Near infrared spectroscopy for fibre based gas detection

Gas sensing systems based on fibre optic linked near infra red absorption cells are potentially a flexible and effective tool for monitoring accumulations of hazardous and noxious gases in enclosed areas such as tunnels and mines. Additionally the same baseline technology is readily modified to measure concentrations of hydrocarbon fuels - notably but not exclusively methane, and monitoring emissions of greenhouse gases. Furthermore the system can be readily implemented to provide intrinsically safe monitoring over extensive areas at up to ~250 points from a single interrogation unit. In this paper we review our work on fibre coupled gas sensing systems. We outline the basic principles through which repeatable and accurate self calibrating gas measurements may be realised, including the recover of detailed line shapes for non contact temperature and / or pressure measurements in addition to concentration assessments in harsh environments. We also outline our experience in using these systems in extensive networks operating under inhospitable conditions over extended periods extending to several years

The Porphyromonas gingivalis hemagglutinins HagB and HagC are major mediators of adhesion and biofilm formation

Porphyromonas gingivalis is a bacterium associated with chronic periodontitis that possesses a family of genes encoding hemagglutinins required for heme acquisition. In this study we generated ΔhagB and ΔhagC mutants in strain W83 and demonstrate that both hagB and hagC are required for adherence to oral epithelial cells. Unexpectedly, a double ΔhagB/ΔhagC mutant had less severe adherence defects than either of the single mutants, but was found to exhibit increased expression of the gingipain-encoding genes rgpA and kgp, suggesting that a ΔhagB/ΔhagC mutant is only viable in populations of cells that exhibit increased expression of genes involved in heme acquisition. Disruption of hagB in the fimbriated strain ATCC33277 demonstrated that HagB is also required for stable attachment of fimbriated bacteria to oral epithelial cells. Mutants of hagC were also found to form defective single and multi-species biofilms that had reduced biomass relative to biofilms formed by the wild-type strain. This study highlights the hitherto unappreciated importance of these genes in oral colonization and biofilm formation

Gas sensing based on optical fibre coupled diode laser spectroscopy : a new approach to sensor systems for safety monitoring

We describe an entirely passive fibre optic network which senses, amongst other species, CH¬4¬ and CO¬¬2 , with sensitivity and selectivity compatible with safety sensing in the mine environment. The basic principle is that a single laser diode source targeted to a particular species addresses up to 200 sensing points which may be spread over an area of dimensions ten or more km. The detection and processing electronics is typically located with the laser source. Several laser sources can be introduced in parallel to enable monitoring multiple species. The network itself, entirely linked through optical fibre, is inherently intrinsically safe. It is self checking for faults at the sensing location and continuously self calibrating. In the methane sensing mode its sensitivity is sub 100ppm and it responds accurately up to 100% methane. It is therefore capable of detecting extremely hazardous gas pockets which are completely missed by other sensor technologies. The network has demonstrated stability with zero maintenance or recalibration over periods in excess of two years. We believe that this system offers unique benefits in the context of mine safety and ventilation system monitoring

Chapter 6 Collapsible Soils in the UK

Metastable soils may collapse because of the nature of their fabric. Generally speaking, these soils have porous textures, high void ratios and low densities. They have high apparent strengths at their natural moisture content, but large reductions of void ratio take place upon wetting and, particularly, when they are loaded because bonds between grains break down upon saturation. Worldwide, there is a range of natural soils that are metastable and can collapse, including loess, residual soils derived from the weathering of acid igneous rocks and from volcanic ashes and lavas, rapidly deposited and then desiccated debris flow materials such as some alluvial fans; for example, in semi-arid basins, colluvium from some semi-arid areas and cemented, high salt content soils such as some sabkhas. In addition, some artificial non-engineered fills can also collapse. In the UK, the main type of collapsible soil is loess, though collapsible non-engineered fills also exist. Loess in the UK can be identified from geological maps, but care is needed because it is usually mapped as ‘brickearth’. This is an inappropriate term and it is suggested here that it should be replaced, where the soils consist of loess, by the term ‘loessic brickearth’. Loessic brickearth in the UK is found mainly in the south east, south and south west of England, where thicknesses greater than 1 m are found. Elsewhere, thicknesses are usually less than 1 m and, consequently, of limited engineering significance. There are four steps in dealing with the potential risks to engineering posed by collapsible soils: (1) identification of the presence of a potentially collapsible soil using geological and geomorphological information; (2) classification of the degree of collapsibility, including the use of indirect correlations; (3) quantification of the degree of collapsibility using laboratory and/or in situ testing; (4) improvement of the collapsible soil using a number of engineering options

A Large Area Fiber Optic Gyroscope on multiplexed fiber network

We describe a fiber optical gyroscope based on the Sagnac effect realized on a multiplexed telecom fiber network. Our loop encloses an area of 20 km2 and coexists with Internet data traffic. This Sagnac interferometer achieves a sensitivity of about (10-8 rad/s)/sqrt(Hz), thus approaching ring laser gyroscopes without using narrow linewidth laser nor sophisticated optics. The proposed gyroscope is sensitive enough for seismic applications, opening new possibilities for this kind of optical fiber sensors

Combined analysis of the salivary microbiome and host defence peptides predicts dental disease

Understanding the triad of host response, microbiome and disease status is potentially informative for disease prediction, prevention, early intervention and treatment. Using longitudinal assessment of saliva and disease status, we demonstrated that partial least squares modelling of microbial, immunological and clinical measures, grouped children according to future dental disease status. Saliva was collected and dental health assessed in 33 children aged 4 years, and again 1-year later. The composition of the salivary microbiome was assessed and host defence peptides in saliva were quantified. Principal component analysis of the salivary microbiome indicated that children clustered by age and not disease status. Similarly, changes in salivary host defence peptides occurred with age and not in response to, or preceding dental caries. Partial least squares modelling of microbial, immunological and clinical baseline measures clustered children according to future dental disease status. These data demonstrate that isolated evaluation of the salivary microbiome or host response failed to predict dental disease. In contrast, combined assessment of both host response together with the microbiome revealed clusters of health and disease. This type of approach is potentially relevant to myriad diseases that are modified by host–microbiome interactions

Limitation of absorption-based fiber optic gas sensors by coherent reflections

Author name used in this publication: W. JinAuthor name used in this publication: M. S. DemokanVersion of RecordPublishe

In silico design of supramolecules from their precursors: Odd–even effects in cage-forming reactions

We synthesize a series of imine cage molecules where increasing the chain length of the alkanediamine precursor results in an odd–even alternation between [2 + 3] and [4 + 6] cage macrocycles. A computational procedure is developed to predict the thermodynamically preferred product and the lowest energy conformer, hence rationalizing the observed alternation and the 3D cage structures, based on knowledge of the precursors alone

Identification and assessment of geohazards affecting pipelines and urban areas

The paper addresses methods and criteria of risk assessment associated with land subsidence threatening pipelines, buildings, and constructions. Currently, there are some practical issues relating to geohazards that should be taken into account while constructing a pipeline. The article provides comparison data on the effects of Spitak earthquake and the natural disaster in Neftegorsk in terms of geohazards impact on the pipeline systems. The suggested risk assessment procedure embraces a wide range of aspects: from soil properties to economic and management issues