Nonlinear behavior and buckling of cylindrical shells subjected to localized external pressure

Buckling loads and postbuckling behavior of cylindrical shells subjected to localized external pressure are considered. The modified extended Kantorovich method with path-tracing technique is applied to determine the buckling loads of the cylindrical shells. It is found that the load is dependent nonmonotonically on geometrical parameters of the area subjected to external pressure. Respective postbuckling shapes show correlation with the shapes corresponding to secondary bifurcation paths for the cases of a cylindrical shell under uniform external pressure and a cylindrical shell under uniform axial load.     

Flameless Combustion Synthesis of Ni and Ag Nanoparticles in Ballasted Systems: A Time‐Resolved X‐ray Diffraction Study

The combustion of cellulose nitrate in ballasted mixtures containing an organic binder and nickel hydroxycarbonate or silver carbonate as precursors resulted Ni or Ag nanoparticles. The formation of Ni and Ag nanoparticles from flameless combustion of cellulose nitrate was monitored by time‐resolved X‐ray diffraction. During the formation of the Ag nanoparticles, the diffraction patterns exhibited only signals from decreasing amounts of the precursor and newly simultaneously formed 20–30 nm silver particles. It was detected that in the systems with Ni precursor the formation of the Ni 5–10 nm crystals proceeded by some 2–3 s diffraction‐silent intermediate states of the whole system.     

Tunneling conductance of break junction with the (100) plane fracture surface of Bi2Sr2CaCu2O8

Using the new method of breaking, the tunnel junctions with the (100) plane fracture surface could be obtained. The observed singularities in conductivity can be explained by tunneling between the different layers (CuO₂→CuO₂, sharp peaks at 2Δ _p−p =64±2mV;CuO ₂→BiO, peaks at 100–140 mV; BiO→BiO, wide maxima at about 250 mV). The tunneling spectra measured at T=4.2–100 K show that a shift of the 2Δ _p−p peak to lower biases is much stronger (from 64 to 37 mV) than the BCS prediction at T/T_c≤0.7. At higher T (up to T_c≈87K) the changes of the spectra look like those expected for gapless superconductivity in agreement with the ARPES data for a-direction.     

Synthesis,photo- and electroluminescent properties of norbornene based platinum-containing copolymers

Norbornene based monomers containing the 2-phenylpyridinato–N,C²′ platinum(II) complex bonded by acetylacetonate or pyrazolonate anchor groups were synthesized and copolymerized with a carbazole-containing norbornene comonomer by ring-opening metathesis polymerization (ROMP). The photo- and electroluminescence spectra of the resulting Pt-copolymers are similar. They consist of broad bands with maxima at 495, 530 and 565 nm which arise from the mixed ligand centered (LC) and metal to ligand charge transfer (MLCT) transitions. The copolymer with the cyclometalated platinum(II) complex bonded to the polymer chain via the pyrazolonate anchor group revealed the highest brightness of electroluminescence (260 cd/m² at 21 V).     

Preparation of chitin–silica composites by in vitro silicification of two-dimensional Ianthella basta demosponge chitinous scaffolds under modified Stöber conditions

Chitin is a biopolymer found in cell walls of various fungi and skeletal structures of numerous invertebrates. The occurrence of chitin within calcium- and silica-containing biominerals has inspired development of chitin-based hybrids and composites in vitro with specific physico-chemical and material properties. We show here for the first time that the two-dimensional α-chitin scaffolds isolated from the skeletons of marine demosponge Ianthella basta can be effectively silicified by the two-step method with the use of Stöber silica micro- and nanodispersions under Extreme Biomimetic conditions. The chitin–silica composites obtained at 120 °C were characterized by the presence of spherical SiO₂ particles homogeneously distributed over the chitin fibers, which probably follows from the compatibility of Si–OH groups to the hydroxyl groups of chitin. The biocomposites obtained were characterized by various analytical techniques such as energy dispersive spectrometry, scanning electron microscopy, thermogravimetric/differential thermal analyses as well as X-ray photoelectron spectroscopy, Fourier transform infrared and Raman spectroscopy to determine possible interactions between silica and chitin molecule. The results presented proved that the character and course of the in vitro chitin silicification in Stöber dispersions depended considerably on the degree of hydrolysis of the SiO₂ precursor.     

Poriferan chitin as a template for hydrothermal zirconia deposition

Chitin is a thermostable biopolymer found in various inorganic--organic skeletal structures of numerous invertebrates including sponges (Porifera). The occurrence of chitin within calcium- and silica-based biominerals in organisms living in extreme natural conditions has inspired development of new (extreme biomimetic) synthesis route of chitin-based hybrid materials in vitro. Here, we show for the first time that 3D-α-chitin scaffolds isolated from skeletons of the marine sponge Aplysina aerophoba can be effectively mineralized under hydrothermal conditions (150°C) using ammonium zirconium(IV) carbonate as a precursor of zirconia. Obtained chitin--ZrO₂ hybrid materials were characterized by FT-IR, SEM, HRTEM, as well as light and confocal laser microscopy. We suggest that formation of chitin--ZrO₂ hybrids occurs due to hydrogen bonds between chitin and ZrO₂.