Describing alpine lake influence on stream network temperatures: A statistical modelling approach     

Samuel P. Carlson  Geoffrey C. Poole 《水文研究》2021,35(3):e14072

Systematic variations in atmospheric heat exchange, surface residence time, and groundwater influx across montane stream networks commonly produce an increasing stream temperature trend with decreasing elevation. However, complex stream temperature profiles that differ from this common longitudinal trend also exist, suggesting that stream temperatures may be influenced by complex interactions among hydrologic and atmospheric processes. Lakes within stream networks form one potential source of temperature profile complexity due to the spatially variable contribution of lake-sourced water to stream flow. We investigated temperature profile complexity in a multi-season stream temperature dataset collected across a montane stream network containing many alpine lakes. This investigation was performed by making comparisons between multiple statistical models that used different combinations of stream and lake characteristics to represent specific hypotheses for the controls on stream temperature. The compared models included a set of models which used a topographically derived estimate of the hydrologic influence of lakes to separate and quantify the effects of stream elevation and lake source-water contributions to longitudinal stream temperature patterns. This source-water mixing model provided a parsimonious explanation for complex stream-network temperature patterns in the summer and autumn, and this approach may be further applicable to other systems where stream temperatures are influenced by multiple water sources. Simpler models that discounted lake effects were more optimal during the winter and spring, suggesting that complex patterns in stream temperature profiles may emerge and subside temporally, across seasons, in response to diversity of water temperatures from different sources.  相似文献   

基于NPSVM模型的超新星识别方法          下载免费PDF全文

王精东  陈星星  梁吴颖  黄泽锋  全少武  沈锦泫  石雄辉 《天文学报》2021,62(2):15-53

巡天观测与高能物理、黑洞天文等领域均有密切的联系.基于星系-超新星二分类问题,研究光谱数据预处理,结合余弦相似度改善PCA(Principal Component Analysis)光谱分解特征提取方法,用SDSS(the Sloan Digital Sky Survey)、WISeREP(the Weizmann Interactive Supernova data REPository)组成的5620条光谱数据集训练支持向量机,可以得到0.498%泛化误差的识别模型和新样本分类概率.使用Neyman-Pearson决策方法建立NPSVM(Neyman-Pearson Support Vector Machine)模型可进一步降低超新星的漏判率.  相似文献   

基于双谱滤波的综合脉冲星时算法研究          下载免费PDF全文

周庆勇  魏子卿  张华  刘思伟  孙鹏飞  张奋  姜坤  刘晓刚  李奎 《天文学报》2021,62(2):19-95

毫秒脉冲星的自转频率非常稳定,提供了一种独立的基于遥远自然天体并能持续数百万乃至数十亿年的时间基准,具有稳定性强、运行时间长、服务范围广等特点.为了减弱毫秒脉冲星计时观测中各种高斯噪声对脉冲星时的影响,研究了一种基于双谱滤波的综合脉冲星时构建算法,处理分析了国际脉冲星计时阵(International Pul-sar Timing Array,IPTA)最新发布的4颗毫秒脉冲星(PSR J0437-4715、J0613-0200、J1713+0747和J1909-3744)的观测数据,分析了不同时间尺度综合脉冲星时的稳定性,并与构成国际原子时(International Atomic Time,TAI)的4家授时单位原子钟稳定性进行了比较.结果表明:双谱滤波算法能够较好地抑制观测噪声,提高综合脉冲星时的稳定性.相比于经典加权算法,综合脉冲星时1 yr、10 yr稳定度从7.77×10^-14、8.56×10^-16分别提高到1.50×10^-14、3.50×10^-16,单脉冲星时稳定性的提升也类似.同时发现,综合脉冲星时稳定性在5 yr及以上时间尺度上优于原子钟稳定性,可用于改善当前原子时的长期稳定性.  相似文献   

黄土洞室掘进深度与围岩位移变化规律研究     

时卫民  王鹏  赵尚毅 《岩土工程技术》2020,(2):70-75

应用PLAXIS 2D/3D有限元分析软件,对某黄土洞室进行了二维、三维分步掘进、三维一次掘进等工况的弹塑性有限元分析,研究分析了不同工况下洞室围岩位移的变化规律,并对掌子面的空间效应进行了分析。分析结果表明,二维与三维分步计算的最终位移基本一致,可以用二维的计算结果来估算洞室开挖的最终位移。三维分步掘进的分析表明,不同埋深的洞室其位移比的变化规律基本一致,当L/B<1时(L为掘进深度,B为洞室跨度),位移比呈线性增加;当L/B>1时,位移比呈非线性增加;当L/B>3时,其最大位移接近最终位移。掌子面的空间效应分析表明,在掌子面处的位移约为最终位移的1/3,距掌子面0.5倍跨度处的位移约为最终位移的2/3,距掌子面2.5倍跨度处的位移基本达到了最终位移。  相似文献   

基于小波变换与神经网络的石羊河流域夏季地温预测模型研究   总被引：1，自引：1，他引：0  

贾东于  李开明  聂晓英  袁春霞  李清峰  高福元 《冰川冻土》2020,42(2):412-422

地温变化在气候反馈效应中起着重要作用， 理解地温及其与影响因素之间的时空关系对预测全球温度变化至关重要。利用1998 - 2017年石羊河流域的逐日常规气象观测资料， 采用小波分析结合BP（Back Propagation）神经网络构建了石羊河流域夏季地温预报模型， 结果表明： 日平均地温预测效果在不同站点均为最佳， 其中预测值和观测值的相关系数均大于0.87， 3 ℃以内的预测概率均大于84%。其中， 民勤地区地温预测效果最好， 预测值和观测值的相关系数达到0.91， 3 ℃以内的预测概率达到86%。日最高地温的预测值与观测值的相关系数高于0.8， 但误差平方和、 标准差较大。永昌地区日最高地温的模拟效果最好， 3 ℃以内的预测概率达到83%。日最低地温的预测与观测值的平均相关系数高于0.66， 3 ℃以内的预报概率高于83%， 但预测值略低。其中， 武威地区日最低地温的预测效果最好， 预测值与观测值的相关系数为0.72， 3 ℃以内的预测概率达到94%。研究成果可为有效弥补干旱、 半干旱区地温观测资料缺失和探讨其与局地气候的关系提供一些参考。  相似文献   

米氏凯伦藻细胞表面膜蛋白质组及其对温度变化的响应研究     

王坤  王沛  张浩  张树峰  王大志 《海洋与湖沼》2019,50(3):652-663

米氏凯伦藻(Karenia mikimotoi)近年在我国福建、浙江和广东沿海经常形成赤潮,其赤潮不仅影响到海洋生态系统的稳定,也严重威胁到水产养殖以及人类生命健康安全。本论文以米氏凯伦藻为研究对象,建立了米氏凯伦藻细胞表面膜蛋白质荧光标记技术和细胞膜蛋白质提取方法,运用荧光差异凝胶电泳技术(2-DDIGE)对膜蛋白质进行了分析,并研究了米氏凯伦藻的膜蛋白质组及其对环境温度变动的响应。实验共鉴定到44个细胞表面膜蛋白,其中有效注释27个,主要为转运蛋白、HSP70蛋白家族和捕光蛋白等。米氏凯伦藻在20°C条件下的细胞生长和光合作用要明显好于16°C和12°C,但16°C和12°C条件下的差别不大,表明低温限制了米氏凯伦藻的生长。当米氏凯伦藻从12°C快速转移至16°C和20°C时,藻细胞密度和光合作用效率短时间迅速降低,但细胞很快即适应温度变化。细胞膜上的转运蛋白和光合作用蛋白在其适应温度变化中起着重要作用。  相似文献   

Adsorption Mechanism and Kinetic Characterization of Bituminous Coal under High Temperatures and Pressures in the Linxing-Shenfu Area     

TAO Chuanqi  WANG Yanbin  LI Yong  NI Xiaoming  GAO Xiangdong 《《地质学报》英文版》2020,94(2):399-408

The majority of coalbed methane(CBM) in coal reservoirs is in adsorption states in coal matrix pores. To reveal the adsorption behavior of bituminous coal under high-temperature and high-pressure conditions and to discuss the microscopic control mechanism affecting the adsorption characteristics, isothermal adsorption experiments under hightemperature and high-pressure conditions, low-temperature liquid nitrogen adsorption-desorption experiments and CO2 adsorption experiments were performed on coal samples. Results show that the adsorption capacity of coal is comprehensively controlled by the maximum vitrinite reflectance(Ro, max), as well as temperature and pressure conditions. As the vitrinite reflectance increases, the adsorption capacity of coal increases. At low pressures, the pressure has a significant effect on the positive effect of adsorption, but the effect of temperature is relatively weak. As the pressure increases, the effect of temperature on the negative effect of adsorption gradually becomes apparent, and the influence of pressure gradually decreases. Considering pore volumes of pores with diameters of 1.7-100 nm, the peak volume of pores with diameters 10-100 nm is higher than that from pores with diameters 1.7-10 nm, especially for pores with diameters of 40-60 nm, indicating that pores with diameters of 10-100 nm are the main contributors to the pore volume. The pore specific surface area shows multiple peaks, and the peak value appears for pore diameters of 2-3 nm, indicating that this pore diameter is the main contributor to the specific surface area. For pore diameters of 0.489-1.083 nm, the pore size distribution is bimodal, with peak values at 0.56-0.62 nm and 0.82-0.88 nm. The adsorption capability of the coal reservoir depends on the development degree of the supermicroporous specific surface area, because the supermicroporous pores are the main contributors to the specific pore area. Additionally, the adsorption space increases as the adsorption equilibrium pressure increases. Under the same pressure, as the maximum vitrinite reflectance increases, the adsorption space increases. In addition, the cumulative reduction in the surface free energy increases as the maximum vitrinite reflectance increases. Furthermore, as the pressure increases, the surface free energy of each pressure point gradually decreases, indicating that as the pressure increases, it is increasingly difficult to adsorb methane molecules.  相似文献   

微量硫化物、硫酸盐硫同位素EA-IRMS在线测试分析     

武晓珮  范昌福  胡斌  高建飞  李延河 《地球学报》2020,41(5):605-612

常规EA-IRMS硫同位素测试中, 硫化银(Ag2S)的需样量为0.2~1.0 mg, 硫酸钡(BaSO4)的需样量为0.35~1.5 mg, 较大的需样量已难以满足珍贵样品及微区样品的分析要求, 因此如何减少测试样品量已成为EA-IRMS测试分析工作中急需解决的问题。通过对EA-IRMS测试系统的研究发现, 在采用常规方法测试样品时, 由于初始He载气流速(100 mL/min)、进入分流接口时的流速(10 mL/min)与进入离子源时流速 (0.3 mL/min)的差异导致样品燃烧产生的目标气体中99.7%的气体被浪费, 样品的总体利用率仅有0.3%。因此如何减少样品在测试过程中的损耗, 提高样品的利用率, 从而减少需样量的关键在于缩小载气流速的差距。本实验在常规EA-IRMS测试技术基础上进行了关键改进,在元素分析仪和分流接口之间设计增加一个由六通阀和自动加热冷阱构成的装置, 自动加热冷阱可在Load模式时收集SO2气体, 六通阀在Load-Inject模式之间切换时可改变He载气流速, 通过与分流接口匹配的反吹He载气(10 mL/min)将冷阱中富集的SO2气体送入分流接口, 从而保证进入分流接口前样品燃烧产生的SO2气体全部收集。这一改进, 理论上可以将样品的利用率提高10倍, 该系统需硫量降至3~13 μg, 并且可以提高反应管的寿命, 降低清灰的频率, 提高工作效率。同时有效避免了拖尾的产生, 提高分析结果的精密度。本次微量样品实验获得的硫同位素数据与常规方法一致, 分析精度优于0.15‰(1SD), 测量值与真值的差异在0.4‰以内, 达到国际同类实验室先进水平。此外, 该方法可为微量有机碳、氮同位素EA-IRMS测试分析工作的开展提供参考经验。  相似文献   

An Automatic Method for Detecting Transients and Variable Sources in AST3 Survey Based on Image Subtraction and Random Forest     

《Chinese Astronomy and Astrophysics》2020,44(1):41-60

AST3-2 (the second Antarctic Survey Telescope) is located in Antarctic Dome A, the loftiest ice dome on the Antarctic Plateau. It produces a huge amount of observational data which require a more efficient data reduction program to be developed. Also the data transmission in Antarctica is much difficult, thus it is necessary to perform data reduction and detect variable and transient sources remotely and automatically in Antarctica, but this attempt is restricted by the unsatisfactory performance of the low power consumption computer in Antarctica. For realizing this purpose, to develop a new method based on the existing image subtraction method and random forest algorithm, taking the AST3-2 2016 dataset as the test sample, becomes an alternative choice. This method performs image subtraction on the dataset, then applies the principle component analysis to extract the features of residual images. Random forest is used as a machine learning classifier, and in the test a recall rate of 97% is resulted for the positive sample. Our work has verified the feasibility and accuracy of this method, and finally found out a batch of candidates for variable stars in the AST3-2 2016 dataset.  相似文献   

阿勒泰地区植被覆盖度及ET对气温变化的响应   总被引：1，自引：0，他引：1       下载免费PDF全文

韩飞飞  闫俊杰  郭斌 《干旱区地理》2019,42(6):1436-1444

研究气温对植被覆盖度和ET (Evapotranspiration，ET)的影响，对干旱区应对气候变化、维系生态系统稳定具有重要意义。基于阿勒泰地区及周边7个气象站，CRU数据集中的气温数据及MODIS ET数据，采用Mann-Kendall非参数检验、植被盖度反演等方法，对阿勒泰地区气温变化对植被覆盖度及ET的影响进行了研究。结果表明：（1）在1901—2016年过去的116 a间，阿勒泰地区年平均气温以0.18 ℃·(10 a)^-1速率增加，在1982年由突变前的2.2 ℃增加到突变后的3.5 ℃。（2）2000—2017年阿勒泰地区植被覆盖度变化的空间差异明显，植被覆盖度增加的面积与降低的面积总体相当；全区66.71%的区域植被覆盖度变化与气温呈负相关，而呈正相关的比例仅占18.55%，且全区气温变暖而盖度降低区域的占比达31.71%。（3）2000—2016年阿勒泰地区ET总体呈降低趋势，整个区域61.65%的面积温度降低、ET降低，而19.92%的区域表现为温度增加而植被ET降低。  相似文献