Characterization of Pressure-Driven and Electro-Kinetically Driven Flow in a Micro-Fluidic Chip Using Particle Imaging Velocimetry

The flow profiles of pressure-driven and electro-kinetic driven flows were compared for a microfluidic chip. It was found that the pressure-driven flow had a parabolic profile while the electro-kinetic flow had a plug shaped flow profile. The measured velocities were similar to those determined by the Poiseuille flow model and the Helmholtz-Smoltchowski equation. Flow uniformity is very important for control in microfluidic mixers. Parabolic flow profiles lead to inconsistent reactions while the more uniform plug shape flow allow for a more steady reaction across the channel. Previous work had been performed to measure the flow of a solution of fluorescent polystyrene beads in PDMS channels using a laser confocal microscope. This showed that particles easily stuck to the channel making it difficult to measure over time. In addition, bubble formation in the channel made measuring velocities difficult. Current work used a LabSmith Video Synchronized microscope with software to measure the flow rates at different areas of the channel. Solutions of fluorescent polystyrene beads were used to visually observe the flow within a channel under a microscope. Four different channels were used for the pressure-driven flows of varying dimensions and materials. The channel with the best measured profile was also measured under electro-kinetic flow. A LabSmith High Voltage Sequencer was used to apply a voltage across the channel for electro-kinetic measurements. This research confirmed the different flow profiles under pressure-driven and electro-kinetic driven flow. Future work can be done to determine how this effects mixing in the channels

Characterization of Pressure Driven and Electro-Kinetically Driven Flow in a Micro-Fluidic Chip Using Particle Imaging Velocimetry

The goal of this research is to compare electro-kinetic and pressure driven flow rates and velocity profiles (near wall vs. middle) in a microfluidic chip made of PDMS using particle imaging velocimetry (PIV) of an aqueous solution of fluorescent polystyrene (PS) particles using a laser confocal microscope (LCM). Microfluidic channels were fabricated out of PDMS using a SU-8 mold to be 25mm long and 180um by 1000um. Pressure-driven data did not show the expected parabolic profile because of the large width to depth ratio. In addition, data showed a calculated average significantly higher than the projected particle velocity through the channel. Unexpected results were hypothesized to be caused by inaccuracies with the syringe pump or interactions with the tubing. The accuracy of the syringe pump was tested and found to be 20% lower for 0.5uL of flow and 4% lower for 0.75uL of flow, making the data even stranger. However, at the low pump rates the syringe pump was pulsing instead of having a consistent flow. This could have led to the inconsistencies seen. Other issues occurred when measuring electro-kinetic flow. Often flow would switch directions at random intervals, possibly due to some kind of charge build up. In addition, bubbles, possibly introduced into the system when connecting tubing or when moving the channel, were very problematic. Changes in temperature, pressure, surface properties of the channel, and properties of the fluid within the channel can cause bubbles to grow. Research suggested a bubble trapping method for temporary relief of keeping bubbles out of the channel. This research will be continued as my master’s thesis next year

Proof of Jacobi identity in generalized quantum dynamics

We prove that the Jacobi identity for the generalized Poisson bracket is satisfied in the generalization of Heisenberg picture quantum mechanics recently proposed by one of us (SLA). The identity holds for any combination of fermionic and bosonic fields, and requires no assumptions about their mutual commutativity.Comment: 9 pages, plain tex file, IASSNS-HEP-93/4

On vulnerability and the ability to act in times of crisis. A plea for more time, more dialogue, more cooperation

Die Verknappung von Zeit und Raum ist ein zentrales kapitalistisches Prinzip, denn nur knappe Güter sind marktfähig. Dies zeigte sich besonders in der Corona-Pandemie, analysiert der Autor in seinem Essay: Es schien, als gäbe es keine Zeit (mehr). Maßnahmen mussten raschest umgesetzt werden. Doch durch schnelles Handeln entstehen zumeist oft nur neue Probleme, die bei ruhigem Nachdenken eventuell hätten verhindert werden können. In der politischen Bildung kann all das reflektiert und Raum geschaffen werden. Es gilt, Eingrenzungen und Beschränkungen der Denkräume zu überwinden, zu erweitern und neue Lösungen zu finden. Didaktische Anknüpfungspunkte bestehen in zweierlei Hinsicht: Technologische Kompetenz im Sinne der Entwicklung von Unterscheidungsmöglichkeiten, wie sie Oskar Negt versteht, kann in der politischen Bildung ebenso gefördert werden, wie Dialog und Kooperation, die es braucht, um im Sinne Klaus Holzkamps zu Handlungsfähigkeit zu gelangen und die individuellen und gesellschaftlichen Handlungsmöglichkeiten zu erweitern. (DIPF/Orig.)Scarcity of time and space is a key capitalist principle, for only scarce goods are marketable. According to the author\u27s analysis in his essay, this was especially apparent during the coronavirus pandemic: It seemed as if there was no time (anymore). Measures had to be implemented as quickly as possible. Yet most of the time, new problems arise from quick action, ones that calm reflection might have been able to prevent. Political education creates a space for reflection on all this. It is necessary to overcome limitations and restrictions of mental space, expand them and find new solutions. There are two angles didactics may take: Technological literacy in the sense of developing one\u27s capacity to differentiate as Oskar Negt understands it can be promoted in political education as can dialogue and cooperation, which are needed in order to acquire the ability to act and to enhance an individual\u27s ability to act in the sense of Klaus Holzkamp. (DIPF/Orig.

Session D, 2017 First Place: Under the Sphagnum: An Observational Analysis of the Relationship Between Distance and Ectomycorrhizal Morphotype Diversity in Larix laricina Within Wetland Ecosystems

Ectomycorrhizal fungi (EMF) form a mutualistic symbiosis with host plants by increasing plants’ uptake of nutrients and water. Many tree seedlings are dependent on EMF for successful establishment in nutrient poor areas, such as wetlands. It was hypothesized that EMF morphotype diversity should decrease as the larch saplings get closer to the center of the bog. Larix laricina was chosen as the EMF host of choice due to its abundance in wetlands around Cranberry Lake. Three sample sites were used and a total of nine trees were sampled from three transect lines at each site. The sites were Forsaith’s Bog, Lost Pond Bog, and an unnamed fen. The distances used consisted of trees from the upland-wetland boundary, trees from the wetland interior, and an intermediate zone. These sites were selected because they possessed abundant stands of Larix laricina and met the DBH requirement of our transects. Twenty root tips were taken from each host sapling. EMFs were classified based on morphological features. EMF diversity was calculated for each tree. A regression analysis on the relationship between distance and diversity of morphotypes showed no significant difference (p=0.051). ANOVA analysis revealed no significant difference between the three sites (p=0.060)

The marketing management concept

Call number: LD2668 .R4 1964 W38