914 resultados para Séneca, Lucio Anneo, ca. 4 a.C.-65 d.C..
Resumo:
catena-Poly[{pentaaqua(L-proline-O)-erbium-mu-(L-proline-O:O')} trichloride], {[Er(C5H9-NO2)2(H2O)5]Cl3}n, M(r) = 594.0, monoclinic, P2(1), a = 8.294 (1), b = 10.981 (3), c = 11.934 (3) angstrom, beta = 107.04 (2)degrees, V = 1039.2 (4) angstrom3, Z = 2, D(x) = 1.90 g cm-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 45.2 cm-1, F(000) = 586, T = 298 K, R = 0.0244 for 1711 unique reflections [I > 3 sigma(I(o))]. The crystal consists of one-dimensional chains of infinite length in which one L-proline ligand bridges two neighboring Er ions, the other L-proline ligand being monodentate.
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WAXD, SAXS, FTIR, DSC and density techniques have been used to investigate the crystal structure, crystal density rho(c), amorphous density rho(a), equilibrium heat of fusion DELTAH(m)degrees and equilibrium melting temperature T(m)degrees. By extrapolating the straight lines in the FTIR absorbance against density plot to zero intensity, rho(c) and rho(a) were estimated to be 1.098 and 1.003 g/cm3 respectively. The rho(c) obtained was too low in value. From X-ray diffraction patterns of uniaxially oriented fibres, the crystal structure of Nylon-1010 was determined. The Nylon-1010 crystallized in the triclinic system, with lattice dimensions: a = 4.9 angstrom, b = 5.4 angstrom, c = 27.8 angstrom, alpha = 49-degrees, beta = 77-degrees, gamma = 63.5-degrees. The unit cell contained one monomeric unit, the space group was P1BAR, and the correct value of rho(c) was 1.135 g/cm3. The degree of crystallinity of the polymer was determined as about 60% (at RT) using Ruland's method. SAXS has been used to investigate the crystalline lamellar thickness, long period, transition zone, the specific inner surface and the electron density difference between the crystalline and amorphous regions for Nylon-1010. The analysis of data was based upon a one-dimensional electron-density correlation function. DELTAH(m)degrees was estimated to be 244.0 J/g by extrapolation of DELTAH(m)degrees in the plot of heat of fusion against specific volume of semicrystalline specimens to the completely crystalline condition (V(sp)c = 1/rho(c)). Owing to the ease of recrystallization of melt-crystallized Nylon-1010 specimens, the well-known Hoffman's T(m)-T(c) method failed in determining T(m)degrees and a Kamide double extrapolation method was adopted. The T(m)degrees value so obtained was 487 K.
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The complexes of Ln(L-Pro)s(H2O)2(ClO4)3(Ln = Pr, Nd and Er. L-Pro = L-Proline) were synthesized and characterized by elemental analysis, IR. spectra and thermal analysis. The singal crystal Pr2(L-Pro)6(H2O)4(ClO4)6 Was also obtained. The crystal belongs to monoclinic, P2(1), a = 0.9879 (3) nm, b = 2.1883 (4) nm, c = 1.3393 (2)nm, beta = 91.23(2)-degrees, V = 2.895(1) nm3, Z = 2. R = 0.035 for 5032 observed reflections. The coordination polyhedron of Pr(III) ion comprises six oxygen atoms from L-Pro molecules and two water molecules. Each L-Pro molecule coordinates to two Pr(III) ions through its carboxyl group which serves as a bridging bidentate ligand to form onedimensional chain structure.
Resumo:
以La_2O_3为基础,碱土金属作为第二组分的二元氧化物催化剂均具有较高的生成C_2活性,特别是La-Ba-O系催化剂具有优良的甲烷氧化偶联活性和稳定性,当La/Ba原子比为2.5时,C_2收率可达20.3%。第三组分的添加有助于提高C_2选择性,特别是添加碱金属,可以抑制完全氧化反应,并提高乙烯/乙烷比。在La:Ba:Na=2.5:1:0.1的催化剂上进行了500/小时的寿命实验,在整个反应期间,催化剂的活性和选择性相当稳定。X-射线物相分析表明,新鲜催化剂除有少量的碳酸钡外,主要是氧化镧和氧化钡的混合物。500小时后的物相基本上是氧化镧和碳酸钡。使用前后催化剂的比表面积及表面La和Ba的分布均无改变。较高的CH_4/O_3比对提高C_2选择性有利,当CH_4:O_2=4:1时,C_2选择性和收率分别为65.1%和19.1%。
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The single crystal of heteropoly blue, HsSiMo12O40.12H2O, the reduced product of molybdenum-silicon heteropoly acid, was prepared by electrochemical reduction and evaporation in nitrogen atmosphere. The Crystal structure of the product was determined. The heteropoly blue H8SiMo12O40.12H2O, Crystallizes space group P1BAR a = 1.3769 (3) nm, b = 1.4346 (4) nm, c = 1.4134 (4) nm, alpha = 120.47 (2)-degrees, beta = 110.70 (2)-degrees, gamma = 66.11 (2)-degrees, Z = 2, R = 0.0608. The heteropoly blue anion was determined to have Keggin Structure and alpha-isomer and it remained the structure of the unreduced heteropoly acid anion. But the distortion of the structure and the changes of bond length and bond angle take place obviously. The four Mo5+ Positions were determined in the structure.
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通过电化学还原的方法得到钼硅杂多酸的还原产物杂多蓝单晶H_8SiMo_(12)O_(40)·12H_2O.测完了它的晶体结构.晶体空间群属PI.α=1.3769(3)nm,b=1.4346(4)nm,c=1.4134(4)nm;α=120.47(2)°,β=110.70(2)°,γ=66.11(2)°;Z=2;R=0.0608.确证杂多蓝阴离子呈现Keggin结构和α-异构体特征,基本保持未还原杂多酸阴离子的结构.但是在结构畸变程度、键角和键长的变化以及结晶水的分布上有明显不同.同时确定了杂多蓝阴离子结构中4个Mo~(5+)离子的位置.
Resumo:
无水NdCl_3与甲基萘锂以1:2摩尔比在THF中反应分离得到一种黑色产物,该产物与环辛四烯反应,分离得到标题化合物,测定了这一新配合物的晶体结构。该晶体属单斜晶系,空间群P2/c,晶胞参数a=1.7858(7)nm,b=1.3243(4)nm,c=1.8085(6)nm,β=106.52(4)°,V=4.10nm~3,D_c=1.268 g/cm~3,Z=4,F(000)=1660,R=0.0774,R_w=0.0733。配合物分子由不相连的阴阳离子对组成,阴离子是由中心钛离子与二个对称的环辛四烯组成,阳离子是由一个锂离子和四个THF分子配位而成,另有二个THF分子作为填充分子存在于晶胞中。
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The complexes named in the title (eta-5-C9H7)3Ln.OC4H8 (Ln = Nd, Gd, Er) were synthesized by the reaction of anhydrous lanthanide trichlorides with indenyl potassium and cyclooctadienyl potassium (1:2:1 molar ratio) in THF. The complexes were characterized by elemental analysis, infrared and H-1-NMR spectroscopy, and mass spectrometry. In addition, the crystal structures of (eta-5-C9H7)3Nd.OC4H8 (1) and (eta-5-C9H7)3Gd.OC4H8 (2) were determined by an X-ray diffraction study. Complexes 1 and 2 belong to hexagonal space group P6(3) with unit cell parameters a = b = 11.843(3), c = 10.304(4) angstrom, V = 1251.7(9) angstrom-3, D(c) = 1.49 g.cm-3, Z = 2 for 1, and a = b = 11.805(2), c = 10.236(2) angstrom, V = 1235.4(6) angstrom-3 D(c) = 1.54 g.cm-3, Z = 2 for 2. The structures were solved by Patterson and Fourier techniques and refined by least-squares to final discrepancy indices of R = 0.049, R(w) = 0.053 using 925 independent reflections with I greater-than-or-equal-to 3-sigma(I) for 1, and R = 0.023, R(w) = 0.025 using 1327 independent reflections with I greater-than-or-equal-to 3-sigma(I) for 2. Coordination numbers for Nd3+ and Gd3+ are 10; the average bond lengths Nd-O and Gd-O are 2.557(21) and 2.459(13) angstrom, respectively. The structural studies showed the complexes to have 3-fold symmetry, but the THF molecule has no such symmetry; consequently the arrangement of carbon atoms in the THF molecule are disordered.
Resumo:
128 samples from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea were analyzed for grain size, clay minerals, biogenic opal content and quartz in order to reconstruct changes in East Asian monsoon climate since 8.5 Ma. An abrupt change of terrigenous mass accumulation rate (MAR), clay mineral assemblage, median grain size and biogenic opal MAR about 5.2 Ma suggests that between 8.5-5.2 Ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern Vietnam. A simple model of East Asian summer monsoon evolution was based on the clay/feldspar ratio, kaolinite/chlorite ratio and biogenic opal MAR. The summer monsoon has two periods of maximum strength at 8.5-7.6 Ma and 7.1-6.2 Ma. Subsequently, there was a relatively stable period at 6.2-3.5 Ma, continued intensification about 3.5-2.5 Ma, and gradually weakening after 2.5 Ma. Since I Ma the monsoon has intensified, with remarkable high-frequency and amplitude variability. Simultaneous increase in sedimentation rates at ODP Sites 1143, 1146 and 1148, as well as in MAR of terrigenous materials, quartz, feldspar and clay minerals at ODP Site 1143 at 3.5-2.5 Ma, may be the erosional response to both global climatic deterioration and the strengthening of the East Asian summer monsoon after about 3-4 Ma. (c) 2006 Elsevier B.V. All rights reserved.
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Recent investigations show that normalized radar cross sections for C-band microwave sensors decrease under high wind conditions with certain incident angles instead of increase, as is the case for low to moderate wind speeds. This creates the problem of ambiguities in high wind speed retrievals from synthetic aperture radar (SAR). In the present work, four geophysical model functions (GMFs) are studied, namely the high wind C-band model 4 (CMOD4HW), C-band model 5 (CMOD5), the high wind vertical polarized GMF (HWGMF_VV), and the high wind horizontal polarized GMF (HWGMF_HH). Our focus is on model behaviours relative to wind speed ambiguities. We show that, except for CMOD4HW, the other GMFs exhibit the wind speed ambiguity problem. To consider this problem in high wind speed retrievals from SAR, we focus on hurricanes and propose a method to remove the speed ambiguity using the dominant hurricane wind structure.
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本文主要阐述运用稳定加液-反应系统,在实验室环境下模拟海水中方解石和文石形成时微量元素共沉淀现象,主要研究微量元素固-液体系中的迁移、转化和分配。进而在对其定量描述的前提下,研究各靶元素的共沉淀行为对各种反应条件的响应,从中提取出可以用于古海洋研究的替代性指标。所研究的微量元素和部分常量元素包括非金属元素硼和砷、碱土金属元素镁、过渡金属元素(锰、钴、镍、铜、和镉)、铀系元素(铀、钍和铅)以及钇和稀土元素。 本实验首先运用pH测试、高精度滴定分析等手段测定了实验的一些基本参数,如[H+]、碱度和[Ca2+],根据计算获得了各碳酸体系要素,并以此为基础建立了5℃、15℃和25℃及pCO2=0.0015 atm.=0.0030atm.下的人工海水中方解石或文石的沉淀动力学方程。研究表明: 1)在各个条件下,方解石或文石的沉淀速率(R)和其在海水中过饱和度(Ω)存在很好的相关性,可基本表达为Log R=k*Log(Ω-1)+b; 2) pCO2对会严重改变海水中的碳酸钙过饱和度,进而影响相应的沉淀速率,但对方解石或文石的沉淀动力学方程没有明显影响; 3)不同温度下所得的方解石或文石各自的沉淀动力学方程存在明显差异,表明这一过程受热力学元素控制。 在方解石和文石沉淀实验中,通过人为添加各种微量元素对它们的共沉淀行为进行模拟。首先通过直接溶解稀释法结合ICP-MS或采用离线螯合系统前处理结合ICP-MS测定海水、固体样品中各靶元素的浓度。在此基础之上通过换算得出各靶元素在海水([Me]sol’n)和方解石或文石沉淀([XMe]overg)中的含量,然后 计算出单个实验中各靶元素介于碳酸钙沉淀和海水之间的分异系数。 实验中通过改变晶核类型(方解石和文石)、温度、pCO2、碳酸钙过饱和度(2-12,以方解石计)、沉淀速率和靶元素起始浓度等参数,得到在不同反应条件下各靶元素的分异系数。基于分异系数之间的差异,各靶元素在方解石和文石沉淀过程中的共沉淀行为被加以分类和界定。在方解石中Mn、Co、Ni、Pb、Th、Cd、Cu、Mg等表现为相容元素。而在文石中Mn、Co、Ni、Cd等都属不相容元素。B、As、U与其他金属离子不同的是这三种元素是以BO33-、AsO33-、UO22+等基团的形式参予共沉淀的,其中BO33-和AsO33-是替代CO32-而UO22+取代Ca2+。 进一步总结各靶元素和反应条件的关系,初步得出碳酸钙沉淀动力学机制、温度、离子半径、碳酸钙矿物的晶格结构、溶液化学组成及其变化是影响微量元素随方解石和文石共沉淀过程的重要因素,并对各靶元素共沉淀模式进行了探讨。最后我们结合实际工作主要是文献中报导的有孔虫、珊瑚等生物钙质壳体或骨架中各靶元素的结果,对比我们的实验从中提取出了一些可应用于古海洋研究的潜在替代性指标,如: 1) 海水中CO32-浓度代用指标——文石U/CaCd/Ca,方解石U/Ca; 2) 海水pH 代用指标——文石B/CaAs/Ca 比; 3) 氧化还原代用指标——方解石Mn/Ca 比; 4) 海水化学代用指标——方解石Co/Ca 比、U/Ca 比文石Cu/CaPb/Ca 比。 5)稀土元素代用指标——方解石质载体中的YREE/Ca。 还有几种元素组合也非常具有价值,如Mn-Co-Ni 组合、B-U 组合。此外指出了现有微量元素古海洋指标应用过程中被忽略了的一些关键性因素,如文石Mg/Ca受到文石沉淀速率的限制、方解石Cd/Ca 比受到沉淀速率和温度的双重影响等。
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To investigate the seasonal and interannual variations in biological productivity in the South China Sea (SCS), a Pacific basin-wide physical - biogeochemical model has been developed and used to estimate the biological productivity and export flux in the SCS. The Pacific circulation model, based on the Regional Ocean Model Systems (ROMS), is forced with daily air-sea fluxes derived from the NCEP (National Centers for Environmental Prediction) reanalysis between 1990 and 2004. The biogeochemical processes are simulated with a carbon, Si(OH)(4), and nitrogen ecosystem (CoSiNE) model consisting of silicate, nitrate, ammonium, two phytoplankton groups (small phytoplankton and large phytoplankton), two zooplankton grazers (small micrograzers and large mesozooplankton), and two detritus pools. The ROMS-CoSiNE model favourably reproduces many of the observed features, such as ChI a, nutrients, and primary production (PP) in the SCS. The modelled depth-integrated PP over the euphotic zone (0-125 m) varies seasonally, with the highest value of 386 mg C m (-2) d (-1) during winter and the lowest value of 156 mg C m (-2) d (-1) during early summer. The annual mean value is 196 mg C m (-2) d (-1). The model-integrated annual mean new production (uptake of nitrate), in carbon units, is 64.4 mg C m (-2) d (-1) which yields an f-ratio of 0.33 for the entire SCS. The modelled export ratio (e-ratio: the ratio of export to PP) is 0.24 for the basin-wide SCS. The year-to-year variation of biological productivity in the SCS is weaker than the seasonal variation. The large phytoplankton group tends to dominate over the smaller phytoplankton group, and likely plays an important role in determining the interannual variability of primary and new production.
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The fecundity, hatching success and naupliar survival of Calanus sinicus were studied in the Yellow Sea during research cruises in April and October 2006, with emphasis on the regulation of reproduction. During both cruises, the egg production rate (EPR) showed large spatial variations (0 to 25.4 eggs female(-1) d(-1)), generally coinciding with the food availability. In April, the abundant phytoplankton and ciliates in the study area supported active reproduction, which would probably initiate the annual population development. In October, females remained immature in the Yellow Sea Cold Water Mass, likely due to the unfavorable environment (poor food and low temperature). However, reproduction and recruitment were high in the neritic region, which may explain the local population recovery in late autumn. Hatching success varied markedly among stations in April (4 to 85%), whereas it was high overall in the neritic region during October (> 90%). Based on the potential recruitment rates, the spring recruitment would be more important for the annual population dynamics, Female gonad maturity, body size and lipid reserve were examined in relation to fecundity. Regression analyses suggested that the reproductive index (defined as the proportion of females with mature gonads) could be an indicator for the EPR of C. sinicus. Among the regulating factors, external food (ciliates and phytoplankton) seems essential for reproduction, whereas inner lipid reserve may mainly serve metabolic needs. Moreover, fecundity is positively related to body size but independent of temperature, which might exert indirect influences on reproduction.
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The abundance of anchovy Engraulis japonicus larvae, >20 mum ciliates, copepod eggs and nauplii, and microzooplankton herbivorous activity were studied in the Yellow Sea in June 2000. Anchovy juveniles and larvae were found in only 6 of the 19 stations sampled. The ciliate communities were dominated by 2 species: Laboea strobila and Strombidium compressum. In the surface waters, the abundance of L. strobila ranged between 0 and 560 ind. l(-1). S. compressum only appeared at Stns 15 to 18 (20 to 3300 ind. l(-1)). L. strobila was found mainly in the top 20 m. The abundance of L. strobila was less than 50 ind, l(-1) in waters deeper than 25 m. S, compressum showed subsurface abundance peaks at the salinity abnormality. Tintinnids occurred occasionally with abundance lower than 100 ind. l(-1), The total ciliate abundance fell in the range of 40 to 3420 ind. l(-1). The ciliate biomass in the surface water and the water column ranged between 0,15 and 6.76 mug C l(-1) and 0.4 and 134.4 mg C m(-2), respectively, In the surface waters, the abundance of copepod eggs and nauplii ranged from 0,3 to 3.1 and 1,1 to 15.6 ind, l(-1), respectively. The average abundance of copepod eggs and nauplii in 4 depth (0, 5, 10 and 20 m) fell in the range of 0.2 to 2.8 and 1.0 to 29.4 ind. l(-1), respectively. As a food item of the E. japonicus post-larvae, the abundance of copepod nauplii and eggs appeared to be low. The abundance peaks of ciliate and E, japonicus post-larvae coincided. Although not found in the gut of E, japonicus post-larvae, aloricate ciliates might be ingested by first-feeding anchovy larvae, preventing initial starvation and prolonging the time to irreversible starvation. On the basis of dilution experiments with positive microzooplankton grazing rates, microzooplankton grazed at rates of 0 to 0.61 d(-1). Grazing pressure of microzooplankton on chlorophyll a standing stock (P-i) and potential chlorophyll a primary production (P-p) were 17 to 46% and 35 to 109% d(-1), respectively.
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The Bohai Sea was the site of the Chinese national GLOBEC programme. During the June 1997 cruises of R/V Science No.1, observations and experiments on zooplankton feeding were conducted. At five 48 h time-series stations the following observations and measurements on zooplankton were carried out: (1) diurnal vertical migration, by collecting samples at different layers every 3 h with a closing net; (2) diurnal feeding rhythms, by gut pigment analysis; and (3) ingestion rate, by both gut pigment analysis and the dilution method. A classification by body size was used to deal with the diversity of species and developmental stages of zooplankton assemblages. Samples were separated into three size groups: small (200-500 mu m), medium (500-1000 mu m) and large (> 1000 mu m). The results showed that the copepods (Calanus sinicus, Paracalanus parvus, Acartia bifilosa and Centropages mcmurrichi) performed clear diurnal vertical migrations. However, their behaviour was different at different stations. The variation in gut pigment content over the 24 h cycle showed strong diurnal feeding rhythms, particularly for the large size group. Gut pigment contents reached their daily maximum during the time from dusk to midnight (18:00-24:00). The peak value was about 10 times the minimum observed in the daytime. The in situ daily grazing rate, based on gut pigment contents and evacuation experiments, was 4.00-12.65 ng chla ind(-1) day(-1) for the small size group, 5.99-66.58 ng chla ind(-1) day(-1) for the medium size group and 31.31-237.13 ng chla ind(-1) day(-1) for the large size group. The copepods consumed only a small part (2.90-13.52%) of the phytoplankton biomass hut about 77% of the daily production. The grazing mortality rate of phytoplankton by microzooplankton (<200 mu m) measured by the dilution method ranged from 0.43 to 0.69 day(-1) The calculated daily consumption of phytoplankton biomass was 35-50%, and 85-319% of the potential production.