cssi/SciSciGPT-SciSciNet huggingface dataset:
A propensity score-matched analysis comparing outpatient and short-stay hospitalization to standard inpatient hospitalization following total ankle arthroplasty.

Given the trend toward value-based care, there has been increased interest in minimizing hospital length of stay (LOS) after orthopedic procedures. Outpatient total ankle arthroplasty (TAA) has become more popular in recent years; however, research on surgical outcomes of this procedure has been limited. This study sought to employ large sample, propensity score-matched analyses to assess the safety of outpatient and short-stay discharge pathways following TAA. The ACS NSQIP database was used to identify 1141 patients who underwent primary and revision TAA between 2007 and 2017. Propensity score matching was used to match patients based on several factors, including age, sex, body mass index (BMI), American Society of Anesthesiologists (ASA) classification, and several comorbidities. The incidence of various 30-day complications was compared between the short and standard LOS groups to assess for any differences in short-term outcomes. A total of 892 patients were included in the final propensity score-matched analysis, with 446 patients in each group. The short LOS group had a significantly lower rate of medical complications (0.2% vs. 2.5%, p = 0.006) and non-home discharge (1.3% vs. 12.1%, p 0.999), return to the OR (0.2% vs. 0.9%, p = 0.374), or mortality (0.7% vs. 0.0%, p > 0.249) between the short and standard LOS groups. Outpatient and short-stay hospitalization had comparable safety to standard inpatient hospitalization after TAA. Outpatient or short-stay TAA should be considered for patients with low risk of short-term complications.
Predicting International Student Enrollment in U.S. Institutions by Institutional Characteristics: Using Fixed and Random Effects.

For the first time, international student enrollment in U.S. institutions of higher education declined for a second straight year in 2017-2018. As a result, this study sought to understand which institutional characteristics predict international student enrollment, informing the international education community regarding possible institutional factors responsible for the decline in international student enrollment by using five-year panel data from 2013 Fall to 2017 Fall. Results from institutional fixed effects models revealed positive relationships between the first-time international undergraduate enrollment and different variables such as institutional grant aid in bachelor’s institutions and student services expenses at private non-profit institutions in suburban settings. Contrary to earlier research, this study’s findings revealed that there is no relationship between state appropriations and first-time international undergraduate enrollment. Implications for research, practice, and international student choice are addressed.
Exploring the efficacy of transfer learning in mining image-based software artifacts

Transfer learning allows us to train deep architectures requiring a large number of learned parameters, even if the amount of available data is limited, by leveraging existing models previously trained for another task. In previous attempts to classify image-based software artifacts in the absence of big data, it was noted that standard off-the-shelf deep architectures such as VGG could not be utilized due to their large parameter space and therefore had to be replaced by customized architectures with fewer layers. This proves to be challenging to empirical software engineers who would like to make use of existing architectures without the need for customization. Here we explore the applicability of transfer learning utilizing models pre-trained on non-software engineering data applied to the problem of classifying software unified modeling language (UML) diagrams. Our experimental results show training reacts positively to transfer learning as related to sample size, even though the pre-trained model was not exposed to training instances from the software domain. We contrast the transferred network with other networks to show its advantage on different sized training sets, which indicates that transfer learning is equally effective to custom deep architectures in respect to classification accuracy when large amounts of training data is not available. Our findings suggest that transfer learning, even when based on models that do not contain software engineering artifacts, can provide a pathway for using off-the-shelf deep architectures without customization. This provides an alternative to practitioners who want to apply deep learning to image-based classification but do not have the expertise or comfort to define their own network architectures.
Constrained Cross-Entropy Method for Safe Reinforcement Learning

We study a safe reinforcement learning problem, in which the constraints are defined as the expected cost over finite-length trajectories. We propose a constrained cross-entropy-based method to solve this problem. The key idea is to transform the original constrained optimization problem into an unconstrained one with a surrogate objective. The method explicitly tracks its performance with respect to constraint satisfaction and thus is well suited for safety-critical applications. We show that the asymptotic behavior of the proposed algorithm can be almost-surely described by that of an ordinary differential equation. Then, we give sufficient conditions on the properties of this differential equation for the convergence of the proposed algorithm. At last, we show the performance of the proposed algorithm in two simulation examples. In a constrained linear–quadratic regulator example, we observe that the algorithm converges to the global optimum with high probability. In a 2-D navigation example, we find that the algorithm effectively learns feasible policies without assumptions on the feasibility of initial policies, even with non-Markovian objective functions and constraint functions.
Programmable low-cost DNA-based platform for viral RNA detection

Detection of viruses is critical for controlling disease spread. Recent emerging viral threats, including Zika virus, Ebola virus, and SARS-CoV-2 responsible for coronavirus disease 2019 (COVID-19) highlight the cost and difficulty in responding rapidly. To address these challenges, we develop a platform for low-cost and rapid detection of viral RNA with DNA nanoswitches that mechanically reconfigure in response to specific viruses. Using Zika virus as a model system, we show nonenzymatic detection of viral RNA with selective and multiplexed detection between related viruses and viral strains. For clinical-level sensitivity in biological fluids, we paired the assay with sample preparation using either RNA extraction or isothermal preamplification. Our assay requires minimal laboratory infrastructure and is adaptable to other viruses, as demonstrated by quickly developing DNA nanoswitches to detect SARS-CoV-2 RNA in saliva. Further development and field implementation will improve our ability to detect emergent viral threats and ultimately limit their impact.
How Perception of Being Recognized or Not Recognized by Instructors as a “Physics Person” Impacts Male and Female Students’ Self-Efficacy and Performance

Physics has historically been portrayed as a field for brilliant men. Many prior studies have focused on the reasons for women’s underrepresentation in physics and related disciplines from different perspectives and strategies to improve the learning environments so that all students can excel in physics courses. Due to societal stereotypes, women often have significantly lower physics self-efficacy than men even when they perform similarly, and many shy away from physics-related majors and careers. Moreover, being recognized by the instructor as a student who can excel in physics can be valuable for all students in physics courses. However, it is particularly important for underrepresented students, including women and ethnic and racial minorities, partly due to the societal stereotypes associated with who can excel in physics and lack of role models.
Equivariant derived categories associated to a sum of two potentials

Abstract Suppose f , g are homogeneous polynomials of degree d defining smooth hypersurfaces X f = V ( f ) ⊂ P m − 1 and X g = V ( g ) ⊂ P n − 1 . Then the sum of f and g defines a smooth hypersurface X = V ( f ⊕ g ) ⊂ P m + n − 1 with an action of μ d scaling the g variables. Motivated by the work of Orlov, we construct a semi-orthogonal decomposition of the derived category of coherent sheaves on [ X ∕ μ d ] provided d ≥ max { m , n } .
Onsager Transport Coefficients and Transference Numbers in Polyelectrolyte Solutions and Polymerized Ionic Liquids

Electrolytes featuring negatively charged polymers, such as nonaqueous polyelectrolyte solutions and polymerized ionic liquids, are currently under investigation as potential high cation transferen...
Heparan sulfate assists SARS-CoV-2 in cell entry and can be targeted by approved drugs in vitro

The cell entry of SARS-CoV-2 has emerged as an attractive drug repurposing target for COVID-19. Here we combine genetics and chemical perturbation to demonstrate that ACE2-mediated entry of SARS-Cov and CoV-2 requires the cell surface heparan sulfate (HS) as an assisting cofactor: ablation of genes involved in HS biosynthesis or incubating cells with a HS mimetic both inhibit Spike-mediated viral entry. We show that heparin/HS binds to Spike directly, and facilitates the attachment of Spike-bearing viral particles to the cell surface to promote viral entry. We screened approved drugs and identified two classes of inhibitors that act via distinct mechanisms to target this entry pathway. Among the drugs characterized, Mitoxantrone is a potent HS inhibitor, while Sunitinib and BNTX disrupt the actin network to indirectly abrogate HS-assisted viral entry. We further show that drugs of the two classes can be combined to generate a synergized activity against SARS-CoV-2-induced cytopathic effect. Altogether, our study establishes HS as an attachment factor that assists SARS coronavirus cell entry and reveals drugs capable of targeting this important step in the viral life cycle.
A Chlorzoxazone-Baclofen Combination Improves Cerebellar Impairment in Spinocerebellar Ataxia Type 1

Background A combination of central muscle relaxants, chlorzoxazone and baclofen (chlorzoxazone-baclofen), has been proposed for treatment of cerebellar symptoms in human spinocerebellar ataxia. However, central muscle relaxants can worsen balance. The optimal dose for target engagement without toxicity remains unknown. Using the genetically precise Atxn1154Q/2Q model of spinocerebellar ataxia type 1, we aimed to determine the role of cerebellar dysfunction in motor impairment. We also aimed to identify appropriate concentrations of chlorzoxazone-baclofen needed for target engagement without toxicity to plan for human clinical trials. Methods We use patch clamp electrophysiology in acute cerebellar slices and immunostaining to identify the specific ion channels targeted by chlorzoxazone-baclofen. Behavioral assays for coordination and grip strength are used to determine specificity of chlorzoxazone-baclofen for improving cerebellar dysfunction without off-target effects in Atxn1154Q/2Q mice. Results We identify irregular Purkinje neuron firing in association with reduced expression of ion channels Kcnma1 and Cacna1g in Atxn1154Q/2Q mice. Using in vitro electrophysiology in brain slices, we identified concentrations of chlorzoxazone-baclofen that improve Purkinje neuron spike regularity without reducing firing frequency. At a disease stage in Atxn1154Q/2Q mice when motor impairment is due to cerebellar dysfunction, orally administered chlorzoxazone-baclofen improves motor performance without affecting muscle strength. Conclusion We identify a tight relationship between baclofen-chlorzoxazone concentrations needed to engage target and levels above which cerebellar function will be compromised. We propose to use this information for a novel clinical trial design, using sequential dose escalation within each subject, to identify dose levels that are likely to improve ataxia symptoms while minimizing toxicity. © 2020 International Parkinson and Movement Disorder Society.
Aphasic Speech Recognition Using a Mixture of Speech Intelligibility Experts.

Robust speech recognition is a key prerequisite for semantic feature extraction in automatic aphasic speech analysis. However, standard one-size-fits-all automatic speech recognition models perform poorly when applied to aphasic speech. One reason for this is the wide range of speech intelligibility due to different levels of severity (i.e., higher severity lends itself to less intelligible speech). To address this, we propose a novel acoustic model based on a mixture of experts (MoE), which handles the varying intelligibility stages present in aphasic speech by explicitly defining severity-based experts. At test time, the contribution of each expert is decided by estimating speech intelligibility with a speech intelligibility detector (SID). We show that our proposed approach significantly reduces phone error rates across all severity stages in aphasic speech compared to a baseline approach that does not incorporate severity information into the modeling process.
Numerical Simulations of a Jet–Cloud Collision and Starburst: Application to Minkowski’s Object

We present results of three-dimensional, multi-physics simulations of an AGN jet colliding with an intergalactic cloud. The purpose of these simulations is to assess the degree of "positive feedback," i.e., jet-induced star formation, that results. We have specifically tailored our simulation parameters to facilitate a comparison with recent observations of Minkowski's Object (MO), a stellar nursery located at the termination point of a radio jet coming from galaxy NGC 541. As shown in our simulations, such a collision triggers shocks, which propagate around and through the cloud. These shocks condense the gas and under the right circumstances may trigger cooling instabilities, creating runaway increases in density, to the point that individual clumps can become Jeans unstable. Our simulations provide information about the expected star formation rate, total mass converted to H i, H2, and stars, and the relative velocity of the stars and gas. Our results confirm the possibility of jet-induced star formation, and agree well with the observations of MO.
Excitations in the Yang-Gaudin Bose gas

We study the excitation spectrum of two-component delta-function interacting bosons confined to a single spatial dimension, the Yang-Gaudin Bose gas. We show that there are pronounced finite-size effects in the dispersion relations of excitations, perhaps best illustrated by the spinon single particle dispersion which exhibits a gap at $2k_F$ and a finite-momentum roton minimum. Such features occur at energies far above the finite volume excitation gap, vanish slowly as $1/L$ for fixed spinon number, and can persist to the thermodynamic limit at fixed spinon density. Features such as the $2k_F$ gap also persist to multi-particle excitation continua. Our results show that excitations in the finite system can behave in a qualitatively different manner to analogous excitations in the thermodynamic limit. The Yang-Gaudin Bose gas is also host to multi-spinon bound states, known as $\Lambda$-strings. We study these excitations both in the thermodynamic limit under the string hypothesis and in finite size systems where string deviations are taken into account. In the zero-temperature limit we present a simple relation between the length $n$ $\Lambda$-string dressed energies $\epsilon_n(\lambda)$ and the dressed energy $\epsilon(k)$. We solve the Yang-Yang-Takahashi equations numerically and compare to the analytical solution obtained under the strong couple expansion, revealing that the length $n$ $\Lambda$-string dressed energy is Lorentzian over a wide range of real string centers $\lambda$ in the vicinity of $\lambda = 0$. We then examine the finite size effects present in the dispersion of the two-spinon bound states by numerically solving the Bethe ansatz equations with string deviations.
Effects of gauge theory based number scaling on geometry

Effects of local availability of mathematics (LAM) and space time dependent number scaling on physics and, especially, geometry are described. LAM assumes separate mathematical systems as structures at each space time point. Extension of gauge theories to include freedom of choice of scaling for number structures, and other structures based on numbers, results in a space time dependent scaling factor based on a scalar boson field. Scaling has no effect on comparison of experimental results with one another or with theory computations. With LAM all theory expressions are elements of mathematics at some reference point. Changing the reference point introduces (external) scaling. Theory expressions with integrals or derivatives over space or time include scaling factors (internal scaling) that cannot be removed by reference point change. Line elements and path lengths, as integrals over space and/or time, show the effect of scaling on geometry. In one example, the scaling factor goes to 0 as the time goes to 0, the big bang time. All path lengths, and values of physical quantities, are crushed to 0 as t goes to 0. Other examples have spherically symmetric scaling factors about some point, x . In one type, a black scaling hole, the scaling factor goes to infinity as the distance, d , between any point y and x goes to 0. For scaling white holes, the scaling factor goes to 0 as d goes to 0. For black scaling holes, path lengths from a reference point, z , to y become infinite as y approaches x . For white holes, path lengths approach a value much less than the unscaled distance from z to x .
Zero branes on a compact orbifold

The non-commutative algebra which defines the theory of zero-branes on T4/Z2 allows a unified description of moduli spaces associated with zero-branes, two-branes and four-branes on the orbifold space. Bundles on a dual space 4/Z2 play an important role in this description. We discuss these moduli spaces in the context of dualities of K3 compactifications, and in terms of properties of instantons on T4. Zero-branes on the degenerate limits of the compact orbifold lead to fixed points with six-dimensional scale but not conformal invariance. We identify some of these in terms of the ADS dual of the (0,2) theory at large N, giving evidence for an interesting picture of ``where the branes live'' in ADS.
High quality epitaxial thin films and exchange bias of antiferromagnetic Dirac semimetal FeSn

FeSn is a topological semimetal (TSM) and kagome antiferromagnet (AFM) composed of alternating Fe3Sn kagome planes and honeycomb Sn planes. This unique structure gives rise to exotic features in the band structures such as the coexistence of Dirac cones and flatbands near the Fermi level, fully spin-polarized 2D surface Dirac fermions, and the ability to open a large gap in the Dirac cone by reorienting the Neel vector. In this work, we report the synthesis of high-quality epitaxial (0001) FeSn films by magnetron sputtering. Using FeSn/Py heterostructures, we show a large exchange bias effect that reaches an exchange field of 220 Oe at 5 K, providing unambiguous evidence of antiferromagnetism and strong interlayer exchange coupling in our films. Field cycling studies show steep initial training effects, highlighting the complex magnetic interactions and anisotropy. Importantly, our work provides a simple, alternative means to fabricate FeSn films and heterostructures, making it easier to explore the topological physics of AFM TSMs and develop FeSn-based spintronics.
Parabolic theory as a high-dimensional limit of elliptic theory

The aim of this article is to show how certain parabolic theorems follow from their elliptic counterparts. This technique is demonstrated through new proofs of five important theorems in parabolic unique continuation and the regularity theory of parabolic equations and geometric flows. Specifically, we give new proofs of an L 2 Carleman estimate for the heat operator, and the monotonicity formulas for the frequency function associated to the heat operator, the two-phase free boundary problem, the flow of harmonic maps, and the mean curvature flow. The proofs rely only on the underlying elliptic theorems and limiting procedures belonging essentially to probability theory. In particular, each parabolic theorem is proved by taking a high-dimensional limit of the related elliptic result.
The Population of Eccentric Binary Black Holes: Implications for mHz Gravitational-wave Experiments

Simons Foundation; NSF [1313252]; IBM Einstein Fellowship from the Institute for Advanced Study, Princeton; US Department of Energy; Packard Foundation; NASA
OBSERVATIONAL EVIDENCE FOR A METAL-RICH ATMOSPHERE ON THE SUPER-EARTH GJ1214b

We report observations of two consecutive transits of the warm super-Earth exoplanet GJ 1214b at 3.6 and 4.5 ?m with the Infrared Array Camera instrument on board the Spitzer Space Telescope. The two transit light curves allow for the determination of the transit parameters for this system. We find these parameters to be consistent with the previously determined values and no evidence for transit timing variations. The main investigation consists of measuring the transit depths in each bandpass to constrain the planet's transmission spectrum. Fixing the system scale and impact parameters, we measure Rp /R = 0.1176+0.0008 ?0.0009 and 0.1163+0.0010 ?0.0008 at 3.6 and 4.5 ?m, respectively. Combining these data with the previously reported MEarth Observatory measurements in the red optical allows us to rule out a cloud-free, solar composition (i.e., hydrogen-dominated) atmosphere at 4.5? confidence. This independently confirms a recent finding that was based on a measurement of the planet's transmission spectrum using the Very Large Telescope (VLT). The Spitzer, MEarth, and VLT observations together yield a remarkably flat transmission spectrum over the large wavelength domain spanned by the data. Consequently, cloud-free atmospheric models require more than 30% metals (assumed to be in the form of H2O) by volume to be consistent with all the observations.
Semidualities from products of trees

Let $K$ be a global function field of characteristic $p$, and let $\Gamma$ be a finite-index subgroup of an arithmetic group defined with respect to $K$ and such that any torsion element of $\Gamma$ is a $p$-torsion element. We define semiduality groups, and we show that $\Gamma$ is a $\mathbb{Z}[1/p]$-semiduality group if $\Gamma$ acts as a lattice on a product of trees. We also give other examples of semiduality groups, including lamplighter groups, Diestel-Leader groups, and countable sums of finite groups.
Brain MRI super resolution using 3D deep densely connected neural networks

Magnetic resonance image (MRI) in high spatial resolution provides detailed anatomical information and is often necessary for accurate quantitative analysis. However, high spatial resolution typically comes at the expense of longer scan time, less spatial coverage, and lower signal to noise ratio (SNR). Single Image Super-Resolution (SISR), a technique aimed to restore high-resolution (HR) details from one single low-resolution (LR) input image, has been improved dramatically by recent breakthroughs in deep learning. In this paper, we introduce a new neural network architecture, 3D Densely Connected Super-Resolution Networks (DCSRN) to restore HR features of structural brain MR images. Through experiments on a dataset with 1,113 subjects, we demonstrate that our network outperforms bicubic interpolation as well as other deep learning methods in restoring 4× resolution-reduced images.
Using satellites to probe extrasolar planet formation

Planetary satellites are an integral part of the hierarchy of planetary systems. Here we make two predictions concerning their formation. First, primordial satellites, which have an array of distinguishing characteristics, form only around giant planets. If true, the size and duration of a planetary system's protostellar nebula, as well as the location of its snow line, can be constrained by knowing which of its planets possess primordial satellites and which do not. Second, all satellites around terrestrial planets form by impacts. If true, this greatly enhances the constraints that can be placed on the history of terrestrial planets by their satellites' compositions, sizes, and dynamics.
ADVANCED DYNAMIC ALGORITHMS FOR THE DECAY OF METASTABLE PHASES IN DISCRETE SPIN MODELS: BRIDGING DISPARATE TIME SCALES

An overview of advanced dynamical algorithms capable of spanning the widely disparate time scales that govern the decay of metastable phases in discrete spin models is presented. The algorithms discussed include constrained transfer-matrix, Monte Carlo with Absorbing Markov Chains (MCAMC), and projective dynamics (PD) methods. The strengths and weaknesses of each of these algorithms are discussed, with particular emphasis on identifying the parameter regimes (system size, temperature, and field) in which each algorithm works best.
Vibronic exciton theory of singlet fission. III. How vibronic coupling and thermodynamics promote rapid triplet generation in pentacene crystals

We extend the vibronic exciton theory introduced in our previous work to study singlet fission dynamics, in particular addressing recent indications of the importance of vibronic coupling in this process. A microscopic and non-perturbative treatment of electronic and selected vibrational degrees of freedom in combination with Redfield theory allows us to dynamically consider clusters of molecules under conditions close to those in molecular crystals that exhibit fission. Using bulk pentacene as a concrete example, our results identify a number of factors that render fission rapid and effective. Strong coupling to high-frequency Holstein modes generates resonances between the photo-prepared singlet and product triplet states. We furthermore find the large number of triplet combinations associated with bulk periodic systems to be critical to the fission process under such vibronically resonant conditions. In addition, we present results including, in an approximate manner, the effects of Peierls coupling, indicating that this factor can both enhance and suppress fission depending on its interplay with vibronic resonance and thermodynamics.
Tentative discovery of a new supernova remnant in cepheus : Unveiling an elusive shell in the Spitzer galactic first look survey

We have discovered an axially symmetric, well-defined shell of material in the constellation of Cepheus, based on imaging acquired as part of the Galactic First Look Survey with the Spitzer Space Telescope. The 86'' × 75'' object exhibits brightened limbs on the minor axis and is clearly visible at 24 μm, but it is not detected in the 3.6, 4.5, 5.8, 8.0, 70, or 160 μm images. Follow-up 7.5-40 μm spectroscopy reveals that the shell is composed entirely of ionized gas and that the 24 μm imaging traces [O IV] 25.89 μm emission solely. The spectrum also exhibits weaker [Ne III] and [S III] emission, and very weak [Ne V] emission. No emission from warm dust is detected. Spectral cuts through the center of the shell and at the northern limb are highly consistent with each other. The progenitor is not readily identified, but with scaling arguments and comparison to well-known examples of evolved stellar objects, we find the observations to be most straightforward to interpret in terms of a young supernova remnant located at a distance of at least 10 kpc, some 400 pc above the Galactic disk. If confirmed, this would be the first supernova remnant discovered initially at infrared wavelengths.
Fourier Analysis of Blazar Variability: Klein-Nishina Effects and the Jet Scattering Environment

The strong variability of blazars can be characterized by power spectral densities (PSDs) and Fourier frequency-dependent time lags. In previous work, we created a new theoretical formalism for describing the PSDs and time lags produced via a combination of stochastic particle injection and emission via the synchrotron, synchrotron self-Compton, and external Compton (EC) processes. This formalism used the Thomson cross section and simple ?-function approximations to model the synchrotron and Compton emissivities. Here we expand upon this work, using the full Compton cross section and detailed and accurate emissivities. Our results indicate good agreement between the PSDs computed using the ?-function approximations and those computed using the accurate expressions, provided the observed photons are produced primarily by electrons with energies exceeding the lower limit of the injected particle population. Breaks are found in the PSDs at frequencies corresponding to the cooling timescales of the electrons primarily responsible for the observed emission, and the associated time lags are related to the difference in electron cooling timescales between the two energy channels, as expected. If the electron cooling timescales can be determined from the observed time lags and/or the observed EC PSDs, then one could in principle use the method developed here to determine the energy of the external seed photon source for EC, which is an important unsolved problem in blazar physics.
Using Resource Graphs to Represent Conceptual Change.

We introduce resource graphs, a representation of linked ideas used when reasoning about specific contexts in physics. Our model is consistent with previous descriptions of coordination classes and resources. It represents mesoscopic scales that are neither knowledge-in-pieces nor large-scale concepts. We use resource graphs to describe several forms of conceptual change: incremental, cascade, wholesale, and dual construction. For each, we give evidence from the physics education research literature to show examples of each form of conceptual change. Where possible, we compare our representation to models used by other researchers. Building on our representation, we analyze another form of conceptual change, differentiation, and suggest several experimental studies that would help understand the differences between reform-based curricula.
A rank inequality for the knot Floer homology of double branched covers

Given a knot K in S , let †.K/ be the double branched cover of S over K . We show there is a spectral sequence whose E page is . b HFK .†.K/;K/ V .n / Z2..q// , for V a Z2 –vector space of dimension two, and whose E page is isomorphic to . b HFK .S;K/ V .n / Z2..q// , as Z2..q//–modules. As a consequence, we deduce a rank inequality between the knot Floer homologies b HFK .†.K/;K/ and b HFK .S;K/ .
Explicit rank bounds for cyclic covers

Let $M$ be a closed, orientable hyperbolic 3-manifold and $\phi$ a homomorphism of its fundamental group onto $\mathbb{Z}$ that is not induced by a fibration over the circle. For each natural number $n$ we give an explicit lower bound, linear in $n$, on rank of the fundamental group of the cover of $M$ corresponding to $\phi^{-1}(n\mathbb{Z})$. The key new ingredient is the following result: for such a manifold $M$ and a connected, two-sided incompressible surface of genus $g$ in $M$ that is not a fiber or semi-fiber, a reduced homotopy in $(M,S)$ has length at most $14g-12$.
Extragalactic H2O Masers

Twenty-five extragalactic H2O masers are known, classified as normal masers and megamasers. The first VLBI synthesis images of a normal maser, the one associated with the IC 133 region of M33, as well as observations of its environs, show it to be comparable physically to the most powerful galactic masers. Inference from past observations of megamasers has been that megamasers are intrinsically different than normal masers, arising from uncommon or extreme physical conditions. However, the first ever synthesis images of a megamaser, the one toward the nucleus of NGC 3079, show that this source too is structurally similar to galactic maser sources.
How Galaxies Form Stars: The Connection between Local and Global Star Formation in Galaxy Simulations

Using a suite of isolated $L_\star$ galaxy simulations, we show that global depletion times and star-forming gas mass fractions in simulated galaxies exhibit systematic and well-defined trends as a function of the local star formation efficiency per freefall time, $\epsilon_{\rm ff}$, strength of stellar feedback, and star formation threshold. We demonstrate that these trends can be reproduced and explained by a simple physical model of global star formation in galaxies. Our model is based on mass conservation and the idea of gas cycling between star-forming and non-star-forming states on certain characteristic time scales under the influence of dynamical and feedback processes. Both the simulation results and our model predictions exhibit two limiting regimes with rather different dependencies of global galactic properties on the local parameters. When $\epsilon_{\rm ff}$ is small and feedback is inefficient, the total star-forming mass fraction, $f_{\rm sf}$, is independent of $\epsilon_{\rm ff}$ and the global depletion time, $\tau_{\rm dep}$, scales inversely with $\epsilon_{\rm ff}$. When $\epsilon_{\rm ff}$ is large or feedback is very efficient, these trends are reversed: $f_{\rm sf} \propto \epsilon_{\rm ff}^{-1}$ and $\tau_{\rm dep}$ is independent of $\epsilon_{\rm ff}$ but scales linearly with the feedback strength. We also compare our results with the observed depletion times and mass fractions of star-forming and molecular gas and show that they provide complementary constraints on $\epsilon_{\rm ff}$ and the feedback strength. We show that useful constraints on $\epsilon_{\rm ff}$ can also be obtained using measurements of the depletion time and its scatter on different spatial scales.
Rigidity in vacuum under conformal symmetry

Motivated in part by Eardley et al. (Commun Math Phys 106(1):137–158, 1986), in this note we obtain a rigidity result for globally hyperbolic vacuum spacetimes in arbitrary dimension that admit a timelike conformal Killing vector field. Specifically, we show that if M is a Ricci flat, timelike geodesically complete spacetime with compact Cauchy surfaces that admits a timelike conformal Killing field X, then M must split as a metric product, and X must be Killing. This gives a partial proof of the Bartnik splitting conjecture in the vacuum setting.
Finding a Sparse Vector in a Subspace: Linear Sparsity Using Alternating Directions

Is it possible to find the sparsest vector (direction) in a generic subspace $\mathcal {S} \subseteq \mathbb {R} ^{p}$ with $\text {dim} \left ({ \mathcal {S} }\right )=n ? This problem can be considered a homogeneous variant of the sparse recovery problem and finds connections to sparse dictionary learning, sparse PCA, and many other problems in signal processing and machine learning. In this paper, we focus on a planted sparse model for the subspace: the target sparse vector is embedded in an otherwise random subspace. Simple convex heuristics for this planted recovery problem provably break down when the fraction of nonzero entries in the target sparse vector substantially exceeds $O(1/\sqrt {n})$ . In contrast, we exhibit a relatively simple nonconvex approach based on alternating directions, which provably succeeds even when the fraction of nonzero entries is $\Omega (1)$ . To the best of our knowledge, this is the first practical algorithm to achieve linear scaling under the planted sparse model. Empirically, our proposed algorithm also succeeds in more challenging data models, e.g., sparse dictionary learning.
Bottleneck Stability for Generalized Persistence Diagrams

In this paper, we extend bottleneck stability to the setting of one dimensional constructible persistences module valued in any small abelian category.
Challenges to Constraining Exoplanet Masses via Transmission Spectroscopy

MassSpec, a method for determining the mass of a transiting exoplanet from its transmission spectrum alone, was proposed by de Wit & Seager. The premise of this method relies on the planet's surface gravity being extracted from the transmission spectrum via its effect on the atmospheric scale height, which in turn determines the strength of absorption features. Here, we further explore the applicability of MassSpec to low-mass exoplanets—specifically those in the super-Earth size range for which radial velocity determinations of the planetary mass can be extremely challenging and resource intensive. Determining the masses of these planets is of the utmost importance because their nature is otherwise highly unconstrained. Without knowledge of the mass, these planets could be rocky, icy, or gas-dominated. To investigate the effects of planetary mass on transmission spectra, we present simulated observations of super-Earths with atmospheres made up of mixtures of H2O and H2, both with and without clouds. We model their transmission spectra and run simulations of each planet as it would be observed with James Webb Space Telescope using the NIRISS, NIRSpec, and MIRI instruments. We find that significant degeneracies exist between transmission spectra of planets with different masses and compositions, making it impossible to unambiguously determine the planet's mass in many cases.
Random Band Matrices in the Delocalized Phase, II: Generalized Resolvent Estimates

This is the second part of a three part series abut delocalization for band matrices. In this paper, we consider a general class of $$N\times N$$ random band matrices $$H=(H_{ij})$$ whose entries are centered random variables, independent up to a symmetry constraint. We assume that the variances $$\mathbb {E} |H_{ij}|^2$$ form a band matrix with typical band width $$1\ll W\ll N$$ . We consider the generalized resolvent of H defined as $$G(Z):=(H - Z)^{-1}$$ , where Z is a deterministic diagonal matrix such that $$Z_{ij}=\left( z\mathbb {1}_{1\leqslant i \leqslant W}+\widetilde{z}\mathbb {1}_{ i > W} \right) \delta _{ij}$$ , with two distinct spectral parameters $$z\in \mathbb {C}_+:=\{z\in \mathbb {C}:{{\,\mathrm{Im}\,}}z>0\}$$ and $$\widetilde{z}\in \mathbb {C}_+\cup \mathbb {R}$$ . In this paper, we prove a sharp bound for the local law of the generalized resolvent G for $$W\gg N^{3/4}$$ . This bound is a key input for the proof of delocalization and bulk universality of random band matrices in Bourgade et al. ( arXiv:1807.01559 , 2018). Our proof depends on a fluctuations averaging bound on certain averages of polynomials in the resolvent entries, which will be proved in Yang and Yin ( arXiv:1807.02447 , 2018).
The DIRECT Project: Influence of Blending on the Cepheid Distance Scale. I. Cepheids in M31

We investigate the influence of blending on the Cepheid distance scale. Blending is the close association of a Cepheid with one or more intrinsically luminous stars. High-resolution HST images are compared with our ground-based data, obtained as part of the DIRECT project, for a sample of 22 Cepheids in the M31 galaxy. The average (median) V-band flux contribution from luminous companions that are not resolved on the ground-based images is about 19% (12%) of the flux of the Cepheid. This is a large effect—at the 10% level for distances. The current Cepheid distance estimates to M31 are all ground based and are thus affected (underestimated). We discuss indirect methods to find which Cepheids are blended, e.g., by the use of well-sampled light curves in at least two optical bands. More generally, our ground-based resolution in M31 corresponds to the HST resolution at about 10 Mpc. Blending leads to systematically low distances in the observed galaxies and therefore to systematically high estimates of H0; we discuss the issue and the implications.
An explanation for dark matter and dark energy consistent with the standard model of particle physics and General Relativity

Analyses of internal galaxy and cluster dynamics typically employ Newton’s law of gravity, which neglects the field self-interaction effects of General Relativity. This may be why dark matter seems necessary. The universe evolution, on the other hand, is treated with the full theory, General Relativity. However, the approximations of isotropy and homogeneity, normally used to derive and solve the universe evolution equations, effectively suppress General Relativity’s field self-interaction effects and this may introduce the need for dark energy. Calculations have shown that field self-interaction increases the binding of matter inside massive systems, which may account for galaxy and cluster dynamics without invoking dark matter. In turn, energy conservation dictates that the increased binding must be balanced by an effectively decreased gravitational interaction outside the massive system. In this article, such suppression is estimated and its consequence for the Universe’s evolution is discussed. Observations are reproduced without need for dark energy.
The Dynamics of Eruptive Prominences

This chapter discusses the dynamical properties of eruptive prominences in relation to coronal mass ejections (CMEs). The fact that eruptive prominences are a part of CMEs is emphasized in terms of their physical association and kinematics. The continued propagation of prominence material into the heliosphere is illustrated using in-situ observations. The solar-cycle variation of eruptive prominence locations is discussed with a particular emphasis on the rush-to-the-pole (RTTP) phenomenon. One of the consequences of the RTTP phenomenon is polar CMEs, which are shown to be similar to the low-latitude CMEs. This similarity is important because it provides important clues to the mechanism by which CMEs erupt. The nonradial motion of CMEs is discussed, including the deflection by coronal holes that have important space weather consequences. Finally, the implications of the presented observations for CME modeling are outlined.
NGC 1266: Characterization of the Nuclear Molecular Gas in an Unusual SB0 Galaxy

With a substantial nuclear molecular gas reservoir and broad, high-velocity CO molecular line wings previously interpreted as an outflow, NGC 1266 is a rare SB0 galaxy. Previous analyses of interferometry, spectrally resolved low-J CO emission lines, and unresolved high-J emission lines have established basic properties of the molecular gas and the likely presence of an active galactic nucleus. Here, new spectrally resolved CO J = 5-4 to J = 8-7 lines from Herschel Space Observatory HIFI observations are combined with ground-based observations and high-J Herschel SPIRE observations to decompose the nuclear and putative outflow velocity components and to model the molecular gas to quantify its properties. Details of the modeling and results are described, with comparisons to previous results and exploration of the implications for the gas excitation mechanisms. Among the findings, like for other galaxies, the nuclear and putative outflow molecular gas are well represented by components that are cool ( K and T outflow ~ 30 K), comprising bulk of the mass (log and log ), and the minority of the luminosity (log and log L outflow/L ☉ ~ 6.5) and warm ( K and T outflow > 100 K), comprising a minority of the mass (log and log M outflow/M ☉ ~ 6.3) but the majority of the luminosity (log and log L outflow/L ☉ ~ 7.2). The outflow has an anomalously high L CO/L FIR of 1.7 × 10–3 and is almost certainly shock excited.
Flux tube spectra from approximate integrability at low energies

We provide a detailed introduction to a method we recently proposed for calculating the spectrum of excitations of effective strings such as QCD flux tubes. The method relies on the approximate integrability of the low-energy effective theory describing the flux tube excitations and is based on the thermodynamic Bethe ansatz. The approximate integrability is a consequence of the Lorentz symmetry of QCD. For excited states, the convergence of the thermodynamic Bethe ansatz technique is significantly better than that of the traditional perturbative approach. We apply the new technique to the lattice spectra for fundamental flux tubes in gluodynamics in D = 3 + 1 and D = 2 + 1, and to k-strings in gluodynamics in D = 2 + 1. We identify a massive pseudoscalar resonance on the worldsheet of the confining strings in SU(3) gluodynamics in D = 3 + 1, and massive scalar resonances on the worldsheet of k = 2.3 strings in SU(6) gluodynamics in D = 2 + 1.
Toward Predicting Success and Failure in CS2: A Mixed-Method Analysis

Factors driving success and failure in CS1 are the subject of much study but less so for CS2. This paper investigates the transition from CS1 to CS2 in search of leading indicators of success in CS2. Both CS1 and CS2 at the University of North Carolina Wilmington (UNCW) are taught in Python with annual enrollments of 300 and 150 respectively. In this paper, we report on the following research questions: 1) Are CS1 grades indicators of CS2 grades? 2) Does a quantitative relationship exist between CS2 course grade and a modified version of the SCS1 concept inventory? and 3) What are the most challenging aspects of CS2, and how well does CS1 prepare students for CS2 from the student's perspective? We provide a quantitative analysis of 2300 CS1 and CS2 course grades from 2013-2019. In Spring 2019, we administered a modified version of the SCS1 concept inventory to 44 students in the first week of CS2. Further, 69 students completed a questionnaire at the conclusion of CS2 to gain qualitative student feedback on their challenges in CS2 and on how well CS1 prepared them for CS2. We find that 56% of students' grades were lower in CS2 than CS1, 18% improved their grades, and 26% earned the same grade. Of the changes, 62% were within one grade point. We find a statistically significant correlation between the modified SCS1 score and CS2 grade points. Students identify linked lists and class/object concepts among the most challenging. Student feedback on CS2 challenges and the adequacy of their CS1 preparations identify possible avenues for improving the CS1-CS2 transition.
Atmospheric Retrieval for Direct Imaging Spectroscopy of Gas Giants in Reflected Light. II. Orbital Phase and Planetary Radius

Future space-based telescopes, such as the Wide-Field Infrared Survey Telescope (WFIRST), will observe the reflected light spectra of directly imaged extrasolar planets. Interpretation of such data presents a number of novel challenges, including accounting for unknown planet radius and uncertain stellar illumination phase angle. Here, we report on our continued development of Markov Chain Monte Carlo retrieval methods for addressing these issues in the interpretation of such data. Specifically, we explore how the unknown planet radius and potentially poorly known observer-planet-star phase angle impacts retrievals of parameters of interest such as atmospheric methane abundance, cloud properties, and surface gravity. As expected, the uncertainty in retrieved values is a strong function of the signal-to-noise ratio (S/N) of the observed spectra, particularly for low metallicity atmospheres, which lack deep absorption signatures. Meaningful results may only be possible above certain S/N thresholds; for cases across a metallicity range of 1–50 times solar, we find that only an S/N of 20 systematically reproduces a value close to the correct methane abundance at all phase angles. However, even in cases where the phase angle is poorly known we find that the planet radius can be constrained to within a factor of two. We find that uncertainty in planet radius decreases at phase angles past quadrature, as the highly forward-scattering nature of the atmosphere at these geometries limits the possible volume of phase space that relevant parameters can occupy. Finally, we present an estimation of possible improvement that can result from combining retrievals against observations at multiple phase angles.