Toward a conceptual model of the calcite surface: hydration,hydrolysis, and surface potential     

《Geochimica et cosmochimica acta》1999,63(19-20):3121-3131

Because of a recent increase in interest in the properties of the calcite surface, there has also been an increase in activity toward development of mathematical models to describe calcite’s surface behaviour, particularly with respect to adsorption and precipitation. For a mathematical model to be realistic, it must be based on a sound conceptual model of atomic structure at the interface. New observations from high resolution techniques have been combined with previously published data to resolve the apparent conflict with results from electrokinetic studies and to present a picture of what the calcite surface probably looks like at the atomic scale.In ultra-high vacuum (10⁻¹⁰ mbar), a cleaved surface remains unreacted for at least an hour, but the unreacted surface does not remain as a termination of the bulk structure. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) show that the outer-most atomic layer relaxes and the surface slightly restructures. In air, dangling bonds are satisfied by hydrolysed water. XPS and time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal the presence of adsorbed OH and H. In AFM images, the features so typical of calcite, namely, alternate-row offset, pairing and height difference, as well as the consistent dependence of these features on the force and direction of tip scanning, are best explained by OH filling of the vacant O sites created during cleavage on the Ca octahedra. Thus there is solid evidence to indicate the presence of OH and H chemi-sorbed at the termination of the bulk calcite structure.Wet chemical studies, however, show that calcite’s pH_pzc (zero point of charge) varies with sample history and solution composition. Electrophoretic mobility measurements indicate that the potential-determining ions are not H⁺ and OH⁻, but rather Ca²⁺ and CO₃²⁻ (or HCO₃⁻ or H₂CO₃⁰). This apparent conflict is resolved by a slight modification of the electrical double layer (EDL) model. At the bulk termination, hydrolysis species are chemi-bonded. At the Stern layer, adsorption attaches Ca²⁺ and CO₃²⁻ (or other carbonate species), but the hydrolysis layer keeps them in outer-sphere coordination to the surface. With dehydration, loss of the hydrolysis species results in direct contact between adsorbed ions and the bulk termination, therefore, inner-sphere sorption is equivalent to extension of the three dimensional bulk network, which is precipitation. Attachment of ions with size and charge compatible with Ca and CO₃ likewise results in coprecipitation and solid–solution formation.  相似文献   

Origin of planetary cores: evidence from highly siderophile elements in martian meteorites     

《Geochimica et cosmochimica acta》1999,63(13-14):2105-2122

We present new bulk compositional data for 6 martian meteorites, including highly siderophile elements Ni, Re, Os, Ir and Au. These and literature data are utilized for comparison versus the siderophile systematics of igneous rocks from Earth, the Moon, and the HED asteroid. The siderophile composition of ALH84001 is clearly anomalous. Whether this reflects a more reducing environment on primordial Mars when this ancient rock first crystallized, or secondary alteration, is unclear. QUE94201 shows remarkable similarity with EET79001-B for siderophile as well as lithophile elements; both are extraordinarily depleted in the “noblest” siderophiles (Os and Ir), to roughly 0.00001 × CI chondrites. As in terrestrial igneous rocks, among martian rocks Ni, Os and Ir show strong correlations vs. MgO. In the case of MgO vs. Ni, the martian trend is displaced toward lower Ni by a large factor (5), but the Os and Ir trends are not significantly displaced from their terrestrial counterparts. For Mars, Re shows a rough correlation with MgO, indicating compatible behavior, in contrast to its mildly incompatible behavior on Earth. Among martian MgO-rich rocks, Au shows a weak anticorrelation vs. MgO, resembling the terrestrial distribution except for a displacement toward 2–3 times lower Au. The same elements (Ni, Re, Os, Ir and Au) show similar correlations with Cr substituted for MgO. Data for lunar and HED rocks generally show less clear-cut trends (relatively few MgO-rich samples are available). These trends are exploited to infer the compositions of the primitive Earth, Mars, Moon and HED mantles, by assuming that the trend intercepts the bulk MgO or Cr content of the primitive mantle at the approximate primitive mantle concentration of the siderophile element. Results for Earth show good agreement with earlier estimates. For Mars, the implied primitive mantle composition is remarkably similar to the Earth’s, except for 5 times lower Ni. The best constrained of the extremely siderophile elements, Os and Ir, are present in the martian mantle at 0.005 times CI, in comparison to 0.007 times CI in Earth’s mantle. This similarity constitutes a key constraint on the style of core-mantle differentiation in both Mars and Earth. Successful models should predict similarly high concentrations of noble siderophile elements in both the martian and terrestrial mantles (“high” compared to the lunar and HED mantles, and to models of simple partitioning at typical low-pressure magmatic temperatures), but only predict high Ni for the Earth’s mantle. Models that engender the noble siderophile excess in Earth’s mantle through a uniquely terrestrial process, such as a Moon-forming giant impact, have difficulty explaining the similarity of outcome (except for Ni) on Mars. The high Ni content of the terrestrial mantle is probably an effect traceable to Earth’s size. For the more highly siderophile elements like Os and Ir, the simplest model consistent with available constraints is the veneer hypothesis. Core-mantle differentiation was notably inefficient on the largest terrestrial planets, because during the final ∼ 1% of accretion these bodies acquired sufficient H₂O to oxidize most of the later-accreting Fe-metal, thus eliminating the carrier phase for segregation of siderophile elements into the core.  相似文献   

南黄海和东海表层水两种粒级颗粒物和颗粒氮含量的分布特征     

裴志超  刘广山  彭安国  门武 《台湾海峡》2010,29(4):510-517

测定了南黄海和东海表层水0.7~53.0μm和〉53.0μm这2种悬浮颗粒物（SPM）、颗粒氮（PN）的含量.其结果表明,南黄海和东海表层水0.7~53.0μm粒级的SPM、PN平均含量分别为4.68 mg/dm3、18.50μg/dm3;而〉53.0μm粒级的SPM、PN平均含量分别为0.20 mg/dm3、2.65μg/dm3.0.7~53.0μm和〉53.0μm粒级的PN/SPM含量平均比值分别为0.78%、1.41%（m/m）,后者约是前者的2倍.统计分析结果表明,尽管这2种粒级的SPM、PN含量和PN/SPM含量比值的范围较大,但约80%的数据集中在较小范围内,即0.7~53.0μm和〉53.0μm粒级SPM含量分别集中在0.37~3.68、0.02~0.29 mg/dm3的范围内;0.7~53.0μm和〉53.0μm粒级PN含量分别集中在2.54~18.90、0.40~2.69μg/dm3的范围内;0.7~53.0μm和〉53.0μm粒级的PN/SPM含量比值分别集中在0.14%~1.00%和0.15%~1.95%之间.研究结果表明,研究海域0.7~53.0μm粒级SPM、PN含量有2个高值区,分别位于近岸海区和东海东北部海区.〉53.0μm粒级SPM、PN含量的分布分为2个部分：南黄海表层水SPM、PN含量分布呈从近岸向外海降低的趋势;而东海表层水SPM、PN含量分布呈断面中间高,并分别向近岸和外海降低的趋势.  相似文献   

Aerobic ammonium oxidation in the oxycline and oxygen minimum zone of the eastern tropical South Pacific off northern Chile (∼20°S)     

《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(16):1032-1041

Aerobic NH₄⁺ oxidation rates were measured along the strong oxygen gradient associated with the oxygen minimum zone (OMZ) of the eastern tropical South Pacific off northern Chile (∼20°S) during 2000, 2003, and 2004. This process was examined by comparing NH₄⁺ rates of change during dark incubations, with and without the addition of allylthiourea, a classical inhibitor of the ammonia monooxygenase enzyme of ammonium-oxidizing bacteria. The contribution of aerobic NH₄⁺ oxidation in dark carbon fixation and NO₂⁻ rates of change were also explored. Thirteen samples were retrieved from the oxycline (252 to ⩽5 μM O₂; 15 to ∼65 m depth) and three from the oxygen minimum core (⩽5 μM O₂; 100–200 m depth). Aerobic NH₄⁺ oxidation rates were mainly detected in the upper part (15–30 m depth) of the oxycline, with rates ranging from 0.16 to 0.79 μM d⁻¹, but not towards the oxycline base (40–65 m depth). In the oxygen minimum core, aerobic NH₄⁺ oxidation was in the upper range and higher than in the upper part of the oxycline (0.70 and 1.0 μM d⁻¹). Carbon fixation rates through aerobic NH₄⁺ oxidation ranged from 0.18 to 0.43 μg C L⁻¹ d⁻¹ and contributed between 33% and 57% of the total dark carbon fixation, mainly towards the oxycline base and, in a single experiment, in the upper part of the oxycline. NO₂⁻ consumption was high (up to 10 μM d⁻¹) towards the oxycline base and OMZ core, but was significantly reduced in experiments amended with allylthiourea, indicating that aerobic NH₄⁺ oxidation could contribute between 8% and 76% of NO₂⁻ production, which in turn could be available for denitrifiers. Overall, these results support the important role of aerobic NH₄⁺ oxidizers in the nitrogen and carbon cycling in the OMZ and at its upper boundary.  相似文献   

注射用丹红(粉针)-中间体-药材HPLC指纹图谱相关性研究     

唐旭利  刘静  李国强  钟惠民  张静 《中国海洋大学学报(自然科学版)》2009,39(1)

探讨中药指纹图谱相关性研究方法,运用Agilent 1100 DAD-HPLC高效液相色谱仪,采用色谱条件:大连依利特SinoChrom ODS-BP(250 mm×4.6 mm,5um)色谱柱,甲醇-0.1%磷酸水梯度洗脱,柱温30℃,流速1.0 mL·min-1检测波长280mm,进样量20uL.建立了的相同条件下丹红注射剂、中间体和药材的HPLC指纹图谱.所建立的指纹图谱个峰分离度较好,指纹信息完整,符合指纹图谱技术规范.进一步利用相似度分析软件进行了指纹图谱相关性分析,揭示了丹红注射剂与中间体和药材具有较好的相关性.共有峰的相对保留时间及相对峰面积参数,可作为中药注射剂质量控制的重要依据.  相似文献   

Physiological and biochemical responses of <Emphasis Type="Italic">Prorocentrum minimum</Emphasis> to high light stress     

So Yun Park  Eun Seok Choi  Jinik Hwang  Donggiun Kim  Tae Kwon Ryu  Taek-Kyun Lee 《Ocean Science Journal》2009,44(4):199-204

Prorocentrum minimum is a common bloomforming photosynthetic dinoflagellate found along the southern coast of Korea. To investigate the adaptive responses of P. minimum to high light stress, we measured growth rate, and generation of reactive oxidative species (ROS), superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) in cultures exposed to normal (NL) and high light levels (HL). The results showed that HL (800 μmol m^?2 s^?1) inhibited growth of P. minimum, with maximal inhibition after 7–9 days. HL also increased the amount of ROS and MDA, suggesting that HL stress leads to oxidative damage and lipid peroxidation in this species. Under HL, we first detected superoxide on day 4 and H₂O₂ on day 5. We also detected SOD activity on day 5 and CAT activity on day 6. The level of lipid peroxidation, an indicator of cell death, was high on day 8. Addition of diphenyleneiodonium (DPI), an NAD(P)H inhibitor, decreased the levels of superoxide generation and lipid peroxidation. Our results indicate that the production of ROS which results from HL stress in P. minimum also induces antioxidative enzymes that counteract oxidative damage and allow P. minimum to survive.  相似文献   

应用双特异分子探针技术定性定量检测圆海链藻(Thalassiosira rotula)     

李秀芹  于志刚  甄毓  蔡青松  米铁柱  李荣秀 《海洋与湖沼》2009,40(1):12-18

设计了一套圆海链藻(Thalassiosira rotula)特异性探针,运用双特异分子探针技术,对圆海链藻(Thalassiosira rotula)进行了定性定量检测.结果表明,本实验中设计的一套探针与其它十几种藻无交叉反应,具有种特异性;细胞裂解液直接杂交检测优于提纯RNA样品检测;对自然样品做了初步检测,发现天然海水中的其它浮游生物对该检测方法影响很小.  相似文献   

Detection of Prorocentrum donghaiense using sandwich hybridization integrated with nuclease protection assay   总被引：1，自引：0，他引：1  

CHEN Jie  ZHEN Yu  MI Tiezhu  YU Zhigang 《海洋学报(英文版)》2009,28(2):121-126

Prorocentrum donghaiense is an important harmful algae bloom (HAB) causing creature in China’s seas, and the conventional visual detection can not cope with long-term monitoring and high-throughput sampling projects. An assay for P. donghaiense with sandwich hybridization integrated with nuclease protection assay (NPA-SH) was established. Tests with mixed samples and spiked field ones confirmed its good specificity and sensitivity. The cell number of P. donghaiense correlated well with the optical density, ...  相似文献   

Photochemical oxidation of benzothiophene in seawater   总被引：3，自引：0，他引：3  

杨桂朋 《中国海洋湖沼学报》2000,18(1):85-91

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A nitrogen and phosphorus dynamic model of mesocosm pelagic ecosystem in the Jiaozhou Bay in China     

LI Keqiang  WANG Xiulin  LIANG Shengkang  SHI Xiaoyong  ZHU Chenjian  CHEN Hu 《海洋学报(英文版)》2008,27(5):98-110

A nitrogen and phosphorus dynamic model of mesocosm pelagic ecosystem was established according to the summary and synthesis of the models available, in which seven state variables （DIN, PO4-P, DON, DOP, phytoplankton, zooplankton and detritus） were included. Logically it had five modules--phytoplankton, zooplankton, dissolved inorganic nutrients, dissolved organic nutrients and detritus. The results showed that this model could simulate the variations of DIN, PO4-P, DON, DOP, POC and phytoplankton biomass in pelagic ecosystem in mesocosm properly, based on the site experiment data in the Jiaozhou Bay in the autumn of 1999 and the summer of 2000. Not only the logical structure but also the model parameters were feasible, and about 20 parameters were made to fit for the Jiaozhou Bay during the simulation. All of these are necessary to study the control mechanism of nutrients biogeochemical cycling in the Jiaozhou Bay and other China＇ s coastal waters.  相似文献