Variable Temperature Thermochromic Switching Under Varying Illumination

Award for Runner-Up Poster Presentation . Abstract Minnesota is home to some of the greatest temperature ranges in the United States, with lows reaching below -40º Celsius and highs reaching nearly 40ºC. This results in higher than average spending on the heating and cooling of buildings. We have been investigating into responsive building materials to help address this. In particular, we have been studying a thermochromic paint that can capture solar energy and transfer it into the building as heat at low temperatures and reflect the energy at higher temperatures to keep the building cooler

A Fiber-Optic Sensor for Leak Detection in a Space Environment

A miniature fiber-optic, laser-based, interferometric leak detector is presented for application as a means to detect on-orbit gas leaks. The sensor employs a fiber-coupled modified Michelson interferometer to detect gas leaks by measuring an increase in gas density in the sensing region. Monitoring changes in the fringe pattern output by the interferometer allows for direct measurement of the gas density in the sensing region and, under the assumption of an equation of state, this can be used to obtain a pressure measurement. Measurements obtained over a pressure range from 20 mtorr to 760 torr using a prototypical interferometer on working gases of air, nitrogen, argon, and helium generally exhibit agreement with a theoretical prediction of the pressure increase required before an interference fringe completely moves over the detector. Additional measurements performed on various gases demonstrate the range of detectable species, measuring sub-torr pressure changes in the process. A high-fidelity measurement places the ultimate pressure resolution for this particular sensor configuration in the 10 mtorr range. Time-resolved data prove the capability of this sensor to detect fast gas flow phenomena associated with transients and pressure waves

Review on Japanese-German-U.S. Cooperation on Laser-Ablation Propulsion

We report on an international cooperation between Nagoya University (NU), Japan and DLR Stuttgart, Germany on scaling issues in laser ablative propulsion. Lessons learned from collaborative work in the laboratory will be summarized with respect to the comparability of experimental methods and corresponding standardization issues. With the background of previous experimental research at the University of Alabama in Huntsville (UAH), experimental work with CO2 lasers in a moderate (NU) and high (DLR) pulse energy range on laser ablation of POM is presented. Profilometry results of target surfaces are compared with fluence distributions from beam propagation modeling. Ablation from flat targets is reported with respect to energy and area scaling and compared with results from ablative propulsion employing parabolic nozzles

Microfluidic Generation of Droplets with a High Loading of Nanoparticles

Microfluidic approaches for controlled generation of colloidal clusters, for example, via encapsulation of colloidal particles in droplets, have been used for the synthesis of functional materials including drug delivery carriers. Most of the studies, however, use a low concentration of an original colloidal suspension (<10 wt %). Here we demonstrate microfluidic approaches for directly making droplets with moderate (10–25 wt %) and high (>60 wt %) particle concentrations. Three types of microfluidic devices, PDMS flow-focusing, PDMS T-junction, and microcapillary devices, are investigated for direct encapsulation of a high concentration of polystyrene (PS) nanoparticles in droplets. In particular, it is shown that PDMS devices fabricated by soft lithography can generate droplets from a 25 wt % PS suspension, whereas microcapillary devices made from glass capillary tubes are able to produce droplets from a 67 wt % PS nanoparticle suspension. When the PS concentration is between 0.6 and 25 wt %, the size of the droplets is found to change with the oil-to-water flow rate ratio and is independent of the concentration of particles in the initial suspensions. Drop sizes from ∼12 to 40 μm are made using flow rate ratios <i>Q</i>_oil/<i>Q</i>_water from 20 to 1, respectively, with either of the PDMS devices. However, clogging occurs in PDMS devices at high PS concentrations (>25 wt %) arising from interactions between the PS colloids and the surface of PDMS devices. Glass microcapillary devices, on the other hand, are resistant to clogging and can produce droplets continuously even when the concentration of PS nanoparticles reaches 67 wt %. We believe that our findings indicate useful approaches and guidelines for the controlled generation of emulsions filled with a high loading of nanoparticles, which are useful for drug delivery applications