Modern perspectives in supercomputer-aided microwave circuit design

The computer-aided simulation and design of microwave integrated circuits often leads to large-size numerical jobs, especially for modern multiple-device MMIC subsystems such as distributed mixers and amplifiers. When this is the case, the use of large computer systems such as vector processors may become very attractive, because of the dramatic reduction of wall-clock time and of the related improvement of cost-to-performance ratio. This paper discusses the application of supercomputers to the solution of a number of such advanced microwave circuit CAD problems. An overview of the performance of general-purpose vectorized algorithms such as system solvers and Fast Fourier Transforms is first presented, in order to give a feeling of the potential of this class of machines in microwave CAD applications. Then a few typical microwave engineering problems are specifically addressed, including the statistical design (yield optimization) of linear circuits, the analysis of nonlinear circuits under multitone excitation, and the optimization of ultrabroadband nonlinear subsystems. In each case, a possible vectorization strategy is studied in depth, and the structure and performance of a specific highly vectorized algorithm are described in detail.     

Chemical synthesis of the RGD-protein decorsin: Pro-->Ala replacement reduces protein thermostability

Decorsin is a 39-residue polypeptide chain, crosslinked by three disulfide bridges, that strongly inhibits platelet aggregation. We report the chemical synthesis and characterization of analogs of decorsin with the aim of investigating the role of proline residues in protein structure, stability and biological activity. Decorsin analogs have been synthesized in which one (P23A and P24A decorsin) or two (P23,24A decorsin) proline residues have been substituted by alanine. The crude synthetic polypeptides were purified by reversed-phase HPLC in their reduced form and allowed to refold oxidatively to their disulfide-crosslinked species. The homogeneity of the synthetic mini-proteins, and also the correct pairing of the three disulfide bridges, were established by a number of analytical criteria, including fingerprinting analysis of the refolded synthetic analogs by using thermolysin and proteinase K as proteolytic enzymes. Replacement of proline by alanine results in a significant and cumulative decrease of the high thermal stability (Tm 74 degrees C) of native decorsin. The mono-substituted analogs display a Tm of 66-67 degrees C, while the double-substituted analog a Tm of 50 degrees C. On the other hand, the overall secondary and tertiary structures were not affected by the Pro-->Ala exchanges, as judged from circular dichroism measurements. Platelet aggregation assays established that the proline substitutions do not impair significantly the biological activity of decorsin. The results of this study clearly indicate that proline residues contribute significantly to the protein thermal stability. Our results are in line with the 'proline rule', previously advanced for explaining the unusual thermal stability of thermophilic enzymes, which usually show an enhanced content of proline residues with respect to their mesophilic counterparts.     

Isotropic microscale mechanical properties of coral skeletons

Scleractinian corals are a major source of biogenic calcium carbonate, yet the relationship between their skeletal microstructure and mechanical properties has been scarcely studied. In this work, the skeletons of two coral species: solitary Balanophyllia europaea and colonial Stylophora pistillata, were investigated by nanoindentation. The hardness H_IT and Young''s modulus E_IT were determined from the analysis of several load–depth data on two perpendicular sections of the skeletons: longitudinal (parallel to the main growth axis) and transverse. Within the experimental and statistical uncertainty, the average values of the mechanical parameters are independent on the section''s orientation. The hydration state of the skeletons did not affect the mechanical properties. The measured values, E_IT in the 76–77 GPa range, and H_IT in the 4.9–5.1 GPa range, are close to the ones expected for polycrystalline pure aragonite. Notably, a small difference in H_IT is observed between the species. Different from corals, single-crystal aragonite and the nacreous layer of the seashell Atrina rigida exhibit clearly orientation-dependent mechanical properties. The homogeneous and isotropic mechanical behaviour of the coral skeletons at the microscale is correlated with the microstructure, observed by electron microscopy and atomic force microscopy, and with the X-ray diffraction patterns of the longitudinal and transverse sections.     

Corrosion in Aluminium Cans with Grape Juice – Influence of Mechanical Damage

The consumption of canned food products from dented cans is not recommended by surveillance and consumer protection agencies due to the possibility of aluminium pick up, which may migrate from package to food/beverage. However, it is necessary to raise scientific data that will support any decision concerning the consumption of this kind of food, especially when the percentage of undernourished persons all over the world is considerable. Drawn and wall ironing–type aluminium cans with 330 ml of ready‐to‐drink grape juice, under three different controlled conditions of can damage as well as without damage, were evaluated for 1 year at 35°C. Aluminium migration, internal pressure and can internal surface appearance were periodically evaluated in order to monitor the package/beverage interaction. The results showed very small variation on the can internal surface appearance and pressure. Even after storage for 365 days, no can presented perforation, although the aluminium migration was increased. The highlight of this work is that after 1 year, for all the evaluated damage conditions, the ready‐to‐drink grape juice in aluminium cans could be considered adequate for human consumption in terms of metal migration from packaging. Copyright © 2013 John Wiley & Sons, Ltd.