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Aubrecht, Donald Michael

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Aubrecht

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Donald Michael

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Aubrecht, Donald Michael
Author's Publications: search.filters.isAuthorOfPublication.31bf5883-bd5c-49fa-adea-dadb46a9975a

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    Tracking vegetation phenology across diverse North American biomes using PhenoCam imagery
    (Nature Publishing Group, 2018) Richardson, Andrew; Hufkens, Koen; Milliman, Tom; Aubrecht, Donald Michael; Chen, Min; Gray, Josh M.; Johnston, Miriam; Keenan, Trevor F.; Klosterman, Stephen T.; Kosmala, Margaret; Melaas, Eli K.; Friedl, Mark A.; Frolking, Steve
    Vegetation phenology controls the seasonality of many ecosystem processes, as well as numerous biosphere-atmosphere feedbacks. Phenology is also highly sensitive to climate change and variability. Here we present a series of datasets, together consisting of almost 750 years of observations, characterizing vegetation phenology in diverse ecosystems across North America. Our data are derived from conventional, visible-wavelength, automated digital camera imagery collected through the PhenoCam network. For each archived image, we extracted RGB (red, green, blue) colour channel information, with means and other statistics calculated across a region-of-interest (ROI) delineating a specific vegetation type. From the high-frequency (typically, 30 min) imagery, we derived time series characterizing vegetation colour, including “canopy greenness”, processed to 1- and 3-day intervals. For ecosystems with one or more annual cycles of vegetation activity, we provide estimates, with uncertainties, for the start of the “greenness rising” and end of the “greenness falling” stages. The database can be used for phenological model validation and development, evaluation of satellite remote sensing data products, benchmarking earth system models, and studies of climate change impacts on terrestrial ecosystems.
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    Droplet Microfluidics: Tools for Screening and Sorting Applications
    (2013-10-15) Aubrecht, Donald Michael; Weitz, David A.; Brenner, Michael; Manoharan, Vinothan
    Microfluidic droplets are a powerful tool for screening large populations of cells, molecules, and biochemical reactions. Droplet systems are able to encapsulate, incubate, screen, and sort millions of samples, providing access to large number statistics that make searching for rare events feasible. Initial development of the microfluidic devices and methods has attracted applications in biology, biochemistry, and material science, but the set of tools remains incomplete. Efforts are required to develop micro-scale droplet analogs for all bulk-scale bench top procedures and instruments. The droplet analogs must be versatile, robust, and process samples rapidly.
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    Monitoring vegetation phenology using an infrared-enabled security camera
    (Elsevier BV, 2014) Petach, Anika; Toomey, Michael; Aubrecht, Donald Michael; Richardson, Andrew
    Sensor-based monitoring of vegetation phenology is being widely used to quantify phenological responses to climate variability and change. Digital repeat photography, in particular, can characterize the seasonality of canopy greenness. However, these data cannot be directly compared to satellite vegetation indices (e.g. NDVI, the normalized difference vegetation index) that require information about vegetation properties at near-infrared (NIR) wavelengths. Here, we develop a new method, using an inexpensive, NIR-enabled camera originally designed for security monitoring, to calculate a “camera NDVI” from sequential visible and visible + NIR photographs. We use a lab experiment for proof-of-concept, and then test the method using a year of data from an ongoing field campaign in a mixed temperate forest. Our analysis shows that the seasonal cycle of camera NDVI is almost identical to that of NDVI measured using narrow-band radiometric instruments, or as observed from space by the MODIS platform. This camera NDVI thus provides different information about the state of the canopy than can be obtained using only visible-wavelength imagery. In addition to phenological monitoring, our method should be useful for a variety of applications, including continuous monitoring of plant stress and quantifying vegetation responses to manipulative treatments in large field experiments.
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    Synchronized reinjection and coalescence of droplets in microfluidics
    (Royal Society of Chemistry (RSC), 2014) Lee, Manhee; Collins, Jesse Kenas; Aubrecht, Donald Michael; Sperling, Ralph A.; Solomon, Laura; Ha, Jong-Wook; Yi, Gi-Ra; Weitz, David; Manoharan, Vinothan
    Coalescence of two kinds of pre-processed droplets is necessary to perform chemical and biological assays in droplet-based microfluidics. However, a robust technique to accomplish this does not exist. Here we present a microfluidic device to synchronize the reinjection of two different kinds of droplets and coalesce them, using hydrostatic pressure in conjunction with a conventional syringe pump. We use a device consisting of two opposing T-junctions for reinjecting two kinds of droplets and control the flows of the droplets by applying gravity-driven hydrostatic pressure. The hydrostatic-pressure operation facilitates balancing the droplet reinjection rates and allows us to synchronize the reinjection. Furthermore, we present a simple but robust module to coalesce two droplets that sequentially come into the module, regardless of their arrival times. These re-injection and coalescence techniques might be used in lab-on-chip applications requiring droplets with controlled numbers of solid materials, which can be made by coalescing two pre-processed droplets that are formed and sorted in devices.