Active control of the turbulent drag by a localized periodical blowing dissymmetric in time

Experimental results on the reaction of the near wall turbulence and drag to a localized time periodical blowing are reported. The injection velocity is periodical and dissymmetric in time, with a rapid acceleration phase followed by a slow deceleration one. The flow is relaminarized during 70% of the oscillation period mainly during the deceleration phase. The latter maintains stable the vorticity layer induced by the blowing and prevents its roll-up contrarily to a sinusoidal time periodical blowing. Thus, a time mean drag reduction of 50% is obtained in the region recovering 200 wall units downstream of the blowing slot and this is 40% larger than the drag reduction obtained by a steady blowing with the same time mean severity parameter. The dissymmetric blowing annihilates considerably the wall turbulence activity and gives better results in terms of drag reduction compared with steady and sinusoidal blowing.

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Palladium(II)‐N‐heterocyclic carbene complexes: synthesis,characterization and catalytic application

N‐Heterocyclic carbenes (NHCs) are of great importance and are powerful ligands for transition metals. A new series of sterically hindered benzimidazole‐based NHC ligands (LHX) ( 2a , 2b , 2c , 2d , 2e , 2f ), silver–NHC complexes ( 3a , 3b , 3c , 3d , 3e , 3f ) and palladium–NHC complexes ( 4a , 4b , 4c , 4d , 4e , 4f ) have been synthesized and characterized using appropriate spectroscopic techniques. Studies have focused on the development of a more efficient catalytic system for the Suzuki coupling reaction of aryl chlorides. Catalytic performance of Pd–NHC complexes and in situ prepared Pd(OAc)₂/LHX catalysts has been investigated for the Suzuki cross‐coupling reaction under mild reaction conditions in aqueous N,N‐dimethylformamide (DMF). These complexes smoothly catalyzed the Suzuki–Miyaura reactions of electron‐rich and electron‐poor aryl chlorides. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis, thermal stability, electronic features, and antimicrobial activity of phenolic azo dyes and their Ni(II) and Cu(II) complexes

Four water soluble azo dyes, 4-(isopropyl)-2-[(E)-(4-chlorophenyl)diazenyl]phenol (L ¹), 4-(isopropyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L²), 4-(sec-butyl)-2-[(E)-(4-chlorophenyl) diazenyl]phenol (L ³), 4-(sec-butyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L ⁴), and their Cu(II) and Ni(II) complexes were synthesized and characterized using spectroscopic methods. Examination of their thermal stability revealed similar decomposition temperature of approximately 260–300°C and that they were more thermally stable than their metal complexes. Ni(II) complexes of ligands L² and L⁴ were more stable than the other coordination compounds. Among the synthesized ligands, L² and the complexes Cu(L³)₂ and Ni(L⁴)₂ showed both antimicrobial and antifungal activity. However, the other ligands and the complexes were poorly active against selected microorganisms.     

Reactions of cyclochlorotriphosphazatriene with 2-mercaptoethanol. Calorimetric and spectroscopic investigations of the derived products

Abstract

The reactions of hexachlorocyclotriphosphazatriene, N₃P₃Cl₆ (1) with 2-mercaptoethanol, 2-HS-CH₂-CH₂-OH (2), in (1:1, 1:2 and 1:3) mole ratios, in excess of NaH, in THF and diethylether solutions yield a total of 6 novel products: one mono spiro, N₃P₃Cl₄[O-CH₂-CH₂-S] (3); one mono-substituted open chain, N₃P₃Cl₅[S-CH₂-CH₂-OH] (4); one dispiro, N₃P₃Cl₂[O-CH₂-CH₂-S]₂ (5); one tri-substituted open chain, N₃P₃Cl₃[S-CH₂-CH₂-OH]₃ (6); one tris-spiro, N₃P₃[O-CH₂-CH₂-S]₃ (7) and one disubstituted open chain, N₃P₃Cl₄[S-CH₂-CH₂-OH]₂ (8) derivatives. The spiro products (3, 5 and 7) are formed as the major products in this system and all of the synthesized compounds are found to be stable at room temperature. The structures of the derived compounds were elucidated by elemental analysis, TLC-MS, ³¹P and ¹H NMR spectral data. For evaluation of melting behavior of derivatives (6) and (7), thermal transition peaks and their corresponding enthalpies were determined via DSC technique.     

Synthesis, characterization, thermal and optical properties of styrene derivatives having pendant p-substituted benzylic ether groups

The derivatives of styrene monomer, 4-chlorophenyl-4-vinylbenzyl ether (M1), 4-methoxyphenyl-4-vinylbenzyl ether (M2), 4-ethylphenyl-4-vinylbenzyl ether (M3) and 1-naphtylphenyl-4-vinylbenzyl ether (M4) were synthesized. The normal free radical polymerization of monomers in 1,4-dioxane were performed by using 2,2′-azobisisobutyronitrile as an initiator at 65 °C. The monomers and their homopolymers were characterized by FT-IR, NMR and elemental analyses measurements. The thermal stability of polymers was investigated by thermogravimetric and differential scanning calorimetric analysis. Thermal degradation activation energies of the polymers were calculated by the Ozawa and Kissinger methods. In addition, photo-stability tests of the polymers under near-UV irradiation were performed.     

A novel ditopic ring-expanded N-heterocyclic carbene ligand-assisted Suzuki-Miyaura coupling reaction in aqueous media

A series of seven-membered ditopic ring-expanded N-heterocyclic carbene (dre-NHC) precursors, bearing sterically demanding and electron-rich aryl groups, were synthesised in moderate yields via the reaction of 1,2,4,5-tetrakis(bromomethyl)benzene with the corresponding N,N′-diarylformamidines in the presence of K₂CO₃ in acetonitrile under an air atmosphere. All new compounds were characterised by HRMS, NMR spectroscopy, and microanalysis, as well as X-ray crystallography for compound 1c. The development of an efficient catalytic system for the Suzuki-Miyaura coupling reaction of aryl chlorides with various boronic acids was also investigated using the in situ generated dre-NHC ligands.     

Synthesis and proton conductivity studies of azole functional organic electrolytes

As an attempt to produce azole functional proton conductors, organic electrolytes with triazole and tetrazole functional groups were synthesized via substitution reaction of 1,3,5-benzenetricarbonyl trichloride with aminotriazole and aminotetrazole. The samples were doped with triflic acid with molar ratios of 0.25 and 0.50. FTIR, nuclear magnetic resonance (NMR), and elemental analysis were used to characterize the resulting materials. Thermogravimetric analysis showed that the samples are thermally stable up to 150?°C. The effect of acid doping on proton conductivity was investigated with impedance spectrometer. Both pure samples and the doped ones revealed high proton conductivity. In anhydrous conditions (TMA)-TriTA_0.50 and TMA-TetTA_0.50 have proton conductivities of 1.8 and 19?mS/cm at 150?°C, respectively. Solid-state NMR studies revealed that there are three different types of hydrogen-bonded acidic proton in the systems. Moreover, these different types of acidic protons present at different ratio in triazole and tetrazole systems.     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively.     

A comparison of the effect of the ellipticity on the small and large solid-core PCF’s characteristics

In this paper we study small and large solid-core PCFs with elliptical shaped air-holes for the hexagonal lattice, which were constructed by omitting one air-hole (small core) and seven air-holes (large core), respectively, and we compare their characteristics with those with circular holes. We use two types of ellipticity: vertical and horizontal. Birefringence, dispersion, and the numerical apertures of the fundamental modes are analyzed using commercial simulation software. Also, the confinement loss is obtained. The effect of ellipticity on these characteristics is investigated in detail. It is found that the type of ellipticity of the air holes affects the numerical aperture and hence confinement loss significantly, but it has no crucial effect on either the dispersion or the birefringence for the small and large core PCFs.     

A one-dimensional silver(I) coordination polymer with saccharin and pyrazine: synthesis,crystal structure,thermal analysis,FTIR spectra,and DFT studies

A silver(I) complex of saccharinate (sac) with pyrazine (pyz), [Ag(sac)(pyz)] _n , has been synthesized and characterized by elemental analysis, IR, thermal analysis, and single-crystal X-ray diffractometry. The complex crystallizes orthorhombic space group Pnma with unit cell parameters of a = 13.0073(9) Å, b = 6.4907(6) Å, c = 13.4007(9) Å, V = 1131.37(15) Å³, and Z = 4. [Ag(sac)(pyz)] _n is a one-dimensional coordination polymer, in which the sac ligand acts as a monodentate ligand through the N atom and the trigonal silver centers are linked by the bridging pyz ligands. The individual chains are connected into two-dimensional supramolemular network by aromatic π(sac)···π(pyz) stacking interactions. The FTIR spectrum of [Ag(sac)(pyz)] _n has been recorded in the region and 4,000–400 cm^?1. The optimized geometry, frequency, and intensity of the vibrational bands of [Ag(sac)(pyz)] _n were obtained by density functional theory (DFT) at the B3LYP level. The vibrational frequencies were calculated and the scaled values have been compared with the experimental FTIR data. The observed and calculated frequencies are found to be in good agreement.