Analysis of a multistate control problem related to food technology

This paper is concerned with an optimal control problem related to the determination of an optimal profile for the steam temperature into the autoclave along the processing of canned foods. The problem studies a system coupling the evolution Navier-Stokes equations with the heat transfer equation by natural convection (the so-called Boussinesq equations), and with the microorganisms removal equation. The essential difficulties in the study of this multistate control problem arise from the lack of uniqueness for the solution of the state system. Here we obtain—after a careful analysis of the problem mathematical formulation—the uniqueness of part of the state, and the existence of optimal solutions.     

First chemoenzymatic synthesis of immunomodulating macrolactam pimecrolimus

The preparation of pimecrolimus, a synthetic derivative of ascomycin endowed with immunomodulatory activity, requires the selective protection of 24-hydroxy group of the ascomycin, before elaboration of the 32-hydroxy group. The aim was achieved by means of two regioselective Candida antarctica lipase-catalyzed steps. The structure of the new key intermediates, 24-, 32-monoacetates, and 24,32-diacetate, was established by means of an unambiguous NMR study.     

Release time calculations for the SPES direct UCx target

A Direct Target for a mid-term RIB ISOL-type facility is being developed at LNL, in the framework of the R&D for the SPES project [1]. Using a 40 MeV proton beam impinging on a UCx thick target of 2.5 g/cm³ density, a production rate of 10¹³ in target fissions per second is expected [2]. The crucial point, when short-lived isotopes are produced in the target, is to build systems (target + ion source) with good release properties and high efficiency. Monte Carlo simulations were performed using the GEANT4 toolkit [3] and the RIBO code [4] in order to optimize our target geometry and to estimate the average release time.     

Substituent effects in the migration step of the Baeyer-Villiger rearrangement. A theoretical study

Quantum mechanical calculations have been performed on the migration step of the Baeyer-Villiger (BV) rearrangements of some acetophenones, p-RC6H4COCH3 (R = CN, Cl, H, CH3, CH3O) with m-chloroperbenzoic acid. The energy barriers, charge distributions, and frontier molecular orbitals determined for the aryl migration step explain the effects of substituents on the reactivity of these ketones. A plot of the log of relative oxidation rates of the ketones versus their corresponding calculated energy barriers of the migration stage showed a downward deviation for the p-OCH3 derivative. This result is consistent with a change in the rate-determining step, from the aryl migration to the carbonyl addition, in the case of p-methoxyacetophenone, according to the suggestion that the rate-determining step of the BV oxidation can change with variations in the substituent group.     

Three-dimensional modelling of inductively coupled plasma torches

A three-dimensional model has been developed for simulating the behaviour of inductively coupled plasma torches (ICPTs), using customized CFD commercial code FLUENT ^?. The helicoidal coil is taken into account in its actual 3-D shape, showing the effects of its non-axisymmetry on the plasma discharge. Steady state, continuity, momentum and energy equations are solved for argon optically thin plasmas under the assumptions of LTE and laminar flow. The electromagnetic field is obtained by solving the 3-D vector potential equation on a grid extending outside the torch region. In order to evaluate the importance of various 3-D effects on calculated plasma temperature and flow fields, comparisons of our new results with the ones obtainable from conventional 2-D models and from an improved 2-D model that includes 3-D coil effects are presented. The presence of wall temperature hot spots due to plasma discharge displacement from the torch axis is evidenced, while the use of the new 3-D code for optimization of induction coil geometry and plasma gas inlet features is foreseen. Received 5 September 2002 Published online 13 December 2002 RID="a" ID="a"e-mail: colombo@ciram.ing.unibo.it     

Atomic scale origin of crack resistance in brittle fracture

We investigate the physical meaning of the intrinsic crack resistance in the Griffith theory of brittle fracture by means of atomic-scale simulations. By taking cubic SiC as a typical brittle material, we show that the widely accepted identification of intrinsic crack resistance with the free surface energy underestimates the energy-release rate. The strain dependence of the Young modulus and surface energy, as well as allowance for lattice trapping, improve the estimate of the crack resistance. In the smallest scale limit, crack resistance can be fitted by an empirical elastoplastic model.     

Algebraic classification of ℂP n instanton solutions

The finite condition for two-dimensional ℂP ⁿ models is discussed noting that one can impose boundary conditions such that the domain of the field is a compact Riemann surface S _g. Holomorphic maps φ: S _g →ℂP ⁿ give finite energy solutions of the classical field equations, which are classified according to standard methods of algebraic geometry. The moduli problem is discussed in detail for S _g =ℂP ¹=S ².     

Phase transition in the phenanthrene crystal. A spectroscopic study

The Raman spectrum of the phenanthrene crystal was investigated between ?190 and +90°C. The results indicate that intermolecular forces play an important role in the solid—solid phase transition at 70°C. The assumption of a molecular conformational change was not confirmed.     

Spectral density method for an anisotropic linear chain

The spectral density method is used to study the thermodynamic properties of an anisotropic antiferromagnetic Heisenberg linear chain in an external magnetic field. Insecond order approximation without the decoupling procedure for the two particle correlation function, we are able to obtain many results in terms of both the temperature and the magnetic field for different values of the anisotropy parameter. The ground state of the model is investigated and the singular behaviour of some thermodynamic quantities near the critical field is determined. In particular, explicit analytical solutions are given for small anisotropy parameters. Our results are compared with the ones obtained by means of other methods and some exact results are reproduced.     

SELECTIVE PHOTOSENSITIZED OXIDATION OF THE METHIONYL RESIDUES IN ELASTASE

In recent years, significant advances have clarified the mechanism of photosensitized oxidations (see, for example, Foote, 1968), especially as regards the nature of the reactive oxidizing agents. This fact stimulated the development of reaction systems which allow selective photooxidation of specific components of biological macromolecules (Spikes and Livingston, 1969; Spikes and MacKnight, 1970). In the field of proteins, the selective conversion of the methionyl residues to the sulfoxide can be achieved by irradiation with visible light in the presence of hematoporphyrin at neutral or acid pH (Jori et al. , 1969).