Open Access Publications - Department of Physics and Astronomy
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Open access publications by faculty, postdocs, and graduate students in the Department of Physics and Astronomy.
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Item The LED calibration systems for the mDOM and D-Egg sensor modules of the IceCube Upgrade: Design, production, testing and use in module calibration(Journal of Instrumentation (JINST), 2025-11-28) Abbasi, R.; Ackermann, M.; Adams, J.; et al.: The IceCube Neutrino Observatory, instrumenting about 1km3 of deep, glacial ice at the geographic South Pole, is due to be enhanced with the IceCube Upgrade. The IceCube Upgrade, to be deployedduringthe2025/26Antarcticsummerseason,willconsistofsevennewstringsofphotosensors, densely embedded near the bottom center of the existing array. Aside from a world-leading sensitivity to neutrino oscillations, a primary goal is the improvement of the calibration of the optical properties of the instrumented ice. This calibration will be applied to the entire archive of IceCube data, improving the angular and energy resolution of the detected neutrino events. For this purpose, the Upgrade strings include a host of new calibration devices. Aside from dedicated calibration modules, several thousand LED flashers have been incorporated into the photosensor modules. We describe the design, production, and testing of these LED flashers before their integration into the sensor modules as well as the use of the LED flashers during lab testing of assembled sensor modules. Keywords: Analogue electronic circuits; Detector alignment and calibration methods (lasers, sources, particle-beams); Instrumentation and methods for time-of-flight (TOF) spectroscopyItem Energy transfer and conversion in magnetic reconnection: Observation and simulation(Physics of Plasmas, 2025-11-19) Roy, S.; Bandyopadhy R.; Adhikari, S.; Yang, Y; Matthaeus, W. H.One of the central problems in collisionless plasma turbulence is to understand the nature of the cross-scale energy transfer and dissipation occurring at kinetic scales. Magnetic reconnection plays an important role in dissipating energy and driving energy transfer in these systems. However, for reconnection, a detailed picture of the fluxes of energy in its several forms, and the conversion among them, until now remains unclear. In this study, a scale filtering method is adopted to explore how energy is converted between different forms and transferred across scales in turbulent magnetic reconnection using a combination of Magnetospheric Multiscale observations and particle-in-cell simulations. Two novel findings of this paper are that both ion and electron dissipation start to occur at sub-ion scale, at nearly same scale, and that most of the energy cascade due to reconnection is carried by the electron fluid.Item Searches for baryon number violation in neutrino experiments: a white paper(Journal of Physics G: Nuclear and Particle Physics, 2024-01-23) Dev, S B; Koerner, L W; Saad, S; Antusch, S; Askins, M; Babu, K S; Barrow, J L; Chakrabortty, J; de Gouvêa, A; Djurcic, Z; Girmohanta, S; Gogoladze, I; Goodman, M C; Higuera, A; Kalra, D; Karagiorgi, G; Kearns, E; Kudryavtsev, V A; Kutter, T; Malinský, M; Martinez Caicedo, D A; Mohapatra, R N; Nath, P; Nussinov, S; Ochoa-Ricoux, J P; Pec, V; Rafique, A; Rodriguez Rondon, J; Shrock, R; Sobel, H W; Stoke, T; Strait, M; Svoboda, R; Syritsyn, S; Takhistov, V; Tsai,Y-T; Wendell, R A; Zhou, aY-LBaryon number conservation is not guaranteed by any fundamental symmetry within the standard model, and therefore has been a subject of experimental and theoretical scrutiny for decades. So far, no evidence for baryon number violation has been observed. Large underground detectors have long been used for both neutrino detection and searches for baryon number violating processes. The next generation of large neutrino detectors will seek to improve upon the limits set by past and current experiments and will cover a range of lifetimes predicted by several Grand Unified Theories. In this White Paper, we summarize theoretical motivations and experimental aspects of searches for baryon number violation in neutrino experiments.Item Probing Voltage- and Electrolyte-Dependent Monolayer Dynamics with 2D-IR Spectroscopy(Journal of the American Chemical Society, 2025-10-24) Jeong, Wonjae; Billings, Kyle R.; Biswas, Aritri; Ryan, Matthew J.; Kwac, Kijeong; Cho, Minhaeng; Kananenka, Alexei A.; Zanni, Martin T.Little is known about structural dynamics at electrode surfaces under applied potential. Here, we report 2D-IR spectra of a 4-mercaptobenzonitrile monolayer on a gold electrode, revealing chemical exchange between two subensembles on sub- to tens-of-picoseconds time scales. Dynamics are measured in 100 mM MgCl2, LiCl, and KCl at −200 and +300 mV vs Ag/AgCl. At +300 mV, all electrolytes exhibited ≥48 ps exchange, while at −200 mV, the slower exchange component ranged from ≥33 to ≥43 ps. The dynamics correlate with ion concentration, according to radial distribution functions calculated from molecular dynamics simulations, suggesting that local ion densities, regardless of valency or sign, slow dynamics. Results show solvation, electric double layer formation, and monolayer reorientation. This work reveals how electrolyte composition modulates molecular reorientation and hydrogen bonding at functionalized electrodes.Item Mechanism of Anomalous Anisotropic Colossal Magnetoresistance in Quasi-2D Mn3Si2Te6 Bulk Single Crystal(Advanced Science, 2025-10-14) Li, Shiqi; He, Xiong; Li, Shuai; Li, Tianyi; Zhang,Wenhao; Yi, Lizhi; Lu,Guangduo; Xia, Zhengcai; Xu, Yunli; Xiao, John Q; Pan, LiqingMn3Si2Te6, quasi-2D ferrimagnetic semiconductor, exhibits anomalous saturated colossal magnetoresistance (CMR) only when a magnetic field is applied along its magnetic hard magnetization axis, suggesting unconventional underlying physics and promising potential for spintronic applications. However, the intrinsic mechanism behind this anomalous anisotropic CMR remain unresolved. In this work, the temperature and angular dependencies of magnetoresistance (MR) in high-quality Mn3Si2Te6 single crystals are systematically investigated. The MR measured within the easy ab-plane shows no saturation, whereas a large negative saturation MR of ≈ −100% is observed along the hard magnetization c-axis below the Curie temperature. To explain this behavior, a novel model is proposed in which in-plane magnetic fields induce quasi-2D magnetotransport, while out-of-plane fields promote a transition to 3D transport. Notably, when the c-axis field exceeds the demagnetizing field, the alignment between spin-polarized carriers and magnetic moments significantly suppresses scattering. The results challenge the applicability of the chiral orbital currents (COC) model in Mn3Si2Te6 single crystals and establish a new framework for controlling the CMR effect in layered magnets, offering a pathway toward future spintronic technologies.Item Establishment of a Mid-Latitude Neutron Monitoring Site at Mt. Gamak in Korea(Journal of Astronomy and Space Sciences, 2025-09-25) Jung, Jongil; Kwak, Young-Sil; Sohn, Jongdae; Oh, Suyeon; Yi, Yu; Kim, Yongkyun; Choi, Seonghwan; Evenson, PaulCosmic ray neutron monitors (NMs) are ground-based detectors that measure secondary neutrons produced by primary cosmic ray particles in the energy range of approximately 500 MeV to several GeV. South Korea operates two NMs: one at Jang Bogo Station in Antarctica and another recently relocated from Daejeon to Mt. Gamak in Geochang, now managed by the Korea Astronomy and Space Science Institute (KASI). Mt. Gamak is geographically comparable to the former Daejeon site, located approximately 100 km to the southeast. The NM at Mt. Gamak’s altitude is approximately 925 meters, which is about four times higher than that of the Daejeon site. In addition, the average atmospheric pressure at Mt. Gamak was 915.9 hPa, about 85 hPa lower than that of Daejeon. The barometric coefficient was approximately –0.7101%/hPa. As a result, the NM at Mt. Gamak records more than twice the count rate observed at the Daejeon site. Given these conditions, the Mt. Gamak NM is expected to play a crucial role in cosmic ray research and in monitoring the solar and space environment in the mid-latitude region.Item Revealing the Accelerating Wind in the Inner Region of Colliding-wind Binary WR 112(The Astronomical Journal, 2025-09-12) Monnier, John D.; Yinuo, Han; Corcoran, Michael F.; Bloot, Sanne; Callingham, Joseph R.; Danchi, William; Edwards, Philip G; Greenhill, Lincoln; Hamaguchi, Kenji; Hankins, Matthew J.; Lau, Ryan; Miller, Jon M.; Moffat, Anthony F. J.; Ruane, Garreth; Russell, Christopher M.P.; Soulain, Anthony; Tinyanont, Samaporn; Tuthill, Peter; Wanga, Jason J.; Williams, Peredur M.Colliding winds in massive binaries generate X-ray-bright shocks, synchrotron radio emission, and sometimes even dusty “pinwheel” spirals. We report the first X-ray detections of the dusty WC+O binary system WR 112 from Chandra and Swift, alongside 27 yr of Very Large Array/Australia Telescope Compact Array radio monitoring and new diffraction-limited Keck images. Because we view the nearly circular orbit almost edge-on, the colliding-wind zone alternates between heavy Wolf–Rayet wind self-absorption and near-transparent O-star wind foreground each 20 yr orbit, producing phase-locked radio and X-ray variability. This scenario leads to a prediction that the radio spectral index is flatter from a larger nonthermal contribution around the radio intensity maximum, which indeed was observed. Existing models that assume a single dust-expansion speed fail to reproduce the combined infrared (IR) geometry and radio light curve. Instead, we require an accelerating postshock flow that climbs from near-stationary to ∼1350 km s−1 in about one orbital cycle, naturally matching the IR spiral from 5″ down to within 0".1, while also fitting the phase of the radio brightening. These kinematic constraints supply critical boundary conditions for future hydrodynamic simulations, which can link hot-plasma cooling, nonthermal radio emission, X-ray spectra, and dust formation in a self-consistent framework. WR 112 thus joins WR 140, WR 104, and WR 70-16 (Apep) as a benchmark system for testing colliding-wind physics under an increasingly diverse range of orbital architectures and physical conditions.Item Terahertz and High-Harmonic Radiation from Ultrafast Light Subgap or Above-Gap Driving of Spin-Orbit Proximitized Antiferromagnetic Mott Insulator(Physical Review Letters, 2025-08-22) Garcia-Gaitan, Federico; Feiguin, Adrian E.; Nikolić, Branislav K.Ultrafast light-driven strongly correlated antiferromagnetic insulators, such as prototypical NiO with a large Mott energy gap ≃4 eV, have recently attracted experimental attention using photons of both subgap [H. Qiu et al., Nat. Phys. 17, 388 (2021)] and above-gap energy [K. Gillmeister et al., Nat. Commun. 11, 4095 (2020)]. In the former context, which is also of great interest to applications, emission of terahertz (THz) radiation is observed from NiO/Pt bilayers, where heavy metal (HM) Pt introduces strong spin-orbit coupling (SOC) effects. However, in contrast to amply studied spintronic THz emitters using femtosecond laser pulse (fsLP)-driven FM/HM (where FM represents a ferromagnetic metal of the conventional type, such as Fe, Ni, or Co) bilayers, where ultrafast demagnetization takes place and is directly related to THz emission, microscopic mechanisms of electromagnetic (EM) radiation from NiO/HM bilayers remain obscure, as the total magnetization of NiO is zero before fsLP application. We employ the two-orbital Hubbard-Hund-Heisenberg model and study, via numerically exact quantum many-body methods, the dynamics of its Néel vector and nonequilibrium magnetization. This reveals nonclassical (i.e., not describable by the Landau-Lifshitz equation) dynamics of Néel vector and nonequilibrium magnetization, changing only in length while not rotating, where the former is substantially reduced in the case of above-gap fsLPs. Additionally, we compute EM radiation by time dependence of magnetization or of local charge currents, finding that both contributions are significant in the THz frequency range only in NiO with proximity SOC introduced by the HM layer. Outside the THz range, we find an integer high-harmonic generation, as well as unusual noninteger harmonics for the above-gap fsLP pump.Item Magnetospheric multiscale observations of electromagnetic ion cyclotron waves associated with cold ion heating in the Earth’s magnetosphere(AIP Advances, 2025-07-25) Abid, A. A.; Qamar, K.; Ahmad, Nisar; Waheed, A; Hussain, M.S.; Qureshi, M. N. S.; Esmaeili, Amin; Alotaibi, B.M; Ishaque, Ommair; Li, Xiaojie; Yao, Guang-Rui; Ji, Yan-FangElectromagnetic ion cyclotron (EMIC) waves play a significant role in shaping the dynamics of Earth’s magnetosphere. On September 13, 2015, EMIC wave activity within the proton band was detected in the inner magnetosphere through observations made by the Magnetospheric Multiscale mission. These waves are understood to arise due to thermal anisotropy in populations of hot protons. Data indicate that EMIC waves extend across a broad range of L shell values in the aftermath of three successive geomagnetic storms, implying that the free energy source responsible for their generation is most likely linked to the injection of energetic ions during storm time intervals. Consequently, it is important to include EMIC wave effects into radiation belt modeling, especially during extended magnetic storm periods and the substorm recovery phase when electric fields are produced. When EMIC waves are intense enough, cold protons and helium ions with low energy can be activated by them. During one observed event, both perpendicular and parallel heating of hydrogen ions by the hydrogen band EMIC waves were recorded. Furthermore, these hydrogen-band EMIC waves were also found to contribute to the heating of helium ions. As a result of this heating mechanism, ions that were previously below detection thresholds become observable, accompanied by a rise in both number density as well as temperature anisotropy of hydrogen and helium ions within the low-energy range of 1–100 eV.Item Preface to theme issue about multi-messenger gravitational lensing(Philosophical Transactions of the Royal Society A, 2025-03-17) Smith, Graham P.; Hendry, Martin A.; Bianco, FedericaMulti-messenger gravitational lensing combines multi-messenger astronomy with gravitational lensing. The first gravitational lensing observations occurred during the 1919 total solar eclipse, and were published in the Philosophical Transactions of the Royal Society A, thus providing early support for Einstein’s theory of General Relativity [1]. Systematic observations of gravitational lenses—beyond the Solar System and the Local Group—began decades later in the late twentieth century [2–4]. The ground-breaking detections of neutrinos from the Sun and SN1987A occurred on a similar timescale [5–9], marking the dawn of multi-messenger astronomy. This field experienced a spectacular renaissance three decades later when gravitational waves (GWs), and electromagnetic (EM) radiation from gamma rays to radio waves were detected from a binary neutron star (BNS) merger in 2017 [10,11]. The first confirmed discoveries of gravitationally lensed transient sources, and the first detection of neutrinos from an extragalactic source were both achieved in parallel with the early GW discoveries [12–14].Item Lipid–GPCR interactions in an asymmetric plasma membrane model(Faraday Discussions, 2025-01-30) Ji, Jingjing; Lyman, EdwardWe report simulations and analysis of the A2A adenosine receptor in its fully active state, in two different membrane environments. The first is a model in which the lipids are distributed asymmetrically according to recent lipidomics, simulations, and biophysical measurements, which together establish the distribution of lipids and cholesterol between the two leaflets. The second is the symmetrized version, which captures the membrane state following loss of lipid asymmetry. By comparing lipid–protein interactions between these two cases we show that solvation by phosphatidyl serine (PS) is insensitive to the loss of asymmetry—an abundance of positively charged sidechains around the cytoplasmic side of the receptor enriches solvation by PS in both membrane states. Cholesterol interactions are sensitive to the loss of asymmetry, with the abundance of cholesterol in the exoplasmic leaflet driving long-lived cholesterol interactions in the asymmetric state. However, one cholesterol interaction site on helix 6 is observed in both cases, and was also observed in earlier work with different membrane models, supporting its identification as a bona fide cholesterol binding site.Item Measurement of Atmospheric Neutrino Oscillation Parameters Using Convolutional Neural Networks with 9.3 Years of Data in IceCube DeepCore(Physical Review Letters, 2025-03-07) Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguilar, J. A.; Ahlers, M.; Alameddine, J. M.; Amin, N. M.; Andeen, K.; et al.The DeepCore subdetector of the IceCube Neutrino Observatory provides access to neutrinos with energies above approximately 5 GeV. Data taken between 2012 and 2021 (3387 days) are utilized for an atmospheric 𝜈𝜇 disappearance analysis that studied 150 257 neutrino-candidate events with reconstructed energies between 5 and 100 GeV. An advanced reconstruction based on a convolutional neural network is applied, providing increased signal efficiency and background suppression, resulting in a measurement with both significantly increased statistics compared to previous DeepCore oscillation results and high neutrino purity. For the normal neutrino mass ordering, the atmospheric neutrino oscillation parameters and their 1𝜎 errors are measured to be Δm2 32=2.40+0.05−0.04×10−3 eV2 and sin2𝜃23=0.54+0.04−0.03. The results are the most precise to date using atmospheric neutrinos, and are compatible with measurements from other neutrino detectors including long-baseline accelerator experiments.Item Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory(The Astrophysical Journal, 2025-03-07) Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguado, T.; Aguilar, J. A.; Ahlers, M.; Alameddine, J. M.; Amin, N. M.; Andeen, K.; et al.We analyzed the 7.92 × 1011 cosmic-ray-induced muon events collected by the IceCube Neutrino Observatory from 2011 May 13, when the fully constructed experiment started to take data, to 2023 May 12. This data set provides an up-to-date cosmic-ray arrival direction distribution in the Southern Hemisphere with unprecedented statistical accuracy covering more than a full period length of a solar cycle. Improvements in Monte Carlo event simulation and better handling of year-to-year differences in data processing significantly reduce systematic uncertainties below the level of statistical fluctuations compared to the previously published results. We confirm the observation of a change in the angular structure of the cosmic-ray anisotropy between 10 TeV and 1 PeV, more specifically in the 100–300 TeV energy range. For the first time, we analyzed the angular power spectrum at different energies. The observed variations of the power spectra with energy suggest relatively reduced large-scale features at high energy compared to those of medium and small scales. The large volume of data enhances the statistical significance at higher energies, up to the PeV scale, and smaller angular scales, down to approximately 6° compared to previous findings.Item Engineering corner states by coupling two-dimensional topological insulators(Physical Review B, 2025-01-06) Liu, Lizhou; An, Jiaqi; Ren, Yafei; Zhang, Ying-Tao; Qiao, Zhenhua; Niu, QianWe theoretically find that the second-order topological insulator, i.e., corner states, can be engineered by coupling two copies of two-dimensional ℤ2 topological insulators with opposite spin helicities. As concrete examples, we utilize Kane-Mele models (i.e., graphene with intrinsic spin-orbit coupling) to realize the corner states by setting the respective graphenes as ℤ2 topological insulators with opposite intrinsic spin-orbit couplings. To exhibit its universality, we generalize our findings to other representative ℤ2 topological insulators, e.g., the Bernevig-Hughes-Zhang model. An effective model is presented to reveal the physical origin of the corner states. We further show that the corner states can also be designed in other topological systems, e.g., by coupling quantum anomalous Hall systems with opposite Chern numbers. Our work suggests that interlayer coupling can be treated as a simple and efficient strategy to drive two-dimensional lower-order topological insulators to the higher-order ones.Item Dispersionless Nonhybrid Density Functional(Journal of Chemical Theory and Computation, 2025-02-11) Rehman, Atta Ur; Szalewicz, KrzysztofA dispersion-corrected density functional theory (DFT+D) method has been developed. It includes a nonhybrid dispersionless generalized gradient approximation (GGA) functional paired with a literature-parametrized dispersion function. The functional’s 9 adjustable parameters were optimized using a training set of 589 benchmark interaction energies. The resulting method performs better than other GGA-based DFT+D methods, giving a mean unsigned error of 0.33 kcal/mol. It even performs better than some more expensive meta-GGA or hybrid dispersion-corrected functionals. An important advantage of using the new functional is that its dispersion energy given by the D component is very close to the true dispersion energy at all intermolecular separations, whereas in other similarly accurate DFT+D approaches, such a dispersion contribution in the van der Waals minimum region is only a small fraction of the true value.Item First Observation of the Complete Rotation Period of the Ultraslowly Rotating Magnetic O Star HD 54879(The Astrophysical Journal, 2024-12-04) Erba, C.; Folsom, C. P.; David-Uraz, A.; Wade, G. A.; Seadrow, S.; Bellotti, S.; Fossati, L.; Petit, V.; Shultz, M. E.HD 54879 is the most recently discovered magnetic O-type star. Previous studies ruled out a rotation period shorter than 7 yr, implying that HD 54879 is the second most slowly rotating known magnetic O-type star. We report new high-resolution spectropolarimetric measurements of HD 54879, which confirm that a full stellar rotation cycle has been observed. We derive a stellar rotation period from the longitudinal magnetic field measurements of P = 2562 +63 -58 days (about 7.02 yr). The radial velocity of HD 54879 has been stable over the last decade of observations. We explore equivalent widths and longitudinal magnetic fields calculated from lines of different elements, and conclude the atmosphere of HD 54879 is likely chemically homogeneous, with no strong evidence for chemical stratification or lateral abundance nonuniformities. We present the first detailed magnetic map of the star, with an average surface-magnetic-field strength of 2954 G, and a strength for the dipole component of 3939 G. There is a significant amount of magnetic energy in the quadrupole components of the field (23%). Thus, we find HD 54879 has a strong magnetic field with a significantly complex topology.Item 2025 roadmap on 3D nanomagnetism(Journal of Physics: Condensed Matter, 2025-02-19) Gubbiotti, Gianluca; Barman, Anjan; Ladak, Sam; Bran, Cristina; et al.The transition from planar to three-dimensional (3D) magnetic nanostructures represents a significant advancement in both fundamental research and practical applications, offering vast potential for next-generation technologies like ultrahigh-density storage, memory, logic, and neuromorphic computing. Despite being a relatively new field, the emergence of 3D nanomagnetism presents numerous opportunities for innovation, prompting the creation of a comprehensive roadmap by leading international researchers. This roadmap aims to facilitate collaboration and interdisciplinary dialogue to address challenges in materials science, physics, engineering, and computing. The roadmap comprises eighteen sections, roughly divided into three blocks. The first block explores the fundamentals of 3D nanomagnetism, focusing on recent trends in fabrication techniques and imaging methods crucial for understanding complex spin textures, curved surfaces, and small-scale interactions. Techniques such as two-photon lithography and focused electron beam-induced deposition enable the creation of intricate 3D architectures, while advanced imaging methods like electron holography and synchrotron x-ray tomography provide nanoscale spatial resolution for studying magnetization dynamics in three dimensions. Various 3D magnetic systems, including coupled multilayer systems, artificial spin-ice, magneto-plasmonic systems, topological spin textures, and molecular magnets are discussed. The second block introduces analytical and numerical methods for investigating 3D nanomagnetic structures and curvilinear systems, highlighting geometrically curved architectures, interconnected nanowire systems, and other complex geometries. Finite element methods are emphasized for capturing complex geometries, along with direct frequency domain solutions for addressing magnonic problems. The final block focuses on 3D magnonic crystals and networks, exploring their fundamental properties and potential applications in magnonic circuits, memory, and spintronics. Computational approaches using 3D nanomagnetic systems and complex topological textures in 3D spintronics are highlighted for their potential to enable faster and more energy-efficient computing.Item Dynamic Imprints of Colliding-wind Dust Formation from WR 140(The Astrophysical Journal Letters, 2025-01-20) Lieb, Emma P.; Lau, Ryan M.; Hoffman, Jennifer L.; Corcoran, Michael F.; Marin, Macarena Garcia; Gull, Theodore R.; Hamaguchi, Kenji; Han, Yinuo; Hankins, Matthew J.; Jones, Olivia C.; Madura, Thomas I.; Marchenko, Sergey V.; Matsuhara, Hideo; Millour, Florentin; Moffat, Anthony F. J.; Morris, Mark R.; Morris, Patrick W.; Onaka, Takashi; Perrin, Marshall D.; Rest, Armin; Richardson, Noel; Russell, Christopher M. P.; Sanchez-Bermudez, Joel; Soulain, Anthony; Tuthill, Peter; Weigelt, Gerd; William, Peredur M.Carbon-rich Wolf–Rayet (WR) binaries are a prominent source of carbonaceous dust that contribute to the dust budget of galaxies. The "textbook" example of an episodic dust-producing WR binary, WR 140 (HD 193793), provides us with an ideal laboratory for investigating the dust physics and kinematics in an extreme environment. This study is among the first to utilize two separate JWST observations, from Cycle 1 ERS (2022 July) and Cycle 2 (2023 September), to measure WR 140's dust kinematics and confirm its morphology. To measure the proper motions and projected velocities of the dust shells, we performed a novel point-spread function (PSF) subtraction to reduce the effects of the bright diffraction spikes and carefully aligned the Cycle 2 to the Cycle 1 images. At 7.7 μm, through the bright feature common to 16 dust shells (C1), we find an average dust shell proper motion of 390 ± 29 mas yr−1, which equates to a projected velocity of 2714 ± 188 km s−1 at a distance of 1.64 kpc. Our measured speeds are constant across all visible shells and consistent with previously reported dust expansion velocities. Our observations not only prove that these dusty shells are astrophysical (i.e., not associated with any PSF artifact) and originate from WR 140, but also confirm the "clumpy" morphology of the dust shells, in which identifiable substructures within certain shells persist for at least 14 months from one cycle to the next. These results support the hypothesis that clumping in the wind collision region is required for dust production in WR binaries.Item Phonons reveal coupled cholesterol-lipid dynamics in ternary membranes(Biophysical Journal, 2024-12-03) Fitzgerald, James E.; Soloviov, Dmytro; Cai, Yong Q.; Heberle, Frederick A.; Ishikawa, Daisuke; Baron, Alfred Q.R.; Bolmatov, Dima; Zhernenkov, Mikhail; Lyman, Edward R.Experimental studies of collective dynamics in lipid bilayers have been challenging due to the energy resolution required to observe these low-energy phonon-like modes. However, inelastic x-ray scattering (IXS) measurements—a technique for probing vibrations in soft and biological materials—are now possible with sub-meV resolution, permitting direct observation of low-energy, phonon-like modes in lipid membranes. Here, IXS measurements with sub-meV energy resolution reveal a low-energy optic-like phonon mode at roughly 3 meV in the liquid-ordered ðLoÞ and liquid-disordered phases of a ternary lipid mixture. This mode is only observed experimentally at momentum transfers greater than 5 nm 1 in the Lo system. A similar gapped mode is also observed in all-atom molecular dynamics (MD) simulations of the same mixture, indicating that the simulations accurately represent the fast, collective dynamics in the L o phase. Its optical nature and the Q range of the gap together suggest that the observed mode is due to the coupled motion of cholesterol-lipid pairs, separated by several hydrocarbon chains within the membrane plane. Analysis of the simulations provides molecular insight into the origin of the mode in transient, nanoscale substructures of hexagonally packed hydrocarbon chains. This nanoscale hexagonal packing was previously reported based on MD simulations and, later, by NMR measurements. Here, however, the integration of IXS and MD simulations identifies a new signature of the Lo substructure in the collective lipid dynamics, thanks to the recent confluence of IXS sensitivity and MD simulation capabilities.Item Electron Dissipation and Electromagnetic Work(JGR: Space Physics, 2024-10-14) Yang, Yan; Adhikari, Subash; Matthaeus, William H.With the increase in technical capabilities of computer simulation in recent years, it has become feasible to quantify the degradation of fluid scale plasma and electromagnetic energies in favor of increases of internal energies. While it is understood that electromagnetic energy can be exchanged with fluid scale velocities, it is the pressure strain interaction that exchanges energy between fluid motions and internal energy. Here using simulations of both turbulence and reconnection we show that for electrons, the pressure strain and electromagnetic work are closely related and are frequently comparable when appropriate time and spatial averaging is applied. Otherwise, the instantaneous spatial averaged pressure strain and electromagnetic work are nearly equal for slowly evolving systems, like the reconnection case, while they differ significantly in rapidly evolving systems, like the turbulence case. This clarifies the relationship between these two quantities, which are each frequently used as measures of dissipation. Key Points - Time integrated volume averaged electromagnetic work does not formally or generally correspond to dissipation - Due to small electron mass, time integrated volume averaged pressure strain and electromagnetic work are nearly equal for electrons - Differences between instantaneous electromagnetic work and pressure strain can be considerable, but for electrons, these average to zero Plain Language Summary The electromagnetic field changes the fluid velocity of each type of plasma particle. Meanwhile, the pressure of each plasma species, interacts with nonuniform fluid velocities to produce heat. The intermediate steps are in general, complicated, but because electrons are so light, a special simplifying approximation holds, equating properly averaged electromagnetic work on electrons to the rate of increase of electron internal energy. This result may help clarify differences in how the reconnection and turbulence communities quantify “dissipation”.