Selective determination of ascorbic acid with a novel hybrid material based 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and the Dawson type ion [P2Mo18O62] immobilized on glassy carbon

In this study, we synthesized a new hybrid material using well-Dawson K₆[P₂Mo₁₈O₆₂]·nH₂O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). CHN elemental analysis showed that one mole of [P₂Mo₁₈O₆₂]⁶⁻ reacts with 6 moles of [BMIM]⁺ to form [BMIM]₆P₂Mo₁₈O₆₂. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid material compared to the parent Dawson POM. The new hybrid material [BMIM]₆P₂Mo₁₈O₆₂ was immobilized on glassy carbon (GC) electrode and the modified electrode was investigated by cyclic voltammetry and amperometry. Compared to the electrochemical behavior of dissolved [P₂Mo₁₈O₆₂]⁶⁻, a slight shift in the redox peaks towards negative potentials is observed for the immobilized [BMIM]₆P₂Mo₁₈O₆₂. The relationship between the peak currents of the deposited [BMIM]₆P₂Mo₁₈O₆₂ film and scan rate is shown to be linear, which demonstrates a surface-confined electron transfer processes. [BMIM]₆P₂Mo₁₈O₆₂ modified electrode showed high sensitivities towards pH and shown to be active even at neutral pH. [BMIM]₆P₂Mo₁₈O₆₂ modified GC electrode was subjected to cyclic voltammetry and amperometry in the presence of ascorbic acid (AA) and found to exhibit a remarkable catalytic activity towards the oxidation of AA. The catalytic oxidation peak of AA at [BMIM]₆P₂Mo₁₈O₆₂ modified GC electrode occurs at low potential of ∼0 V vs Ag/AgCl at neutral pH and shifts to more positive potentials when pH decreases. Comparison between [BMIM]₆P₂Mo₁₈O₆₂ and [P₂Mo₁₈O₆₂]⁶⁻ modified GC films towards the oxidation of AA suggests that the significant decrease in the overpotentials recorded with [BMIM]₆P₂Mo₁₈O₆₂ film is related to the presence of ionic liquid cation in the hybrid material, which probably plays the role of the redox mediator. The resulting AA sensor [BMIM]₆P₂Mo₁₈O₆₂/GC has a significant sensitivity of ∼63 nA/μM AA, fast response time (<9 s), low detection limit (<0.1 μM), high selectivity towards endogenous interferences such as uric acid, acetaminophen and dopamine, a linear range from 0.1 μM to at least 22 mM AA and was stable for at least 2 weeks. In addition, such AA sensors can operate in a pH range from 0 to at least 7.     

Mechanisms of crack propagation in dry plaster

Controlled crack propagation tests were performed on single edge notched bend samples to investigate the crack growth behaviour of dry plaster. The influence of the relative notch depth on the crack resistance curve has been studied and appears to be very important. The results are discussed considering a qualitative model based on the specific microstructure of plaster and in situ observations of the crack propagation. Two mechanisms acting at different scales and undergoing complex interactions are involved: crack bridging by small gypsum crystals acting locally behind the crack tip and secondary cracking in a macroscopic frontal process zone. Interaction of the main crack with secondary ones undergoes substantial branching and crack accelerations leading to bridging destruction due to sudden crack opening.     

Epoxide Hydrolase‐Catalysed Kinetic Resolution of a Spiroepoxide,a Key Building Block of Various 11‐Heterosteroids

Two microbial epoxide hydrolases – i.e., Aspergillus niger (AnEH) and Rhodococcus erythropolis (the so‐called “Limonene EH”: LEH) were used to achieve, for the first time, the biocatalysed hydrolytic kinetic resolution (BHKR) of spiroepoxide rac‐ 1 . This compound is a strategic key building block allowing the synthesis of 11‐heterosteroids. Interestingly enough, the two enzymes exhibited opposite and therefore complementary enantioselectivity allowing us to isolate the residual (R,R)‐ 1 (from AnEH) and the residual (S,S)‐ 1 (from LEH) in nearly enantiopure forms (>98 %). Their absolute configurations were determined by X‐ray crystallography. An opposite regioselectivity of the oxirane ring opening for both enantiomers of substrate 1 , determined using H₂¹⁸O labelling and chiral GC‐MS analysis, was also observed, corresponding to an attack at the less substituted carbon atom using AnEH, and at the most substituted carbon atom using LEH. A chemical process‐improving methodology was also developed. This allowed us to obtain both enantiomers of the substrate in high enantiomeric purity (99 %) and optimised quantity. In the case of the AnEH, the use of a biphasic (water/isooctane) reaction medium allowed us to increase the global substrate concentration up to 200 g/ L. The preparation of both enantiomers of 1 clearly paves the way to the preparative scale synthesis and biochemical evaluation of the corresponding 11‐heterosteroid enantiomers.     

The Solutions on One-Dimensional Dirac Oscillator with Energy-Dependent Potentials and Their Effects on the Shannon and Fisher Quantities of Quantum Information Theory

Journal of Low Temperature Physics - In this paper, we focus, at first, on the exact solutions on the one-dimensional Dirac oscillator with the energy-dependent potentials. Then, the influence of...     

Sparse Representations to Replace TOFD Images in Non-destructive Testing of Materials

This paper describes a proposed method for the selection of relevant samples of ultrasonic signals during automatic material inspection. Instead of the well-known time of flight diffraction (TOFD) images, data are stored as a sparse matrix in which the elements only indicate whether a defect has been detected. This technique avoids storage of useless signals received during probe displacement in cases of low and high signal-to-noise ratios that correspond to coarse-grained and fine-grained materials, respectively. The approach is based on comparing the positions of maximum amplitudes, which are randomly located when signals only consist of noise but are in the same signal range when a defect is detected. The matrix elements are then applied as inputs to a self organizing map by neural networks to produce a normalized sparse matrix as the output, with a constant number of elements. This approach will be beneficial to enable the use of selected data in intelligent systems requiring a fixed number of inputs to characterize defects.     

How to explain modern security concepts to your children

At the main cryptography conference, CRYPTO, in 1989, Quisquater and colleagues published a paper showing how to explain the complex notion of zero-knowledge proof in a simpler way that children can understand. In the same line of work, this article presents simple and intuitive explanations of various modern security concepts and technologies, including symmetric encryption, public key encryption, homomorphic encryption, intruder models (CPA, CCA1, CCA2), and security properties (OW, IND, NM). The explanations given in this article may also serve in demystifying such complex security notions for non-expert adults.     

Applicability of Adapted Reservoir Operation for Water Stress Mitigation Under Dry Year Conditions

This paper introduces the conjunctive use of a deterministic water quality model and water balance criteria for supporting the assessment of simulation and to evaluate the effectiveness of proposed operation strategies. By this, the applicability of enhanced reservoir operation strategies addressing both water quality as well as water quantity aspects under water deficit conditions in dry years can be shown. Arguments will be developed to address stakeholders and decision makers in the context of a more conservative past operation regime. Results are presented for the Kaparas reservoir, which is located in the lower Amu Darya River, on the border of Turkmenistan and Uzbekistan. As being one out of four large reservoirs of the Tuyamuyun Hydro Complex (THC), the Kaparas reservoir could be increasingly used for drinking water supply for the lower Amu Darya region. The results for the dry year 2001 indicates that the combination of simulation together with practical assessment criteria confirm the applicability of adapted operation rules for THC reservoirs and ways can be found to supply the local population (of the lower Amu Darya region) with more potable water of higher quality even subject to a parallel reduction of water deficits. Future aggravation of water stress due to increasing population growth and water quality deterioration will require a more comprehensive consideration of water quality aspects in many arid and semi arid regions. The experience gained during this study emphasizes the fact that classical deterministic water quality models provide effective tools to address even more complex water quality problems under water stressed conditions, provided processing of results is performed, to support the decision making process.     

[As8W48O184], a new crown-shaped heteropolyanion: Electrochemistry and electrocatalytic properties towards reduction of nitrite

The electrochemical behavior of the new crown-shaped heteropolyanion [As₈W₄₈O₁₈₄]⁴⁰⁻ was investigated. Compared to the analogous complex [P₈W₄₈O₁₈₄]⁴⁰⁻, [As₈W₄₈O₁₈₄]⁴⁰⁻ displayed a close similar behavior. As previously reported for [P₈W₄₈O₁₈₄]⁴⁰⁻, [As₈W₄₈O₁₈₄]⁴⁰⁻ is found to be stable in a large range of pH, roughly from 0 to 8 and found to be slightly more soluble than [P₈W₄₈O₁₈₄]⁴⁰⁻. Comparison between the cyclic voltammetry curves of the two complexes reveals that the potentials of the redox waves of [As₈W₄₈O₁₈₄]⁴⁰⁻ are slightly shifted towards the positive values. Contrary to the high dependence of [P₈W₄₈O₁₈₄]⁴⁰⁻ to buffer capacity of the supporting electrolyte, interestingly, [As₈W₄₈O₁₈₄]⁴⁰⁻ displays less sensitivity. The numerous possibilities for chemical applications opened up by the electrochemistry of this new complex are exemplified here by the good linear relationship between the peak potentials of the redox waves as a function of pH and, by the electrocatalytic reduction of nitrite.     

A method to improve and automate flat defect detection during ultrasonic inspection

In the nondestructive testing of materials, ultrasonic imagery can detect and characterize defects that are present in a structure. Data are displayed in the form of images, and processing algorithms can be applied for automatic detection and characterization. However, when using diffracted waves, the amplitude is often too low, and the signals are difficult to distinguish from the noise. Other times, the volume of data requires significant computation time. In this paper, we propose a method that can avoid image formation by replacing it with a sparse matrix and significantly reducing the amount of data to process; this allows for the enhancement and the automation of the detection of thin and flat defects such as cracks. The elements of the sparse matrix form a curve, which is sufficient to characterize defects in many cases. These elements are selected from diffracted signals using the split‐spectrum processing method. In this way, the signal‐to‐noise ratio is improved, and the position of the echo signal is accurately determined. When a crack is present in a material, the points of the sparse matrix form a parabola and classical tools of pattern recognition such as the Hough transform can detect it, thus providing significant help in decision‐making processes. Copyright © 2011 John Wiley & Sons, Ltd.     

Impact of Treated Wastewater Reuse on Agriculture and Aquifer Recharge in a Coastal Area: Korba Case Study

Treated wastewater (TWW) reuse has increasingly been integrated in the planning and development of water resources in Tunisia. The present study aimed the evaluation of the environmental and health impact that would have the reuse of TWW for crops direct irrigation or for the recharge of the local aquifer in Korba (Tunisia). For this purpose water analyses were carried on the TWW intended for the aquifer recharge and on underground water of this area. As for underground water before recharge, no contamination by organic matter or heavy metals is shown but high salinity, nitrate, potassium and chloride concentrations are detected. The bacteriological analyses show the occurrence of faecal streptococcus, thermo-tolerant coliforms, total coliforms and E coli, but absence of salmonella. These results indicate that this water is not suitable for irrigation worse still for drinking purpose. The monitoring of TWW pollutants has demonstrated that oxygen demands (COD and BOD) do not exceed the Tunisian standards for TWW used in agriculture (NT 106.03) except for August when samples reach high values (COD = 139 mg O₂ L^− 1, BOD = 34). It is also the case for temperature, electrical conductivity (EC), salinity and pH. Heavy metal concentrations are under the detection limit. The determination of nutrients shows relatively low concentrations of nitrates, nitrites and orthophosphate (the maxima in mg L^− 1 are respectively 6.6, 5.6 and 0.92) whereas the potassium levels are high (up to 48.8 mg L^− 1) and the ammonia levels very high, reaching 60.6 mg L^− 1. As for bacteriological pollution, while no salmonella and intestinal nematods are detected, high concentrations of total coliforms, thermo-tolerant coliforms, faecal streptococci and E. coli are analysed. Consequently, the better use of TWW in this region would be the use of infiltration basins for the recharge of the deteriorated aquifer by TWW. It would give the opportunity to better the quality of the TWW reaching the groundwater by an additional treatment for bacteriological and suspended solid (TSS) contaminants while being an alternative water for the aquifer recharge and a coastal barrier against seawater intrusion.