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Antenna arrays based on aperiodic tilings have been shown to exhibit low sidelobe levels and modest bandwidths over which grating lobes are suppressed. In addition, compared to conventional periodic arrays, these arrays are naturally thinned (i.e., mean interelement spacing is greater than [lambda]/2). The generation of these arrays involves placing array elements at the locations of the vertices of an aperiodic tiling. To obtain a realizable design, the entire array is then scaled and truncated to achieve a desired minimum element spacing and aperture size. This paper demonstrates that it is possible to greatly extend the bandwidth of these arrays by incorporating a simple perturbation scheme into the basic array generation process. The implementation of this perturbation scheme is straightforward and it lends itself well to being combined with an optimization technique such as the genetic algorithm. It is successfully used to generate arrays that have large bandwidths (peak sidelobe level [less than or equal to] -10 dB with no grating lobes) of up to a minimum element spacing of 5[lambda]. Moreover, the flexibility of this technique will be further demonstrated by introducing a slight variation of the basic scheme that is capable of generating arrays with extremely wide bandwidths. An example will be presented for an array design that has a bandwidth corresponding to a minimum element spacing of up to 11[lambda]. Index Terms--Aperiodic arrays, aperiodic tilings, broadband arrays, genetic algorithms (GAs), tiling theory, wideband arrays.

Open-sleeve dipoles are versatile antennas primarily because they have several design parameters that can be varied to achieve a wide range of VSWR performance and operating bandwidth. By properly adjusting their parameters, it is possible to create versions of these antennas that have either a broadband or a dual-band response. In this paper, a new variation of the conventional open-sleeve dipole antenna is introduced, which we call an end-loaded planar open-sleeve dipole (ELPOSD). This configuration provides a degree of miniaturization while retaining a comparable bandwidth in terms of the VSWR response to that of conventional open-sleeve dipoles. Several designs are presented for the conventional and end-loaded configurations that demonstrate the VSWR and miniaturization capabilities of this class of antennas. Measured results have been compared with simulations and found to be in good agreement for an end-loaded planar open-sleeve monopole. Index Terms--Broadband antennas, genetic algorithms (GAs), open-sleeve dipole, printed antennas, small antennas.

We have constructed a cavity ring-down spectrometer employing a near-IR external cavity diode laser capable of measuring [sup.13]C/[sup.12]C isotopic ratios in C[O.sub.2] in human breath. The system, which has a demonstrated minimum detectable absorption loss of 3.2 x [10.sup.-11] [cm.sup.-1] [Hz.sup.-1/2], determines the isotopic ratio of [sup.13]C[sup.16]0[sup.16]0/[sup.12]C[sup.16]0[sup.16]0 by measuring the intensities of rotationally resolved absorption features of each species. As in isotope ratio mass spectrometry (IRMS), the isotopic ratio of a sample is compared to that of a standard C[O.sub.2] sample calibrated to the Pee Dee Belemnite scale and reported as the sample's [delta][sup.13]C value. Measurements of eight replicate C[O.sub.2] samples standardized by IRMS and consisting of 5% C[O.sub.2] in [N.sub.2] at atmospheric pressure demonstrated a precision of 0.22 [per thousand] for the technique. [delta][sup.13]C values were also obtained for breath samples from individuals testing positive and negative for the presence of Helicobacter pylori, the leading cause of peptic ulcers in humans. This study demonstrates the ability of the instrument to obtain [delta][sup.13]C values in breath samples with sufficient precision to serve as a useful medical diagnostic.

Research was conducted to examine the contributions of individual solvent molecules to solvent reorganization directly by probing the energy of the d -> pi metal-to-ligand charge transfer transition in the low-spipn bis(2,2',2'-terpyridyl)iron(II) complex as a function of solvent number in gas-phase clusters with dimethyl sulfoxide. Results indicate that tetragonal distortion of the ligand field arises from strong sigma bonding.

An analysis of the solvent dependence of Eop for the metal-to-ligand charge transfer (MLCT) transition in small gas-phase clusters identified from photodepletion action spectra is presented. The findings reveal that a solvent dependence correlated with the behavior predicted by a dielectric continuum model was observed in Eop for MLCT in the coordination complex [Fe(terpy)2]2+ isolated in clusters with few solvent molecules.

Students of beginning chemistry determine whether the FD&C dyes of M&M candies fluoresce and, if they do, determine the color of the fluorescence under a long-wavelength hand-held UV lamp in an expansion of the usual beginning chemistry lab in which students learn by paper chromatography. Fluorescence quenching may also be studied.

Presents a letter to the editor on chromatographic analysis.

Examines the use of cavity ring-down spectroscopy in determining stable isotope ratios. Determination of isotope ratios for carbon dioxide in human breath; Capability of the cavity diode laser to measure isotopic ratios; Association of the presence of Helicobacter pyroli with peptic ulcers.