CHANGES OF QUATERNARY CLIMATE OF LOESS DISTRICT IN CHINA

On the basis of the data of sporo-pollen analysis, the weathering index of loess and paleosol layers and the climatic differences between the periods of the formation of loess and paleosol as reflected by intensities of natural remanent magnetization of loess and paleosol, it may be confirmed that the loess layers represent the climate of glacial stages, while paleosol was formed during interglacial stages. The climatic changes in the loess area of China have undergone 23 cycles which were combined with the paleomagnetic dating. TL ages of paleosol layers and the average ages of termination could be excellently correlated with the δ~(18)O stages of deep sea core V_(28-239). Thus, it may be recognized that the Luochuan and Xi'an loess-paleosol sequences are the typical climatostratigraphy in China and even in the world.     

PRELIMINARY STUDY ON SEDIMENTARY CHARACTERISTICS AND EVOLUTION OF PALAEOCLI MATE OF QARHAN SALT LAKE IN QAIDAM BASIN

Qarhan salt lake which covers an area of 5800 square kilometres is a large playa in Qaidam basin, Qinghai Province. The salt-bearing layers are usually 40 m thick, the maximum thickness being 73 m.The sedimentation of the lake has the following basle characteristics: (1) The salt-containing layers are principally composed of interbedded halite and clastic sediments, and they are either lacking in sulfate deposits or deficient in carbonate sediments. (ii) The sedimentary differentiation is not sufficient, and all of the halite layers almost contain mud, sand, carbonates and gypsum in varying degrees; there exist mixtures of gypsum and halite in the intercalations of clastic sediments. (iii) The salt-carrying beds are associated with aeolian deposits. The authors found for the first time that Malan loess exists in the salt-bearing layers of Qarhan salt lake.Features of evolution of palaeoclimate: A lot of evaporite deposits had appeared in Qarhan salt lake by the end of Late Pleistocene, 24,000—25,000 ye     

THE FORMING PROCESS OF THICK LAYERED GROUND ICE

In this article, a new idea is suggested. According to this idea, the thick layered groundice is formed by repeated-segregation, which is characterized by the following processes: (i)Moisture migration to the freezing front where ice lensing proceeds upward from permafrost.(ii) The law of unequal migration of unfrozen water plays its part, the combining effectof the following processes, the upward migration of unfrozen water in frozen active layerin cold season, the water migration and ice lensing in the frozen ground behind freezingfront during upward freezing, and the water migration and ice lensing in the still frozen groundbeneath the thawing plane in warm season. (iii) Self-purification of ice. (iv) Syngeneticgrowth of ground ice due to the addition of material onto the ground surface. (v) Year-to-year repeating of processes mentioned above. Thus, a new type of ground ice——repeated-segregation ice is distinguished.     

THE TYPES OF LOESS PORES IN CHINA AND THEIR RELATIONSHIP WITH COLLAPSIBILITY

This paper presents chiefly a classification of the loess pores in the Loess Platcau according to their origin and size and deals with the characteristics of different sorts of pores and their distributional regularities in regions and loess layers of various ages. The relationship between various pores and collapsibility is also discussed in the paper. We come tto a conclusion that the supporting openings are one of the important factors causing the subsidence on wetting because of their looseness and unstability.     

THE NUCLEAR TRACK DEPTH PROFILE OF THE JILIN METEORITE

Using 43 documented drill core samples of the H_5-chondrite "Jilin" the depth profile of GCR-and fission track densities was established. The track profile essentially reflects the GCR-track record of the second (4π-) irradiation stage of "Jilin". Relics of the track record of the first (2π-) exposure are indicated by a deviation from the theoretical depth profile of the 4π-exposure. No Pu-244 fission is observed ia the fission track background near the meteorite center. The atmospheric ablation thickness of the two drill cores A and B normal and parallel to the assumed surface of the "Jilin" parent body was found to be 11±4 cm, respectively. A minimum shielding depth of the "top" part of core A during the 2π-exposure is estimated to be～30 cm. Near surface deviations of the experimental track data from theory are ascribed to a short-term moderate heating event (equivalent to 24h,～370℃) no more than 0.4 Ma ago. The resulting partial track annealing in a surface layer of ～15—20 cm thickness of t     

ANISOTROPY OF MAGNETIC SUSCEPTIBILITY AND ORIGIN OF THE CHINESE LOESS AND ITS SIGNIFICANCE TO THE QUATERNARY RESEARCH*

Anisotropy of magnetic susceptibility is used in the present study to reveal thedepositional fabric on the original (windblown) loess and secondary (redeposited) loess. The two kinds of sediments mentioned above can be distinguished in terms of their susceptibility anisotropy, e.g. anisotropy degree, magnetic foliation and lineation parameters. On this basis the magnetic fabric of the Pliocene red soil underlaying the loess is studied, and compared with the results of a typical residue-deposited red clay in South China. Considering its geological features, the red soil in Xifeng is regarded probably as aeolian in origin also.     

PROBLEMS OF QUATERNARY ENVIRONMENTAL EVOLUTION AND GEOMORPHOLOGICAL DEVELOPMENT IN THE LUSHAN

The major Quaternary climatic deterioration of the Lushan area occurred mainly in LatePleistocene when a periglacial environment prevailed on the high summits above 1000 m a.s.l.with resulting frost shattering and gelifluction. The data from sporo-pollen analysis, fossilfauna, paleosols and the elevation of the snowline in the ice ages prove that conditions for thedevelopment of the glaciers did not exist in the Lushan during early and middle Quaternaryperiod. Evidence of former glaciation has not been found in the study on the type sedimen-tary sections in Yejialong and Dajiaochang gully. There are many relict landforms belong-ing to hot and humid tropical climate rather than to glacial one. The problems of the land-form development of the Lushan are also discussed.     

STRATIGRAPHIC AND GEOCHRONOLOGIC ANALYSES OF THE QUATERNARY DEPOSITS IN THE THREE-LAKE REGION OF QAIDAM BASIN

The Qaidam Basin is a larger sedimentary basin in western China where the thickness of the Quaternary deposits is in the range of 2000-3000 m at its subsiding center. This paper first dates palaeomagnetically the cores obtained from the five continuously sampled intervals and those from a typical profile, determineds the age of the index fossil zones, and calculates the deposition rates for the varve deposits based on the sedimentological analysis. As a result, we can calculate the ages of the various characteristic beds (including fossil zones, seismic reflection beds, and marker layers of electrical properties) for any given borehole-section when it was divided into facies, and check the validity of the chronology. According to all those studies, the stratigraphic and geochronologic analysis program of the Quaternary deposits in the Qaidam Basin has permitted a detailed discussion to be made in this paper.     

THE HISTORICAL CLIMATIC RECORDS IN ICE CORES FROM THE SURFACE LAYER OF WILKES LAND, ANTARCTICA

The information preserved in the surface layer of the Antarctic ice sheet is so abundant and detailed that in the areas with a high accumulation rate the annual climatic changes in the past can be distinguished. After conducting an investigation into the stratigraphical features of ice cores from two typical shallow boreholes in the Wilkes Land, one inland and another near the margin, analyzing δ(~18)O and the gross β radioactivity in the cores, as well as anslyzing the power spectra of δ~(18)O, the authors present some important assessments on the climatic information in the past several decades therein such as the annual mean temperature and precipitation, and suggest that there is a period of 11 years with which the climate changes cyclically in East Antactica. Such a studying method will be of value in both theory and practice to the inland Antarctica, where direct meteorological observation is deficient.     

Assembling Co_9S_8 nanoflakes on Co_3O_4 nanowires as advanced core/shell electrocatalysts for oxygen evolution reaction

Rational design of advanced cost-effective electrocatalysts is vital for the development of water electrolysis. Herein, we report a novel binder-free efficient Co_9S_8@Co_3O_4 core/shell electrocatalysts for oxygen evolution reaction(OER) via a combined hydrothermal-sulfurization method. The sulfurized net-like Co_9S_8 nanoflakes are strongly anchored on the Co_3O_4 nanowire core forming self-supported binder-free core/shell electrocatalysts. Positive advantages including larger active surface area of Co_9S_8 nanoflakes,and reinforced structural stability are achieved in the Co_9S_8@Co_3O_4 core/shell arrays. The OER performances of the Co_9S_8@Co_3O_4 core/shell arrays are thoroughly tested and enhanced electrocatalytic performance with lower over-potential(260 m V at 20 m A cm~(-2)) and smaller Tafel slopes(56 mV dec-1) as well as long-term durability are demonstrated in alkaline medium. Our proposed core/shell smart design may provide a new way to construct other advanced binder-free electrocatalysts for applications in electrochemical catalysis.     

一些Ag+、Cu+簇的合成和结构研究

由于银,铜簇合物有助于催化理论的研究,近20年来,许多学者对它们的合成方法、成簇规律和结构特点进行了许多探索。本文报道了[Me_4N]_6[Ag_6[S_2C=C(CN)_2)_6]·H_2O(Ⅰ)、[Et_4N]_4[Cu_8(S_2C=C(CN)_2)_6](Ⅱ)和[Me_4N]_4[Cu_5Ag_3(S_2C=C(CN)_2)_6]·H_2O(Ⅲ)的化学合成,化合物(Ⅰ)和(Ⅱ)的晶体和分子结构,以及从化合物(Ⅲ)的ICP元素分析和红外光谱分析,探讨它的结构特征。     

Crystallization, melting, and structure of water nanoparticles at atmospherically relevant temperatures

Water nanoparticles play an important role in atmospheric processes, yet their equilibrium and nonequilibrium liquid-ice phase transitions and the structures they form on freezing are not yet fully elucidated. Here we use molecular dynamics simulations with the mW water model to investigate the nonequilibrium freezing and equilibrium melting of water nanoparticles with radii R between 1 and 4.7 nm and the structure of the ice formed by crystallization at temperatures between 150 and 200 K. The ice crystallized in the particles is a hybrid form of ice I with stacked layers of the cubic and hexagonal ice polymorphs in a ratio approximately 2:1. The ratio of cubic ice to hexagonal ice is insensitive to the radius of the water particle and is comparable to that found in simulations of bulk water around the same temperature. Heating frozen particles that contain multiple crystallites leads to Ostwald ripening and annealing of the ice structures, accompanied by an increase in the amount of ice at the expense of the liquid water, before the particles finally melt from the hybrid ice I to liquid, without a transition to hexagonal ice. The melting temperatures T(m) of the nanoparticles are not affected by the ratio of cubic to hexagonal layers in the crystal. T(m) of the ice particles decreases from 255 to 170 K with the particle size and is well described by the Gibbs-Thomson equation, T(m)(R) = T(m)(bulk) - K(GT)/(R - d), with constant K(GT) = 82 ± 5 K·nm and a premelted liquid of width d = 0.26 ± 0.05 nm, about one monolayer. The freezing temperatures also decrease with the particles' radii. These results are important for understanding the composition, freezing, and melting properties of ice and liquid water particles under atmospheric conditions.     

铝硫二元团簇的组分及其光解规律

硫与金属元素所形成的二元团簇具有很多重要的特性,已受到人们的普遍重视.用激光-串级飞行时间质谱仪,我们曾研究了硫与过渡金属钽、铁等的二元团簇.最近我们选取主族金属元素铝,研究了铝硫团簇的形成及其光解,实验结果表明,与钽硫或铁硫团簇相比,铝硫团簇无论在其组份构成还是在其光解方面,都表现出鲜明的特有规律性.实验的主要参数如下:溅射用激光为Nd:YAG 二倍频,其输出强度控制在约10~7W·cm~(-2),激光的重复频率10Hz 样品位于激光束的焦点附近,由焦距f=50cm 的透镜调整其聚焦状     

三核钼－硫簇合物的低热固相合成及其晶体结构

三核钼－硫配合物Ｍｏ_３Ｓ_７（ｄｔｃ）_３Ｉ·Ｓ_８·２ＣＨ_２Ｃｌ_２（ｄｔｃ＝Ｃ_４Ｈ_８ＮＣＳ_２~－）是由低热固相合成得到的。晶体属单斜晶系，Ｍ_ｒ＝１５００．１９，空间群Ｐ２_１／ｎ，ａ＝１１．８８１（３），ｂ＝１５．５５９（４），ｃ＝２６．１９７（７），β＝９８．５３（２）°，Ｖ＝４７８９Ａ~３，Ｚ＝４，Ｄ_ｃ＝２．０８ｇ／ｃｍ~３，Ｆ（０００）＝２９２０，μ（ＭｏＫα）＝２５．２４ｃｍ~（－１），对于２３９７个Ｉ≥３σ（Ｉ）的独立衍射点，最终偏离因子Ｒ＝０．０６０，Ｒ＝０．０６６。该配合物的基本骨架是［Ｍｏ_３Ｓ_７（ｄｔｃ）_３］~＋，其簇芯为［Ｍｏ_３Ｓ_７］~（４＋）单元，３中Ｍｏ原子组成正三角形平面，Ｍｏ－Ｍｏ的平均键长力２．７２３，Ｍｏ原子平面上的硫原子形成盖帽的μ_３－Ｓ，其Ｍｏ－Ｓ平均键长为２．３８３Ａ，３个Ｓ_２基团分别位于三角形３个棱的外侧，并分别与邻近的两个Ｍｏ原子结合形成１２中Ｍｏ－Ｓ键。与μ_３－Ｓ相对而位于平面另一侧的Ⅰ原子与３个μ_２－Ｓ连结，平均距离为３．２５７Ａ，成键作用较弱。     

限制在疏水板中的新的六边形-四边形三层冰结构

对限制在两个光滑的疏水板间的水进行了分子动力学模拟,观察到了两种晶体结构,都满足冰规则．在1GPa的压强和1．0nm的板间距下获得的新的冰相是平坦的六边形-四边形三层冰．在此结构中,靠近板的两层（外层）中的水分子形成六边形环,中间层的水分子形成四边形环．对于外层的水分子,其四个氢键中的三个在同一层中,另一个氢键与中间层连接．对于中间层的水分子,四个氢键中的两个在同。层中,而另外两个氢键与两个不同的外层相连．虽然三层的形状不同,但其面密度却接近相等．另一种结构是在0．8nm的板问距和100MPa的侧向压下获得的平坦的六边形双层冰．模拟中的相变既有一阶相变,也有连续相变．     

Theoretical Study on the Excited-state Intramolecular Hydrogen Abstraction Reactions of Butanal

The excited-state intramolecular hydrogen abstraction reactions of butanal have been investigated using the CAS-MP2/6-311＋G^＊//CASSCF/6-31G^＊ methods. Calculated results show that the hydrogen transfer induced fluorescence quenching of the n,π^＊-excited state of covalent butanal with three paths： （1） The first path corresponds to direct S0-react reconstitution, which involves the first S1 decay by partial hydrogen atom transfer. （2） The second stepwise mechanism can be viewed as a full hydrogen atom transfer followed by a partial hydrogen atom back transfer, electron transfer （near S1/S0 or S0-TS） and finally a proton transfer to S0-react. （3） On the triplet surface, the surface crossing to the singlet state would be clearly much efficient at the T1/S0 region due to the large SOC value of 8.3 cm^-1. The S0-react decay route from T1/S0 was studied with an intrinsic reaction coordinate （IRC） calculation at the CASSCF level, resulting in the S0-React minimum.     

Ultrafast electron transfer, localization and solvation at ice–metal interfaces: Correlation of structure and dynamics

The interaction of an excess electron with a polar molecular environment is well known as electron solvation. This process is characterized by an energetic stabilization and by changes of the electronic spatial extent due to screening of the localized charge through molecular rearrangement. At metal–ice interfaces we photo-inject delocalized electrons from the metal substrate into adsorbed ice layers and analyze the ultrafast dynamics of electron transfer, localization and solvation by femtosecond time- and angle-resolved two-photon photoemission spectroscopy. To acquire further understanding of the individual steps of the complex process we vary the interfacial structure. The substrate is changed between Cu(1 1 1) and Ru(0 0 1) and the electron dynamics in ice islands are compared to closed D₂O layers. Contrasting crystalline and amorphous ice we found that electron solvation is mediated through electron localization at favorable structural sites, which occurs very efficiently in amorphous ice, but is less likely in a crystalline layer. Next, we find that in an open ice structure like ice islands the energetic stabilization due to electron solvation proceeds at a rate of 1 eV/ps which is three times faster than in a closed ice layer. We attribute this behavior to differences in the molecular coordination, which determines the molecular mobility and, thus, the transfer rate of electronic energy to solvent modes. The substrate’s electronic structure, on the other hand, is important to understand the transfer rates from electrons in ice back to the metal. First experiments on trapped electrons in crystalline ice underline the potential to study electron solvation not only during the equilibration process, but also in quasi-static conditions, where we find that the stabilization continues, although at much weaker rates.     

The Climatic Fluctuation and Important Events of Holocene Megathermal in China

Data from various sources including the ice core, inland lakes , paleosols in loess and eolian sands, sea level fluctuations, paleozoological, archeological evidences especially palynology and bontanical studies of China are reviewed . Holocene Megathermal mainly appeared during 8. 5-3 ka BP and lasted for 5. 5 ka. There were several strong climatic fluctuations and cooling events during this period, e. g. it was an unstable temperature fluctuation phase during 8. 5-7. 2 ka BP and was accompanied with the increase of the precipitation as well as the northward and westward migration of the vegetation zone ; the rapid development of Neolithic Culture happened in this phase. It was a stable warm and wet phase from 7. 2 to 6 ka BP, i. e. Megathermal Maximum, when monsoon was rainfall almost throughout China, plants were unprecedentedly flourished, and the Yangshao Culture reached its climax. It is characterized by strong climatic fluctuation and adverse environment during 6-5 ka BP and the impact of strong     

New application of a traditional analytical method – arsenic removal from water works sludge during iron(III) chloride coagulant production

A new method for the detection of trace elements in polar ice cores using laser ablation with subsequent inductively coupled plasma mass spectrometry analysis is described. To enable direct analysis of frozen ice samples a special laser ablation chamber was constructed. Direct analysis reduces the risk of contamination. The defined removal of material from the ice surface by means of a laser beam leads to higher spatial resolution (300– 1000 μm) in comparison to investigations with molten ice samples. This is helpful for the detection of element signatures in annual layers of ice cores. The method was applied to the successful determination of traces for the elements Mg, Al, Fe, Zn, Cd, Pb, some rare-earth elements (REE) and minor constituents such as Ca and Na in ice cores. These selected elements serve as tracer elements for certain sources and their element signatures detected in polar ice cores can give hints to climate changes in the past. We report results from measurements of frozen ice samples, the achievable signal intensities, standard deviations and calibration graphs as well as the first signal progression of ²⁰⁸Pb in an 8,000-year-old ice core sample from Greenland. In addition, the first picture of a crater on an ice surface burnt by an IR laser made by cryogenic scanning electron microscopy is presented.