The Nitro Ketal Approach to Furane Systems. Total Synthesis of Racehic Bilobanone

Continuing our studies with the chemistry of ketals of β-nitro ketones¹, we wish to describe a new furane synthesis exemplified by a total synthesis of the sesquiterpene bilobanone 1 ².     

Stability and Bifurcation Analysis of a Spinning Space Tether

A detailed, geometrically exact bifurcation analysis is performed for a model of a power-generating tethered device of interest to the space industries. The structure, a short electrodynamic tether, comprises a thin, long rod that is spun in a horizontal configuration from a satellite in low Earth orbit, with a massive electrically conducting disk at its free end. The system is modelled using a Cosserat formulation leading to a system of Kirchhoff equations for the rod's shape as a function of position and time. Moving to a rotating frame, incorporating the effects of internal damping, intrinsic curvature due to the deployment method and novel force and moment boundary conditions at the contactor, the problem for steady rotating solutions is formulated as a two-point boundary value problem. Using numerical continuation methods, a bifurcation analysis is carried out varying rotation speeds up to many times the critical resonance frequency. Spatial finite differences are used to formulate the stability problem for each steady state and the corresponding eigenvalues are computed. The results show excellent agreement with earlier multibody dynamics simulations of the same problem.     

Two Coordination Modes of CO in Zeolites: A Temperature-Dependent Equilibrium

CO interacts with exchangeable cations M⁺ (gray spheres in the picture) of zeolites to form M⁺⋅⋅⋅CO and M⁺⋅⋅⋅OC species (C: black; O: white) which are in a temperature-dependent equilibrium. For Na-ZSM-5 (M⁺=Na⁺) the difference in interaction energy amounts to 3.8 kJ mol⁻¹, as determined by means of variable-temperature FT-IR spectroscopy.     

Advances in White Wine Protein Stabilization Technologies

The unstable proteins in white wine cause haze in bottles of white wine, degrading its quality. Thaumatins and chitinases are grape pathogenesis-related (PR) proteins that remain stable during vinification but can precipitate at high temperatures after bottling. The white wine protein stabilization process can prevent haze by removing these unstable proteins. Traditionally, bentonite is used to remove these proteins; however, it is labor-intensive, generates wine losses, affects wine quality, and harms the environment. More efficient protein stabilization technologies should be based on a better understanding of the main factors and mechanisms underlying protein precipitation. This review focuses on recent developments regarding the instability and removal of white wine proteins, which could be helpful to design more economical and environmentally friendly protein stabilization methods that better preserve the products´ quality.     

Construction of Arnold tongue structures for coupled periodic oscillators

Arnold tongue structures generated due to the mutual entrainment of two periodic oscillators are studied experimentally and numerically. This mutual entrainment is provoked due to the mutual (bidirectional) coupling between the two oscillators. In experiments, this bidirectional coupling is achieved by immersing a pair of anodes (oscillators) in a common electrolytic solution. A voltage mismatch between these anodes renders the time period of the uncoupled oscillators non-identical. Moreover, the coupling strength between the two oscillators is uniquely determined by the Euclidean distance separating them. Systematically varying the distance between these two anodes as a function of their voltage mismatch, phase locked domains were located. Subsequently, Arnold tongue structures were constructed in the experiments. Numerical simulations, using a model for electrochemical corrosion, corroborate our experimental findings.     

Highly sintered nickel oxide: surface morphology and FTIR investigation of CO adsorbed at low temperature

The monolayer of CO molecules adsorbed at low temperature on highly sintered nickel oxide, gives rise to a very symmetric IR absorption band at 2136 cm⁻¹ (θ_max) with a full-width at half-maximum (FWHM) of 3.7 cm⁻¹. This band shifts to higher frequenc upon decreasing the coverage, reaching the 2152 cm⁻¹ value for θ→0. The observed shift is due to changes in the lateral interactions (dynamic and static) among the adsorbed molecules. The observed spectral simplicity implies that most of the adsorbed CO molecules occupy crystallographically identical sites with a similar environment. Moreover, the remarkably small half-width indicates that inhomogeneous broadening effects, due to surface defects, are very small and that NiO microcrystals behave as single crystals. The morphology of microcrystals has been studied by SEM, AFM and HRTEM techniques: it was concluded that the surface termination of the sample is mainly represented by the (100) and (111) faces.     

Fourier transforms method for measuring thermal lens induced in diluted liquid samples

Drawing on interferometry and Fourier analysis, this paper describes the use of a two-beam thermal lens technique for measuring thermo-optical properties in optical materials. The procedure consists of yield interference patterns deformed by a localized photothermal effect. The photothermal phase shift is locally induced by the pump beam focused on a tested sample located on an on-axis probe beam, which is the first arm of a Mach-Zehnder interferometer. The plane where the effect is localized is imaged onto a CCD camera. Then two interferograms are recorded: one without effect and the other one with the induced photothermal phase. Fourier analysis performed on these interferograms allow us to plot the thermal lens map and, therefore, to estimate thermo-optic constant of Malachite Green in water solution. The method is applied to measure low linear absorptions of a diluted sample of Rhodamine B in water solution at 633 nm, showing that the proposed technique allows to measure photothermal phase shift as low as 3.1 mrad at 8 mW of input power in diluted materials.     

Spectrally-resolved white-light interferometry as a profilometry tool

Phase-shifting interferometry and white-light interferometry are reliable techniques for surface analysis in which the optical path difference has to be changed by some transducer to evaluate the phase. We present here a different procedure in which optical path modulation is completely avoided. This technique is based on the spectral analysis of white-light interferograms. By means of a spectroscopic device, a non-visible interferogram is split into its monochromatic components and absolute, unambiguous values of the phase are obtained along the spectral axis. Only one interferogram is required to obtain the profile of one-dimensional surfaces with nanometric resolution.     

Alternating chaotic and periodic dynamics in Chern-Simons-Higgs theory with scalar magnetic interaction

The dynamical behavior of a Chern-Simons-Higgs system is studied for the spatially homogeneous case. The model, described by interacting gauge and scalar fields includes two parity and time violating terms: the Chern-Simons and the scalar magnetic interaction. For the pure Chern-Simons part of the theory the equations of motion are integrable. In general, however, the model system exhibits an interesting pattern of chaos to order transitions as the scalar magnetic moment is varied. The system dynamics are analyzed using a combination of standard techniques, such as phase space portraits, Lyapunov exponents, and Fourier spectra. (c) 2000 American Institute of Physics.