Linear and nonlinear optical properties of carbon nanotube-coated single-mode optical fiber gratings

Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment.     

Inverse problem approaches for stationary Fourier transform spectrometers

A design of a miniaturized stationary Fourier transform IR spectrometer has been developed that produces a two-dimensional interferogram. The latter is disturbed by effects like parasitic interferences or disparities in the cutoff wavelength of the pixels. Thus, a simple Fourier transform cannot be used to estimate the spectrum of the scene. However, as these defects are deterministic, they can be measured and taken into account by inversion methods. A regularization term can also be added. The first experimental results prove the efficiency of this processing methodology.     

A sliced inverse regression approach for data stream

In this article, we focus on data arriving sequentially by blocks in a stream. A semiparametric regression model involving a common effective dimension reduction (EDR) direction \(\beta \) is assumed in each block. Our goal is to estimate this direction at each arrival of a new block. A simple direct approach consists of pooling all the observed blocks and estimating the EDR direction by the sliced inverse regression (SIR) method. But in practice, some disadvantages appear such as the storage of the blocks and the running time for large sample sizes. To overcome these drawbacks, we propose an adaptive SIR estimator of \(\beta \) based on the optimization of a quality measure. The corresponding approach is faster both in terms of computational complexity and running time, and provides data storage benefits. The consistency of our estimator is established and its asymptotic distribution is given. An extension to multiple indices model is proposed. A graphical tool is also provided in order to detect changes in the underlying model, i.e., drift in the EDR direction or aberrant blocks in the data stream. A simulation study illustrates the numerical behavior of our estimator. Finally, an application to real data concerning the estimation of physical properties of the Mars surface is presented.     

New aspects of the Hunsdiecker-Barton halodecarboxylation—syntheses of phospha-shikimic acid and derivatives

We report an efficient synthetic approach to phospha-isosteres of important intermediates of the shikimic acid pathway by the application of the Hunsdiecker-Barton halodecarboxylation to cyclohexenylcarboxylic acids. As examples, phospha-shikimic acid, its 3-dehydro derivative and the respective monomethyl esters were synthesized. The approach has proven equally useful in the synthesis of isosteres of the antiviral agent oseltamivir.     

ATMOS (ATM optical switching)—system perspective

The expected traffic growth from new broadband services will require network capacities that can be beneficially provided by optical WDM transport networks. Optical packet techniques are essential for large networks to provide flexibility and granularity. A layered network architecture with a transparent optical layer and optical packet layers has been elaborated. Four switching concept options for large optical ATM switch fabrics in the public network and small access nodes are presented. The technology for the related key functions of space and wavelength switching was developed in the RACE ATMOS project and the feasibility of concepts and technologies was verified in four system demonstrators.     

Homogeneous turbulence subjected to rotation-dominated plane distortion

A new configuration of distorted homogeneous turbulence is investigated in the domain of rotation-dominated elliptical flows. The experimental results are compared with exact numerical solutions obtained in Fourier space for the linear part of the problem. The inherently periodic character of the flow results in typical oscillatory variations of the anisotropy and the pressure-strain correlations. A new two-point closure approach of the EDQNM type is proposed for the nonlinear problem; it is based on a representation of the spectral tensor by scalar functions expanded in terms of spherical harmonics.     

α‐Peptide–Oligourea Chimeras: Stabilization of Short α‐Helices by Non‐Peptide Helical Foldamers

Short α‐peptides with less than 10 residues generally display a low propensity to nucleate stable helical conformations. While various strategies to stabilize peptide helices have been previously reported, the ability of non‐peptide helical foldamers to stabilize α‐helices when fused to short α‐peptide segments has not been investigated. Towards this end, structural investigations into a series of chimeric oligomers obtained by joining aliphatic oligoureas to the C‐ or N‐termini of α‐peptides are described. All chimeras were found to be fully helical, with as few as 2 (or 3) urea units sufficient to propagate an α‐helical conformation in the fused peptide segment. The remarkable compatibility of α‐peptides with oligoureas described here, along with the simplicity of the approach, highlights the potential of interfacing natural and non‐peptide backbones as a means to further control the behavior of α‐peptides.