On a method for determining limit cycles in nonlinear circuits

A theory for determining the existence, number and position of limit cycles in perturbed Hamiltonian systems, that depends on a small parameter, is presented. The limit cycle emerges from the periodic trajectories surrounding a centre of the unperturbed system. By means of this theory a sinusoidal oscillator with a nonlinear element has been analysed. It is shown that only the terms with odd degrees in the approximation polynomial of the nonlinear element's characteristic exert an influence on the initiation of limit cycles.     

Sardinian goat’s milk as source of bacteriocinogenic potential protective cultures

Goat breeding in Sardinia constitutes an important source of income for farming and shepherding activities. In this study 170 LAB strains were isolated from Sardinian goat’s milk and tested for bacteriocins production against several food-borne pathogenic microorganisms. Four isolates (SD1, SD2, SD3 and SD4) were selected for their effective inhibition on Listeria monocytogenes. The strains were classified as members of Enterococcus genus, according to their biochemical and physiological characteristics, and then genetically identified as Enterococcus faecium. In MRS broth at 37 °C, bacteriocins SD1 and SD2 were produced at much higher levels (51200 AU/ml) compared to bacteriocin SD3 (3200 AU/ml) and bacteriocin SD4 (800 AU/ml). Their peptides were inactivated by proteolytic enzymes, but not when treated with α-amylase, catalase and lipase. The four bacteriocins remained stable at pH from 2.0 to 12.0, after exposure to 100 °C for 120 min and were not affected by the presence of surfactants and salts (N-Laourylsarcosine, NaCl, SDS, Triton X-100, Tween 20, Tween 80 and urea). Their molecular size was determined to be approximately 5 kDa by tricine-SDS-PAGE.Since the strains exhibited a strong antimicrobial activity against 21 L. monocytogenes strains and 6 Salmonella spp. isolates, they should be considered as potential bio-preservatives cultures for fermented food productions. Moreover, due to their technological features, the four strains could be taken in account for using as adjunct NSLAB (non-starter lactic acid bacteria) rather than as starter culture.     

Solid‐state structural evolution of poly(ethylene terephthalate) during step uniaxial stretching from different initial morphologies: An in situ wide angle x‐ray scattering study

This work reports an in situ wide‐angle X‐ray scattering (WAXS) study of the structural evolution of PET with distinct initial morphologies during step uniaxial stretching in the solid state. Two types of samples were analyzed under synchrotron X‐ray radiation, namely quasi‐amorphous (QA) and semicrystalline (SC) (with 2D and 3D order). Results show that initially different QA morphologies evolve following the same stages: (i) stage I (before neck), at almost constant orientation level the amorphous phase evolves into mesophase; (ii) stage II (neck formation), there is a rapid increase of polymer orientation and the appearance of a periodical mesophase from the highly oriented mesophase; (iii) stage III (necking propagation), there is a leveling off of the average polymer orientation together with partial conversion of the periodical mesophase and mesophase into highly oriented amorphous. The behaviors of the two SC morphologies are completely distinct. A 2D order crystalline morphology evolves with stretching likewise the QA through three stages: (i) at early stages of deformation the polymer orientation remains unchanged while the amorphous phase amount increases slightly, stage I; (ii) in stage II, a fast increase of polymer orientation is accompanied by large formation of mesophase; and (iii) in stage III there is the level off of polymer orientation as the chains approach their finite extensibility and the 3D crystalline order is achieved. Evolution of SC sample with 3D crystalline order mainly features constant orientation increase together with mesophase increment. Structure deformation models are suggested. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

RTP requirements to yield uniform and repeatable ultra-shallow junctions with low energy boron and BF2 ion implants

Ion implants of 2.0 and 5.0 keV ¹¹B⁺ and 2.2, 5.0, and 8.9 keV ⁴⁹BF ₂ ⁺ at a dose of 1E15/cm² were investigated. Anneal conditions were developed which produced highly activated yet shallow junctions. The effects of oxygen were studied previously by us^1–12 and found to be an important variable to control in order to produce uniform and repeatable sheet resistance and junction depths. A purge procedure and integrated oxygen sensor were developed to measure and control the oxygen background concentration for each anneal to assure repeatable results. “Shelf-life,” that is dwell time between implant and anneal, was investigated. It was found that, for low energy implants, the amount of native oxide grown affects retained dose, sheet resistance (Rs), and uniformity. Controlled oxygen level repeatability and shelf life results are presented and equipment designs are discussed.     

Reducing the breakage rate in glass tempering

An analytical procedure based on L. M. Kachanov's model of fracture front propagation is examined. Its purpose is to predict the fracture of sheet glass in the course of tempering. The conditions under which fracture is likely to take place and the time to fracture are determined. Translated from Steklo i Keramika No. 10, pp. 10–11, October, 1997.     

Photoinduced circular anisotropy in side-chain azobenzene polyesters

We report for the first time the inducing of large circular anisotropy in previously unoriented films of side-chain azobenzene polyesters on illumination with circularly polarized light at a wavelength of 488 nm. The circular dichroism and optical activity are measured simultaneously in real time at two wavelengths, 488 nm and 633 nm. The photoinduced optical activity has been measured to be 10⁴ deg/cm and the circular dichroism has been found to be on the order of 0.3.     

Electro-optic effect in proton exchanged LiNbO3 andLiTaO3 waveguides

Electro-optic properties of proton-exchanged (PE) waveguide layers in LiTaO₃ and LiNbO₃ are studied and related to their optical characteristics. The proton-exchange process induces a degradation of the electro-optic activity in both types of waveguides, PE LiNbO₃ and PE LiTaO₃. The measured electro-optic effect is close to the detection sensitivity even when the exchange regime is performed at low temperatures for short periods of time. The PE samples have been annealed (APE waveguides) and the changes of their r₃₃ electro-optic coefficient has been followed at successively higher temperatures and periods of time. Subjected to annealing at temperatures between 265-420°C, the LiTaO₃ layers show a partially recovered r₃₃ coefficient, the recovering being different for quick and slow cooling of the samples. In thin APE LiNbO₃ waveguiding layers a restoration of r₃₃ up to 75% of the bulk value is observed due to the annealing at temperatures between 200-340°C     

New azobenzene polymers for light-controlled optical elements

Three new azobenzene polymers have been synthesized by polymerization of cyanazobenzene monomers with different numbers of methylene groups attached to the cyanazobenzene dye. The rearrangement of the anisotropic azobenzene moieties in them was initiated by illumination with linearly polarized light (488 nm), and the optical anisotropy due to this arrangement has been investigated. The photobirefringence can be erased by illumination with circularly polarized light and re-induced to the same value with linearly polarized light. We show that films from these polymers can be used as optically controlled reversible polarization elements.     

A branch-and-bound method for optimal atom-type assignment in de novo ligand design

This paper investigates a computational procedure for the determination of the atom types on the vertices of a molecular skeleton to optimize interaction with the receptor site whilst maintaining a synthetically reasonable structure. The connectivity of the skeleton is analysed and appropriate atom types are compiled for each vertex. Receptor ionization and conformational states are generated by varying the positions of hydrogen atoms and electron lone pairs in the carboxyl, rotatable hydroxyl and amino groups. The structure is divided into small non-overlapping substructures. Atom types are assigned exhaustively onto each of the substructures using a depth-first search method; chemical rules are applied to reject unacceptable atom combinations early on. An empirical interaction score is calculated and the representatives of each partial structure are stored in ascending order according to their scores. The branch-and-bound procedure is then used to find the structures with the lowest scores. The method is illustrated using five protein-ligand complexes.     

Changes in the physicochemical and optical properties of chalcogenide thin films from the systems As—S and As—S—TI

Changes in some physical and optical properties of thermally evaporated thin films from the systems As—S and As—S—Tl over a wide range of concentrations have been investigated. The influence of the conditions of vacuum deposition and light exposure has been demonstrated. The optical transmission and reflection of thin layers deposited on BK-7 optical substrates have been measured in the spectral region of 350–2000 nm and the linear (n) and nonlinear (n ₂) refractive indices and optical band-gap, E _g, as well as the oscillator fitting constants, were calculated. Boling's formula is used to predict n ₂ from the dispersion and the magnitude of n. Data for changes in the glass-transition temperature, T _g, microhardness, and rate of dry etching of thin chalcogenide films before and after exposure to light are presented. The addition of Tl in As₂S₃ leads to an increase in the refractive index and decrease in the optical band-gap. After illumination a photodarkening or photobleaching effect was observed depending on the evaporation conditions. Some of the layers change their etching rate in a plasma which make them suitable for practical applications. Conclusions on the homogeneity of the layers and the origin of photostructural changes in them are drawn.