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21.
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. 相似文献
22.
Sylvain Meille Malika Sadaoui Pascal Reynaud Gilbert Fantozzi 《Journal of the European Ceramic Society》2003,23(16):3105-3112
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. 相似文献
23.
Anne‐Lise Bottalla Malika Ibrahim‐Ouali Maurice Santelli Roland Furstoss Alain Archelas 《Advanced Synthesis \u0026amp; Catalysis》2007,349(7):1102-1110
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. 相似文献
24.
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... 相似文献
25.
Thouraya Merazi-Meksen Akila Kemmouche Malika Boudraa Bachir Boudraa 《Journal of Nondestructive Evaluation》2017,36(4):67
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. 相似文献
26.
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. 相似文献
27.
Applicability of Adapted Reservoir Operation for Water Stress Mitigation Under Dry Year Conditions 总被引:3,自引:2,他引:1
Oliver Olsson Malika Ikramova Melanie Bauer Jochen Froebrich 《Water Resources Management》2010,24(2):277-297
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. 相似文献
28.
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. 相似文献
29.
Thouraya Merazi Meksen Bachir Boudraa Malika Boudraa 《International Journal of Adaptive Control and Signal Processing》2012,26(5):375-383
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. 相似文献
30.
Foued El Ayni Semia Cherif Amel Jrad Malika Trabelsi-Ayadi 《Water Resources Management》2011,25(9):2251-2265
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. 相似文献