Time-resolved fluorescence with an optical-fiber probe

Time-resolved fluorescence measurements are made with an optical-fiber probe approximately 16 m long. Fluorescence lifetimes for 1.00 μM solutions of rhodamine-B and rose bengal in ethanol were found to be 2.78 ± 0.04 ns and 0.77 ± 0.07 ns, respectively, similarin accuracy and precision to values obtained with conventional techniques. Calculations are used to investigate the limitations in remote determinations caused by temporal broadening. Results indicate that fiber lengths approaching 1 km can be used without significant loss in accuracy or precision.     

Semi-invariants in surgery

A semi-invariant in surgery is an invariant of a quadratic Poincaré complex which is defined in terms of a null-cobordism. We define five such gadgets: the semicharacteristic, the semitorsion, the cross semitorsion, the torsion semicharacteristic, and the cross torsion semicharacteristic. We describe applications to the evaluation of surgery obstructions, especially in the odd-dimensional case.     

A stationary,pairwise independent,absolutely regular sequence for which the central limit theorem fails

Summary A strictly stationary finite-state non-degenerate random sequence is constructed which satisfies pairwise independence and absolute regularity but fails to satisfy a central limit theorem. The mixing rate for absolute regularity is only slightly slower than that in a corresponding central limit theorem of Ibragimov.This work was partially supported by NSF grant DMS 86-00399     

Critical comparison of sources and detection methods in atomic spectrometry

Summary Over the past three decades, the nature of atomic spectrometric analysis has changed dramatically. In the 1960's, flame and furnace atomic absorption were dominant, with furnace techniques gradually achieving prominence. In contrast, the 1970's witnessed the introduction of the inductively coupled plasma (ICP) and the direct current plasma (DCP). Although the ICP is still the most frequently used excitation source, the decade of the 1980's has seen a resurgence of interest in the glow-discharge lamp (GDL) and the microwave-induced plasma (MIP). Today, novel sources are continually being introduced, supported by combinations of gas mixtures and operated alternatively at DC, microwave or radio frequencies. These advances must be assessed against the backdrop of more unconventional atom-formation techniques that involve the use of high-powered lasers, rare-gas sputtering systems, or tandem (coupled) sources.In a similar vein, modes of detection have changed significantly over the past 30 years. While chemical flames and furnaces were the atom reservoirs of choice, atomic absorption was favored, in large measure because of its simplicity. In contrast, in the period of the 1970's, the attributes of the ICP made emission spectrometry the most attractive, in large part because of its straightforward adaptation to simultaneous multielement approaches. The most common configurations for such emission-based measurements were the direct-reading spectrometer, borrowed from earlier arc and spark days, and the slew/scan arrangement, in which desired spectral regions were scanned slowly, but regions of less interest bypassed hastily. In both systems, it was recognized that background correction was becoming increasingly important.In the 1980's, we have come to realize that other detection techniques might ultimately prove superior to a conventional emission measurement. For example, plasma-source mass spectrometry has already demonstrated detection limits several orders of magnitude lower than can be achieved routinely by emission. Similarly, atomic or ionic fluorescence, excited by a laser source, has been shown capable of detecting as little as a few thousand atoms. Ultimately, techniques such as resonance ionization spectrometry are appealing, despite their complexity, since they are capable of detecting even a single atom.Adding to this rather complicated situation is the question of how emission might best be detected if it is the measurement of choice. The traditional direct-reading and slew/scan approaches are convenient and well established. However, they lack the ability to detect a complete atomic-emission spectrum, a feature offered long ago by a photographic film or plate. Now, such capability exists in multichannel electronic readout devices, of either the linear or two-dimensional variety. The advent of charge-coupled devices (CCD), charge-injection devices (CID) and integrated linear photodiode array packages (PDA) makes it possible to consider replacing single-channel detectors with an electronic analog of the photographic plate. Similarly, the use of Fourier-transform spectrometry, produced by means of a moderate-resolution interferometer, affords the option not only of simultaneous multielement analysis, but also of simultaneous monitoring of background levels, accurate registration of atomic-emission wavelengths, and relatively rapid scan speeds.In this paper, a few of the more attractive alternatives in this apparently bewildering array of options will be outlined. The most attractive of the options will be compared with each other in an attempt to assess not only what the most attractive current choices are in atomic spectrometric analysis but also what the future might bring.     

Spectra for Factorable Matrices on ℓ p

We obtain the spectra and fine spectra for factorable matrices, considered as bounded linear operators over ℓ^p , 1 < p < ∞.     

Spectra and Fine Spectra for Factorable Matrices

We obtain the spectra and fine spectra for factorable triangular matrices. Our results contain some previous work of the authors as special cases.     

Search for up-down quark mass differences via isospin symmetry breaking

We performed a series of experiments employing the two pion production reactions p + d → ³He + π⁰ and p + d → ³H + π⁺. The two isopin related reactions differ by a Clebsch Gordan coefficient of 2. We searched for deviations in this ratio in complete angular distributions in the range of the Δ excitation as well as in the vicinity of the η production threshold.