Styrene polymerization catalyzed by nickel complexes bearing hydroxyindanone-iminate ligands

Activated by methylaluminoxane, mononuclear bis（hydroxyindanone-iminate）nickel complexes Ni[ArN=CC2H3（CH3）C6H2（R）O]2 （Ar = 2,6-i-Pr2C6H3, R=Me（1）, R=CI（2）, and R=H（3）） showed good activity for the styrene polymerization. The effect of many reaction parameters including the AI/Ni ratio, temperature, and reaction time on catalytic activities of catalytic systems and the molecular weights of the obrained polystyrene was ascertained. The highest activity of 1.34×10^5g（PS）·mol^-1（Ni）·h^-1 was obtained under the optimum reaction condition. The ^13C NMR spectra of the polymers revealed that the polymer was isotactic-rich atactic polystyrene. And the coordination mechanism was confirmed by the analyses of the polymer chain end-groups.     

dr1127： A novel gene of Deinococcus radiodurans responsible for oxidative stress

The functional analysis of dr1127,a novel gene in Deinococcus radiodurans was performed in this pa-per. The dr1127 gene was found occasionally in our microarray and 2-DE gel experiments. Mutation of the dr1127 gene decreased the γ-radiation and H2O2 resistance of D. radiodurans,and weakened the scavenging abilities of cell extracts for free radicals (superoxide anion,hydrogen peroxide,and hy-droxyl radical). Further oxidative damage assays demonstrated that the purified DR1127 protein of D. radiodurans could bind to double stranded DNA in vitro and protect DNA from oxidative damage in this way. These results suggest that the dr1127 gene is an important gene that can maintain γ-radiation and oxidative resistance in D. radiodurans and may take part in the oxidative stress process.     

Synthesis and properties of novel gemini surfactant with short spacer

Cationic gemini surfactant dimethylene-1,2-bis(dodecyldiethylammonium bromide), referred to as C12C2C12(Et) was synthesized, and its surface property and aggregation behavior in aqueous solution were studied. The value of γ at the critical micelle concentration (γcmc) is much smaller than that of the surfactant homologues with longer spacer. Spherical and elongated micelles were formed in the aqueous solution of this gemini surfactant,and the spherical micelles were absolutely dominant compared to the elongated micelles at our studied concentration quantitatively.     

Experimental and theoretical studies of the reaction between cationic vanadium oxide clusters and acetylene

The time of flight mass spectrometer coupled with a laser ablation/supersonic expansion cluster source and a fast flow reactor was adopted to study the reactivity of cationic vanadium oxide clusters （VinOS,） toward acetylene （C2H2） molecules under gas phase （P, - 1.14 kPa）, under near room temperature （T, - 350 K） conditions. Association products, VmOnC2H2^＋ （m,n = 2,4; 2,6; 3,7-8; 4,9-11; 5,12-13; 6,13-16, and 7,17）, are observed. The oxidation of C2H2 by （V2Os）n^＋ （n = 1 -3） is experimentally identified. The reactivity of （V2O5）n^＋ decreases as n increases. Density functional theory （DFT） calculations were carried out to interpret the reaction mechanisms. The DFT results indicate that a terminal oxygen atom from V2O5^＋ can transfer overall barrierlessly to C2H2 at room temperature, which is in agreement with the experimental observation. Other experimental results such as the observation of V206C2H2^＋ and nonobservation of V2O7,8C2H2^＋ in the experiments are also well interpreted based on the DFT calculations. The reactivity of vanadium oxide clusters toward acetylene and other hydrocarbons may be considered in identifying molecular level mechanisms for related heterogeneous catalysis.     

Vegetation evolution on the central Chinese Loess Plateau since late Quaternary evidenced by elemental carbon isotopic composition

There are many controversial issues in loess studies such as natural vegetation types on the Chinese Loess Plateau during the historical periods and the spatial and temporal evolution of C3/C4 plants. Elemental carbon isotopic composition （δ^13Cec） in the loess section may offer new evidence for these problems. Elemental carbon （EC） is produced by incomplete combustion of vegetation, and its carbon isotopic composition has a very small difference from that of the formal vegetation, then δ^13Cec can be used as a record to recover the changes of vegetation. Elemental carbon was extracted by applying the oxidation method from the Ioess-paleosol sequence in the central Chinese Loess Plateau, and its car- bon isotope composition was analyzed by the isotope mass spectrometer. The results showed that the vegetation in this region was a mixed type of C3 and C4 plants, dominated with C3 plants in most of the time. Since late Quaternary, C3/C4 plants may not follow a simple glacial-interglacial cycle mode on the Chinese Loess Plateau, but showing fluctuations. C3 plants increased gradually in L4 period, and more C3 plants occurred during $3 period, and C4 plants increased again during L3-- L2 periods, after that, Cs plants dominated again during S1 --S0 periods. During periods of paleosol development, C3 plants were abundant in S3 and S1, and there were more Ca plants in S2 and SO. During periods of loess sedimen- tation, there were more C3 plants in L4 and L1, and there were more C4 plants in L3 and L2. On the orbital timescale, the vegetation variations revealed by δ^13Cec record are consistent with the results of pollen data and also similar to the results obtained by organic carbon isotopic composition since the last glacial period.     

Comparison of the carbon isotope composition of total organic carbon and long-chain <Emphasis Type="Italic">n</Emphasis>-alkanes from surface soils in eastern China and their significance

Surface soil samples collected over a high spatial resolution in eastern China were analyzed for carbon isotope composition （δ^13C） of total organic carbon （TOC） and higher plant-derived long-chain n-alkanes, with the latter reported as weighted mean values. The two sets of δ^13C values are significantly correlated and show similar trends in spatial variation. The spatial distribution of δ^13C shows less negative values in the mid-latitudes between 31°N and 40°N and more negative ones at higher and lower latitudes. This is consistent with previously reported carbon isotope data from surface soil phytoliths in the same region and suggests that the mid-latitude area provides relatively favorable growing condi- tions for C4 plants. Furthermore, δ^13C values of both TOC and long-chain n-alkanes from 12 surface soil samples collected from a small grassland in north China displayed similar carbon isotope values and the difference between paired δ^13C of a soil samples remains relatively constant. Our data demonstrate that in eastern China, soil δ^13C composition of both TOC and long-chain n-alkanes is effective indicators of C3/C4 ratios of the prevailing vegetation. This work suggests that -22‰ and -32‰ are good es- timated end members for the weighted mean δ^13C values of long-chain n-alkanes （C27, C29 and C31 n-alkanes） from soils under dominant C4 or C3 vegetation, allowing us to reconstruct paleovegetation trends.     

Measurement of ethylene and methane production in a temperate forest soil using inhibition of acetylene and carbon monoxide

We studied in the laboratory the effects of acetylene （C2H2） concentrations on the accumulation and consumption of ethylene and methane in a temperate pine forest soil, and in situ ethylene and methane production and flush effects of nitrogen sources on both productions in the pine forest stand （Pinus sylvestris L.）. The addition of C2H2 at concentrations more than 50 Pa C2H2 in the headspace caused a more than 95% reduction in rates of ethylene and methane consumption in forest soil compared to those with no C2H2. Furthermore, addition of acetylene within a range of 50 to 10, 000 Pa C2H2 induced a similar rate of methane accumulation in forest soil. Hence, it can be concluded that presence of more than 50 Pa C2H2 in the headspace is an effective method to measure methane production in forest soil. The addition of C2H2 at concentrations more than 50 Pa C2H2 induced an increasing concentration of ethylene in the headspace （P≤0.05）, indicating the reduction of acetylene to ethylene in forest soil. Using inhibition of 0.5 kPa C2H2 in combination with 5 kPa carbon monoxide that inhibits the reduction of acetylene in a short term, it was observed that there was a larger in situ methane production rate （218±26 μg C m^-2 h^-1（μg C per square meter per hour, the same below）） than in situ ethylene production rate （92±6 μg C m^-2 h^-1） in the pine forest soil. The addition of nitrogen sources such as urea, urea plus a nitrification inhibitor dicyandiamide, and potassium nitrate, could induce a 5-fold greater increase in rates of in situ ethylene and methane production compared to those in the control, particularly in the latter （P≤0.05）. The results can promote in situ measurement of ethylene and methane production in forest soils at different sites.     

Low temperature thermodynamic study of the stable and metastable phases of vanadium

The low temperature thermodynamics of the stable phase of vanadium has been assessed by the polynomial and Debye models from the experimental data available in literature. By means of the con-strained nonlinear least squares curve fitting arithmetic,two sets of parameter values have been de-termined. Expressions of the thermodynamic functions Cp(T) and G(T)-H(298.15 K) at 0―298.15 K are presented. The low temperature thermodynamics of the metastable phase of vanadium can only be extrapolated by the Debye model. The expression of the thermodynamic function Cp(T) at 0―298.15 K is presented.     

Modification of TiO2 nanotubes arrays by CdS and their photoelectrocatalytic hydrogen generation properties

In order to realize hydrogen generation under visible light, novel CdS/TiO2 nanotubes arrays are developed by electrochemical anodizaUon of Ti in 0.15 mol/L NHTF ＋ 0.08 mol/L H2C2O4 electrolyte. The diameter of the nanotube is 80-100 nm and the length is approximately 550 nm. The CdS nano-particles are deposited on the TiO2 nanotubes arrays by chemical bath deposition （CBD） in the ammonia-thiourea system. A 300 W Xe lamp is used as the light source, CdS/TiO2 nanotube arrays are used as the photoanode with the application of 1.0 V bath voltage, and 0.1 mol/L Na2S ＋ 0.04 mol/L Na2SO3 solution is used as the electrolyte, then the rate of photoelectrocatalytic hydrogen generation is 245.4 μL/（h·cm^2）. This opens new perspectives for photoelectrocatalytic hydrogen generation by using CdS/TiO2 nanotubes arrays.     

Fluorescence and sensitization performance of phenylene-vinylene-substituted polythiophene

A new kind of polythiophene derivative, Poly(3-{2-[4-(2-ethylhexyloxy)-phenyl]-vinyl}-2,2′-bithiophene) (PTh), was applied in dye-sensitized solar cell to extend the light response of nanocrystalline TiO2 electrode. UV-vis absorption and fluorescence spectra were employed to investigate the interaction of PTh with nanocrystalline TiO2. The absorption coefficient of the PTh was high in visible part of spec- trum, and the fluorescence emission of the PTh can be efficiently quenched by TiO2 nanoparticles ow- i...     

Latitudinal shift and tilt of the ring current during magnetic storms

The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However, we always observe a larger ΔH at higher latitude stations than lower ones, implying that the ERC could tilt or/and shift with respect to the equatorial plane during intense storms. In this paper, we analyze 11 intense magnetic storms from 2000 to 2004, and introduce two configurational factors to characterize the topology of storm time ring current. The results show that ERC has occasionally deviated off equatorial plane with both tilt angle δ_t≈13°―25° and latitude shift δ_s≈0°―21.8°. The ground disturbed field distribution should be improved as ΔH_k = ΔH_maxcos(φ_k-δ ), which agree well with the geomagnetic observations.     

Direct electrochemistry and electrocatalysis of horseradish peroxidase in MnO2 nanosheet film

A novel material MnO2 nanosheet has been used as the support matrix for the immobilization of horseradish peroxidase （HRP）. HRP entrapped in MnO2 nanosheet film exhibits facile direct electron transfer with the electron transfer rate constant of 6.86 s^-1. The HRP/MnO2 nanosheet film gives a reversible redox couple with the apparent formal peak potential （E^0＇） of -0.315 V （vs. Ag/AgCl） in pH 6.5 phosphate buffer solution （PBS）. The formal potential E^0＇ of HRP shifts linearly with pH with a slope of -53.75 mV.pH^-1, denoting that an electron transfer accompanies single-proton transportation. The immobilized HRP shows an electrocatslytic activity to the reduction of H2O2. The response time of the biosensor for H2O2 is less than 3 s, and the detection limit is 0.21 μmol · L^-1 based on signal/noise = 3.     

Pyrolysis of oil at high temperatures: Gas potentials, chemical and carbon isotopic signatures

Although the gas cracked from oil has been believed to be one of the important sources in highly ma-tured marine basins, there are still some debates on its resource potentials and chemical and isotopic compositions. In this study a Cambrian-sourced marine oil sample from the Silurian reservoir of well TZ62 in the central Tarim basin was pyrolyzed using sealed gold tubes with two different pyrolysis schemes: continuous pyrolysis in a closed system and stepwise semi-open pyrolysis. The results show that the maximum weight yield of C_1–5 gases occurs at EasyRo=2.3% and the residual gas poten-tial after this maturity is only 43.4 mL/g, about 12% of the yield of 361 mL/g at EasyRo=2.3%. Combined with the results of kinetic modeling, the main stage of gas generation from oil cracking is believed within the EasyRo=1.6%―2.3%. The increase in the volume yield of C_1–5 gases at EasyRo>2.3% in a closed system is mainly related to the re-cracking of previously formed C_2–5 wet gases, not the direct cracking of oil. The stepwise pyrolysis experiments show that the gas from the cracking of residual oil at EasyRo>2.3% is characterized by very high dryness index (higher than 92%) and heavy methane carbon isotopes ranging from -28.7‰ to -26.7‰, which is quite different from the gases from the con-tinuous pyrolysis in a closed system. The kinetic modeling of methane carbon isotope fractionation shows that the carbon isotopes of methane within the main stage of gas generation (EasyRo<2.3%) are far lighter than the carbon isotopes of the precursor oils under a geological heating rate of 2 ℃/Ma. The above observations and results provide some new clues to the accurate recognition and objective re-source evaluation of oil cracking gas in highly mature marine basins.     

A novel Pd/silicalite-1 composite membrane for hydrogen separation

A novel Pd/silicalite-1 composite membrane supported on the macroporous tubular stainless steel substrate was successfully fabricated by electroless plating at 303 K. The structure, morphology and gaseous permeability of the membrane were detected by X-ray diffractiometry （XRD）, scanning electron microscopy （SEM） and single-gas permeation test, respectively. Results confirm the formation of a thin, smooth, and continuous Pd/silicalite-1 composite membrane. The obtained composite membrane shows a high H2 permeance of 1.15×10^-6 mol. m^-2. s^-1. Pa^-1 with moderate H2 selectivity of 250 for H2/N2 at 773 K, at 0.1 MPa pressure drop, suggesting the potential application for H2 separation.     

Fabrication of the 19-filament Fe/Cu clad MgB2 wire via in situ powder-in-tube method

Using commercial amorphous B powder (92% in purity) and Mg powder (99% in purity) as starting materials, 19-filament Fe/Cu clad MgB2 wires were fabricated by an in situ powder-in-tube method. Heat treatment was performed at 700℃ for 1 h under an argon gas atmosphere. The influence of Mg/B ratio on the microstructure and superconducting properties of the wires was investigated. It was found that the major phases of MgB2 wires were MgB2 accompanied with relatively small amounts of MgO and Fe2B impurities. With 5% excess Mg addition, the onset TC slightly decreased. However, the transport JC at 4.2 K and 4 T reached 1.07×104 A·cm-2, increasing by a factor of 1.4 compared to the stoichiometric sample. Moreover, the Mg1.05B2 sample showed an improved field dependence of JC, suggesting that less voids and smaller grain size of the Mg1.05B2 core lead to better grain connectivity and stronger flux pinning.     

Structural dependences of the <Emphasis Type="Italic">η</Emphasis><Superscript>6</Superscript> complexes of 3-amino-9-ethylcarbazole with chromium tricarbonyl fragment on third-order optical nonlinearities

Degenerate four-wave mixing measurements, using the 35 ps pulses at 532 nm, have been employed to investigate the third-order nonlinear optical parameters of two chromium tricarbonyl complexes η6-bonded to 3-amino-9-ethylcarbazole at either the NH2-substituted aryl ring （1） or the unsubstituted ring （2） and their precursor 3-amino-9-ethylcarbazole （AECz）. The second-order hyperpolarizability y of the compounds 1 and 2 were found to be 42.9×10^-31 and 35.9×10^-31 esu, respectively, approximately one order of magnitude greater than AECz. The relation between the molecular structure and second-order hyperpolarizability of the compounds I and 2 was explored in detail based on the three-level model and the density functional theory （DFT） calculation. The theoretical results indicate that the spatial distribution of electron density has the profound role in the third-order nonlinear optical properties.     

Holocene climatic and environmental changes recorded in Baahar Nuur Lake core in the Ordos Plateau, Inner Mongolia of China

A 5.3 m lake core was drilled in Baahar Nuur Lake in the Ordos Plateau, and measurements of meangrain size, organic δ 13C (δ 13Corg), organic carbon content (TOC), C/N, carbonate content, carbonate δ 13C(δ 13Ccar) and δ 18O (δ 18Ocar) were conducted for retrieving the Holocene chronosequence of climaticchanges based on 15 AMS 14C dates. The record documented four major stages of climate change inthe Ordos Plateau: (IV) a cold and dry condition before ～7.65 14C ka BP; (III) a warm and humid stagebetween ～7.65 and ～5.40 ka BP; (II) a generally drier and cooler climate since ～5.40 ka BP with twohumid events occurring from ～4.70 to ～4.60 ka BP and from ～4.20 to ～3.70 ka BP, and (I) a dry climatecharacterized by complete desiccation of the lake after 3.70 ka BP. Stage III can be further divided intothree sub-stages: (IIIa) a warm and humid episode from ～7.65 to ～6.70 ka BP, (IIIb) a warm and relativelydry episode from ～6.70 to ～6.20 ka BP, and (IIIc) the magthermal and maghumid episode of the Holo-cene from ～6.20 to ～5.40 ka BP.     

Temperature effects on ethylene and methane production from temperate forest soils

Change in temperature affects the activity of soil microorganisms.However,there is limited knowledge about temperature effects on ethylene(C2H4) and methane(CH4) production from forest soils.Topsoil samples(0―5 cm) collected from different temperate forest stands(e.g.,Pinus sylvestris L.,Cryptomeria japonica,and Quercus serrata) were used to compare C2H4 and CH4 production from soils at temperature from 5 to 35℃ under oxic and anoxic conditions.The rates of C2H4 and CH4 production from soils under oxic cond...     

Different climatic controls of soil δ 13Corg in three mid-latitude regions of the Northern Hemisphere since the Last Glacial period

Paleoecological records of soil δ^13Corg from three regions in the middle latitudes of the Northern Hemisphere, including the Chinese Loess Plateau （CLP）, the Great Plains and adjacent areas of North America and northwestern Europe, showed different variations since the Last Glacial period. An attempt was made to evaluate the causes for the difference in δ^13Corg on the basis of the modern climatic data collected in these regions and of the modern C3 and C4 plant distributions. The analysis indicates that temperature, especially the growing season temperature, has a dominant control on the growth of C4 plants. When the mean annual or growing season temperatures are below the ＂threshold value＂, the growth of C4 plants is limited. When the temperature is above the ＂threshold value＂, C4 plants can grow under a wide range of precipitation. However, when the precipitation is high enough to favor the growth of trees, the proportions of C4 plants in local biomass will decline. The implicit control factor recovered by sedimentary records is consistent with the control factor on modern C3/C4 distribution. Pure C3 plants have been dominating the local biomass since the Last Glacial period in European loess region, mainly owing to the low local temperature. The increases in C4 plants from the late Pleistocene to the Holocene in the Chinese Loess Plateau, the Great Plains and adjacent areas, mainly reflect the influence of increasing temperature.     

Monte Carlo simulations for two-dimensional Ising system far from equilibrium

With a dynamic Monte Carlo simulation, which is free of critical slowing down, the critical behavior of two-dimensional Ising model at non-equilibrium states is investigated. We focus on the two-time autocorrelation function A(t, t' ) to identify the dynamic exponent z in two different evolution stages, quenched from a high temperature state and a completely ordered state to the critical state at TC, re-spectively. By using the heat-bath algorithm, the dynamic critical exponent is estimated as z ≈ 2.16. As a result, the universality of the scaling behavior is verified numerically, and the exponent λC is deter-mined complete by λC = β /ν for the evolutions from an initial completely ordered state.