An investigation on microscopic and macroscopic stability phenomena of composite solids with periodic microstructure

An analysis of the effects of microscopic instabilities on the homogenized response of heterogeneous solids with periodic microstructure and incrementally linear constitutive law is here carried out. In order to investigate the possibility to obtain a conservative prediction of microscopic primary instability in terms of homogenized properties, novel macroscopic constitutive stability measures are introduced, corresponding to the positive definiteness of the homogenized moduli tensors relative to a class of conjugate stress–strain pairs.Numerical simulations, addressed to hyperelastic microstructural models representing cellular solids and reinforced composites, are worked out through the implementation of an innovative one-way coupled finite element formulation able to determine sequentially the principal equilibrium solution, the incremental equilibrium solutions providing homogenized moduli and the stability eigenvalue problem solution, for a given monotonic macrostrain path. Both uniaxial and equibiaxial loading conditions are considered.The exact microscopic stability region in the macrostrain space, obtained by taking into account microstructural details, is compared with the macroscopic stability regions determined by means of the introduced macroscopic constitutive measures. These results highlight how the conservativeness of the adopted macroscopic constitutive stability measure with respect to microscopic primary instability, strictly depends on the type of loading condition (tensile or compressive) and the kind of microstructure.     

Lidar measurements of atmospheric transmissivity

Summary The possibility of performing atmospheric-transmissivity measurements by lidar is considered. In the present paper two distinct methods have been successfully applied. The first one is based on the detection of the Raman return from molecular nitrogen. An alternative method is based on the simultaneous detection of the elastic and N₂ Raman returns. Measurements based on both techniques are discussed in detail, the second technique producing more accurate results. Through this technique an estimation of the ?ngstr?m coefficient can also be obtained.     

Decision algorithms for elementary topology I. Topological syllogistics with set and map constructs,connectedness, and cardinality comparison

In this paper we give a decision procedure for a topological syllogistic, denoted ?²,∞, involving, besides the standard Boolean set operators (∩, ∩, ′ (set complementation)) and predicates ( ? (membership), = (equality)), also the Kuratowski closure operator, continuous and closed maps with the notion of direct and inverse images, surjectivity and injectivity, as well as point evaluation, the singleton operator {·}, a predicate for comparing the cardinalities of two given sets, and a predicate expressing that a given set is topologically connected. Several examples are also discussed. © 1994 John Wiley & Sons, Inc.     

Cellular Simulation

Cellular simulation, a method of organizing simulation models to improve experimental efficiency, is described and shown to have the further advantages of reconciling the event based approach with the activity approach to simulation modelling and to have implication for modelling large systems.     

A study of high transverse energy interactions of 150 and 300 GeV pions and protons on a hydrogen target using a large acceptance calorimeter

Interactions of 150 GeV pions and 300 GeV pions and protons on hydrogen which result in final states with large transverse energy in the central rapidity region ?0.88 < y < 0.67 were studied with a calorimeter trigger. The dependence of the cross section on the azimuthal acceptance of the trigger, on the beam energy and on the incident particle type and the jet properties of the events were investigated. No dominant two-jet structure was found. Nevertheless, the parton spectrum in the colliding hadrons appears to be relevant for large transverse energy reactions.     

Stoichiometric hydrogenation of the heterobimetallic (α-alkynyl) complex [μ(1σ, 23η3H2CC  CCH3)] [(CO)3FeCo(CO)3]

The title compound reacts with molecular hydrogen at 60°C giving rise to the homometallic complexes Fe(CO)₅ and Co₂(CO)₈, and a very rich mixture of gaseous hydrocarbons (e.g. butenes from partial hydrogenation, butane from total hydrogenation and methane and propene from selective hydrogenolysis of the organic chain).The influence of concentration of the title complex, and partial pressure of hydrogen or carbon monoxide on the hydrogenation rate have been investigated. Although an unequivocal mechanism cannot be ascertained from the kinetic data owing to the complexity of the reaction, the pattern of products strongly indicates that the σ-interaction between the iron atom and the organic chain is preserved in the transition state.     

Synthesis of cavity extended cyclotriveratrylenes

Aromatic nucleophilic substitution reaction of cyclotriguaiacylene 1 with fluorobenzene derivatives bearing electron-withdrawing groups X (CHO, COCH(3), CN, NO(2)) in the para position gives a series of cyclotriveratrylene derivatives (3a-d), where the X substituents can be transformed to hydrogen-bond donor groups to afford new CTV-based heteroditopic receptors. The substituents of compounds 3a-d favor the facile demethylation reaction of the CTV derivatives. Attempts to perform alkylation reactions on derivatives (8c,d) evidenced the formation of a stereoisomeric mixture of symmetrical and unsymmetrical compounds.     

Direct resolution of racemic compounds on chiral microbore columns by sub- and supercritical fluid chromatography

Fast resolutions of racemic compounds (sulfoxides, amino alcohols, and α-methylarylacetic acids derivatives) were achieved on a chiral microbore column using carbon dioxide and a polar methanol/dioxane modifier. The stationary phase used in this study contains the 3,5-dinitrobenzoyl derivative of R,R(?)-1,2-diaminocyclohexane (DACH-DNB) as the chiral moiety, anchored to a silica gel surface by covalent bonds. Both thermodynamic and kinetic separation performances were improved by using a super- or subcritical carbon dioxide mobile phase (SFC, SubFC).     

The behaviour of 2-nitrothiophene and of 3-nitrothiophene with some nucleophiles

The reactivity of 2-nitrothiophene (1) and of 3-nitrothiophene (II) with some nucleophiles has been studied. According to calculated electronic densities I can receive nucleophilic attack at C₃ and C₅ depending on the nucleophile used, but II only at C₂. With N-lithium piperidine both I and II also give coupling products (VII and XI respectively) of the hithienyl type.     

Identification of polymers by library search of pyrolysis mass spectra and pattern recognition analysis

A library of mass spectra of polymers containing about 200 entries is described. These spectra were obtained by direct pyrolysis-electron-impact mass spectrometry, i.e., by heating the polymers in the direct insertion probe for solid samples at a constant heating rate and recording repetitive mass spectra during the temperature rise. The library can be used both as a data base for library searches and as a training set for a pattern recognition analysis. The algorithm used to generate and search the files and a few applications of the library search and pattern recognition analysis are presented.