Naturally Occurring Xanthones from Terrestrial Flora -(tabulation of phytoxanthones under different classification systems along with their plant sources and 13C NMR data; 205 refs.). -(MANDAL, S.; DAS, P. C.; JOSHI, P. C.; J. Indian Chem. Soc. 69 (1992) 10, 611-636; Dep. Chem., Univ. Coll.
A polycrystalline ceramic, a new type of complex tungsten bronze type structure, having a general formula Li 2 Pb 2 Y 2 W 2 Ti 4 V 4 O 30 has been prepared relatively at low temperature using a mixed-oxide technique after optimizing the calcination conditions on the basis of thermal analysis. The material has been characterized by different experimental techniques. The formation of the material under the reported conditions has been confirmed by an X-ray diffraction technique. A preliminary structural analysis of the material showed the formation of single phase compound in an orthorhombic crystal structure at room temperature. Studies of dielectric properties (ε r , tanδ ) of the above compound as a function of temperature at different frequencies exhibit a ferroelectric phase transition of diffuse type. The electrical properties of the material have been studied using ac impedance spectroscopy technique. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructure. The temperature dependence of electrical relaxation phenomenon in the material has been observed. The bulk resistance, evaluated from complex impedance spectra, is found to decrease with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR)-type behavior similar to that of semiconductors. A small contribution of grain boundary effect was also observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The ac conductivity spectra exhibit a typical signature of an ionic conducting system, and are found to obey Jonscher's universal power law.
Microbial biofilms are complex structures wherein the planktonic cells change their growth mode to the sessile form. This kind of growth is assisted by the formation of a matrix of extracellular polymeric substances (EPS) which encapsulates the bacterial cells within it and thus, provides an additional protection. These biofilms are highly resistant to high concentration of antibiotics and poses a great threat towards public health. These biofilms are even beyond the access of a normal human immune system and are involved in infections of teeth, lungs and many other diseases. There lies an immediate need to replace the extensive use of antibiotics with new emerging strategies. The review intends to provide an insight on the various perspectives of microbial biofilms including their formation, composition, mechanism of communication (Quorum sensing) and pathogenicity. Recent emerging strategies have also been discussed that can be considered for successful eradication or inhibition of biofilms and related infections.
The proton emission in neutron deficient nuclei with [Formula: see text] has been investigated within the framework of axially deformed relativistic mean field (RMF) theory using NL3 and density-dependent DD-ME1 and DD-ME2 parameters. The quasi-bound states from which the proton emission is probable are determined. The RMF densities are folded with the M3Y effective nucleon–nucleon interaction to obtain the nuclear potential. The total interaction potential consisting of nuclear, Coulomb and centrifugal potentials is used to calculate the proton decay half-lives using the Wentzel–Kramers–Brillouin (WKB) approximation. For this, we have used the [Formula: see text], [Formula: see text] being the single-particle energy of the decaying proton near the Fermi surface. The calculated proton decay half-lives for different nuclei are in consonance with experimental data.
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