No abstract available

[en] Short communication

[en] The composting process has been consolidated as one of the most accurate techniques for the treatment and recycling of the organic wastes. Along such process three different stages can be recognized taking into account temperature evolution, so the automation equipment's used to control the process at industrial scale must work on the control elements (fans, valves, sprinklers, etc.) with the objective that each of the stages is developed in a correct way. However, the organic wastes high variability, and the great amount of variables which can influence the microbial activity (responsible of the process), makes difficult to predict the behaviour a specific waste will develop once inside the bioreactor. (Author)

[en] The NMR chemical shift spectra of diamond, chemical-vapor-deposited (CVD) diamond, and diamondlike amorphous carbon are computed from first principles. The results of our calculation are in excellent agreement with experiments, and are useful for the interpretation of the NMR spectra in terms of the microscopic structure of the materials. In particular, we show that the NMR and Raman linewidths in polycrystalline CVD diamond are due to stress fluctuations, and we support a heterogeneous model for the amorphous hydrogenated phase. copyright 1997 The American Physical Society

No abstract available

[en] Results of the shielding against the Earth's magnetic field on a large volume are given. The experimental procedure is based on a multilayer μ-metal shield and a series of correcting electric coils. A final average value of (8.1±4.4) mG is obtained in a volume of about 20 m³. (orig.)

[en] We present an ab initio approach for the computation of the magnetic susceptibility χ of insulators. The approach is applied to compute χ in diamond and in solid neon using density functional theory in the local density approximation, obtaining good agreement with experimental data. In solid neon, we predict an observable dependence of χ upon pressure. copyright 1996 The American Physical Society

[en] We present a theory for the ab initio computation of NMR chemical shifts (σ) in condensed matter systems, using periodic boundary conditions. Our approach can be applied to periodic systems such as crystals, surfaces, or polymers and, with a supercell technique, to nonperiodic systems such as amorphous materials, liquids, or solids with defects. We have computed the hydrogen σ for a set of free molecules, for an ionic crystal LiH, and for a H-bonded crystal HF, using density functional theory in the local density approximation. The results are in excellent agreement with experimental data. copyright 1996 The American Physical Society

[en] An energy functional for orbital-based O(N) calculations is proposed, which depends on a number of nonorthogonal, localized orbitals larger than the number of occupied states in the system, and on a parameter, the electronic chemical potential, determining the number of electrons. We show that the minimization of the functional with respect to overlapping localized orbitals can be performed so as to attain directly the ground-state energy, without being trapped at local minima. The present approach overcomes the multiple-minima problem present within the original formulation of orbital-based O(N) methods; it therefore makes it possible to perform O(N) calculations for an arbitrary system, without including any information about the system bonding properties in the construction of the input wave functions. Furthermore, while retaining the same computational cost as the original approach, our formulation allows one to improve the variational estimate of the ground-state energy, and the energy conservation during a molecular dynamics run. Several numerical examples for surfaces, bulk systems, and clusters are presented and discussed

[en] Full text: In order to build electronic components using graphene a band gap needs to be obtained. One way of achieving this is by restricting the structures in space to finite width, for example as a nanoribbon. They expose edges that are usually highly reactive and thus would easily adsorb atoms from the gas phase. We have studied the stability of carbon nanoribbons exposed to various elements and molecules, including hydrogen and oxygen, water and ammonia, using thermodynamical considerations. The total energies were obtained by total energy calculations employing the density-functional theory. We report the various structures found to be stable at different temperatures and pressures, and analyse the electronic structure evaluating quantities that could be experimentally verified. (author)