Determining salinity using a multimode fiber optic surface plasmon resonance dip-probe

For the first time a fiber optic surface plasmon resonance sensor with demonstrated accuracy and precision of less than 200 ppm salinity is presented for calibration across a range of temperatures and salinities. Also shown is the potential for the sensor system to reach precisions of 10 ppm or less. Calibration models are constructed for 28-48‰ salinity and a method for translating the calibration models to account for varying temperatures between 0 and 25 °C are demonstrated. The long-term susceptibility of the fiber optic sensor to fouling and drift is discussed.     

In situ Detection of Cobaloxime Intermediates During Photocatalysis Using Hollow-Core Photonic Crystal Fiber Microreactors

Hollow-core photonic crystal fibers (HC-PCFs) provide a novel approach for in situ UV/Vis spectroscopy with enhanced detection sensitivity. Here, we demonstrate that longer optical path lengths than afforded by conventional cuvette-based UV/Vis spectroscopy can be used to detect and identify the Co^I and Co^II states in hydrogen-evolving cobaloxime catalysts, with spectral identification aided by comparison with DFT-simulated spectra. Our findings show that there are two types of signals observed for these molecular catalysts; a transient signal and a steady-state signal, with the former being assigned to the Co^I state and the latter being assigned to the Co^II state. These observations lend support to a unimolecular pathway, rather than a bimolecular pathway, for hydrogen evolution. This study highlights the utility of fiber-based microreactors for understanding these and a much wider range of homogeneous photocatalytic systems in the future.     

Error analysis of QR decompositions by Givens transformations

The error analysis for computing the QR decomposition by Givens transformations was given originally by Wilkinson for n×n square matrices, and later by Gentleman for n×p (pn) tall thin matrices. The derivations were sufficiently messy that results were quoted by analogy to the derivation of a specific case. A certain lemma makes possible a much simpler derivation, which incidentally substantially tightens the bound. Moreover, it applies to variants of the method other than those originally considered, and suggests why observed errors are even less than this new bound.     

R: A Language for Data Analysis and Graphics

Abstract

In this article we discuss our experience designing and implementing a statistical computing language. In developing this new language, we sought to combine what we felt were useful features from two existing computer languages. We feel that the new language provides advantages in the areas of portability, computational efficiency, memory management, and scoping.