Supramolecular structure of S-(+)-marmesin—a linear dihydrofuranocoumarin

The title compound, C₁₄H₁₄O₄, a linear dihydrofuranocoumarin, was isolated from the bark ofAegle marmelos, a plant widely used in Ayurvedic system of medicine for the treatment of various ailments. The crystal structure was determined from X-ray diffraction data using direct methods. The compound crystallizes into monoclinic space group P2₁ with unit cell parameters:a] = 5.721(1) Å, b= 13.810(1) Å, c= 7.864(2) Å, β = 100.39(1)°, Z = 2. The structure was refined by full-matrix least-squares to a finalR value of 0.0523 for 1184 observed reflections. The benzopyran moiety is perfectly planar. The dihedral angle between the pyrone and benzene rings is 0.3(1)°. The furan ring has a 2α-envelope conformation. The molecules are linked by O-H…O hydrogen bonds into chains and these chains are linked into sheets by C-H…O hydrogen bonds. Further, the π-π stacking and C-H…π (arene) interactions link all of the sheets into a supramolecular structure.     

Magnetic Properties of an Antiferromagnetic d-Wave Singlet and π-Triplet Superconductor

In this study we focus on the magnetic properties of a system consisting of Spin Density Wave (SDW) order, d-wave singlet and π-triplet superconductivity (SC) taken on the same footing within a mean-field treatment. The competition and coexistence of these order parameters manifest the H-T phase diagrams of all antiferromagnetic superconductors. An experimental probe to such a multicomponent state can be provided by magnetic measurements such as NMR or magnetization techniques. We have calculated, both analytically and numerically, the static spin susceptibility of our multicomponent system as a function of temperature and external magnetic field under particle–hole asymmetry. Our results can serve as a way to identify these novel multicomponent states. An application to the identification of the high-field low-temperature phase in CeCoIn₅ is discussed.      

Thermopower ofAg_{2 + \delta } S across theα-β transitionacross theα-β transition

Thermopower data of S in both of itsα- andβ-phases are reported and the results are compared with the data on Se. Communication No. 129 from the Solid State and Structural Chemistry Unit.     

X-ray crystallographic and conductance study of CuNiSnO4 synthesized by two different methods

Two new ternary oxidic compositions of CuNiSnO₄ have been prepared. The ternary composition Cu²⁺Ni²⁺SnO₄ in orthorhombic symmetry with lattice dimensionsa ₀=5·773 ± 0·01 Å;b ₀=8·377 ± 0·01 Å;c ₀=10·094 ± 0·01 Å, while Cu⁺Ni³⁺SnO₄ is also orthorhombic but with lattice dimensionsa ₀=5·737 ± 0·01 Å;b ₀=7·125 ± 0·01 Å andc ₀=10·071 ± 0·01 Å. The variation of electrical conductance with temperature indicates the semiconducting nature of these compositions. Hot-probe method indicatesp-type semiconduction in both the compositions     

Differentiating random upper semicontinuous functions under the integral sign

In this paper we analyze sufficient conditions to guarantee the differentiability under the integral sign of a certain class of random upper semicontinuous functions depending on a real-valued parameter. Several concepts of differential for this mappings are considered: the Fréchet differentiability of the support function, the π-differentiability, the De Blasi differentiability, and thes-differentiability.     

Effect of hydrogen on mechanical properties of β -titanium alloys

Conflicting opinions exist in the literature on the manner in which hydrogen influences the mechanical properties ofβ-titanium alloys. This can be attributed to theβ-stabilizing effect of hydrogen in these materials leading to major changes in the microstructure as a result of hydrogen charging. The resulting (extrinsic) effect of hydrogen on the mechanical properties can possibly cover up the direct (intrinsic) influences. On the basis of experimentally determined thermodynamic and kinetic data regarding the interaction of hydrogen withβ-titanium alloys, hydrogen concentrations of up to 8 at.% were established in three commercial alloys by means of hydrogen charging from the gas phase. In order to separate intrinsic and extrinsic effects the charging was carried out during one step of the two-step heat treatment typical of metastableβ-titanium alloys, while the other step was performed in vacuum. The results on the single-phaseβ condition represent the intrinsic hydrogen effect. Monotonic and cyclic strength increase at the expense of ductility with increasing hydrogen concentration. The brittle to ductile transition temperature shifts to higher values and the fatigue crack propagation threshold value decreases. The microstructure of the metastable, usually two-phaseβ-titanium alloys is strongly affected by hydrogen, although the extent of this effect depends not only on the hydrogen concentration but also on the temperature of charging. This microstructural influence (extrinsic effect) changes the mechanical properties in the opposite direction as compared to the intrinsic hydrogen effect.     

New aspects of the β–α polymorphic transition in plastically deformed isotactic polypropylene studied by microindentation hardness

The β–α polymorphic transition in plastically deformed isotactic polypropylene (iPP) was characterized by means of microindentation hardness. For this purpose microindentations were mapped onto the surface of the necking zone of a tensile loaded injection molded β-iPP “dumb-bell” specimen. Results evidence a sharp decrease of the H-values instead of the expected H-increase due to the β–α polymorphic transition. Far away from the necking zone an H-increase is detected. It is shown that the destruction of the starting isotropic spherulitic structure and the decrease of crystallinity in the necking zone gives rise to lower H-values. However, at larger distances from the neck, the emerging fibre structure induces a better chain orientation that results in a slight H-increase. Analysis of the isotropic and necked samples before and after their annealing using DSC and WAXS supports the assumption regarding the role of the microvoids in decreasing the hardness value.     

The <Emphasis Type="Italic">α–β</Emphasis> Transition of Nitrogen

It is well-known that, aside from its triple point, nitrogen exhibits a solid-to-solid transition at about 35 K that is of some interest as a secondary reference temperature. During the recently published highly accurate measurements of the triple point of nitrogen (Metrologia 43, 435 (2006)), an extensive study was made also of the solid α–β transition of nitrogen, using both the continuous heating method and the pulse-heating method. This transition is of significantly lower quality than the triple point of nitrogen. A very high thermal resistance and a large time constant characterize the transition. Therefore, even the determination of the self-heating of the thermometer requires a very long time. A value of T ₉₀ = 35.620 K with an expanded uncertainty U = 8 mK for the coverage factor k = 2 was found, differing by +6 mK from the published CCT-recommended value. The reproducibility of the value was better than ± 5 mK. In addition to the temperature value found for the transition, a comparison is made with previous measurements on this point, and an overview is given of the available information about it.     

Microstructural features of Cd0·8Zn0·2Te thin films studied by X-ray diffraction and electron microscopy

Thin films of synthesized Cd_0·8Zn_0·2Te have been deposited on glass substrate at different substrate temperatures. Different microstructural parameters like crystallite size, rms strain, dislocation density, stacking fault probability and stacking fault energy are determined by XRD, SEM, TEM and TED. XRD and XPS have been used to determine the composition. Variations of the microstructural parameters with film thickness and substrate temperature have been studied in order to obtain optimum growth condition for maximum particle size and least microstructural defects. An effort has been made to correlate the experimental results.     

Local lattice anomalies in underdoped YBa2Cu3O7-Σ probed by X-ray absorption fine structure

Temperature-dependent local lattice anomalies in underdoped YBa₂Cu₃O_7-Σ are studied by extended X-ray absorption fine structure (EXAFS) in a fluorescence mode. The in-plane polarized Cu A^-EXAFS is measured on underdoped epitaxial YBa₂Cu₃O_7-Σ films (100-120 nm) prepared onto SrTiO₃ substrates using a pulsed laser ablation technique. The Fourier transform (FT) results for a sample withT _c = 55K (△T = 4K) shows an in-plane lattice anomaly atT* = 83 K (~ 1.5T _c ) below which the in-plane oxygen distribution consists of the two Cu-O peaks separated by 0.2-0.3 A. The contribution of the elongated Cu-O bond increases on loweringT, indicating either the in-plane rhombic distortion of the square-planar CuO₄ or the tilting of the CuO₅ pyramid. Contrary to the anomalies in spin susceptibility and transport measurements indicating the presence of a spin gap, the onset temperature of the in-plane lattice anomaly (T*) shifts to the lowerT _c on decreasing the carrier density. The results suggest that the in-plane local lattice anomaly is anextrinsic lattice effect which is not directly related to the spin-phonon interaction.     

Enzyme-catalyzed preparation of supramolecular structured hydrogel of polypseudorotaxanes derived from the self-assembly of α-CDs with 3-arm p-hydroxyphenylpropionate terminated PEG

A kind of novel 3-D cross-linked supramolecular structured hydrogels has been fabricated via enzymatic oxidative coupling of polypseudorotaxanes (PPRs) derived from the self-assembly of α-cyclodextrins (α-CDs) with 3-arm p-hydroxyphenylpropionate terminated PEG (3-HPPP) as a macromer by using horseradish peroxidase (HRP)/H₂O₂ catalytic system. The enzymatic cross-linking of the macomer or PPRs made with a smaller amount of α-CDs was found to be much faster than that by ordinary chemical pathways, showing the promise to be used as the surgical adhesive and sealant which are needed to rapidly function in vivo. The gelation time was highly extended and the gel content was considerably decreased by increasing the α-CDs to macromer feeding molar ratio. Thereby these hydrogels exhibited a decreasing trend in dynamical mechanical properties with increasing the amount of α-CDs in regard to the blank hydrogel made without α-CD addition.     

Dynamic strength and failure behavior of titanium alloy Ti-6Al-4V for a variation of heat treatments

In our study, samples of Ti-6Al-4V were subjected to modifications of an aging treatment where temperatures for solution annealing and final aging as well as the cooling rate were varied. The titanium alloy was annealed above and below the β-transus temperature followed by cooling in a vacuum furnace or by water quenching. Additionally, the final annealing temperature was varied. Compression tests under quasistatic and dynamic loading rates were performed to determine the flow stress and strain hardening behavior. Furthermore, instrumented Charpy impact tests on U-notch specimen were performed at room temperature to monitor the load-time response of deformation and fracturing. The obtained high rate mechanical properties are discussed and correlated with the present microstructure. Our results reveal a very strong effect of the microstructure on the material behavior and will assist to choose the appropriate heat treatment technology, especially if impact loaded or safety structures have to be considered.     

X-ray study of the air-oxidiseda-Ga2Se3 and Ga2Te3 powders

X-ray studies of the stoichiometrically prepareda-Ga₂Se₃ and Ga₂Te₃ are reported after various stages of air-oxidation in the temperature ranges 250 to 825° C and 250 to 650° C respectively. Diffractometric powder data of Ga₂Te₃ are also reported over the complete 2ϑ range with remarkable difference in the relative intensities of the (444) and (642) reflections. Ina-Ga₂Se₃ the oxidation proceeds by formation of the most stable phase, beta-gallium sesquioxide, complete oxidation occurring at 650° C. For Ga₂Te₃ a mixture of Ga₂TeO₆ and TeO₂ is obtained as the intermediate oxidation products in the range 500 to 600° C, while at 450° C some extra lines which could be indexed on the super-lattice cell of Ga₂Te₃, along with Te and unchanged Ga₂Te₃ lines, are observed. Oxidation at the higher temperature of 650° C led to the disappearance of TeO₂ lines leaving Ga₂TeO₆ as the final well-crystallised phase.     

Formation of Nd2Fe14B hydride by milling of anhydride particles in toluene in a closed reactor

When milling micrometer thin Nd₂Fe₁₄B platelets, of an average 1–2 mm diameter, in toluene in a closed reactor, part of the toluene decomposes at the surface of the platelets and yields nascent hydrogen and carbon/low hydrocarbons. The hydrogen diffuses into the Nd₂Fe₁₄B platelets and the carbon forms a thin surface passivation layer of the platelets, forming the stable Nd₂Fe₁₄BH _x ,x ≤ 5, hydride at room temperature. On heating in a calorimeter, the hydrogen desorbs off the sample with a well-defined endotherm between 370 and 425 K. An N₂ gas atmosphere, if used during the heating, facilitates the H-desorption process with the modified kinetic parameters. For example, the enthalpy of the H-desorption ΔH and the related activation energyE _a have the measured values ΔH = 153 J/g andE _a = 58·2 kJ/mol in argon and ΔH = 256 J/g andE _a = 41·6 kJ/mol in N₂. It is argued that N₂ gas has a fast reaction with the H atoms desorbing off the thin sample platelets and forms NH₃ gas with an instantaneous decrease of the total external gas pressure at the sample. This supports the fast desorption of H atoms in the sample with the modified desorption kinetics in N₂ gas.     

Transport properties of MoSe x Te2−x (0 ≤x ≤ 2) single crystals

The layer type MoSe _x Te_2−x (0 ≤x ≤ 2) have been grown in single crystalline form by chemical vapour transport technique using bromine as the transporting agent. The electrical resistivity and Hall mobility perpendicular to thec-axis of the crystals were measured at room temperature. The variation of the Seeback coefficient with temperature was also investigated.     

Conductometric Study of Some Metal Halides in Glycerol + Water Mixtures

Electrolytic conductivities of potassium halides, KX (X = Cl⁻, Br⁻, I⁻) have been investigated in 10, 20, and 30 mass% glycerol + H₂O mixtures at 298.0, 308.0, and 318.0 K. The conductance data have been analyzed by the Fuoss-conductance–concentration equation in terms of the limiting molar conductance (Λ⁰), the association constant (K _A ), and the distance of closest approach of ion (R). The association constant (K _A ) tends to increase in the order: 10 mass% < 20 mass% < 30 mass% glycerol + water mixtures, while it decreases with temperature. Thermodynamic parameters ΔH ⁰, ΔG ⁰, and ΔS ⁰ are obtained and discussed. Also, Walden products (Λ⁰η) are reported. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.     

Synthesis Parameters and Their Effects on the Resistivity Anomaly in GdPr1113 Ceramic

Tetragonal Gd_1−x Pr _x BaSrCu₃O_7−δ (GdPr1113) polycrystalline high-temperature superconducting ceramic samples have been synthesized by the standard solid-state reaction process with different calcination and sintering temperatures and characterized by XRD and SEM. The optimum synthesis temperatures for obtaining single phase varied with Pr doping. Higher temperatures were necessary to obtain single phase for x ≥ 0.3. It was found that higher synthesis temperatures improved the electrical characteristics of these materials. The effects of different calcination and sintering temperatures on the anomalous hump in the ρ(T) curves observed at about 80 K is investigated. The percentage of the phase causing the anomaly decreases with the increase of the synthesis temperatures. PACS: 74.72.Bk, 74.62.Bf, 74.25.Fy     

Effect of praseodymium substitution on the growth and properties of Y1−x Pr x Ba2Cu3O7−δ (o <x < 0·4) single crystals

In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium substituted (partially) large single crystals of high temperature superconducting Y_1−x Pr _x Ba₂Cu₃O_7−δ (x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm³ and 4 × 1 × 1 mm³, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y_0·8Pr_0·2Ba₂Cu₃O_7−δ and Y_0·6Pr_0·4Ba₂Cu₃O_7−δ materials are ≈ 2 × 3 × 0·1 mm³ and 5 × 1 × 1 mm³ and ≈ 1 × 1·5 × 0·1 mm³ and 7 × 0·2 × 0·1 mm³, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T _c) of the oxygenated crystals were found to depend on the Pr-content. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

An X-ray diffraction study of defect parameters in a Ti-base alloy

Detailed studies based on the well established method of Fourier line shape analysis have been made on the X-ray diffraction profile of hexagonal titanium alloy of nominal composition Ti-6.58% Al-3.16% Mo-1.81% Zr-008% Fe-0.012% N-0.0078% C. While deformation fault probability, α, has been found to be quite high compared to that of pure titanium, the deformation growth fault parameter, β, shows a negative value ruling out the presence of growth fault in this alloy in the deformed state.     

Enhanced Superconducting Properties of Air-Processed GdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript> Single Domains with BaCO<Subscript>3</Subscript>/BaCuO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Addition

Single domain GdBa₂Cu_7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed Gd123 was successfully enhanced by addition of both BaCO₃ and BaCuO_2−x , which suppress the formation of Gd_1+x Ba_2−x Cu₃O_7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO₃ and 0.05 to 0.1, M BaCuO_2−x per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band formed by Gd₂BaCuO₅ particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and 8, mm in thickness and a high critical current density J _c up to 91,200, A/cm² was achieved at 77, K under self-field.