Bifurcations and subharmonic resonances in multi-degree-of-freedom panel models

This paper describes the nonlinear, postcritical behavior of parametrically excited, shallow, cylindrical panels, which are modeled with two or four degrees of freedom. The analysis shows complicated dynamic behavior. Stable, periodic motions coexist with the trivial solution for very small values of the excitation amplitude. Moreover, a stable, chaotic attractor could be found coexisting with the trivial solution.

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Sommario Si studia il comportamento postcritico nonlineare di pannelli cilindrici ribassati, soggetti ad eccitazione parametrica e modellati con due o quattro gradi di libertà. L'analisi evidenzia un comportamento dinamico complesso. Moti periodici stabili coesistono con la soluzione banale per valori molto piccoli dell'ampiezza dell'eccitazione. Un attrattore caotico stabile coesiste altresì con tale soluzione per alcuni valori della frequenza dell'eccitazione.

     

Validation of the Charm MRL-3 for fast screening of beta-lactam antibiotics in raw milk

The biochemicals utilized in the Charm MRL beta-Lactam test (8 min test) were applied to faster flowing lateral components to create a new 3 min, one-step beta-lactam test called Charm MRL-3 (Charm Sciences Inc., Lawrence, MA). This new test was validated at T&V-ILVO according to Commission Decision 2002/657/EC. The following analytical parameters were checked: test specificity, detection capability, and test robustness (impact of deviation of the test protocol, and impact of the milk composition, batch differences of reagents). Further, the suitability of the Charm MRL-3 to screen heat-treated milk or milk from animal species other than the cow was also tested. Finally, the test was integrated in the monitoring of dairy samples to check the occurrence of false-negative or false-positive results, and the test was also included in a national ring trial and an international proficiency study. The results proved that the Charm MRL-3 is a fast, simple, and reliable cows' milk test that can be used at the farm level in order to prevent tanker milk contamination, or at the entrance of the dairy plant to screen tanker milk for the presence of beta-lactam antibiotics.     

Thiadiazoloquinoxalines: tuning physical properties through smart synthesis

The synthesis of π-conjugated acceptors based on thiadiazoloquinoxaline (TQ) derivatives is described. Apart from reporting on the functionalization of the TQ core, the influence of the substituents was studied by UV-vis absorption and emission spectroscopy, cyclic voltammetry measurements, and DFT calculations. By changing the donor as well as the π-spacer, a fine-tuning of the photo- and electrochemical properties was achieved.     

Preparation of flexible and elastic poly(trimethylene carbonate) structures by stereolithography

3D porous and non-porous structures are designed and prepared by stereolithography using resins based on PTMC macromers. Tough, flexible network films prepared in this manner show E moduli of ≈3.8 MPa and high elongations at break >900%; tensile strengths are ≈4.2 MPa. These values increase with increasing PTMC macromer molecular weight. To reach suitable viscosities for processing, up to 45 wt% propylene carbonate is added as non-reactive diluent. The solid specimens have compression moduli of 3.1-4.2 MPa, similar to the values determined in tensile testing. The built porous structures show porosities of 53-66% and average pore sizes of 309-407 μm. The compression moduli of the porous structures are significantly lower than those of the solid structures.     

Core, shell, and surface-optimized dendrimers for blue light-emitting diodes

We present a novel core-shell-surface multifunctional structure for dendrimers using a blue fluorescent pyrene core with triphenylene dendrons and triphenylamine surface groups. We find efficient excitation energy transfer from the triphenylene shell to the pyrene core, substantially enhancing the quantum yield in solution and the solid state (4-fold) compared to dendrimers without a core emitter, while TPA groups facilitate the hole capturing and injection ability in the device applications. With a luminance of up to 1400 cd/m(2), a saturated blue emission CIE(xy) = (0.15, 0.17) and high operational stability, these dendrimers belong to the best reported fluorescence-based blue-emitting organic molecules.     

Redox properties of 8-quinolinol and implications for its mode of action

8-Quinolinol (oxine, 8-hydroxyquinoline) is a simple aromatic alkaloid with allelopathic, antibacterial, antifungal, and cytotoxic activities. Generally, it is assumed that 8-quinolinol toxicity depends on transition metal chelation that negatively affects their availability for metalloenzymes in the cell or reactive oxygen species generation (ROS), which are formed following reduction of molecular oxygen by autoxidation of the redox active metal central atom of the 8-quinolinol complex. On the contrary, beneficial effects of 8-quinolinol and its derivatives in the medication of certain degenerative diseases are known. In this context, the activity of 8-quinolinol derivatives is attributed to their antioxidant activity following iron complex formation. To address this controversial issue, we explore the possible anti- or pro-oxidant effects of 8-quinolinol and its iron complexes in the deoxyribose degradation assay, by cyclic voltammetry and in a biological assay. The antibacterial effects of 8-quinolinol and its complex with iron were evaluated on Curtobacterium flaccumfacies and Paenibacillus amylolyticus. 8-Quinolinol showed strong antioxidant activity in the deoxyribose degradation assay. This activity may not depend exclusively on iron chelation, but probably more on the notable reducing properties of 8-quinolinol; it proved to be a more efficient antioxidant than the flavonoids catechin and quercetin. By contrast, 8-quinolinol showed no pro-oxidative effects in the deoxyribose degradation assay, both in free form and in complex with iron, as it may occur with redox cyclers. Cyclic voltammetry confirmed this too. 8-Quinolinol significantly inhibited bacterial growth and respiration. Idiosyncratically, its 50:1 mixture with iron(III) ions was less active compared with free 8-quinolinol; it even caused a U-shaped nonlinear hormetic effect on growth and failed to inhibit respiration as totally as the pure mixture; the respiration was even accelerated compared with the control as a result of lower stress. Our results support the notion that complex formation with either iron or other transition metals affects the reducing power of 8-quinolinol, but, in contrast to general assumptions, this study finds no support that complex formation with iron represents the major mode of action.