Low-loss surface modes and lossy hybrid modes in metamaterial waveguides

We show that waveguides with a dielectric core and a lossy metamaterial cladding (metamaterial-dielectric guides) can support hybrid ordinary-surface modes previously only known for metal-dielectric waveguides. These hybrid modes are potentially useful for frequency filtering applications as sharp changes in field attenuation occur at tailorable frequencies. Our results also show that the surface modes of a metamaterial-dielectric waveguide with comparable electric and magnetic losses can be less lossy than the surface modes of an analogous metal-dielectric waveguide with electric losses alone. Through a characterization of both slab and cylindrical metamaterial-dielectric guides, we find that the surface modes of the cylindrical guides show promise as candidates for all-optical control of low-intensity pulses.     

Communication: Phase incremented echo train acquisition in NMR spectroscopy

We present an improved and general approach for implementing echo train acquisition (ETA) in magnetic resonance spectroscopy, particularly where the conventional approach of Carr-Purcell-Meiboom-Gill (CPMG) acquisition would produce numerous artifacts. Generally, adding ETA to any N-dimensional experiment creates an N + 1 dimensional experiment, with an additional dimension associated with the echo count, n, or an evolution time that is an integer multiple of the spacing between echo maxima. Here we present a modified approach, called phase incremented echo train acquisition (PIETA), where the phase of the mixing pulse and every other refocusing pulse, φ(P), is incremented as a single variable, creating an additional phase dimension in what becomes an N + 2 dimensional experiment. A Fourier transform with respect to the PIETA phase, φ(P), converts the φ(P) dimension into a Δp dimension where desired signals can be easily separated from undesired coherence transfer pathway signals, thereby avoiding cumbersome or intractable phase cycling schemes where the receiver phase must follow a master equation. This simple modification eliminates numerous artifacts present in NMR experiments employing CPMG acquisition and allows "single-scan" measurements of transverse relaxation and J-couplings. Additionally, unlike CPMG, we show how PIETA can be appended to experiments with phase modulated signals after the mixing pulse.     

Melting Point and Composition Distribution of Polyolefins by Fractionation

The fractionation technique described in this paper was used to characterize the melting-point, monomer, and blocking distributions for polymers and copolymers. It is different from the molecular-weight fractionation technique in that the fractions are obtained by using a single solvent to extract the solid polymer below its melting point at stepwise-increasing temperatures. The reproducibility of this technique is excellent, and the technique is sufficient to distinguish pellet-to-pellet variation in a commercially available polypropylene. It was used to show the influence of preparation variables on the melting-point distributions of polyethylene and polypropylene and on the monomer and blocking distribution of copolymers, and to distinguish copolymers from blends.     

Weakly supercyclic operators

Inspired by a recent result that a weakly hypercyclic operator may fail to be norm hypercyclic, we show there exists a weakly supercyclic operator that fails to be norm supercyclic. Moreover, despite a classical result of Hilden and Wallen that every unilateral weighted backward shift is supercyclic, we show such an operator may have a weakly supercyclic vector that is not a norm supercyclic vector. In addition to these results, we extend a result of Kitai by showing a hyponormal operator cannot be weakly hypercyclic.     

Colour, design and virtual reality at JET

Joint European torus (JET) is the world's largest nuclear fusion research facility investigating the use of nuclear fusion, the process that powers the stars, as a source of clean, limitless electrical energy.The JET machine undergoes an on-going program of upgrades and modifications facilitating a broad scientific program of experimentation. Maintenance of the JET machine is carried out remotely using telemanipulators mounted on a robotic Boom, employing a ‘man in the loop’ approach. The system relies on the use of real time 3D computer graphic models in a ‘virtual reality’ environment for preparation and support of remote-handling operations. Colour is used in this virtual environment to emphasise robots from the vessel environment and to highlight materials, components and systems requiring special care.     

Characterization of copper-exchanged Na-A,X and Y zeolites with X-ray photoelectron spectroscopy and transmission electron microscopy

Copper-exchanged sodium- A, X and Y zeolites have been characterized with X-ray photoelectron Spectroscopy (XPS), with supporting electron microscopy and X-ray diffraction measurements. Under reducing conditions (CO, H₂, 250–450° C), four distinct chemical states of copper have been identified. These are intrazeolite Cu(II), Cu(I) and 1 nm metal clusters, and externally segregated copper metal crystallites. We report spectroscopic data for both the Cu 2p_{$\text{3}\text{2}$} and Auger L₃M_4,5M_4,5 lines. Whereas Cu(II) and metallic copper crystallites have normal spectroscopic parameters, Cu(I) and 1 nm Cu clusters in the reduced zeolites lie in new areas of the two-dimensional chemical state plot.The reduction sequence of Cu(II), Cu(I), Cu clusters and Cu crystallites is different on the A zeolite compared with X and Y. One nm metal clusters are identified as an intermediate phase on the A with transmission electron microscopy (TEM) and XPS prior to external diffusion and crystallite formation. The ease of formation of the cluster intermediate in the A zeolite may be a consequence of the larger diffusion barrier imposed by the 0.42nm supercage aperture compared with the 0.74nm aperture in the X and Y zeolites.     

Semiconductor lasers and fiber lasers for fiber-optic telecommunications

Be performance characteristics of semiconductor lasers for fiber telecommunication systems will be reviewed. Modulation speed, intensity noise, singlefrequency line width, and tunability are addressed. In addition, recent results concerning the same characteristics in single-frequency, tunable, fiber lasers are reviewed and compared with the semiconductor laser.     

Comparison of two mass-selective detectors with special reference to the analysis of residues of anabolics

In the analysis of residues of anabolic agents the use of combined techniques, especially gas chromatography-mass spectrometry, is of increasing interest. When this method is used for the analysis of residues of anabolics it is very important to have a knowledge of the characteristics of the different types of apparatus on the market and to be sure that the results are not "apparatus-dependent". In this study two mass-selective detectors, the Hewlett-Packard 5970 and the ion trap detector 800, were compared by injecting the same samples of derivatized anabolics (standard solutions) into the two systems.