MAGNETIC SUSCEPTIBILITY OF CHINESE LOESS AS A PALAEOCLIMATIC INDICATOR

Through the studies on low temperature susceptibility, frequency dependent susceptibility, isothermal remanent magnetization, low temperature magnetization and demagnetization for loess and palaeosols one can easily reveal some significant characters of rock magnetism for the magnetic minerals of ultrafine grain sizes, those are very difficult to identify by general geological methods. It is shown in the present study that both loess and palaeosols cover magnetic grain size from superparamagnetism, single domain to multidomain. Loess samples with relative high peramagnetic minerals are dominantly of thermally stable characteristics while palaeosols have relatively high percentage of superparamagnetic grain (0.01—0.03μm). The relative grain size of magnetite is always finer in palaeosol with higher susceptibility than in loess, indicating that many tiny ferri-ferromagnetic minerals formed during the process of soll formation, which has caused a higher susceptibility in palaeosols than in loess. The cli     

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.     

THE COMPARISON OF LANZHOU LOESS PROFILE WITH VOSTOK ICE CORE IN ANTARCTICA OVER THE LAST GLACIATION CYCLE

Loess near Lanzhou in the late Pleistocene is very sensitive to climatic fluctuations. The Beiyuan terrace profile in Linxia City, of which the curve of susceptibility tallies with the trend of isotopic curves of Vostok 2083 m ice core in Antarctica, is 35m thick. There are five layers of paleosols under Malan loess(L_1). Upper three layers (S_(1-a),S(1-b)and S_(1-c) correspond to three warm stages in last interglaciation, Interstadial of Last Glacial (C stage in Antarctic ice core)was clearly recorded in the Beiyuan profile, in which three layers of paleosols and two of loess were formed. The lowest section of the profile belongs to penultimate glaciation, in which fossils of cold-drought-resistant mammal and mollusc have been discovered.     

IDENTIFICATION OF PARTIAL MUTATIONAL SITES IN HUMAN MITOCHONDRIAL DNA IN THE CHINESE AND ITS SIGNIFICANCE

A simple method for the identification of mutational sites in human mitochondrial DNA (mtDNA) was described. It was based on the human Cambridge sequence as a relative standard sequence and a single base pair substitution in mtDNA as a unique mutational form. The partial mutational sites can be determined using this method which was characterized by combining the restriction mapping with the analysis for the table of human mtDNA potential mutational sites with rapidity and simplicity. In the meanwhile, six mtDNA mutational sites found in Chinese population were identified by means of this method.     

疏水性磁性微球的制备及对盐藻的吸附研究

采用疏水性材料制备微米级磁性微球,并应用于对盐藻的吸附分离研究,考察了pH值,吸附作用时间,NaCl浓度以及磁性微球添加量对盐藻吸附的影响.结果显示磁性微球对盐藻的吸附受溶液的离子强度影响较大;pH值在一定范围内对盐藻的吸附有较大影响;延长吸附作用时间和加大磁性微球的添加量可以增加对盐藻的吸附量.通过调节pH和施加机械搅拌,磁性微球上吸附的盐藻可以很好被洗脱下来,磁性微球可以多次重复使用.     

PRELIMINARY STUDY ON MECHANISM OF PLANT ROOTS TO INCREASE SOIL ANTISCOURIBILITY ON THE LOESS PLATEAU

The effects of the root system of trees, shrubs and grasses on the hydraulic andphysical properties of soil and their interrelation with increasing soil anti--scouribility byroots are quantitatively demonstrated in this paper for the first time. Based on the analysisof the leading factors of roots to increase the soil anti--scouribility, a mathematical modelon increasing soil anti-scouribility by roots is established. The value in application of themodel is to explain the mechanism of roots to increase the soil anti-scouribility and toevaluate the increasing effects of soil anti-scouribility by roots in different layers of soilThe calculated results of the values in soil anti--scouribility intensified by roots at variousintensities of rainfall and slopes of the model have higher precision, all of the meanmaximum deviations between the estimated and observed values being less than 1.417 s/g.     

THE STATUS OF CONSTRUCTIVISM IN CHEMICAL EDUCATION RESEARCH AND ITS RELATIONSHIP TO THE TEACHING AND LEARNING OF THE CONCEPT OF IDEALIZATION IN CHEMISTRY

A review of the chemical education research literature suggests that the term constructivism is used in two ways: experience-based constructivism and discipline-based constructivism. These two perspectives are examined as an epistemology in relation to the teaching and learning of the concept of idealization in chemistry. It is claimed that experience-based constructivism is powerless to inform the origin of such concepts in chemistry and while discipline-based constructivism can admit such theoretical concepts as idealization it does not offer any unique perspectives that cannot be obtained from other models. Chemical education researchers do not consistently appeal to constructivism as an epistemology or as a teaching/learning perspective and it is shown that, while it draws attention to worthwhile teaching/learning strategies, it cannot be considered as foundational to chemical education research and tends to be used more as an educational label than as an undergirding theory.     

THE CATALYTIC EFFECTS OF OXYGEN AND AMINES IN THE REDOX-INITIATED DIMERIZATION OF N-VINYLCARBAZOLE*

The redox reaction between N-vinylcarbazole (NVC) and various oxidants including Ce(Ⅳ), Fe(Ⅲ)and benzoylperoxide in methanol proceeds via the initial formation of the NVC N-cation radical which in turn leads to the formation of the NVC cyclic dimer, trans-1,2-dicarbazylcyclobutane. Molecular oxygen and a few arylamines are able to accelerate the rate of the formation and increase the yield of the dimer. The mechanism of this process and the functions of oxygen and arylamines are presented as follows: The participation of molecular oxygen is to facilitate the dissociation of the resulting reduced metal ion and the NVC N-cation radical ion pair or charge transfer complex, thereby releasing the free NVC N-cation radical and increase the rate of the formation and yield of the dimer. The arylamine in this reaction between NVC and oxidants can be viewed as electron transfer agent between NVC and the oxidant. Because the amines are present in small amount relative to the oxidants and can be regenerated in pr     

THE PRECURSOR OF INSTABILITY FOR NONLINEAR SYSTEMS AND ITS APPLICATION TO EARTHQUAKE PREDICTION

By analysing the instability process of various nonlinear systems, we conclude that their instability precursors are the continual heightening of the response rate or response ratio.Applying this theory to earthquake prediction, we adopt the periodical change of the stress in crust caused by the tide-generating force as the loading and unloading. If we can measure the ratio of the response (such as crust deformation, gravity and seismicity) during the loading period to that during the unloading period, this parameter must contain some characteristic information about the seismogenic process.With nine earthquakes (M≥7) data that occurred in Chinese mainland during 1970-1988, we take the sum of square root o?energy of small earthquakes, which is called the released strain by Benioff, as the response to the tidal loading and unloading. We find that the response ratios of seven earthquakes increase obviously before the main earthquakes.     

SYNTHESIS AND-CHARACTERIZATION OF THE SOLUBLE, HIGH MOLECULAR WEIGHT AND LADDERLIKE POLYHYDROSILSESQUIOXANE AND ITS COPOLYMERS

The high molecular ladderlike polyhydrosilsesquioxane (LPHSQ) and its copolymer, ladderlike random copolymethylhydrosilsesquioxane (LR-PMHSQ) and ladderlike block copolymethylsilsesqui-oxane(LB-PMHSQ) have been synthesized by a preaminolysis reaction of the corresponding trichlorosilane with 1 ,4-phenylene diamine(PDA) then by hydrolysis and polycondensation reactions The thermographs of these polymers measured by DSC method indicate that these macromolecular backbones are very rigid as seen from the DSC curves which are almost horizontal from room temperature until 350 ~C without noticeable glass transition. The content of Si—H group in the polymers can be regulated by changing the composition of the two copolymerized monomers. So the ladderlike polymers including its copolymers can be the useful precursors for the functional polymers, especially such as fishbone-like liquid crystalline polymers.     

TRANSFER OF THE ATRAZINE-RESISTANT GENE OF BLACK NIGHTSHADE TO SOYBEAN CHLOROPLAST GENOME AND ITS EXPRESSION IN TRANSGENIC PLANTS

The atrazine-resistant psbA gene of black nightshade was transferred to the chloroplast genome of atrazine-susceptible soybean by means of ovary microinjection during the stage of zygote. The identification was carried out by using the methods of spraying the leaves directly with atrazine solution, examining the change of leaf fluorescence kinetics under a brighter light induction, molecular hybridization, etc. The experimental results show that the transgenic soybean plants do have been obtained for the first time.     

RAMAN SPECTROSCOPY OF C,H,L AND LL CHONDRITES AND ITS SIGNIFICANCE IN EXPLORING THE FORMATION ENVIRONMENTS OF METEORITES AND THEIR TAXONOMY

The comparison of Raman spectra of the chondrites (C, H, L, LL) has confirmed thatthere exist two types of meteorite carbon: one is the primary carbon present in carbonaceouschondrites (c) and the other is the secondary carbon contained in ordinary chondrites (H, L,LL). The parameter of order (I_G/I_D intensity ratio, similarly hereinafter) of primary car-bon tends to decrease with increasing petrologic type and it can reflect the temperature ofdust carrier at the time plasma gases in the early nebula were condensed to form primarycarbonaceous material and the hydrogen content in primary carbonaceous material. This kindof primary carbonaceous material maybe has not experienced late stage thermometamorphismwithin the parent body of chondrites, indicating that the carbonaceous chondrites wereformed and retained in the low temperature region of the solar system. The parameter oforder of the secondary carbon tends to increase with increasing petrologic type and it can re-flect the degree of graphitization o     

THE STRUCTURE AND OPTICAL PROPERTIES OF COPOLYMER OF CHOLESTERIC ESTER

The structure and switching properties of liquid crystalline side chain copolymers of cholesteric ester of 1,2-hydroxypropyl 2,4-di-isocyanatoluene methylmethacrylate (PHCPM) have been studied in detail. The cholesteric mesophase of PHCPM is shown by polarizing microscopy, X-ray diffraction and selective light reflection. Solution of PHCPM in CHCl_3 is optically anisotropic; its optical properties were determined by specific rotation [α], circular dichroism (CD) and wide-angle hght scattering (WALS) methods.     

钛硅酸钠无机离子交换材料的制备及对铯的吸附性能研究

用水热合成法合成粉末状钛硅酸钠,考察了它对Cs的吸附效果。实验表明,所合成的钛硅酸钠对Cs的吸附效果较好。在30℃,1mol/L的H 环境下对Cs的吸附分配比为6066,饱和吸附量可以达到1.74mmol/g。尤其在高酸度条件下钛硅酸钠对Cs良好的吸附效果,使其在处理酸性高放废液中具有一定的应用价值。吸附稳定性很好,不易洗脱。     

ALTERATION IN CHROMATIN CONFORMATION OF PROLIFERATING AND DIFFERENTIATING ENZYME GENES IN NORMAL MOUSE LIVER AND ASCITES HEPATOMA CELLS AND ITS RELATION TO THE GENE EXPRESSION OF ENZYMES

Nuclei from the normal mouse liver were partially digested with micrococcal nuclease, followed by DNA extraction, agarose gel clectrophoresis and dot blot hybridization with ~(32)P-labeled cDNA probes of CPS_1 and ACT complex, It was clearly shown that the CPS_1 genes were distributed on the monomer, dimer. and trimer of nucleosomes, while the genes coding for ACT complex were distributed on the condensed oligonucleosomes. An opposite manner of distribution of CPS_1 and ACT complex genes was, however, noted in the case of ascites hepatoma cells, in which the specific activity of ACT was 13 times higher than that in the normal liver, while that of CPS_1 was remarkably reduced. Similar patterns of change in mRNA level of CPS_1 and ACT complex were observed in the normal mouse liver and ascites hepatoma cells, indicating a close relationship between chromatin structure and gene expression of these enzymes.     

THE EFFECT AND FUNCTION OF AliBu_2OR'''' ON BUTADIENE-PROPYLENE ALTERNATING COPOLYMERIZATION CATALYZED BY VO(OR)_2Cl-AIiBu_3 SYSTEM

Four kinds of AliBu_2OB' with different R' were synthesized. The effect of AliBu_2OR'/AliBu_3 mole ratio on the conversion, the [η] of copolymer and catalytic efficiency were studied. The conversion was increased obviously and the catalytic efficiency was 2.7 times higher than before. The effect of the amount of AliBu_2OR' on the valence state of vanadium ion and the change of the valence state of vanadium ion with reaction temperature and time were studied. The VIS and IR spectra of the trinary-component catalyst system were measured. The model of active center including AliBu_2OR' was proposed. The function of AliBu_2OB was explained.