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Journal of Radioanalytical and Nuclear Chemistry -     

Dislocation unpinning model of acoustic emission from alkali halide crystals

The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations. Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate, the time constantτ _s for surface annihilation of dislocations and the pinning timeτ _p of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related to the AE from alkali halide crystals.     

Dielectric properties of KDP-type ferroelectric crystals in the presence of external electric field

Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities, temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease with electric field.     

Structural,magnetic and Mössbauer spectral studies of nanosize aluminum substituted nickel zinc ferrites

Nanosize aluminum substituted nickel zinc ferrites were prepared through aerosol route and characterized using TEM, XRD, magnetic measurements and Mössbauer spectroscopy. The particle size of as obtained samples was found to be ∼10 nm which increases up to ∼85 nm upon annealing at 1200 °C. The unit cell parameter ‘a’ decreases linearly with concentration of aluminum due to the small ionic radius of aluminum. The saturation magnetization for all the samples after annealing at 1200 °C lies in the range 12.9–72.6 emu/g and decreases linearly with concentration of aluminum. Room temperature Mössbauer spectra of all as obtained samples of ferrite compositions exhibited a broad doublet suggesting super paramagnetic nature. This doublet is further resolved into two doublets and assigned to the surface region and internal region atoms of the particles. The samples annealed at 1200 °C show broad sextets, which were fitted with five sextets, indicating different local environment of both tetrahedrally and octahedrally coordinated Fe cation.     

Generalized fractional programming duality: A parametric approach

Using a parametric approach, duality is presented for a minimax fractional programming problem that involves several ratios in the objective function.The first author is thankful to Natural Science and Engineering Research Council of Canada for financial support through Grant A-5319, and the authors are thankful to the anonymous referees for useful suggestions.     

Engel type identities with derivations for right ideals in prime rings

Let R be a prime ring of char R≠2, d a non-zero derivation of R and ρ a non-zero right ideal of R such that [[d(x),d(y)]_n [y,x]_m] = 0 for all x,y ∈ ρ or [[d(x),d(y)]_n d[y,x]_m] = 0 for all x,y ∈ ρ, n, m ≥ 0 are fixed integers. If [ρ,ρ]ρ ≠ 0, then d(ρ)ρ = 0.     

Self-organized ZnAl2O4 nanostructures grown on -sapphire

Self-organized ZnAl₂O₄ nanostructures with the appearance (in SEM) of high aspect ratio horizontal nanowires are grown on uncatalysed c-sapphire by vapour phase transport. The nanostructures grow as three equivalent crystallographic variants on c-sapphire. Raman and cathodoluminescence spectroscopy confirm that the nanostructures are not ZnO and TEM shows that they are the cubic spinel, zinc aluminate, ZnAl₂O₄, formed by the reaction of Zn and O with the sapphire substrate.     

SHI induced modification in CR-39 polycarbonate by positron annihilation lifetime studies

CR-39 is a polycarbonate widely used as SSNTD for recording nuclear charged particles and in other applications. Latent ion tracks produced in the polymers due to the damage produced by the passage of Swift Heavy Ions contain amorphous material with highest degree of disorder, changing the free volume properties which have strong correlation with the macroscopic properties of the material. Positron annihilation lifetime spectroscopy (PALS) provides direct information about the dimension, content and hole size distribution of free volume in polymers. The effect of irradiation of ⁴⁰Ar (14.9 MeV/n) ions on CR-39 polycarbonate by Positron Annihilation Lifetime Spectroscopy (PALS) is reported here. PALS provides a non-destructive and non-interfering probe, having high detection efficiency for free volume hole properties. From o-Ps lifetime mean free volume hole radius and average free volume of the micro-voids have been calculated. PAL measurement shows an increase in free volume on irradiation.