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.     

Bose-Einstein condensation in spin-polarized atomic hydrogen: A new superfluid

We find that in the spin-polarized hydrogen, Bose condensation occurs for certain quantized values of the magnetic field. Once the field is fixed, sweeping of the radio-frequency results in nuclear magnetic resonance so that condensation and NMR occur simultaneously. We have found that nuclear self-induced transparency occurs. A new excitation designated by the present author as superboojum, which is a discontinuity in the hydrodynamic equations in spin-polarized hydrogen having finite nuclear as well as electronic spin is discovered.     

A comparison of the von Mises and Hencky equivalent strains for use in simple shear experiments

The von Mises equivalent strain increment is derived for the case of large strain simple shear (torsion testing). This is used, in conjunction with the von Mises yield surface, to define the von Mises equivalent stress as well as the incremental work per unit volume. Integration of the equivalent strain increment leads to the definition of the von Mises equivalent strain for torsion. The Hencky equivalent strain increment is derived from the Hencky strain defined as the logarithm of the semi major and minor axes of the strain ellipse. This is then used, via the incremental work, to derive the ‘Hencky equivalent stress’. In the Onaka approach, the numerical values of the principal strain increments were integrated without taking into account the continuous rotation of the strain ellipse. This invalid operation leads to an expression for the equivalent strain increment that cannot be applied to the large strains considered by Onaka. Using the correct increments of the Hencky strain, it is shown that the shear strain increments turn negative and consequently, the incremental work becomes negative when the shear is large.     

Mössbauer and magnetic studies on nanocrystalline NiFe2O4 particles prepared by ethylene glycol route

NiFe₂O₄ nanoparticles have been synthesized by co-precipitation method at 145°C in N₂ atmosphere using ethylene glycol as solvent and capping agent. This gives the promising synthesis route for nanoparticles at low temperature. The as-synthesized NiFe₂O₄ is subsequently heated at 400°C, 500°C, 700°C and 800°C. Crystallite size increases with the heat treatment temperature. The heat treatment temperature has direct effect on the electron paramagnetic resonance and intrinsic magnetic properties. The room temperature Mössbauer spectrum of the 800°C heated sample shows the two sextets pattern indicating that the sample is ferrimagnetic and Fe^3?+? ions occupy both tetrahedral and octahedral sites of spinel structure.