Action des hydrazines fluoroalkylées sur les phosphoallènes: synthèse d’hydrazones N-fluoroalkylées β-phosphonatées

Ten phosphorylated β-hydrazones of structure R₂P(O)C(NNHR_F)CHR₂′ were prepared in 54-91% yield by heating the allenes R₂P(O)CHCCR₂′ with fluorinated hydrazines H₂NNHR_F in chloroform or methanol [R=Ph, OCH₂C(Me)₂CH₂O or OCH₂C(Me)(Pr)CH₂O, R′=H or Me and R_F=CH₂CF₃ or C₆F₅]. Two cyclohexyl derivatives were prepared similarly from R₂P(O)CHCCy. The triphenyl derivatives Ph₂P(O)CH₂C(NNHCH₂CF₃)Ph and Ph₂P(O)CH₂C(NNHC₆F₅)Ph were made in 91 and 68% yield by heating the ketones Ph₂P(O)CH₂C(O)Ph with an ethanol solution of the corresponding hydrazines. The stereochemistry of the hydrazones was determined by multinuclear NMR experiments. Compounds with C(NNHR_F)Me groups exist as a mixture of Z and E isomers, with the Z form predominating (fluorinated group syn to phosphorus). Those with C(NNHR_F)CHMe₂, C(NNHR_F)Cy or C(NNHR_F)Ph groups were formed selectively, the Z isomers being the only products. The results are explained by steric hindrance, the bulkier isopropyl, cyclohexyl or phenyl group disfavouring the E configuration. , , , NMR data, coupling constants and IR data are reported.     

Flexible all-plastic mirrors for the THz range

We present a simple and cheap approach to fabricate large-area stop-band filters and mirrors for the THz range. This approach extends the well-known concept of dielectric mirrors to the far infrared. We use alternating layers of different polymer materials with a typical thickness of several tens of micrometers to build a flexible all-plastic mirror. The structures are characterized by THz time-domain spectroscopy. The experimental results are in good agreement with transfer-matrix simulations. Received: 28 September 2001 / Accepted: 4 October 2001 / Published online: 20 December 2001     

Wigner Measures Approach to the Classical Limit of the Nelson Model: Convergence of Dynamics and Ground State Energy

We consider the classical limit of the Nelson model, a system of stable nucleons interacting with a meson field. We prove convergence of the quantum dynamics towards the evolution of the coupled Klein–Gordon–Schrödinger equation. Also, we show that the ground state energy level of \(N\) nucleons, when \(N\) is large and the meson field approaches its classical value, is given by the infimum of the classical energy functional at a fixed density of particles. Our study relies on a recently elaborated approach for mean field theory and uses Wigner measures.     

Eco‐friendly conductive polymer nanocomposites (CPC) for solar absorbers design

To reduce both the cost and the environmental impact of copper‐based thermal solar absorbers, we have investigated their possible substitution by bio‐based conductive polymer nanocomposite (CPC) elements. Our results show that carbon nanotubes (CNT) have no significant influence on polymers’ calorimetric properties such as T_m and T_g but lead to a strong increase in crystallinity of poly(lactic acid) (PLA) and to a lesser extent of poly(amide 12) poly(amide 12) (PA12) for 2 and 3 CNT wt % respectively. Percolation thresholds as low as 0.5 and 0.58 were obtained for PA12 and PLA, respectively, and visco‐elastic properties such as η*, G’ and G” were found to increase exponentially with CNT content confirming the formation of a CNT network within the matrix. All CPC are absorbing more energy in the visible and infrared than in the ultraviolet wavelength ranges. Finally, the thermal conductivity k of PLA–CNT and PA12–CNT were increased, respectively, of 85% and 24%, to reach 0.28 W.m^?1.K^?1 and 0.26 W.m^?1.K^?1, for only 5 wt% CNT. The figure of merit suggests that PA12 is the polymer which satisfies at best all criteria, particularly combining a lower viscosity at almost equivalent thermal conductivity and absorptivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Visible‐Light‐Driven Strain‐Increase Ring Contraction Allows the Synthesis of Cyclobutyl Boronic Esters

There are a limited number of ring‐contraction methodologies which convert readily available five‐membered rings into strained four‐membered rings. Here we report a photo‐induced radical‐mediated ring contraction of five‐membered‐ring alkenyl boronate complexes into cyclobutanes. The process involves the addition of an electrophilic radical to the electron‐rich alkenyl boronate complex, leading to an α‐boryl radical. Upon one‐electron oxidation, ring‐contractive 1,2‐metalate rearrangement occurs to give a cyclobutyl boronic ester. A range of radical precursors and vinyl boronates can be employed, and chiral cyclobutanes can be accessed with high levels of stereocontrol. The process was extended to the preparation of benzofused cyclobutenes and the versatility of the boronic ester was demonstrated by conversion to other functional groups.     

Classification systems based on rough sets under the belief function framework

In this paper, we present two classification approaches based on Rough Sets (RS) that are able to learn decision rules from uncertain data. We assume that the uncertainty exists only in the decision attribute values of the Decision Table (DT) and is represented by the belief functions. The first technique, named Belief Rough Set Classifier (BRSC), is based only on the basic concepts of the Rough Sets (RS). The second, called Belief Rough Set Classifier, is more sophisticated. It is based on Generalization Distribution Table (BRSC-GDT), which is a hybridization of the Generalization Distribution Table and the Rough Sets (GDT-RS). The two classifiers aim at simplifying the Uncertain Decision Table (UDT) in order to generate significant decision rules for classification process. Furthermore, to improve the time complexity of the construction procedure of the two classifiers, we apply a heuristic method of attribute selection based on rough sets. To evaluate the performance of each classification approach, we carry experiments on a number of standard real-world databases by artificially introducing uncertainty in the decision attribute values. In addition, we test our classifiers on a naturally uncertain web usage database. We compare our belief rough set classifiers with traditional classification methods only for the certain case. Besides, we compare the results relative to the uncertain case with those given by another similar classifier, called the Belief Decision Tree (BDT), which also deals with uncertain decision attribute values.     

Phase transitions and vibrational study of Rb2SeO4·Te(OH)6 and Rb1.12(NH4)0.88SO4·Te(OH)6

Calorimetry, conductivity, IR and Raman studies of the two ionic-protonic conductors Rb₂SeO₄·Te(OH)₆ (RbSeTe) and Rb_1.12(NH₄)_0.88SO₄·Te(OH)₆ (RNST) have been recorded and analyzed. These compounds crystallize in the monoclinic system, the space groups being, respectively, P2₁/c and P2₁/a for (RbSeTe) and (RNST) with four formula units in their unit cells.

The main feature of these atomic arrangements is the coexistence of two independent and different types of anions in the unit cell, connected by hydrogen bonds, which insure the cohesion of the crystalline edifice. Differential scanning calorimetry traces show three peaks for both the materials, corresponding to three phase transitions, at 430, 470 and 493 K for RbSeTe and at 418, 458 and 483?K for RNST.

A sudden surge in the temperature dependence of conductivity confirms the presence of the third transition, which is characterized by a high conductivity. The Raman spectra of these two materials were investigated in the range 295–600?K and IR spectra achieved at room temperature between 10 and 4000?cm^?1, confirm the presence of the phase transitions and show that anionic groups coexist independently in the same crystal.     

Investigation of electrocoagulation reactor design parameters effect on the removal of cadmium from synthetic and phosphate industrial wastewater

This study investigates the effect of reactor design parameters on cadmium removal from industrial wastewater discharged by the Tunisian Chemical Group (TCG) to improve as much as possible efficiency and cost of electrocoagulation (EC) process. Based on an examination of the design parameters one by one, the best cadmium removal was achieved for an inter-electrode distance (d_ie) of 0.5 cm, monopolar connection mode, stirring speed of 300 rev min^?1, surface-area-to-volume ratio (S/V) of 13.6 m^?1, and an initial temperature of 50 °C. These operating conditions are allowed to achieve efficient removal in a relatively short operating time with the lowest energy consumption and cost possible. The present study proved that the parameters that have an effect on the operating cost are the electrode configuration, inter-electrode distance and S/V ratio. The energy consumption, the pH evolution, and the treatment cost were studied. The investigation of the effect of all the selected optimum EC design parameters together on the removal of cadmium from the TCG wastewater proved that the treatment was highly efficient; 100% of cadmium removal was reached in 5 min, with a very low power consumption (1.6 kW h m^?3) and very low cost (0.116 TND m^?3). Moreover, EC was found to be capable of removing cadmium as well as other pollutants at the same time from the case-study industrial wastewater. The investigation carried out in this work explores and proposes a very cost-effective treatment method to remove heavy metals from industrial wastewater if compared to results reported about cost of this treatment process through other widely used technologies such as coagulation (4.36 Tunisian National Dinar (TND) m^?3) and precipitation (9.96 TND m^?3) employed in previous studies.     

Small cycle structure for words in conjugation invariant random permutations

We study the cycle structure of words in several random permutations. We assume that the permutations are independent and that their distribution is conjugation invariant, with a good control on their short cycles. If, after successive cyclic simplifications, the word $w$ still contains at least two different letters, then we get a universal limiting joint law for short cycles for the word in these permutations. These results can be seen as an extension of our previous work (Kammoun and Maïda. Electron. Commun. Probab. 2020;25:1-14.) from the product of permutations to any non-trivial word in the permutations and also as an extension of the results of Nica (Random Struct. Algorithms1994;5:703-730.) from uniform permutations to general conjugation invariant random permutations. In particular, we get optimal assumptions in the case of the commutator of two such random permutations.