Definition and properties of ideal amorphous solids

It is proposed that two ideal amorphous structures, type I and type II, based on maximally random jammed packing of spheres of equal size, form a distinct class of ideal amorphous solids. The ideal amorphous structures contain wide variations in local density, limited by the condition of solidity. Four distinct characteristics, based on statistical geometry and topology, are shown to define this class. Voronoi tessellations carried out on simulated cells of random packed spheres and amorphous polymers give a broad distribution of individual volumes, skewed, with a tail at the high volume end.     

Anionic polymerization of β-lactones initiated with potassium hydride. A convenient route to polyester macromonomers

The anionic polymerization of 2-oxetanone and 4-methyl-2-oxetanone initiated with the potassium hydride/18-crown-6 complex was investigated. The α-proton abstraction of the monomer was found to proceed at the initiation step of this polymerization. The salt of the unsaturated carboxylic acid formed initiates further propagation, leading to functionalized polyesters with unsaturated, dead end-groups.     

Development of zinc alkyl/air systems as radical initiators for organic reactions

This paper reports a series of comparative experiments on the activity of carbon- and oxygen-centred radical species in a model reaction of the radical addition of THF to imines mediated by a series of zinc alkyl/air reaction systems. The study strongly contradicts the notion that generally R˙ radicals are the initiating species in organic reactions mediated by R_nM/air systems, and simultaneously demonstrates that oxygen-centred radical species are the key intermediates responsible for the initiation process. In addition, a new efficient RZn(L)/air initiating system for radical organic reactions exampled by a model reaction of radical addition of THF to imines is developed. Moreover, the isolation and structural characterization of the first zinc alkylperoxide supported by a carboxylate ligand, [Zn₄(μ₃-OOtBu)₃(μ₄-O)(O₂CEt)₃]₂, as well as the novel octanuclear zinc oxo(alkoxide) aggregate with entrapped O–THF species, [Zn₄(μ₄-O)(μ₃-2-O–THF)(O₂CEt)₅]₂, provide clear mechanistic signatures for the mode of function of the RZn(O₂CR′)/air system.     

Nucleoside-metallacarborane conjugates for base-specific metal labeling of DNA

A general approach to the synthesis of nucleoside conjugates between derivatives of thymidine (T), 2'-O-deoxycytidine (dC), 2'-O-deoxyadenosine (dA), and 2'-O-deoxyguanosine (dG), and metallacarborane complexes is described. Metallacarborane-nucleoside derivatives are prepared by reaction of the dioxane-metallacarborane adduct with a base-activated 3',5'-protected nucleoside. In the case of T and dG a mixture of regioisomers, which is easily separable by chromatographic methods, is obtained, thus yielding a series of modifications containing metallacarborane groups at the 2-O, 3-N, 4-O and 1-N, 2-N, 6-O locations, respectively; dC and dA are alkylated at the exo-amino function. The proposed methodology provides a route for the synthesis and study of nucleic acids modified with metallacarboranes at designated locations and a versatile approach to the incorporation of metals into DNA.     

Neue Methode zur Kontrolle der Sulfonierung von einigen aromatischen Kohlenwasserstoffen

Zusammenfassung Es wurde eine schnelle und genaue volumetrische Methode zur Kontrolle des Sulfonierungsverfahrens von Benzol, Toluol und Naphthalin ausgearbeitet.     

Digital model of a vacuum circuit breaker for the analysis of switching waveforms in electrical circuits

The article presents a method of modelling a vaccum circuit breaker in the ATP/EMTPpackage, the results of the verification of the correctness of the developed digitalcircuit breaker model operation and its practical usefulness for analysis of overvoltagesand overcurrents occurring in commutated capacitive electrical circuits and also examplesof digital simulations of overvoltages and overcurrents in selected electricalcircuits.     

Effect of Re addition on the crystallization,heat treatment and structure of the Cu–Ni–Si-Cr alloy

Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the Fe₆₇Nb₅B₂₈ metallic glasses prepared by melt-spinning method. DSC traces exhibit that the crystallization takes place through a single exothermic reaction, and it processes a good thermal stability in thermodynamics. The activation energies for nucleation and grain growth processes were calculated to be 536 ± 22 and 559 ± 20 kJ mol^?1 by Kissinger equation, respectively, and 551 ± 24 and 574 ± 20 kJ mol^?1 by Ozawa equation, respectively. It means that the grain growth process is more difficult than the nucleation process. The variation of local Avrami exponent n(x) with crystallized fraction x demonstrates that the crystallization mechanism varies at different stages. The n(x) is larger than 2.5 at the initial stage of 0 < x < 0.3, implying a mechanism of diffusion-controlled three-dimensional growth with increasing nucleation rate. The n(x) decreases from 2.5 to 1.5 in the range of 0.3 < x < 0.65, suggesting that the crystallization belongs to three-dimensional nucleation and grain growth with decreasing nucleation rate. And n(x) lies between 1.0 and 1.5 in the range of 0.65 < x < 0.95, indicating that the crystallization corresponds to the growth of particles with an appreciable initial volume. Low-temperature annealing corresponds to the precipitation of α-Fe, Fe₂B, and Fe₂₃B₆ phases, and further annealing leads to the formation of α-Fe, Fe₂B, and FeNbB phases. The magnetic properties in relation to microstructure change of the Fe₆₇Nb₅B₂₈ metallic glasses are discussed.     

Determination of microgram amounts of azide by gas chromatography

Azide ions (5–120 μg) are oxidized by cerium(IV) in an acidic medium. The nitrogen evolved is displaced by helium carrier and quantified by gas chromatography with a thermal conductivity detector. The relative standard deviation is <5%. Many sulphur anions, cyanide and some metal ions which form azide complexes do not interfere.     

Mechanical and thermal properties of green polylactide composites with natural fillers

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.