A comparison of transition state of phenol in H-atom abstraction by methyl and methylperoxyl radicals

DFT method was employed to locate transition state for H-atom transfer from phenol by methyl radical and methylperoxyl radical. The reaction pathway energy profiles and the structure of transition state show that a common feature is the out-of-plane structure of the transition state: in contrast to the en- ergetic minima of a hydrogen-bonded intermediate, the hydrogen bond in transition structures is con- siderably twisted out of the aromatic ring. From the values of enthalpy (△H) and activation energy (Ea) obtained, it is found that the rate of the reaction of peroxyl radical with phenolic antioxidant is higher than that of alkyl radical with antioxidant. Spin density distributions show that the electron transmis- sion is between methyl (methylperoxyl) radical and phenol.     

Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions,transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal re-action coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path,which proceeds via two steps: i) two reactants form an intermediate (IM1),which is an exothermal re-action of 8.62 kJ·mol?1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift,in which the energy barrier is 44.53 kJ·mol?1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm,in which the reaction has a bigger spontaneity capability,equi-librium constant (K) and higher rate constant (k).     

Channel noise-induced phase transition of spiral wave in networks of Hodgkin-Huxley neurons

The phase transition of spiral waves in networks of Hodgkin-Huxley neurons induced by channel noise is investigated in detail.All neurons in the networks are coupled with small-world connections,and the results are compared with the case for regular networks,in which all neurons are completely coupled with nearest-neighbor connections.A statistical variable is defined to study the collective behavior and phase transition of the spiral wave due to the channel noise and topology of the network.The effect of small-world connection networks is described by local regular networks and long-range connection with certain probability p.The numerical results confirm that (1) a stable rotating spiral wave can be developed and maintain robust with low p,where the breakup of the spiral wave and turbulence result from increasing the probability p to a certain threshold;(2) appropriate intensity of the optimized channel noise can develop a spiral wave among turbulent states in small-world connection networks of H-H neurons;and (3) regular connection networks are more robust to channel noise than small-world connection networks.A spiral wave in a small-world network encounters instability more easily as the membrane temperature is increased to a certain high threshold.     

The magnetic properties of Serbian loess and its environmental significance

This paper reports a loess-paleosol sequence located in the Danube River basin,Serbia,which formed at least since the latest part of the early Pleistocene,and before the paleomagnetic B/M boundary.Various magnetic parameters of the Serbian V-L1-V-S4 loess-paleosol sequence have been measured and analyzed in the Titel Loess Plateau.These parameters show a very similar magnetic behavior compared with that of the Chinese loess.There is a general positive relationship between magnetic susceptibility() and pedogenesis.The main contributors to are the magnetic grains of SP(superparamagnetic) and SD(single domain) magnetic domains,while MD(multi domain) contributes only a small percentage.The difference in between loess and paleosol mainly is caused by pedogenesis.The very fine magnetic minerals increase gradually with increasing soil development(from loess to soil),and they lead to higher.The thermomagnetic curves show thatmagnetic minerals in the loess layers are magnetite and maghemite,both providing a major contribution to.In contrast the paleosol layers mainly are composed of magnetite,with almost no or a very small amount of maghemite,as implied by a reversible thermomagnetic behavior.This indicates that pedogenic conditions during V-S3 and V-S4 strong soil development have resulted in maghemite that is no longer stable,and has been resolved or converted to other stable phase minerals.This likely indicates that soil moisture during V-S3 and V-S4 development exceeded a critical condition of maghemite stability.     

Density functional theory calculation on the C―H bond insertion reaction of dibromocarbene with acetaldehyde

The insertion reaction mechanism of CBr_2 with CH_3CH_O has been studied by using the B3LYP/6-31G(d) method. The geometries of reactions, transition state and products were completely optimized. All the energy of the species was obtained at the CCSD(T)/6-31G(d) level. All the transition state is verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The results show that the propionaldehyde (~HP1) is the main product of CH_2 insertion with CH_3CH_O. The calculated results indicated that all the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CBr_2 not only can insert the C_α-H [reaction I(1)]) but also can react with C_β-H [reaction II(1)]. The statistical thermodynamics and Eyring transition state theory with Wigner correc- tion are used to study the thermodynamic and kinetic characters of I(1) and II(1) in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature rang is 250 to 1750 K and 250 to 1600 K at 1.0 atm for I(1) and II(1) respectively. The rate constant and equilibrium constant are distinct in the range from 250 to 1000 K so that I(1) more easily occurs, while the reactions are not selected in the temperature range of 1000-1600 K     

A first-principles study of displacive β to ω transition in Ti-V alloys

The ground state properties of β and ω phases in Ti-(0–30 at%)V alloys were calculated, and subsequently thermodynamics and energy barriers of the displacive β to ω transition were investigated by first-principles. The results show that the lattice parameters of β and ω phases decreases with increasing V content in Ti-V alloys. The principal lattice strains for the β to ω transition are highly compositional dependent, and the volume variation decreases with increasing V content. The mechanical stability of the ω phase increases initially at the V content around 10 at% and then decreases with increasing V content. Based on the quasiharmonic Debye model, a metastable diffusionless phase diagram has been established, showing that the ω phase is thermodynamically more stable than the β phase at room temperature, anticipating a spontaneous transition from β to ω phases in Ti-V alloys. The calculations of energy pathways indicate that there is an energy barrier during the displacive βto ω transition in Ti-V alloys at temperatures from 100 to 500 K, but not at 0 K.     

The propagation of seafloor spreading in the southwestern subbasin, South China Sea

On the basis of the summary of basic characteristics of propagation, the dynamic model of the tectonic evolution in the South-western Subbasin (SWSB), South China Sea (SCS), has been established through high resolution multi-beam swatch bathymetry and multi-channel seismic profiles, combined with magnetic anomaly analysis. Spreading propagates from NE to SW and shows a transition from steady seafloor spreading, to initial seafloor spreading, and to continental rifting in the southwest end. The spreading in SWSB (SCS) is tectonic dominated, with a series of phenomena of inhomogeneous tectonics and sedimentation.     

Gas-liquid phase coexistence and finite-size effects in a two-dimensional Lennard-Jones system

The gas-liquid phase coexistence in a two-dimensional Lennard-Jones system is investigated using Maxwell construction method together with molecular dynamics simulations.The results of phase coexistence in different truncations of the potential are compared with data obtained from the literature,and the corresponding critical properties calculated.The crossover from Ising-like to mean field behavior is observed and confirmed as the temperature approaches the critical point from below.Performing simulations on systems with different sizes,we find that a finite size effect is more significant than those shown in most of the previous results,and a lower critical temperature is obtained when the full extent of this finite size effect is considered.     

Sequence analysis of the Microcystis aeruginosa FACHB-912 phytochrome gene supports positive selection in cyanobacteria

The phytochrome gene from Microcystis aeruginosa FACHB-912,isolated from algal blooms in Taihu Lake in China,was sequenced and found to code for a wavelength transition light receptor protein.The gene was composed of five distinct domains:a PAS fold domain,a GAF domain,a phytochrome domain,a His Kinase A(phosphoacceptor) domain,and a histidine kinase domain.Red-absorbing phytochrome,far-red-absorbing phytochrome,and photoconversion kinetics were monitored via the spectral characteristics of the protein.To detect positive selection,homologous sequences from cyanobacterium phytochrome genes were obtained from GenBank.Potential selective pressure was identified by phylogenetic analysis with maximum likelihood analyses.The frequency of the phytochrome gene being subjected to selective constraints suggests that positive selection is a potentially important mechanism that promotes the evolution of the cyanobacteria phytochrome gene.The sites identified in this study provide targets for further research on the structural-functional role of these residues,and on the correlation with the mechanism of algal blooms.     

Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau

Loess deposit in the northeastern Qinghai-Tibetan Plateau offers an excellent record of climate and environment changes in this region.We have conducted multiparameter mineral magnetic analyses of smaples of loess deposits from the Dongchuan,Lalakou and Panzishan sections.The methods used include magnetic susceptibility,fre-quency-dependent suceptibility,temperature-dependent susceptibility,isothermal remanent magnetization acquisibility.Maghemite and hematite is also present in the loess layers and paleosol horizons.The higher concentration of maghemite in paleosols suggests that the formation of maghemite occurred during in situ pedogenesis,which plays an important role in the enhancement of the magnetic susceptibitily.Similar to that in the Chinese Loess Plateau lying to the east of the Liupan Mountains,magnetic granulometry in the studied loess and paleosols is predominantly pseudo-single-domain(PSD). However,the mean grain-size of the ferrimagnetic minerals in loess is evidently coarser (larger PSD and multiomain-like) than in paleosols (mainly PSD).The magnetic susceptibility of loess and paleosols is positively correlated with the content of ultrafine magnet-ite/maghemite grains,and hence with the intensity of in situ pedogenesis.Therefore,the enhanced magnetic susceptibility in the studied loess-paleosol sequences can be interpreted as being due to climatically induced in situ pedogenesis.     

Susceptibility variations of multiple origins of loess from the Ily Basin (NW China)

The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.     

Analysis of the ecological environment around 10000 a BP in Zhaitang area,Beijing: A case study of the Donghulin Site

The transition from Paleolithic to Neolithic around 10000 a BP was a significant event in human history. We have analyzed the paleoenvironment in the Zhaitang area (Beijing) based on samples from an early Neolithic site at Donghulin. This site is considered to demonstrate the Paleolithic-Neolithic transition in this area. The site yielded burials with several human skeletons, known as "Donghulin man". We conducted a geomorphological and quaternary geological investigation in the Donghulin area, and also analyzed sediments and pollen, enabling us to discuss the living environment of the local people. Donghulin man lived mainly from 11100-9600 cal a BP; a period of warming following the Younger Dryas. The climate was good, the land was covered by dry temperate grassland, and later, wet temperate meadow steppe. "Donghulin man" usually inhabited the floodplain; this was flat, warm, and wet, with abundant plants and animals for a favorable living environment. Our research helps to rebuild the living environment of humans in the Beijing area around 10000 a BP, and to understand more about the environmental setting in north China during the Paleolithic-Neolithic transition.     

Forcing mechanisms for East-Asia monsoonal variations during the late pleistocene

Based on the climate records derived from loess deposits in north-central China, the characteristics of the East-Asia paleomonsoonal changes during the Late Pleistocene are summarized as follows: (ⅰ) The 0.1_Ma climate period is predominant in both summer and winter monsoonal changes over East Asia; (ⅱ) The East-Asia monsoonal variation is different from the Indian monsoon during the Late Pleistocene; (ⅲ) There is a ～5_ka time lag of the East-Asia monsoon changes relative to the theoretically calculated solar radiation changes; (ⅳ) There is a general trend toward increase in winter monsoon and decrease in summer monsoon in the last glaciation; (ⅴ) In the East-Asia monsoonal region, the amplitude of glacial-to-interglacial cycles shows a remarkable increase from south to north. To explain these characteristics, a conceptual model is developed and the forcing of global ice volume variations in the monsoonal history is emphasized.     

Dynamic behavior of the He II-He I phase transition under gravity

The phase transition of superfluid helium (He II) to normal fluid helium (He I) is studied in this note. The He II -He I interface is found to move upwards under finite heat current. The temperature tracks are measured by four high resolution temperature sensors (HRTs). And the shifting of the λ　point temperature (phase transition temperature) along the cell is studied experimentally and theoretically. Under gravity, the shifting of the λ point temperature in creases with the pressure. The experimental results agree well with the theoretical ones.     

Computational algorithms for simulating the grain structure formed on steel billets using cellular automaton and chaos theories

The development of some computational algorithms based on cellular automaton was described to simulate the structures formed during the solidification of steel products. The algorithms described take results from the steel thermal behavior and heat removal previously calculated using a simulator developed by present authors in a previous work. Stored time is used for displaying the steel transition from liquid to mushy and solid. And it is also used to command computational subroutines that reproduce nucleation and grain growth. These routines are logically programmed using the programming language C++ and are based on a simultaneous solution of numerical methods (stochastic and deterministic) to create a graphical representation of different grain structures formed. The grain structure obtained is displayed on the computer screen using a graphical user interface (GUI). The chaos theory and random generation numbers are included in the algorithms to simulate the heterogeneity of grain sizes and morphologies.     

Study on an Organic Hybrid Made from Chlorinated Polyethylene and 2,2''''-methylene-bis- (4-methyl-6-cyclohexylphenol)

The dynamic mechanical properties and miscibility of an organic hybrid made from chlorinated polyethylene (CPE) and 2, 2'-methyIene-bis-( 4-methyl-6-cyclohexylphenol) ( ZKF ) are mainly discussed in this paper. It is found that ZKF acts as an antiplasticizer in CPE matrix and has good miscibility even with large ratio in CPE /ZKF hybrids. The glass transition temperature of various CPE /ZKF hybrids determined by DSC give a good fit to Wood's equation. Bifunctional ZKF is supposed to improve the intermolecular force of CPE, and the improvement is developed when the ZKF content increases. On the other hand, the viscoelastic properties are highly improved with the addition of ZKF. TA and tanδ peak values increase when the ZKF content increase in the CPE /ZKF hybrids, the damping capacity has been improved during the glass transition of CPE /ZKF hybrids. In addition, the glass transition temperature shifts to room temperature from the low temperature with the continuous addition of ZKF to CPE.     

U-Pb ages of zircon grains reveal a proximal dust source of the Xiashu loess,Lower Yangtze River region,China

Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits （the Xiashu loess） in the lower reaches of the Yangtze River. Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau （CLP） have been proposed. Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique. This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess. The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior. Instead, the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River, indicating the dominance of proximal dust source. Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China, possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.     

Effect of chlorine doping on the structural, morphological, optical and electrical properties of spray deposited CdS thin films

CdS and chlorine doped CdS(CdS:Cl) thin films with different Cl-doping levels(0,2,4,6 and 8 at%) have been deposited on glass substrates by a spray pyrolysis technique using a perfume atomizer.The effect of Cl doping on the structural,morphological,optical and electrical properties of the films was investigated.XRD patterns revealed that all the films exhibit hexagonal crystal structure with a preferential orientation along the(0 0 2) plane irrespective of the Cl doping level.The particle size value decreases from 22.03 nm to 18.12 nm with increase in Cl concentration.Optical band gap is blue-shifted from 2.48 eV to 2.73 eV with increase in Cl doping concentration.All the films have resistivity in the order of 10~4 Ω cm.The obtained results confirm that chlorine as an anionic dopant material can enhance the physical properties of CdS thin films to a large extent.     

Decomposed characteristic of azo dyes by ozonization with ultrasonic enhancement

Azo dyes have been used in many industries (textile mill, printing and dyeing mill, paper and pulp mill) and have caused great environmental pollution due to complicated constitution and high chemical stability. The construction of azo dyes can be destroyed by ozonization, but not thoroughly when the ozone dosage is controlled to a certain extent and the operating cost is higher. Ozonization decomposed ability with ultrasonic enhancement on azo dyes has been demonstrated in the study. The conclusion derived from this investigation may be summarized as follows: (1) The decoloration rate of arsenazoⅠsolutions during sonozone treatment is more rapid than the rate obtained with ozone alone because the complicated constitution has been destroyed by the O free radical from ozone decomposition. (2) The destructing pathway of arsenazoⅠby ozone with ultrasound is identical with that of by ozone alone: the breakdown of —N== N— bonds, the conversion of benzene ring to carboxylic acid, and —HSO₃ bonds to H₂SO₄. So, pH value of the arsenazo Ⅰ solution continuously drops down to 3.2.     

Experimental observation of deep crust fluid-NaCl aqueous solution at elevated temperatures and pressures and its significance

In order to reveal the nature of deep crust fluids, the phase relations of NaCI-saturat-ed solution at high temperatures and pressures in a hydrothermal diamond anvil cell (HDAC) are investigated. Salinity of the solutions observed is about 35%-50% . The temperatures for the observation range from 25 to 850℃ and the pressures from 1 atm to about 1 GPa. A supercritical single phase, liquid phase (L), vapor phase (V), solid phase (H), L+H, H + V+L and the near-critical phases L + V can be observed. A two-phase (L + V) immiscibility field for the NaCI solution has been discovered to lie in a wide range of temperatures and pressures: from 250( ±3) to 721℃. Within this field there are two parts, where the upper high temperature part of the two-phase regions is very unstable in character. It is possible to observe a "critical phenomenon". In some of our experiments an "explosion" almost constantly occurred at the interface between the liquid and vapor phases, making the interface obscure, and a continuous transition between the two phases could be found. By a visual microscope it was found that in the two-phase immiscible field near to the critical state the vapor phase and liquid phase compose a crystal structure geometry. It is a special solution structure that was found under a microscope. This discovery is important for us to understand the reason of increasing electronic conductivity of NaCI aqueous solution with respect to temperatures and pressures. And also, it will be easy to interpret the variation of electronic conductivity in the earth crust.