Experimental identification of chaotic fibers

In a 2D parameter space, by using nine experimental time series of a Chua’s circuit, we characterized three codimension-1 chaotic fibers parallel to a period-3 window. To show the local preservation of the properties of the chaotic attractors in each fiber, we applied the closed return technique and two distinct topological methods. With the first topological method we calculated the linking numbers in the sets of unstable periodic orbits, and with the second one we obtained the symbolic planes and the topological entropies by applying symbolic dynamic analysis.     

Preliminary Studies for Cephamycin C Purification Technique

A study was made for purification of cephamycin C from fermentation of Streptomyces clavuligerus. Initially, the culture broth was clarified by microfiltration and ultrafiltration, after which the resulting permeates were subjected to nonspecific adsorption and ion-exchange chromatography on resin columns. The antibiotic activity was measured by the biological method at each stage by assaying its activity against the Escherichia coli ESS, super sensitive to β-lactam antibiotic. The purification processes were assessed in relation to the variables affecting each step. The purification efficiency by nonspecific adsorption was monitored by UV spectrophotometry, while the ion-exchange adsorption fractions were assessed by NMR spectroscopy. Some of the fractions obtained during purification were also analyzed by mass spectrometry (LC/MS and LC/MS/MS) to identify the cephamycin C molecule. These preliminary results proved the process feasibility.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Sensor Array: Impedimetric Label‐Free Sensing of DNA Hybridization in Real Time for Rapid,PCR‐Based Detection of Microorganisms

A novel, impedance‐based electronic sensor format was used for label‐free, real‐time detection of microbial DNA on oligonucleotide probe arrays. Detection limits of 5–10 nM were achieved for single‐stranded, PCR‐amplified DNA targets. Hybridization selectivity yielded 9‐ to 12‐fold signal increases for specific targets, and the sensor arrays were re‐used multiple times without significant signal degradation. These and other features of the SHARP Laboratories of America (SLA) sensor array, such as its ability to acquire continuous measurements of DNA as it accumulates on the array surface, make it an attractive biosensor platform for field detection and monitoring of sentinel and/or pathogenic microorganisms.     

Enhancement of antibiotic effect via gold:silver-alloy nanoparticles

A strategy for the development of novel antimicrobials is to combine the stability and pleiotropic effects of inorganic compounds with the specificity and efficiency of organic compounds, such as antibiotics. Here we report on the use of gold:silver-alloy (Au:Ag-alloy) nanoparticles, obtained via a single-step citrate co-reduction method, combined to conventional antibiotics to enhance their antimicrobial effect on bacteria. Addition of the alloy nanoparticles considerably decreased the dose of antibiotic necessary to show antimicrobial effect, both for bacterial cells growing in rich medium in suspension and for bacterial cells resting in a physiological buffer on a humid cellulose surface. The observed effect was more pronounced than the sum of the individual effects of the nanoparticles and antibiotic. We demonstrate the enhancement effect of Au:Ag-alloy nanoparticles with a size distribution of 32.5 ± 7.5 nm mean diameter on the antimicrobial effect of (i) kanamycin on Escherichia coli (Gram-negative bacterium), and (ii) a β-lactam antibiotic on both a sensitive and resistant strain of Staphylococcus aureus (Gram-positive bacterium). Together, these results may pave the way for the combined use of nanoparticle–antibiotic conjugates towards decreasing antibiotic resistance currently observed for certain bacteria and conventional antibiotics.     

Constant-pH molecular dynamics with ionic strength effects: protonation-conformation coupling in decalysine

A new implementation of the stochastic titration method for constant-pH molecular dynamics is presented, which introduces ionic strength effects in the simulations. In addition, the new implementation uses a faster molecular dynamics algorithm and an improved treatment of protonation events and of their effect on force field parameters. This new methodology is applied to a decalysine peptide, yielding very good quantitative agreement with experiments, both in terms of titration and helix-coil transition. The results show a significant dependence on ionic strength, illustrating the importance of including this parameter in constant-pH molecular dynamics simulations. Overall, the method seems to properly capture the protonation-conformation coupling and its dependence on ionic strength.     

Parametrization of 1-butyl-3-methylimidazolium hexafluorophosphate/nitrate ionic liquid for the GROMOS force field

A united-atom model of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]) and 1-butyl-3-methylimidazolium nitrate ([BMIM][NO(3)]) is developed in the framework of the GROMOS96 43A1(1) force field. These two ionic liquids are parametrized, and their equilibrium properties in the 298-363 K temperature range are subjected to validation against known experimental properties, namely, density, self-diffusion, shear viscosity, and isothermal compressibility. The ionic radial/spatial distributions, pi interaction, gauche/trans populations of the butyl tail, and enthalpies of vaporization are also reported. The properties obtained from the molecular dynamics simulations agree with experimental data and have the same temperature dependence. The strengths and weakness of our model are discussed.     

Kolmogorov-Sinai entropy from recurrence times

Observing how long a dynamical system takes to return to some state is one of the most simple ways to model and quantify its dynamics from data series. This work proposes two formulas to estimate the KS entropy and a lower bound of it, a sort of Shannon's entropy per unit of time, from the recurrence times of chaotic systems. One formula provides the KS entropy and is more theoretically oriented since one has to measure also the low probable very long returns. The other provides a lower bound for the KS entropy and is more experimentally oriented since one has to measure only the high probable short returns. These formulas are a consequence of the fact that the series of returns do contain the same information of the trajectory that generated it. That suggests that recurrence times might be valuable when making models of complex systems.     

Transmission of information and synchronization in a pair of coupled chaotic circuits: An experimental overview

We propose a rationale for experimentally studying the intricate relationship between the rate of information transmission and synchronization level in active networks, applying theoretical results recently proposed. We consider two non-identical coupled Chua’s circuit with non-identical coupling strengths in order to illustrate the proceeding for experimental scenarios of very few data points coming from highly non-coherent coupled systems, such that phase synchronization can only be detected by methods that do not rely explicitely on the calculation of the phase. A relevant finding is to show that for the coupled Chua’s circuit, the larger the level of synchronization the larger the rate of information exchanged between both circuits. We further validate our findings with data from numerical simulations, and discuss an extension to arbitrarily large active networks.     

Micro-displacement or bending measurement using a long-period fibre grating in a self-referenced fibre optic intensity sensor

The measurement of micro-displacement or bending using a long-period fibre grating (LPG) in a self-referenced fibre optic intensity sensor is presented. The sensing head is based on a LPG whose attenuation peak changes as a function of its micro-displacement or bending and the fibre optic intensity sensor is referenced in frequency. Two other LPGs were used as rejection filters, located at the output of the optical source to shorten its spectral width. The implemented experimental set-up is described and, the results are presented being considered the measurement range and the intrinsic resolution.