Ion flux dropout observed near dipolarization front

An ion flux dropout near the dipolarization front （DF） at around XGSM =- 11 RE in the Earth＇ s plasma sheet was observed by Time History of Events and Macroscale Interaction during substorms （THEMIS） on March 31, 2009. The ion differential energy fluxes at energies from 450 eV to 150 keV measured by the ESA and SST instruments from THC began to decrease about 2 s before the detection of the DF and reached a local minimum 6 s later. Then, the ion fluxes gradually increased to form a dropout around the DF. The spatial extent of the dropout was about 4,000 km. For energies above 20 keV, the ion fluxes after the dropout are greater than those before it, contrary to the fluxes at energies below 20 keV. The associated ion density variation indicates that the ion flux dropout coincides with the ion density dropout. Taking advantage of multipoint observations, THD, THC, and THE detected the same DF consecutively. Only THC detected an obvious ion flux dropout; THD observed an indistinct one about 2 s before THC; no high-energy （E 〉 30 keV） ion flux dropout was observed by THE. Our study suggests that the ion flux dropout may evolve with the earthward-propagating DF, and its properties can depend on locations relative to the DF.     

Theoretical investigation of negative refraction in metallic and ferromagnetic composites

A new design of LHM (left handed material) is suggested, in which the wave vector k and the energy flow S (the Poyming veclor) are in the opposite direction. Metallic cores or lines are coated with ferromagnetic layers to obtain negative permittivity and permeability. This design may bring some improvements over the binary design, such as higher homogeneity, smaller volume size, lower power loss, higher convenience and economy. The analytical expressions for the permiltivily s and permeability μ are shown to be negative in certain direction and frequency regions. Two specific structures are theoretically discussed and proved to be left-handed.     

Nanostructured transition metal nitride composites as energy storage material

There are growing demands for the next generation lithium ion batteries with high energy density as well as high power performance for renewable energy storage and electric vehicles application.Recently,nanoscale materials with outstanding energy storage capability have received considerable attention due to their unique effect caused by the reduced dimensions.This review describes some recent developments of our group in research of transition metal nitride nanocomposites in application of energy storage,especially for lithium ion battery and supercapacitor.The strategies of mixed conduction(electron and ion) network with a favorable charge transportation interface in the design of the nanocomposites for such devices are highlighted.     

Downward current electron beams observed at the dipolarization front

The strong field-aligned pitch angle distribution of electrons is observed right at the dipolarization front (DF) before the arriving of a high speed flow when the four Cluster satellites are traveling in the magnetotail around 15 R E on July 22, 2001. The increased electron fluxes only last for a short time period at the DF, corresponding to just a few bouncing periods for 1 keV electrons. The field-aligned current contributed by these electrons agrees well with that calculated by the magnetic field observations by four satellites at the front. These electron streams are found in the energy range of 0.2-2 keV, peak around 1 keV. It is suggested that these downward current electrons may be originated near the aurora region by some kinds of potential structure. The occurrence of these electrons implies that the formation of the dipolarization front and the associated field-aligned current play an important role in the magnetosphere-ionosphere coupling.     

Modulation on flow field by solid particles in gas-solid two-phase turbulent free shear flows

In order to understand the interaction between fluid and particles, a two-way coupled three-dimensional mixing layer laden with particles at a Stokes number of 5 with different mass loadings is numerically studied. The pseudospectral method is used for the flow fluid and the Lagrangian approach is used to trace particles. The concept of computational particles is introduced to vary the mass loading of particles. The momentum coupling effect introduced by a particle is approximated to the point force. The simulation results show that the coherent structures are still dominant in the mixing layer, but the flow field is modulated by particles. The addition of the particles enhances the energy of all the Fourier modes with non-zero spanwise wavenumber, and the enhancement increases with the augment of the mass loading. A higher mass loading results in a lower energy at fundamental wavenumber and streamwise subharmonic Fourier mode of the fluid in the phase of Kelvin-Helmholtz rolling up, but for large-scale vortex structures pairing, the energy of the fluid increases as the mass loading increases. Similar trends can also be found in the developments of the turbulent kinetic energy and the momentum thickness.     

A Low-Cost Dual Energy CT System with Sparse Data

Dual Energy CT （DECT） has recently gained significant research interest owing to its ability to discriminate materials, and hence is widely applied in the field of nuclear safety and security inspection. With the current technological developments, DECT can be typically realized by using two sets of detectors, one for detecting lower energy X-rays and another for detecting higher energy X-rays. This makes the imaging system expensive, limiting its practical implementation. In 2009, our group performed a preliminary study on a new low-cost system design, using only a complete data set for lower energy level and a sparse data set for the higher energy level. This could significantly reduce the cost of the system, as it contained much smaller number of detector elements. Reconstruction method is the key point of this system. In the present study, we further validated this system and proposed a robust method, involving three main steps： （1） estimation of the missing data iteratively with TV constraints; （2） use the reconstruction from the complete lower energy CT data set to form an initial estimation of the projection data for higher energy level; （3） use ordered views to accelerate the computation. Numerical simulations with different number of detector elements have also been examined. The results obtained in this study demonstrate that 1 ＋ 14% CT data is sufficient enough to provide a rather good reconstruction of both the effective atomic number and electron density distributions of the scanned object, instead of 2 sets CT data.     

Significant heat transfer enhancement for R123 condensation by micromembrane cylinder

Renewable energy or low grade energy utilizations need high performance of phase change heat exchangers. Suspending micromembrane cylinder in tube(called modulated heat transfer tube) increases the void fractions or vapor qualities near the tube wall to significantly enhance heat transfer. The R123 condensation heat transfer with horizontal position was investigated. The results for the bare tube and modulated heat transfer tube were tested case by case. It is found that the modulated heat transfer tube significantly enhance the condensation heat transfer, with the heat transfer enhancement factors(EF)covering the range of 1.118–2.124. The comprehensive performance evaluation criteria(PEC) had the range of0.71–1.66, with most of runs behaving PEC larger than 1.0.For the two-phase outlet conditions, the EF values are increased with increases in the vapor mass fluxes, Gxin,where G is the mass flux and xinis the inlet vapor mass quality. The EF values are inversely related to Gxinfor the subcooled liquid outlet cases. The enhanced heat transfer mechanisms are analyzed with the observed images together with the discussion of pressure and velocity distributions.     

Simulation study of discharge processes in thunderstorm

The discharge characteristics in thunderstorm have been calculated by using a numerical cloud model. The results indicate that discharge processes occur when simulated thunderstorm developed at the stage of 30-45 min and initial locations of discharge mainly distributes between 4.4-4.8 km and 6.4-6.8 km above the ground (corresponding to ambient temperature of - 10℃ and -25℃. In simulated thunderstorm with a tripole electric structure, 10% of discharges occur between upper positive charge area and middle negative charge area and propagate upwards (from middle negative charge area to upper positive charge area); while, 90% of discharges occur between lower positive charge area and middle negative charge area and propagate downwards (from negative charge area to lower positive charge area). There is a positive correlation between updraft and discharge. The occurrence of discharge process needs hydrometer with a specified concentration and size in cloud (corresponding to ≥ 5 mm/h for precipitation on the ground). The maximum value of precipitation lags the peak of discharge number by a period of about several minutes. The discharge and its variation in thunderstorm are an important factor for monitoring and forecasting thunderstorm.     

Overview on high-resolution ocean modeling in JAMSTEC

In view of the importance of ocean component for representing climate change, efforts are underway to implement a high-resolution nesting model system in Model for Interdisciplinary Research on Climate （MI- ROC） for the North Pacific using the same ocean model as used in the coupled model MIROC5. By comparing double （10 km for the northwestern Pacific, 50 km for the rest of the Pacific） and triple （double nesting plus 2 km resolution near Japan） nesting, it turns out that relative vorticity is drastically enhanced near Japan with 2 km resolution. It is hoped that such an elaborated nesting system will reveal detailed processes for the ocean heat uptake by, e.g., intermediate water and mode water formation for which the＂perturbed region＂ near Japan is the key region.     

METALLIC PHASE AND INSULATING CHARACTER OF ALKALI-EARTH METAL DOPED C60①

The three dimensional EHMO crystal orbital calculations for crystalline Ba6 C60,Ca3 C60 and Ca5 C60 are reported. The ground state of partially doped Ca3 C60 is found to be insulating with an indirect energy gap of 0. 5eV. In contrast, the. Cas C60 forms a metallic conducting phase with a set of three half - filled bands crossing the Fermi level which is Found to locate close to a peak of the density of state. The character of crystal orbitals near the Fermilevel for both Ca3 C60 and Ca5 C60 is completely carbon - like. In both cases the Ca3 atoms are almost fully ionized and C60 molecules form a stable negative, charge state with six to ten additional electrons. The conductivity of Ba6 C60 is resute.4 from the incomplete charge tranfer. The valance charge of every Ba ion is about 0. 33. The total charge tranfer of six Ba atoms is almost the same as that of five Ca atoms.     

Anti-planetward auroral electron beams at Saturn

Strong discrete aurorae on Earth are excited by electrons, which are accelerated along magnetic field lines towards the planet. Surprisingly, electrons accelerated in the opposite direction have been recently observed. The mechanisms and significance of this anti-earthward acceleration are highly uncertain because only earthward acceleration was traditionally considered, and observations remain limited. It is also unclear whether upward acceleration of the electrons is a necessary part of the auroral process or simply a special feature of Earth's complex space environment. Here we report anti-planetward acceleration of electron beams in Saturn's magnetosphere along field lines that statistically map into regions of aurora. The energy spectrum of these beams is qualitatively similar to the ones observed at Earth, and the energy fluxes in the observed beams are comparable with the energies required to excite Saturn's aurora. These beams, along with the observations at Earth and the barely understood electron beams in Jupiter's magnetosphere, demonstrate that anti-planetward acceleration is a universal feature of aurorae. The energy contained in the beams shows that upward acceleration is an essential part of the overall auroral process.     

A simulation study of ionization depletion in the auroral ionosphericF-region caused by strong convection electric field

THe effects of strong convection electric field on the electron density in the auroral ionosphericF-region have been simulated numerically by means of a physical model. It is found that an enhancement of electric field directed west-northward in post-noon or west-southward in pre-noon results in an ionization depletion with its maximum at altitudes 40–50 km higher than that of theF ₂ peak. When the enhanced electric field lasts for 45 min and has a maximum about 32 mV/m, the resulted ionization depletions reach their maximum at the time just ∼10 min behind the time when the convection electric field and ion temperature enhancements reach their maximum. This is consistent well with EISCAT observations. The magnitudes of the percentage ionization depletions and their recovery time are dependent not only on the intensity of the electric field, but also on the diurnal variation phase of the background electron density. Foundation item: Supported by the National Natural Science Foundation of China (49674241, 40074039) and the Research Fund for the Doctoral Program of Higher Education in China Biography: Cai Hong-tao (1976-), male, Ph. D. candidate, research direction: polar ionospheric modeling.     

Molecule modification and mass deposition induced by the implantation of low energy Fe+ ion beams into amino acids

Fe⁺ ion beams with the energy of 110 keV were implanted into films of L(+)-cysteine (HSCH₂CH(NH₂)COOH). One of the single crystals grown in hydrochloric acid solution with the implanted samples through slow evaporation was structurally characterized by the X-ray crystallography. The crystal is monoclinic, space group C2, with a = 1.8534(4) nm, b = 0.5234(1) nm, c = 0.7212(1) nm, β= 103.72°, V = 0.67965(3) nm³, Z = 4, F(000) = 144.0, D{clac} = 1.763 g · cm⁻³, μ(MoK _a = 1.06 mm⁻¹, T = 293(2) K. R = 0.0379, wR = 0.0835 for 660 observed reflections (I > 2σ(I)). The structural formula of the crystal compound is (CH₂CH(NH₂)NO₂)ClFe (M _r = 180.38 u). Products of heavy ion beam irradiation were purified and it was directly confirmed that the implanted Fe⁺ ions had been deposited in the novel molecules. The same doses of Fe⁺ ion beams of the same energy were implanted into films of L(+)-cysteine hydrochloride monohydrate. FTIR spectroscopy of the implanted samples proved that some of the original molecules were seriously damaged and significant modifications were induced.     

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.     

The determination of atmospheric phosphine in Ny-Ålesund

Phoshpine (PH3), a volatile and toxic gas, has been proved to commonly exist in the environment. The determination of gaseous phosphine and its emission fluxes in Ny-Ålesund is reported in this paper. Results showed that gaseous phosphine exist in Arctic atmosphere commonly and the concentration of phosphine ranged from 16.3–600.2 ng/m³, with the maximum concentration of phosphine in tundra areas and the minimum in surface air of ocean. The concentration of phosphine ranged from 65.79–1259 ng/m³ in colliery atmosphere at different altitudes and the maximum was found in the center of colliery. Emission fluxes of phosphine were different in various Arctic areas. Emission fluxes of phosphine from protected areas, with average concentration of 32.13±5.353 ng m^–2 h^–1, were higher than from other areas. And the flux of phosphine from ocean was lower.     

Dissociation of methanol in intense femtosecond laser field

Methanol was irradiated by 80 fs laser pulse, intensity range of 10¹³–10¹⁴ W/cm². A TOF-mass spectrometer was coupled to the laser system and used to detect the ions produced. The parent ions CH₃OH⁺ appeared firstly at the laser intensity of 1.4×10¹³ W/cm². While the laser intensity was gradually increased, the parent ions were dissociated and the primary ions CH₂OH⁺ were given as verified from the irradiation of deuterated methanol (CH₃OD) showing the C—H bond cracking firstly. While the laser intensity was further increased to 2.0 × 10¹³ W/cm², the C—O bonds of the parent ions also broke to give CH₃ ⁺. When the laser intensity was higher, smaller fragment ions like CH⁺, C⁺, OH⁺ and O⁺ also appeared. Among the fragment ions, only H⁺ ion yield had anisotropic angular distribution dependence on the laser polarization vector in the dissociation of methanol. All the experimental observations show that the dissociation of methanol proceeds through stepwise mechanism but not Coulomb explosion.     

Crustal P-wave velocity structure in Lower Yangtze region： Reinterpretation of Fuliji-Fengxian deep seismic sounding profile

A deep seismic sounding profile in this paper, from Fuliji in Anhui Province to Fengxian of Shanghai City, is located at eastern China (Fig. 1). The field work was jointly accomplished by the Chinese Geological and Mineral Bureau, the China Seismological …     

Li3O+超碱团簇的结构及储氢性能的理论研究

采用杂化密度泛函理论(DFT)的B3LYP方法,在6-311++G (d, p)基组水平上对Li₃O ^{0, +}超碱团簇的几何结构和稳定性进行理论计算,并研究了Li₃O⁺团簇的储氢性能。结果表明,Li₃O⁺团簇结构相比中性Li₃O团簇结构的动力学稳定性要高。氢分子在Li₃O⁺团簇表面能以介于物理吸附与化学吸附之间的形式吸附,每个Li原子最多可以有效吸附三个H₂,储氢质量分数可达33.01 wt%。H₂分子在Li₃O⁺团簇表面的平均吸附能范围为1.959~3.591 kCal/mol,该吸附能满足在近室温条件下可逆吸放氢反应的热力学要求。     

Variation of b value with hypocentral depth in Beijing area： Implications for earthquake nucleation

We relocated 2098 earthquakes that occurred in Beijing area between 1980 and 2000 using a double-difference (DD) earthquake location algorithm, and obtained the high-precision relative locations of 1825 events, b values versus depth were investigated with the relocated hypocenters. The results show that the b values decrease with the increasing hypocentral depth systematically. A dramatic variation in b is observed around the depth of 8 km. It indicates that there are more smaller earthquakes at shallow depth (0-8 km), while more larger earthquakes at greater depth (8--25 km). The physical mechanism behind this phenomenon can be explained by the variations in material heterogeneity and lithostatic stress condition. Large earthquakes are more likely to nucleate at greater depth with more homogenous material and higher lithostatic stress. On the basis of the results, we suggest that future strong earthquakes in Beijing area tend to occur below the depth of 8 km.     

飞秒激光场中甲醇产物离子的角分布

利用直流切片离子成像技术结合飞行时间质谱技术,我们研究了甲醇(CH_3OH)分子在800 nm飞秒激光场中的多光子解离和库仑爆炸过程.获得了甲醇分子在光场中的飞行时间质谱和产物离子的切片影像,分析得到了不同库仑爆炸通道碎片离子的动能分布和角度分布.本文对比分析了C-O键断裂产生H_2O~+的H转移通道和产生OH~+的非H转移通道的角分布,计算了不同激光强度下两个通道的各向异性参数α_2和(cos~2θ),并根据产物离子角度分布与激光强度和离子价态的关系,揭示了甲醇分子在飞秒光场中的准直机制为动力学准直.