Shaking table tests and numerical investigation of two-sided damping constraint for end-stop impact protection

During strong earthquakes, structural pounding may occur between the equipment and the surrounding moat wall because of the limited separation distance and the deformations of the isolator. A potential mitigation measure for this problem is the incorporation of collision bumpers. The aim of the paper is to study the experimental dynamic response and to formulate numerical model of a base-isolated SDOF oscillator excited by a harmonic base acceleration and symmetrically bounded by two unilateral deformable and dissipative constraints. Static tests have been first performed to determine the static characteristics and the support conditions of the bumpers, and successively, shaking table tests have been carried out to investigate two different configurations: the absence and the presence of bumpers. In both configurations, tests were carried out with the same type of excitation to the base. Different values of the table acceleration peak were applied, different amplitude values of the total gap between mass and bumpers were considered, and also two different types of bumpers were employed. The experimental dynamic responses in the absence and in the presence of bumpers have been compared, and the results obtained in the presence of bumpers have also been used to identify some characteristics of the dynamics with impact (force and time of contact between mass and bumpers, energy dissipated by the bumpers during the impact, and coefficient of restitution). A suitable model has been developed to numerically simulate the behavior of the system by using a general-purpose computer code, achieving a good agreement with the experimental results.     

The behaviour of nonlinear oscillators subjected to ramped forcing

This paper considers the behaviour of a mechanical oscillator with cubic non-linearity subjected to a forcing excitation whose frequency remains constant while the amplitude is ramped, growing until it reaches a predetermined value. We concentrate on the nature of the basins of attraction whose size indicates the stability of the system, in a structural sense. The reduced level of forecing at the initial stages of ramping produces a delay in bifurcational events when compared to the constant sinusoidally forced counterpart. Preliminary results show that for some parameter values the area of basin does not increase monotonically as the length of ramping is varied. A preliminary version was presented at BIFCHAOS '92, Workshop held at L'Aquila, Italy, on 20–21 May 1992.     

Towards a General Theory of Quantized Fields on the Anti-de Sitter Space-Time

 We propose a general framework for studying quantum field theory on the anti-de-Sitter space-time, based on the assumption of positivity of the spectrum of the possible energy operators. In this framework we show that the n-point functions are analytic in suitable domains of the complex AdS manifold, that it is possible to Wick rotate to the Euclidean manifold and come back, and that it is meaningful to restrict AdS quantum fields to Poincaré branes. We give also a complete characterization of two-point functions which are the simplest example of our theory. Finally we prove the existence of the AdS-Unruh effect for uniformly accelerated observers on trajectories crossing the boundary of AdS at infinity, while that effect does not exist for all the other uniformly accelerated trajectories. Received: 3 December 2001 / Accepted: 26 July 2002 Published online: 21 October 2002     

Large-eddy simulation of impinging jets on smooth and rough surfaces

We performed large-eddy simulations (LES) of forced impinging jets over smooth and rough surfaces, containing large-scale, azimuthal vortices generated by the enhanced primary instability in the jet shear layer. The interaction between these vortices and the turbulence in the wall jet that is formed downstream of the impingement region determines their rate of decay. To explore the surface-roughness effects on the evolution of the vortices, sand-grain-like surfaces are generated using uniformly distributed but randomly oriented ellipsoids. The flow is compared to our previous LES of jets impinging on a smooth surface. In spite of the severe modification caused by the roughness on the near-wall flow, the vortex development is not significantly altered. Slightly faster decay of the primary vortices is observed in the rough-wall case compared to the smooth-wall one; the secondary vortex that detaches from the wall and is lifted up has larger vorticity. The highly disturbed near-wall flow is advected outward and affects the evolution of the primary vortex for a longer period during the vortex interaction. The robust turbulent generation mechanism in the outer shear layer, however, mitigates the changes in vortex behaviour. The momentum deficit and the enhancement of turbulence due to the surface roughness play a key role during this process.     

Conversion of oximes to carbonyl compounds by triscetylpyridinium tetrakis(oxodiperoxotungsto) phosphate (PCWP)-mediated oxidation with hydrogen peroxide

Aromatic and aliphatic oximes have been deoximated in chloroform-water to the corresponding aldehydes with dilute hydrogen peroxide and triscetylpyridinium tetrakis (oxodiperoxotungsto) phosphate as catalyst. The presence of dipolarophiles in the reaction mixtures allows a competitive reaction that converts oximes into isoxazole and isoxazoline derivatives via the intermediate formation of nitrile oxide species.     

Design and synthesis of bis-amide and hydrazide-containing derivatives of malonic acid as potential HIV-1 integrase inhibitors

HIV-1 integrase (IN) is an attractive and validated target for the development of novel therapeutics against AIDS. In the search for new IN inhibitors, we designed and synthesized three series of bis-amide and hydrazide-containing derivatives of malonic acid. We performed a docking study to investigate the potential interactions of the title compounds with essential amino acids on the IN active site.     

Structural Elucidation of C6H4+. Using Chemical Reaction Monitoring: Charge Transfer Versus Bond Forming Reactions

Mass spectrometry is a powerful tool but when used on its own, without specific activation of ions, the ion mass is the single observable and the structural information is absent. One way of retrieving this information is by using ion–molecule reactions. We propose a general method to disentangle isomeric structures by combining mass spectrometry, tunable synchrotron light source, and quantum-chemistry calculations. We use reactive chemical monitoring technique, which consists in tracking reactivity changes as a function of photoionization energy i. e. the ionic structure. We illustrate the power of this technique with charge transfer reactions of C₆H₄^+. isomers with allene and propyne and discuss its universal applicability. Furthermore, we emphasize the special reactivity characteristics of distonic ions, where strong charge transfer reactivity but very limited reactivity involving bond formation and following cleavages were observed and attributed to the unconventional ortho-benzyne distonic cation.     

Electron-transfer-induced reductive cleavage of chlorinated aryloxyalkanoic acids

We investigated the degradation of chlorinated herbicides, with an aryloxyalkanoic acid skeleton, under reductive electron transfer reaction conditions. Although Li and Na metals proved useless, activated forms of these metals, either their soluble naphthalene radical anions or 1,2-diarylethane dianions, promoted the degradation of the starting materials to various extents. Indeed, lithium naphthalenide promoted both extensive dehalogenation and dealkylation of chlorinated aryloxyalkanoic acids, with formation of the corresponding phenols as the main reaction products. In contrast, the employment of 1,2-diphenyl-1,2-disodioethane as a reducing agent led, in most examples, to the chemoselective recovery of the corresponding dechlorinated acids.     

Atomic force microscopy and X-ray photoelectron spectroscopy characterization of low-energy ion sputtered mica

We report for the first time on muscovite mica surfaces nanostructured by a low-energy defocused Ar ion beam: ripple structures self-organize on macroscopic areas, with wavelength and roughness in the range 40-140 nm and 0.5-15 nm respectively, according to ions dose. In detail we address structural and chemical variations of the surface layer induced by sputtering. X-ray Photoelectron Spectroscopy (XPS) survey spectra reveal selective sputtering and Al surface enrichment whereas Atomic Force Microscopy (AFM) force-spectroscopy experiments indicate reduced charging of irradiated specimens under aqueous electrolyte solutions. Such experimental evidences contribute to clarify the chemical and physical properties of nanostructured mica samples, in view of their potential use as templates for aligned deposition of organic molecules and investigations on nanolubrication phenomena.