Colour changes by laser irradiation of reddish building limestones

We have used X-ray photoelectron spectroscopy (XPS) as a novel method to investigate the causes of colour changes in a reddish limestone under irradiation by a Q-switched Nd:YAG 1064 nm laser. We irradiated clean dry and wet surfaces of Pidramuelle Roja, a building stone frequently used in the Asturian heritage, at fluences ranging from 0.12 to 1.47 J cm−2. We measured the colour coordinates and undertook XPS analysis of the state of oxidation of iron both before and after irradiation. Visible colour changes and potential aesthetic damage occurred on dry surfaces from a fluence of 0.31 J cm−2, with the stone showing a greening effect and very intense darkening. The colour change on dry surfaces was considerably higher than on wet surfaces, which at the highest fluence (1.47 J cm−2) was also above the human visual detection threshold. The use of XPS demonstrated that the change in colour (chroma and hue) is associated with a reduction in the iron oxidation state on dry surfaces during laser irradiation. This points out to a potential routinary use of XPS to analyse causes of colour changes during laser cleaning in other types of coloured building stones

Was Alpha deadlier than wild-type Covid? Analysis in rural England

Background: It is useful to document whether each newly dominant SARS-CoV-2 variant of concern was more or less dangerous than preceding dominant variant(s). We assessed if the emergence of the Alpha (B.1.1.7) variant in autumn 2020 could be linked to higher case fatality rates, compared to original wild-type COVID-19, subgrouping by age band, sex, deprivation or month of diagnosis as potential risk factors. Methods: Observational study and secondary analysis were conducted of SARS-CoV-2 cases diagnosed due to medical need or occupational exposure in an administrative area of Eastern England, UK (base population 1 million), who first tested positive in the period 1 March 2020 to 28 February 2021. Multivariate logistic regression was performed to examine relationships of age group, sex, deprivation group and month of diagnosis with case fatality rates within 28 days of diagnosis. Marginal probabilities for risk of dying were calculated separately for the first two main ‘wave’ periods of the English pandemic. Results: Older age and male sex consistently raised the risk of mortality in both wave periods. Higher deprivation was linked to mortality risk in the first wave period, but not in the second wave. Mortality decreased over time during the first wave period, but slightly increased over time during the second wave. Cases were younger in the second wave, and median age of the deceased varied little between waves. Interpretation: The Alpha variant of SARS-CoV-2 did not lead to higher mortality rates for any age, deprivation or sex group, compared to case fatality rates in the early part of the pandemic period

Application limits of Q-Switched Nd: YAG laser irradiation for stone cleaning based on colour measurements

The application limits of the laser-cleaning technique for different types of building stones have been investigated by measuring colour variations. The selected stones differ in their chemical and mineralogical composition, colour, texture and crystallinity degree. The experimentation was carried out with a Q-switched Nd:YAG laser. The colour variations on stones associated with different operative fluences were measured using a colorimeter. Further, surface morphological changes were examined under SEM. From the calculation of colour differences, a damage threshold fluence was established for each stone type. The response of the stones to laser radiation at a particular fluence was found to be mainly conditioned by their chemical and mineralogical composition and, to a less extent, by their textural characteristics

Automated retinal image quality assessment on the UK Biobank dataset for epidemiological studies.

Morphological changes in the retinal vascular network are associated with future risk of many systemic and vascular diseases. However, uncertainty over the presence and nature of some of these associations exists. Analysis of data from large population based studies will help to resolve these uncertainties. The QUARTZ (QUantitative Analysis of Retinal vessel Topology and siZe) retinal image analysis system allows automated processing of large numbers of retinal images. However, an image quality assessment module is needed to achieve full automation. In this paper, we propose such an algorithm, which uses the segmented vessel map to determine the suitability of retinal images for use in the creation of vessel morphometric data suitable for epidemiological studies. This includes an effective 3-dimensional feature set and support vector machine classification. A random subset of 800 retinal images from UK Biobank (a large prospective study of 500,000 middle aged adults; where 68,151 underwent retinal imaging) was used to examine the performance of the image quality algorithm. The algorithm achieved a sensitivity of 95.33% and a specificity of 91.13% for the detection of inadequate images. The strong performance of this image quality algorithm will make rapid automated analysis of vascular morphometry feasible on the entire UK Biobank dataset (and other large retinal datasets), with minimal operator involvement, and at low cost

Suitability of UK biobank retinal images for automatic analysis of morphometric properties of the vasculature

To assess the suitability of retinal images held in the UK Biobank--the largest retinal data repository in a prospective population-based cohort--for computer assisted vascular morphometry, generating measures that are commonly investigated as candidate biomarkers of systemic disease.Non-mydriatic fundus images from both eyes of 2,690 participants--people with a self-reported history of myocardial infarction (n=1,345) and a matched control group (n=1,345)--were analysed using VAMPIRE software. These images were drawn from those of 68,554 UK Biobank participants who underwent retinal imaging at recruitment. Four operators were trained in the use of the software to measure retinal vascular tortuosity and bifurcation geometry.Total operator time was approximately 360 hours (4 minutes per image). 2,252 (84%) of participants had at least one image of sufficient quality for the software to process, i.e. there was sufficient detection of retinal vessels in the image by the software to attempt the measurement of the target parameters. 1,604 (60%) of participants had an image of at least one eye that was adequately analysed by the software, i.e. the measurement protocol was successfully completed. Increasing age was associated with a reduced proportion of images that could be processed (p=0.0004) and analysed (p<0.0001). Cases exhibited more acute arteriolar branching angles (p=0.02) as well as lower arteriolar and venular tortuosity (p<0.0001).A proportion of the retinal images in UK Biobank are of insufficient quality for automated analysis. However, the large size of the UK Biobank means that tens of thousands of images are available and suitable for computational analysis. Parametric information measured from the retinas of participants with suspected cardiovascular disease was significantly different to that measured from a matched control group

Cristalización de sales en rocas monumentales porosas y su auscultación mediante emisión acústica

Entre las causas de deterioro de los materiales pétreos monumentales se encuentra la acción de las sales solubles neoformadas en el interior de los mismos. Estas sales, en la mayoría de los casos no son estables y dependiendo de las condiciones ambientales pueden sufrir una serie de procesos cíclicos (cristalización-disolución, hidratación-deshidratación, etc) que pueden dar lugar a la concentración de tensiones en el material que las contiene. Dentro de estas sales, existen algunas particularmente dañinas, como los sulfatos. Éstos se generan frecuentemente en zonas contaminadas, donde son habituales las atmósferas ácidas. Entre los sulfatos cabe destacar la acción del sulfato de sodio, que conduce a un deterioro de las rocas más rápido que cualquiera de las otras sales, sobre todo en rocas sedimentarias muy porosas, ampliamente utilizadas en edificaciones monumentales. En esta tesis se profundiza en los mecanismos implicados en la acción de las sales solubles (fundamentalmente del sulfato de sodio), desde un punto experimental en el laboratorio, aplicando una técnica no destructiva de auscultación, la emisión acústica, capaz de registrar las ondas elásticas generadas por la liberación de energía del material sometido a tensiones. Se espera, asimismo, que esta técnica pueda ser aplicada en el propio monumento, en un futuro próximo, para el estudio "in situ" de la degradación de los materiales de edificación debida a la acción de las sales solubles

Carbon in black crusts from the Tower of London

This paper investigates the origin, fluxes, and transformation of carbon compounds within black crusts on the stone walls of the Tower of London. The crusts were analyzed for elemental and organic carbon, including the water soluble fraction. Elemental carbon and low solubility compounds such as oxalates appeared to be conserved because of long residence times. Conversely, more soluble ions, like chloride and formate would be removed from the layers relatively quickly by rainfall. At higher organic carbon concentrations acetic acid may be produced within the crusts from biological transformations. Currently, traffic sources contribute to increasingly organic rich crusts. The deposition of elemental carbon to buildings darkens surfaces and has important aesthetic implications. The increased organic content may have further aesthetic consequence by changing the color of buildings to warmer tones, particularly browns and yellows. Management of historic buildings requires us to recognize the shift away from simple gypsum crusts to those richer in organic materials

Estudios experimentales sobre la consolidación y protección de los materiales calcáreos de la Catedral de Oviedo. 2ª parte

We have carried out a series of accelerated artificial ageing tests to study the evolution of the silico-organic treatment products applied to calcareous materials of the Catedral of Oviedo. Test valoration has been made both by visual examination and weight loss measuring. We conclude by comparing different behaviours of treated stones with diverse products in the tests monitored.Se han realizado una serie de ensayos de envejecimiento artificial acelerado para estudiar la evolución de los productos de tratamiento silico-orgánicos aplicados a los materiales calcáreos de la Catedral de Oviedo. La valoración de los resultados se ha realizado mediante observación visual y medidas de pérdida de peso. Se concluye comparando los distintos comportamientos de las piedras tratadas con diferentes productos frente a estos ensayos