The Role of Diaphanous in Ring Canal Development in Drosophila melanogaster

Infertility is a widespread condition that does not always have a known cause, and for which we often do not have a cure. One potential cause of infertility is defects in gametogenesis, or the formation of sperm and egg. During gametogenesis in most organisms, the developing sperm and egg are connected to each other or to supporting cells through intercellular bridges, allowing transfer of materials between cells. Defects in these connections can lead to infertility. The developing fruit fly egg is an excellent model system to study intercellular bridges, or ring canals. Rich in f-actin and actinbinding proteins, ring canals expand ~20 fold during oogenesis, and this expansion is accompanied by a 134-fold increase in the amount of actin in the structure. Ring canal expansion depends on the Arp2/3 complex; mutations in Arp2/3 complex members lead to decreased expansion and ring canal collapse. Interestingly, the Arp2/3 mutant phenotype has been reported to affect later stages of oogenesis (beginning at stage 5). This suggests that other actin nucleators could be involved in promoting ring canal growth prior to this point. I have characterized a role for the formin-family actin nucleator, Diaphanous (Dia), during oogenesis. Depletion of Dia leads to defects in normal ring canal structure and expansion, which are distinct from those observed following depletion of the Arp2/3 complex members. Future work will determine the mechanisms that promote the localization and activation of Arp2/3 and Diaphanous in the context of ring canal formation and expansion

A classification of spanning surfaces for alternating links

A classification of spanning surfaces for alternating links is provided up to genus, orientability, and a new invariant that we call aggregate slope. That is, given an alternating link, we determine all possible combinations of genus, orientability, and aggregate slope that a surface spanning that link can have. To this end, we describe a straightforward algorithm, much like Seifert's Algorithm, through which to construct certain spanning surfaces called layered surfaces. A particularly important subset of these will be what we call basic layered surfaces. We can alter these surface by performing the entirely local operations of adding handles and/or crosscaps, each of which increases genus. The main result then shows that if we are given an alternating projection P(L) and a surface S spanning L, we can construct a surface T spanning L with the same genus, orientability, and aggregate slope as S that is a basic layered surface with respect to P, except perhaps at a collection of added crosscaps and/or handles. Furthermore, S must be connected if L is non-splittable. This result has several useful corollaries. In particular, it allows for the determination of nonorientable genus for alternating links. It also can be used to show that mutancy of alternating links preserves nonorientable genus. And it allows one to prove that there are knots that have a pair of minimal nonorientable genus spanning surfaces, one boundary-incompressible and one boundary-compressible.Comment: 31 pages, 34 figure

Redemption in Shaw 203

When a celebrated columnist taught a May Term course on writing, it was his students who took him to school

Field Doctor

As team chiropractor for the Chicago Bears, Josh Akin ’03 helps keep gridiron warriors at the top of their game

The Real Time Display Builder (RTDB)

The Real Time Display Builder (RTDB) is a prototype interactive graphics tool that builds logic-driven displays. These displays reflect current system status, implement fault detection algorithms in real time, and incorporate the operational knowledge of experienced flight controllers. RTDB utilizes an object-oriented approach that integrates the display symbols with the underlying operational logic. This approach allows the user to specify the screen layout and the driving logic as the display is being built. RTDB is being developed under UNIX in C utilizing the MASSCOMP graphics environment with appropriate functional separation to ease portability to other graphics environments. RTDB grew from the need to develop customized real-time data-driven Space Shuttle systems displays. One display, using initial functionality of the tool, was operational during the orbit phase of STS-26 Discovery. RTDB is being used to produce subsequent displays for the Real Time Data System project currently under development within the Mission Operations Directorate at NASA/JSC. The features of the tool, its current state of development, and its applications are discussed

On bias in social reviews of university courses

University course ranking forums are a popular means of disseminating information about satisfaction with the quality of course content and instruction, especially with undergraduate students. A variety of policy decisions by university administrators, instructional designers and teaching staff affect how students perceive the efficacy of pedagogies employed in a given course, in class and online. While there is a large body of research on qualitative driving factors behind the use of academic rating sites, there is little investigation of the (potential) implicit student bias on said forums towards desirable course outcomes at the institution level. To that end, we examine the connection between course outcomes (student-reported GPA) and the overall ranking of the primary course instructor, as well as rating disparity by nature of course outcomes, for several hundred courses taught at Virginia Tech based on data collected from a popular academic rating forum. We also replicate our analysis for several public universities across the US. Our experiments indicate that there is a discernible albeit complex bias towards course outcomes in the professor ratings registered by students.Comment: WebSci'19 Companion Proceeding

Sums of Evenly Spaced Binomial Coefficients

We provide a combinatorial proof of a formula for the sum of evenly spaced binomial coefficients. This identity, along with a generalization, are proved by counting weighted walks on a graph