Densely Functionalized 2-Methylideneazetidines: Evaluation as Antibacterials

Twenty-two novel, variously substituted nitroazetidines were designed as both sulfonamide and urethane vinylogs possibly endowed with antimicrobial activity. The compounds under study were obtained following a general procedure recently developed, starting from 4-nitropentadienoates deriving from a common β-nitrothiophenic precursor. While being devoid of any activity against fungi and Gram-negative bacteria, most of the title compounds performed as potent antibacterial agents on Gram-positive bacteria (E. faecalis and three strains of S. aureus), with the most potent congener being the 1-(4-chlorobenzyl)-3-nitro-4-(p-tolyl)azetidine 22, which displayed potency close to that of norfloxacin, the reference antibiotic (minimum inhibitory concentration values 4 and 1–2 μg/mL, respectively). Since 22 combines a relatively efficient activity against Gram-positive bacteria and a cytotoxicity on eucharyotic cells only at 4-times higher concentrations (inhibiting concentration on 50% of the cultured eukaryotic cells: 36 ± 10 μM, MIC: 8.6 μM), it may be considered as a promising hit compound for the development of a new series of antibacterials selectively active on Gram-positive pathogens. The relatively concise synthetic route described herein, based on widely available starting materials, could feed further structure–activity relationship studies, thus allowing for the fine investigation and optimization of the toxico-pharmacological profile.     

Numerical experiments with two approximate inverse preconditioners

We present the results of numerical experiments aimed at comparing two recently proposed sparse approximate inverse preconditioners from the point of view of robustness, cost, and effectiveness. Results for a standard ILU preconditioner are also included. The numerical experiments were carried out on a Cray C98 vector processor. This work was partially supported by the GA AS CR under grant 2030706 and by the grant GA CR 205/96/0921.     

Metal-organic deposition of YBCO and BSCCO platelets,films and wires

Il Nuovo Cimento D - Metal-Organic Deposition (MOD) technique has been used for the first time, in the spray version, to obtain thin and thick films of BSCCO on substrates like MgO and Ag and, in...     

Random behaviour of nonlinear waves in a closed basin

Summary This paper concerns the Hamiltonian formulation of non-linear waves in a closed basin. Using the spectral representation of the functional Hamiltonian, we transform our problem in continuous mechanics into a problem in classical mechanics. Truncating the new Hamiltonian at the first order in the slope of the surface elevation and considering only two degrees of freedom, we study the statistical behaviour of this system. We find that under a critical energy the motion in phase space appears to be ordered, whereas above the critical value we have a random behaviour.

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Riassunto Questo lavoro tratta il problema delle onde non lineari in un bacino chiuso nella sua formulazine hamiltoniana. Usando la rappresentazione spettrale dell’hamiltoniana, si trasforma il problema di meccanica dei continui in problema di meccanica classica. Troncando la nuova hamiltoniana al primo ordine nello sviluppo in pendenza della superficie e considerando solo due gradi di libertà, si studia il comportamento statistico del sistema. Si trova che sotto una certa energia critica il moto nello spazio delle fasi è ordinato, mentre sopra il valore critico si ha un comportamento stocastico.

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Резюме В этой статье рассматривается гамильтонова формулировка нелинейных волн в замкнутом резервуаре. Используя спектральное представление рункции Гамильтона, мы преобразуем нашу проблему в механике сплошных сред в проблему классической механики. Обрезая новый Гамильтониан на первом порядке по наклону поверхности возвышения и рассматривая только две степени свободы, мы исследем статическое поведение этой системы. Мы находим, что ниже критической энергии движение в фазовом пространстве оказывается упорядоченным, тогда как выце критической энергии мы имеем случайное поведение.

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Research partially sponsored by C.N.R. ≪Progetti Finalizzati Oceanografia≫     

Population dynamics at high Reynolds number

We study the statistical properties of population dynamics evolving in a realistic two-dimensional compressible turbulent velocity field. We show that the interplay between turbulent dynamics and population growth and saturation leads to quasilocalization and a remarkable reduction in the carrying capacity. The statistical properties of the population density are investigated and quantified via multifractal scaling analysis. We also investigate numerically the singular limit of negligibly small growth rates and delocalization of population ridges triggered by uniform advection.     

Intermittency and universality in fully developed inviscid and weakly compressible turbulent flows

We perform high-resolution numerical simulations of homogenous and isotropic compressible turbulence, with an average 3D Mach number close to 0.3. We study the statistical properties of intermittency for velocity, density, and entropy. For the velocity field, which is the only quantity that can be compared to the isotropic incompressible case, we find no statistical differences in its behavior in the inertial range due either to the slight compressibility or to the different dissipative mechanism. For the density field, we find evidence of "frontlike" structures, although no shocks are produced by the simulation.     

On the Heat Transfer in Rayleigh–Bénard Systems

In this paper we discuss some theoretical aspects concerning the scaling laws of the Nusselt number versus the Rayleigh number in a Rayleigh–Bénard cell. We present a new set of numerical simulations and compare our findings against the predictions of existing models. We then propose a new theory which relies on the hypothesis of Bolgiano scaling. Our approach generalizes the one proposed by Kadanoff, Libchaber, and coworkers and solves some of the inconsistencies raised in the recent literature.     

Stochastically perturbed Landau-Ginzburg equations

We analyze several aspects of a reaction-diffusion equation in two space dimensions with cubic nonlinearity, stochastically perturbed by white noise in time and in space. This equation needs renormalization, and physical implications of this circumstance are discussed. In particular, for sufficiently large coupling constant the effective potential becomes a double well and rare transitions from one minimum to the other are possible. These, however, are revealed only by large-scale fluctuations which exhibit a bimodal distribution. Fluctuations below a critical scale have unimodal distribution and do not see the double well. This phenomenon is connected with the singular character of local fluctuations in two or more space dimensions. The theoretical results are confirmed by numerical simulations. The possible physical relevance of our results is illustrated in connection with the analysis of certain observations of atmospheric fields.