Browsing by Author "Thompson, J. E. (TTU)"
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Item Additive manufacturing (3D printing) for analytical chemistry(2021) Agrawaal, Harsshit (TTU); Thompson, J. E. (TTU)In recent years, 3D printing, also known as additive manufacturing, has received unprecedented level of interest and attention in the field of analytical chemistry due to its capability for rapid prototyping, decreased fabrication time, one-step fabrication, and ever increasing palette of functional print materials. The process of 3D printing works by depositing or polymerizing thin layers of material layer-by-layer in order to fabricate the desired object. Although all the 3D printers are designed to fulfil the same task, their size, resolution, compatible material, need for post-print processing of the object, and cost can vary significantly. This review presents a brief discussion on working principles and presents comparisons between stereolithography, digital light processing, two-photon polymerization, material jetting, fused deposition modeling, laminated object manufacturing, selective laser sintering, continuous interface liquid printing, aerosol jet printing, and bio-printing. The review also presents select applications in the field of analytical chemistry in which 3D printing was used to advance science. Applications considered advance chromatography, extraction and preconcentration, electrochemical applications, microfluidic devices, and spectroscopy. Although, 3D printing has much to offer analytical chemistry, the cost, need for post processing of devices, limited print materials, and need for higher resolution still limits broader application of the technology. We conclude further advances in printer performance and increasingly functional materials are required to achieve the full potential of additive manufacturing in the future.Item Effect of particle mixing morphology on aerosol scattering and absorption: A discrete dipole modeling study(2014) Zhang, Qing (TTU); Thompson, J. E. (TTU)Atmospheric aerosol particles may undergo phase separation due to differences in miscibility. This alters the morphology of particles such that they are no longer well-mixed, simple spheres. As a result, scattering and absorption of sunlight in Earth's atmosphere could be affected. In turn, this may alter direct climate forcing by aerosols. In this work we examine the impact of phase separation on aerosol optics for the bi-sphere, core-shell, and engulfed morphologies. We find bi-spherical particles often exhibit very different scattering and absorption cross-sections for a mid-visible wavelength (0.53 lm) relative to an equivalent, volume-weighted spherical case. Optical differences are largely driven by the particle shape, rather than differences in refractive index between phases. However, when averaged across a typical urban particle size distribution, the differences in light scattering largely vanish and bi-sphere and volume equivalent models generally agreed to within 10% for dielectric particles. For particles that are light absorbing, the bi-sphere and volume averaged cases often yielded dissimilar results with the volume- averaged case reflecting absorption >10% more than the phase separated particles. This was particularly true for bi-spheres in which one component particle is strongly light absorbing. Core-shell and engulfed morphologies yield volume scattering efficiencies within a few percent of volume-weighted spheres. However, modeled light absorption between the phase separated and volume averaged models frequently differ by >20% when inclusions absorb light strongly. Therefore, modeling light absorption of mixed-phase particles through the volume-mixing rule cannot be recommended.Item Personal exposure estimates via portable and wireless sensing and reporting of particulate pollution(2020) Agrawaal, Harsshit (TTU); Jones, Courtney (TTU); Thompson, J. E. (TTU)Low-cost, portable particle sensors (n = 3) were designed, constructed, and used to monitor human exposure to particle pollution at various locations and times in Lubbock, TX. The air sensors consisted of a Sharp GP2Y1010AU0F dust sensor interfaced to an Arduino Uno R3, and a FONA808 3G communications module. The Arduino Uno was used to receive the signal from calibrated dust sensors to provide a concentration (µg/m3) of suspended particulate matter and coordinate wireless transmission of data via the 3G cellular network. Prior to use for monitoring, dust sensors were calibrated against a reference aerosol monitor (RAM-1) operating independently. Sodium chloride particles were generated inside of a 3.6 m3 mixing chamber while the RAM-1 and each dust sensor recorded signals and calibration was achieved for each dust sensor independently of others by direct comparison with the RAM-1 reading. In an effort to improve the quality of the data stream, the effect of averaging replicate individual pulses of the Sharp sensor when analyzing zero air has been studied. Averaging data points exponentially reduces standard deviation for all sensors with n < 2000 averages but averaging produced diminishing returns after approx. 2000 averages. The sensors exhibited standard deviations for replicate measurements of 3–6 µg/m3 and corresponding 3σ detection limits of 9–18 µg/m3 when 2000 pulses of the dust sensor LED were averaged over an approx. 2 minute data collection/transmission cycle. To demonstrate portable monitoring, concentration values from the dust sensors were sent wirelessly in real time to a ThingSpeak channel, while tracking the sensor’s latitude and longitude using an on-board Global Positioning System (GPS) sensor. Outdoor and indoor air quality measurements were made at different places and times while human volunteers carried sensors. The measurements indicated walking by restaurants and cooking at home increased the exposure to particulate matter. The construction of the dust sensors and data collected from this research enhance the current research by describing an open-source concept and providing initial measurements. In principle, sensors can be massively multiplexed and used to generate real-time maps of particulate matter around a given location.