More Like this

1. Applying a Transformative Justice Approach to Encourage the Participation of Black and Latina Girls in Computing

   https://doi.org/10.1145/3451345  

   Erete, Sheena; Thomas, Karla; Nacu, Denise; Dickinson, Jessa; Thompson, Naomi; Pinkard, Nichole (December 2021, ACM Transactions on Computing Education)

   Global protests and civil unrest in 2020 has renewed the world’s interest in addressing injustice due to structural racism and oppression toward Black and Latinx people in all aspects of society, including computing. In this article, we argue that to address and repair the harm created by institutions, policies, and practices that have systematically excluded Black and Latina girls from computer science, an intersectional, transformative justice approach must be taken. Leveraging testimonial authority, we share our past 8 years of experience designing, implementing, and studying Digital Youth Divas, a programmatic and systemic approach to encouraging middle school Black and Latina girls to participate in STEM. Specifically, we propose three principles to counter structural racism and oppression embedded in society and computing education: computing education must (1) address local histories of injustice by engaging community members; (2) counter negative stereotypes perpetuated in computer science by creating inclusive safe spaces and counter-narratives; and (3) build sustainable, computational capacity in communities. To illustrate each principle, we provide specific examples of the harm created by racist policies and systems and their effect on a specific community. We then describe our attempt to create counter structures and the subsequent outcomes for the girls, their families, and the community. This work contributes a framework for STEM and computing educators to integrate transformative justice as a method of repairing the harm that both society and the field of computing has and continues to cause Black and Latinx communities. We charge policy makers, educators, researchers, and community leaders to examine histories of oppression in their communities and to adopt holistic, transformative approaches that counter structural oppression at the individual and system level. 

   more » « less
2. Effects of Counter‐Ion Size on Delocalization of Carriers and Stability of Doped Semiconducting Polymers

   https://doi.org/10.1002/aelm.202000595  

   Thomas, Elayne_M; Peterson, Kelly_A; Balzer, Alex_H; Rawlings, Dakota; Stingelin, Natalie; Segalman, Rachel_A; Chabinyc, Michael_L (October 2020, Advanced Electronic Materials)

   Abstract Since doped polymers require a charge‐neutralizing counter‐ion to maintain charge neutrality, tailored and high degrees of doping in organic semiconductors requires an understanding of the coupling between ionic and electronic carrier motion. A method of counter‐ion exchange is utilized using the polymeric semiconductor poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] ‐C₁₄to deconvolute the effects of ionic/polaronic interactions with the electrical properties of doped semiconducting polymers. In particular, exchanging the counter‐ions of the dopant nitrosonium hexafluorophosphate enables investigation into the role of counter‐ion size from 5.2 to 8.2 Å in diameter. The orientational order of the polymeric crystallites is not affected with this exchange process while effectively modifying the counter‐ion distance to the charge carrier. Doped films have electrical conductivities of 320 S cm⁻¹and are not sensitive to an increased ion‐polaron distance. It is posited that other factors dominate the electrical properties at a device scale, such as the morphology and presence of domain boundaries. Interestingly, the temperature stability of the doped film can be drastically improved with the use of counter‐ions containing less labile bonds. This platform serves as a unique way to retain the morphology of polymeric thin films while studying charge interactions at the local scale. 

   more » « less
3. $$\alpha $$-event characterization and rejection in point-contact HPGe detectors

   https://doi.org/10.1140/epjc/s10052-022-10161-y  

   Arnquist, I. J.; Avignone, F. T.; Barabash, A. S.; Barton, C. J.; Bertrand, F. E.; Blalock, E.; Bos, B.; Busch, M.; Buuck, M.; Caldwell, T. S.; et al (March 2022, The European Physical Journal C)

   Abstract P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We have characterized a PPC detector’s response to $$\alpha $$ α particles incident on the sensitive passivated and p $$^+$$ + surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the Majorana Demonstrator experiment, a search for neutrinoless double-beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) in $$^{76}$$ 76 Ge. $$\alpha $$ α decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of $$\alpha $$ α identification, reliably identifying $$\alpha $$ α background events on the passivated surface of the detector. We demonstrate effective rejection of all surface $$\alpha $$ α events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the $$0\nu \beta \beta $$ 0 ν β β region of interest window by an order of magnitude in the Majorana Demonstrator   and will be used in the upcoming LEGEND-200 experiment. 

   more » « less
4. A Computational Analysis of Bubble-Structure Interaction in Near-Field Underwater Explosion

   https://doi.org/10.1115/IMECE2021-72854  

   Ma, Wentao; Ozenkoski, Timothy; Wang, Kevin (November 2021, Proceedings of ASME 2021 International Mechanical Engineering Congress and Exposition)

   Underwater explosion poses a significant threat to the structural integrity of ocean vehicles and platforms. Accurate prediction of the dynamic loads from an explosion and the resulting structural response is crucial to ensuring safety without overconservative design. When the distance between the explosive charge and the structure is relatively small (i.e., near-field explosion), the dynamics of the gaseous explosion product, i.e., the “bubble”, comes into play, rendering a multiphysics problem that features the interaction of the bubble, the surrounding liquid water, and the solid structure. The problem is highly nonlinear, as it involves shock waves, large deformation, yielding, contact, and possibly fracture. This paper investigates the two-way interaction between the cyclic expansion and collapse of an explosion bubble and the deformation of a thin-walled elastoplastic cylindrical shell in its vicinity. Intuitively, when a shock wave impinges on a thin cylindrical shell, the shell would collapse in the direction of shock propagation. However, some recent laboratory experiments have shown that under certain conditions the shell collapsed in a counter-intuitive mode in which the direction of collapse is perpendicular to that of shock propagation. In other words, the nearest point on the structural surface moved towards the explosion charge, despite being impacted by a compressive shock. This paper focuses on replicating this phenomenon through numerical simulation and elucidating the underlying mechanisms. A recently developed computational framework (“FIVER”) coupling a nonlinear finite element structural dynamics solver and a finite volume compressible fluid dynamics solver is used to complete this study. The solver utilizes an embedded boundary method to track the wetted surface of the structure (i.e. the fluid-structure interface), which is capable of handling large structural deformation and topological changes (e.g., fracture). The solver also adopts the level set method for tracking the bubble surface (i.e. the liquid-gas interface). The fluid-structure and liquid-gas interface conditions are enforced by constructing and solving one-dimensional multi-material Riemann problems, which naturally accommodates the propagation of shock waves across the interfaces. In this paper, mesh refinement study is made to examine the sensitivity of the results to various meshing parameters. The results show that the intermediate level of refinement is appropriate in terms of both the accuracy and the computation costs. Next, the deformation history of both the bubble and the structure are presented and analyzed to provide a detailed view of the counter-intuitive collapse mode mentioned above. We show that timewise, the structural collapse spans multiple cycles of bubble oscillation. Additional details about the time-histories of fluid pressure, structure displacement, and bubble size are presented to elucidate this dynamic bubble-structure interaction and the resulting structural failure. 

   more » « less
5. Effects of fixed charge group physicochemistry on anion exchange membrane permselectivity and ion transport

   https://doi.org/10.1039/D0CP00018C  

   Ji, Yuanyuan; Luo, Hongxi; Geise, Geoffrey M. (April 2020, Physical Chemistry Chemical Physics)

   Understanding the effects of polymer chemistry on membrane ion transport properties is critical for enabling efforts to design advanced highly permselective ion exchange membranes for water purification and energy applications. Here, the effects of fixed charge group type on anion exchange membrane (AEM) apparent permselectivity and ion transport properties were investigated using two crosslinked AEMs. The two AEMs, containing a similar acrylonitrile, styrene and divinyl benzene-based polymer backbone, had either trimethyl ammonium or 1,4-dimethyl imidazolium fixed charge groups. Membrane deswelling, apparent permselectivity and ion transport properties of the two AEMs were characterized using aqueous solutions of lithium chloride, sodium chloride, ammonium chloride, sodium bromide and sodium nitrate. Apparent permselectivity measurements revealed a minor influence of the fixed charge group type on apparent permselectivity. Further analysis of membrane swelling and ion sorption, however, suggests that less hydrophilic fixed charge groups more effectively exclude co-ions compared to more hydrophilic fixed charge groups. Analysis of ion diffusion properties suggest that ion and fixed charge group enthalpy of hydration properties influence ion transport, likely through a counter-ion condensation, ion pairing or binding mechanism. Interactions between fixed charge groups and counter-ions may be stronger if the enthalpy of hydration properties of the ion and fixed charge group are similar, and suppressed counter-ion diffusion was observed in this situation. In general, the hydration properties of the fixed charge group may be important for understanding how fixed charge group chemistry influences ion transport properties in anion exchange membranes. 

   more » « less