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  1. The influence of additives on the detonation velocity of a polyethylene wax/RDX formulation was examined. Additives included species of various shock impedance: glass microballoons; glass microspheres; polymethyl methacrylate (PMMA) microspheres; thermally expandable microspheres (TEMs); and PMMA microencapsulated pentaerythritol tetranitrate (PETN). Performance of the insensitive explosive 2,4-dinitroanisole (DNAN) was enhanced by addition of PETN-either neat or encapsulated, but encapsulation did not increase the sensitivity of the formulation. The energy contribution of the encapsulated PETN to the detonation front of the insensitive explosive 2,4-dinitroanisole (DNAN) was also demonstrated. Present in 5 wt%, the encapsulated PETN allowed DNAN to sustain a reaction (5.36 km/s) at 13 mm, well below its critical diameter. 
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    Free, publicly-accessible full text available June 20, 2024
  2. Free, publicly-accessible full text available April 3, 2024
  3. Abstract Background

    In introductory biology classrooms, cell and molecular concepts are often taught separate from those related to evolution and ecology, and usually in completely different courses. Furthermore, many examples used to teach introductory concepts are difficult for students to relate to. To address these issues, we developed curricular materials focused on the topic of breast cancer that: (1) aim to teach students how to integrate the various sub-disciplines of biology, with evolution as the unifying theme, and (2) aim to present course materials using relatable examples such as human health and disease. To assess the potential value of these materials, we asked students to complete a pre-unit and post-unit assessment before and after completing the interactive course unit on breast cancer.


    We found that after learning about breast cancer, students reported that learning about biology in the context of human health made their learning experience easier, more interesting, and more relatable. After the unit, students also rated evolutionary concepts as being more important for understanding human health and disease.


    These results have important implications for developing introductory biology curricula that have more personal appeal to students and may thus translate to better learning outcomes, as well as help students better understand the process of evolution as it occurs in humans.

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  4. Abstract

    As one of the least understood aerosol processes, nucleation can be a dominant source of atmospheric aerosols. Sulfuric acid (SA)-amine binary nucleation with dimethylamine (DMA) has been recognized as a governing mechanism in the polluted continental boundary layer. Here we demonstrate the importance of trimethylamine (TMA) for nucleation in the complex atmosphere and propose a molecular-level SA-DMA-TMA ternary nucleation mechanism as an improvement upon the conventional binary mechanism. Using the proposed mechanism, we could connect the gaseous amines to the SA-amine cluster signals measured in the atmosphere of urban Beijing. Results show that TMA can accelerate the SA-DMA-based new particle formation in Beijing by 50–100%. Considering the global abundance of TMA and DMA, our findings imply comparable importance of TMA and DMA to nucleation in the polluted continental boundary layer, with probably higher contributions from TMA in polluted rural environments and future urban environments with controlled DMA emissions.

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  5. Abstract Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica 1–3 . Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland 4 , making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre 2,3,5 . The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat 3,6 , both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base 7,8 , resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates. 
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    Free, publicly-accessible full text available February 16, 2024
  6. Abstract

    On 1 September 2021, the remnants of Hurricane Ida transformed into a lethal variant of tropical cyclone in which unprecedented short‐duration rainfall from clusters of supercells produced catastrophic flooding in watersheds of the Northeastern US. Short‐duration rainfall extremes from Ida are examined through analyses of polarimetric radar fields and rain gauge observations. Rainfall estimates are constructed from a polarimetric rainfall algorithm that is grounded in specific differential phase shift (KDP) fields. Rainfall accumulations at multiple locations exceed 1000‐year values for 1–3 hr time scales. Radar observations show that supercells are the principal agents of rainfall extremes. Record flood peaks occurred throughout the eastern Pennsylvania—New Jersey region; the peak discharge of the Elizabeth River is one of the most extreme in the eastern US, based on the ratio of the peak discharge to the sample 10‐year flood at the gaging station. As with other tropical cyclones that have produced record flooding in the Northeastern US, Extratropical Transition was a key element of extreme rainfall and flooding from Ida. Tropical and extratropical elements of the storm system contributed to extremes of atmospheric water balance variables and Convective Available Potential Energy, providing the environment for extreme short‐duration rainfall from supercells.

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  7. Abstract. Chemical ionization mass spectrometry with the nitrate reagent ion (NO3- CIMS) was used to investigate the products of the nitrate radical(NO3) initiated oxidation of four monoterpenes in laboratory chamber experiments. α-Pinene, β-pinene, Δ-3-carene, andα-thujene were studied. The major gas-phase species produced in each system were distinctly different, showing the effect of monoterpenestructure on the oxidation mechanism and further elucidating the contributions of these species to particle formation and growth. By comparinggroupings of products based on the ratios of elements in the general formula CwHxNyOz, therelative importance of specific mechanistic pathways (fragmentation, termination, and radical rearrangement) can be assessed for eachsystem. Additionally, the measured time series of the highly oxidized reaction products provide insights into the ratio of relative production andloss rates of the high-molecular-weight products of the Δ-3-carene system. The measured effective O:C ratios of reaction products wereanticorrelated with new particle formation intensity and number concentration for each system; however, the monomer : dimer ratios of products had a smallpositive trend. Gas-phase yields of oxidation products measured by NO3- CIMS correlated with particle number concentrations for eachmonoterpene system, with the exception of α-thujene, which produced a considerable amount of low-volatility products but noparticles. Species-resolved wall loss was measured with NO3- CIMS and found to be highly variable among oxidized reaction products in ourstainless steel chamber. 
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  8. Abstract

    Understanding the recent history of Thwaites Glacier, and the processes controlling its ongoing retreat, is key to projecting Antarctic contributions to future sea-level rise. Of particular concern is how the glacier grounding zone might evolve over coming decades where it is stabilized by sea-floor bathymetric highs. Here we use geophysical data from an autonomous underwater vehicle deployed at the Thwaites Glacier ice front, to document the ocean-floor imprint of past retreat from a sea-bed promontory. We show patterns of back-stepping sedimentary ridges formed daily by a mechanism of tidal lifting and settling at the grounding line at a time when Thwaites Glacier was more advanced than it is today. Over a duration of 5.5 months, Thwaites grounding zone retreated at a rate of >2.1 km per year—twice the rate observed by satellite at the fastest retreating part of the grounding zone between 2011 and 2019. Our results suggest that sustained pulses of rapid retreat have occurred at Thwaites Glacier in the past two centuries. Similar rapid retreat pulses are likely to occur in the near future when the grounding zone migrates back off stabilizing high points on the sea floor.

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