摘要： 为了从根本上消灭存在于数学基础中的各种悖论，使数学建筑在高度可靠的基础上，发现形式逻辑只能用于同一律，矛盾律和排中律这三大规律都成立的讨论域 (称为可行域) 内，否则就会产生包括悖论在内的各种错误，而在形式逻辑的适用范围即可行域内，只要前提可靠，推导严格，悖论是不存在的。根据该结论，分析了说谎者悖论和理发师悖论等一些历史上比较著名的悖论的形成原因，同时指出了数学基础中皮亚诺公理的应用和康托尔定理、区间套和对角线法证明中的一些逻辑错误，提出了能够避免这些错误的统一的定义自然数、有理数和无理数的建议。
分类： 计算机科学 >> 自然语言理解与机器翻译 提交时间： 2018-09-27
摘要： 加权极限学习机对不同类别的样本赋予不同的权值，在一定程度上提高了分类准确 率,但加权极限学习机只考虑了不同类别样本之间差异，忽视了样本噪声和同类样本之间的 差异。本文提出了一种基于文本类别信息熵的极限学习机集成方法，该方法以Adaboost.M1 为算法框架，通过文本的类内分布熵和类间分布熵生成文本类别信息熵，由文本类别信息熵 构造代价敏感矩阵，把代价敏感极限学习机集成到Adaboost.M1 框架中。实验结果表明，该 方法与其他类型的极限学习机相比较有更好的准确性和泛化性。
分类： 图书馆学、情报学 >> 文献学 提交时间： 2018-09-27
摘要： 【目的】分析基础学科期刊论文被引的分布特点，探究低被引论文区间的界定和评价方法。【方法】以SCI Expanded为数据源，65种凝聚态物理学期刊（CMJ）为研究对象，用统计学原理和文献计量学方法，比较分析论文被引频次在大于h-index、小于篇均被引Cipp、以及一个期刊的最低被引论文的累计被引频次为期刊总被引频次T的5%、10%和20%区域内论文的被引特性，以此确定CMJ最合理的低被引区。 【结果】第一，CMJ整体零被引率rN0仅为10%，可视为一个高质量的期刊集合。第二，一个期刊的最低被引论文的累计被引达到20%T的区域（Tci20%）和一个期刊中单篇被引在小于平均被引（Cicipp）的区域（Tcicipp）具有被界定为低被引区的统计学依据。第三，零被引率（rN0）、低被引率（RLC，rN x）和低被引密度（DLC，rTcix）与传统评价指标IF、h-index、Cipp以及Np、Tci不存在强相关性，满足作为独立评价指标的充分条件。【结论】第一，由rN0、RLC和DLC构成一个复合指标Evel {rN0，rN x%，rTcix%} 用来描述一个期刊的低被引特性；由h-index和特定区域内的篇均被引构成另一个复合指标Evel {h，Ci20%，Cicipp，Cih }，用于期刊的被引结构特征的比较。第二，研究表明期刊被引结构可以被构形分类，而评价参数在不同被引区域有可能存在竞争优势；因此对期刊的低被引的评价要以分析被引结构为前提。期刊的综合评价应该使用多参数多维度指标。
分类： 统计学 >> 数理统计学 提交时间： 2018-09-26
摘要： 受许多事物具有齐夫现象的启发，本文提出了排序后PPS抽样方法，并给出了修正汉森-赫维茨估计量及其方差。在此过程中本文解决了，长期以来抽样调查实践中将重要单元直接入样时，多少重要单元直接入样没有明确方法的问题，本文给出了理论依据和具体的确定方法。最后通过一个例子和中国城市人口抽样调查的案例，展示了修正汉森-赫维茨估计量的优势，并对这一研究方法做了总结和展望。
分类： 数学 >> 数学（综合） 提交时间： 2018-09-23
摘要： The aim of this paper is to study the heterogeneous optimization problem \begin{align*} \mathcal {J}(u)=\int_{\Omega}(G(|\nabla u|)+qF(u^+)+hu+\lambda_{+}\chi_{\{u>0\}} )\text{d}x\rightarrow\text{min}, \end{align*} in the class of functions $ W^{1,G}(\Omega)$ with $ u-\varphi\in W^{1,G}_{0}(\Omega)$, for a given function $\varphi$, where $W^{1,G}(\Omega)$ is the class of weakly differentiable functions with $\int_{\Omega}G(|\nabla u|)\text{d}x0$ respectively. We also establish growth rate near the free boundary for each non-negative minimizer of $\mathcal {J}(u)$ with $\lambda_+=0$, and $\lambda_+>0$ respectively. Furthermore, under additional assumption that $F\in C^1([0,+\infty); [0,+\infty))$, local Lipschitz regularity is carried out for non-negative minimizers of $\mathcal {J}(u)$ with $\lambda_{+}>0$.
分类： 数学 >> 数学（综合） 提交时间： 2018-09-22
摘要： In this paper, we prove several regularity results for the heterogeneous, two-phase free boundary problems $\mathcal {J}_{\gamma}(u)=\int_{\Omega}\big(f(x,\nabla
u)+(\lambda_{+}(u^{+})^{\gamma}+\lambda_{-}(u^{-})^{\gamma})+gu\big)\text{d}x\rightarrow \text{min}$
under non-standard growth conditions. Included in such problems are
heterogeneous jets and cavities of Prandtl-Batchelor type with
$\gamma=0$, chemical reaction problems with $0 2$ for $p-$Laplace equations, but
also in the singular
case of $1
分类： 数学 >> 数学（综合） 提交时间： 2018-09-22
摘要： We establish regularity of solutions to the $G$-Laplace equation $-\text{div}\ \bigg(\frac{g(|\nabla u|)}{|\nabla u|}\nabla u\bigg)=\mu$, where $\mu$ is a nonnegative Radon measure satisfying $\mu (B_{r}(x_{0}))\leq Cr^{m}$ for any ball $B_{r}(x_{0})\subset\subset \Omega$ with $r\leq 1$ and $m>n-1-\delta\geq 0$. The function $g(t)$ is supposed to be nonnegative and $C^{1}$-continuous in $[0,+\infty)$, satisfying $g(0)=0$, and for some positive constants $\delta$ and $g_{0}$, $\delta\leq \frac{tg'(t)}{g(t)}\leq g_{0}, \forall t>0$, that generalizes the structural conditions of Ladyzhenskaya-Ural'tseva for an elliptic operator.
分类： 数学 >> 数学（综合） 提交时间： 2018-09-22
摘要： Explicit equations are obtained to convert Cartesian coordinates to elliptic coordinates, based on which an elliptic-coordinate function can be readily mapped on a uniform Cartesian mesh.Application to Kirchhoff vortex is provided.
分类： 生物学 >> 生物工程 提交时间： 2018-09-21 合作期刊: 《中国生物工程杂志》
摘要： 目的：构建携带金黄色葡萄球菌类肠毒素K（Staphylococcal Enterotoxin-like K, SElK）和绿色荧光蛋白（GFP）融合基因的工程菌，并对SElK-GFP融合蛋白进行初步生物学活性分析。方法：利用PCR和Overlap PCR克隆获得SElK-GFP融合基因，并插入pET28a表达载体中，通过菌落PCR，质粒双酶切及测序验证后，将构建成功的pET28a-SElK-GFP质粒转化到E.coli BL21菌株中进行诱导表达，通过 Ni+亲和磁珠试剂盒纯化获得SElK-GFP融合蛋白；并利用MTT法检测SElK-GFP刺激小鼠脾淋巴细胞增殖；ELISA法检测SElK-GFP尾静脉注射后小鼠血清中细胞因子IL-2和IFN-γ的分泌水平。结果：成功构建能够表达SElK-GFP融合蛋白的工程菌，纯化获得高纯度的SElK-GFP融合蛋白可观测到明显的绿色荧光，融合蛋白生物学活性分析表明，SElK-GFP能够呈剂量依赖性地显著刺激小鼠脾淋巴细胞增殖；同时ELISA检测发现SElK-GFP可显著增加小鼠血清中细胞因子IL-2及IFN-γ的分泌水平。结论：本研究成功克隆、表达及纯化获得高纯度的SElK-GFP融合蛋白，其不仅保留了SElK的超抗原活性，同时兼具GFP绿色荧光的可视性，为深入研究SElK生物学活性提供有利工具。
分类： 生物学 >> 生物工程 提交时间： 2018-09-21 合作期刊: 《中国生物工程杂志》
摘要： 形状记忆聚合物是由固定相和可逆相构成的具有在外界刺激条件下诱导形状改变特性的一类高分子智能材料。相较于传统的形状记忆合金与陶瓷，其具有特定的生物可降解性、更高的机械性能调控空间、更强的形变恢复能力及更优良的生物相容性。凭借材料特性，近阶段针对形状记忆聚合物在组织工程领域的应用研究愈发广泛，包括血管组织、骨骼肌组织、神经组织与骨组织等方面。文章综述近年来形状记忆聚合物在多种组织工程领域研究中的实验创新、技术突破与应用拓展，例如将其作为新型多孔血管支架、骨骼肌修复支架、神经修复导管与骨缺损填充物等。可预见随着技术和材料的不断发展，形状记忆聚合物在组织工程领域的应用将更加成熟。
分类： 生物学 >> 生物工程 提交时间： 2018-09-21 合作期刊: 《中国生物工程杂志》
摘要： 目的：下调脂肪特异性蛋白27（Fsp27）基因表达联合杨梅素干预，观察对3T3-L1细胞中脂质代谢的影响，并探究脂滴发生、发展变化的调控机制。方法：常规培养3T3-L1前脂肪细胞，采用“鸡尾酒”法诱导其分化为成熟脂肪细胞。脂质体法转染sh-Fsp27干扰载体，以杨梅素浓度为100 μmol/L的完全培养基干预成熟脂肪细胞72 h。油红O染色，观察脂滴形态及大小的变化；酶法测定细胞内甘油及甘油三酯的含量，观察细胞脂质代谢的变化。Western blot检测Fsp27、激素敏感性甘油三酯脂肪酶（HSL）、甘油三酯脂肪酶（ATGL）以及丝裂原活化蛋白激酶（MAPK）信号通路蛋白的表达。结果：1. 3T3-L1细胞诱导分化后，形态由纤维样变成圆形，并伴随有细胞体积的增大。2. 与对照组相比，杨梅素组和转染组细胞中甘油三酯含量下降，甘油含量升高（P<0.05）。与其他三组相比，联合干预组细胞中甘油三酯含量减少，甘油含量增加（P<0.05）。3. 与对照组相比，其余三组细胞内Fsp27蛋白的表达量均降低，ATGL和PPARγ的表达量升高（P<0.05）。另外，联合干预组和杨梅素组细胞内HSL的表达量和p-p38MAPK/ p38MAPK的比值均大于sh-Fsp27组和对照组（P<0.05）。结论：1. Fsp27基因沉默与杨梅素联合干预可以更大程度地促进脂肪分解代谢。2.杨梅素可通过激活MAPK信号通路，上调HSL和ATGL的蛋白表达来发挥其促脂解的作用；sh-Fsp27干扰载体通过调节PPARγ和Fsp27蛋白的表达，增加ATGL含量来加速脂肪分解。
分类： 生物学 >> 生物工程 提交时间： 2018-09-21 合作期刊: 《中国生物工程杂志》
摘要： 甾体药物是仅次于抗生素的全球第二大类药物，具有抗炎、抗过敏、调节内分泌等重要功效。对甾体母核特定位点进行有效的氧化修饰，是引入药效活性的关键。研究表明，P450酶是催化甾体特异性氧化的一类关键酶家族。目前，电子传递效率和催化特异性是限制P450酶催化功能的重要因素，会导致目标甾体产物产量低、副产物积累严重等问题。因此，本文将围绕提高P450酶的催化效率及特异性方面的研究工作，系统综述工程化P450催化甾体类物质的方法策略和相关研究进展，并对催化甾体化合物的P450酶的设计和优化的未来发展进行展望，为该方面工作的深入研究提供指导。
分类： 图书馆学、情报学 >> 图书馆管理 提交时间： 2018-09-21
摘要： 专业图书馆管理体制改革成功的关键在于从全球管理体制改革趋势的高度，把握管理体制改革的走向，认清“事业经营企业化”的全球性趋势，从而赋予专业图书馆改革坚定、明确的方向和清晰、完整的指导思想和理论依据。
分类： 数学 >> 数学（综合） 提交时间： 2018-09-18
摘要： 本文研究一类高阶非线性微分方程的Lyapunov 不等式，是对《Lyapunov-type inequalities for $\psi$-Laplacian equations》有关结论的进一步探讨和推广
分类： 地球科学 >> 地球科学史 提交时间： 2018-09-18 合作期刊: 《干旱区科学》
摘要： Reduced tillage provides ecological and economic benefits to arable land on the Loess Plateau of China, where soil erosion has long been a serious problem and soil water availability is largely restricted. However, high abundances of weeds in reduced tillage systems cause significant yield losses. In this study, we explored the effects of no-tillage and stubble retention on the number and density of weeds and weed seeds in a 12-year maize-winter wheat-common vetch rotation on the Loess Plateau. Four treatments including conventional tillage, no-tillage, conventional tillage+stubble retention and no-tillage+stubble retention were designed and applied. We found that no-tillage increased the number of weed species and weed density in most of the crops, while stubble retention decreased weed density in maize and tended to suppress weeds in both no-tillage treatments (no-tillage and no-tillage+stubble retention). No-tillage led to an increase in the number of weed species in the weed seedbank and tended to increase seed density during the spring growth of winter wheat, but it decreased seed density during post-vetch fallow. Stubble retention tended to reduce seed density during the spring growth of winter wheat and post-vetch fallow. We concluded that no-tillage can promote weeds in the experimental crop rotation, while stubble retention suppresses weeds in untilled fields. The combined effects of stubble retention and no-tillage on weed suppression varied among the three crops. Based on these results, we recommend stubble retention in untilled legume-crop rotations on the Loess Plateau to improve the control of weeds.
分类： 地球科学 >> 地球科学史 提交时间： 2018-09-18 合作期刊: 《干旱区科学》
摘要： High and efficient use of limited rainwater resources is of crucial importance for the crop production in arid and semi-arid areas. To investigate the effects of different soil and crop management practices (i.e., mulching mode treatments: flat cultivation with non-mulching, flat cultivation with straw mulching, plastic-covered ridge with bare furrow and plastic-covered ridge with straw-covered furrow; and planting density treatments: low planting density of 45,000 plants/hm2, medium planting density of 67,500 plants/hm2 and high planting density of 90,000 plants/hm2) on rainfall partitioning by dryland maize canopy, especially the resulted net rainfall input beneath the maize canopy, we measured the gross rainfall, throughfall and stemflow at different growth stages of dryland maize in 2015 and 2016 on the Loess Plateau of China. The canopy interception loss was estimated by the water balance method. Soil water storage, leaf area index, grain yield (as well as it components) and water use efficiency of dryland maize were measured or calculated. Results showed that the cumulative throughfall, cumulative stemflow and cumulative canopy interception loss during the whole growing season accounted for 42.3%–77.5%, 15.1%–36.3% and 7.4%–21.4% of the total gross rainfall under different treatments, respectively. Soil mulching could promote the growth and development of dryland maize and enhance the capability of stemflow production and canopy interception loss, thereby increasing the relative stemflow and relative canopy interception loss and reducing the relative throughfall. The relative stemflow and relative canopy interception loss generally increased with increasing planting density, while the relative throughfall decreased with increasing planting density. During the two experimental years, mulching mode had no significant influence on net rainfall due to the compensation between throughfall and stemflow, whereas planting density significantly affected net rainfall. The highest grain yield and water use efficiency of dryland maize were obtained under the combination of medium planting density of 67,500 plants/hm2 and mulching mode of plastic-covered ridge with straw-covered furrow. Soil mulching can reduce soil evaporation and retain more soil water for dryland maize without reducing the net rainfall input beneath the maize canopy, which may alleviate the contradiction between high soil water consumption and insufficient rainfall input of the soil. In conclusion, the application of medium planting density (67,500 plants/hm2) under plastic-covered ridge with bare furrow is recommended for increasing dryland maize production on the Loess Plateau of China.
分类： 地球科学 >> 地球科学史 提交时间： 2018-09-18 合作期刊: 《干旱区科学》
摘要： Net primary productivity (NPP), as an important variable and ecological indicator in grassland ecosystems, can reflect environmental change and the carbon budget level. The Ili River Valley is a wetland nestled in the hinterland of the Eurasian continent, which responds sensitively to the global climate change. Understanding carbon budget and their responses to climate change in the ecosystem of Ili River Valley has a significant effect on the adaptability of future climate change and sustainable development. In this study, we calculated the NPP and analyzed its spatio-temporal pattern of the Ili River Valley during the period 2000–2014 using the normalized difference vegetation index (NDVI) and an improved Carnegie-Ames-Stanford (CASA) model. Results indicate that validation showed a good performance of CASA over the study region, with an overall coefficient of determination (R2) of 0.65 and root mean square error (RMSE) of 20.86 g C/(m2•a). Temporally, annual NPP of the Ili River Valley was 599.19 g C/(m2•a) and showed a decreasing trend from 2000 to 2014, with an annual decrease rate of –3.51 g C/(m2•a). However, the spatial variation was not consistent, in which 55.69% of the areas showed a decreasing tendency, 12.60% of the areas remained relatively stable and 31.71% appeared an increasing tendency. In addition, the decreasing trends in NPP were not continuous throughout the 15-year period, which was likely being caused by a shift in climate conditions. Precipitation was found to be the dominant climatic factor that controlled the inter-annual variability in NPP. Furthermore, the correlations between NPP and climate factors differed along the vertical zonal. In the medium-high altitudes of the Ili River Valley, the NPP was positively correlated to precipitation and negatively correlated to temperature and net radiation. In the low-altitude valley and high-altitude mountain areas, the NPP showed a negative correlation with precipitation and a weakly positive correlation with temperature and net radiation. The results suggested that the vegetation of the Ili River Valley degraded in recent years, and there was a more complex mechanism of local hydrothermal redistribution that controlled the growth of vegetation in this valley ecosystem.
分类： 地球科学 >> 地球科学史 提交时间： 2018-09-18 合作期刊: 《干旱区科学》
摘要： Estimation of above-ground biomass is vital for understanding ecological processes. Since direct measurement of above-ground biomass is destructive, time consuming and labor intensive, canopy cover can be considered as a predictor if a significant correlation between the two variables exists. In this study, relationship between canopy cover and above-ground biomass was investigated by a general linear regression model. To do so, canopy cover and above-ground biomass were measured at 5 sub-life forms (defined as life forms grouped in the same height classes) using 380 quadrats, which is systematic-randomly laid out along a 10-km transect, during four sampling periods (May, June, August, and September) in an arid rangeland of Marjan, Iran. To reveal whether obtained canopy cover and above-ground biomass of different sampling periods can be lumped together or not, we applied a general linear model (GLM). In this model, above-ground biomass was considered as a dependent or response variable, canopy cover as an independent covariate or predictor factor and sub-life forms as well as sampling periods as fixed factors. Moreover, we compared the estimated above-ground biomass derived from remotely sensed images of Landsat-8 using NDVI (normalized difference vegetation index), after finding the best regression line between predictor (measured canopy cover in the field) and response variable (above-ground biomass) to test the robustness of the induced model. Results show that above-ground biomass (response variable) of all vegetative forms and periods can be accurately predicted by canopy cover (predictor), although sub-life forms and sampling periods significantly affect the results. The best regression fit was found for short forbs in September and shrubs in May, June and August with R2 values of 0.96, 0.93 and 0.91, respectively, whilst the least significant was found for short grasses in June, tall grasses in August and tall forbs in June with R2 values of 0.71, 0.73 and 0.75, respectively. Even though the estimated above-ground biomass by NDVI is also convincing (R2=0.57), the canopy cover is a more reliable predictor of above-ground biomass due to the higher R2 values (from 0.75 to 0.96). We conclude that canopy cover can be regarded as a reliable predictor of above-ground biomass if sub-life forms and sampling periods (during growing season) are taken into account. Since, (1) plant canopy cover is not distinguishable by remotely sensed images at the sub-life form level, especially in sparse vegetation of arid and semi-arid regions, and (2) remotely sensed-based prediction of above-ground biomass shows a less significant relationship (R2=0.57) than that of canopy cover (R2 ranging from 0.75 to 0.96), which suggests estimating of plant biomass by canopy cover instead of cut and weighting method is highly recommended. Furthermore, this fast, nondestructive and robust method that does not endanger rare species, gives a trustworthy prediction of above-ground biomass in arid rangelands.
分类： 地球科学 >> 地球科学史 提交时间： 2018-09-18 合作期刊: 《干旱区科学》
KRAMP, Katja
SCHMITT, Thomas
LANG, Petra
JESCHKE, Michael
SCHÄFER, Philipp
KULANEK, Dustin
ZHANG, Ximing
YU, Ruide
THOMAS, Frank M
摘要： Many riparian (Tugai) forests growing along rivers in arid and hyper-arid regions of Central Asia are dominated by the Euphrates poplar (Populus euphratica). Besides generative reproduction, which is only possible upon flooding events and at a distance to the groundwater of less than 2 m, this phreatophytic tree species also reproduces vegetatively by forming clones that can cover land surface areas of several hectares. Along a gradient of groundwater distances, we investigated whether the fraction of clones in P. euphratica stands (1) increases with increasing distance to the water table; (2) is higher if supplied with water via river cut-offs; and (3) approaches 100% at a short distance to the groundwater, but at high salt concentrations in the upper soil layers, which would prevent germination and establishment of seedlings. AFLP (Amplified Fragment Length Polymorphism) analyses were conducted on leaf samples taken from mature P. euphratica trees growing at the fringes of the Taklimakan Desert in stands with different distances (2–12 m) to the groundwater at two plots at the middle and the lower reaches of the Tarim River and in a stand close to Ebinur Lake, Xinjiang, China. Genetic diversity was large among plots, but considerably smaller within plots. We found the highest genetic diversity (caused by regeneration from seeds) at plots that have a short distance to the groundwater or are supplied with additional water. There was no significant relationship between groundwater distance and clonal fraction. All investigated trees at the saline Ebinur Lake site belonged to one single clone. Our results demonstrate that the genetic pattern of this widespread species is not easily predictable even over small distances as it is a result of a complex interplay of stand history and dispersal of propagules (pollen, seeds, and vegetative diaspores) by wind and water. In conservation and restoration schemes, P. euphratica stands with a high genetic diversity and stands that grow at short distances to the water table and are regularly subjected to flooding (which favors generative over clonal reproduction) should be prioritized.
分类： 地球科学 >> 地球科学史 提交时间： 2018-09-18 合作期刊: 《干旱区科学》
摘要： Mixed or chloride salty ions dominate in saline soils, and exert wide-ranging adversely affect on soil biological processes and soil functions. The objectives of this study were to (1) explore the impacts of mixed (0, 3, 6, 10, 20 and 40 g Cl–/SO42– salt/kg dry soil) and chloride (0, 1.5, 3, 5, 8 and 15 g Cl– salt/kg dry soil) salts on soil enzyme activities, soil physiological functional (Biolog) profiles and microbial community structure by using soil enzymatic, Biolog-Eco microplates as well as denaturing gradient gel electrophoresis (DEEG) methods, and (2) determine the threshold concentration of soil electronic conductivity (EC1:5) on maintaining the functional and structural diversity of soil microbial community. The addition of either Cl– or mixed Cl–/SO42– salt obviously increased soil EC, but adversely affected soil biological activities including soil invertase activity, soil microbial biomass carbon (MBC) and substrate-induced respiration (SIR). Cl– salt showed a greater deleterious influence than mixed Cl–/SO42– salt on soil enzymes and MBC, e.g., the higher soil MBC consistently appeared with Cl–/SO42– instead of Cl– treated soil. Meanwhile, we found that SIR was more reliable than soil basal respiration (SBR) on explaining the changes of soil biological activity responsive to salt disturbance. In addition, microbial community structures of the soil bacteria, fungi, and Bacillus were obviously affected by both salt types and soil EC levels, and its diversity increased with increasing of mixed Cl–/SO42– salt rates, and then sharply declined down after it reached critical point. Moreover, the diversity of fungal community was more sensitive to the mixed salt addition than other groups. The response of soil physiological profiles (Biolog) followed a dose-response pattern with Cl– (R2=0.83) or mixed Cl–/SO42– (R2=0.89) salt. The critical threshold concentrations of salts for soil physiological function were 0.45 dS/m for Cl– and 1.26 dS/m for Cl–/SO42–, and those for soil microbial community structural diversity were 0.70 dS/m for Cl– and 1.75 dS/m for Cl–/SO42–.
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