离散系统一维不稳定流形的数值计算方法

针对二维离散系统的一维不稳定流形,本文提出一种新的算法,基本思想就是按照不稳定流形上的点的像和原像的增长比例来增长流形。同时,对该算法进行了精确的误差分析,并将该算法应用到Shear映射的不稳定流形计算中。该算法也可用于计算二维不稳定流形上的轨道,计算速度快,精度高。     

Fullerene Additives Convert Ambipolar Transport to p‐Type Transport while Improving the Operational Stability of Organic Thin Film Transistors

Many high charge carrier mobility (μ) active layers within organic field‐effect transistor (OFET) configurations exhibit non‐linear current–voltage characteristics that may drift with time under applied bias and, when applying conventional equations for ideal FETs, may give inconsistent μ values. This study demonstrates that the introduction of electron deficient fullerene acceptors into thin films comprised of the high‐mobility semiconducting polymer PCDTPT suppresses an undesirable “double‐slope” in the current–voltage characteristics, improves operational stability, and changes ambipolar transport to unipolar transport. Examination of other high μ polymers shows general applicability. This study also shows that one can further reduce instability by tuning the relative electron affinity of the polymer and fullerene by creating blends containing different fullerene derivatives and semiconductor polymers. One can obtain hole μ values up to 5.6 cm² V^–1 s^–1 that are remarkably stable over multiple bias‐sweeping cycles. The results provide a simple, solution‐processable route to dictate transport properties and improve semiconductor durability in systems that display similar non‐idealities.     

脉冲噪声环境下基于分数低阶循环相关的MUSIC算法

该文以稳定分布作为噪声模型,研究了脉冲噪声环境下循环平稳信号的波达方向估计问题。针对在脉冲噪声环境中基于传统2阶循环相关的算法效果显著退化的问题,该文提出了基于分数低阶循环相关的分数低阶循环MUSIC算法(FLOCC-MUSIC)。将分数低阶循环相关与MUSIC算法相结合,可以有效抑制脉冲噪声的同频带干扰。计算机仿真表明了此算法可有效完成高斯噪声和脉冲噪声条件下的波达方向估计,其性能优于传统的基于2阶循环相关的Cyclic-MUSIC。     

Biodegradation characteristics of heavy oil and correlation with group composition and carbon isotopes

Shallow heavy oil is abundant but seriously biodegraded in Chepaizi Uplift and many biomarkers cannot be used effectively. Therefore, some new parameters and methods are used to analyze the biodegradation extent, classification, and oil–source of heavy oil samples. The acid value and group compositions are used to evaluate the biodegradation extent. Carbon isotopes are not only used to calculate the percentage of complex combined oil, but also to correlate oil–source in Chepaizi Uplift. δ¹³C of oil is used together with biomarkers that can bear serious degradation, such as pregnanes, tricyclic terpanes, and gammacerane. The crossplots of δ¹³C and biomarkers are effective correlation tools, such as the crossplot of δ¹³C and C₂₁/C₂₃ tricyclic terpanes. δ¹³C in different group compositions also show excellent oil–source correlation results. These methods to study biodegraded heavy oil are not only helpful to clarify the biodegradation extent of shallow heavy oil in an extensive area, but also effective to classify heavy oil and correlate oil–source.     

Origin of shale gas in the Triassic Yanchang Formation,Ordos Basin,China

The Chang 7 Member shale gas of the Upper Triassic Yanchang Formation, Ordos Basin, is a representative of continental shale gas in China. The Chang 7 shale is currently in the oil window, suggesting it should primarily be producing oil, but an exploratory well found high levels of gas production. In addition, the methane carbon isotopic composition (δ¹³C₁) of Chang 7 shale gas is generally depleted in ¹³C relative to that calculated by Ro, according to the δ¹³C-Ro equation. It is uncertain whether Chang 7 shale gas has mixed with biogenic gas or early thermogenic gas. In this study, over 100 samples of fresh shale cores were collected from the Yanchang Formation, and on-site gas desorption experiments and experimental analysis were carried out. Measured shale gas content was considerable, and was found to be proportional to the abundance of organic matter. Through comprehensive evaluation of the gas composition and δ¹³C₁, it was concluded that there was no biogenic gas contribution to the shale gas in the study area. The negative δ¹³C₁ of shale gas was due to the different formation mechanisms of shale gas and conventional natural gas. Methane in shale gas reservoirs is the result of methane accumulation at all stages, which increases the shale gas content.     

鄂尔多斯盆地天环坳陷北段桌子山组白云岩碳氧同位素特征及意义

通过空间展布和不同类型白云岩的碳氧同位素特征,诠释了鄂尔多斯盆地西部天环坳陷北段奥陶系桌子山组白云岩的成因和储层地质学意义。研究区白云岩主要有微-粉晶白云岩、残余砂屑细晶白云岩和细-中晶白云岩3种,其中微-粉晶白云岩δ¹³C、δ¹⁸O平均值为0.78‰和-5.0‰;残余砂屑细晶白云岩δ¹³C、δ¹⁸O平均值为0.53‰和-6.5‰;细-中晶白云岩δ¹³C、δ¹⁸O平均值为0.47‰和-6.3‰。桌子山组白云岩碳氧同位素的组成位于正常海相碳酸盐岩范围之内,说明其白云石化流体来源于囚禁的古海水。白云岩碳氧同位素演化特征及成岩作用特征,指示微-粉晶白云岩为准同生阶段白云石化的产物,而残余砂屑细晶白云岩及细-中晶白云岩则为浅埋藏白云石化的产物。     

烃源岩中无机矿物对有机质生烃的影响

对华北下花园地区下马岭组及鄂尔多斯盆地延长组2组低成熟泥岩全岩及分离的干酪根样品开展有水热解实验,探讨了烃源岩源内无机矿物对有机质生烃及同位素分馏的影响。实验结果表明,两组全岩有水体系液态烃及气态烃产率不同程度低于干酪根有水体系,CO₂及H₂产率则明显偏高。同时,全岩有水热解体系气体产物异构烃含量相对较低,表明烃源岩中无机矿物的加入抑制了水-有机质的反应并一定程度上改变了反应途径。稳定同位素的分析结果表明,相同热演化程度下,2组全岩及相应干酪根热解生成的甲烷碳同位素变化不大,但前者生成的二氧化碳碳同位素显著升高,且气态烃氢同位素更低。表明全岩有水热解体系下,烃源岩中的无机矿物参与到有机质热解过程中,改变了CO₂产率及同位素组成,并存在H₂间接加氢作用。     

Evolution of hydrothermal explosions at Rehai geothermal field, Tengchong volcanic region, China

During the period 1993–2003 over 20 hydrothermal eruptions occurred at Rehai geothermal field, in Tengchong volcanic region, Yunnan Province, southwestern China. Initially, the explosions occurred on the bed of the Zaotang River, and later along a NW–SE striking fault cross-cutting the river. The explosion activity intensified with time. The free gas samples collected from springs created by the explosions show ³He/⁴He ratios of 1.17, 2.22 and 4.05 Ra (Ra = 1.4 × 10⁻⁶) for the three distinguishable stages of ever-increasing magnitude of the explosions, respectively. Data on helium isotopes and gas chemistry indicate that the source of the gases feeding the explosions has progressively shifted from shallower to greater depth. Following this trend, larger hydrothermal explosions will probably occur in the future, so that this hazard must be taken into serious consideration.     

Power generation characteristics of a sandwich‐type self‐heating thermoelectric generator with spatially varying embedded heat source

Power generation characteristics of a sandwich‐type thermoelectric generator in which the heat source is embedded into thermoelectric elements are investigated. Our previous work on a similar concept only considered a uniform heat source distribution inside thermoelectric elements. In this work, the effect of the spatial distribution of a heat source is examined. In particular, the effect of the concentration of heat source near the one end, that is, the hot end, is intensively studied as a potential means of improving the efficiency of the device. Although the effects of heat source concentration in impractical cases without heat transfer limitations on the cold side remain ambiguous, it become clear that heat source concentration indeed has positive effects in more realistic cases with finite heat transfer coefficients imposed on the cold side. Because of the relatively low efficiency of typical thermoelectric generation, a significant amount of heat must be dissipated from the cold end of the thermoelectric element. Greater heat source concentration near the hot end leads to more effective utilization of available heat source, reduces the amount of heat rejected at the cold end, and lowers the hot end temperature of the thermoelectric element. Overall, it is suggested that heat source concentration can be used as a method to achieve more efficient operation and better structural integrity of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

Ergodic Hyperbolic Attractors of Endomorphisms

Let μ be an SRB-measure on an Axiom A attractor Δ of a C ²-endomorphism (M, f). As is known, μ-almost every x ϵ Δ is positively regular and the Lyapunov exponents of (f, T f) at x are constants λ⁽ⁱ⁾(f, μ), 1 ≤ i ≤ s. In this paper, we prove that Lebesgue-almost every x in a small neighborhood of Δ is positively regular and the Lyapunov exponents of (f, T f) at x are the constants λ⁽ⁱ⁾(f, μ), 1 ≤ i ≤ s. This result is then generalized to nonuniformly completely hyperbolic attractors of endomorphisms. The generic property of SRB-measures is also proved. 2000 Mathematics Subject Classification. 37D20, 37D25, 37C40. This work was supported by the 973 Funds of China for Nonlinear Science, the NSFC 10271008, and the Doctoral Program Foundation of the Ministry of Education.