Impact of Water Consumption and Saturation-Dependent Corrosion Rate on Hydrogen Generation and Migration from an Intermediate-Level Radioactive Waste Repository

The corrosion of metals contained in intermediate-level long-lived waste (ILW) under reduced chemical condition will lead to the production of hydrogen gas during the post-closure phase of a deep geological repository for radioactive waste. According to previous investigations by Talandier et al. (Proceedings of TOUGH symposium 2006, Berkeley, 2006), the period of concern covers several 1,000 years after closure of a repository in a clay host rock (Callovo-Oxfordian). The limited hydrogen transport efficiency of the host rock will lead to significant saturation of the concrete waste canister pore space and voids with a gas phase and pressure build-up within the emplacement drifts. On the other hand, the water availability is limited as a result of (i) the low permeability of the clay host rock and (ii) the desaturation of the rock mass close to the drift wall due to the ventilation of the drifts during the operational phase of the repository. In former numerical simulations it was assumed that under the reducing chemical conditions prevailing in the repository, the corrosion rate would be a function of the available metal surface and the temperature only. In this paper, simulation results based on new phenomenological functions are presented, which were implemented in TOUGH2. These allow taking into account (i) a water saturation dependency of the hydrogen generation rate, (ii) the water consumption due to the corrosion process, and (iii) the total metal mass available for corrosion. The paper presents results of 1D radial and 2D vertical simulations of a typical cross-section of a waste emplacement drift and the surrounding rock mass. The interactions between water availability from the low permeable clay, the dependency of the hydrogen generation rates from the water saturation of the waste package and the hydrogen migration in the host rock are demonstrated.     

A simplified poly(dimethylsiloxane) capillary electrophoresis microchip integrated with a low-noise contactless conductivity detector

A contactless conductivity detector integrated into a poly(dimethylsiloxane) microchip for electrophoresis is presented. It adopted the simplest configuration of electrodes commonly used in this detection mode for capillary electrophoresis microchips. Although the chip is based on a simple and effective design, it is able to obtain low detection levels due to the low noise of the detection circuit. A circuit based on a lock-in amplifier was designed on printed circuit boards to read out the signal. The property of the detection cell was studied by applying excitation signals of different frequencies and different amplitudes. It was found that the best detection limit could be achieved with a frequency of 50?kHz and amplitude of 20?V. The performance of the detector was demonstrated by successfully separating and detecting several inorganic ions and also a mixture of heavy metal ions. An average detection limit of 0.4?μM was obtained for inorganic cations. This value is significantly improved compared to similar microchip-based detectors. The presented detector could be promising for mass production due to its properties, such as simple construction, high degree of integration, high performance and low cost.     

Evaluation of settled floor dust for the presence of microbial metabolites and volatile anthropogenic chemicals in indoor environments by LC-MS/MS and GC-MS methods

This study reports on detection of a large number of biological and anthropogenic pollutants using LC-MS/MS and GC-MS technologies in settled floor dust (SFD). The latter technique was applied to obtain a general picture on the presence of microbial as well as non-microbial volatile organic compounds, whereas the targeted LC-MS/MS analysis focused on identification of species specific secondary metabolites. In the absence of moisture monitoring data the relevance of finding of stachybotrylactam and other metabolites of tertiary colonizers are confined only to accidental direct exposure to SFD. To the best of our knowledge 30 of the 71 identified volatile organic compounds (VOCs) are newly reported in SFD matrix. Coordinated application of “AMDIS and Spectconnect” was found beneficial for the evaluation and identification of prime volatile pollutants in complex environmental samples. Principal component analysis (PCA) of peak areas of 18 microbial volatile organic compounds (MVOCs) resulted in identification of nonanal as potential MVOC marker. Two more volatiles toluene and 1-tetradecanol though had discriminative influence, are not regarded as MVOC markers, considering their probable alternate origin from paints and cosmetics, respectively.     

Axially chiral bichromophoric fluorescent dyes

A new life for Kurt Mislow's authentic amines: Diaminobiphenyls were applied as the framework materials for the synthesis of axially chiral bichromophoric systems with strong CD and CPL effects.     

Dielectrophoretic assembly of lead zirconate titanate microtubes

Lead zirconate titanate (PZT) microtubes were assembled onto pre-patterned substrates using dielectrophoresis of a colloidal suspension of microtubes dispersed in isopropyl alcohol. High aspect ratio tubes with an outer diameter of 2 μm and length of about 30 μm were prepared by vacuum infiltration of mesoporous silicon templates. An interdigitated electrode structure with gap sizes ranging from 2 μm to 15 μm was patterned on a silicon substrate via conventional lithography. This allowed a non-uniform alternating electric field to be generated. The influence of the electrode gap along with the effects of the waveform, amplitude and frequency of an applied signal on the dielectrophoretic assembly of PZT microtubes was investigated. A square wave signal of 5 and 10 Hz was found to be the most effective in assembling the microtubes on a 12 μm electrode gap. The results show potential for the dielectrophoretic technique in realizing integrated 3D devices using the high aspect ratio piezoelectric tube structures as building blocks.     

A novel 2D vanadium(V)-isonicotinohydrazide coordination polymer, C15H16AgN4O8V: Synthesis, structure, catalytic activity and DFT calculation

A novel two-dimensional 3d-4d transition metal-based coordination polymer [VO(OCH₃)(OHCH₃)(L)Ag(NO₃)]_∞ (1) has been synthesized and characterized by single crystal X-ray diffraction and fluorescence spectroscopy (H₂L = (E)-N′-(2-hydroxybenzylidene)isonicotinohydrazide). The coordination sphere of each V center is octahedral and chelates to a tridentate ligand L, while the tetrahedral conformation of Ag center consists of two O and two N atoms. Infinite zigzag chains of Ag-tetrahedrals are formed. The hydrazinide L²⁻ ligands of octahedral-V centers link adjacent chains to form an undulated heterometal based 2D layer. DFT calculations on 1 reproduced the geometric parameters and the electronic absorptions were predicted. The coordination polymer 1 showed very selective heterogeneous catalytic activity with 77-89% conversion in oxidation of alkenes, cyclooctane and benzyl alcohol by H₂O₂.     

Computing logarithms digit-by-digit

In this work, we present an algorithm for computing logarithms of positive real numbers, that bears structural resemblance to the elementary school algorithm of long division. Using this algorithm, we can compute successive digits of a logarithm using a 4-operation pocket calculator. The algorithm makes no use of Taylor series or calculus, but rather exploits properties of the radix-d representation of a logarithm in base d. As such, the algorithm is accessible to anyone familiar with the elementary properties of exponents and logarithms.     

A numerical study of highly-diluted,burner-stabilised dimethyl ether flames

Recently, a new burner was designed by Zhang et al. (Proc. Combust. Inst. 34 [2013], 763–770) to enable the investigation of 1D, premixed flames at atmospheric pressure with a temperature in the burnt gases near 1500 K. It consists of a matrix burner plate with alternating fuel and oxidiser feeds that, because of small-scale nozzles, mix quite rapidly. Flames at high dilution and reduced temperatures such as realised here are of relevance for the understanding of low-temperature combustion strategies. In this work, we examine the burner with regard to the validity of the 1D assumption for the investigated flames. Experimental measurements are conducted and 1D and 3D simulations are performed in which the chemistry is described by a detailed chemistry approach based on a reduced reaction scheme derived from the mechanism of Fischer et al. (Int. J. Chem. Kinetics 32 [2000], 713–740). The experimental results are compared to 1D simulations with two different temperature treatments. First, the unburnt temperature is set to the measured temperature closest to the burner surface; second, the experimental temperature profile is prescribed in the whole simulation domain without solving the energy equation. The comparison shows that the 1D simulation predicts the experimental results reasonably well, if the experimentally obtained temperature profile is prescribed in the simulation domain. Differences are found in the mole fractions of methyl and formaldehyde. Further comparisons of the experimental data with 3D simulation results and comparisons of 3D and 1D simulation results indicate that the differences between measured and computed mole fractions of these species are not a result of the 3D nature of the experimental flame and might be attributed to the chemical mechanism. The conclusion is that the measurement data can be used for validation purposes with the 1D simulation setup shown here if the measured temperature profiles are prescribed in the 1D simulation domain.     

Reporting requirements for sulphur isotope measurements on environmental samples†

It is strongly encouraged that authors reporting sulphur isotope data for environmental samples provide detailed information regarding (1) the reproducibility of their extraction procedure for the sulphur compound of interest, (2) the measuring gas and mass spectrometer technique used, and (3) the δ³⁴S values assigned for the reference materials utilised in the study. This would greatly facilitate comparisons of sulphur isotope data generated in different laboratories world-wide.