Some illustrative examples of the use of a spectral-element method in ocean acoustics

Some numerical results in the time domain obtained with the spectral-element method are presented in order to illustrate the high potential of this technique for modeling the propagation of acoustic waves in the ocean in complex configurations. A validation for a simple configuration with a known solution is shown, followed by some simulations of the propagation of acoustic waves over different types of ocean bottoms (fluid, elastic, and porous) to emphasize the wide variety of media that can be considered within the framework of this method. Finally, a movie illustrating upslope propagation over a viscoelastic wedge is presented and discussed.     

Interplay between H‐Bonding and Alkyl‐Chain Ordering in Self‐Assembly of Monodendritic L‐Alanine Derivatives

This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules.     

Bubble tree compactification of moduli spaces of vector bundles on surfaces

We announce some results on compactifying moduli spaces of rank 2 vector bundles on surfaces by spaces of vector bundles on trees of surfaces. This is thought as an algebraic counterpart of the so-called bubbling of vector bundles and connections in differential geometry. The new moduli spaces are algebraic spaces arising as quotients by group actions according to a result of Kollár. As an example, the compactification of the space of stable rank 2 vector bundles with Chern classes c ₁ = 0, c ₁ = 2 on the projective plane is studied in more detail. Proofs are only indicated and will appear in separate papers.     

Some contributions with Petri nets for the modelling, analysis and control of HDS

Petri nets (PN) are useful for the modelling, analysis and control of hybrid dynamical systems (HDS) because PN combine in a comprehensive way discrete events and continuous behaviours. On one hand, PN are suitable for modelling the discrete part of HDS and for providing a discrete abstraction of continuous behaviours. On the other hand, continuous PN are suitable for modelling the continuous part of HDS and for working out a continuous approximation of the discrete part in order to avoid the complexity associated with the exponential growth of discrete states. This paper focuses on the advantages of PN as a modelling tool for HDS. Investigations of such models for diagnosis and control issues are detailed.

Taking inspiration from the discrete event approach, sensor selection for diagnosis is discussed according to the structural analysis of the PN models. Faults are represented with fault transitions and a faulty behaviour occurs when a sequence of transitions is fired that contains at least one fault transition. Minimal sets of observable places are defined for detecting and isolating faulty behaviours.

Taking inspiration from the continuous time approach, flow control of HDS modelled with continuous PN is also investigated. Gradient-based controllers are introduced in order to adapt the firing speeds of some controllable transitions according to a desired trajectory of the marking. The equilibria and stability of the controlled system are studied with Lyapunov functions.     

Quantum transport in complex systems

We derive the influence function and the effective dynamics of a quantum systems coupled to a chaotic environment, using very general parametric and banded random matrices to describe the quantum properties of a chaotic bath. We find that only in certain limits the thermalization can result from the environment. We study the general transport problems including escape, fusion and tunneling (fission). Presented by D. Kusnezov at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Chemical Analysis of the Luminous Slime Secreted by the Marine Worm Chaetopterus (Annelida,Polychaeta)

The marine annelid Chaetopterus variopedatus produces bioluminescence by an unknown and potentially novel mechanism. We have advanced the study of this fascinating phenomenon, which has not been investigated for nearly 60 years after initial studies were first reported for this species. Here, we show that the luminous slime produced by the worm exhibits blue fluorescence that matches the bioluminescence emission. This result suggests that the oxyluciferin emitter is present. However, while the blue fluorescence decays over time green fluorescence is increasingly revealed that is likely associated with products of the luminescence reaction. LC/MS and fluorescence analysis of harvested luminescent material revealed riboflavin as the major green fluorescent component. Riboflavin is usually associated with the mechanism of light production in bacteria, yet luminous bacteria were not found in the worm mucus, and accordingly were not reported to be directly responsible for the light emission, which is under nervous control in the worm. We therefore propose a hypothesis in which riboflavin or a structurally related derivative serves as the emitter in the worm's light producing reaction.     

The rapid identification and quantification of iso-α-acids and reduced iso-α-acids in blood using UHPLC-MS/MS: validation of a novel marker for beer consumption

A method for the detection of iso-α-acid (IAA) type ingredient congeners that are derived from the hop plant (Humulus lupulus L.) was developed to detect recent consumption of beer in blood. Three structurally similar but chemically altered IAA, also used as beer-specific ingredients, are known as “reduced IAA”, consisting of the rho-, tetrahydro-, and hexahydro-IAA were also targeted. The use of a simple protein precipitation extraction and ultrahigh-performance liquid chromatography system coupled with a tandem mass spectrometer system enabled detection of these analytes in both antemortem and postmortem blood. Extracts were injected onto a C₁₈ solid-core column under gradient elution to achieve separation of isobaric analogs and isomers within a 10-min run time. Electrospray ionization in negative multiple reaction monitoring mode was used to monitor three transitions for each of the analytes that were ultimately grouped together to form a calibration curve for quantification of each of the four IAA groups. The method was fully validated according to international guidelines that included extraction efficiency, matrix effects, process efficiency, ion suppression/enhancement of co-eluting analytes, selectivity, crosstalk, accuracy and precision, stabilities, and lower limits of quantification. Finally, applicability of the method described was demonstrated by the detection of IAA ingredient congeners in the blood of a volunteer following the consumption of a relatively small amount of beer in a pilot study.