Performance of the Bowen ratio systems on a 22 deg slope

The Bowen ratio energy balance technique was used to assess the energy fluxes on inclined surfaces during the First ISLSCP Field Experiment (FIFE). Since air flow over sloping surface may differ from that over flat terrain, it is important to examine whether Bowen ratio measurements taken on sloping surfaces are valid. In this study, the suitability of using the Bowen ratio technique on sloping surfaces was tested by examining the assumptions that the technique requires for valid measurements. This was accomplished by studying the variation of Bowen ratio measurements along a selected slope at the FIFE site. In September 1988, four Bowen ratio systems were set up in a line along the 22 degree north-facing slope with northerly air flow (wind went up the slope). In July of 1989, six Bowen ratio systems were similarly installed with southerly air flow (the wind went down slope). Results indicated that, at distances between 10 to 40 meters from the top of the slope, no temperature or vapor pressure gradient parallel to the slope was detected. Uniform Bowen ratio values were obtained on the slope, and thus the sensible or latent heat flux should be similar along the slope. This indicates that the assumptions for valid flux measurements are reasonably met at the slope. The Bowen ratio technique should give the best estimates of the energy fluxes on slopes similar to that in this study

High-fidelity simulation of an ultrasonic standing-wave thermoacoustic engine with bulk viscosity effects

We have carried out boundary-layer-resolved, unstructured fully-compressible Navier--Stokes simulations of an ultrasonic standing-wave thermoacoustic engine (TAE) model. The model is constructed as a quarter-wavelength engine, approximately 4 mm by 4 mm in size and operating at 25 kHz, and comprises a thermoacoustic stack and a coin-shaped cavity, a design inspired by Flitcroft and Symko (2013). Thermal and viscous boundary layers (order of 10 $\mathrm{\mu}$m) are resolved. Vibrational and rotational molecular relaxation are modeled with an effective bulk viscosity coefficient modifying the viscous stress tensor. The effective bulk viscosity coefficient is estimated from the difference between theoretical and semi-empirical attenuation curves. Contributions to the effective bulk viscosity coefficient can be identified as from vibrational and rotational molecular relaxation. The inclusion of the coefficient captures acoustic absorption from infrasonic ($\sim$10 Hz) to ultrasonic ($\sim$100 kHz) frequencies. The value of bulk viscosity depends on pressure, temperature, and frequency, as well as the relative humidity of the working fluid. Simulations of the TAE are carried out to the limit cycle, with growth rates and limit-cycle amplitudes varying non-monotonically with the magnitude of bulk viscosity, reaching a maximum for a relative humidity level of 5%. A corresponding linear model with minor losses was developed; the linear model overpredicts transient growth rate but gives an accurate estimate of limit cycle behavior. An improved understanding of thermoacoustic energy conversion in the ultrasonic regime based on a high-fidelity computational framework will help to further improve the power density advantages of small-scale thermoacoustic engines.Comment: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech, 201

The Acceptability and Visual Impact of 0.01% Atropine in a Caucasian Population

Myopia is a condition of enormous public health concern, affecting up to 2.5 billion people worldwide. The most effective treatment to prevent myopia progression is atropine but at the cost of accommodative paresis and mydriasis, necessitating the use of bifocal glasses. Low-dose atropine (0.01%) has been found to be almost as effective with significantly reduced side effects. Since there are well-recognised differences in the effect of atropine between heavily pigmented Asian eyes and Caucasian eyes, this study aimed to determine the acceptability and tolerability of 0.01% atropine (by measuring visual performance and quality of life) as a treatment for myopia control in a Caucasian population exhibiting light irides. Methods 14 university students aged 18–27 were recruited to the study. Participants received one drop of 0.01% atropine daily into each eye over 5 days. A range of physiological, functional and quality of life measures were assessed at baseline, day 3 and day 5. Results The effect of atropine was statistically significant for pupil size (p=0.04) and responsiveness (p\u3c0.01). While amplitude of accommodation reduced, the change was not statistically significant. Visual acuity (distance and near) and reading speed were not adversely affected. While there was a slight increase in symptoms such as glare, overall there was no quality of life impact associated with the use of low-dose atropine

Comparison of ground and satellite based measurements of the fraction of photosynthetically active radiation intercepted by tall-grass prairie

The fraction, of photosynthetically active radiation absorbed by vegetation, F sub ipar, is an important requirement for estimating vegetation biomass productivity and related quantities. This was an integral part of a large international effort; the First ISLSCP Field Experiment (FIFE). The main objective of FIFE was to study the effects of vegetation on the land atmosphere interactions and to determine if these interactions can be assessed from satellite spectral measurements. The specific purpose of this experiment was to find out how well measurements of F sub ipar relate to ground, helicopter, and satellite based spectral reflectance measurements. Concurrent measurements of F sub ipar and ground, helicopter, and satellite based measurements were taken at 13 tall grass prairie sites in Kansas. The sites were subjected to various combinations of burning and grazing managements

Ultrasonic thermoacoustic energy converter

pre-printThermoacoustic prime movers have been developed for operation in the low ultrasonic frequency range by scaling down the device size. The developed engines operate at frequencies up to 23 kHz. They are self-sustained oscillators whose dimensions scale inversely with operating frequency. The smallest one being 3.4mm long with a 1mm diameter bore, i.e. the engine inner volume of 2.67 mm3 . The generated sound levels reached intensities in the range of 143 dB - 150 dB in the low ultrasonic range. The miniaturization of thermoacoustic engines will lead to the development of device arrays

COREQ checklist: Is Optometry Ready for Myopia Control? Education and other Barriers to the Treatment of Myopia.

Background With the increasing prevalence of myopia there is growing interest in active myopia control. However, the majority of progressive myopes are still prescribed single vision spectacles. This prospective study aims to elucidate the knowledge and attitudes of optometrists toward myopia control, and thereby identify perceived barriers to the implementation of a risk focused model of myopia management

Is Optometry Ready for Myopia Control? Education and other Barriers to the Treatment of Myopia

Background With the increasing prevalence of myopia there is growing interest in active myopia control. However, the majority of progressive myopes are still prescribed single vision spectacles. This prospective study aims to elucidate the knowledge and attitudes of optometrists toward myopia control, and thereby identify perceived barriers to the implementation of a risk focussed model of myopia management. Methods A series of four focus group discussions were conducted involving optometrists in different settings and career stages. Results The key finding to emerge is a clear disconnect between academic optometrists, optometry students and clinicians in practice. Academic faculty considered themselves competent in managing progressive myopia and believed the optometry curriculum provides undergraduates with sufficient clinical skills and knowledge to practise myopia control. Final-year optometry students regarded themselves as knowledgeable about myopia control but lack confidence in their ability to practise myopia control, with only one student indicating they would initiate myopia control therapy. The majority of clinicians do not offer myopia control treatments, other than to communicate lifestyle advice to modify risk of myopia progression. Clinicians alluded to a lack of availability of myopia control interventions and identified a range of barriers relating to their training, clinical practice and public health challenges, financial, technological and other constraints that affect the implementation of such interventions. Conclusion It appears optometrists have to yet embrace myopia control as a core element of the clinical eye care service they provide. Education, training, finance, and time restrictions, as well as limited availability of myopia control therapies were among the main perceived barriers to myopia control. This study revealed a distinct need for alignment between optometric training and the public health need for effective myopia control

Is optometry ready for myopia control? Education and other barriers to the treatment of myopia

Background: With the increasing prevalence of myopia there is growing interest in active myopia control. However, the majority of progressive myopes are still prescribed single vision spectacles. This prospective study aims to elucidate the knowledge and attitudes of optometrists toward myopia control, and thereby identify perceived barriers to the implementation of a risk focussed model of myopia management

The Spatial Frequency Content of Urban and Indoor Environments as a Potential Risk Factor for Myopia Development

To examine the hypothesis that the spatial frequency spectra of urban and indoor environments differ from the natural environment in ways that may promote the development of myopia. Methods: A total of 814 images were analyzed from three datasets; University of California Berkeley (UCB), University of Texas (UT), and Botswana (UPenn). Images were processed in Matlab (Mathworks Inc) to map the camera color characteristics to human cone sensitivities. From the photopic luminance images generated, two-dimensional spatial frequency (SF) spectra were calculated and converted to one-dimensional spectra by rotational averaging. The spatial filtering profile of a 0.4 Bangerter foil, which has been shown to induce myopia experimentally, was also determined. Results: The SF slope for natural scenes followed the recognized 1/fα relationship with mean slopes of -1.08, -0.90, and -1.04 for the UCB, UT and UPenn image sets, respectively. Indoor scenes had a significantly steeper slope (-1.48, UCB; -1.52, UT; P \u3c 0.0001). Urban environments showed an intermediate slope (-1.29, UCB; -1.22, UT) that was significantly different from the slopes derived from the natural scenes (P \u3c 0.0001). The change in SF content between natural outdoor scenes and indoors was comparable to that induced by a 0.4 Bangerter foil, which reduced the SF slope of a natural scene from -0.88 to -1.47. Conclusions: Compared to natural outdoor images, man-made outdoor and indoor environments have spatial frequency characteristics similar to those known to induce form-deprivation myopia in animal models. The spatial properties of the man-made environment may be one of the missing drivers of the human myopia epidemic