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Characterization of the Alfvén Transition in the Young Solar Wind using Parker Solar Probe Observations Approaching Solar Maximum
No full textOriginal content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/ Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
This article was originally published in The Astrophysical Journal. The version of record is available at: https://doi.org/10.3847/1538-4357/ae2c78Close to Earth, the solar wind is usually super-Alfvénic, i.e., the speed of the solar wind is much larger than the Alfvén speed. However, in the lower coronal regions, the solar wind is mostly sub-Alfvénic. With the Parker Solar Probe (PSP) crossing the boundary between the sub- and super-Alfvénic flow, R. Bandyopadhyay et al. performed a turbulence characterization of the sub-Alfvénic solar wind with initial data from encounters 8 and 9. In this study, we reexamine the turbulence properties such as turbulence amplitude, anisotropy of the magnetic field variance, intermittency, and switchback strength using PSP data from encounters 8–19. The later orbits probe lower altitudes and experience sub-Alfvénic conditions more frequently, providing a greater statistical coverage to contrast sub- and super-Alfvénic solar wind. These later orbits also extend the observations from near solar minimum at launch to near solar maximum conditions. Also, by isolating the intervals where the solar wind speed is approximately equal to the Alfvén speed, we explore the transition in more detail. We show that the amplitude of the normalized magnetic field fluctuation is smaller for the sub-Alfvénic samples. While solar wind turbulence in general is shown to be anisotropic, the sub-Alfvénic samples are more anisotropic than the super-Alfvénic samples, in general. Further, we show that the sub- and super-Alfvénic samples do not show much distinction in terms of intermittency strength. Finally, consistent with prior results, we find no evidence for polarity reversing >90° switchbacks in the sub-Alfvénic solar wind.This work is supported at the University of Delaware in part by the PSP/ISOIS project through subcontract SUB0000165 from Princeton to the University of Delaware, and by the PUNCH project under subcontract N99054DS. J.G. is supported by the Delaware NASA Space Grant program grant number 80NSSC20M0045 at the University of Delaware. A.U., R.C., and S.A. are partially supported in part by NASA under grant No. 80NSSC22K1639. R.C. is also supported by NASA grant No. 80NSSC22K1020. This research is also supported in Thailand by the National Science and Technology Development Agency (NSTDA) and the National Research Council of Thailand (NRCT) through the High-Potential Research Team Grant Program (N42A650868)
Manipulating carbon, electron, and nitrogen exchange in syntrophic Clostridium co-cultures for robust, scalable, carbon-negative chemical production
No full textPapoutsakis, Eleftherios T.The classic acetone-butanol-ethanol (“ABE”) fermentation, which is based on Clostridium acetobutylicum, suffers from low carbon efficiency because 33-50% of carbon from the sugar substrate is lost as CO2 due to decarboxylation reactions in C. acetobutylicum’s central carbon metabolism. Gas fermentation, using acetogenic organisms such as Clostridium autoethanogenum or Clostridium ljungdahlii, can effectively assimilate gaseous carbon in the form of CO, but these organisms grow much more poorly on CO2 compared to CO, and, when grown on CO2, they make primarily acetate instead of more reduced products like alcohols. Our group has recently shown that cocultures between C. acetobutylicum and C. ljungdahlii have the potential to overcome many of the disadvantages associated with using only one of the two organisms in isolation. These C. acetobutylicum-C. ljungdahlii cocultures show improved carbon efficiency, large substrate and product portfolios, and unprecedented prokaryotic interspecies cell fusion events which involve large scale exchange of protein, RNA, and DNA. ☐ Building on and extending this work, this thesis describes an RNAseq study designed to uncover genes in both C. acetobutylicum and C. ljungdahlii which are important to the unique coculture phenotype, especially the interspecies cell fusion events. This study utilized a (to our knowledge) novel approach to test differential gene expression in response to direct microbial interspecies contact by isolating RNA from C. acetobutylicum and C. ljungdahlii grown in a transwell system, separated physically by a permeable membrane, and comparing it with RNA extracted from a normal mixed coculture. Using this methodology, we identified several genes from a putative Type VII secretion system operon in C. acetobutylicum which are upregulated by direct contact with C. ljungdahlii and which may be “fusogen” proteins involved in interspecies cell fusion. The gene expression data also revealed major differential regulation of amino acid metabolism (most especially of arginine, histidine, and tryptophan) in both C. acetobutylicum and C. ljungdahlii in coculture, which, when combined with amino acid secretion kinetics, helped to identify transfer of amino acids from C. acetobutylicum to C. ljungdahlii as a previously unknown layer of syntrophic cross-feeding between the coculture partners. Using this gene expression data, we also reconstructed a (to our knowledge) novel histidine catabolism pathway in C. ljungdahlii which substantially increases the energy efficiency of C. ljungdahlii growth on CO2 and demonstrated that C. ljungdahlii monocultures grown on CO2 with supplemental histidine grow much faster and to higher cell densities than controls grown only on CO2. ☐ Next, this thesis describes how the coculture between C. acetobutylicum and C. ljungdahlii can be repurposed for carbon-negative production of isopropanol from glucose (in which all of the glucose carbon is assimilated to soluble products along with some external CO2). This study presents detailed analysis showing how, due to interspecies electron exchange, the presence of the acetogen, C. ljungdahlii, enables C. acetobutylicum to synthesize much higher yields of acetone (which is then converted to isopropanol by C. ljungdahlii) in the coculture than would be possible in a C. acetobutylicum monoculture. Using high density, small scale pseudo perfusion experiments, we show that higher cell densities (and thus tighter interspecies proximity) strengthen this electron exchange to enable enhanced acetone and isopropanol yields. Finally, we demonstrate how, using a perfusion bioreactor, prolonged high density cocultures of C. acetobutylicum and C. ljungdahlii can produce isopropanol as the sole alcohol product from carbon-negative fermentation for over 100 hours with strong productivity. ☐ Next, this thesis describes how the coculture between C. acetobutylicum and C. ljungdahlii can be converted from obligate commensalism (C. ljungdahlii requires C. acetobutylicum for carbon in the form of CO2, but C. acetobutylicum does not require C. ljungdahlii for growth) to obligate mutualism (C. acetobutylicum requires C. ljungdahlii for nitrogen). This was achieved by designing a minimal medium with nitrate as the sole nitrogen source. C. acetobutylicum cannot use nitrate, but C. ljungdahlii can use nitrate and, when it has more than it needs, converts the excess nitrate to ammonia (a nitrogen source C. acetobutylicum can use) and secretes it into the culture medium. Based on this strategy, we test and demonstrate how varying the nitrogen source ratio in batch cultures and varying the nitrate feed rate in fed-batch cultures can be used to maintain a stable species ratio in the coculture, increase carbon efficiency, and improve yields of isopropanol and butanol. ☐ Finally, this thesis addresses an important open question in the gas fermentation literature: why do acetogens like Clostridium ljungdahlii show such a strong preference for growing on CO compared to CO2? We show that, though the presence of high energy substrates, such as fructose, can produce some form of catabolite repression, the true limitation on CO2 fixation by C. ljungdahlii (and similar acetogens) is the extremely low solubility of H2 (the electron donor for CO2 fixation in C. ljungdahlii) relative to CO2 and CO. By alleviating the H2 mass transfer limitation with increased mixing (via roller bottles) and high H2 partial pressure, we demonstrate (by far) the fastest doubling time ever recorded for C. ljungdahlii (or similar acetogens, to our knowlege) growing on only CO2 and H2, a doubling time equivalent to the fastest doubling time ever recorded by C. ljungdahlii (or similar acetogen) using CO. We discuss the significance of these findings for the future of gas fermentation and describe how coculturing acetogens with solventogenic organisms, such as C. acetobutylicum, can help to overcome H2 insolubility and potentially enable scalable and economically competitive CO2-negative fermentation.University of Delaware, Department of Chemical and Biomolecular EngineeringPh.D
Demystifying water and carbon cycling of ghost forests: harbingers of coastal change in a warming world
No full textChin, Yu-PingLevia, Delphis F.Coastal forests are undergoing rapid, climate-driven mortality and are transitioning from carbon sinks to emergent carbon sources under accelerating sea-level rise, fundamentally reorganizing how carbon moves through these ecosystems. This study investigates how canopy decline in sweet gum trees, Liquidambar styraciflua, alters the generation, molecular composition, and redox functionality of dissolved organic matter (DOM) exported via stemflow, a concentrated pathway that links the canopy directly to the forest floor. Stemflow acts as a focal point of water and carbon delivery, creating transient biogeochemical hotspots at the base of trees where rainfall is funneled and chemically transformed. The overarching hypothesis guiding this work is that sea level rise driven tree stress and mortality disrupt canopy-groundwater carbon coupling by altering physiological processes within trees and, in turn, changing the quantity, composition, and routing of DOC and water through coastal forest ecosystems. ☐ Hydrologic monitoring across healthy, moribund, and dead trees revealed that localized water inputs from stemflow drive sharp, event-scale increases in near-trunk groundwater levels. Around healthy trees, small storms below 16 mm produced threshold-like rises in water table elevation, whereas recharge was more uniform in areas around dead trees. Mean stemflow volumes declined from healthy trees to moribund trees and were negligible in dead trees. Despite DOC concentrations that were nearly double in dead-tree stemflow relative to healthy trees, total DOM flux per unit basal area declined by more than 70 %, indicating a collapse of canopy-mediated carbon delivery. Groundwater DOM near mortality zones exhibited stronger humic and terrestrial fluorescence and reduced microbial and protein-like components, consistent with reduced vertical carbon transfer and altered subsurface processing. ☐ Molecular analysis confirmed that sugars - including neutral sugars, amino sugars, and raffinose - constitute a major and previously overlooked fraction of stemflow carbon. Total neutral sugar concentrations averaged 871 ± 1434 µM, roughly ten times higher than global forest mean values. Diagnostic ratio1s of neutral sugars distinguished moribund trees, indicating cell-wall remodeling and microbial turnover under physiological stress. Cumulative sugar fluxes followed a unique and episodic trend with moribund trees, consistent with transient leakage during metabolic decline. The episodic release of these highly labile carbohydrates during the moribund phase represents a substantial carbon pulse to near-trunk soils, fueling short-lived microbial and nutrient turnover. As canopy function collapsed, both sugar and DOC fluxes diminished sharply, signaling the loss of concentrated, high-quality energy inputs that once sustained microbial hotspots at the forest base. ☐ Optical, lignin, and electrochemical analyses revealed that the oxidative state of stemflow DOM shifted systematically with canopy health. Healthy trees contained reduced, antioxidant-rich organic matter, whereas moribund and dead trees showed oxidized, lignin-dominated DOM and diminished antioxidant content. Lignin phenol composition shifted toward greater vanillyl and syringyl oxidation, reflected in higher lignin oxidation ratios, capturing a transition from reactive to inert carbon. These patterns show that canopy decline directly reduces the redox buffering potential of exported DOM, constraining the ability of near-surface soils to maintain reduced conditions during storm events. ☐ Tree mortality is redefining carbon and nutrient cycling in coastal forests by coupling hydrological, molecular, and electrochemical change. The collapse of stemflow generation, loss of biolabile carbon fluxes, and oxidation of canopy-derived DOM mark a transition in forest function from systems that actively cycle and reduce carbon to those that passively release it. By tracing these transformations from rainfall to groundwater, this work identifies stemflow as a sensitive indicator of forest physiological decline and a mechanistic link between canopy health and subsurface carbon reactivity. As sea level rises, coastal forests lose not only their canopy cover but also their capacity to mediate the flow of carbon and electrons that sustain ecosystem resilience.University of Delaware, Department of Civil, Construction and Environmental EngineeringPh.D
Photonic Integrated Circuits for Angle-of-Arrival and Frequency Estimation
No full textThis article was originally published in IEEE/OSA Journal of Lightwave Technology. The version of record is available at: https://doi.org/10.1109/JLT.2025.3638647
©2025 The Authors. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/This paper demonstrates concurrent spatial and spectral signal classification using two photonic integrated circuits (PICs) implemented in a 30-element Ka-band (26.5-40 GHz) antenna array. The received signals are coherently up-converted to the optical-domain using lithium niobate phase modulators. The up-converted RF signal is beamformed in a star-coupler PIC to instantaneously image angle-of-arrival to a single output channel that is amplified and input to an arrayed waveguide grating (AWG) PIC, which instantaneously channelizes the RF frequency into increments of approximately 1 GHz. A switching scheme is used to calibrate the AWG as well as alternate between frequency and beam location measurement. This work implements these devices in a radiometer that can localize RF beams both spatially and spectrally with minimal latency and computational requirements. Future applications will include advanced wireless communications and sensing.10.13039/100000104-National Aeronautics and Space Administration
10.13039/100000006-Office of Naval Research (Grant Number: N00014-23-1-2742
Red Noise–based False Alarm Thresholds for Astrophysical Periodograms via Whittle’s Approximation to the Likelihood
No full textThis article was originally published in The Astronomical Journal. The version of record is available at: https://doi.org/10.48550/arxiv.2512.18205
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence https://creativecommons.org/licenses/by/4.0/ . Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Astronomers who search for periodic signals using Lomb–Scargle periodograms rely on false alarm level (FAL) estimates to identify statistically significant peaks. Although FALs are often calculated from white noise models, many astronomical time series suffer from red noise. Prewhitening is a statistical technique in which a continuum model is subtracted from the log power spectrum estimate, after which the observer can proceed with a white-noise treatment. Here we present a prewhitening-based method of calculating frequency-dependent FALs. We fit power laws and autoregressive models of order 1 to each Lomb–Scargle periodogram by minimizing the Whittle approximation to the negative log-likelihood (NLL), then calculate FALs based on the best-fit model power spectrum. Our technique is a novel extension of the Whittle NLL to datasets with uneven time sampling. We demonstrate FAL calculations using observations of α Cen B, GJ 581, HD 192310, synthetic data from the radial velocity (RV) fitting challenge, and Kepler observations of a differential rotator. The Kepler data analysis shows that only true rotation signals are detected by red noise FALs, while white noise FALs suggest all spurious peaks in the low-frequency range are significant. A high-frequency sinusoid injected into α Cen B
observations exceeds the 1% red noise FAL despite having only 8.9% of the power of the dominant rotation signal. In a periodogram of HD 192310 RVs, peaks associated with differential rotation and planets are detected against the 5% red noise FAL without iterative model fitting or subtraction. The software for calculating red noise–based FALs is available on GitHub.This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (DOI: 10.26093/cds/vizier). The original description of the VizieR service was published in F. Ochsenbein et al. (2000). This work is supported by the National Science Foundation (NSF) grant 2307978. This material is based on work supported by the U.S. Department of Energy, Office of Science, under contract number DE-AC02-06CH11357.
Facilities: ESO:3.6m - European Southern Observatory's 3.6 meter Telescope (European Southern Observatory (ESO) 3.6m Telescope at La Silla Observatory), HET - McDonald Observatory's Hobby-Eberly Telescope (University of Texas, Austin 9.3m Hobby-Eberly Telescope at McDonald Observatory), Kepler - The Kepler Mission (NASA 0.95m Kepler Satellite Mission).
Software: Astropy (Astropy Collaboration et al. 2013,2018, 2022)
HPV vaccination intention among unvaccinated international and domestic college students in the U.S.: A cross-sectional survey
No full textThis article was originally published in Human Vaccines & Immunotherapeutics. The version of record is available at: https://doi.org/10.1080/21645515.2025.2601422
© 2026 The Author(s). Published with license by Taylor & Francis Group, LLC.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/),
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article
has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.
Version of record at: https://doi.org/10.1080/21645515.2025.2601422Nearly 85% of people will contract human papillomavirus (HPV) at some point in their lives. When given at the recommended ages, the HPV vaccine can prevent over 90% of HPV-related cancers. However, vaccination rates among young adults, including college students, remain low. Moreover, millions of international students enrolled in U.S. tertiary institutions may not have had access to preventive vaccines, including the HPV vaccine, in their countries of origin. This cross-sectional study conducted in October 2021, guided by the Theory of Planned Behavior (TPB), examined how attitudes, perceived behavioral control (PBC), and subjective norms relate to college students’ intentions to receive the HPV vaccine. Conducted at a U.S. university, the study recruited 199 unvaccinated students through the university registrar’s office and Amazon Mechanical Turk. Data were collected during the study period using an anonymous Qualtrics survey and analyzed using descriptive statistics, t-tests, and generalized linear models. We aimed to examine the influence of independent variables including attitude, subjective norms, and PBC, on the dependent variable, intention to receive the HPV vaccine. Of the 419 students who completed the survey, 199 (61 domestic and 138 international) who had not received the HPV vaccine were included in the study. The mean age of these participants was 21.27 y (SD = 3.29), with 135 males and 64 females. For both international and domestic students, attitudes toward HPV vaccination and subjective norms were significantly associated with higher vaccination intentions (international: attitude B = 0.11, p = .004; norms B = 0.38, p < .001; domestic: attitude B = 0.09, p = .027; norms B = 0.40, p < .001) in regression analyses. No significant differences were observed between the two groups in attitudes, perceived behavioral control, subjective norms, or vaccination intentions. These findings provide partial support for the TPB in explaining HPV vaccination intentions among college students. Public health initiatives and university-based programs may benefit from applying this framework by fostering positive attitudes and reinforcing supportive social norms. For routine practice, healthcare providers and campus health centers should integrate targeted education and outreach to improve vaccine uptake, particularly among international students. Future research should evaluate the effectiveness of TPB-based interventions in increasing actual vaccination rates and explore additional factors influencing vaccine intentions across diverse student populations.The authors would like to thank the Sherwood foundation [RN031103—LIUSF] who provided research funding to help us focus on the vaccination status among international and domestic students in the United States. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
The characterization and device fabrication of germanium-tin and titanium dioxide heterojunction
No full textZeng, YupingGeSn alloy, a group-IV semiconductor known for its tunable bandgap, offers promising performance in near- and mid-infrared optoelectronic applications. However, its low thermal stability and doping limitations also lead to challenges in device fabrication. To address the issue, Titanium dioxide (TiO2), with its reasonable chemical stability, capability for low-temperature deposition, and optical transparency in visible and near-infrared light, serves as a viable n-type component for GeSn alloy. ☐ In this research, a Heterojunction photodiode incorporating p-type GeSn and n-type TiO2 is fabricated to investigate the performance of GeSn and TiO2 incorporation. X-ray diffraction (XRD) is used to analyze the structural characteristics of various materials, while reciprocal space mapping (RSM) is employed to investigate the properties of GeSn films. Electrical measurements, such as current–voltage (I–V) analysis and CTLM testing, are conducted to evaluate device performance and contact resistance.University of Delaware, Department of Electrical and Computer EngineeringM.S
Unnamed Figures: Black Presence and Absence in the Early American North
No full text"As a preface to this manuscript, portions of this dissertation are reproduced, with permission from the American Folk Art Museum, from exhibition and publication text authored by me for the project Unnamed Figures: Black Presence and Absence in the Early American North. See Appendix A for the Museum's letter of permission."--Acknowledgements, page vi.Van Horn, JenniferDespite powerful historical scholarship disproving New England’s wishful thinking about its past, the presence of early Black history in the region is still commonly forgotten. This dissertation explores how, even in the context of such gaps in the archive and collective memory, images and objects from the seventeenth century through the nineteenth can further advance our understanding of Black experiences in early New England and serve as a mnemonic for raised awareness of these histories. Chapters focus on a series of depictions with Black figures in the margins, from a suite of overmantel landscapes by Revolutionary-era Connecticut artist Winthrop Chandler to portraits of white sitters featuring Black attendants made for or by Anglo-American New Englanders: Boston merchant Samuel Shrimpton, Rhode Island planter and counterfeiter John Potter, and Connecticut-born portraitist Ralph Earl. A handmade doll memorializing the formerly enslaved man Darby Vassall extends the discussion into antebellum Massachusetts, serving as a case study in white efforts to continue to control the narrative of Black history in the region. ☐ An examination of the idiosyncrasies of these images illuminates white artists’ and patrons’ conflicted relationships to slavery and Black presence, while simultaneously opening a window onto the lived experience of Black New Englanders. Through the inclusion of little-known Black stories in relationship to these objects, this dissertation brings the supposed periphery into the center, questioning the assumption that the primary motivation behind a work is the most important basis for investigation, and aiming to restore in some small measure the realities of New England’s multicultural history amid a predominantly white visual record that has all but erased it.University of Delaware, Department of Art HistoryPh.D
The multifaceted role of digital transformation in restaurant resilience
No full textThis article was originally published in International Journal of Contemporary Hospitality Management.. The version of record is available at: https://doi.org/10.1108/IJCHM-05-2025-0690
© Woojin Lee, SooCheong (Shawn) Jang and Hong Soon Kim. Published by Emerald Publishing Limited. This article is published under the Creative Commons Attribution (CC BY 4.0) licence. Anyone may reproduce, distribute, translate and create derivative works of this article (for both commercial and non-commercial purposes), subject to full attribution to the original publication and authors. The full terms of this licence may be seen at http://creativecommons.org/licences/by/4.0/Purpose – This study aims to investigate the impact of digital transformation (DT) on organizational resilience in the restaurant industry. By examining DT across front-of-house (FoH) and back-of-house (BoH) operations, this study analyzes how DT shapes resilience in terms of revenue, profitability and firm value.
Design/methodology/approach – DT is measured using text analysis of firm’s 10-K reports, combined with financial data from COMPUSTAT. Difference-in-differences and two-way panel regressions are used to examine resilience in terms of stability and flexibility. Findings – FoH DT significantly enhances both revenue stability and flexibility. BoH DT has a significant impact on profitability stability, and overall DT adoption enhances firm value stability during the pandemic.
Practical implications – Managers should leverage FoH DT to stabilize and accelerate revenue recovery during demand shocks and use BoH DT to reinforce cost-based stability, while clearly communicating DT initiatives to investors to enhance recognition of resilience value.
Originality/value – This study conceptualizes DT as a dual-function capability that simultaneously supports operational stability and adaptive flexibility, revealing differentiated DT effects across financial outcomes in the restaurant industry
Catholic persuasion: power and prestige in early American civil life
No full textHeyrman, Christine LeighMost Americans are familiar with histories of antebellum nativism and anti-Catholicism, but “Catholic Persuasion: Power and Prestige in Early American Civil Life,” offers a new narrative: the story of how the Revolution and the early republic created American Catholics by unleashing the forces that established them as Americans. By exploring Catholics’ ability to develop political, ideological, and cultural credibility through a concept I call political aesthetics, this dissertation explains how they secured prominence in the public sphere and civil society. Early American Catholics became culture sculptors, drawing together ideology and expression to join immediately in the mutual construction of American political culture. As Catholics honed their skills during the early national period, they won hearts and minds, demonstrating their political and cultural belonging. But success bred contempt, and the ironies of success lie at the heart of this history. As Catholics contributed to and mastered the American political and persuasive pose to secure their participation in civil life, their rising stature drew the ire of rivals. It is a history for which there is no historiography, an extraordinary moment in time that has been left out of our collective memory and national narrative. Not only was this world possible, but it existed.University of Delaware, Department of HistoryPh.D