���񱦵�

�ٲ��ٱ�:��9/3/2015

����𲹰���:��Carly Matson​��

�ٱ�貹���ٳ���Գ�:��Mathematics

�վ��ٱ���:��Knots

Abstract:��Knots are ubiquitous in our world. We use them to tie our shoes, knit our sweaters, and prevent our boats from floating away. There are many different kinds of knots, and one can be turned into another through the process of untying and retying. But what happens when you take the two loose ends of a knot and join them together? We obtain the mathematical version of a knot, an object that can be pulled and twisted into different shapes but that has no beginning or end. Intuitively we realize that it is no longer true that any knot can be transformed into any other. In this talk I will discuss a few of the techniques for distinguishing one knot from another as well as some of the connections between this theory and other areas of math and science.

�ٲ��ٱ�:��9/17/15

����𲹰���:��Sarah Crump​��

�ٱ�貹���ٳ���Գ�:��Geology

Title:��Relics of a colder past: Exposure ages from Neoglacial moraines on Baffin Island, Arctic Canada

�������ٰ�������:��Temperature changes in the Arctic have been about 3-4 times greater (for both warming and cooling events) than the rest of the Northern Hemisphere during the last 3 million years. This is primarily a result of positive feedback mechanisms related to changes in sea ice, snow cover, and glacier extent, and in turn, this Arctic amplification influences the climate system globally. As such, records of past climate change from the Arctic are particularly important for understanding the Earth’s climate system and predicting how future warming might play out. Alpine glaciers respond sensitively to changes in temperature and precipitation, and the deposits they leave behind during advances—specifically, terminal moraines—provide valuable clues about past cold times. In this talk, I will present a brief overview of why and how geologists go about reconstructing climate and glacier history and then focus in on my efforts to date moraines that represent glacier advances during the last ~5,000 years on Baffin Island.

�ٲ��ٱ�:��10/1/15

����𲹰���:��Ian Martiny​��

�ٱ�貹���ٳ���Գ�:��Computer Science

�վ��ٱ���:��3n + 1 Problem

�������ٰ�������:��The 3n + 1 problem (also known as the Collatz Conjecture, Ulam’s Conjecture, the Syracuse Problem, etc.) was proposed in the 1930s and can be stated through iterations of the function:

The conjecture states that no matter what positive integer is chosen there is a k such that C (k) (n) = 1 for some k ≥ 1. Informally this says that after some number of iterations of the function C we will get an answer of 1. For example C(5) = 16, C(16) = 8, C(8) = 4, C(4) = 2, C(2) = 1. Thus after 5 iterations from the starting number 5, C reached 1 - or C (5)(5) = 1.

This has been numerically verified for numbers as large as 5.764 × 1018, meaning for any given number, x, less than 5.764×1018 after some number of iterations of C on x we will eventually reach the number 1. The conjecture states this will always happens, for every positive integer.

This conjecture is very easy to state but has remained unsolved for the past 80 years. We will discuss basics of this function: how it behaves, and a speed up that lets us compute this a bit faster. We will next talk about one of the reasons this conjecture is so difficult to prove (in general) and go through the process of creating a “common sense” solution to the question of “how many iterations are necessary to reach 1?”

Finally we will discuss the some common but important results on this problem that have given researchers insight on how this function behaves and discuss whether the 3n + 1 conjecture is a good problem. This talk is accessible to all audiences, and assumes no formal background in mathematics; all necessary background will be covered in the talk.

�ٲ��ٱ�:��10/29/15

����𲹰���:��Bryce Bjork​��

�ٱ�貹���ٳ���Գ�:��Physics

�վ��ٱ���:��Simplifying complex chemical kinetics through multiplexed spectroscopy

�������ٰ�������:��The complexity of a chemical reaction increases dramatically with the number of molecules that participate. In order to really understand a reaction, it is important to determine reaction rates, quantum yields, and ro-vibrational temperatures for all participating molecules, which can become infeasible for complicated reactions. Traditionally, the experimentalist has had to sacrifice either spectral bandwidth or absorption sensitivity, resulting in instruments that have the capability either detect one molecule very sensitively or many molecules with significantly reduced sensitivity. For chemical kinetics, this means that many experiments can only provide a small amount of the information required to understand the reaction. The optical frequency comb has significantly changed this situation, providing broad spectral bandwidth for multiplexed molecular detection while also containing a spectral structure that permits coupled to an optical enhancement cavity for improved absorption sensitivity. In my presentation, I will describe the basics of cavity-enhanced optical frequency comb spectroscopy (CE-DFCS) and discuss the use of the technique to study an important chemical reaction in combustion and atmospheric chemistry, OH+CO → H+CO2, with high-sensitivity and microsecond time-resolution.

�ٲ��ٱ�:��11/5/15

����𲹰���:��Steffanie Guillermo​

�ٱ�貹���ٳ���Գ�:��Psychology

�վ��ٱ���:��Mechanisms underlying attention to race

�������ٰ�������:��Existing research on attention to race demonstrates that attention is more pronounced for racial outgroup versus ingroup faces. The majority of this work examines White participants’ attention to Blacks, a racial group stereotypically associated with threat. These lines of work typically conclude that threat-based associations drive attention. However, more recent evidence finds preferential attention to non-threatening East Asian faces, arguing that novelty is sufficient to prompt attentional biases. This raises the possibility that mechanisms other than threat underlie race-based attention. The current research examined attention allocation to racial outgroup versus ingroup faces. Attention was measured with an exogenous cueing task that assessed attentional capture and holding towards faces of each racial group. Across two studies, we found that attention is biased towards Black and Latino versus White faces. In a third study, we tested various possible mechanisms. We found that perceived threat was related to the magnitude of race-based attention; however, results indicated that this relationship was stronger for ingroup, White faces. Implications of these findings will be discussed, as well as future directions to more carefully examine the relationships between threat and attention to race.

�ٲ��ٱ�:��11/12/15

����𲹰���:��Trey Laurence​

�ٱ�貹���ٳ���Գ�:��Aerospace Engineering��

�վ��ٱ���:��An alternative method for wind sensing with small UAS

�������ٰ�������:��Unmanned aircraft offer many advantages for obtaining meteorological measurements over the more established methods (radar, weather balloons, etc). Currently, one of the best ways to perform wind sensing with sUAS is using a multi-hole probe. While MHPs offer an accurate way to measure the relative winds, they are expensive and require significant consideration as to where to mount on the aircraft. My research is focused on developing an alternative to the multi-hole probe using numerous pressures sensors distributed across the surface of the aircraft. Since wind sensing is only one of the focuses of the Research and Engineering Center for Unmanned Aircraft, I will also talk about other projects the lab has been part of.

�ٲ��ٱ�:��12/3/15

����𲹰���:��Ty Tuff

�ٱ�貹���ٳ���Գ�:��Ecology and Evolutionary Biology

�վ��ٱ���:��Relative motion as an ecological mechanism

�������ٰ�������:��Do migratory birds move or do we? Pole-to-pole migrants are permanently detached from the surface of Earth and we observe their movement as oscillating between Earth’s north and south poles. That perspective is enriched when we realize that those birds occupy their own moving reference frame and see humans and habitats moving in their own unique directions below them. This is one of many examples where our fundamental ecological understanding changes when we consider relative motion. In this talk, I will present my model for analyzing multiple moving perspectives and walk you through the engineering process for applying those mathematical tools to questions about the natural world. I’ve rendered some flashy visuals to lure you from your winter slumber, so please join me at the top of the ivory tower for my STEMinar talk describing relative motion as an ecological mechanism.

�ٲ��ٱ�:��12/10/15

����𲹰���:��Amanda Grenell​

�ٱ�貹���ٳ���Գ�:�����𳾾����ٰ�����

�վ��ٱ���:��Investigation of nanocrystal heterostructures for photochemical hydrogen production

�������ٰ�������:��The growing need for energy harvesting that has minimal environmental impact has been recognized by scientists and society. One exciting solution is artificial photosynthesis, in which solar energy is converted directly into fuels. However, the process of generating fuels from sunlight is complicated because it occurs in several steps: absorption of light and subsequent generation of charges in the light harvesting material, transport of charges to a catalyst, and finally the catalyzed, multi-electron fuel-generating reaction. A major challenge of efficiently producing solar fuels is to control and optimize the rates of these steps. Due to their highly tunable properties, semiconducting nanocrystals (NCs) are promising light harvesting components of artificial photosynthetic systems. Previous work has demonstrated that CdS NCs can be coupled to the enzyme hydrogenase, and the resulting biomimetic complex photochemically produces H2 with quantum yields up to 20%. However, the competition between the rate of electron transfer (ET) to hydrogenase and the rate of electron-hole recombination in the NC limits this yield. My project aims to increase the efficiency of ET and therefore the yield of H2 production by slowing down electron-hole recombination. This is accomplished by controlling localization of excited charge carriers within NCs made of two different materials, known as heterostructures. Using time-resolved transient absorption spectroscopy, I can study the relationships between NC structure, NC photophysics, and ET to hydrogenase. Since ET is a key step in efficient harvesting of solar energy by NCs, these fundamental studies will inform the design of future solar energy conversion architectures.��

��