An all-fiber frequency-shifted feedback laser for optical ranging; signal variation with distance

A recent paper [L.P. Yatsenko et al., Opt. Commun. 242 (2004) 581] provided a first-principles prediction for the optical ranging signals obtained when using a frequency-shifted feedback (FSF) laser system, seeded by a phase-modulated laser. Such a system has many useful advantages over other alternative FSF laser techniques. We report here experimental verification of that theory, specifically the variation of the amplitude modulation signal with both distance and modulation index of the seed laser. We describe the operation of an all-fiber FSF laser that uses an Er³⁺-doped active fiber as the gain medium. To improve the signal and minimize the noise we seed the FSF laser with a phase-modulated (PM) laser; the measurement of distance derives from a measurement of amplitude modulation within a narrow frequency interval. We demonstrate that the resulting system is capable of fast and precise measurements. With the bandwidth limitations of our current system we achieved an accuracy better than 0.1 mm. Although measurements based on interferometry offer the potential for much greater accuracy under carefully controlled conditions, the present method does not suffer from the presence of a material-dependent phase shift at the surface of the measured object.     

Poset algebras over well quasi-ordered posets

A new class of partial order-types, class is defined and investigated here. A poset P is in the class iff the poset algebra F(P) is generated by a better quasi-order G that is included in L(P). The free Boolean algebra F(P) and its free distributive lattice L(P) have been defined in [ABKR]. The free Boolean algebra F(P) contains the partial order P and is generated by it: F(P) has the following universal property. If B is any Boolean algebra and f is any order-preserving map from P into a Boolean algebra B, then f can be extended to a homomorphism of F(P) into B. We also define L(P) as the sublattice of F(P) generated by P. We prove that if P is any well quasi-ordering, then L(P) is well founded, and is a countable union of well quasi-orderings. We prove that the class is contained in the class of well quasi-ordered sets. We prove that is preserved under homomorphic image, finite products, and lexicographic sum over better quasi-ordered index sets. We prove also that every countable well quasi-ordered set is in . We do not know, however if the class of well quasi-ordered sets is contained in . Additional results concern homomorphic images of posets algebras. The third author was supported by the following institutions: Israel Science Foundation (postdoctoral positions at Ben Gurion University 2000–2002), The Fields Institute (Toronto 2002–2004), and by The Nato Science Fellowship (University Paris VII, CNRS-UMR 7056, 2004).     

Ruthenium-based light-driven molecular machine prototypes: synthesis and properties

In the past years, many dynamic systems often referred to as "molecular machines" have been elaborated. They are generally set in motion by external stimuli like chemical, electrochemical, or photochemical reactions. Light irradiation seems particularly promising since the input signal can be switched on and off fast and readily on a very small place. In this tutorial review, we will highlight recent advances in the design and synthesis of various ruthenium(II) complexed rotaxanes, catenanes, scorpionates or macrocycles. In these compounds, one part of the system is set in motion by photochemically expelling a given chelate. We will discuss the behaviour of various topologically non-trivial systems like catenanes and rotaxanes as well as acyclic and macrocyclic models.     

Temporal Control of Membrane Fusion through Photolabile PEGylation of Liposome Membranes

Membrane fusion results in the transport and mixing of (bio)molecules across otherwise impermeable barriers. In this communication, we describe the temporal control of targeted liposome–liposome membrane fusion and contents mixing using light as an external trigger. Our method relies on steric shielding and rapid, photoinduced deshielding of complementary fusogenic peptides tethered to opposing liposomal membranes. In an analogous approach, we were also able to demonstrate precise spatiotemporal control of liposome accumulation at cellular membranes in vitro.     

Intractable high‐Tg thermoplastics processed with epoxy resin: Interfacial adhesion and mechanical properties of the cured blends

The intractable, high‐temperature‐resistant thermoplastics (TPs) polyphenylenether (PPE) and polyetherimide (PEI) were processed by dissolution into epoxy–amine precursors and a subsequent reaction of the precursors. Because the TP concentration was higher than the critical concentration, the phase separation produced a dispersion of crosslinked thermoset (TS) particles into a TP matrix. The morphology of the blends was examined with transmission electron microscopy and dynamic mechanical thermal spectroscopy, which showed completion of the phase separation. The interfacial adhesion at the TP‐matrix/TS‐particle interface was estimated on TP/TS bilayers to be 10 J/m² in PEI blends, whereas it was 70 J/m² in PPE blends, where there is strong evidence for in situ grafting between PPE phenolic chain ends and glycidyl functions of the reactive TS. Yielding in the compressive mode occurred at an intermediate yield stress between the components' values, and the anelastic deformation was separated from the plastic deformation. Fractures in the tensile mode occurred through debonding at the matrix/particle interfaces and coalescence of these defects, which led to microcrack formation and brittle failure. Mode I fracture toughness was, therefore, higher for PPE blends than for PEI blends, a result of the higher interfacial adhesion. However, a decrease from pure TP was observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 363–373, 2001     

Epoxy – diamine thermoset/thermoplastic blends: thermoset reactions and rheological evolutions during curing

Isothermal rates of reaction during the cure of epoxy‐amine/thermoplastic blends were studied. Epoxy‐amine reaction induces a phase separation. Experimental results show that when TP concentration is higher than 30 wt% an increase of reaction rate is observed after phase separation. A modelling of the kinetics of each phase before and after phase separation, shows that in the epoxy‐amine rich phase, gelation occurs for a conversion close to 0.6. Rheological behaviour was studied during the cure. The viscosity was found greatly dependent of the morphology, the epoxy amine conversion and of the evolution of the phase composition. Modelling of the viscosity using simple relations gives a good fit of the experimental results during the cure.     

Luminescent lanthanide-binding peptides: sensitising the excited states of Eu(III) and Tb(III) with a 1,8-naphthalimide-based antenna

The investigation into the luminescence properties of a lanthanide-binding peptide, derived from the Ca-binding loop of the parvalbumin, and modified by incorporating a 1,8-naphthalimide (Naph) chromophore at the N-terminus is described. Here, the Naph is used as a sensitising antenna, which can be excited at lower energy than classical aromatic amino acids, such as tryptophan (the dodecapeptide of which was also synthesised and studied herein). The syntheses of the Naph antenna, its solid phase incorporation into the dodecapeptide, and the NMR investigation into the formation of the corresponding lanthanide complexes in solution is presented. We also show that this Naph antenna can be successfully employed to sensitize the excited states of both europium and terbium ions, the results of which was used to determined the stability constants of their formation complexes, and we demonstrated that our peptide 'loop' can selectively bind these lanthanide ions over Ca(II).     

X-ray fluorescence from the element with atomic number Z=120

An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18) s has been deduced for Z=120 from the measured x-ray multiplicity.