Optical transitions of Eu3+ ions in EuCl3 solutions

The optical absorption spectra of EuCl₃ in aqueous and acidic solutions were measured in the visible anduv regions of the spectrum. The concentration as well as the temperature of the solutions were varied to establish an accurate free-ion energy level scheme of Eu³⁺. The energy levels were assigned on the basis of a correlation between the calculated and the experimentally observed transition energies and associated band intensities.     

Role of anisotropy and interactions in magnetic nanoparticle systems

Magnetic nanoparticle systems are characterized by several competing effects like anisotropy, an inherent disorder, the long range dipolar and the short range exchange interactions due to clustering effects. The sensitivity of the observed static and dynamical properties of these systems like the blocking temperature, the hysteresis and the susceptibility, to the methods of preparation, annealing and the resulting morphology is a manifestation of this. However, given the complexity of the system, it is often difficult to isolate the effects which might be dominant in a particular sample, which has a direct bearing on the desired applications. In this paper we report the effects of anisotropy, interactions and particle concentration on the temperature dependent remanence and coercivity through a numerical simulation on an array of single domain magnetic particles which incorporates all the above mentioned factors. Our results show that it is possible to distinguish between purely anisotropic systems and interacting systems with these measurements. In confirmation of our simulation results we also present the experimental results on the remanence and coercivity of nanomagnetic nickel ferrite composites.     

Effects of fish farm loading on sea grass Posidonia oceanica at Vrgada Island (Central Adriatic): a nitrogen stable isotope study

Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant ¹⁵N enrichment (up to 4.7‰ at p?<?0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of ¹⁵N-enriched fish farm derived nitrogen waste.     

On the Diastereoselectivity of the Aqueous-Acid-Catalyzed Intramolecular Aldol Condensation of 3-Oxocyclohexaneacetaldehydes

The factors responsible for the diastereoselective formation of the 6-endo-hydroxybicyclo[2.2.2]octan-2-one by acid-catalyzed intramolecular aldol reaction of 3-oxocyclohexaneacetaldehydes have been investigated. This study, carried out on (1SR,4RS,6RS)-6-hydroxybicyclo[2.2.2]octan-2-one 1a , (1SR,4RS,6SR)-6-hydroxybicyclo[2.2.2]octan-2-one 1b , and 3,3-(ethylenedioxy)cyclohexaneacetaldehyde 2a , allowed to demonstrate the absence of intramolecular H-bonding in 1a as a stabilizing factor, and to ascertain the presence of unfavorable steric interactions in 1b .     

Raman scattering study of the phase sequence in A2BX4 halides

Raman spectra of Cs₂ZnI₄ single crystal have been measured in different scattering orientations covering the successive phase transitions down to 68 K. Two second order anomalies at around ice temperature (270 K) and at ～ 92 K are observed. The anomaly around ice temperature exhibits the features of a normal-incommensurate transition evidenced by softening of a low-lying lattice phonon whose frequency decreases as the transition temperature is approached from below whereas the latter one appears to arise from usual structural distortions.     

Dynamical Systems and Adaptive Timestepping in ODE Solvers

Initial value problems for ODEs are often solved numerically using adaptive timestepping algorithms. These algorithms are controlled by a user-defined tolerance which bounds from above the estimated error committed at each step. We formulate a large class of such algorithms as discrete dynamical systems which are discontinuous and of higher dimension than the underlying ODE. By assuming sufficiently strong finite-time convergence results on some neighbourhood of an attractor of the ODE we prove existence and upper semicontinuity results for a nearby numerical attractor as the tolerance tends to zero.This assumption of sufficiently strong finite-time convergence results is then examined for adaptive algorithms that use a pair of explicit Runge-Kutta methods of different order to estimate the one-step error. For arbitrary Runge-Kutta pairs the necessary finite-time convergence results fail to hold on a set of points in the phase space that includes all the equilibria of the ODE. Therefore, in general, the asymptotic convergence results cannot be applied to attractors containing equilibria. However, for a particular class of Runge-Kutta pairs, the finite-time convergence results can be strengthened to include neighbourhoods of equilibrium points for which the Jacobian is invertible.     

Domain decomposition methods for hyperbolic problems

In this paper a method is developed for solving hyperbolic initial boundary value problems in one space dimension using domain decomposition, which can be extended to problems in several space dimensions. We minimize a functional which is the sum of squares of the L ² norms of the residuals and a term which is the sum of the squares of the L ² norms of the jumps in the function across interdomain boundaries. To make the problem well posed the interdomain boundaries are made to move back and forth at alternate time steps with sufficiently high speed. We construct parallel preconditioners and obtain error estimates for the method. The Schwarz waveform relaxation method is often employed to solve hyperbolic problems using domain decomposition but this technique faces difficulties if the system becomes characteristic at the inter-element boundaries. By making the inter-element boundaries move faster than the fastest wave speed associated with the hyperbolic system we are able to overcome this problem.