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The Neoproterozoic witnessed several low latitude glaciations (i.e., the Sturtian, Marinoan and Gaskiers glaciations) and the geodynamic reorganization of cratonic blocks after the breakup of Rodinia. Trace element and stable isotope geochemistry from approximately coeval carbonate deposits on continental marginal sea and foreland basins (Yangtze Platform, China; Otavi and Nama Groups, Namibia) have shown fluctuating oxygen increase on the marine shelves. To gain an increasingly global picture of the bio-geochemical conditions in late Neoproterozoic seawater, we here present new redox-sensitive trace element, stable (C, O) and radiogenic (Nd, Sr) isotope records of carbonates from the Cryogenian Blaubeker and Court, and the Ediacaran Buschmannsklippe Formations (Witvlei Group, Namibia). Shale-normalised REE + Y patterns of post-Sturtian and post-Marinoan carbonates parallel modern seawater showing positive La, Gd and Y anomalies. Negative Ce anomalies argue for their preservation in increasingly more oxidising sea/porewater conditions in the Witvlei Basin from the Ediacaran on. While Cryogenian carbonates underwent radiogenic basin-fluid type overprinting, Ediacaran carbonates upsection record pristine Sr isotopic compositions that match the global Neoproterozoic seawater curve. Partly coupled negative correlations between Sr and Nd suggest long-term shifts in continental weathering and short-term changes in ocean circulation patterns. The δ13Ccarb values range from −7.2 to +3.5 ‰ and record a negative isotope excursion in the upper part of the Witvlei stratigraphy. This excursion might be equivalent to the ‘Shuram’ carbon isotope excursion (CIE). However, the causes, global extent and correlation of the Shuram CIE are still debated. Typical for carbonates of the putative Shuram excursion are less pronounced Ce anomalies, lower Y/Ho ratios, and lower bio-essential and redox-sensitive trace metal concentrations, arguing for periodic redoxcline oscillations in a redox-stratified late Neoproterozoic shelf environment. The overall long-term decrease in redox-sensitive element enrichments throughout the Witvlei Group argues for a progressively increasing, presumably biologically-driven metal cycling towards values typical for Phanerozoic carbonates. The combination of changes in local weathering flux and ambient redox conditions in the late Neoproterozoic ocean may have caused dynamic (bio)geochemical metal cycling, predating (and possibly promoting) the metazoan radiation documented in the overlying Nama Group.

There is relatively abundant groundwater in some hill and gully regions of the Loess Plateau aquifer. The region has an arid to semiarid climate with low precipitation and high potential evaporation, and thus, groundwater recharge processes remain unclear. This study aimed to investigate recharge mechanisms and soil water movement in the Loess Plateau aquifer and to assess the recharge to shallow loess aquifers using soil profiles. In general, we found that the δ18O and δ2H values of soil water varied both with season and with soil profile depth. The seasonal stable isotopic values in the soil profiles also differed between wet and dry years. In particular, soil water and groundwater isotopic values responded to precipitation. This response suggests that seasonal precipitation is the main source of recharge to soil water and groundwater and that soil water is involved in groundwater recharge. The precipitation infiltration, soil water replenishment, and groundwater recharge are complicated processes. Two main modes of infiltration allow water to move downward through the unsaturated zone and recharge groundwater can be concluded. The primary mode is preferential infiltration through microtopographic features. This channel-like infiltration can rapidly move precipitation downward to deep soil layers, greatly reducing evaporation even under the arid to semiarid conditions of the study area. The secondary mode is a combination of matrix flow, which includes inside preferential infiltration though finger-like flow in the upper layer and piston-like flow in the deeper layer. The upper finger-like flow can cause rapid infiltration to below the root zone during less intense rain or snowmelt. The annual precipitation through preferential flow is the dominant recharge mode for the shallow groundwater in the loess aquifers. These two modes of recharge maintain perennial groundwater in the arid to semiarid hill and gully regions of the Loess Plateau.

A SDC electrolyte film with gradient structure rooted on porous alumina substrate has been prepared by using a gas-phase controlling convection–diffusion approach. Investigation on the fabrication principles and the co-precipitation kinetics turned out the gradient distribution of hydroxide product of Ce(OH) 3 and Sm(OH) 3 in a porous substrate could be formed as induced by the down-toward diffusion of NH 3 ·H 2 O in polar solvent along vertical direction and the up-toward convection of Sm 3+ and Ce 3+ ions over the cross-section of porous substrate, and the aim ratio of Ce to Sm of 4:1 in the sediment phase would be achieved by controlling component concentration in bulk solution. As a result, Sm 0.2 Ce 0.8 O 2.0 (SDC) electrolyte film with gradient microstructure could be fabricated after a subsequent sintering treatment at a high temperature. Investigation of crystal phase, structural, compositional characteristics of the sintered SDC/substrate specimens proved that a uniform and dense SDC film with an average grain size of ∼ 500 nm spread over on the surface of substrate, and a correct cubic fluorite phase has been formed. Gradient variation presented in both the microstructure of SDC/substrate and the component contents over the cross-section of the SDC/substrate. Numerical analysis on the EDX data presented three component parts were sectioned, including a dense SDC layer of ∼ 25 μm, a uniform filling layer of ∼ 140 μm and a successive diffuse layer stretching as far as ∼ 250 μm. Effect of bulk pH on thickness and surface microstructure of SDC film has been discussed. This microstructure-optimization approach will be applicable to fabricate electrode-supported gradient electrolyte films for IT-SOFC.

The redox and interactive behaviour of flavin adenine dinucleotide (FAD) with a ruthenium (Ru)-modified glassy carbon electrode (GCE) was investigated. The electron-transfer kinetics on the Ru-modified GCE gives an apparent electron-transfer coefficient, α app of 0.56, and an apparent heterogeneous electron transfer rate constant, k app of 2.32 s−1, respectively. The cyclic voltammetry (CV) complemented by alternating cyclic voltammetry (ACV) shows reduction of FAD to be a quasi-reversible reaction involving FAD adsorption. The adsorption of FAD on the Ru-modified GCE fits a Langmuir adsorption isotherm. The large apparent negative Gibbs energy of adsorption ΔG ads (−38.2 kJ mol−1) of FAD onto the Ru-modified GCE confirmed a strong chemical adsorption of FAD on the surface. The deposited Ru islands block surface sites for FAD adsorption and the electron-transfer communication between FAD and the electrode surface does not significantly improve with a deposited Ru monolayer.

An improved procedure for extraction and purification of boron from natural samples is presented. The separation and purification of boron was carried out using a boron-specific resin, Amberlite IRA743, and a mixed ion exchange resin, Dowex 50W × 8 and Ion Exchanger II resin. Using the mixed ion exchange resin which adsorbs all cations and anions except boron, the HCl and other cations and anions left in eluant from the Amberlite IRA 743 were removed effectively. In this case, boron loss can be avoided because the boron-bearing solution does not have to be evaporated to reach dryness to dislodge HCl. The boron recovery ranged from 97.6% to 102% in this study. The isotopic fractionation of boron can be negligible within the precision of the isotopic measurement. The results show that boron separation for the isotopic measurement by using both Amberlite IRA 743 resin and the mixed resin is more effective than that using Amberlite IRA 743 resin alone. The boron in samples of brine, seawater, rock, coral and foraminifer were separated by this procedure. Boron isotopic compositions of these samples were measured by thermal ionization mass spectrometry in this study.

The interaction of flavin adenine dinucleotide (FAD) with a glassy carbon electrode (GCE) surface was investigated in terms of the FAD adsorption thermodynamics and kinetics, the subsequent electroreduction mechanism, and the corresponding electron-transfer rate. The kinetics of FAD electroreduction at the GCE was found to be an adsorption-controlled process. A set of electroreduction kinetic parameters was calculated: the true number of electrons involved in the FAD reduction, n=1.76, the apparent transfer coefficient, alpha(app)=0.41, and the apparent heterogeneous electron-transfer rate constant, k(app)=1.4 s(-1). The deviation of the number of exchanged electrons from the theoretical value for the complete reduction of FAD to FADH(2) (n=2) indicates that a small portion of FAD goes to a semiquinone state during the redox process. The FAD adsorption was well described by the Langmuir adsorption isotherm. The large negative apparent Gibbs energy of adsorption (DeltaG(ads)=-39.7 +/-0.4 kJ mol(-1)) indicated a highly spontaneous and strong adsorption of FAD on the GCE. The energetics of the adsorption process was found to be independent of the electrode surface charge in the electrochemical double-layer region. The kinetics of FAD adsorption was modeled using a pseudo-first-order kinetic model.

In recent years, remarkable advances in research of the mechanical and structural properties of single polymer chains have been achieved thanks to atomic force microscope (AFM)‐based single molecule force spectroscopy (SMFS). This technique offers great possibilities to investigate the mechanical properties of a single polymer chain by static/dynamic force‐extension measurements at the mesoscale level. Data are analyzed with the help of appropriate theoretical models, such as statistical mechanics models for freely jointed chains (FJC) or worm‐like chains (WLC), which can well describe the moderate entropy‐controlled stretch of most polymers, and with semiclassical models, which are being modified using quantum mechanics principles to account for entropic and enthalpic contributions to stretching in the high‐force Hookean regime. In this article we review the theoretical models of single chain stretching, the latest progress in force‐extension measurements by static and dynamic AFM modes for poly...

The isotopic composition of dissolved boron, in combination with the elemental concentrations of B, Cl and salinities in freshwater-seawater mixed samples taken from the estuary of the Changjiang River, the largest one in China, was investigated in detail in this study. Brackish water and seawater samples from the estuary of the Changjiang River were collected during low water season in November, 1998. Boron isotopic compositions were determined by the Cs2BO2 +-graphite technique with a analytical uncertainty of 0.2‰ for NIST SRM 951 and an average analytical uncertainty of 0.8‰ for the samples. The isotopic compositions of boron, expressed in δ11B, and boron concentrations in the Changjiang River at Nanjing and seawater from the open marine East Sea, China, are characterized by δ11B values of −5.4‰ and 40.0‰, as well as 0.0272 and 4.43 mg B/L, respectively. Well-defined correlations between δ11B values, B concentrations and Cl concentrations are interpreted in terms of binary mixing between river input water and East Sea seawater by a process of straightforward dilution. The offsets of δ11B values are not related to the contents of clastic sediment and to the addition of boron. These relationships favor a conservative behavior of boron at the estuarine of the Changjiang River.

A new method for the removal SO42-, reacted with BaCO3, for isotopic measurement of chlorine is described in this study. The sample solution was first taken through a W form resin and a small excess of high-purity BaCO3 powder was added into the effluent. The released Ba2+ by the dissolution of BaCO3 reacts with SO42- to form a BaSO4 precipitate. Comparison with the traditional method based on ion exchange of a Ba2+ form resin showed that the new method has a much higher efficiency in removing SO42- and is suitable for the isotopic measurement of chlorine in sample with low Cl- and high SP42-. (c) 2006 Elsevier B.V All rights reserved. A new method for the removal SO42-, reacted with BaCO3, for isotopic measurement of chlorine is described in this study. The sample solution was first taken through a W form resin and a small excess of high-purity BaCO3 powder was added into the effluent. The released Ba2+ by the dissolution of BaCO3 reacts with SO42- to form a BaSO4 precipitate. Comparison with the traditional method based on ion exchange of a Ba2+ form resin showed that the new method has a much higher efficiency in removing SO42- and is suitable for the isotopic measurement of chlorine in sample with low Cl- and high SP42-. (c) 2006 Elsevier B.V All rights reserved.

Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ 11 B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH) 4 - is the dominant spe-cies incorporated into the biogenic calcite structure. The isotopic fractionation factors a between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH) 3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH) 3 is attributed to the formation of Mg(OH) 2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH) 2 precipitated from artificial seawater shows that heavier 11 B is enriched in Mg(OH) 2 precipitation, which suggests that isotopically heavier B(OH) 3 species incorporated preferentially into Mg(OH) 2 precipitation. This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.

An ionization depressor, 1% H3PO4 was used to eliminate the isobaric interference that has been of a great concern during the procedure of boron isotopic ratio analysis by thermal ionization mass spectrometer (TIMS). Our experiments have shown that it appears to be an effective method to completely restrain the formation of isobaric ions of CNO− and Cs2CNO+ in the ionization source of mass spectrometer. We have also discussed the optimum proportion of depressor to nitrite for precise analysis of boron isotopes in natural samples based on a conditional experiment. In this case, the pretreatment of boron extraction from natural samples is greatly simplified since it is not necessary to remove nitrite and organic matter completely. In virtue of the method, we determined boron isotope in different types of natural samples, and our results are consistent with previous reports.

The characteristics of non-reductive thermal ion emission in thermal ionization mass spectrometry for six kinds of graphite with different origins, purity and crystal structure and one high pure carbon powder are studied. The results show that the efficacy of non-reductive thermal ion emission of graphite is weakly related to the purity and particle size of graphite while dependent on the crystal microstructure of graphite. Graphite with a perfect crystal structure has a higher efficiency of non-reductive thermal ion emission.