Bentonite nanoparticle stability and the effect of fulvic acids: Experiments and modelling

In this study, the critical coagulation concentration (CCC) for FEBEX bentonite colloids is determined by colloid coagulation studies under variation of pH, electrolyte concentration, and fulvic acid (GoHy-573FA) content. For CaCl$_{2}$ electrolyte solution, a pH-independent Ca-CCC of 1 mmol L$^{-1}$ is found. In the case of NaCl background electrolyte, a pH-dependent Na-CCC can be determined with 15 ± 5 mmol L$^{-1}$ at pH 6, 20 ± 5 mmol L$^{-1}$ at pH 7, 200 ± 50 mmol L$^{-1}$ at pH 8, 250 ± 50 mmol L$^{-1}$ at pH 9, and 350 ± 100 mmol L$^{-1}$ at pH 10, respectively. The addition of 1 mg L$^{-1}$ dissolved organic carbon in the form of fulvic acid (FA) increases the Ca-CCC to 2 mmol L$^{-1}$. An association of FA with FEBEX bentonite colloids as surface coating can clearly be identified by scanning transmission X-ray microscopy (STXM). The experimental bentonite stability results are described by means of an extended DLVO (Derjaguin–Landau–Verwey–Overbeek) approach summing up hydration forces, short-range Born repulsion, van der Waals attraction, and electrical double layer repulsion. The measured zeta (ζ)-potential of the bentonite colloids is applied as platelet face electrokinetic potential and the edge electrokinetic potential is estimated by the combination of silica and alumina ζ-potential data in the ratio given by the FEBEX bentonite structural formula. Adjusting the montmorillonite face electrokinetic potential by a maximum of ±15.9 mV is sufficient to successfully reproduce the measured stability ratios. Due to the uncertainty in the ζ-potential measurement, only semiquantitative calculations of the stability ratio can be given

Coming of voting age. Evidence from a natural experiment on the effects of electoral eligibility

In recent years, several jurisdictions have lowered the voting age, with many more discussing it. Sceptics question whether young people are ready to vote, while supporters argue that allowing them to vote would increase their specific engagement with politics. To test the latter argument, we use a series of register-based surveys of over 10,000 German adolescents. Knowing the exact birthdates of our respondents, we estimate the causal effect of eligibility on their information-seeking behaviour in a regression discontinuity design. While eligible and non-eligible respondents do not differ in their fundamental political dispositions, those allowed to vote are more likely to discuss politics with their family and friends and to use a voting advice application. This effect appears to be stronger for voting age 16 than for 18. The right to vote changes behaviour. Therefore, we cannot conclude from the behaviour of ineligible citizens that they are unfit to vote

How well suited are current thermodynamic models to predict or interpret the composition of (Ba,Sr)SO₄ solid-solutions in geothermal scalings?

In this study, we report results of the analysis of a particularly interesting scaling sample from the geothermal plant in Neustadt-Glewe in northern Germany, which contained 19% Galena (PbS) and 81% of a heterogeneous assemblage of (Ba,Sr)SO₄ crystals with varying compositions, 0.15 < X$_{Ba}$ < 0.53. A main fraction of the sample (~56%) has a barite content of X$_{Ba}$ ≈ 0.32. We try to relate the solid composition of the (Ba,Sr)SO₄ solid-solution to the conditions at the geothermal plant concerning temperature, pressure, and solution composition, and discuss it with respect to the challenges in modelling the composition of (Ba,Sr)SO₄ solid-solutions on the basis of thermodynamic mixing models. We note that considerable uncertainties are related to the description of (Ba,Sr)SO₄ formation by means of thermodynamic models. The scaling composition observed in this study would be in line with endmember solubilities as predicted by the PhreeqC-Pitzer database for 70 °C and an interaction parameter, a0 = 1.6. According to such a model, the scaling heterogeneity would reflect bimodal precipitation behaviour due to various degrees of depletion of the brine with respect to X(Ba)($_{aq}$). Minor fluctuations in X(Ba)($_{aq}$): 0.0017 < X(Ba)($_{aq}$) < 0.0042 explain the full range of observed solid compositions. The choice especially of the interaction parameter seems to some extent arbitrary. This knowledge gap strongly limits the interpretation of (Ba,Sr) SO₄ compositions. Thus, it is not possible to distinguish between kinetic and thermodynamic effects on partitioning or to use the solid-solution composition to draw conclusions about the precipitation conditions (e.g. Temperature)

Fractionation of Suwannee River fulvic acid and Aldrich humic acid on α\alpha-Al2_2O3_3: spectroscopic evidence

International audienceSorptive fractionation of Suwannee River Fulvic Acid (SRFA) and Purified Aldrich Humic Acid (PAHA) on $\alpha$-Al$_2$O$_3$ at pH 6 was probed in the supernatant using different spectroscopic techniques. Comparison of dissolved organic carbon (DOC) analysis with UV/Vis spectrophotometric measurements at 254 nm, including Specific UV absorbance (SUVA) calculation, revealed a decrease in chromophoric compounds for the non sorbed extracts after a 24 h contact time. This fractionation, only observable below a certain ratio between initial number of sites of humic substances and of $\alpha$-Al$_2$O$_3$, seems to indicate a higher fractionation for PAHA. C(1s) near-edge X-ray absorption fine structure spectroscopy (NEXAFS) confirmed this trend and points to a decrease in phenolic moieties in the supernatant and to an eventual increase in phenolic moieties on the surface. Time-resolved luminescence spectroscopy (TRLS) of Eu(III) as luminescent probe showed a decrease in the ratio between the $^5$D0$\rightarrow$$^7$F$_2$ and $^5$D0$\rightarrow$$^7$F$_1$ transitions for the fractionated organic matter (OM) that is thought to be associated to a lower energy transfer from the OM to Eu(III) due to the loss of polar aromatics. These modifications in the supernatant are a hint for the modification of sorbed humic extracts on the surface

Temporary Disenfranchisement: Negative Side Effects of Lowering the Voting Age

How does losing one’s right to vote again after having been eligible to vote before affect political fundamentals such as political efficacy? We draw attention to the hitherto neglected phenomenon “temporary disenfranchisement,” which, for instance, occurs regularly in states that extended the franchise to underage citizens in some but not all elections. If an election with voting age 16 is closely followed by an election with voting age 18, underage voters who are eligible for the former will have no right to vote in the latter. Using original panel data on young citizens in Germany and a differences-in-differences design, we find that temporary disenfranchisement results in a decrease in external efficacy, which remains even after regaining eligibility. Our findings highlight an important side effect of selective voting rights extensions and bear insights that are relevant to other cases of temporary disenfranchisement due to residential mobility, citizenship, or felony disenfranchisement

Scaling properties of granular materials

Given an assembly of viscoelastic spheres with certain material properties, we raise the question how the macroscopic properties of the assembly will change if all lengths of the system, i.e. radii, container size etc., are scaled by a constant. The result leads to a method to scale down experiments to lab-size.Comment: 4 pages, 2 figure

Modelling of radionuclides migration in the low pH cement / clay interface

Reactive transport modelling activities described in this work are focused on the definition of the conceptual model and the selection of the chemical and transport parameters to be applied on laboratory through diffusion experiments performed in KIT-INE (see contribution of Ait Mouheb et al., this proceedings). The model includes different coupled processes which are thought to play a role in a through diffusion experiment of HTO, 36Cl-, 129Iand Be across the interface between bentonite porewater and low pH cement. One of these processes is the impact of porosity changes due to dissolution / precipitation reactions

NANO GEOCHEMISTRY

It is our great pleasure to briefly introduce our motivation to collect scientific contributions for this Special Issue, entitled “Nano Geochemistry”. The geophysical and chemical dynamics at the solid–water interface, ultimately, control the transport properties of natural and engineered colloids/nanoparticles via, e.g., mineral dissolution/precipitation reactions and the variation in nano- to microscale surface roughness [1,2]. The nanoparticles present can significantly influence the mobility of strongly sorbing organic and/or inorganic contaminants in groundwater systems, frequently used as a drinking-water resource [3]. In addition, wetting/drying cycles in the vadose zone have attracted interest, concerning the mobility of organic nanoparticles/colloids [4], and the nanoparticle composition and element redox state can significantly change, especially in karst systems, due to seasonal variations [5]. More pronounced changes, due to extreme weather events, potentially triggered by climate change, have been observed [6]. The generation of these nanoparticles based on the nucleation and growth theory (classical or non-classical crystallization pathway) for the formation of nanoparticles in natural systems is still a matter of debate. It could be shown, e.g., for magnetite, that the nanoparticle formation in natural systems proceeds through rapid agglomeration of nanometric primary particles. In contrast to the nucleation of other minerals, no intermediate bulk phase is involved [7]. Nucleation and nanoparticle formation, associated with surfaces, are also key aspects of the formation of, e.g., Au ore deposits and hydrothermal vents [2,8], also referred to as the field of nanogeolog

Cloning and characterization of an adenoviral vector for highly efficient and doxycycline – suppressible expression of bioactive human single – chain interleukin 12 in colon cancer

BACKGROUND: Interleukin-12 (IL-12) is well characterized to induce cellular antitumoral immunity by activation of NK-cells and T-lymphocytes. However, systemic administration of recombinant human IL-12 resulted in severe toxicity without perceptible therapeutic benefit. Even though intratumoral expression of IL-12 leads to tumor regression and long-term survival in a variety of animal models, clinical trials have not yet shown a significant therapeutic benefit. One major obstacle in the treatment with IL-12 is to overcome the relatively low expression of the therapeutic gene without compromising the safety of such an approach. Our objective was to generate an adenoviral vector system enabling the regulated expression of very high levels of bioactive, human IL-12. RESULTS: High gene expression was obtained utilizing the VP16 herpes simplex transactivator. Strong regulation of gene expression was realized by fusion of the VP16 to a tetracycline repressor with binding of the fusion protein to a flanking tetracycline operator and further enhanced by auto-regulated expression of its fusion gene within a bicistronic promoter construct. Infection of human colon cancer cells (HT29) at a multiplicity of infection (m.o.i.) of 10 resulted in the production of up to 8000 ng/10(6 )cells in 48 h, thus exceeding any published vector system so far. Doxycycline concentrations as low as 30 ng/ml resulted in up to 5000-fold suppression, enabling significant reduction of gene expression in a possible clinical setting. Bioactivity of the human single-chain IL-12 was similar to purified human heterodimeric IL-12. Frozen sections of human colon cancer showed high expression of the coxsackie adenovirus receptor with significant production of human single chain IL-12 in colon cancer biopsies after infection with 3*10(7 )p.f.u. Ad.3r-scIL12. Doxycycline mediated suppression of gene expression was up to 9000-fold in the infected colon cancer tissue. CONCLUSION: VP16 transactivator-mediated and doxycycline-regulated expression of the human interleukin-12 gene enables highly efficient and tightly controlled cytokine expression in human cancer. These data illustrate the potential of the described adenoviral vector system for the safe and superior expression of therapeutic genes in the treatment of colorectal cancer and other malignancies