The Game of Electrons: Organocatalytic Higher-Order Cycloadditions Involving Fulvene- and Tropone-Derived Systems

The great progress that took place in the field of higher-order cycloadditions involving fulvene- and tropone-derived systems in the last few years is astonishing. By application of organocatalytic activation modes, new higher-order reactivities have been identified and described in the literature. These approaches take advantage of the high reliability of organocatalysis, at the same time expanding its potential and paving new directions for its further evolution. In this Minireview, the progress in the field of organocatalytic higher-order cycloadditions involving fulvene- and tropone-derived systems is summarized and insights into mechanistic aspects of the developed reactivities are provided. Furthermore, the discussion on the nomenclatural issues related to cycloaddition reactions has been conducted and solutions to clarify the picture proposed.     

Dynamics of a stainless steel turning process by statistical and recurrence analyses

This paper explores the cutting force oscillations. Forces have been measured during the stainless steel turning. We provide the results of standard statistical analysis of the corresponding time series together with their recurrence properties. We claim that the system, which initially exhibits regular vibrations, is unstable to chaotic oscillation for some fairly larger cutting depths. This characteristic transition in the cutting dynamics can be monitored by recurrences and could have the important implications to design a new control procedure.     

Radioactivity of honey from northern Poland

This work shows significant variations in the values of ²¹⁰Po in different analyzed Polish voivodeships. Statistical analysis of ²¹⁰Po activity concentrations in honey samples showed significant differences between place of honey collecting, kind of honey and morphological structure of plants from which bees collected nectar.

     

Nonlinear vibration of a quarter-car model excited by the road surface profile

We examine the Melnikov criterion for a transition to chaos in case of a single–degree–of–freedom nonlinear oscillator with the Duffing potential with a nonlinear hard stiffness and a kinematic excitation term caused by the road profile. Using the new effective Hamiltonian we have examined appearance of homoclinic orbits in a quarter car model. Cross–sections of stable and unstable manifolds defined the condition of transition to chaos through a homoclinic bifurcation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stress energy minimization as a tool in the material layout design of shallow shells

The present research deals with the compliance minimization problem of an elastic thin shallow shell subjected to simultaneous in-plane and bending loads. In this context, our goal is to lay out a given amount of material in the volume of a shell assuming that the distribution in the direction transversal to its middle surface S is homogeneous. The discussion hence reduces to the question of finding the optimal material arrangement on S. Similar problems were solved in the framework of two dimensional elasticity or Kirchhoff plate theory and the present research attempts to generalize these results. Following the pattern emerging from the above mentioned considerations, our research starts from the minimum compliance problem of a structure made of two elastic materials whose volumetric fractions are fixed. The existence of a solution to thus posed optimization task is guaranteed if the fine-scale microstructural composites are admitted in the analysis. Their constitutive tensors can be obtained by certain averaging ensuing from the theory of homogenization for periodic media. Additionally, by the Castigliano Theorem, the compliance minimization problem is equivalent to the one for structural stress energy. In turn, the lower estimation of the energy is achieved in two steps: (i) its modification by a certain energy-like functional, and (ii) utilizing the quasiconvexity property of thus obtained expression. As a result, formulae describing the effective stress energy of one-material shallow shell and the material distribution function are explicitly derived.     

Effect of nanosilica type on protective properties of composite ceramic coatings deposited on steel 316L by sol–gel technique

Trilayer SiO₂ coatings were obtained from sol modified with nanosilica differing in its specific surface and hydrophilic and hydrophobic properties. Each of the successively deposited coating layers was sintered at ever lower temperatures: 300, 250 and 200 °C. Examinations under a JSM 5800LV Joel scanning electron microscope showed that each SiO₂ coating includes a smooth, uncracked, thin layer covering the entire steel 316L basis and an outer layer made up of grains forming clusters of different size and density depending on the nanosilica used. The corrosion resistance of the coatings in Ringer’s solution was evaluated on the basis of polarization studies. A comparison of the passive region widths, the passive region current intensities, the cathode current densities at potential E_SCE = ?750 mV, the anode region potentials corresponding to a current density of 2 μA/cm², the through-coating porosity and the polarization resistance values shows the coatings obtained from sol modified with hydrophilic nanopowder to be superior. As regards the tested hydrophobic powders, additive ^®R972 (S_BET = 110 m²/g) ensures good protective properties. If hydrophobic silica with larger specific surface (^®R974, ^®R812, S_BET with respectively 170 and 260 m²/g) is used, the deposited coatings only slightly improve the protecting properties of steel 316L. The deposited coatings are uncracked. Even at their highest compactness, the surface grains and grain clusters, do not form a tight outer shell as evidenced by, for example, the poor protective properties of the coatings produced from sol modified by hydrophobic silica ^®R812. The latter coatings’ protective properties are the poorest at the highest grain compactness. If hydrophobic nanosilica with small specific surface (^®130 and ^®150) is used the resulting layers have low grain compactness and good protective properties (probably smooth thicker layers directly coat the steel basis).     

Organocatalytic Domino Michael–Knoevenagel Condensation Reaction for the Synthesis of Optically Active 3‐Diethoxyphosphoryl‐2‐oxocyclohex‐3‐enecarboxylates

Versatile dominoes : A novel, organocatalytic, Michael–Knoevenagel condensation domino reaction of ethyl 4‐diethoxyphosphoryl‐3‐oxobutanoate with various aryl‐ and aliphatic‐substituted α,β‐unsaturated aldehydes catalyzed by a chiral diarylprolinol ether has been successfully performed. The reaction proceeds in a highly enantio‐ and diastereoselective manner giving access to optically active 6‐substituted‐3‐diethoxyphosphoryl‐2‐oxocyclohex‐3‐enecarboxylates (see scheme).

     

Cholesterol and phytosterols effect on sphingomyelin/phosphatidylcholine model membranes--thermodynamic analysis of the interactions in ternary monolayers

In this work thermodynamic analysis of the interactions between lipids in ternary sphingomyelin/DPPC/sterol Langmuir films were performed to compare the effect of cholesterol, beta-sitosterol and stigmasterol on a model membrane. The condensing effect of the respective sterols and the interactions between molecules in ternary mixtures were analyzed on the basis of the excess area per molecule and the excess free energy of mixing values. The stability of the mixed monolayers was verified with the free energy of mixing values. The conclusions on the ordering effect of sterols were drawn from the analysis of the compression modulus values. It was found that the stoichiometry of the mixed films of the highest thermodynamic stability and of the strongest interactions is the same for all the sterols investigated. The results obtained prove that the mammalian sterol induces the strongest contraction of the area and reveals the strongest stabilizing and ordering effect among the investigated sterol. Stigmasterol was found to condense a model membrane in a weaker extent as compared to beta-sitosterol, however, the differences in ordering properties of both phytosterols are less pronounced. The magnitude of the influence of the investigated sterols on a model membrane was thoroughly discussed from the point of view of the structure of their side chain, which determines the geometry of a sterol molecule.     

Identification of chaos in a cutting process by the 0–1 test

We have examined the cutting process by using a two degrees of freedom non-smooth model with a friction component. Instead of the standard Lyapunov exponent treatment a statistical ‘0–1’ test based on the asymptotic properties of a non-harmonic Brownian motion chain has been successively applied to reveal the nature of the cutting process. In this test we calculated the control parameter K which is approaching asymptotically to 0 or 1 for regular and chaotic motions, respectively. The presented approach is independent on the integration procedure as we defined a characteristic distance between the points forming the time series used in the test separately.