Senior Recital: Rachel Fuerstman, mezzo-soprano

https://digitalwindow.vassar.edu/musi_senior/1028/thumbnail.jp

Maze solvers demystified and some other thoughts

There is a growing interest towards implementation of maze solving in spatially-extended physical, chemical and living systems. Several reports of prototypes attracted great publicity, e.g. maze solving with slime mould and epithelial cells, maze navigating droplets. We show that most prototypes utilise one of two phenomena: a shortest path in a maze is a path of the least resistance for fluid and current flow, and a shortest path is a path of the steepest gradient of chemoattractants. We discuss that substrates with so-called maze-solving capabilities simply trace flow currents or chemical diffusion gradients. We illustrate our thoughts with a model of flow and experiments with slime mould. The chapter ends with a discussion of experiments on maze solving with plant roots and leeches which show limitations of the chemical diffusion maze-solving approach.Comment: This is a preliminary version of the chapter to be published in Adamatzky A. (Ed.) Shortest path solvers. From software to wetware. Springer, 201

Drop Traffic in Microfluidic Ladder Networks with Fore-Aft Structural Asymmetry

We investigate the dynamics of pairs of drops in microfluidic ladder networks with slanted bypasses, which break the fore-aft structural symmetry. Our analytical results indicate that unlike symmetric ladder networks, structural asymmetry introduced by a single slanted bypass can be used to modulate the relative drop spacing, enabling them to contract, synchronize, expand, or even flip at the ladder exit. Our experiments confirm all these behaviors predicted by theory. Numerical analysis further shows that while ladder networks containing several identical bypasses are limited to nearly linear transformation of input delay between drops, mixed combination of bypasses can cause significant non-linear transformation enabling coding and decoding of input delays.Comment: 4 pages, 5 figure

Emergent behavior in particle-laden microfluidic systems informs strategies for improving cell and particle separations

Colloidal particles placed in an energy landscape interact with each other, giving rise to complex dynamic behavior that affects the ability to process and manipulate suspensions of these particles. Propagating across scales ranging from the local behavior of 10's of particles to non-local behavior encompassing >10[superscript 6] particles, these particle interactions are pervasive and challenging to describe quantitatively, especially in the confined environments typical of microfluidic devices. To better understand the effects of particle interactions in this context, we have performed experiments and simulations involving a simple microfluidic device in which hydrodynamic and electrostatic forces are leveraged to concentrate and separate particle mixtures. These investigations reveal the mechanisms underlying the dynamic patterns formed by micron-scale particles as they impinge on a dielectrophoretic force barrier: their tendency to aggregate and recirculate under constant operating conditions, and to reorganize when the operating conditions are changed. The emergent behaviors of these ensembles of interacting particles exhibit features of dynamical frustration and cooperativity that suggest non-intuitive strategies for concentrating and sorting suspensions. Finally, we present a simple analytic model based on hydrodynamic coupling that captures important features of strongly interacting particle suspensions.National Institutes of Health (U.S.) (Grant EB005753)National Science Foundation (U.S.). Instrument Development for Biological Research (Grant DBI-0852654)Singapore-MIT Allianc

Teacher training for political science PhD students in Europe: determinants of a tool for enhanced teaching in higher education

In this paper we examine the state of teacher training for political science PhD candidates in the European Union and make a comparison with the situation in the United States. We investigate the determinants of supply and demand of teacher training. On the supply side, we suggest that research orientation and quality assurance are factors that might enhance institutional willingness to provide training. On the demand side, we examine the influence of gender, career plans, year of study, and career status on student motivation to undergo teacher training. We find that about half of EU institutions offering PhD programs also provide some form of teacher training; this closely follows American trends. We also uncover that while research orientation has a significant positive effect on the willingness of universities to provide training in pedagogy, quality assurance does not. Of the four factors we put forward as potential influences on student demand for teacher training, only future plans have a significant effect. We argue that similarities in the situation of teacher training in the United States and the European Union make transatlantic dialogue in graduate education worthwhile. Moreover, the positive impact of teacher training on the quality of teaching and learning as well as the positive valuation of training by more than two-thirds of PhD students in our sample makes us conclude that teacher training should be more widely available

On-chip pressure measurements and channel deformation after oil absorption

Microfluidic channels moulded from the soft polymer poly(dimethylsiloxane) (PDMS) are widely used as a platform for mimicking biological environments, and can be used for the simulation of fluid filled structures such as blood and lung vessels. The control of pressure and flow rate within these structures is vital to mimic physiological conditions. The flexibility of PDMS leads to pressure-induced deformation under flow, leading to variable flow profiles along a device. Here, we investigate the change in Young’s modulus of microfluidic channels due to infiltration of mineral oil, a PDMS permeable fluid, and how this affects the resulting pressure profile using a novel pressure measurement method. We found a 53% decrease in Young’s modulus of PDMS due to mineral oil absorption over the course of 3 h accounted for lower internal pressure and larger channel deformation compared to fresh PDMS at a given flow rate. Confocal fluorescence microscopy used to image channel profiles before and after the introduction of mineral oil showed a change in pressure-induced deformation after infiltration of the oil. Atomic force microscopy (AFM) nanoindentation was used to measure Young’s modulus of PDMS before (2.80±0.032.80±0.03 MPa) and after (1.32±0.041.32±0.04 MPa) mineral oil absorption. Raman spectroscopy showed the infiltration of mineral oil into PDMS from channel walls and revealed the diffusion coefficient of mineral oil in PDMS

Droplets Formation and Merging in Two-Phase Flow Microfluidics

Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed

Non-photolithographic plastic-mold-based fabrication of cylindrical and multi-tiered poly(dimethylsiloxane) microchannels for biomimetic lab-on-a-chip applications

To overcome the limitations of conventional lithography for generating cylindrical and multi-tiered microchannels, we demonstrate a facile and alternative route for non-photolithographic fabrication of plastic molds via micro-milling combined with hot embossing. First, semi-cylindrical negative channels were engraved on poly(methylmethacrylate) (PMMA) using a ball mill, and the obtained semi-cylindrical negative channel structure was transferred onto poly(ethyleneterephthalate) (PET) via hot embossing performed at a temperature intermediate between the glass transition temperature (Tg) values of the two thermoplastics. In this way, a positive semi-cylindrical channel structure was formed on the PET without distorting the original patterns on the PMMA. The PET mold with positive structures was then replicated onto poly(dimethylsiloxane) (PDMS) to produce negative semi-cylindrical channels, and by aligning two identical PDMS replicas, a cylindrical microchannel with a completely circular cross section was formed. Second, multi-tiered channel structures were readily obtained by controlling the depths of the microchannels in the micro-milling process. The effectiveness of the fabricated cylindrical and multi-tiered microchannels was evaluated by constructing a microvascular network and human liver sinusoid structure as proof-of-concept experiments. The simple fabrication and high precision in the resulting structures will pave the way for the construction of disposable biomimetic Lab-on-a-Chip (LOC) platforms with low manufacturing cost in a simple and facile manner feasible for mass production

Maze Solving Using Fatty Acid Chemistry

This study demonstrates that the Marangoni flow in a channel network can solve maze problems such as exploring and visualizing the shortest path and finding all possible solutions in a parallel fashion. The Marangoni flow is generated by the pH gradient in a maze filled with an alkaline solution of a fatty acid by introducing a hydrogel block soaked with an acid at the exit. The pH gradient changes the protonation rate of fatty acid molecules, which translates into the surface tension gradient at the liquid–air interface through the maze. Fluid flow maintained by the surface tension gradient (Marangoni flow) can drag water-soluble dye particles toward low pH (exit) at the liquid–air interface. Dye particles placed at the entrance of the maze dissolve during this motion, thus exhibiting and finding the shortest path and all possible paths in a maze