Adsorption von Jodid und Jod durch Phosphate

Ohne Zusammenfassung     

Adh?sive Bindung verschiedener Materialien an harten Zahnmaterialien. VIII. Nickel- und Kupfer-Ionen an Hydroxyapatit. Die Rolle des Ionenaustausches und der Oberfl?chenkernbildung

Ohne Zusammenfassung     

Stress-induced crystallization of poly(ethylene terephthalate)

Quenched amorphous films of poly(ethylene terephthalate) (PET) are stretched at temperatures less than T_g; changes in density, wide-angle x-ray diffraction, and small-angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide-angle x-ray diffraction and of both V_V and H_V small-angle light scattering patterns. The formation of oriented rodlike superstructure may be discerned from small-angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide-angle x-ray diffraction and small-angle light scattering. The rodlike morphology changes to form spherulitelike aggregates as observed by small-angle light scattering and light micrographs. A model is proposed to explain the observations. Studies are extended to stretching films of PET above their T_g and observing changes in birefringence, density, wide-angle x-ray diffraction and small-angle light scattering as a function of elongation and stretching temperature. The formation of defomed spherulitelike superstructure may be discèrned from light micrographs. Results are compared with those obtained upon stretching films below T_g.     

Structural and dielectric properties of Pb5(Ge,Si)O11

The ferroelectric lead germanate (Pb₅Ge₃O₁₁) and its isomorphous compounds are important because of their uses as pyroelectric and electro-optic devices. Comparison of inter-planar d-spacings of Pb₅Ge_3−x Si _x O₁₁ (x=0, 0.3, 0.7 and 1.00) suggests that there is no change in basic structure of Pb₅Ge_3−x Si _x O₁₁ when Si is substituted for Ge in small quantity (x<1). The dielectric properties of the Si-substituted compounds have been studied as a function of temperature (30 to 200°C). The ferroelectric-paraelectric phase transition has been observed at 185°C. The Si doping causes (a) Curie point to shift towards low temperature, (b) peak value of the dielectric constant to decrease and (c) phase transition diffuse. The fast increase in dielectric constant of pure Pb₅Ge₃O₁₁ with temperature (beyond transition temperature) may be attributed to the development of space charge polarization in the system.     

Surface remodeling of bones induced by intra-medullary nailing

The paper is devoted to a study on the surface remodeling of bones. Anisotropy and piezoelectricity of bone tissue (as per previous experimental studies) are incorporated in the analysis. Surface remodeling induced by intra-medullary nailing is of primary concern in the study.     

A variable temperature EPR study of the manganites (La1/3Sm2/3)2/3SrxBa0.33−xMnO3 (x=0.0, 0.1, 0.2, 0.33): Small polaron hopping conductivity and Griffiths phase

Four manganite samples of the series, (La_1/3Sm_2/3)_2/3Sr_xBa_0.33−xMnO₃, with x=0.0, 0.1, 0.2 and 0.33, were investigated by X-band (∼9.5 GHz) electron paramagnetic resonance (EPR) in the temperature range 4-300 K. The temperature dependences of EPR lines and linewidths of the samples with x=0.0, 0.1 and 0.2, containing Ba²⁺ ions, exhibit similar behavior, all characterized by the transition temperatures (T_C) to ferromagnetic states in the 110-150 K range. However, the sample with x=0.33 (containing no Ba²⁺ ions) is characterized by a much higher T_C=205 K. This is due to significant structural changes effected by the substitution of Ba²⁺ ions by Sr²⁺ ions. There is an evidence of exchange narrowing of EPR lines near T_min, where the linewidth exhibits the minimum. Further, a correlation between the temperature dependence of the EPR linewidth and conductivity is observed in all samples, ascribed to the influence of small-polaron hopping conductivity in the paramagnetic state. The peak-to-peak EPR linewidth was fitted to ΔB_pp(T)=ΔB_pp,min+A/Texp(−E_a/k_BT), with E_a=0.09 eV for x=0.0, 0.1 and 0.2 and E_a=0.25 eV for x=0.33. From the published resistivity data, fitted here to σ(T)∝1/T exp(−E_σ/k_BT), the value of E_σ, the activation energy, was found to be E_σ=0.18 eV for samples with x=0.0, 0.1 and 0.2 and E_σ=0.25 eV for the sample with x=0.33. The differences in the values of E_a and E_σ in the samples with x= 0.0, 0.1and 0.2 and x=0.33 has been ascribed to the differences in the flip-flop and spin-hopping rates. The presence of Griffiths phase for the samples with x=0.1 and 0.2 is indicated; it is characterized by coexistence of ferromagnetic nanostructures (ferrons) and paramagnetic phase, attributed to electronic phase separation.     

Analysis of vibrational,structural, and electronic properties of rivastigmine by density functional theory

The present work deals with the structural, electronic, and vibrational analysis of rivastigmine. Rivastigmine, an antidementia medicament, is credited with significant therapeutic effects on the cognitive, functional, and behavioural problems that are commonly associated with Alzheimer’s dementia. For rivastigmine, a number of minimum energy conformations are possible. The geometry of twelve possible conformers has been analyzed and the most stable conformer was further optimized at a higher basis set. The electronic properties and vibrational frequencies were then calculated using a density functional theory at the B3LYP level with the 6-311+G(d, p) basis set. The different molecular surfaces have also been drawn to understand the activity of the molecule. A narrower frontier orbital energy gap in rivastigmine makes it softer and more reactive than water and dimethylfuran. The calculated value of the dipole moment is 2.58 debye.     

Dielectric, thermal and optical study of an unusually shaped liquid crystal

Dielectric measurements have been carried out for the determination of real and imaginary parts of the permittivity of a newly synthesized, unusually shaped liquid crystal. The sample has been investigated in the frequency range from 100 Hz to 10 MHz within a temperature range 80-130 °C. The dielectric measurements in the smectic A phase indicate a Cole-Cole type of dispersion, and the activation energy was found to be 5.5 meV by using the Arrhenius plot of relaxation time. In addition to this, thermal and optical transmittance studies have also been conducted in the above mentioned temperature range, and the temperature dependence of these parameters has been discussed in detail. The phase transition temperature obtained from a differential scanning calorimetry (DSC) study matches within 2 °C that was obtained from an optical transmittance study. The dielectric and optical behavior of the unusually shaped liquid crystal has been explained on the basis of a proposed theoretical model in which a sample possesses two different conformers having induced polarizations in opposite directions.     

Effect of meso aryl substituents on the synthesis of core-modified expanded porphyrins

[reaction: see text] Synthesis and characterization of core-modified [26]hexaphyrin (1.1.1.1.0.0). A meso aryl rubyrin isomer and a new 54pi-modified dodecaphyrin are reported.