Materials Literature
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A comparison of the crystal structure of the dimeric enzyme citrate synthase from the psychrophilic Arthrobacter strain DS2-3R with that of the structurally homologous enzyme from the hyperthermophilic Pyrococcus furiosus reveals a significant difference in the accessibility of their active sites to substrates. In thi…
A description of the pressure dependence of the structural relaxation time has been derived from the Adam-Gibbs theory by writing the configurational entropy in terms of the excess heat capacity and the molar thermal expansion. This new equation was tested successfully on dielectric relaxation data for an epoxy compou…
The dielectric, ferroelectric and piezoelectric characteristics of Sr 1- x Ca x Bi 2 Ta 2 O 9 ( x =0–1) ceramics were examined. The samples were prepared by a conventional ceramic technique at 1260°C to 1340°C for 2 h. The Curie temperature of samples gradually rose from 324°C to 896°C when x was increased. The coerci…
Structural properties of calcined ${\mathrm{ZrO}}_{2}$ nanopowders having various sizes were investigated by Raman spectroscopy, x-ray diffraction, and high-resolution transmission electron microscopy. For grain sizes of the order of a few nanometers the Raman spectrum is typical of an amorphous material as is the cor…
Second-harmonic generation was observed in Ge(20)As(25)S(55) chalcogenide glass irradiated by an electron beam. The second-harmonic intensity increased with increasing electron-beam current and accelerating voltage. The second-harmonic generation in Ge(20)As(25)S(55) glass was caused by the space-charge electrostatic…
Resonant grating reflection filters operating at normal incidence are investigated. At normal incidence these structures are shown to have characteristics different from those of structures operated at oblique incidence. We show how higher-order diffraction within the structure laterally confines the incident energy a…
We carry out Monte Carlo simulations to investigate the effect of molecular shape on liquid-crystal order. In our approach, each model mesogen consists of several soft spheres bonded rigidly together. The arrangement of the spheres may be straight (to represent uniaxial molecules), Z-shaped (for biaxial molecules), or…
Nickel complexes of eight differently substituted 2,2′-bidipyrrins have been prepared and fully characterized. The X-ray analyses of three of these complexes revealed helical chiral molecules. Despite the tetrahedral deviation from the square-planar coordination geometry at the metal centres, all compounds were found…
The condensation of pyrrole and benzaldehyde has generally been carried out with trifluoroacetic acid (TFA)(20-50 mM), BF 3 -etherate (1 mM), or more recently with BF 3 -etherate in the presence of a salt. Differences in the reaction course with TFA or BF 3 -etherate prompted studies of the combined use of BF 3 -ether…
To obtain dense, fine‐grained ceramics, fine particles and advanced powder processing, such as colloidal processing, are needed. Al 2 O 3 and ZrO 2 particles are dispersed in colloidal suspensions by electrosteric repulsion because of polyelectrolyte absorbed on their surfaces. However, additional redispersion treatme…
Abstract The effects of La2O3 doping on sintering characteristics and electric properties were studied. Dense, fine-grained ceramics were obtained by La2O3 doping which reduced grain boundary mobility and suppressed rapid grain growth induced by the phase transformation from the low-to high-temperature forms. The diel…
Abstract The ultrasonic enhancement on the hydrolysis of diethyl 1,2-benzenedicarboxylate results from the dissipated heat when the cavitation micro-bubbles were vigorously collapsed. The effective temperature in a solution depends on the nature of the dissolved gas. The relatively broad region that spreads from the i…
Commercial copolymers of 1-octene and ethylene: metallocene catalyzed (mLLDPE) and Ziegler-Natta catalyzed (znLLDPE), a low density polyethylene (LDPE), and high density polyethylene (HDPE), were characterized with respect to branching, crystallization behaviour and dynamic-mechanical properties. It was found that the…
An imide dicarboxylic acid was prepared from 1,6-diaminohexane and trimellitic anhydride and esterified with ethanol. This imide monomer was polycondensed with three different poly(tetramethylene oxide) diols (PTMO-650, PTMO-1000 and PTMO-2000) and with an excess of 1,4-dihydroxybutane. When PTMO-1000 was used, and ev…
X‐ray tomography has been used to investigate the density variations in SiC joints formed using polymer pastes. It has been demonstrated that X‐ray tomography provides accurate bulk density measurements and volumetric density gradients. The results suggest that the magnitude of the applied pressure after green state j…
Abstract The phase transitions of the solid solutions (Ca 1- x Sr x ) 2 MgSi 2 O 7 (0 ≤ x ≤ 0.32) of modulated melilites are studied by X-ray diffraction. The variation of the intensity and the FWHM of satellite reflections reveal different transition temperatures. Two ranges of different ordering are found in the ran…
Abstract New sulfamates KLi(NH 2 SO 3 ) 2 , RbLi ⋅ (NH 2 SO 3 ) 2 and CsLi(NH 2 SO 3 ) 2 were prepared from non-stoichiometric (ratio Li: Me = 3:1) aqueous solutions of LiNH 2 SO 3 and MeNH 2 SO 3 (Me = K, Rb, Cs) at room temperature. Large single crystals of KLi(NH 2 SO 3 ) 2 were grown from these solutions by contro…
Banana plant juice, taken from paradica and maghraby banana pseudostem, as well as black liquor resulting from pulping the banana plant with either 10 or 23 per cent sodium hydroxide (w/w), were identified for their chemical composition. On the other hand the use of these admixtures as anti-corrosive materials was stu…
During a comparative study of second-harmonic generation (SHG) and sum-frequency generation (SFG) in single-crystal and polycrystalline ZnSe, the polycrystalline material showed a dot pattern in the SHG as well as in the SFG output. No such pattern was found in the output from the single-crystal ZnSe sample. The secon…
Abstract The design and construction of a biaxial loading machine is presented in this paper. Two major concerns are addressed in designing the machine: alignment between the loading axes and the specimen, and shear stresses (friction) that may develop between the loading platens and the specimen. The alignment requir…