A catalog of DB white dwarfs from the LAMOST DR5 and construction of templates

In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST database and applied them to train the machine learning process.Following the recognition procedure, we chose 351 DB spectra of 287 objects, 53 of which were new identifications. We then utilized all the DBWD spectra from both SDSS DR14 and LAMOST DR5 to construct DB templates for LAMOST 1 D pipeline reductions. Finally, by applying DB parameter models provided by D. Koester and the distance from Gaia DR2, we calculated the effective temperatures, surface gravities and distributions of the 3 D locations and velocities of all DBWDs.     

2014—2019年浅源中强地震辐射能量的快速测定

根据地震波衰减特性,采用一维速度模型开展了快速测定辐射能量ES和能量震级Me的方法研究.利用全球地震台网和国家数字测震台网提供的宽频带资料,测定了2014—2019年间MW≥6.0的115次浅源地震的辐射能量和能量震级,将计算结果与其它机构的结果进行对比.结果表明:利用本文方法可在得到地震数据半小时内计算出稳定的Me,...     

Incorporating dynamic factors for improving a GIS‐based solar radiation model

Solar radiation has been a major input to agricultural, hydrological, and ecological modeling. However, solar radiation is usually influenced by three groups of dynamic factors: sun–earth position, terrain, and atmospheric effects. Therefore, an integrated approach to accurately consider the impacts of those dynamic factors on solar radiation is essential to estimate solar radiation over rugged terrain. In this study, a spatial and temporal gap‐filling algorithm was proposed to obtain a seamless daily MODIS albedo dataset. A 1 km‐resolution digital elevation model was used to model the impact of local topography and shading by surrounding terrain on solar radiation. A sunshine‐based model was adopted to simulate radiation under the influence of clouds. A GIS‐based solar radiation model that incorporates albedo, shading by surrounding terrain, and variations in cloudiness was used to address the spatial variability of these factors in mountainous terrain. Compared with other independent solar radiation products, our model generated a more reliable solar radiation product over rugged terrain, with an R² of 0.88 and an RMSE of 2.55 MJ m^?2 day^?1. The improved solar radiation products and open source app can be used further in practice or scientific research.     

Influence of small-molecule material on performance of polymer solar cells based on MEH-PPV:PCBM blend

In this work, the influence of a small-molecule material, tris(8-hydroxyquinoline) aluminum (Alq₃), on bulk heterojunction (BHJ) polymer solar cells (PSCs) is investigated in devices based on the blend of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). By doping Alq₃ into MEH-PPV:PCBM solution, the number of MEH-PPV excitons can be effectively increased due to the energy transfer from Alq₃ to MEH-PPV, which probably induces the increase of photocurrent generated by excitons dissociation. However, the low carrier mobility of Alq₃ is detrimental to the efficient charge transport, thereby blocking the charge collection by the respective electrodes. The balance between photon absorption and charge transport in the active layer plays a key role in the performance of PSCs. For the case of 5 wt.% Alq₃ doping, the device performance is deteriorated rather than improved as compared with that of the undoped device. On the other hand, we adopt Alq₃ as a buffer layer instead of commonly used LiF. All the photovoltaic parameters are improved, yielding an 80% increase in power conversion efficiency (PCE) at the optimum thickness (1 nm) as compared with that of the device without any buffer layer. Even for the 5 wt.% Alq₃ doped device, the PCE has a slight enhancement compared with that of the standard device after modification with 1 nm (or 2 nm) thermally evaporated Alq₃. The performance deterioration of Alq₃-doped devices can be explained by the low solubility of Alq₃, which probably deteriorates the bicontinuous D-A network morphology; while the performance improvement of the devices with Alq_3 as a buffer layer is attributed to the increased light harvesting, as well as blocking the hole leakage from MEH-PPV to the aluminum (Al) electrode due to the lower highest occupied molecular orbital (HOMO) level of Alq₃ compared with that of MEH-PPV.     

Study on vegetation and climate changes in Beijing region since late pleistocene

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一阶非线性泛函方程解的振动性(英文)

考虑两类带有分布型超前或滞后量的方程 (Ⅰ)x'(t)=a(t)x(t)+φ, (Ⅱ)x'(t)=a(t)x(t)-φ.其中β(t)>a(t),t+a(t)→∞(t→∞),f(x)和φ(u)是满足某些条件的非线性函数。 本文给出了方程(Ⅰ)和(Ⅱ)的所有解振动的若干充分性判定定理。作为应用,我们又讨论了如下方程的振动性,并给出了相应的判定准则。 (Ⅲ)x'(t)=a(t)x(t)+φ[sum from i=1 to n a_i(t)f(x(t+τ_i(t)))], (Ⅳ)x'(t)=a(t)x(t)-φ[sum from i=1 to n a_i(t)f(x(t+τ_i(t)))] 本文的结果是张炳根的若干结果的推广。     

珠江口盆地?琼东南盆地深水区新生代构造沉积演化对比分析

南海北部陆缘记录了南海形成演化的历史,但是其新生代构造沉积演化特征在东段和西段的差异及其原因目前还不太清楚。本文分别在珠江口盆地和琼东南盆地的深水区选择了数口构造地理位置相似的井通过精细地层回剥分析,重建了两沉积盆地的沉积速率和沉降速率并结合前人研究成果进行了对比分析。研究结果发现,两沉积盆地在裂陷期的沉积和沉降特征基本相似,但是两者在裂后期的构造沉积演化特征差异明显。珠江口盆地深水区沉积和沉降速率都表现为幕式变化特征,其中沉积速率表现为“两快三慢”的特征而沉降速率表现为“两快一慢”的特征。琼东南盆地深水区的沉积速率表现为“地堑式”变化特征,但是沉降速率表现为“台阶式”上升的变化特征。琼东南盆地“台阶式”上升的沉降速率推测主要是受到海南地幔柱伴随红河断裂的右旋走滑而向西北漂移的影响,这也与南海西北部的岩浆活动以及周围盆地的沉降特征吻合。红河断裂在2.1 Ma BP的右旋走滑控制了琼东南盆地1.8 Ma BP以来的快速沉积和加速沉降分布。     

Geochemical characteristics of sediment as indicators of post-glacial environmental changes off the Shandong Peninsula in the Yellow Sea

Core NYS-101, which was recovered at a water depth of 49 m northeast of the Shandong Peninsula in the North Yellow Sea, penetrates the Holocene subaqueous clinoform that wraps around the Shandong Peninsula. The uppermost 18 m of this well-dated core was deposited after about 13 cal kyr BP during the post-glacial transgression. We focused on trace and rare earth element (REE) chemistries of the core sediments in the uppermost 18 m to investigate the sediment provenance and factors controlling the sediment composition. On the basis of down-core distributions of REE fractionation parameters and of ratios among REEs and other immobile elements, we divided the uppermost 18 m into three distinct compositional intervals: Interval 1 (above 6.08 m, from the time tens of years earlier than 6500 cal yr BP up to the present), Interval 2 (13.90–6.08 m, from about 8200 cal yr BP to the boundary between Intervals 1 and 2), and Interval 3 (below 13.90 m, from about 13,000 to 10,400 cal yr BP). The chondrite- and upper continental crust (UCC)-normalized REE fractionation patterns of Intervals 3 and 2 are similar to those of Yellow River sediments, but the patterns in Interval 1 are obviously different.     

Changes in vegetation and landscape patterns with altered river water-flow in arid West China

Landsat TM images of Tarim Basin in western China for 1986, 1999 and 2004 were analyzed for quantifying the patterns of landscape change relating to changes in water supply. Results showed that vegetation area and NDVI mostly decreased from 1986 to 1999, and increased from 1999 to 2004, while changes in desert area displayed an inverse pattern. Saline alkali soil showed a tendency of increase from 1999 to 2004. Spatially, percentage of vegetation area decreased and percentage of desert area increased with distance from the river in the upper section, while such patterns were not observed for both the middle and the lower sections. Landscape displayed a pattern of fragmentation from 1986 to 1999 and integration from 1999 to 2004. Shape of vegetation patches tended to become more regular from 1986 to 1999 and more irregular from 1999 to 2004. Our results indicated hydrological control of spatio-temporal variations of vegetation and landscape pattern in arid regions. Water diversion can be effective for raising the local groundwater level and improving plant growth, but its effect is largely restricted to areas adjacent to the water pathway.     

黄土滑坡滑带土的特点——以天水椒树湾滑坡为例

黄土滑坡已成为影响黄土地区公路、铁路等基础设施建设的主要因素,滑坡的形成在一定程度上就是滑带土变形破坏过程。从黄土滑坡滑带土的分类、物理力学性质、宏观与微观特征等方面进行了较系统的研究,探究其变形和破坏规律。结合甘肃天水的黄土滑坡实例进行了具体分析。