Investigating the effect of nanolime treatment on the drying kinetics of Clipsham limestone

Climate change poses an ever-increasing risk to our stone built heritage. Among conservation actions, the use of consolidant products is considered a possible response to this challenge, and the adoption of nanolimes has been widely studied showing promising results. However, while the effectiveness and method of application has been assessed, few studies have probed the changes in drying kinetics following treatment. In fact, a drastic alteration of the water transport might lead to further anomalies. This study investigates the influence of nanolimes dispersed in ethanol on the drying kinetics of Clipsham limestone using cavity ring-down spectroscopy. The degree of treatment was assessed by gravimetry, Raman spectroscopy, optical microscopy, colorimetry, optical profilometry and thin section analysis. Results showed an increase in the dry mass, observable colour changes and decrease in surface roughness. Small but reproducible increases were observed in the evaporation flux for phase I behaviour following treatment, however, no changes were observed in the total mass of water released or the phase II diffusivity. Determination of the activation energy associated with phase II drying was unchanged following treatment . These results indicate that following treatment there has been little-to-no change in the internal surfaces and structure of the stone to affect vapour transport

OH detection by absorption of frequency-doubled diode laser radiation at 308nm

Radiation at 308 nm has been obtained by frequency doubling the output of a commercial diode laser cooled to 165 K. A single pass through a crystal of LiIO3 converted 1 mW of 616 nm radiation to 50 pW of UV, and this was used to detect the OH radical in absorption in a flow tube. Possible extensions of the method for detection of OH in the atmosphere are discussed

High performance continuous-wave laser cavity enhanced polarimetry using RF-induced linewidth broadening

We present precise optical rotation measurements of gaseous chiral samples using near-IR continuous-wave cavity-enhanced polarimetry. Optical rotation is determined by comparing cavity ring-down signals for two counter-propagating beams of orthogonal polarisation which are subject to polarisation rotation by the presence of both an optically active sample and a magneto-optic crystal. A broadband RF noise source applied to the laser drive current is used to tune the laser linewidth and optimise the polarimeter, and this noise-induced laser linewidth is quantified using self-heterodyne beat-note detection. We demonstrate the optical rotation measurement of gas phase samples of enantiomers of α-pinene and limonene with an optimum detection precision of 10 µdeg per cavity pass and an uncertainty in the specific rotation of ∼0.1 deg dm−1 (g/ml)−1 and determine the specific rotation parameters at 730 nm, for (+)- and (−)-α-pinene to be 32.10 ± 0.13 and −32.21 ± 0.11 deg dm−1 (g/ml)−1, respectively. Measurements of both a pure R-(+)-limonene sample and a non-racemic mixture of limonene of unknown enantiomeric excess are also presented, illustrating the utility of the technique

Exhaled Breath Isoprene Rises During Hypoglycemia in Type 1 Diabetes.

Work was supported by the NIHR Cambridge Biomedical Research Centre including salary support for SN. Hormonal assays were performed by Keith Burling and colleagues in the NIHR Cambridge Biomedical Research Centre Core Biochemical Assay Laboratory. Clamp studies were performed in the Cambridge NIHR/ Wellcome Trust Clinical Research Facility.This is the author accepted manuscript. The final version is available from the American Diabetes Association via http://dx.doi.org/10.2337/dc16-046

Cavity ringdown studies of the E–H transition in an inductively coupled oxygen plasma: comparison of spectroscopic measurements and modelling

The absolute number density of ground state oxygen atoms, O(3P), present in a 100 mTorr oxygen plasma has been determined as a function of operating power using cavity ringdown spectroscopy (CRDS). The dissociation fraction increases by an order of magnitude from ∼0.8% at 50 W to 8% at 250 W and reflects a similar increase in the electron density over this power range. Emission spectra show that the E–H switchover is accompanied by increased rotational heating of O2 and this behaviour is also observed in the translational temperatures determined by fitting the Doppler limited O(3P) CRDS data. The measurements are contextualised via a volume averaged kinetic model that uses the measured absolute densities of O(3P) and O2(a1Δg, v = 0) as a function of power as its benchmarks. Despite the inherent spatial inhomogeneity of the plasma, the volume averaged model, which uses a minimal set of reactions, is able to both reproduce previous measurements on the absolute density of O− and to infer physically reasonable values for both the electron temperature and number density as the E–H switch over is traversed. Time-resolved emission measurements return a value of 0.2 for the wall loss coefficient for O2(b1Σg+); as a consequence, the number density of O2(b1Σg+) is (at least) one order of magnitude less than O2(a1Δg)

Direct monitoring of drying kinetics of building limestones using cavity ring-down spectroscopy

Enhanced understanding of the drying kinetics of building materials is important to explain durability and improve conservation. Cavity ring-down spectroscopy has been demonstrated to be an effective method to investigate drying kinetics, and is here applied to investigate the drying behaviour of five commonly used building limestones, and one sandstone. Although the time period for phase I drying increases with increasing porosity, the constant mass flux remains essentially unchanged. This is not so for phase II drying diffusivities which are reported for Portland Whit Bed limestone, Portland Base Bed limestone, Clipsham limestone, Bath limestone, Savonnières limestone and Stoke Hall sandstone, and are found to be in the range 3.0 - 6.5 × 10⁻⁹ m² s⁻¹ at 25 °C. Differences in the phase II diffusivity do not appear to be solely controlled by porosity. Activation energies associated with phase II drying for Clipsham limestone, Portland Base Bed limestone and Stoke Hall sandstone, are determined to be 31.9 ± 1.8, 29.4 ± 1.4 and 27.1 ± 2.2 kJ mol⁻¹, respectively

Rapid passage effects in nitrous oxide induced by a chirped external cavity quantum cascade laser

A widely tunable pulsed external cavity quantum cascade laser operating around 8 μm has been used to make rotationally resolved measurements of rapid passage effects in the absorption spectrum of N2 O. Rapid passage signals as a function of laser power and N2 O pressure are presented. Comparisons are drawn with measurements performed on the same transition with a standard distributed feedback quantum cascade laser. The initial observations on rapid passage effects induced with an external cavity quantum cascade laser show that such high power, widely tunable radiation sources may find applications in both nonlinear optics and optical sensing experiments. © 2009 American Institute of Physics

Continuous-wave cavity-enhanced polarimetry for optical rotation measurement of chiral molecules

Precise optical rotation measurements play an important role in the analysis of chiral molecules in various fields, especially in biological chemistry and pharmacology. In this paper, we demonstrate a new variant of continuous-wave cavity-enhanced polarimetry for detecting the optical activity of two enantiomers of a chiral molecule at 730 nm. It is based on a signal-reversing technique for which the chiral specific rotation is directly determined by the cavity ring-down signal from two counter-propagating beams in a bow-tie cavity. In particular, we ensure reproducible excitation of both modes by broadening the linewidth of a diode laser source by application of a radio frequency perturbation to its injection current. The performance of the polarimeter is demonstrated for the specific rotation of (+)- and (−)-α-pinene in different environments, including the pure vapor, open air, and the liquid phase; the detection precision ranges between 10–5 and 10–4 degrees per cavity pass depending on the environment. The apparatus is a robust and practical tool for quantifying chirality and can be developed for the entire visible and near-infrared spectral regions