疑源类的早期辐射及其意义

通过对元古宙至寒武纪早期疑源类的分析研究表明：新元古代早期和晚期疑源类的辐射分别与全球范围内超级大陆（rodinia)形成及海洋中锶同位素^87Sr/^86Sr值显著上升，陆源物质增加，δ^13C值由负值转为正值的时期相吻合；早寒武世疑源类的辐射与超级大陆（pannotia)的形成、裂解对全球环境的影响有关。认为疑源类在早寒武世的适应辐射，改变了全球生物的营养结构，“中型浮游动物”对小个体棘刺疑源类的有效利用，可能是引发“寒武爆发”的原因之一。     

基于残差加权经验过程方法的自回归模型分布变点监测

Change monitoring of distribution in time series models is an important issue.This paper proposes a procedure for monitoring changes in the error distribution of autoregressive time series,which is based on a weighed empirical process of residuals with weights equal to the regressors.The asymptotic properties of our monitoring statistic are derived under the null hypothesis of no change in distribution.The finite sample properties are investigated by a simulation.As it turns out,the procedure is not only able to detect distributional changes but also changes in the regression coefficient and mean.Finally,we apply the statistic to a groups of financial data.     

Thermal oxidative degradation of additive-free polypropylene pellets investigated by multichannel Fourier-transform chemiluminescence spectroscopy

Thermal oxidative degradation of additive-free polypropylene pellets heated isothermally in dry air at 150 and 180 °C (below and above the melting point of 163 °C) was investigated by multichannel Fourier-transform chemiluminescence spectroscopy. The initial peak wavelength of chemiluminescence emission at 490 nm remained constant during the early stages of thermal degradation, but new emissions developed with time in the red spectral region over an extended oxidation period. The time-dependent luminescence spectra were deconvoluted into three emission bands by least-squares fitting using Gaussian curves. We concluded that at least three groups of luminescent species (luminophores), having different conjugation lengths, were generated by thermal oxidation over extended periods and show luminescence around 490, 660, and 740 nm.     

Transiting the molecular potential energy surface along low energy pathways: The TRREAT algorithm

The Transition Rapidly exploring Random Eigenvector Assisted Tree (TRREAT) algorithm is introduced to perform searches along low curvature pathways on a potential energy surface (PES). The method combines local curvature information about the PES with an iterative Rapidly exploring Random Tree algorithm (LaValle, Computer Science Department, Iowa State University, 1998, TR98–11) that quickly searches high‐dimensional spaces for feasible pathways between local minima. Herein, the method is applied to identifying conformational changes of molecular systems using Cartesian coordinates while avoiding a priori definition of collective variables. We analyze the pathway identification problem for alanine dipeptide, cyclohexane and glycine using nonreactive and reactive forcefields. We show how TRREAT‐identified pathways can be used as valuable input guesses for double‐ended methods such as the Nudged Elastic Band when ascertaining transition state energies. This method can be utilized to improve/extend the reaction databases that lie at the core of automatic chemical reaction mechanism generator software currently developed to build kinetic models of chemical reactions. © 2013 Wiley Periodicals, Inc.     

The Photodecomposition of 1,l-Dichloro-2,2-bis(5′-chloro-2′-methoxyphenyl)ethylene (MPE), an Analogue of DDE

The solution-phase photodecomposition of l, l-dichloro-2,2-bis(5′-chloro-2′-methoxy-phenyl)ethylene (MPE) has been studied at an excitation wavelength of 313 nm in the presence of O₂ as well as in vacuum-degassed solutions. Only two non-volatile compounds are produced: 2,5-dichloro-3-(5′-chloro-2′-methoxyphenyl)benzofuran (BFD) and a minor product which was not identified. The BFD represents approximately 90% of the total non-volatiles. The volatile products were identified as CH₃Cl, CH₄ and HC1, with CH₃C1 being approximately 99.9 % of the total volatiles. Photolyses were carried out in C₆H₁₂ and CCI₄ solvents, the same products being observed in both solvents. Variation of MPE concentration has little or no effect on the relative quantum yield of decomposition. The photodecomposition of MPE does not follow the same pathway as the photodecomposition of DDE.     

You cannot fight the pressure: Structural rearrangements of active pharmaceutical ingredients under magic angle spinning

Although solid-state nuclear magnetic resonance (NMR) is a versatile analytical tool to study polymorphs and phase transitions of pharmaceutical molecules and products, this work summarizes examples of spontaneous and unexpected (and unwanted) structural rearrangements and phase transitions (amorphous-to-crystalline and crystalline-to-crystalline) under magic angle spinning (MAS) conditions, some of them clearly being due to the pressure experienced by the samples. It is widely known that such changes can often be detected by X-ray powder diffraction (XRPD); here, the capability of solid-state NMR experiments with a special focus on ¹H-¹³C frequency-switched Lee–Goldburg heteronuclear correlation (FSLG HETCOR)/MAS NMR experiments to detect even subtle changes on a molecular level not observable by conventional 1D NMR experiments or XRPD is presented. Furthermore, it is shown that a polymorphic impurity combined with MAS can induce a crystalline-to-crystalline phase transition. This showcases that solid-state NMR is not always noninvasive and such changes upon MAS should be considered in particular when compounds are studied over longer time spans.     

Prodigiosin of Serratia marcescens ZPG19 Alters the Gut Microbiota Composition of Kunming Mice

Prodigiosin is a red pigment produced by Serratia marcescens with anticancer, antimalarial, and antibacterial effects. In this study, we extracted and identified a red pigment from a culture of S. marcescens strain ZPG19 and investigated its effect on the growth performance and intestinal microbiota of Kunming mice. High-performance liquid chromatography/mass spectrometry revealed that the pigment had a mass-to-charge ratio (m/z) of 324.2160, and thus it was identified as prodigiosin. To investigate the effect of prodigiosin on the intestinal microbiota, mice (n = 5) were administered 150 μg/kg/d prodigiosin (crude extract, 95% purity) via the drinking water for 18 days. Administration of prodigiosin did not cause toxicity in mice. High-throughput sequencing analysis revealed that prodigiosin altered the cecum microbiota abundance and diversity; the relative abundance of Desulfovibrio significantly decreased, whereas Lactobacillus reuteri significantly increased. This finding indicates that oral administration of prodigiosin has a beneficial effect on the intestinal microbiota of mice. As prodigiosin is non-toxic to mouse internal organs and improves the mouse intestinal microbiota, we suggest that it is a promising candidate drug to treat intestinal inflammation.     

Modeling DNA beacons at the mesoscopic scale

We report model calculations on DNA single strands which describe the equilibrium dynamics and kinetics of hairpin formation and melting. Modeling is at the level of single bases. Strand rigidity is described in terms of simple polymer models; alternative calculations performed using the freely rotating chain and the discrete Kratky-Porod models are reported. Stem formation is modeled according to the Peyrard-Bishop-Dauxois Hamiltonian. The kinetics of opening and closing is described in terms of a diffusion-controlled motion in an effective free-energy landscape. Melting profiles, dependence of melting temperature on loop length, and kinetic time scales are in semiquantitative agreement with experimental data obtained from fluorescent DNA beacons forming poly(T) loops. Variation in strand rigidity is not sufficient to account for the large activation enthalpy of closing and the strong loop length dependence observed in hairpins forming poly(A) loops. Implications for modeling single strands of DNA or RNA are discussed.     

塔里木河流域中下游典型地物光谱变化规律

由于塔里木河流域中下游距离河道在垂直向的差别,以及气候与人为因素的影响,使植被的空间分布具有异构性.典型地物光谱变化的研究为中下游生态环境的遥感监测提供了基础,实验研究表明:绿色全荣植物中,棉花由于其具有明显绿峰、水分吸收谷和近红外的高反射峰而更加容易识别,其他植物主要差别则集中在550,680,1420 nm附近的反射峰、吸收谷和1920～2500 nm之间的反射率;与绿色植被相比,枯枝的光谱在可见光部分的绿峰和红光吸收谷不明显,但在可见光部分波形有所差别,而与流沙土壤光谱相比,各波段反射率变化较大;对比不同荣枯比例的植物光谱发现,同一种植物随着荣枯配比的变化,除可见光绿峰、近红外反射峰和各水分吸收谷变化外,最明显的是在近红外1420～1820 nm之间和短波红外1920～2500 nm之间反射率随着枯枝的比例增加而明显升高;关于土壤光谱,中下游各断面占主要类型的流沙土光谱相差不大,但是盐碱土和含有一定水分的盐碱土则变化较大,而且反射率基本低于流沙土,结壳土则除在近红外和短波红外部分变化更加平缓而有所差别外,其余波段接近流沙土;同样的土壤背景下,近红外和短波红外部分反射率的差别能够在一定程度上反映覆盖度的变化.     

Dual-modality and dual-energy gamma ray densitometry of petroleum products using an artificial neural network

The prediction of volume fractions in order to measure the multiphase flow rate is a very important issue and is the key parameter of multi-phase flow meters (MPFMs). Currently, the gamma ray attenuation technique is known as one of the most precise methods for obtaining volume fractions. The gamma ray attenuation technique is based on the mass attenuation coefficient, which is sensitive to density changes; density is sensitive in turn to temperature and pressure fluctuations. Therefore, MPFM efficiency depends strongly on environmental conditions. The conventional solution to this problem is the periodical recalibration of MPFMs, which is a demanding task. In this study, a method based on dual-modality densitometry and artificial intelligence (AI) is presented, which offers the advantage of the measurement of the oil–gas–water volume fractions independent of density changes. For this purpose, several experiments were carried out and used to validate simulated dual modality densitometry results. The reference density point was established at a temperature of 20 °C and pressure of 1 bar. To cover the full range of likely density fluctuations, four additional density sets were defined (at changes of ±4% and ±8% from the reference point). An annular regime with different percentages of oil, gas and water at different densities was simulated. Four features were extracted from the transmission and scattered detectors and were applied to the artificial neural network (ANN) as inputs. The input parameters included the ²⁴¹Am full energy peak, ¹³⁷Cs Compton edge, ¹³⁷Cs full energy peak and total scattered count, and the outputs were the oil and air percentages. A multi-layer perceptron (MLP) neural network was used to predict the volume fraction independent of the oil and water density changes. The obtained results show that the proposed ANN model achieved good agreement with the real data, with an estimated root mean square error (RMSE) of less than 3.