Search

White dwarfs (WDs) showing transits from orbiting planetary debris provide significant insights into the structure and dynamics of debris disks. This is a rare class of objects with only eight published systems. In this work, we perform a systematic search for such systems within 500 pc in the Gaia-eDR3 catalog of WDs using the light curves from the Zwicky Transient Facility (ZTF) and present six new candidates. Our selection process targets the top 1% most photometrically variable sources identified using a combined variability metric from ZTF and Gaia eDR3 photometry, boosted by a metric space we define using von Neumann statistics and Pearson-Skew as a novel discovery tool to identify these systems. This is followed by optical spectroscopic observations of visually selected variables to confirm metal pollution. Four of the six systems show long-timescale photometric variability spanning several months to years, resulting either from long-term evolution of transit activity or dust and debris clouds at wide orbits. Among them, WD J1013-0427 shows an indication of reddening during the long-duration dip. Interpreting this as dust extinction makes it the first system to indicate an abundance of small dust grains (radius $\lesssim$$0.3~{\rm \mu m}$) in the occulting material. The same object also shows metal emission lines that map an optically thick eccentric gas disk orbiting within the star's Roche limit. For each candidate, we infer the abundances of the photospheric metals and estimate accretion rates. We show that transiting debris systems tend to have higher inferred accretion rates compared to the general population of metal-polluted WDs. Growing the number of these systems will further illuminate such comparative properties in the near future. Separately, we also serendipitously discovered an AM CVn showing a very long-duration outburst $-$ only the fourth such system to be known., Comment: 28 pages, 16 figures, 6 tables. Version after first PASP review. Resubmitting in a week. Comments are Welcome!

Drone-based beam measurements are a promising avenue to tackle the critical challenge of calibration for 21 cm cosmology telescopes. In this paper, we introduce a new drone-based calibration system for 400-800 MHz radio observatories, describing its instrumentation and first deployment. We discuss measurements of the TONE array, a CHIME/FRB outrigger pathfinder, and present results, including full 2D high spatial resolution beam maps in both co- and cross-polarization, as well as comparisons to simulations. The polarized beam maps cover a 70 degree by 70 degree grid, capturing the first two sidelobes and measuring the TONE main beam and first sidelobe with 7-9% statistical errors. We investigate polarization angle alignment with frequency, finding significant polarization leakage in the TONE antennas at frequencies above 600 MHz, and a polarization axis rotation with frequency. We describe statistical and systematic errors, as well as measurements of radio frequency interference from the drone and equipment. Our drone system is the first to incorporate a broad-band switched calibration source in the drone payload, enabling background subtraction and direct measurements of the RFI emitted by the drone. The results presented are the first drone-based 2D measurements of cross-polar beam structure and of polarization alignment of an array. The high frequency and spatial resolution achieved with this system have revealed the rich structure of the beam of each antenna, and enabled comparisons between individual dishes and to electromagnetic simulations., Comment: Submitted to ApJ

Carbon stars (with atmospheric C/O$>1$) range widely in temperature and luminosity, from low mass dwarfs to asymptotic giant branch stars (AGB). The main sequence dwarf carbon (dC) stars have inherited carbon-rich material from an AGB companion, which has since transitioned to a white dwarf. The dC stars are far more common than C giants, but no reliable estimates of dC space density have been published to date. We present results from an all-sky survey for carbon stars using the low-resolution XP spectra from Gaia DR3. We developed and measured a set of spectral indices contrasting C$_{\rm 2}$ and CN molecular band strengths in carbon stars against common absorption features found in normal (C/O$<1$) stars such as CaI, TiO and Balmer lines. We combined these indices with the XP spectral coefficients as input to supervised machine-learning algorithms trained on a vetted sample of known C stars from LAMOST. We describe the selection of the carbon candidate sample, and provide a catalog of 43,574 candidates dominated by cool C giants in the Magellanic Clouds and at low galactic latitude in the Milky Way. We report the confirmation of candidate C stars using intermediate ($R\sim 1800$) resolution optical spectroscopy from the Fred Lawrence Whipple Observatory, and provide estimates of sample purity and completeness. From a carefully-vetted sample of over 600 dCs, we measure their local space density to be $\rho_0\,=\,1.96^{+0.14}_{-0.12}\times10^{-6}\,\text{pc}^{-3}$ (about one dC in every local disk volume of radius 50\,pc), with a relatively large disk scale height of $H_z\,=\,856^{+49}_{-43}\,$pc., Comment: Accepted to ApJ, 25 pages, 9 figures, 10 tables

Heavy axions that couple to both quantum electrodynamics and quantum chromodynamics with masses on the order of MeV - GeV and high-scale decay constants in excess of $\sim$$10^8$ GeV may arise generically in e.g. axiverse constructions. In this work we provide the most sensitive search to-date for the existence of such heavy axions using Fermi-LAT data towards four recent supernovae (SN): Cas A, SN1987A, SN2023ixf, and SN2024ggi. We account for heavy axion production in the proto-neutron-star cores through nuclear and electromagnetic processes and then the subsequent decay of the axions into photons. While previous works have searched for gamma-rays from SN1987A using the Solar Maximum Mission that observed SN1987A during the SN itself, we show that using Fermi Large Area Telescope data provides an approximately five orders of magnitude improvement in flux sensitivity for axions with lifetimes larger than around 10 years. We find no evidence for heavy axions and exclude large regions of previously-unexplored parameter space., Comment: 11 + 18 pages, 2 + 17 figures, 0 + 3 tables, video abstract at https://youtu.be/sv0qHuz-2Y4

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is an upcoming radio interferometric telescope designed to constrain dark energy through the 21cm intensity mapping of Baryon Acoustic Oscillations (BAO). Instrumental systematics must be controlled and carefully characterized to measure the 21cm power spectrum with fidelity and achieve high-precision constraints on the cosmological parameters. The chromaticity of the primary beam is one such complicated systematic, which can leak the power of spectrally smooth foregrounds beyond the ideal horizon limits due to the complex spatial and spectral structures of the sidelobes and the mainlobe. This paper studies the chromaticity of the HIRAX Stokes I primary beam and its effects on accurate measurements of the 21cm power spectrum. To investigate the effect of chromaticity in the 21cm power spectrum, we present a physically motivated beam modeling technique, which uses a flexible basis derived from traditional optics that can account for higher-order radial and azimuthal structures in the primary beam. We investigate the impact of imperfect knowledge of the mainlobe and sidelobes chromaticity in the power spectrum space by subtracting a simple foreground model in simulated snapshot visibilities to recover the H$\textsc{i}$ power spectrum. Additionally, we find that modeling up to the octupolar azimuthal order feature (fourth-order angular variation) in the primary beam is sufficient to reduce the leakage outside the wedge with minimal bias., Comment: 20 pages, 12 figures. Prepared for submitting in the Astrophysical Journal (ApJ)

The quantum chromodynamics (QCD) axion arises as the pseudo-Goldstone mode of a spontaneously broken abelian Peccei-Quinn (PQ) symmetry. If the scale of PQ symmetry breaking occurs below the inflationary reheat temperature and the domain wall number is unity, then there is a unique axion mass that gives the observed dark matter (DM) abundance. Computing this mass has been the subject of intensive numerical simulations for decades since the mass prediction informs laboratory experiments. Axion strings develop below the PQ symmetry-breaking temperature, and as the string network evolves it emits axions that go on to become the DM. A key ingredient in the axion mass prediction is the spectral index of axion radiation emitted by the axion strings. We compute this index in this work using the most precise and accurate large-scale simulations to date of the axion-string network leveraging adaptive mesh refinement to achieve the precision that would otherwise require a static lattice with 262,144$^3$ lattice sites. We find a scale-invariant axion radiation spectrum to within 1% precision. Accounting for axion production from strings prior to the QCD phase transition leads us to predict that the axion mass should be approximately $m_a\in(45,65)$ $\mu \mathrm{eV}$. However, we provide preliminary evidence that axions are produced in greater quantities from the string-domain-wall network collapse during the QCD phase transition, potentially increasing the mass prediction to as much as 300 $\mu$eV., Comment: 7 + 25 pages, 3 + 18 figures, 0 + 4 tables, supplementary animations at https://tinyurl.com/AxionStringsAMR, video abstract at https://tinyurl.com/rxfnbt9c

Precision optical filters are key components for current and future photonic technologies. Here, we demonstrate a low loss spectral filter consisting of an ultrasteep bandpass feature with a maximum gradient of (90.6$\pm$0.7) dB/GHz, centred within a notch filter with (128$\pm$6) dB of suppression. The filter consists of a fiber Bragg grating with multiple $\pi$-phase discontinuities inscribed into a single mode photosensitive fiber. The measured performance closely matches the simulated spectrum calculated from the design parameters indicating a high degree of confidence in the repeatability and manufacture of such devices. These filters show great promise for applications reliant on high-frequency resolution noise suppression, such as quantum networking, and highlight the opportunities for the versatility, efficiency, and extreme suppression offered by high-performance fiber Bragg grating devices., Comment: 7 pages, 4 figures

We present a reconstruction of the line-of-sight motions of the local interstellar medium (ISM) based on the combination of a state-of-the-art model of the three-dimensional dust density distribution within 1.25 kpc from the Sun and the HI and CO line emission within Galactic latitudes $|b| < 5^{\circ}$. We use the histogram of oriented gradient (HOG) method to match the plane-of-the-sky 3D dust distribution across distances with the atomic and molecular line emission. We identify a significant correlation between the 3D dust model and the line emission. We employ this correlation to assign line-of-sight velocities to the dust across density channels and produce a face-on map of the local ISM radial motions with respect to the local standard of rest (LSR). We find that most of the material in the 3D dust model follows the large-scale pattern of Galactic rotation; however, we also report local departures from the rotation pattern with standard deviations of 12.1 and 6.1 km/s for the HI and CO line emission, respectively. The mean kinetic energy densities of these streaming motions are around 0.68 and 0.18 eV/cm$^{3}$ from either gas tracer. Assuming homogeneity and isotropy in the velocity field, these values are within a factor of a few of the total kinetic energy density. These kinetic energy values are roughly comparable to other energy densities, thus confirming the near-equipartition introduced by the feedback loops connecting the physical processes in the local ISM. Yet, we find energy and momentum overdensities of around a factor of ten concentrated in the Radcliffe Wave, the Split, and other local density structures. Although we do not find evidence of the Local Spiral Arm impact in these overdensities, their distribution suggests the influence of other large-scale effects that, in addition to supernova feedback, shape the energy distribution in the Solar neighborhood., Comment: 32 pages, 43 figures, submitted to Astronomy & Astrophysics (15NOV2024)

Low mass axion-like particles could be produced in abundance within the cores of hot, compact magnetic white dwarf (MWD) stars from electron bremsstrahlung and converted to detectable X-rays in the strong magnetic fields surrounding these systems. In this work, we constrain the existence of such axions from two dedicated Chandra X-ray observations of $\sim$40 ks each in the energy range $\sim$1 - 10 keV towards the magnetic white dwarfs (MWDs) WD 1859+148 and PG 0945+246. We find no evidence for axions, which constrains the axion-electron times axion-photon coupling to $|g_{a\gamma \gamma} g_{aee}| \lesssim 1.54 \times 10^{-25}$ ($3.54 \times 10^{-25}$) GeV$^{-1}$ for PG 0945+246 (WD 1859+148) at 95% confidence for axion masses $m_a \lesssim 10^{-6}$ eV. We find an excess of low-energy X-rays between 1 - 3 keV for WD 1859+148 but determine that the spectral morphology is too soft to arise from axions; instead, the soft X-rays may arise from non-thermal emission in the MWD magnetosphere., Comment: 10 pages, 14 figures, video abstract at https://youtu.be/yfj8JoC1jKQ

Classical Wolf-Rayet stars are descendants of massive OB-type stars that have lost their hydrogen-rich envelopes, and are in the final stages of stellar evolution, possibly exploding as type Ib/c supernovae. It is understood that the mechanisms driving this mass-loss are either strong stellar winds and or binary interactions, so intense studies of these binaries including their evolution can tell us about the importance of the two pathways in WR formation. WR 138 (HD 193077) has a period of just over 4 years and was previously reported to be resolved through interferometry. We report on new interferometric data combined with spectroscopic radial velocities in order to provide a three-dimensional orbit of the system. The precision on our parameters tend to be about an order of magnitude better than previous spectroscopic techniques. These measurements provide masses of the stars, namely $M_{\rm WR} = 13.93\pm1.49M_{\odot}$ and $M_{\rm O} = 26.28\pm1.71M_{\odot}$. The derived orbital parallax agrees with the parallax from \textit{Gaia}, namely with a distance of 2.13 kpc. We compare the system's orbit to models from BPASS, showing that the system likely may have been formed with little interaction but could have formed through some binary interactions either following or at the start of a red supergiant phase, but with the most likely scenario occurring as the red supergiant phase starts for a $\sim 40M_\odot$ star., Comment: accepted to ApJ

Classical Wolf-Rayet stars are the descendants of massive OB stars that have lost their hydrogen envelopes and are burning helium in their cores prior to exploding as type Ib/c supernovae. The mechanisms for losing their hydrogen envelopes are either through binary interactions or through strong stellar winds potentially coupled with episodic mass-loss. Amongst the bright classical WR stars, the binary system WR\,137 (HD\,192641; WC7d + O9e) is the subject of this paper. This binary is known to have a 13-year period and produces dust near periastron. Here we report on interferometry with the CHARA Array collected over a decade of time and providing the first visual orbit for the system. We combine these astrometric measurements with archival radial velocities to measure masses of the stars of $M_{\rm WR} = 9.5\pm3.4 M_\odot$ and $M_{\rm O} = 17.3\pm 1.9 M_\odot$ when we use the most recent \textit{Gaia} distance. These results are then compared to predicted dust distribution using these orbital elements, which match the observed imaging from \textit{JWST} as discussed recently by Lau et al. Furthermore, we compare the system to the BPASS models, finding that the WR star likely formed through stellar winds and not through binary interactions. However, the companion O star did likely accrete some material from the WR's mass-loss to provide the rotation seen today that drives its status as an Oe star., Comment: Accepted to ApJ

Massive evolved stars such as red supergiants and hypergiants are potential progenitors of Type II supernovae, and they are known for ejecting substantial amounts of matter, up to half their initial mass, during their final evolutionary phases. The rate and mechanism of this mass loss play a crucial role in determining their ultimate fate and the likelihood of their progression to supernovae. However, the exact mechanisms driving this mass ejection have long been a subject of research. Recent observations, such as the Great Dimming of Betelgeuse, have suggested that the activity of large convective cells, combined with pulsation, could be a plausible explanation for such mass loss events. In this context, we conducted interferometric observations of the famous yellow hypergiant, $\rho$ Cassiopeiae using the CHARA Array in H and K-band wavelengths. $\rho$ Cas is well known for its recurrent eruptions, characterized by periods of visual dimming ($\sim$1.5-2 mag) followed by recovery. From our observations, we derived the diameter of the limb-darkened disk and found that this star has a radius of $1.04\pm0.01$ milliarcseconds (mas), or $564 - 700 R_\odot$. We performed image reconstructions with three different image reconstruction software packages, and they unveiled the presence of giant hot and cold spots on the stellar surface. We interpret these prominent hot spots as giant convection cells, suggesting a possible connection to mass ejections from the star's envelope. Furthermore, we detected spectral CO emission lines in the K-band ($\lambda=2.31-2.38 \mu$m), and the image reconstructions in these spectral lines revealed an extended circumstellar envelope with a radius of $1.45\pm0.10$ mas., Comment: 21 pages, 13 figures, 4 tables, Accepted by ApJ

The Lunar Surface Electromagnetics Experiment at Night (LuSEE-Night) is a project designed to investigate the feasibility of observing the Cosmic Dark Ages using an instrument on the lunar far-side. LuSEE-Night will measure the redshifted 21 cm transition of neutral hydrogen over a frequency range of 0.1-50 MHz, covering the redshift range 27 < z < 1100. The LuSEE-Night instrument is a radio frequency spectrometer, consisting of four horizontal monopole antennas, arranged to give wide zenith-pointing beams with two orthogonal linear polarizations. This combination of polarization, spectral, and angular sensitivity will be necessary to separate the cosmological signal from significantly stronger foreground emissions. LuSEE-Night will observe in drift scan during lunar night while the moon shields it from radio frequency interference from both the Earth and sun, and will transmit science and telemetry data back to Earth via an orbital relay during the lunar day. LuSEE-Night will have to operate in a challenging environment: its electronics must operate under hard radiation, the instrument must be thermally isolated during the cold 100~K lunar night, and have a thermal rejection path to survive the 390~K daytime temperature, and its photovoltaic and battery systems must provide sufficient power to operate during two weeks of lunar night. Furthermore, the instrument spectrometer must be powered throughout the lunar night using only a 7~kWh battery, due to mass limitations. Here we describe the power generation, storage, and delivery subsystems of the LuSEE-Night instrument, and the simulations which were performed to design the power subsystems and ensure instrument survival and operation throughout the long lunar night. We also describe the Concept of Operations (ConOps) developed for the LuSEE-Night mission, which derives from the power management simulations., Comment: 17 pages, 13 figures, to be published in SPIE Astronomical Telescopes and Instrumentation

Transcranial ultrasonic stimulation (TUS) is rapidly gaining traction for non-invasive human neuromodulation, with a pressing need to establish protocols that maximise neuromodulatory efficacy. In this review, we aggregate and examine empirical evidence for the relationship between tunable TUS parameters and in vitro and in vivo outcomes. Based on this multiscale approach, TUS researchers can make better informed decisions about optimal parameter settings. Importantly, we also discuss the challenges involved in extrapolating results from prior empirical work to future interventions, including the translation of protocols between models and the complex interaction between TUS protocols and the brain. A synthesis of the empirical evidence suggests that larger effects will be observed at lower frequencies within the sub-MHz range, higher intensities and pressures than commonly administered thus far, and longer pulses and pulse train durations. Nevertheless, we emphasise the need for cautious interpretation of empirical data from different experimental paradigms when basing protocols on prior work as we advance towards refined TUS parameters for human neuromodulation., Comment: 28 pages, 2 figures; author list updated

Transcranial ultrasonic stimulation (TUS) has the potential to usher in a new era for human neuroscience by allowing spatially precise and high-resolution non-invasive targeting of both deep and superficial brain regions. Currently, fundamental research on the mechanisms of interaction between ultrasound and neural tissues is progressing in parallel with application-focused research. However, a major hurdle in the wider use of TUS is the selection of optimal parameters to enable safe and effective neuromodulation in humans. In this paper, we will discuss the major factors that determine both the safety and efficacy of TUS. We will discuss the thermal and mechanical biophysical effects of ultrasound, which underlie its biological effects, in the context of their relationships with tunable parameters. Based on this knowledge of biophysical effects, and drawing on concepts from radiotherapy, we propose a framework for conceptualising TUS dose., Comment: 10 pages, 2 figures, reference added: arXiv:2407.01232, author list edited. Last two authors listed are joint last authors

The Cepheid AW Per is a component in a multiple system with a long period orbit. The radial velocities of Griffin (2016) cover the 38 year orbit well. An extensive program of interferometry with the CHARA array is reported here, from which the long period orbit is determined. In addition, a {\it Hubble Space Telescope} high resolution spectrum in the ultraviolet demonstrates that the companion is itself a binary with nearly equal mass components. These data combined with a distance from {\it Gaia} provide a mass of the Cepheid (primary) of M$_1$ = 6.79 $\pm$ 0.85 $M_\odot$. The combined mass of the secondary is M$_S$ = 8.79 $\pm$ 0.50 $M_\odot$. The accuracy of the mass will be improved after the fourth Gaia data release expected in approximately two years., Comment: Accepted for ApJ

The ESO public survey VISTA Variables in the V\'ia L\'actea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from $2009-2015$. Upon its conclusion, the complementary VVV eXtended (VVVX) survey has expanded both the temporal as well as spatial coverage of the original VVV area, widening it from $562$ to $1700$ sq. deg., as well as providing additional epochs in $JHK_{\rm s}$ filters from $2016-2023$. With the completion of VVVX observations during the first semester of 2023, we present here the observing strategy, a description of data quality and access, and the legacy of VVVX. VVVX took $\sim 2000$ hours, covering about 4% of the sky in the bulge and southern disk. VVVX covered most of the gaps left between the VVV and the VISTA Hemisphere Survey (VHS) areas and extended the VVV time baseline in the obscured regions affected by high extinction and hence hidden from optical observations. VVVX provides a deep $JHK_{\rm s}$ catalogue of $\gtrsim 1.5\times10^9$ point sources, as well as a $K_{\rm s}$ band catalogue of $\sim 10^7$ variable sources. Within the existing VVV area, we produced a $5D$ map of the surveyed region by combining positions, distances, and proper motions of well-understood distance indicators such as red clump stars, RR Lyrae, and Cepheid variables. In March 2023 we successfully finished the VVVX survey observations that started in 2016, an accomplishment for ESO Paranal Observatory upon 4200 hours of observations for VVV+VVVX. The VVV+VVVX catalogues complement those from the Gaia mission at low Galactic latitudes and provide spectroscopic targets for the forthcoming ESO high-multiplex spectrographs MOONS and 4MOST., Comment: 17 pages, 11 figures (+ appendix). Accepted for publication in Astronomy and Astrophysics in section 14: Catalogs and data

Thermal higgsino dark matter (DM), with a mass near 1.1 TeV, is one of the most well-motivated and untested DM candidates. Leveraging recent hydrodynamic cosmological simulations that give DM density profiles in Milky Way analogue galaxies we show that the line-like gamma-ray signal predicted from higgsino annihilation in the Galactic Center could be detected at high significance with the upcoming Cherenkov Telescope Array (CTA) and Southern Wide-field Gamma-ray Observatory (SWGO) for all but the most pessimistic DM profiles. We perform the most sensitive search to-date for the line-like signal using 15 years of data from the Fermi Large Area Telescope, coming within an order one factor of the necessary sensitivity to detect the higgsino for some Milky Way analogue DM density profiles. We show that H.E.S.S. has sub-leading sensitivity relative to Fermi for the higgsino at present. In contrast, we analyze H.E.S.S. inner Galaxy data for the thermal wino model with a mass near 2.8 TeV; we find no evidence for a DM signal and exclude the wino by over a factor of two in cross-section for all DM profiles considered. In the process, we identify and attempt to correct what appears to be an inconsistency in previous H.E.S.S. inner Galaxy analyses for DM annihilation related to the analysis effective area, which may weaken the DM cross-section sensitivity claimed in those works by around an order of magnitude., Comment: 42 pages, 38 figures, video abstract at https://youtu.be/8VxOuEDm16A

Recent research has begun to assess people's perceptions of voice user interfaces (VUIs) as dialogue partners, termed partner models. Current self-report measures are only available in English, limiting research to English-speaking users. To improve the diversity of user samples and contexts that inform partner modelling research, we translated, localized, and evaluated the Partner Modelling Questionnaire (PMQ) for non-English speaking Western (German, n=185) and East Asian (Japanese, n=198) cohorts where VUI use is popular. Through confirmatory factor analysis (CFA), we find that the scale produces equivalent levels of goodness-to-fit for both our German and Japanese translations, confirming its cross-cultural validity. Still, the structure of the communicative flexibility factor did not replicate directly across Western and East Asian cohorts. We discuss how our translations can open up critical research on cultural similarities and differences in partner model use and design, whilst highlighting the challenges for ensuring accurate translation across cultural contexts., Comment: Accepted at ACM CUI '24

A growing literature on speech interruptions describes how people interrupt one another with speech, but these behaviours have not yet been implemented in the design of artificial agents which interrupt. Perceptions of a prototype proactive speech agent which adapts its speech to both urgency and to the difficulty of the ongoing task it interrupts are compared against perceptions of a static proactive agent which does not. The study hypothesises that adaptive proactive speech modelled on human speech interruptions will lead to partner models which consider the proactive agent as a stronger conversational partner than a static agent, and that interruptions initiated by an adaptive agent will be judged as better timed and more appropriately asked. These hypotheses are all rejected however, as quantitative analysis reveals that participants view the adaptive agent as a poorer dialogue partner than the static agent and as less appropriate in the style it interrupts. Qualitative analysis sheds light on the source of this surprising finding, as participants see the adaptive agent as less socially appropriate and as less consistent in its interactions than the static agent., Comment: Accepted to CUI 2024 - 6th Conference on Conversational User Interfaces

Helically close-packed states of filaments are common in natural and engineered material systems, ranging from nanoscopic biomolecules to macroscopic structural components. While the simplest models of helical close-packing, described by the ideal rope model, neglect anisotropy perpendicular to the backbone, physical filaments are often quite far from circular in their cross-section. Here, we consider an anisotropic generalization of the ideal rope model and show that cross-section anisotropy has a strongly non-linear impact on the helical close-packing configurations of helical filaments. We show that the topology and composition of the close-packing landscape depends on the cross-sectional aspect ratio and is characterized by several distinct states of self-contact. We characterize the local density of these distinct states based on the notion of confinement within a 'virtual' cylindrical capillary, and show that states of optimal density vary strongly with the degree of anisotropy. While isotropic filaments are densest in a straight configuration, any measure of anisotropy leads to helicity of the maximal density state. We show the maximally dense states exhibit a sequence of transitions in helical geometry and cross-sectional tilt with increasing anisotropy, from spiral tape to spiral screw packings. Furthermore, we show that maximal capillary density saturates in a lower bound for volume fraction of $\pi/4$ in the large-anisotropy, spiral-screw limit. While cross-sectional anisotropy is well-known to impact the mechanical properties of filaments, our study shows its strong effects to shape the configuration space and packing efficiency of this elementary material motif., Comment: 32 pages, 15 figures

We perform the most sensitive search to-date for the existence of ultralight axions using data from the NuSTAR telescope. We search for stellar axion production in the M82 starburst galaxy and the M87 central galaxy of the Virgo cluster and then the subsequent conversion into hard X-rays in the surrounding magnetic fields. We sum over the full stellar populations in these galaxies when computing the axion luminosity, and we account for the conversion of axions to photons by using magnetic field profiles in simulated IllustrisTNG analogue galaxies. We show that analyzing NuSTAR data towards these targets between roughly 30 to 70 keV shows no evidence for axions and leads to robust constraints on the axion-photon coupling at the level of $|g_{a\gamma\gamma}| \lesssim 6.4 \times 10^{-13}$ GeV$^{-1}$ for $m_a \lesssim 10^{-10}$ eV at 95% confidence., Comment: 7+15 pages, 3+21 figures, supplementary data at https://github.com/orionning676/M82_M87_NuSTAR_Axion, video abstract at https://youtu.be/NHN09bSg_Ag

Coherent diffractive imaging is unique as the only route for achieving diffraction-limited spatial resolution in the extreme ultraviolet and X-ray regions, limited only by the wavelength of the light. Recently, advances in coherent short wavelength light sources, coupled with progress in algorithm development, have significantly enhanced the power of x-ray imaging. However, to date, high-fidelity diffraction imaging of periodic objects has been a challenge because the scattered light is concentrated in isolated peaks. Here, we use tabletop 13.5nm high harmonic beams to make two significant advances. First we demonstrate high-quality imaging of an extended, nearly-periodic sample for the first time. Second, we achieve sub-wavelength spatial resolution (12.6nm) imaging at short wavelengths, also for the first time. The key to both advances is a novel technique called modulus enforced probe, which enables robust, quantitative, reconstructions of periodic objects. This work is important for imaging next generation nano-engineered devices., Comment: 15 pages, 5 figures

Inspired by adhesive bio-filamentous structure, such as bacterial pili, this work details the methods used to fabricate and characterize a surface-anchored array of thin, flexible and shape-responsive mesoscale polymer ribbons with a length-to-thickness aspect ratio of up to 100,000. The resulting structures exhibit geometrically complex and dynamic morphologies consistent with elastocapillary bending that experience an increase in curvature over hours of aging due to creep. We develop a computational image analysis framework to generate 3D reconstructions of these densely crowded geometries and extract quantitative descriptors to demonstrate morphological changes due to aging. We demonstrate the robustness of this quantitative method by characterizing the creep-induced change in an aging ribbon array's shape and develop a scaling relationship to describe the importance of ribbon thickness for shape and dynamical observations. These methods demonstrate an essential baseline to probe morphology-property relationships of mesoscale polymer ribbon arrays fabricated from a variety of materials in numerous environments. Through the introduction of perfluorodecalin droplets, we illustrate the potential of these ribbon arrays towards applications in adhesive, microrobotic, and biomedical devices., Comment: 29 pages, 8 figures, supplemental included at the end

Label-free optical absorption microscopy techniques have evolved as effective tools for non-invasive chemical specific structural, and functional imaging. Yet most modern label-free microscopy modalities target only a fraction of the contrast afforded by an optical absorption interaction. We introduce a comprehensive optical absorption microscopy technique, Photon Absorption Remote Sensing (PARS), which simultaneously captures the dominant light matter interactions which occur as a pulse of light is absorbed by a molecule. In PARS, the optical scattering, attenuation, and the transient radiative and non-radiative relaxation processes are collected at each optical absorption event. This provides a complete representation of the absorption event, providing unique contrast presented here as the total absorption (TA) and quantum efficiency ratio (QER) measurements. By capturing a complete view of each absorption interaction, PARS bridges many of the specificity challenges associated with label-free imaging, facilitating recovery of a wider range of biomolecules than independent radiative or non-radiative modalities. To show the versatility of PARS, we explore imaging across a wide range of biological specimens, from single cells to in-vivo imaging of living subjects. These examples of label-free histopathological imaging, and vascular imaging illustrate some of the numerous fields where PARS may have profound impacts. Overall PARS may provide comprehensive label-free contrast in a wide variety of biological specimens, providing otherwise inaccessible visualizations, and representing a new a source of rich data to develop new AI and machine learning methods for diagnostics and visualization., Comment: 23 pages, 10 figures

A theory of martingales for censoring is developed. The Doob-Meyer martingale is shown to be inadequate in general, and a repaired martingale is proposed with a non-predictable centering term. Associated martingale transforms, variation processes, and covariation processes are developed based on a measure of half-predictability that generalizes predictability. The development is applied to study the Kaplan Meier estimator.

Electromagnetic fields surrounding pulsars may source coherent ultralight axion signals at the known rotational frequencies of the neutron stars, which can be detected by laboratory experiments (e.g., pulsarscopes). As a promising case study, we model axion emission from the well-studied Crab pulsar, which would yield a prominent signal at $f \approx 29.6$ Hz regardless of whether the axion contributes to the dark matter abundance. We estimate the relevant sensitivity of future axion dark matter detection experiments such as DMRadio-GUT, Dark SRF, and CASPEr, assuming different magnetosphere models to bracket the uncertainty in astrophysical modeling. For example, depending on final experimental parameters, the Dark SRF experiment could probe axions with any mass $m_a \ll 10^{-13}$ eV down to $g_{a\gamma\gamma} \sim 3 \times 10^{-13}$ GeV$^{-1}$ with one year of data and assuming the vacuum magnetosphere model. These projected sensitivities may be degraded depending on the extent to which the magnetosphere is screened by charge-filled plasma. The promise of pulsar-sourced axions as a clean target for direct detection experiments motivates dedicated simulations of axion production in pulsar magnetospheres., Comment: 8+5 pages, 2 figures, video abstract at https://www.youtube.com/watch?v=YRZW4tPtIDk

Marginal structural models have been widely used in causal inference to estimate mean outcomes under either a static or a prespecified set of treatment decision rules. This approach requires imposing a working model for the mean outcome given a sequence of treatments and possibly baseline covariates. In this paper, we introduce a dynamic marginal structural model that can be used to estimate an optimal decision rule within a class of parametric rules. Specifically, we will estimate the mean outcome as a function of the parameters in the class of decision rules, referred to as a regimen-response curve. In general, misspecification of the working model may lead to a biased estimate with questionable causal interpretability. To mitigate this issue, we will leverage risk to assess "goodness-of-fit" of the imposed working model. We consider the counterfactual risk as our target parameter and derive inverse probability weighting and canonical gradients to map it to the observed data. We provide asymptotic properties of the resulting risk estimators, considering both fixed and data-dependent target parameters. We will show that the inverse probability weighting estimator can be efficient and asymptotic linear when the weight functions are estimated using a sieve-based estimator. The proposed method is implemented on the LS1 study to estimate a regimen-response curve for patients with Parkinson's disease., Comment: 25 pages, 2 figures, 2 tables

Conversational user interfaces (CUIs) have become an everyday technology for people the world over, as well as a booming area of research. Advances in voice synthesis and the emergence of chatbots powered by large language models (LLMs), notably ChatGPT, have pushed CUIs to the forefront of human-computer interaction (HCI) research and practice. Now that these technologies enable an elemental level of usability and user experience (UX), we must turn our attention to higher-order human factors: trust and reliance. In this workshop, we aim to bring together a multidisciplinary group of researchers and practitioners invested in the next phase of CUI design. Through keynotes, presentations, and breakout sessions, we will share our knowledge, identify cutting-edge resources, and fortify an international network of CUI scholars. In particular, we will engage with the complexity of trust and reliance as attitudes and behaviours that emerge when people interact with conversational agents.