra from the low-background facility at Kuo-Sheng Neutrino Laboratory are derived.     

四川成都市唐昌镇土壤硒分布特征及影响因素

硒是人体必须的微量元素之一,食用含硒农产品是人体获取硒元素的重要途径。调查土壤硒的含量特征、划定富硒区、查明硒空间分布和迁移富集的影响因素,对富硒土地资源利用和富硒农产品开发具有重要意义。本文选择成都市唐昌镇采集土壤样品,采用原子荧光光谱法(AAS)和电感耦合等离子体发射光谱/质谱法(ICP-OES/MS)等方法测定土壤中的Se、As、总有机碳(TOC)等组分含量和pH值,运用方差分析、相关性分析、地理探测器等方法对土壤硒含量、分布特征及影响因素进行探讨。结果表明：(1)研究区土壤硒含量范围为0.082～1.10mg/kg,平均含量为0.337mg/kg,分别是成都市、四川省和全国土壤硒平均含量的1.47、4.02和1.16倍;(2)全镇99.2%的土壤硒呈足硒及富硒状态,且土壤硒含量随着深度增加总体呈降低趋势,空间分布上,高硒区整体呈北西向带状分布于战旗、柏木、大云和竹林等村落;(3)相关性分析表明土壤Pb、Cr、Ni、Cd、Hg、As、总钾(TK)、总氮(TN)、pH、TOC和海拔高度对土壤硒的富集迁移均有极为显著(P<0.01)的影响,但影响程度不一;(4)地理探测器的因子...     

一次伴随阵风锋的下击暴流天气分析

利用湖北省区域站资料、Micaps常规观测资料和雷达资料,对2017年盛夏季节一次副高控制下的下击暴流事件进行分析,结果表明:①本次过程是一次典型的由脉冲风暴产生的大风天气,过程中出现明显的阵风锋;②受地形及局地热力条件共同作用,强回波向西南方向移动;③阵风锋形成初期与回波主体距离很近,强回波持续时间长,造成局地的强降水,强下沉气流和强降水导致了大范围的大风天气,此时大风主要分布在强回波移动方向的前沿附近;④后期阵风锋快速移动,远离回波主体,回波迅速减弱,强下沉气流向外流出导致地面出现大风,地面出现两条阵风锋,且两条阵风锋相遇,此时大风主要出现在两条阵风锋交汇处和雷暴冷出流最强处,对临近预报有一定的参考意义。     

Monte carlo simulation of in situ gamma-spectra recorded by NaI (Tl) detector in the marine environment

To develop a Na I(Tl) detector for in situ radioactivity monitoring in the marine environment and enhance the confidence of the probability of the gamma-spectrum analysis, Monte Carlo simulations using the Monte Carlo N-Particle( MNCP) code were performed to provide the response spectra of some interested radionuclides and the background spectra originating from the natural radionuclides in seawater recorded by a Na I(Tl) detector. A newly developed 75 mm × 75 mm Na I(Tl) detector was calibrated using four reference radioactive sources 137 Cs, 60 Co, 40 K and 54 Mn in the laboratory before the field measurements in seawater. A simulation model was established for the detector immersed in seawater. The simulated spectra were all broadened with Gaussian pulses to reflect the statistical fluctuations and electrical noise in the real measurement. The simulated spectra show that the single-energy photons into the detector are mostly scattering low-energy photons and the high background in the low energy region mainly originates from the Compton effect of the high energy γ-rays of natural radionuclides in seawater. The simulated background spectrum was compared with the experimental one recorded in field measurement and they seem to be in good agreement. The simulation method and spectra can be used for the accurate analysis of the filed measurement results of low concentration radioactivity in seawater.     

Scintillation efficiency for low energy nuclear recoils in liquid xenon dark matter detectors

We perform a theoretical study of the scintillation efficiency of the low energy region crucial for liquid xenon dark matter detectors. We develop a computer program to simulate the cascading process of the recoiling xenon nucleus in liquid xenon and calculate the nuclear quenching effect due to atomic collisions. We use the electronic stopping power extrapolated from experimental data to the low energy region, and take into account the effects of electron escape from electron–ion pair recombination using the generalized Thomas-Imel model fitted to scintillation data. Our result agrees well with the experiments from neutron scattering and vanishes rapidly as the recoil energy drops below 3 keV.     

Improving photoelectron counting and particle identification in scintillation detectors with Bayesian techniques

Many current and future dark matter and neutrino detectors are designed to measure scintillation light with a large array of photomultiplier tubes (PMTs). The energy resolution and particle identification capabilities of these detectors depend in part on the ability to accurately identify individual photoelectrons in PMT waveforms despite large variability in pulse amplitudes and pulse pileup. We describe a Bayesian technique that can identify the times of individual photoelectrons in a sampled PMT waveform without deconvolution, even when pileup is present. To demonstrate the technique, we apply it to the general problem of particle identification in single-phase liquid argon dark matter detectors. Using the output of the Bayesian photoelectron counting algorithm described in this paper, we construct several test statistics for rejection of backgrounds for dark matter searches in argon. Compared to simpler methods based on either observed charge or peak finding, the photoelectron counting technique improves both energy resolution and particle identification of low energy events in calibration data from the DEAP-1 detector and simulation of the larger MiniCLEAN dark matter detector.