Mixed-mode oscillations in complex-plasma instabilities

Instabilities in dusty plasmas are frequent phenomena. We show that some instabilities can be described by mixed-mode oscillations often encountered in chemical systems or neuronal dynamics and studied through dynamical system theories. The time evolution of these instabilities is studied through the change in the associated waveform. Frequency and interspike interval are analyzed and compared to results obtained in other scientific fields concerned by mixed-mode oscillations.     

Simultaneous coherent imaging and strain measurement using coupled photorefractive holography and shearography

By coupling photorefractive holography with speckle shearography, it is possible to simultaneously perform both coherent imaging and strain measurement. Use of the photorefractive effect, which is insensitive to incoherently scattered light, is a significant advantage in coherent imaging as described. Experimental results obtained from a centrally loaded steel plate are presented.     

Selective acoustic cues for French voiceless stop consonants

The objective of this study is to define selective cues that identify only certain realizations of a feature, more precisely the place of articulation of French unvoiced stops, but have every realization identified with a very high level of confidence. The method is based on the delimitation of "distinctive regions" for well chosen acoustic criteria, which contains some exemplars of a feature and (almost) no other exemplar of any other feature in competition. Selective cues, which correspond to distinctive regions, must not be combined with less reliable acoustic cues and their evaluation should be done on reliable elementary acoustic detector outputs. A set of selective cues has been defined for the identification of the place of /p,t,k/, and then tested on a corpus of sentences. The cues were estimated from formant transitions and the transient segment (an automatic segmentation of the transient part of the burst has been designed). About 38% of the feature realizations have been identified by selective cues on the basis of their very distinctive patterns. The error rate, which constitutes the crucial test of our approach, was 0.7%. This opens the way to interesting applications for the improvement of oral comprehension, lexical access, or automatic speech recognition.     

Cosmic strings in a space–time with positive cosmological constant

We study Abelian strings in a fixed de Sitter background. We find that the gauge and Higgs fields extend smoothly across the cosmological horizon and that the string solutions have oscillating scalar fields outside the cosmological horizon for all currently accepted values of the cosmological constant. If the gauge to Higgs boson mass ratio is small enough, the gauge field function has a power-like behaviour, while it is oscillating outside the cosmological horizon if Higgs and gauge boson mass are comparable. Moreover, we observe that Abelian strings exist only up to a maximal value of the cosmological constant and that two branches of solutions exist that meet at this maximal value. We also construct radially excited solutions that only exist for non-vanishing values of the cosmological constant and are thus a novel feature as compared to flat space–time. Considering the effect of the de Sitter string on the space–time, we observe that the deficit angle increases with increasing cosmological constant. Lensed objects would thus be separated by a larger angle as compared to asymptotically flat space–time.     

New Synthetic Approach to Naphtho[1,2‐b]furan and 4′‐Oxo‐Substituted Spiro[cyclopropane‐1,1′(4′H)‐naphthalene] Derivatives

A one‐step synthesis of ethyl 2,3‐dihydronaphtho[1,2‐b]furan‐2‐carboxylate and/or ethyl 4′‐oxospiro[cyclopropane‐1,1′(4′H)‐naphthalene]‐2′‐carboxylate derivatives 2 and 3 , respectively, from substituted naphthalen‐1‐ols and ethyl 2,3‐dibromopropanoate is described (Scheme 1). Compounds 2 were easily aromatized (Scheme 2). In the same way, 3,4‐dibromobutan‐2‐one afforded the corresponding 1‐(2,3‐dihydronaphtho[1,2‐b]furan‐2‐yl)ethanone and/or spiro derivatives 8 and 9 , respectively (Scheme 6). A mechanism for the formation of the dihydronaphtho[1,2‐b]furan ring and of the spiro compounds 3 is proposed (Schemes 3 and 4). The structures of spiro compounds 3a and 3f were established by X‐ray structural analysis. The reactivity of compound 3a was also briefly examined (Scheme 9).     

Stars and dendrimer‐like architectures by the divergent method using controlled radical polymerization

Using novel multihalide compounds based on 4‐tert‐butylcalix[4,6,8]arenes as initiators, molecularly well‐defined polystyrenes (PS) and poly[alkyl‐(meth)acrylates] could be obtained by atom transfer radical polymerization (ATRP). This core‐first approach and therefore the very same initiators also served to derive star block copolymers. Dendrimer‐like architectures based on poly(ethylene oxide) (PEO) and PS were prepared upon combination of anionic polymerization for the inner PEO part and ATRP for the outer PS shell.     

Anisotropic mesh adaptation: towards user‐independent,mesh‐independent and solver‐independent CFD. Part I: general principles

The present paper is the lead article in a three‐part series on anisotropic mesh adaptation and its applications to structured and unstructured meshes. A flexible approach is proposed and tested on two‐dimensional, inviscid and viscous, finite volume and finite element flow solvers, over a wide range of speeds. The directional properties of an interpolation‐based error estimate, extracted from the Hessian of the solution, are used to control the size and orientation of mesh edges. The approach is encapsulated into an edge‐based anisotropic mesh optimization methodology (MOM), which uses a judicious sequence of four local operations: refinement, coarsening, edge swapping and point movement, to equi‐distribute the error estimate along all edges, without any recourse to remeshing. The mesh adaptation convergence of the MOM loop is carefully studied for a wide variety of test cases. The mesh optimization generic coupling of MOM with finite volume and finite element flow solvers is shown to yield the same final mesh no matter what the starting point is. It is also shown that on such optimized meshes, the need for computational fluid dynamics (CFD) stabilization artifices, such as upwinding or artificial viscosity, are drastically reduced, if not altogether eliminated, in most well‐posed formulations. These two conclusions can be considered significant steps towards mesh‐independent and solver‐independent CFD. The structure of the three‐part series is thus, 1, general principles; 2, methodology and applications to structured and unstructured grids; 3, applications to three‐dimensional flows. Copyright © 2000 John Wiley & Sons, Ltd.     

Quantum twisted codes

A major contribution of [1] is a reduction of the problem of correcting errors in quantum computations to the construction of codes in binary symplectic spaces. This mechanism is known as the additive or stabilizer construction. We consider an obvious generalization of these quantum codes in the symplectic geometry setting and obtain general constructions using our theory of twisted BCH‐codes (also known as Reed–Solomon subspace subcodes). This leads to families of quantum codes with good parameters. Moreover, the generator matrices of these codes can be described in a canonical way. © 2000 John Wiley & Sons, Inc. J Combin Designs 8: 174–188, 2000     

Atom‐Precise Organometallic Zinc Clusters

The bottom‐up synthesis of organometallic zinc clusters is described. The cation {[Zn₁₀](Cp*)₆Me}⁺ ( 1 ) is obtained by reacting [Zn₂Cp*₂] with [FeCp₂][BAr₄^F] in the presence of ZnMe₂. In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower‐nuclearity clusters {[Zn₉](Cp*)₆} ( 2 ) and {[Zn₈](Cp*)₅(^tBuNC)₃}⁺ ( 3 ). According to DFT calculations, 1 and 2 can be described as closed‐shell species that are electron‐deficient in terms of the Wade–Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal–metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements).