Secure key distribution over a 500 km long link using a Raman ultra‐long fiber laser

In traditional communication systems the transmission medium is considered as a given characteristic of the channel, which does not depend on the properties of the transmitter and the receiver. Recent experimental demonstrations of the feasibility of extending the laser cavity over the whole communication link connecting the two parties, forming an ultra‐long fiber laser (UFL), have raised groundbreaking possibilities in communication and particularly in secure communications. Here, a 500 km long secure key distribution link based on Raman gain UFL is demonstrated. An error‐free distribution of a random key with an average rate of 100 bps between the users is demonstrated and the key is shown to be unrecoverable to an eavesdropper employing either time or frequency domain passive attacks.     

Influence of iterated Gram–Schmidt orthonormalization in the asymptotic numerical methodInfluence de l'orthonormalisation itérative de Gram–Schmidt dans la méthode asymptotique numérique

In this paper we discuss the influence of Gram–Schmidt orthonormalization for the computation of the rational representation in the asymptotic numerical method. Classical, modified and iterated Gram–Schmidt algorithms are compared using the ordinary and the mass scalar products. The accuracy of the proposed algorithms are tested on elastic shells. To cite this article: R. Jamai, N. Damil, C. R. Mecanique 331 (2003).     

Synthese de 5-Aryl-3-[(1-dialcoxyphosphonyl)methyl]-1,2,4-triazoles a Partir d'Imidates N-Chloroacyles

A variety of 5-aryl-3-[(1-dialcoxyphosphonyl)methyl]-1,2,4-triazoles 3 has been synthesized efficiently by treatment of trialkylphosphites with 5-aryl-3-chlorométhyl-1,2,4-triazoles 2 . Compound 2 has been prepared by action of N-chloroacylimidates 1 with hydrazines. The structure of triazoles 2 and 3 have been unequivocally confirmed by means of IR, 1 H, 13 C, 31 P NMR spectroscopy and mass spectra.     

Hindered Rotation in Some Organic Dithiocarbamates

Abstract

Hindered rotation in alkyldithiocarbamates of the type RR′NC(= S)SR″ [R, R′, R″ = Me, Me, Et (1); PhCH₂, Me, Et (2); PhCH₂, H, Et (3); PhCH₂, H, Me (4) and O(CH₂CH₂)₂, Et (5)′ has been investigated using variable-temperature ¹H NMR spectroscopy in CDCl₃, C₆D₆, and DMSO-d₆ solutions. Rotational parameters were calculated by the coalescence temperature method. Nitrogen substituent effects on the free energy of activation and on the equilibrium constant of unsymmetrical conformers at room temperature are discussed.     

MOLECULAR REARRANGEMENT OF SULPHUR COMPOUNDS (PART I). PYROLYSIS OF SOME SUBSTITUTED RHODANINE

Abstract

Thermal rearrangement of 3-phenylrhodanine (I) and 5-benzylidene-3-phenylrhodanine (IV) in air has been thoroughly investigated. Homolytic cleavage of (C—S) and (C—N) bonds occurred, followed by a series of hydrogen abstractions, coupling, and cyclization reactions. The isolated products of compound (I) are CS₂, CO, H₂S, NH₃, aniline, dibenzylamine, tribenzylamine, thioglycolic acid, phenyl isothiocyanate, bibenzyl. stilbene, p-arninoacetophenone, thiocarbanilide, 2-thioxoindole and 2,3,4,5-tetraphenylthiophene. In case of compound (IV), the isolated products are CS₂, H₂S, H₂O, CO, phenyl isothiocyanate, benzothiophene, 2-phenylquinoline, aniline, thiocarbanilide, 2-phenylindole, cinnamic acid and polystyrene. A suitable mechanism has been suggested to account for the obtained products.     

Reactivite Des α -Phosphonylketones Dans la Reaction de Gewald: Synthese de Nouveaux Derives de L′aminophosphonothiophene

The reaction of α -phosphonylketones 1 with active methylenenitriles 2 leads to phosphonoalkylidenes 3 . The reaction of compounds 3 with sulfur under basic conditions leads to the new 2-amino-4-phosphonothiophenes 4 . The structure of all obtained products was confirmed by NMR (¹H, ³¹P, ¹³C) and IR spectroscopy, and in some cases by mass spectrometry.     

X-ray and computational structural study of neutral <Emphasis Type="Italic">bis</Emphasis>(<Emphasis Type="Italic">N,N,N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-tetramethylthiophosphoramidoyl)-methylamine

The structure of bis(N,N,N′,N′-tetramethylthiophosphoramidoyl)-methylamine 1 has been determined by single-crystal X-ray diffraction. The compound 1 crystallizes in the monoclinic system, with a space group P2₁/c, a = 11.836(2) Å, b = 11.659(2) Å, c = 12.796(5) Å and β = 95.28(3)°, V = 1758.3(5) Å³ and Z = 4. The X-ray crystallographic data have been assessed by semi-empirical and ab-initio density functional theory and by Hartree–Fock molecular orbital methods. A comparative study of the results of the different methods is given.     

Removal of Evans Blue by using Nickel-Iron Layered Double Hydroxide (LDH) Nanoparticles: Effect of Hydrothermal Treatment Temperature on Textural Properties and Dye Adsorption

Summary: The use of low-cost adsorbent has been investigated as a replacement for the current expensive methods of removing dyes from wastewater. The sorption of acid dye (Evans Blue) from aqueous effluents onto anionic clays (hydrotalcite-like) has been studied. Hydrotalcite may be an effective adsorbent of organic molecules due to its hydrophobic nature and the accessibility of its interlayer region. Ni/Fe layered double hydroxide (LDH), with a molar ratio of 3, were synthesised by coprecipitation followed by hydrothermal treatment at different temperatures (85, 100 and 140 °C) for 4 days. The materials were characterised by X-ray powder diffraction (XRD), infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption-desorption (BET). The diffractograms and FT-IR spectroscopy of the fresh materials showed that the hydrotalcite is present in all samples. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO, XRD and Infrared spectroscopy complemented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity. TEM showed that crystal size increased with aging temperature, so that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. The surface area decreased with increasing the hydrothermal treatment temperature. The effects of various parameters such as hydrothermal treatment temperature, crystallite size, contact time and calcination on the extent of adsorption were investigated. The studies of the removal efficiency of the reactive textile dye: Evans Blue (Direct Blue 53) by NiFeCO₃ HDLs showed that the effect of hydrothermal treatment temperature on adsorption increases with aging temperature. The Evans Blue (EB) removal percent increased with increasing contact time. Above the 70%, 50% and 20% of EB adsorption occurred in the first 2 min for HDL-140, HDL-100 and HDL-85°C respectively. Furthermore, it was found that the calcined materials are much more effective than the original LDH in removing Evans Bleu dye from an aqueous solution.     

Mixed Aluminum‐Magnesium‐Rare Earth Allyl Catalysts for Controlled Isoprene Polymerization: Modulation of Stereocontrol

Summary: The performances of readily available Ln(allyl)₂Cl(MgCl₂)₂ · (THF)₄ precursors (Ln = Nd, 1 ; Y, 2 ; La, 3 ), in combination with alkyl aluminum activators [MAO, AlMe₃, AlEt₃, Al(iBu)₃], have been studied in isoprene polymerization. The catalyst combination 1 /MAO (1:30) shows a high activity (average TOFs up to ca. 5 × 10⁴ mol (Ip) · mol (Nd)⁻¹ · h⁻¹ at 20 °C) and produces polyisoprene in a controlled fashion with up to 98.5% cis content, number‐average molecular weights in reasonable agreement with calculated values, and relatively narrow polydispersities index ( = 1.20–1.70). The yttrium precursor 2 affords systems with much lower activity and degree of control, but enables the formation of either 1,4‐cis‐enriched (75%) or 1,4‐trans‐enriched (91%) polyisoprenes, simply replacing the MAO activator by AlEt₃ or Al(iBu)₃, respectively.

Formation of 1,4‐cis‐ or 1,4‐trans‐enriched polyisoprenes upon activation with MAO.