Predicting dry eye using non-invasive techniques of tear film surface assessment

PURPOSE. To measure tear film surface quality in healthy and dry eye subjects using three noninvasive techniques of tear film quality assessment and to establish the ability of these noninvasive techniques to predict dry eye. METHODS. Thirty four subjects participated in the study, and were classified as dry eye or normal, based on standard clinical assessments. Three non-invasive techniques were applied for measurement of tear film surface quality: dynamic-area high-speed videokeratoscopy (HSV), wavefront sensing (DWS) and lateral shearing interferometry (LSI). The measurements were performed in both natural blinking conditions (NBC) and in suppressed blinking conditions (SBC). RESULTS. In order to investigate the capability of each method to discriminate dry eye subjects from normal subjects, the receiver operating curve (ROC) was calculated and then the area under the curve (AUC) was extracted. The best result was obtained for the LSI technique (AUC=0.80 in SBC and AUC=0.73 in NBC), which was followed by HSV (AUC=0.72 in SBC and AUC=0.71 in NBC). The best result for DWS was AUC=0.64 obtained for changes in vertical coma in suppressed blinking conditions, while for normal blinking conditions the results were poorer. CONCLUSIONS. Non-invasive techniques of tear film surface assessment can be used for predicting dry eye and this can be achieved in natural blinking as well as suppressed blinking conditions. In this study, LSI showed the best detection performance, closely followed by the dynamic-area HSV. The wavefront sensing technique was less powerful, particularly in natural blinking conditions.

Widening the gap between measurement and modelling of secondary organic aerosol properties?

The link between measured sub-saturated hygroscopicity and cloud activation potential of secondary organic aerosol particles produced by the chamber photo-oxidation of α-pinene in the presence or absence of ammonium sulphate seed aerosol was investigated using two models of varying complexity. A simple single hygroscopicity parameter model and a more complex model (incorporating surface effects) were used to assess the detail required to predict the cloud condensation nucleus (CCN) activity from the subsaturated water uptake. Sub-saturated water uptake measured by three hygroscopicity tandem differential mobility analyser (HTDMA) instruments was used to determine the water activity for use in the models. The predicted CCN activity was compared to the measured CCN activation potential using a continuous flow CCN counter. Reconciliation using the more complex model formulation with measured cloud activation could be achieved widely different assumed surface tension behavior of the growing droplet; this was entirely determined by the instrument used as the source of water activity data. This unreliable derivation of the water activity as a function of solute concentration from sub-saturated hygroscopicity data indicates a limitation in the use of such data in predicting cloud condensation nucleus behavior of particles with a significant organic fraction. Similarly, the ability of the simpler single parameter model to predict cloud activation behaviour was dependent on the instrument used to measure sub-saturated hygroscopicity and the relative humidity used to provide the model input. However, agreement was observed for inorganic salt solution particles, which were measured by all instruments in agreement with theory. The difference in HTDMA data from validated and extensively used instruments means that it cannot be stated with certainty the detail required to predict the CCN activity from sub-saturated hygroscopicity. In order to narrow the gap between measurements of hygroscopic growth and CCN activity the processes involved must be understood and the instrumentation extensively quality assured. It is impossible to say from the results presented here due to the differences in HTDMA data whether: i) Surface tension suppression occurs ii) Bulk to surface partitioning is important iii) The water activity coefficient changes significantly as a function of the solute concentration.

Heat strain, hydration status, and symptoms of heat illness in surface mine workers

The aim of the research program was to evaluate the heat strain, hydration status, and heat illness symptoms experienced by surface mine workers. An initial investigation involved 91 surface miners completing a heat stress questionnaire; assessing the work environment, hydration practices, and heat illness symptom experience. The key findings included 1) more than 80 % of workers experienced at least one symptom of heat illness over a 12 month period; and 2) the risk of moderate symptoms of heat illness increased with the severity of dehydration. These findings highlight a health and safety concern for surface miners, as experiencing symptoms of heat illness is an indication that the physiological systems of the body may be struggling to meet the demands of thermoregulation. To illuminate these findings a field investigation to monitor the heat strain and hydration status of surface miners was proposed. Two preliminary studies were conducted to ensure accurate and reliable data collection techniques. Firstly, a study was undertaken to determine a calibration procedure to ensure the accuracy of core body temperature measurement via an ingestible sensor. A water bath was heated to several temperatures between 23 . 51 ¢ªC, allowing for comparison of the temperature recorded by the sensors and a traceable thermometer. A positive systematic bias was observed and indicated a need for calibration. It was concluded that a linear regression should be developed for each sensor prior to ingestion, allowing for a correction to be applied to the raw data. Secondly, hydration status was to be assessed through urine specific gravity measurement. It was foreseeable that practical limitations on mine sites would delay the time between urine collection and analysis. A study was undertaken to assess the reliability of urine analysis over time. Measurement of urine specific gravity was found to be reliable up to 24 hours post urine collection and was suitable to be used in the field study. Twenty-nine surface miners (14 drillers [winter] and 15 blast crew [summer]) were monitored during a normal work shift. Core body temperature was recorded continuously. Average mean core body temperature was 37.5 and 37.4 ¢ªC for blast crew and drillers, with average maximum body temperatures of 38.0 and 37.9 ¢ªC respectively. The highest body temperature recorded was 38.4 ¢ªC. Urine samples were collected at each void for specific gravity measurement. The average mean urine specific gravity was 1.024 and 1.021 for blast crew and drillers respectively. The Heat Illness Symptoms Index was used to evaluate the experience of heat illness symptoms on shift. Over 70 % of drillers and over 80 % of blast crew reported at least one symptom. It was concluded that 1) heat strain remained within the recommended limits for acclimatised workers; and 2) the majority of workers were dehydrated before commencing their shift, and tend to remain dehydrated for the duration. Dehydration was identified as the primary issue for surface miners working in the heat. Therefore continued study focused on investigating a novel approach to monitoring hydration status. The final aim of this research program was to investigate the influence dehydration has on intraocular pressure (IOP); and subsequently, whether IOP could provide a novel indicator of hydration status. Seven males completed 90 minutes of walking in both a cool and hot climate with fluid restriction. Hydration variables and intraocular pressure were measured at baseline and at 30 minute intervals. Participants became dehydrated during the trial in the heat but maintained hydration status in the cool. Intraocular pressure progressively declined in the trial in the heat but remained relatively stable when hydration was maintained. A significant relationship was observed between intraocular pressure and both body mass loss and plasma osmolality. This evidence suggests that intraocular pressure is influenced by changes in hydration status. Further research is required to determine if intraocular pressure could be utilised as an indirect indicator of hydration status.

A plasmonic 'ac Wheatstone bridge' circuit for high-sensitivity phase measurement and single-molecule detection

In this paper, a plasmonic “ac Wheatstone bridge” circuit is proposed and theoretically modeled for the first time. The bridge circuit consists of three metallic nanoparticles, shaped as rectangular prisms, with two nanoparticles acting as parallel arms of a resonant circuit and the third bridging nanoparticle acting as an optical antenna providing an output signal. Polarized light excites localized surface plasmon resonances in the two arms of the circuit, which generate an optical signal dependent on the phase-sensitive excitations of surface plasmons in the antenna. The circuit is analyzed using a plasmonic coupling theory and numerical simulations. The analyses show that the plasmonic circuit is sensitive to phase shifts between the arms of the bridge and has the potential to detect the presence of single molecules.

Path planning using surface shape and ground properties

This paper presents a path planning technique for ground vehicles that accounts for the dynamics of the vehicle, the topography of the terrain and the wheel/ground interaction properties such as friction. The first two properties can be estimated using well known sensors and techniques, but the third is not often estimated even though it has a significant effect on the motion of a high-speed vehicle. We introduce a technique which allows the estimation of wheel slip from which frictional parameters can be inferred. We present simulation results which show the importance of modelling topography and ground properties and experimental results which show how ground properties can be estimated along a 350m outdoor traverse.

Technical note : a technique for measuring the surface area of articular cartilage in acetabular fractures

The aim of this study was to develop a reliable technique for measuring the area of a curved surface from an axial computed tomography (CT) scan and to apply this clinically in the measurement of articular cartilage surface area in acetabular fractures. The method used was a triangulation algorithm. In order to determine the accuracy of the technique, areas of hemispheres of known size were measured to give the percentage error in area measurement. Seven such hemispheres were machined into a Perspex block and their area measured geometrically, and also from CT scans by means of the triangulation algorithm. Scans of 1, 2 and 4 mm slice thickness and separation were used. The error varied with slice thickness and hemisphere diameter. It was shown that the 2 mm slice thickness provides the most accurate area measurement, while 1 mm cuts overestimate and 4 mm cuts underestimate the area. For a hemisphere diameter of 5 cm, which is of similar size to the acetabulum, the error was -11.2% for 4 mm cuts, +4.2% for 2 mm cuts and + 5.1% for 1 mm cuts. As expected, area measurement was more accurate for larger hemispheres. This method can be applied clinically to quantify acetabular fractures by measuring the percentage area of intact articular cartilage. In the case of both column fractures, the percentage area of secondary congruence can be determined. This technique of quantifying acetabular fractures has a potential clinical application as a prognostic factor and an indication for surgery in the long term.

Noninvasive in vivo assessment of soft contact lens type on tear film surface quality

To evaluate the effect of soft contact lens type on the in vivo tear film surface quality (TFSQ) on daily disposable lenses and to establish whether two recently developed techniques for noninvasive measurement of TFSQ can distinguish between different contact lens types.

Compaction control of topography and fault network structure along strike-slip faults in sedimentary basins

Strike-slip faults commonly display structurally complex areas of positive or negative topography. Understanding the development of such areas has important implications for earthquake studies and hydrocarbon exploration. Previous workers identified the key factors controlling the occurrence of both topographic modes and the related structural styles. Kinematic and stress boundary conditions are of first-order relevance. Surface mass transport and material properties affect fault network structure. Experiments demonstrate that dilatancy can generate positive topography even under simple-shear boundary conditions. Here, we use physical models with sand to show that the degree of compaction of the deformed rocks alone can determine the type of topography and related surface fault network structure in simple-shear settings. In our experiments, volume changes of ∼5% are sufficient to generate localized uplift or subsidence. We discuss scalability of model volume changes and fault network structure and show that our model fault zones satisfy geometrical similarity with natural flower structures. Our results imply that compaction may be an important factor in the development of topography and fault network structure along strike-slip faults in sedimentary basins.

A catchment modelling approach integrating surface and groundwater processes, land use and distribution of nutrients : Elimbah Creek, southeast Queensland

As the world’s population is growing, so is the demand for agricultural products. However, natural nitrogen (N) fixation and phosphorus (P) availability cannot sustain the rising agricultural production, thus, the application of N and P fertilisers as additional nutrient sources is common. It is those anthropogenic activities that can contribute high amounts of organic and inorganic nutrients to both surface and groundwaters resulting in degradation of water quality and a possible reduction of aquatic life. In addition, runoff and sewage from urban and residential areas can contain high amounts of inorganic and organic nutrients which may also affect water quality. For example, blooms of the cyanobacterium Lyngbya majuscula along the coastline of southeast Queensland are an indicator of at least short term decreases of water quality. Although Australian catchments, including those with intensive forms of land use, show in general a low export of nutrients compared to North American and European catchments, certain land use practices may still have a detrimental effect on the coastal environment. Numerous studies are reported on nutrient cycling and associated processes on a catchment scale in the Northern Hemisphere. Comparable studies in Australia, in particular in subtropical regions are, however, limited and there is a paucity in the data, in particular for inorganic and organic forms of nitrogen and phosphorus; these nutrients are important limiting factors in surface waters to promote algal blooms. Therefore, the monitoring of N and P and understanding the sources and pathways of these nutrients within a catchment is important in coastal zone management. Although Australia is the driest continent, in subtropical regions such as southeast Queensland, rainfall patterns have a significant effect on runoff and thus the nutrient cycle at a catchment scale. Increasingly, these rainfall patterns are becoming variable. The monitoring of these climatic conditions and the hydrological response of agricultural catchments is therefore also important to reduce the anthropogenic effects on surface and groundwater quality. This study consists of an integrated hydrological–hydrochemical approach that assesses N and P in an environment with multiple land uses. The main aim is to determine the nutrient cycle within a representative coastal catchment in southeast Queensland, the Elimbah Creek catchment. In particular, the investigation confirms the influence associated with forestry and agriculture on N and P forms, sources, distribution and fate in the surface and groundwaters of this subtropical setting. In addition, the study determines whether N and P are subject to transport into the adjacent estuary and thus into the marine environment; also considered is the effect of local topography, soils and geology on N and P sources and distribution. The thesis is structured on four components individually reported. The first paper determines the controls of catchment settings and processes on stream water, riverbank sediment, and shallow groundwater N and P concentrations, in particular during the extended dry conditions that were encountered during the study. Temporal and spatial factors such as seasonal changes, soil character, land use and catchment morphology are considered as well as their effect on controls over distributions of N and P in surface waters and associated groundwater. A total number of 30 surface and 13 shallow groundwater sampling sites were established throughout the catchment to represent dominant soil types and the land use upstream of each sampling location. Sampling comprises five rounds and was conducted over one year between October 2008 and November 2009. Surface water and groundwater samples were analysed for all major dissolved inorganic forms of N and for total N. Phosphorus was determined in the form of dissolved reactive P (predominantly orthophosphate) and total P. In addition, extracts of stream bank sediments and soil grab samples were analysed for these N and P species. Findings show that major storm events, in particular after long periods of drought conditions, are the driving force of N cycling. This is expressed by higher inorganic N concentrations in the agricultural subcatchment compared to the forested subcatchment. Nitrate N is the dominant inorganic form of N in both the surface and groundwaters and values are significantly higher in the groundwaters. Concentrations in the surface water range from 0.03 to 0.34 mg N L..1; organic N concentrations are considerably higher (average range: 0.33 to 0.85 mg N L..1), in particular in the forested subcatchment. Average NO3-N in the groundwater has a range of 0.39 to 2.08 mg N L..1, and organic N averages between 0.07 and 0.3 mg N L..1. The stream bank sediments are dominated by organic N (range: 0.53 to 0.65 mg N L..1), and the dominant inorganic form of N is NH4-N with values ranging between 0.38 and 0.41 mg N L..1. Topography and soils, however, were not to have a significant effect on N and P concentrations in waters. Detectable phosphorus in the surface and groundwaters of the catchment is limited to several locations typically in the proximity of areas with intensive animal use; in soil and sediments, P is negligible. In the second paper, the stable isotopes of N (14N/15N) and H2O (16O/18O and 2H/H) in surface and groundwaters are used to identify sources of dissolved inorganic and organic N in these waters, and to determine their pathways within the catchment; specific emphasis is placed on the relation of forestry and agriculture. Forestry is predominantly concentrated in the northern subcatchment (Beerburrum Creek) while agriculture is mainly found in the southern subcatchment (Six Mile Creek). Results show that agriculture (horticulture, crops, grazing) is the main source of inorganic N in the surface waters of the agricultural subcatchment, and their isotopic signature shows a close link to evaporation processes that may occur during water storage in farm dams that are used for irrigation. Groundwaters are subject to denitrification processes that may result in reduced dissolved inorganic N concentrations. Soil organic matter delivers most of the inorganic N to the surface water in the forested subcatchment. Here, precipitation and subsequently runoff is the main source of the surface waters. Groundwater in this area is affected by agricultural processes. The findings also show that the catchment can attenuate the effects of anthropogenic land use on surface water quality. Riparian strips of natural remnant vegetation, commonly 50 to 100 m in width, act as buffer zones along the drainage lines in the catchment and remove inorganic N from the soil water before it enters the creek. These riparian buffer zones are common in most agricultural catchments of southeast Queensland and are indicated to reduce the impact of agriculture on stream water quality and subsequently on the estuary and marine environments. This reduction is expressed by a significant decrease in DIN concentrations from 1.6 mg N L..1 to 0.09 mg N L..1, and a decrease in the �15N signatures from upstream surface water locations downstream to the outlet of the agricultural subcatchment. Further testing is, however, necessary to confirm these processes. Most importantly, the amount of N that is transported to the adjacent estuary is shown to be negligible. The third and fourth components of the thesis use a hydrological catchment model approach to determine the water balance of the Elimbah Creek catchment. The model is then used to simulate the effects of land use on the water balance and nutrient loads of the study area. The tool that is used is the internationally widely applied Soil and Water Assessment Tool (SWAT). Knowledge about the water cycle of a catchment is imperative in nutrient studies as processes such as rainfall, surface runoff, soil infiltration and routing of water through the drainage system are the driving forces of the catchment nutrient cycle. Long-term information about discharge volumes of the creeks and rivers do, however, not exist for a number of agricultural catchments in southeast Queensland, and such information is necessary to calibrate and validate numerical models. Therefore, a two-step modelling approach was used to calibrate and validate parameters values from a near-by gauged reference catchment as starting values for the ungauged Elimbah Creek catchment. Transposing monthly calibrated and validated parameter values from the reference catchment to the ungauged catchment significantly improved model performance showing that the hydrological model of the catchment of interest is a strong predictor of the water water balance. The model efficiency coefficient EF shows that 94% of the simulated discharge matches the observed flow whereas only 54% of the observed streamflow was simulated by the SWAT model prior to using the validated values from the reference catchment. In addition, the hydrological model confirmed that total surface runoff contributes the majority of flow to the surface water in the catchment (65%). Only a small proportion of the water in the creek is contributed by total base-flow (35%). This finding supports the results of the stable isotopes 16O/18O and 2H/H, which show the main source of water in the creeks is either from local precipitation or irrigation waters delivered by surface runoff; a contribution from the groundwater (baseflow) to the creeks could not be identified using 16O/18O and 2H/H. In addition, the SWAT model calculated that around 68% of the rainfall occurring in the catchment is lost through evapotranspiration reflecting the prevailing long-term drought conditions that were observed prior and during the study. Stream discharge from the forested subcatchment was an order of magnitude lower than discharge from the agricultural Six Mile Creek subcatchment. A change in land use from forestry to agriculture did not significantly change the catchment water balance, however, nutrient loads increased considerably. Conversely, a simulated change from agriculture to forestry resulted in a significant decrease of nitrogen loads. The findings of the thesis and the approach used are shown to be of value to catchment water quality monitoring on a wider scale, in particular the implications of mixed land use on nutrient forms, distributions and concentrations. The study confirms that in the tropics and subtropics the water balance is affected by extended dry periods and seasonal rainfall with intensive storm events. In particular, the comprehensive data set of inorganic and organic N and P forms in the surface and groundwaters of this subtropical setting acquired during the one year sampling program may be used in similar catchment hydrological studies where these detailed information is missing. Also, the study concludes that riparian buffer zones along the catchment drainage system attenuate the transport of nitrogen from agricultural sources in the surface water. Concentrations of N decreased from upstream to downstream locations and were negligible at the outlet of the catchment.

Introducing standardized protocols for anthropological measurement of virtual subadult crania using computed tomography

Objectives This study introduces and assesses the precision of a standardized protocol for anthropometric measurement of the juvenile cranium using three-dimensional surface rendered models, for implementation in forensic investigation or paleodemographic research. Materials and methods A subset of multi-slice computed tomography (MSCT) DICOM datasets (n=10) of modern Australian subadults (birth—10 years) was accessed from the “Skeletal Biology and Forensic Anthropology Virtual Osteological Database” (n>1200), obtained from retrospective clinical scans taken at Brisbane children hospitals (2009–2013). The capabilities of Geomagic Design X™ form the basis of this study; introducing standardized protocols using triangle surface mesh models to (i) ascertain linear dimensions using reference plane networks and (ii) calculate the area of complex regions of interest on the cranium. Results The protocols described in this paper demonstrate high levels of repeatability between five observers of varying anatomical expertise and software experience. Intra- and inter-observer error was indiscernible with total technical error of measurement (TEM) values ≤0.56 mm, constituting <0.33% relative error (rTEM) for linear measurements; and a TEM value of ≤12.89 mm2, equating to <1.18% (rTEM) of the total area of the anterior fontanelle and contiguous sutures. Conclusions Exploiting the advances of MSCT in routine clinical assessment, this paper assesses the application of this virtual approach to acquire highly reproducible morphometric data in a non-invasive manner for human identification and population studies in growth and development. The protocols and precision testing presented are imperative for the advancement of “virtual anthropology” into routine Australian medico-legal death investigation.

In vitro assessment of surface congruency and integration of chondrocytes at adjacent edges of micro-fabricated clefts on cartilage

Osteochondral grafts are common treatment options for joint focal defects due to their excellent functionality. However, the difficulty is matching the topography of host and graft(s) surfaces flush to one another. Incongruence could lead to disintegration particularly when the gap reaches subchondoral region. The aim of this study is therefore to investigate cell response to gap geometry when forming cartilage-cartilage bridge at the interface. The question is what would be the characteristics of such a gap if the cells could bridge across to fuse the edges? To answer this, osteochondral plugs devoid of host cells were prepared through enzymatic decellularization and artificial clefts of different sizes were created on the cartilage surface using laser ablation. High density pellets of heterologous chondrocytes were seeded on the defects and cultured with chondrogenic differentiation media for 35 days. The results showed that the behavior of chondrocytes was a function of gap topography. Depending on the distance of the edges two types of responses were generated. Resident cells surrounding distant edges demonstrated superficial attachment to one side whereas clefts of 150 to 250 µm width experienced cell migration and anchorage across the interface. The infiltration of chondrocytes into the gaps provided extra space for their proliferation and laying matrix; as the result faster filling of the initial void space was observed. On the other hand, distant and fit edges created an incomplete healing response due to the limited ability of differentiated chondrocytes to migrate and incorporate within the interface. It seems that the initial condition of the defects and the curvature profile of the adjacent edges were the prime determinants of the quality of repair; however, further studies to reveal the underlying mechanisms of cells adapting to and modifying the new environment would be of particular interest.

Nanosphere monolayer-templated, ion-assisted nanofeature etching in dielectric materials : a numerical simulation of nanoscale ion flux topography

The results of numerical simulations of nanometer precision distributions of microscopic ion fluxes in ion-assisted etching of nanoscale features on the surfaces of dielectric materials using a self-assembled monolayer of spherical nanoparticles as a mask are presented. It is shown that the ion fluxes to the substrate and nanosphere surfaces can be effectively controlled by the plasma parameters and the external bias applied to the substrate. By proper adjustment of these parameters, the ion flux can be focused onto the areas uncovered by the nanospheres. Under certain conditions, the ion flux distributions feature sophisticated hexagonal patterns, which may lead to very different nanofeature etching profiles. The results presented are generic and suggest viable ways to overcome some of the limitations of the existing plasma-assisted nanolithography.

Azimuthal surface waves in a coaxial semiconductor structure with metal walls

The dispersion properties and topography of the fields of azimuthal surface wave (ASW) in a coaxial semiconductor structure with metal walls, placed in an external magnetic field, are investigated analytically and numerically. It is shown that an ASW phase-shifting device can be realized in the proposed structure. The conditions are indicated for which wave perturbations exist having frequencies that depend on the direction of phase change.

Surface magnetoplasma waves at the interface between a plasma-like medium and a metal in the Voigt geometry

Theoretical and experimental results associated with the studies of different properties of surface-type waves (SW) in plasma-like medium-metal structures are reviewed. The propagation of surface waves in the Voigt geometry (the SW propagate across the external magnetic field, which is parallel to the interface) is considered. Various problems dealing with the linear properties of the SW (dispersion characteristics, electromagnetic fields topography, influence of the inhomogeneity of the medium, etc.); excitation mechanisms of the plasma-metal waveguide structures (parametric, drift, diffraction, etc. mechanisms); nonlinear effects associated with SW propagation (higher harmonics generation, self-interaction, nonlinear damping, nonlinear interactions, etc.) are presented. In many cases the results are valid for both gaseous and solid-state plasmas. © 1999 Elsevier Science B.V. All rights reserved.

Firm-customer mobile digital connectedness : conceptualization, measurement and implications

Firm-customer digital connectedness for effective sensing and responding is a strategic imperative for contemporary competitive firms. This research-in-progress paper conceptualizes and operationalizes the firm-customer mobile digital connectedness of a smart-mobile customer. The empirical investigation focuses on mobile app users and the impact of mobile apps on customer expectations. Based on pilot data collected from 127 customers, we tested hypotheses pertaining to firm-customer mobile digital connectedness and customer expectations. Our test analysis using linear and non-linear postulations reveals those customers raise their expectations as they increase their digital interactions with a firm.