Topological stabilization for synchronized dynamics on networks

A general scheme is proposed and tested to control the symmetry breaking instability of a homogeneous solution of a spatially extended multispecies model, defined on a network. The inherent discreteness of the space makes it possible to act on the topology of the inter-nodes contacts to achieve the desired degree of stabilization, without altering the dynamical parameters of the model. Both symmetric and asymmetric couplings are considered. In this latter setting the web of contacts is assumed to be balanced, for the homogeneous equilibrium to exist. The performance of the proposed method are assessed, assuming the Complex Ginzburg-Landau equation as a reference model. In this case, the implemented control allows one to stabilize the synchronous limit cycle, hence time-dependent, uniform solution. A system of coupled real Ginzburg-Landau equations is also investigated to obtain the topological stabilization of a homogeneous and constant fixed point.     

Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

Temporal variations of iodine-127, potassium-40 and technetium-99 concentrations in Fucus serratus in the English Channel

The trends of¹²⁷I,⁴⁰K, and⁹⁹Tc levels were measured for several years inFucus serratus collected in 3 different Channel coastal stations. The results demonstrated cyclic seasonal variations of the levels, with maximum values in winter and minimum values in summer (ranging between 2 and 3). Ash levels evolved with a similar cycle, which allowed to estimate that the cycle thus observed was related to the alga biological activity and not to the releases. Trends of⁹⁹Tc levels were more complex. At Roscoff, a station little exposed to the releases, levels varied with the same annual cycle as natural elements. At Herquemoulin, a station close to the release point, the trend was mainly related to the released activities with a delay of about 1 year. At Wimereux, a distant station more strongly affected by sea currents, the cycle appeared in 1983 and 1984 but was hidden in 1985 and 1986 by the arrival of waters more strongly labelled because of the larger releases that occurred in 1985 (26 TBq), instead of 12 TBq in 1983 and 1984.     

Characterization of structural variations in the peptidoglycan of vancomycin-susceptible <Emphasis Type="Italic">Enterococcus faecium</Emphasis>: Understanding glycopeptide-antibiotic binding sites using mass spectrometry

Enterococcus faecium, an opportunistic pathogen that causes a significant number of hospital-acquired infections each year, presents a serious clinical challenge because an increasing number of infections are resistant to the so-called antibiotic of last resort, vancomycin. Vancomycin and other new glycopeptide derivatives target the bacterial cell wall, thereby perturbing its biosynthesis. To help determine the modes of action of glycopeptide antibiotics, we have developed a bottom-up mass spectrometry approach complemented by solid-state nuclear magnetic resonance (NMR) to elucidate important structural characteristics of vancomycin-susceptible E. faecium peptidoglycan. Using accurate-mass measurements and integrating ion-current chromatographic peaks of digested peptidoglycan, we identified individual muropeptide species and approximated the relative amount of each. Even though the organism investigated is susceptible to vancomycin, only 3% of the digested peptidoglycan has the well-known d-Ala-d-Ala vancomycin-binding site. The data are consistent with a previously proposed template model of cell-wall biosynthesis where d-Ala-d-Ala stems that are not cross-linked are cleaved in mature peptidoglycan. Additionally, our mass-spectrometry approach allowed differentiation and quantification of muropeptide species seen as unresolved chromatographic peaks. Our method provides an estimate of the extent of muropeptides containing O-acetylation, amidation, hydroxylation, and the number of species forming cyclic imides. The varieties of muropeptides on which the modifications are detected suggest that significant processing occurs in mature peptidoglycan where several enzymes are active in editing cell-wall structure.     

Mild hydrolytic cleavage of α-ferrocenylalkyl-O-methyl ethers

The conversion of α-ferrocenylalkyl-O-methyl ethers into the corresponding alcohols was successfully achieved by solvolysis in water/acetone mixtures. The content of water in the solvent markedly influenced the reaction rates. The reactivity of structurally different classes of ferrocenyl ethers was evaluated and in most cases high yields of ferrocenyl alcohols or diols were obtained in a few hours without any additive. Deprotection of less reactive substrates was accelerated in the presence of montmorillonite. The method is simple, environmentally benign and valuable in providing easy access to a variety of ferrocenyl derivatives through the use of the –O-methyl ether protective group.     

Heterogeneous dynamics in columnar liquid crystals of parallel hard rods

In the wake of previous studies on the rattling-and-jumping diffusion in smectic liquid crystal phases of colloidal rods, we analyze here for the first time the heterogeneous dynamics in columnar phases. More specifically, we perform computer simulations to investigate the relaxation dynamics of a binary mixture of perfectly aligned hard spherocylinders. We detect that the columnar arrangement of the system produces free-energy barriers that the particles should overcome to jump from one column to another, thus determining a hopping-type diffusion. This phenomenon accounts for the non-Gaussian intercolumn diffusion and shows a two-step structural relaxation that is remarkably analogous to that of out-of-equilibrium glass-forming systems and gels. Surprisingly enough, slight deviations from the behavior of simple liquids due to transient cages is also observed in the direction perpendicular to this plane, where the system is usually referred to as liquidlike.     

Software Review Chaos Data Analyzer,Professional Version. By J. Sprott and G. Rowlands

Nonlinear Dynamics, Psychology, and Life Sciences -     

Random Fractal Time Series and the Teen-Birth Phenomenon

The number of babies born to teenagers ranging in ages from 10 to 19 in the state of Texas during the years 1964 to 1990 is not strictly regular, but has both a systematic and random component. Herein we use the relative dispersion, the ratio of the standard deviation to the mean of a time series, to show by systematically aggregating the teen-birth data, that the correlation in the number of teen births is a modulated inverse power law. This scaling of the aggregated relative dispersion indicates the existence of long-time memory in the underlying control process and that the social process leading to teen pregnancy and having a baby are random, fractal and nonlinear. It is shown that this statistical behavior is the same as that observed in other sexual partner selection processes. We discuss the possible allometric nature of time series having such an inverse power-law character, and the implications of such memory for the properties of social control systems.     

Photoexcitation of the methionine-iron bond in iron(III) cytochrome c: bimolecular reaction with NADH

When iron(III) cytochrome c aqueous solutions containing NADH are irradiated with polychromatic light (wavelength greater than 280 nm), iron(II) cytochrome c and NAD+ in the stoichiometric ratio 2/1 are observed to be the principal reaction products, independently of the presence of oxygen; in addition, a minor process due to direct photodegradation of the nucleotide is observed. The selection of monochromatic 290 nm irradiation light (at which NADH has an absorbance minimum) and an adequate reactant concentration allowed parallel reactions to be minimized and new information to be obtained on the mechanism of the photoredox process. The experimental results are consistent with a reaction mechanism whereby NADH donates one electron to a "reactive intermediate" of the hemoprotein formed from the light-induced methionine-to-iron charge transfer excited state. In this process an NAD. radical is formed which, in deaerated solution, immediately reduces another molecule of the hemoprotein, and is itself oxidized to NAD+. In aerated solution, the NAD. radical rapidly reacts with oxygen to give NAD+ and superoxide O2- anion radical which, in turn, reduces the second iron(III) cytochrome c molecule.     

Base-Promoted Elimination Reactions of Acetaldehyde N-Alkyl-N,N-Dimethylhydrazonium Salts. A Convenient Synthesis of N,N-Dimethylalkylamines

The title reaction was utilized for efficient conversion of S_N2-reactive alkyl halides to the corresponding N,N-dimethylaIkylamines.