中国南京与美国德克萨斯稻田甲烷排放的比较

Field measurements of methane emission from rice paddies were made in Nanjing, China and in Texas, USA, respectively. Soil temperature at approximately 10 cm depth of the flooded soils was automatically recorded. Aboveground biomass of rice crop was measured approximately every 10 days in Nanjing and every other week in Texas. Seasonal variation of soil temperature in Nanjing was quite wide with a magnitude of 15.3℃ and that in Texas was narrow with a magnitude of 2.9℃. Analysis of methane emission fluxes against soil temperature and rice biomass production demonstrated that the seasonal course of methane emission in Nanjing was mostly attributed to soil temperature changes, while that in Texas was mainly related to rice biomass production. We concluded that under the permanent flooding condition, the seasonal trend of methane emission would be determined by the soil temperature where there was a wide variation of soil temperature, and the seasonal trend would be mainly determined by rice biomass production if there are no additional organic matter inputs and the variation of soil temperature over the rice growing season is small.     

The isotopic composition and elemental abundance of lutetium in meteorites and terrestrial samples and the 176Lu cosmochronometer

The isotopic composition of lutetium has been measured in a range of terrestrial and meteoritic materials using solid-source mass spectrometric techniques. The meteoritic and terrestrial isotopic abundances are identical within experimental errors. The absolute ¹⁷⁵Lu/¹⁷⁶Lu ratio as determined in this work is 37.36 ± 0.07 at the 95% confidence level. On the basis of this measurement the atomic weight of lutetium has been calculated to be 174.967 ± 0.002, which is in good agreement with the currently accepted figure of 174.97 ± 0.01.Using the stable isotope dilution technique the abundance of lutetium has been determined in 25 stone, 1 stony-iron and 8 iron meteorites, and in 12 standard rocks, with an accuracy of ±5% at the 95% confidence level. In general, there is good agreement between this work and other published data.The ¹⁷⁶Lu-¹⁷⁶Hf pair has been proposed as an s process nucleocosmochronometer, because of the long half-life of ¹⁷⁶Lu and the unique fact that both are s process isobars. The isotopic and elemental abundances of lutetium as measured in this work have been used with published nuclear data to estimate the mean age of s process nucleosynthesis for this isobaric pair, using the Schramm-Wasserburg formalism. The mean age cannot be accurately determined at the present time because of the lack of 30 keV neutron capture cross-section data for s only process nuclides and an accurate measurement of the branching ratio of ¹⁷⁵Lu + n. However, it is possible to place constraints on the nuclear parameters in this mass region using a reasonable s process chronology based on the decay of ¹⁷⁶Lu.     

A simple analytic model of reconnection in a high-temperature turbulent sheet

We present a simple model of high-temperature (T≥10⁸ K) turbulent current sheets forming in magnetic-reconnection regions on the Sun. The model is based on an empirical formula by de Kluiver et al. (1991) for turbulent plasma conductivity and is apparently valid over a wide range of physical conditions. A comparison of the new results with known test calculations suggests agreement between the theoretical and empirical approaches to calculating the anomalous conductivity in turbulent plasma. The energy release in current sheets is powerful enough for flares, coronal transients, and coronal mass ejections to be interpreted.     

Stellar contents of two young open clusters: NGC 663 and 654

UBVRI CCD photometry in a wide field around two young open clusters, NGC 663 and 654, has been carried out. Hα and polarimetric observations for the cluster NGC 654 have also been obtained. We use the photometric data to construct colour–colour and colour–magnitude diagrams, from which we can investigate the reddening, age, mass and evolutionary states of the stellar contents of the these clusters. The reddening across the cluster regions is found to be variable. There is evidence for anomalous reddening law in both clusters; however, more infrared and polarimetric data are needed to conclude about the reddening law. Both clusters are situated at about a distance of 2.4 kpc. Star formation in both clusters is found to be a continuous process. In the case of NGC 663, star formation seems to have taken place sequentially, in the sense that formation of low-mass stars precedes the formation of most massive stars. Whereas, in the case of NGC 654, formation of low-mass stars did not cease after the formation of most massive stars in the cluster.     

A constitutive model for mechanical and chemo‐mechanical compaction in sedimentary basins and finite element analysis

Compaction and associated fluid flow are fundamental processes in sedimentary basin deformation. Purely mechanical compaction originates mainly from pore fluid expulsion and rearrangement of solid particles during burial, while chemo‐mechanical compaction results from Intergranular Pressure‐Solution (IPS) and represents a major mechanism of deformation in sedimentary basins during diagenesis. The aim of the present contribution is to provide a comprehensive 3D framework for constitutive and numerical modeling of purely mechanical and chemo‐mechanical compaction in sedimentary basins. Extending the concepts that have been previously proposed for the modeling of purely mechanical compaction in finite poroplasticity, deformation by IPS is addressed herein by means of additional viscoplastic terms in the state equations of the porous material. The finite element model integrates the poroplastic and poroviscoplastic components of deformation at large strains. The corresponding implementation allows for numerical simulation of sediments accretion/erosion periods by progressive activation/deactivation of the gravity forces within a fictitious closed material system. Validation of the numerical approach is assessed by means of comparison with closed‐form solutions derived in the context of a simplified compaction model. The last part of the paper presents the results of numerical basin simulation performed in one dimensional setting, demonstrating the ability of the modeling to capture the main features in elastoplastic and viscoplastic compaction. Copyright © 2016 John Wiley & Sons, Ltd.     

Imaging planets around nearby white dwarfs

We suggest that Jovian planets will survive the late stages of stellar evolution, and that white dwarfs will retain planetary systems in wide orbits (≳5 au). Utilizing evolutionary models for Jovian planets, we show that infrared imaging with 8-m class telescopes of suitable nearby white dwarfs should allow us to resolve and detect companions ≳3 M _JUP. Detection of massive planetary companions to nearby white dwarfs would prove that such objects can survive the final stages of stellar evolution, place constraints on the frequency of main-sequence stars with planetary systems dynamically similar to our own and allow direct spectroscopic investigation of their composition and structure.     

Comparison of cell- and vertex-centered discretization methods for flow in a two-dimensional discrete-fracture–matrix system

Simulations of flow for a discrete-fracture model in fractured porous rocks have gradually become more practical, as a consequence of increased computer power and improved simulation and characterization techniques. Discrete-fracture models can be formulated in a lower-dimensional framework, where the fractures are modeled in a lower dimension than the matrix, or in an equi-dimensional form, where the fractures and the matrix have the same dimension.     

Noble metals in the insoluble carbonaceous substance of black shales and ores: Direct atomic emission data

The way of extraction of insoluble carbonaceous substance (ICS) from black shales and technique of determination of noble metals (NM) in it by direct arc atomic emission analysis (AEA) were developed. The first results are reported on the determination of mineral-bound noble metals in ICS concentrates, which were extracted from the rocks and ores of the Sukhoi Log, Vernyi, Vasil’evskoe, Kuranakh, Daugyztau, Bakyrchik, Kamennoe, El’dorado, and other deposits.