[en] In this article the author discusses the problem of nuclear safety in the 'Third World', especially in the light of the recent accident at Three Mile Island, U.S.A.; but economic pressures in developing countries mean that safety may not always come first. Western insistence on safety may also be seen as an attempt to hamper Third World progress. (author)

[en] The refusal of the Indian Government to sign the Non-Proliferation Treaty, the implications of this refusal on the supply of nuclear fuels for the Indian reactors by the US and the effect on the Indian nuclear programme of this ban are discussed. (UK)

[en] A trend has been perceived in the field of composite materials to employ carbon nanotubes as reinforcement in synthesizing composites of unique properties. In this endeavor, free standing structures of Al-based nanostructured composite with carbon nanotubes as second phase particles has been synthesized by plasma spray forming technique. Optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy has been carried out to analyze the composite structure and to verify the retention of carbon nanotubes. Besides, density and microhardness measurements have been performed to understand the effect of carbon nanotube reinforcement on the mechanical properties of the composite. The characterization affirms the presence of unmelted and chemically unreacted carbon nanotubes in the composite. Moreover, the composite experienced an increase in relative microhardness due to the presence of carbon nanotube

[en] Glasses with composition xBi₂O₃.(30-x)K₂O.70B₂O₃ doped with 2 mol% of V₂O₅ have been prepared over the range 0≤x≤15 (in mol%). The electron paramagnetic resonance spectra of VO²⁺ in these glasses have been recorded in the X-band (∼9.3 GHz) at room temperature. The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that, with increase in Bi₂O₃:K₂O ratio, tetragonal distortion of the V⁴⁺O₆ complex increases and there is an expansion of the 3d_xy orbit of unpaired electron in the vanadium ion. The values of theoretical optical basicity have also been reported. The molecular orbital coefficients have been calculated by recording the optical transmission spectra in the wavelength range 500-850 nm. The direct-current electrical conductivity, σ, has been measured in the temperature range 443-523 K. σ decreases with increase in Bi₂O₃:K₂O ratio because of the decrease in the mobility and number of mobile K⁺ ions and there is no electronic contribution to the conductivity by Bi₂O₃

[en] Complete text of publication follows. There are two main methods for modelling recombination and spin dynamics in radiation chemical systems: a Monte Carlo random flights method (MC), in which the trajectories of the diffusing species are followed explicitly; the Independent Reaction Times method (IRT), in which reaction times are sampled from appropriate marginal distribution functions. This paper reports recent developments to both methods, which extend the range of systems for which they can be used. The main chemical problem with the IRT method is the problem of dealing with secondary reactions of reactive products. The main difficulty is the requirement to generate distances from the new particle to the remaining reactants. Several methods have been proposed in the past, none of which is wholly satisfactory. This paper reports a new 'First Passage Approach' algorithm that allows the new distance to be generated conditional on the IRT that already existed for that pair. This removes a source of bias that is present in the current methods. Tests against full MC simulations show (i) that the new method introduces new particles with the correct spatial distribution and (ii) that it is more accurate than current methods in modelling the subsequent kinetics. Methods for simulating coherent spin evolution in radiation chemical systems have been proposed and implemented before, but it has not been possible to include incoherent spin relaxation in the Hilbert space formalism used. A method for simulating spin relaxation based on discrete events suggested by Brocklehurst has been implemented in both MC and IRT models and tested for a single radical pair against methods using Liouville space and the density matrix formulation. Essentially exact agreement is found, permitting spin models to be generalised with the addition of spin relaxation (both T1 and T2). Spin effects leading to polarisation require the action of distance-dependent interactions such as exchange. It is straightforward to include these in trajectory based MC simulations as the spin evolution becomes an integration along the diffusion path. However, it has always been thought to be impossible to do this using the much faster IRT method. By partitioning the space surrounding each particle into small shells and including the first passage times between these shells it is possible to generalise the IRT method to model these interactions with a comparable accuracy to the MC method, both for neutral and charged pairs. This new method makes it possible to simulate effects such as polarisations with a much better statistical precision than before because of the ability to perform many more realisations.

[en] Complete text of publication follows. In low permittivity solvents ion recombination is dominated by the effects of the relative drift of the ions caused by the Coulomb attraction. However, such systems are frequently investigated by scavenging methods. Since the work of Tachiya on electric field effects, drift has been known to affect the steady-state scavenging rate constant. However, during the recombination drift depends on the instantaneous distance between the ions, and is therefore inherently transient. This paper describes an investigation of this problem using simulation methods. It is found that, within the constraint of the diffusion approximation, there are conditions where the Smoluchowski time-dependent rate constant underestimates the degree to which scavenging intercepts geminate recombination. For this to be a substantial effect the initial distance between the ions must be relatively small (e.g. 4 nm) compared to the typical thermalisation distance of an electron (e.g. 8 nm). Simulations have been used to generate numerical time-dependent rate constants for scavenging. But these proved barely more successful than the Smoluchowski theory, in spite of having been calculated from the simulation results. Stratification of results by recombination time shows that there is a strong correlation between the recombination time and the scavenging time. It was hypothesised that this correlation arises through the strong transient drift as the ions approach one another. This hypothesis was confirmed by the application of a novel simulation method in which the ion trajectories are simulated conditional on the recombination time. It was found that in every case the scavenging rate increases sharply just prior to recombination. This dependence of scavenging rate on recombination time is a fundamental breakdown of the assumptions underlying both the theory of diffusion kinetics and the IRT method. Nonetheless, a path decomposition method has been devised that allows IRT simulations to be corrected for this effect with good accuracy.

[en] Glasses with composition xBi₂O₃·(70-x)B₂O₃·30Li₂O containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤20 (in mol%). The electron paramagnetic resonance (EPR) spectra of VO²⁺ ions of these glasses have been recorded in the X-band (∼9.13 GHz) at room temperature. Spin Hamiltonian parameters (SHP), g_parallell, g_{perpendicular}, A_parallell, Ag_{perpendicular}, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra in the wavelength range of 500-850 nm. It has been observed that the octahedral symmetry around V⁴⁺ ion is improved, and the 3d_xy orbit of the unpaired electron of the vanadium ion expands with increase in Bi₂O₃:B₂O₃ ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The dc conductivity increases with an increase in temperature. The dc conductivity variation with Bi₂O₃ content shows mixed glass-former effect at x=8 mol%. For x=10 mol%, the conductivity decreases with increase in Bi₂O₃ content because of the decrease in the mobility and the number of Li⁺ ions available for the conduction

[en] Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2xMX·(0.30-x)M₂O·0.70B₂O₃ (M=Na or K; X=Cl or Br) (0.01≤x≤0.10) containing 2.0 mol% of V₂O₅ have been studied. The spin-Hamiltonian parameters (SHP) of the VO²⁺ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients (α² and γ²) have been calculated. It is observed that in KX·K₂O·B₂O₃ (X=Cl or Br) glasses, the tetragonal nature of V⁴⁺O₆ complex decreases with KBr for x≥0.05. An increase in the 2KX:K₂O ratio (x≥0.05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of NaX·Na₂O·B₂O₃ (X=Cl or Br) glasses, the SHP are independent of change in 2NaX:M₂O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, Λ_th. It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10^-6 Ω^-1 m^-1 at low temperatures and 10^-4 Ω^-1 m^-1 at high temperatures. In MCl·M₂O·B₂O₃ (M=Na or K) glasses, the conductivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr·M₂O·B₂O₃ (M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content

[en] Mass filter ion transmission factors are presented for a wide range of initial beam divergence properties, from parallel beams to highly divergent beams. Relationships between resolution, aperture size and sensitivity are discussed. Analytical solutions for trajectory maxima are investigated, with the help of which peak shapes, transmission and other mass filter properties can be rapidly determined. (Auth.)

[en] Given the design parameters of the ADITYA tokamak and its radio-frequency heating system, the high-bootstrap regime of operation is determined. Secondly, a mixed zero/one-dimensional transport model is used to simulate the transient plasma behavior towards a steady state. This yields bounds on plasma and radio-frequency system parameters that will permit access to the steady desired state. Thirdly, the profiles for the rotational transform thus obtained are examined for stability. 11 refs, 3 figs, 2 tabs