A unique method for reducing losses of bends in dielectric optical wave guide

The dielectric optical wave guide is finding growing attention at millimeter wave frequencies. However the dielectric optical waveguide radiates at bends and thus transmission loss increases. These radiations are in the outword direction of bends. This output radiation at output bends arises due to change in phase velocities of the propagating wave at the centre of the dielectric guide and the phase velocity at the outer surface of the dielectric guide. A unique methiod is suggested to avoid these radiation losses.Experimental results are also shown at microwave frequencies.     

Magnetic superconductors: Model theories and experimental properties of rare-earth compounds

Superconducting and magnetically long-range ordered states were believed to be mutually exclusive phenomena. The discovery of rare-earth compounds in recent years, which exhibit both superconductivity and magnetic ordering (ferromagnetic, antiferromagnetic or sinusoidal), has led to considerable theoretical and experimental work on such systems.In the present article, we give a review of various theoretical models and important experimental results. In the theoretical sections, we start with the Abrikosov-Gorkov pair breaking theory for dilute alloys and discuss its improvement in the work of Müller-Hartmann and Zittartz. Then, in the context of magnetic superconductors, various microscopic theories that have been advanced are presented. These predict re-entrant behaviour in some systems (ferromagnetic superconductors) and coexistence regions in others (particularly antiferromagnetic superconductors). Following this, phenomenological generalized Ginzburg-Landau theories for two kinds of orders (superconducting and magnetic) are presented. A section dealing with renormalization group analysis of phase diagrams in magnetic superconductors is given.In experimental sections, the properties of each rare-earth compounds (ternary as well as some tetranery) are reviewed. These involve susceptibility, heat capacity, resistivity, upper critical field, neutron scattering and magnetic resonance measurements. The anomalous behaviour of the upper critical field of antiferromagnetic superconductors near the Néel temperature is discussed both in theory sections and experimental section for various systems.     

Electron impact ionization of Zn+ and Ga+

We have investigated the contribution of excitation-autoionization to the electron impact ionization of Zn⁺ and Ga⁺ using the binary encounter approximation. Hartree-Fock velocity distributions for the bound electrons have been used throughout the calculations of direct and indirect ionization cross-sections. The calculated cross-sections are in good agreement with recent experiments. We have also compared our results with other theoretical calculations.     

Recombination in electron-hole droplets in polar and non-polar indirect band gap semiconductors and carrier concentration power law

The dependence of the recombination relaxation rate on the carrier concentration, n, is examined in detail. It is found that in polar indirect band gap semiconductors the phonon-induced recombination rate varies as $\text{n}{}^{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}$ at low temperatures. This is a new power law. On the other hand, in the non-polar materials, the relaxation rate varies as a linear combination of n², $\text{n}{}^{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}$ and $\text{n}{}^{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}$ terms. We find the experimental evidence for the occurence of $\text{n}{}^{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}$ and $\text{n}{}^{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}$ contributions for the first time.     

The effect of the oscillatory rotations of an ion upon the orbit of the electrons of a neighboring atom: The hyperfine coupling ofMn2+ in KNO3 over a phase transition

The change in the electronic orbit ofMn²⁺ ion due to the switching on of oscillatory rotations of NO^-₃ ions upon a phase transformation is observed through the change in the hyperfine coupling and correctly predicted.     

Condensation of the spin-polarized atomic hydrogen on the superfluid helium

The interaction of the spin-polarized hydrogen atoms in the bulk as well as on the surface of the superfluid helium with the third-sound ripplons is investigated. The dispersion relation is found to show a kink at a particular wave vector at which new quasiparticles appear.     

Electron spin resonance of Mn2+ in NaCl single crystal and lattice defects

The electron spin resonance spectra of Mn²⁺ in NaCl single crystals are investigated in detail. Seven different spectra (I, II, III₁, III₂, IV, V and VI) are observed. The spectra I–IV are the same as those observed by earlier workers, while the spectra V and VI are observed here for the first time. The local symmetry at the paramagnetic ion is orthorhombic for the spectra IV and V and tetragonal for the spectrum VI about the crystallographic [001] direction. The properties of the spectrum IV are explained in terms of an associated pair Mn²⁺: O₂ ^2? with O₂ ^2? molecular ion at the nearest neighbour anion site in the [001] direction with its internuclear axis in the (001) plane. The spectrum V is assigned to the associated pair Mn²⁺: O₂ ^2? coupled with a nearby cation vacancy in the [001] direction and the spectrum VI to Mn²⁺ ion associated with OH^? ion at the anion site in the [001] direction with a probable second neighbour cation vacancy. All the observed spectra are analysed in terms of the parameters of the usual spin-Hamiltonian.     

Dependence of mechanoluminescence in rochelle-salt crystals on the charge-produced during their fracture

The dependence of mechanoluminescence in rochelle-salt crystals on the charge-produced during their fracture is found to be linear up to the applied stress of 344 kg/cm². This fact is discussed on the basis of the instability of cracks in a crystal and it is concluded that the new surfaces created by mobile cracks are responsible for the appearance of mechanoluminescence in rochelle-salt crystals.