Influence of the loading path on the strength of fiber-reinforced composites subjected to transverse compression and shear

The influence of the loading path on the failure locus of a composite lamina subjected to transverse compression and out-of-plane shear is analyzed through computational micromechanics. This is carried out using the finite element simulation of a representative volume element of the microstructure, which takes into account explicitly fiber and matrix spatial distribution within the lamina. In addition, the actual failure mechanisms (plastic deformation of the matrix and interface decohesion) are included in the simulations through the corresponding constitutive models. Two different interface strength values were chosen to explore the limiting cases of composites with strong or weak interfaces. It was found that failure locus was independent of the loading path for the three cases analyzed (pseudo-radial, compression followed by shear and shear followed by compression) in the composites with strong and weak interfaces. This result was attributed to the fact that the dominant failure mechanism in each material was the same in transverse compression and in shear. Failure is also controlled by the same mechanisms under a combination of both stresses and the failure locus depended mainly on the magnitude of the stresses that trigger fracture rather than in the loading path to reach the critical condition.     

Annealing effects on the magnetization of Co–Ni–B amorphous nanoparticles

Chemically prepared (Co_xNi_1−x)_1−yB_y (x=0.5, 0.75, 1; y≈0.4) amorphous fine particles were characterized by X-ray diffraction, DTA and TGA, and in situ magnetic measurement as a function of annealing temperature in an inert atmosphere. Magnetic measurement performed in as-prepared and 150°C annealed samples shows an increase of the saturation magnetization and magnetic moment after thermal treatment. Room temperature magnetization increases by factors of 3.5, 1.8, and 1.5, for x=0.5, 0.75, and 1, respectively. These measurements may indicate a local re-ordering of the amorphous phase at temperatures much lower than the full crystallization temperature.     

Infrared and Raman spectroscopic investigation of Eu3+-doped mono and Di-urethanesil hybrid siliceous materials

The general features of two series of sol-gel derived materials, designatedurethanesils (Ut), have been investigated by infrared and Raman spectroscopies with the goal of elucidating the chemical environment of the Eu³⁺ cations. The host frameworks of the two families of ormolytes studied have been represented by m-Ut(350) and d-Ut(300), where m stands for mono, d stands for di, 350 and 300 are the average molecular weights of the organic precursors (poly(ethylene glycol) methyl ether, PEGME, and poly(ethylene glycol), PEG, respectively). The hybrid matrix of the mono-xerogels is composed by a siliceous backbone bonded by means of urethane linkages (-NHC (=O)O-) to pendant methyl end capped oligopolymer chains with approximately 7 oxyethylene units, whereas that of the di-xerogels is based on a siliceous network grafted through urethane groups to both ends of poly(oxyethylene) segments containing about 6 (OCH₂CH₂) repeat units. Both classes of materials have been doped with europium triflate (Eu(CF₃SO₃)₃). The doped samples have been identified by m-Ut(350)_nEu(CF₃SO₃)₃ and d-Ut(300)_nEu(CF₃SO₃), where n is the molar ratio of (OCH₂CH₂) repeat units per Eu³⁺ ion. Materials with n ranging from ∞ to 5 have been analyzed. The spectral data obtained provide evidence that the cations begin to coordinate to the ether oxygen atoms of the oligopolymer chains at n=40 in the mono-urethanesils and at n=10 in the di-urethanesils. In mono-urethanesils samples with n>40 and in di-urethanesils materials with n>10, the Eu³⁺ coordinate exclusively to the carbonyl oxygen atoms of the urethane linkages. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Paraxial designing of planar waveguide variable-index focusing elements: Part 2—lenses of elliptical symmetry

A paraxial ray-optics formalism proposed for designing radially symmetric variable-index lenses is extended to the case of lenses of elliptical symmetry of the index profile.     

Effect of the environment on the stability of surfactant–polypeptide self‐assembled complexes: Molecular dynamics simulations of stoichiometric complexes formed by N‐dodecyltrimethylammonium and poly(α,L‐glutamate) in chloroform,methanol, and water

A series of molecular dynamics simulations have been performed to study the supramolecular structure of self‐assembled complexes formed by N‐dodecyltrimethylammonium cations and the synthetic polypeptide poly(α,L ‐glutamate). The influence of the type of solvent has been investigated, considering explicit environments of chloroform, water, and methanol on a stoichiometric complex containing 15 residues. In chloroform, the complex stabilizes in a regular structure: the polypeptide adopts an α‐helix conformation that is regularly surrounded by surfactant molecules to form electrostatic interactions through a multiple interaction pattern. However, this structure destabilizes in methanol and water: (a) the α‐helix unfolds in the two solvents and (b) the electrostatic links between the surfactant molecules and the polyanion are disrupted in aqueous solution, although these interactions are still preserved in methanol. The role of the solvent environment in stabilizing or destabilizing the polypeptide secondary structure, the organization of the surfactant molecules, and predominantly the surfactant–polypeptide supramolecular organization is discussed in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1122–1133, 2006     

A mew method of synthesis of 1,2,3,4-telrahydro-5H-5-oxo-1,4-benzodiazepines

A new one-step facile method for the synthesis of 1,12,3,4-tetrahydro5H-5-oxo-1,4-benzo-diuzepines is described. The method involves the addition of methyl anlhranilates to elhyl-enimine followed by intramolecular cyclizalion of the resulting intermediate compounds. Another attempted method starting from β-anilinoethylisocyanales is also described.     

Analogs of propranolol. Synthesis of 3-alkylamino-1-(3-benzo[b]thienyloxy)-2-propanols

The synthesis by two alternative routes of 1-(3-benzo[b]thienyloxy)-3-isopropylamino-2-propanol hydrochloride ( 1a HCl), a thiophenic isoster of Propranolol, and related compounds, is reported. The protecting and enolizing properties of the 2-methoxycarbonyl group on benzo[b]thiophene-3-one, along with its facile removal, are utilized in the first route. In the second one, conversion of 3-bromobenzo[b]thiophene in 1-(3-benzo[b]thienyloxy)-2,3-o-isopropylidenepropane is the key step. On the other hand, hydrolysis of 1-(3-benzo[b]furanyloxy)-2,3-o-isopropylidenepropane to the corresponding diol, in order to obtain a furanic isoster of Propranolol (17a ), was unsuccessful.     

Quantum field theory in curved space-time as thermo field dynamics

The strong analogy between states defined in the context of quantum field theory in curved space-time (QFT-CST) and the ones defined in the thermo field dynamics (TFD) of Takahashi and Umezawa [1] is shown. This analogy is useful in order to introduce the entropy operator in CST in the same way as in TFD. When the extremum condition in the thermodynamical potential is imposed, a family of Bogoliubov transformations that give us a planckian spectrum is found, even in pathological cases such as the minimally coupled scalar field.