Stretched exponential relaxation and dispersive conductivity behavior in lithium bismuth silicate glasses

Glasses having compositions xLi₂O∙(85 − x)Bi₂O₃∙15SiO₂ (x = 35, 40, and 45 mol%) were prepared by normal melt quenching technique. Electrical relaxation and conductivity in these glasses were studied using impedance spectroscopy in the frequency range from 20 Hz to 1 MHz and in the temperature range from 453 to 603 K. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency were extracted from the impedance spectra. The dc conductivity increases with increase in Li₂O content providing modified glass structure and large number of mobile lithium ions. Similar values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions overcome the same energy barrier while conducting and relaxing. The non-exponential character of relaxation processes increases with decrease in stretched exponential parameter ‘β’ as the composition parameter ‘x’ increases. The observed conductivity spectra follow a power law with exponent ‘s’ which increases regularly with frequency and approaches unity at higher frequencies. Nearly constant losses (NCL) characterize this linearly dependent region of the conductivity spectra. A deviation from the ‘master curve’ for various isotherms of conductivity spectra was also observed in the high-frequency region and at low temperatures, which supports the existence of different dynamic processes like NCL in addition to the ion hopping processes in the investigated glass system.     

Effect of current density on the microstructure and corrosion behaviour of plasma electrolytic oxidation treated AM50 magnesium alloy

Plasma electrolytic oxidation (PEO) of an AM50 magnesium alloy was accomplished in a silicate-based electrolyte using a DC power source. Coatings were produced at three current densities, i.e. 15 mA cm⁻², 75 mA cm⁻², and 150 mA cm⁻² and were characterised for thickness, roughness, microstructural morphology, phase composition, and corrosion resistance. Even though the 15 min treated coatings produced at higher current density levels were thicker, they showed poor corrosion resistance when compared to that of the coatings obtained at 15 mA cm⁻². Short-term treatments (2 min and 5 min) at 150 mA cm⁻² yielded coatings of thickness and corrosion resistance comparable to that of the low current density coatings. The superior corrosion resistance of the low thickness coatings is attributed to the better pore morphology and compactness of the layer.     

Electronic and magnetic behavior of ultrathin Ti nanowires

We report theoretical results on the magnetic behavior of free standing nanowires of Ti. Four different structures of Ti nanowires-linear, ladder, dimerized, and zigzag-with nonmagnetic, ferromagnetic, and anti-ferromagnetic configurations were considered. Exploration of magnetism in these atomic chains leads to ferromagnetic behavior for all the structures: zigzag structure shows almost degenerate ferromagnetic and anti-ferromagnetic states though. The zigzag structure of Ti nanowires is favored of all for low values of nearest neighbor distances, whereas the dimerized structure is favored at larger atomic separations. Our work helps to resolve the controversy in the predicted ground state magnetic nature of zigzag chains of Ti as reported in recent previous works. The maximum value of magnetic moment (0.93 μ_B/atom) occurs in the ladder chains while the zigzag chains show the minimum value (0.17 μ_B/atom). Interestingly, all the structures in the magnetic configuration show metastable state except the dimerized structure. Ferromagnetic dimerized nanowires seem to be a potential candidate for use in spintronics. The projected density of states shows that d_x²_−y² and d_xy bands play a leading role in magnetism of linear and ladder structures, whereas there is no outstanding contribution from a particular d-orbital for zigzag and dimerized nanowires. The charge density plots suggest that linear and zigzag structures have metallic bonding whereas covalent bonding is predominant in the dimerized and ladder structures. The estimated diameters for the favored ferromagnetic configuration of these ultrathin nanowires lie in the range 1.9-3.4 Å and indicate the instability of the ladder structure, as also projected by the relative cohesive energy and relative break force values.     

Performance of a 4×10 Gbit/s optical time domain multiplexed system using SMZ switching

Optical time division multiplexing (OTDM) is emerging and promising alternative for future high-speed photonic networks because of its ability to accommodate higher bit rate and flexible bandwidth. Among other factors the performance of an OTDM system largely depends upon the switching characteristics of a de-multiplexer (DEMUX). Symmetric Mach-Zehnder (SMZ) have been found to be most suitable than all the available de-multiplexing switches because of compact size, thermal stability, and low power operation. In this paper, we simulate four-channel OTDM systems (all channel multiplexer (MUX) and DEMUX) with a Mach-Zehnder modulator and SMZ DEMUX to investigate the impact of signal power, pulse width and control signal power on BER.     

CH...pi interaction for rhenium-based rectangles: an interaction that is rarely designed into a host-guest pair

Alkoxy- and thiolato-bridged Re(I) molecular rectangles [{(CO)3Re(mu-ER)2Re(CO)3}2(mu-bpy)2] (ER = SC4H9, 1a; SC8H17, 1b; OC4H9, 2a; OC12H25, 2b; bpy = 4,4'-bipyridine) exhibit strong interactions with several planar aromatic molecules. The nature of their binding was studied by spectral techniques and verified by X-ray diffraction analysis. Standard absorption and fluorescence titrations showed that a relatively strong 1:1 interaction occurs between aromatic guests such as pyrene and these rectangles. The results of a single-crystal X-ray diffraction analysis show that the recognition of 1 with a pyrene molecule is mainly due to CH...pi interactions and the face of the guest pyrene is located over the edges of the bpy linkers of 1. This is a fairly novel example of an interaction that is rarely designed into a host-guest pair. Furthermore, the interaction of 1 with Ag+ results in the self-organization of supramolecular arrays, as revealed by solid-state data.     

Synthesis and the Crystal Structure of (<Emphasis Type="Italic">E</Emphasis>)-2-(7-(3-(Thiophen-2-yl)acrylamido)-2,3-dihydro-5-oxobenzo[e][1,4]oxazepin-1(5H)-yl)ethyl acetate

Abstract  

Details of the synthesis and crystal structure determination of (E)-2-(7-(3-(thiophen-2-yl)acrylamido)-2,3-dihydro-5-oxobenzo[e][1,4]oxazepin-1(5H)-yl)ethyl acetate are presented. The compound crystallizes in the triclinic P−1 space group (a = 8.3377(17), b = 9.792(2), c = 12.469(3) ?, α = 96.39(3)°, β = 108.50(3)°, γ = 97.68(3)°, V = 943.9(3) ?³, Z = 2). Interesting features of the structure include intermolecular hydrogen bonding between the amide proton on one molecule and the carbonyl oxygen of the dihydrooxazepinone ring on an adjacent molecule, the boat conformation of the dihydrooxazepinone ring, and π-π stacking between thiophene and phenyl rings on adjacent molecules with a distance between centroids of 3.79(2) ?.     

Ionic liquid-based sodium ion-conducting composite gel polymer electrolytes: effect of active and passive fillers

Journal of Solid State Electrochemistry - We report the studies on composite gel polymer electrolytes (GPEs) comprising 0.5&nbsp;M solution of sodium trifluoromethane sulfonate (Na-triflate or...     

Synthesis of potential impurities of cloxacillin sodium drug substance

The present work describes the synthesis and characterization of six related compounds of cloxacillin sodium ( 1 ) viz penicilloic acid of cloxacillin (2) , (3-(2-chlorophenyl)-5-methylisoxazole-4-carbonyl) glycine (Glycine analogue of cloxacillin) (3), CMICAA adduct of cloxacillin (4) , (4S)-2-(carboxy(3-(2-chlorophenyl)-5-methylisoxazole-4-carboxamido) methyl)-3-(2-ethylhexanoyl)-5,5-dimethylthiazolidine-4-carboxylic acid (N-2-ethylhexanoyl penicilloic acid of cloxacillin) ( 5 ), N-Acetylated penicilloic acid of cloxacillin ( 6 ), and Cloxacillin Penicillamide (7) . These related compounds are very essential in the process development of cloxacillin sodium and are used as reference standards to determine the quality of the drug substance.     

Studies of iron(II) and iron(III) complexes with fac-N2O, cis-N2O2 and N2O3 donor ligands: models for the 2-His 1-carboxylate motif of non-heme iron monooxygenases

Enzymes in the oxygen-activating class of mononuclear non-heme iron oxygenases (MNOs) contain a highly conserved iron center facially ligated by two histidine nitrogen atoms and one carboxylate oxygen atom that leave one face of the metal center (three binding sites) open for coordination to cofactor, substrate, and/or dioxygen. A comparative family of [Fe(II/III)(N(2)O(n))(L)(4-n))](±x), n = 1-3, L = solvent or Cl(-), model complexes, based on a ligand series that supports a facially ligated N,N,O core that is then modified to contain either one or two additional carboxylate chelate arms, has been structurally and spectroscopically characterized. EPR studies demonstrate that the high-spin d(5) Fe(III)g = 4.3 signal becomes more symmetrical as the number of carboxylate ligands decreases across the series Fe(N(2)O(3)), Fe(N(2)O(2)), and Fe(N(2)O(1)), reflecting an increase in the E/D strain of these complexes as the number of exchangeable/solvent coordination sites increases, paralleling the enhanced distribution of electronic structures that contribute to the spectral line shape. The observed systematic variations in the Fe(II)-Fe(III) oxidation-reduction potentials illustrate the fundamental influence of differential carboxylate ligation. The trend towards lower reduction potential for the iron center across the [Fe(III)(N(2)O(1))Cl(3)](-), [Fe(III)(N(2)O(2))Cl(2)](-) and [Fe(III)(N(2)O(3))Cl](-) series is consistent with replacement of the chloride anions with the more strongly donating anionic O-donor carboxylate ligands that are expected to stabilize the oxidized ferric state. This electrochemical trend parallels the observed dioxygen sensitivity of the three ferrous complexes (Fe(II)(N(2)O(1)) < Fe(II)(N(2)O(2)) < Fe(II)(N(2)O(3))), which form μ-oxo bridged ferric species upon exposure to air or oxygen atom donor (OAD) molecules. The observed oxygen sensitivity is particularly interesting and discussed in the context of α-ketoglutarate-dependent MNO enzyme mechanisms.     

Synthesis,structural and electrical properties of Ti modified Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2−xTi_xO₇ (x=0.00, 0.2, 0.4, 0.6 and 0.8) have been synthesized by standard high temperature solid state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural and electrical properties of the pure Bi₂Sn₂O₇ ceramic have been studied by X-ray diffraction followed by SEM, dielectric and dc conductivity studies. The structural analysis indicates that the increase of titanium contents do not lead to any secondary phase. The frequency and temperature dependent dielectric studies have been carried out. It is found that the Ti doping reduces the material particle size. The size of the particles are strongly influenced by the addition of titanium to the system. The substitution of Ti for Sn ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The activation energies of all the compounds were calculated using the relation σ=σ₀exp(−Ea/kT).