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Abstract. Immersion freezing, initiated by ice-nucleating particles (INPs) in supercooled aqueous droplets, plays an important role in the formation of ice crystals within clouds. The efficiency of immersion freezing depends strongly on INP composition and, crucially, on the mixing state – how chemical species are distributed across the particle population. Here, we quantify the impact of aerosol mixing state on immersion freezing using a combined theoretical and particle-resolved modeling approach. We derive analytical expressions for the frozen fraction of internally and externally mixed INP populations based on classical nucleation theory, showing that the frozen fraction is sensitive to whether ice-active species are present in all particles or only in a subset of the population. We introduce a multi-species immersion freezing scheme into the particle-resolved model PartMC, using the water activity-based immersion freezing model (ABIFM) to compute freezing probabilities for mixed-composition particles. To improve computational efficiency, we implement a Binned Tau-Leaping algorithm and demonstrate an order-of-magnitude speedup with minimal accuracy loss. Simulations reproduce the analytical trends in limiting cases and extend the analysis to more general aerosol populations, where mixing state continues to exert a substantial control on frozen fraction. Sensitivity analyses across particle size, species type, and cooling condition reveal that the mixing state effect is most pronounced when small amounts of highly efficient INPs are mixed with less efficient materials. These findings underscore the need to represent aerosol mixing state explicitly in models of heterogeneous ice nucleation to reduce uncertainty in cloud-phase partitioning. 

We compare the exam security of three proctoring regimens of Bring-Your-Own-Device, synchronous, computer-based exams in a computer science class: online un-proctored, online proctored via Zoom, and in-person proctored. We performed two randomized crossover experiments to compare these proctoring regimens. The first study measured the score advantage students receive while taking un-proctored online exams over Zoom-proctored online exams. The second study measured the score advantage of students taking Zoom-proctored online exams over in-person proctored exams. In both studies, students took six 50-minute exams using their own devices, which included two coding questions and 8–10 non-coding questions. We find that students score 2.3% higher on non-coding questions when taking exams in the un-proctored format compared to Zoom proctoring. No statistically significant advantage was found for the coding questions. While most of the non-coding questions had randomization such that students got different versions, for the few questions where all students received the same exact version, the score advantage escalated to 5.2%. From the second study, we find no statistically significant difference between students’ performance on Zoom-proctored vs. in-person proctored exams. With this, we recommend educators incorporate some form of proctoring along with question randomization to mitigate cheating concerns in BYOD exams. 

We present the design of a portable coronagraph, CATEcor (where CATE stands for Continental-America Telescope Eclipse), that incorporates a novel “shaded-truss” style of external occultation and serves as a proof-of-concept for that family of coronagraphs. The shaded-truss design style has the potential for broad application in various scientific settings. We conceived CATEcor itself as a simple instrument to observe the corona during the darker skies available during a partial solar eclipse, or for students or interested amateurs to detect the corona under ideal noneclipsed conditions. CATEcor is therefore optimized for simplicity and accessibility to the public. It is implemented using an existing dioptric telescope and an adapter rig that mounts in front of the objective lens, restricting the telescope aperture and providing external occultation. The adapter rig, including occulter, is fabricated using fusion deposition modeling (FDM; colloquially “3D printing”), greatly reducing cost. The structure is designed to be integrated with moderate care and may be replicated in a university or amateur setting. While CATEcor is a simple demonstration unit, the design concept, process, and trades are useful for other more sophisticated coronagraphs in the same general family, which might operate under normal daytime skies outside the annular-eclipse conditions used for CATEcor. 

This full research paper explores how second-chance testing can be used as a strategy for mitigating students’ test anxiety in STEM courses, thereby boosting students’ performance and experiences. Second-chance testing is a testing strategy where students are given an opportunity to take an assessment twice. We conducted a mixed-methods study to explore second-chance testing as a potential solution to test anxiety. First, we interviewed a diverse group of STEM students (N = 23) who had taken courses with second-chance testing to ask about the stress and anxiety associated with testing. We then administered a survey on test anxiety to STEM students in seven courses that offered second-chance tests at Midwestern University (N = 448). We found that second-chance testing led to a 30% reduction in students’ reported test anxiety. Students also reported reduced stress throughout the semester, even outside of testing windows, due to the availability of second-chance testing. Our study included an assortment of STEM courses where second-chance testing was deployed, which indicates that second-chance testing is a viable strategy for reducing anxiety in a variety of contexts. We also explored whether the resultant reduction in test anxiety led to student complacency, encouraged procrastination, or other suboptimal student behavior because of the extra chance provided. We found that the majority of students reported that they worked hard on their initial test attempts even when second-chance testing was available. 

We present results of a dual eclipse expedition to observe the solar corona from two sites during the annular solar eclipse of 14 October 2023 using a novel coronagraph designed to be accessible for amateurs and students to build and deploy. The coronagraph (CATEcor) builds on the standardized eclipse observing equipment developed for the Citizen CATE 2024 experiment. The observing sites were selected for likelihood of clear observations, for historic relevance (near the Climax site in the Colorado Rocky Mountains), and for centrality to the annular eclipse path (atop Sandia Peak above Albuquerque, New Mexico). The novel portion of CATEcor is an external occulter assembly that slips over the front of a conventional dioptric telescope, forming ashaded-trussexternally occulted coronagraph. CATEcor is specifically designed to be easily constructed in a garage or “makerspace” environment. We successfully observed some bright features in the solar corona to an altitude of approximately 2.25 R_⊙during the annular phases of the eclipse. Future improvements to the design, in progress now, will reduce both stray light and image artifacts; our objective is to develop a design that can be operated successfully by amateur astronomers at sufficient altitude even without the darkened skies of a partial or annular eclipse.