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  1. Abstract Recent discoveries of water-rich Neptune-like exoplanets require a more detailed understanding of the phase diagram of H 2 O at pressure–temperature conditions relevant to their planetary interiors. The unusual non-dipolar magnetic fields of ice giant planets, produced by convecting liquid ionic water, are influenced by exotic high-pressure states of H 2 O—yet the structure of ice in this state is challenging to determine experimentally. Here we present X-ray diffraction evidence of a body-centered cubic (BCC) structured H 2 O ice at 200 GPa and ~ 5000 K, deemed ice XIX, using the X-ray Free Electron Laser of the Linac Coherent Light Sourcemore »to probe the structure of the oxygen sub-lattice during dynamic compression. Although several cubic or orthorhombic structures have been predicted to be the stable structure at these conditions, we show this BCC ice phase is stable to multi-Mbar pressures and temperatures near the melt boundary. This suggests variable and increased electrical conductivity to greater depths in ice giant planets that may promote the generation of multipolar magnetic fields.« less
    Free, publicly-accessible full text available December 1, 2023
  2. In the Northern Hemisphere, recurrence of transient Rossby wave packets over periods of days to weeks, termed RRWPs, may repeatedly create similar weather conditions. This recurrence leads to persistent surface anomalies and high-impact weather events. Here, we demonstrate the significance of RRWPs for persistent heatwaves in the Southern Hemisphere (SH). We investigate the relationship between RRWPs, atmospheric blocking, and amplified quasi-stationary Rossby waves with two cases of heatwaves in Southeast Australia (SEA) in 2004 and 2009. This region has seen extraordinary heatwaves in recent years. We also investigate the importance of transient systems such as RRWPs and two other persistentmore »dynamical drivers: atmospheric blocks and quasi-resonant amplification (QRA). We further explore the link between RRWPs, blocks, and QRA in the SH using the ERA-I reanalysis dataset (1979–2018). We find that QRA and RRWPs are strongly associated: 40% of QRA days feature RRWPs, and QRA events are 13 times more likely to occur with an RRWPs event than without it. Furthermore, days with QRA and RRWPs show high correlations in the composite mean fields of upper-level flows, indicating that both features have a similar hemispheric flow configuration. Blocking frequencies for QRA and RRWP conditions both increase over the south Pacific Ocean but differ substantially over parts of the south Atlantic and Indian Ocean.« less
    Free, publicly-accessible full text available January 14, 2023
  3. Growing evidence points to recurring influence campaigns on social media, often sponsored by state actors aiming to manipulate public opinion on sensitive political topics. Typically, campaigns are performed through instrumented accounts, known as troll accounts; despite their prominence, however, little work has been done to detect these accounts in the wild. In this paper, we present TROLLMAGNIFIER, a detection system for troll accounts. Our key observation, based on analysis of known Russian sponsored troll accounts identified by Reddit, is that they show loose coordination, often interacting with each other to further specific narratives. Therefore, troll accounts controlled by the samemore »actor often show similarities that can be leveraged for detection. TROLLMAGNIFIER learns the typical behavior of known troll accounts and identifies more that behave similarly. We train TROLLMAGNIFIER on a set of 335 known troll accounts and run it on a large dataset of Reddit accounts. Our system identifies 1,248 potential troll accounts; we then provide a multi-faceted analysis to corroborate the correctness of our classification. In particular, 66% of the detected accounts show signs of being instrumented by malicious actors (e.g., they were created on the same exact day as a known troll, they have since been suspended by Reddit, etc.). They also discuss similar topics as the known troll accounts and exhibit temporal synchronization in their activity. Overall, we show that using TROLLMAGNIFIER, one can grow the initial knowledge of potential trolls provided by Reddit by over 300%.« less
    Free, publicly-accessible full text available January 1, 2023
  4. Arctic oil spills are particularly detrimental as they cause extensive ice melting in addition to the environmental pollution they create. However, few studies have been undertaken to reveal how oil-ice interactions impact ice melting. A simultaneous measurement method is developed to investigate the heat transfer pathways from oil slicks to ice. Functional luminescent probes are dissolved in a liquid immiscible with water, which imitates spilled oil. Another luminescent probe is added to seeding particles in order to increase their luminescent intensity. Dual-luminescence imaging and particle imaging velocimetry (PIV) are combined into a single simultaneous measurement method. The developed measurement systemmore »shows simultaneous temperature and velocity measurements for natural convection of the immiscible liquid. Successful implementation of the two measurement techniques together is a step toward analyzing heat transfer pathways in a spilled oil adjacent to an ice body, which indicates the extent of melting.« less
    Free, publicly-accessible full text available November 20, 2022
  5. A series of experiments were conducted to investigate the melting of ice adjacent to a water-immiscible liquid layer (n-dodecane) exposed to radiation from above. The experimental setup consisted of a borosilicate container containing an ice wall and a layer of n-dodecane heated from above. In addition to tracking the movement of the melt front, Particle Image Velocimetry (PIV) and Background Oriented Schlieren (BOS) measurements were conducted on the liquid-phase . Two distinct melting regimes were found to dominate the melting process. First was the uniform melting across the contact area with the immiscible liquid layer for low radiation levels (~1more »kW/m 2 ). Second was the lateral intrusion regime, where a depression near free surface of the liquid forms in ice and grows laterally for radiation level greater than ~1 kW/m 2 . The ice surface remained flat and smooth in uniform melting regime, whereas in the lateral intrusion regime a series of rivulets were formed that carved valleys on the ice. PIV measurements showed a surface flow toward the ice for all heat flux levels caused by surface-tension forces. Increase of the heat flux levels caused a transition to multi-roll structure in the flow field. This multi-roll structure, which is accompanied by a recirculation zone near the ice, increased heat transfer coefficient near the surface of the liquid causing lateral intrusion regime. BOS measurements indicated presence of density gradients below the free surface of n-dodecane and in regions near ice that are caused by local small-scale temperature gradients. The current experiments were conducted to explore the melting dynamics and to shed light on the processes that influence the ice melting. Implications of such mechanisms in a real-life scenario, i.e. oil spill in ice-infested waters, needs to be explored further by using more liquids and improved accuracy with diagnostic techniques.« less
    Free, publicly-accessible full text available October 10, 2022
  6. A series of experiments were conducted to investigate the flow field of a top-heated liquid fuel adjacent to an ice block. The experimental setup consisted of a borosilicate container containing an ice wall and a layer of n-heptane heated from above. Particle Image Velocimetry (PIV) and Background Oriented Schlieren (BOS) measurements were conducted on the liquid -phase. PIV measurements showed a surface flow toward the ice caused by surface -tension forces, which is driven by the horizontal temperature gradients on the liquid surface. A recirculation zone was observed under the free surface and near the ice. The combination of themore »two flow patterns caused lateral intrusion in the ice, instead of a uniform melting across ice surface. BOS measurements indicated presence of density gradients below the free surface of n-heptane and in regions near the ice block. These density gradients were created by local small-scale temperature gradients. The current experiments were conducted to explore the processes that influence the ice melting by immiscible liquid layers.« less
  7. Arctic oil spills are particularly detrimental as they could cause extensive ice melting in addition to the environmental pollution they create. Floating oil slicks amongst ice floes absorb ambient energy and transfer that energy to the ice to aggravate melting in the thaw season. However, few studies have been undertaken to reveal how oil-ice interactions impact ice melting. This research employs a measurement technique to investigate the heat transfer pathways from oil slicks to the ice. Dual-luminescence imaging and particle imaging velocimetry (PIV) in a side cooled cavity is performed for temperature and velocity measurements of Toluene, respectively. Dual-luminescence imagingmore »captured the spatial temperature distribution of the fuel. Consecutive imaging of the seeding particles in PIV provided the spatial velocity field of the fuel in the cavity. The results show that the convective field is directly coupled with the temperature field, i.e., the temperature difference instigates a flow in the liquid. Successful implementation of the two measuring techniques together is a step toward analyzing heat transfer pathways in a liquid fuel adjacent to an ice body, indicating the extent of melting.« less
  8. More women than men in the US graduate college, but women constitute only 16% of the engineering workforce [1]. Women frequently attribute their lack of persistence in engineering to a chilly academic climate [2]. Researchers have suggested that developing a robust engineering identity could moderate a climate effect and support improved retention and graduation of female engineers [2]. However, there is little empirical data on interrelationships among gender, perceived academic climate in engineering programs, engineering identity, and belonging to an engineering community. We drew on social identity theory and extant literature to develop four research questions: 1) Are there anymore »differences between men and women regarding perceived academic climate, sense of belonging, and engineering identity? 2) Does academic climate predict engineering identity in the same way for women and men? 3)Does sense of belonging mediate the relationship between perceived academic climate and engineering identity? 4) Do engineering students who are women demonstrate different relationships among perceived climate, engineering identity, and belongingness from men? We used survey data from a multi-year NSF-funded project (Award # 1726268, #1726088, and #1725880/2033129) that incorporated experimental course-based interventions to build an inclusive curriculum. Surveys were administered at the beginning and end of the semester. We found that at the end of the semester women engineering undergraduates reported lower engineering identity though the initial engineering identity, perceived academic climate, and sense of belonging were the same for both men and women engineering undergraduates. Multiple regression analyses with 601 first-year engineer majors (21% female) indicated perceived climate and gender accounted for 48% of engineering identity variability. The interaction between perceived climate and gender on engineering identity was not statistically significant. Mediation analysis revealed that sense of belonging (b=0.42, 95% CI [0.30, 0.53]) mediated the relationship between perceived climate and engineering identity for both males and females. Sense of belonging was critical in engineering identity. Moderated mediation analysis indicated gender did not moderate the indirect effect of perceived climate on engineering identity through a sense of belonging.« less
  9. Recent explosions with devastating consequences have re-emphasized the relevance of fire safety and explosion research. From earlier works, the severity of the explosion has been said to depend on various factors such as the ignition location, type of a combustible mixture, enclosure configuration, and equivalence ratio. Explosion venting has been proposed as a safety measure in curbing explosion impact, and the design of safety vent requires a deep understanding of the explosion phenomenon. To address this, the Explosion Venting Analyzer (EVA)—a mathematical model predicting the maximum overpressure and characterizing the explosion in an enclosure—has been recently developed and coded (Processmore »Saf. Environ. Prot. 99 (2016) 167). The present work is devoted to methane explosions because the natural gas—a common fossil fuel used for various domestic, commercial, and industrial purposes—has methane as its major constituent. Specifically, the dynamics of methane-air explosion in vented cylindrical enclosures is scrutinized, computationally and experimentally, such that the accuracy of the EVA predictions is validated by the experiments, with the Cantera package integrated into the EVA to identify the flame speeds. The EVA results for the rear-ignited vented methane-air explosion show good agreement with the experimental results.« less