cssi/SciSciGPT-SciSciNet huggingface dataset:
FURTHER EVALUATION OF BOOTSTRAP RESAMPLING AS A TOOL FOR RADIO-INTERFEROMETRIC IMAGING FIDELITY ASSESSMENT

We report on a broader evaluation of statistical bootstrap resampling methods as a tool for pixel-level calibration and imaging fidelity assessment in radio interferometry. Pixel-level imaging fidelity assessment is a challenging problem, important for the value it holds in robust scientific interpretation of interferometric images, enhancement of automated pipeline reduction systems needed to broaden the user community for these instruments, and understanding leading-edge direction-dependent calibration and imaging challenges for future telescopes such as the Square Kilometre Array. This new computational approach is now possible because of advances in statistical resampling for data with long-range dependence and the available performance of contemporary high-performance computing resources. We expand our earlier numerical evaluation to span a broader domain subset in simulated image fidelity and source brightness distribution morphologies. As before, we evaluate the statistical performance of the bootstrap resampling methods against direct Monte Carlo simulation. We find that both model-based and subsample bootstrap methods continue to show significant promise for the challenging problem of interferometric imaging fidelity assessment when evaluated over the broader domain subset. We report on their measured statistical performance and guidelines for their use and application in practice. We also examine the performance of the underlying polarization self-calibration algorithm used in this study over a range of parallactic angle coverage.
Symplectic Floer homology of area-preserving surface diffeomorphisms

The symplectic Floer homology HF∗(ϕ) of a symplectomorphism ϕ:Σ→Σ encodes data about the fixed points of ϕ using counts of holomorphic cylinders in ℝ×Mϕ, where Mϕ is the mapping torus of ϕ. We give an algorithm to compute HF∗(ϕ) for ϕ a surface symplectomorphism in a pseudo-Anosov or reducible mapping class, completing the computation of Seidel’s HF∗(h) for h any orientation-preserving mapping class.
A new goodness-of-fit statistic and its application to 21-cm cosmology

The reduced chi-squared statistic is a commonly used goodness-of-fit measure, but it cannot easily detect features near the noise level, even when a large amount of data is available. In this paper, we introduce a new goodness-of-fit measure that we name the reduced psi-squared statistic. It probes the two-point correlations in the residuals of a fit, whereas chi-squared accounts for only the absolute values of each residual point, not considering the relationship between these points. The new statistic maintains sensitivity to individual outliers, but is superior to chi-squared in detecting wide, low level features in the presence of a large number of noisy data points. After presenting this new statistic, we show an instance of its use in the context of analyzing radio spectroscopic data for 21-cm cosmology experiments. We perform fits to simulated data with four components: foreground emission, the global 21-cm signal, an idealized instrument systematic, and noise. This example is particularly timely given the ongoing efforts to confirm the first observational result for this signal, where this work found its original motivation. In addition, we release a Python script dubbed \texttt{psipy} which allows for quick, efficient calculation of the reduced psi-squared statistic on arbitrary data arrays, to be applied in any field of study.
Three-dimensional Features of the Outer Heliosphere Due to Coupling between the Interstellar and Heliospheric Magnetic Field. V. The Bow Wave, Heliospheric Boundary Layer, Instabilities, and Magnetic Reconnection

The heliosphere is formed due to interaction between the solar wind (SW) and local interstellar medium (LISM). The shape and position of the heliospheric boundary, the heliopause, in space depend on the parameters of interacting plasma flows. The interplay between the asymmetrizing effect of the interstellar magnetic field and charge exchange between ions and neutral atoms plays an important role in the SW-LISM interaction. By performing three-dimensional, MHD plasma / kinetic neutral atom simulations, we determine the width of the outer heliosheath - the LISM plasma region affected by the presence of the heliosphere - and analyze quantitatively the distributions in front of the heliopause. It is shown that charge exchange modifies the LISM plasma to such extent that the contribution of a shock transition to the total variation of plasma parameters becomes small even if the LISM velocity exceeds the fast magnetosonic speed in the unperturbed medium. By performing adaptive mesh refinement simulations, we show that a distinct boundary layer of decreased plasma density and enhanced magnetic field should be observed on the interstellar side of the heliopause. We show that this behavior is in agreement with the plasma oscillations of increasing frequency observed by the plasma wave instrument onboard Voyager 1. We also demonstrate that Voyager observations in the inner heliosheath between the heliospheric termination shock and the heliopause are consistent with dissipation of the heliospheric magnetic field. The choice of LISM parameters in this analysis is based on the simulations that fit observations of energetic neutral atoms performed by IBEX.
Relaxation in N-body Simulations of Disk Galaxies

I use N-body simulations with two mass species of particles to demonstrate that disk galaxy simulations are subject to collisional relaxation at a higher rate than is widely assumed. Relaxation affects the vertical thickness of the disk most strongly, and drives the velocity ellipsoid to a moderately flattened shape similar to that observed for disk stars in the solar neighborhood. The velocity ellipsoid in simulations with small numbers of particles quickly approaches this shape, but shot noise also dominates the in-plane behavior. Simulations with higher, but reachable, numbers of particles relax slowly enough to be considered collisionless, allowing the in-plane dispersions to rise due to spiral activity without heating the vertical motions. Relaxation may have affected many previously published simulations of the formation and evolution of galaxy disks.
The IA-congruence kernel of high rank free metabelian groups

The congruence subgroup problem for a finitely generated group Γ and G ≤ A u t ( Γ ) asks whether the map Ĝ → A u t ( Γ ) is injective, or more generally, what its kernel C ( G , Γ ) is. Here X denotes the profinite completion of X . In this paper we investigate C ( I A ( Φ n ) , Φ n ) , where Φ n is a free metabelian group on n ≥ 4 generators, and I A ( Φ n ) = ker ( A u t ( Φ n ) → G L n ( ℤ ) ) . We show that in this case C ( I A ( Φ n ) , Φ n ) is abelian, but not trivial, and not even finitely generated. This behavior is very different from what happens for a free metabelian group on n = 2 or 3 generators, or for finitely generated nilpotent groups.
APSIDAL BEHAVIOR AMONG PLANETARY ORBITS: TESTING THE PLANET-PLANET SCATTERING MODEL

Planets in extrasolar systems tend to interact such that their orbits lie near a boundary between apsidal libration and circulation, a "separatrix," with one eccentricity periodically reaching near zero. One explanation, applied to the υ And system, assumed three original planets on circular orbits. One is ejected, leaving the other two with near-separatrix behavior. We test that model by integrating hundreds of hypothetical, unstable planetary systems that eject a planet. We find that the probability that the remaining planets exhibit near-separatrix motion is small (<5% compared with nearly 50% of observed systems). Moreover, while observed librating systems are evenly divided between aligned and antialigned pericenter longitudes, the scattering model strongly favors alignment. Alternative scattering theories are proposed, which may provide a more satisfactory fit with observed systems.
On the Ubiquity and Stellar Luminosity Dependence of Exocometary CO Gas: Detection around M Dwarf TWA 7

Millimeter observations of CO gas in planetesimal belts show a high detection rate around A stars, but few detections for later type stars. We present the first CO detection in a planetesimal belt around an M star, TWA 7. The optically thin CO (J=3-2) emission is co-located with previously identified dust emission from the belt, and the emission velocity structure is consistent with Keplerian rotation around the central star. The detected CO is not well shielded against photodissociation, and must thus be continuously replenished by gas release from exocomets within the belt. We analyze in detail the process of exocometary gas release and destruction around young M dwarfs and how this process compares to earlier type stars. Taking these differences into account, we find that CO generation through exocometary gas release naturally explains the increasing CO detection rates with stellar luminosity, mostly because the CO production rate from the collisional cascade is directly proportional to stellar luminosity. More luminous stars will therefore on average host more massive (and hence more easily detectable) exocometary CO disks, leading to the higher detection rates observed. The current CO detection rates are consistent with a ubiquitous release of exocometary gas in planetesimal belts, independent of spectral type.
VNI 3.1 MC-simulation program to study high-energy particle collisions in QCD by space-time evolution of parton-cascades and parton-hadron conversion

Abstract VNI is a general-purpose Monte Carlo event generator, which includes the simulation of lepton-lepton, lepton-hadron, lepton-nucleus, hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions. On the basis of renormalization-group improved parton description and quantum-kinetic theory, it uses the real-time evolution of parton cascades in conjunction with a self-consistent hadronization scheme that is governed by the dynamics itself. The causal evolution from a specific initial state (determined by the colliding beam particles) is followed by the time development of the phase-space densities of partons, pre-hadronic parton clusters, and final-state hadrons, in position space, momentum space and color space. The parton evolution is described in terms of a space-time generalization of the familiar momentum-space description of multiple (semi) hard interactions in QCD, involving 2 → 2 parton collisions, 2 → 1 parton fusion processes, and 1 → 2 radiation processes. The formation of color-singlet pre-hadronic clusters and their decays into hadrons, on the other hand, is treated by using a spatial criterion motivated by confinement and a non-perturbative model for hadronization. This article gives a brief review of the physics underlying VNI, which is followed by a detailed description of the program itself. The latter program description emphasizes easy-to-use pragmatism and explains how to use the program (including a simple example), annotates input and control parameters, and discusses output data provided by it.
Lessons from a large-scale assessment: Results from conceptual inventories

Conceptual gains improve with increased use of instructional materials informed by physics education research.
Existence of rational points on smooth projective varieties

Fix a number field k. We prove that if there is an algorithm for deciding whether a smooth projective geometrically integral k-variety has a k-point, then there is an algorithm for deciding whether an arbitrary k-variety has a k-point and also an algorithm for computing X(k) for any k-variety X for which X(k) is finite. The proof involves the construction of a one-parameter algebraic family of Châtelet surfaces such that exactly one of the surfaces fails to have a k-point.
Rethinking the Value of Labels for Improving Class-Imbalanced Learning

Real-world data often exhibits long-tailed distributions with heavy class imbalance, posing great challenges for deep recognition models. We identify a persisting dilemma on the value of labels in the context of imbalanced learning: on the one hand, supervision from labels typically leads to better results than its unsupervised counterparts; on the other hand, heavily imbalanced data naturally incurs "label bias" in the classifier, where the decision boundary can be drastically altered by the majority classes. In this work, we systematically investigate these two facets of labels. We demonstrate, theoretically and empirically, that class-imbalanced learning can significantly benefit in both semi-supervised and self-supervised manners. Specifically, we confirm that (1) positively, imbalanced labels are valuable: given more unlabeled data, the original labels can be leveraged with the extra data to reduce label bias in a semi-supervised manner, which greatly improves the final classifier; (2) negatively however, we argue that imbalanced labels are not useful always: classifiers that are first pre-trained in a self-supervised manner consistently outperform their corresponding baselines. Extensive experiments on large-scale imbalanced datasets verify our theoretically grounded strategies, showing superior performance over previous state-of-the-arts. Our intriguing findings highlight the need to rethink the usage of imbalanced labels in realistic long-tailed tasks. Code is available at this https URL.
The z ~ 4 Lyman Break Galaxies: Colors and Theoretical Predictions* **

We investigate several fundamental properties of z ~ 4 Lyman break galaxies by comparing observations with the predictions of a semianalytic model based on the cold dark matter theory of hierarchical structure formation. We use a sample of B435-dropouts from the Great Observatories Origins Deep Survey and complement the Advanced Camera for Surveys optical B435, V606, i775, and z850 data with the Very Large Telescope Infrared Spectrometer and Array Camera J, H, and Ks observations. We extract B435-dropouts from our semianalytic mock catalog using the same color criteria and magnitude limits that were applied to the observed sample. We find that the i775-Ks colors of the model-derived and observed B435-dropouts are in good agreement. However, we find that the i775-z850 colors differ significantly, indicating perhaps that either too little dust or an incorrect extinction curve has been used. Motivated by the reasonably good agreement between the model and observed data, we present predictions for the stellar masses, star formation rates, and ages for the z ~ 4 Lyman break sample. We find that according to our model, the color selection criteria used to select our z ~ 4 sample surveys 67% of all galaxies at this epoch down to z850 < 26.5. We find that our model predicts a ~40% mass buildup between the z ~ 4 and z ~ 3 epochs for the UV rest-frame L* galaxies. Furthermore, according to our model, at least 50% of the total stellar mass resides in relatively massive UV-faint objects that fall below our observational detection limit.
Conformal Symmetry as a Template for QCD

Conformal symmetry is broken in physical QCD; nevertheless, one can use conformal symmetry as a template, systematically correcting for its nonzero β function as well as higher-twist effects. For example, commensurate scale relations which relate QCD observables to each other, such as the generalized Crewther relation, have no renormalization scale or scheme ambiguity and retain a convergent perturbative structure which reflects the underlying conformal symmetry of the classical theory. The “conformal correspondence principle” also dictates the form of the expansion basis for hadronic distribution amplitudes. The AdS/CFT correspondence connecting superstring theory to superconformal gauge theory has important implications for hadron phenomenology in the conformal limit, including an all-orders demonstration of counting rules for hard exclusive processes as well as determining essential aspects of hadronic light-front wavefunctions. Theoretical and phenomenological evidence is now accumulating that QCD couplings based on physical observables such as τ decay become constant at small virtuality; i.e., effective charges develop an infrared fixed point in contradiction to the usual assumption of singular growth in the infrared. The near-constant behavior of effective couplings also suggests that QCD can be approximated as a conformal theory even at relatively small momentum transfer. The importance of using an analytic effective charge such as the pinch scheme for unifying the electroweak and strong couplings and forces is also emphasized. Invited talk given at the
Electron tomography for functional nanomaterials

Modern nanomaterials contain complexity that spans all three dimensions—from multigate semiconductors to clean energy nanocatalysts to complex block copolymers. For nanoscale characterization, it has been a long-standing goal to observe and quantify the three-dimensional (3D) structure—not just surfaces, but the entire internal volume and the chemical arrangement. Electron tomography estimates the complete 3D structure of nanomaterials from a series of two-dimensional projections taken across many viewing angles. Since its first introduction in 1968, electron tomography has progressed substantially in resolution, dose, and chemical sensitivity. In particular, scanning transmission electron microscope tomography has greatly enhanced the study of 3D nanomaterials by providing quantifiable internal morphology and spectroscopic detection of elements. Combined with recent innovations in computational reconstruction algorithms and 3D visualization tools, scientists can interactively dissect volumetric representations and extract meaningful statistics of specimens. This article highlights the maturing field of electron tomography and the widening scientific applications that utilize 3D structural, chemical, and functional imaging at the nanometer and subnanometer length scales.
Constructing a non-additive non-interacting kinetic energy functional approximation for covalent bonds from exact conditions.

We present a non-decomposable approximation for the non-additive non-interacting kinetic energy (NAKE) for covalent bonds based on the exact behavior of the von Weizsacker (vW) functional in regions dominated by one orbital. This covalent approximation (CA) seamlessly combines the vW and the Thomas-Fermi functional with a switching function of the fragment densities constructed to satisfy exact constraints. It also makes use of ensembles and fractionally occupied spin-orbitals to yield highly accurate NAKE for stretched bonds while outperforming other standard NAKE approximations near equilibrium bond lengths. We tested the CA within Partition-Density Functional Theory (P-DFT) and demonstrated its potential to enable fast and accurate P-DFT calculations.
Observational Constraints on Correlated Star Formation and Active Galactic Nuclei in Late-stage Galaxy Mergers

Galaxy mergers are capable of triggering both star formation and active galactic nuclei (AGN) and therefore may represent an important pathway in the co-evolution of galaxies and supermassive black holes (SMBHs). However, correlated enhancements of merger-induced star formation and AGN triggering may be hidden by the variable conditions and timescales during which they occur. In Paper I, we presented evidence of merger-triggered AGN in a sample of six late-stage galaxy mergers (2-8 kpc nuclear separations). In this follow-up work, we use multi-wavelength Hubble Space Telescope imaging and additional archival data to examine their star-forming properties to test for merger-triggered star formation, and if it is correlated with SMBH growth. We find that the morphological asymmetries are correlated with enhanced specific star formation rates, indicating the presence of merger-triggered star formation. Additionally, the stellar populations become younger with increasing radius from the nucleus, indicating that the merger-induced star formation primarily occurs on global scales. However, we also find that the star formation rate enhancements are consistent with or lower than those of larger separation galaxy pair samples. This result is consistent with simulations predicting a decline of the global star formation rates in late-stage galaxy mergers with 10^8 yrs likely exists between the peak of global star formation and the onset of AGN triggering in 80% of the systems.
What Does a Successful Postdoctoral Fellowship Publication Record Look Like

Obtaining a prize postdoctoral fellowship in astronomy and astrophysics involves a number of factors, many of which cannot be quantified. One criterion that can be measured is the publication record of an applicant. The publication records of past fellowship recipients may, therefore, provide some quantitative guidance for future prospective applicants. We investigated the publication patterns of recipients of the NASA prize postdoctoral fellowships in the Hubble, Einstein, and Sagan programs from 2014 through 2017, using the NASA ADS reference system. We tabulated their publications at the point where fellowship applications were submitted, and we find that the 133 fellowship recipients in that time frame had a median of 6 ± 2 first-author publications, and 14 ± 6 co-authored publications. The full range of first-author papers is one to 15, and for all papers ranges from two to 76, indicating very diverse publication patterns. Thus, while fellowship recipients generally have strong publication records, the distribution of both first-author and co-authored papers is quite broad; there is no apparent threshold of publications necessary to obtain these fellowships. We also examined the post-PhD publication rates for each of the three fellowship programs, between male and female recipients, across the four years of the analysis and find no consistent trends. We hope that these findings will prove a useful reference to future junior scientists.
Exponential ergodicity of mirror-Langevin diffusions

Motivated by the problem of sampling from ill-conditioned log-concave distributions, we give a clean non-asymptotic convergence analysis of mirror-Langevin diffusions as introduced in Zhang et al. (2020). As a special case of this framework, we propose a class of diffusions called Newton-Langevin diffusions and prove that they converge to stationarity exponentially fast with a rate which not only is dimension-free, but also has no dependence on the target distribution. We give an application of this result to the problem of sampling from the uniform distribution on a convex body using a strategy inspired by interior-point methods. Our general approach follows the recent trend of linking sampling and optimization and highlights the role of the chi-squared divergence. In particular, it yields new results on the convergence of the vanilla Langevin diffusion in Wasserstein distance.
Attacking strategies and temporal analysis involving Facebook discussion groups

Online social network (OSN) discussion groups are exerting significant effects on political dialogue. In the absence of access control mechanisms, any user can contribute to any OSN thread. Individuals can exploit this characteristic to execute targeted attacks, which increases the potential for subsequent malicious behaviors such as phishing and malware distribution. These kinds of actions will also disrupt bridges among the media, politicians, and their constituencies. For the concern of Security Management, blending malicious cyberattacks with online social interactions has introduced a brand new challenge. In this paper we describe our proposal for a novel approach to studying and understanding the strategies that attackers use to spread malicious URLs across Facebook discussion groups. We define and analyze problems tied to predicting the potential for attacks focused on threads created by news media organizations. We use a mix of macro static features and the micro dynamic evolution of posts and threads to identify likely targets with greater than 90% accuracy. One of our secondary goals is to make such predictions within a short (10 minute) time frame. It is our hope that the data and analyses presented in this paper will support a better understanding of attacker strategies and footprints, thereby developing new system management methodologies in handing cyber attacks on social networks.
Lorentz-violating gravity and the bootstrap procedure

In conventional gravitational physics, the so-called ``bootstrap procedure'' can be used to extrapolate from a linear model of a rank-2 tensor to a full non-linear theory of gravity (i.e., general relativity) via a coupling to the stress-energy of the model. In this work, I extend this procedure to a ``Lorentz-violating'' gravitational model, in which the linear tensor field and the matter fields ``see'' different metrics due to a coupling between the tensor field and a background vector field. The resulting model can be thought of as a generalized Proca theory with a non-minimal coupling to conventional matter. It has a similar linearized limit to the better-known ``bumblebee model'', but differs at higher orders in perturbation theory. Its effects are unobservable in FRW spacetimes, but are expected to be important in anisotropic cosmological spacetimes.
Roche Lobe Overflow from Dwarf Stellar Systems

We use both analytical analyses and numerical simulations to examine the evolution of residual gas within tidally-limited dwarf galaxies and globular clusters. If the gas sound speed exceeds about 10% of the central velocity dispersion, as is the case for ionized gas within small stellar systems, the gas shall have significant density at the tidal radius, and the gas may be lost on timescales as short as a few times the sound crossing time of the system. In colder systems, the density at the tidal radius is much lower, greatly reducing the mass loss rate, and the system may retain its gas for a Hubble time. The tidally removed gas shall follow an orbit close to that of the original host system, forming an extended stream of ionized, gaseous debris. Tidal mass loss severely limits the ability of dwarf systems to continuously form stars. The ordinary gas content in many dwarf galaxies is fully ionized during high red-shift epochs, possibly preventing star formation in some systems, leading to the formation of starless, dark-matter concentrations. In either the field or in the center of galaxy clusters, ionized gas may be retained by dwarf galaxies, even though its sound speed may be comparable to or even exceed the velocity dispersion. These processes may help to explain some observed differences among dwarf galaxy types, as well as observations of the haloes of massive galaxies.
Complete Dictionary Recovery Over the Sphere I: Overview and the Geometric Picture

We consider the problem of recovering a complete (i.e., square and invertible) matrix $ A_{0}$ , from $ Y \in \mathbb R ^{n \times p}$ with $ Y = A_{0} X_{0}$ , provided $ X_{0}$ is sufficiently sparse. This recovery problem is central to theoretical understanding of dictionary learning, which seeks a sparse representation for a collection of input signals and finds numerous applications in modern signal processing and machine learning. We give the first efficient algorithm that provably recovers $ A_{0}$ when $ X_{0}$ has $O \left ({ n }\right )$ nonzeros per column, under suitable probability model for $ X_{0}$ . In contrast, prior results based on efficient algorithms either only guarantee recovery when $ X_{0}$ has $O(\sqrt {n})$ zeros per column, or require multiple rounds of semidefinite programming relaxation to work when $ X_{0}$ has $O(n)$ nonzeros per column. Our algorithmic pipeline centers around solving a certain nonconvex optimization problem with a spherical constraint. In this paper, we provide a geometric characterization of the objective landscape. In particular, we show that the problem is highly structured with high probability: 1) there are no “spurious” local minimizers and 2) around all saddle points the objective has a negative directional curvature. This distinctive structure makes the problem amenable to efficient optimization algorithms. In a companion paper, we design a second-order trust-region algorithm over the sphere that provably converges to a local minimizer from arbitrary initializations, despite the presence of saddle points.
Throwing stones and collecting bones: Looking for Poisson‐like random measures

We show that in a broad class of random counting measures one may identify only three that are rescaled versions of themselves when restricted to a subspace. These are Poisson, binomial and negative binomial random measures. We provide some simple examples of possible applications of such measures.
An EM-based iterative method for solving large sparse linear systems

ABSTRACTWe propose a novel iterative algorithm for solving a large sparse linear system. The method is based on the EM algorithm. If the system has a unique solution, the algorithm guarantees conve...
The Propitious Role of Solar Energetic Particles in the Origin of Life

We carry out 3-D numerical simulations to assess the penetration and bombardment effects of Solar Energetic Particles (SEPs), i.e. high-energy particle bursts during large flares and superflares, on ancient and current Mars. We demonstrate that the deposition of SEPs is non-uniform at the planetary surface, and that the corresponding energy flux is lower than other sources postulated to have influenced the origin of life. Nevertheless, SEPs may have been capable of facilitating the synthesis of a wide range of vital organic molecules (e.g. nucleobases and amino acids). Owing to the relatively high efficiency of these pathways, the overall yields might be comparable to (or even exceed) the values predicted for some conventional sources such as electrical discharges and exogenous delivery by meteorites. We also suggest that SEPs could have played a role in enabling the initiation of lightning. A notable corollary of our work is that SEPs may constitute an important mechanism for prebiotic synthesis on exoplanets around M-dwarfs, thereby mitigating the deficiency of biologically active ultraviolet radiation on these planets. Although there are several uncertainties associated with (exo)planetary environments and prebiotic chemical pathways, our study illustrates that SEPs represent a potentially important factor in understanding the origin of life.
Differential distributed space-time coding with imperfect synchronization

Differential distributed space-time coding (D-DSTC) has been considered to improve both diversity and data-rate in cooperative communications in the absence of channel information. However, conventionally, it is assumed that relays are perfectly synchronized in the symbol level. In practice, this assumption is easily violated due to the distributed nature of the relay networks. This paper proposes a new differential encoding and decoding process for D-DSTC systems with two relays. The proposed method is robust against synchronization errors and does not require any channel information at the destination. Moreover, the maximum possible diversity and symbol-by-symbol decoding are attained. Simulation results are provided to show the performance of the proposed method for various synchronization errors and the fact that our algorithm is not sensitive to synchronization error.
WHITE DWARF MERGERS ON ADAPTIVE MESHES. I. METHODOLOGY AND CODE VERIFICATION

Author(s): Katz, MP; Zingale, M; Calder, AC; Swesty, FD; Almgren, AS; Zhang, W | Abstract: The Type Ia supernova (SN Ia) progenitor problem is one of the most perplexing and exciting problems in astrophysics, requiring detailed numerical modeling to complement observations of these explosions. One possible progenitor that has merited recent theoretical attention is the white dwarf (WD) merger scenario, which has the potential to naturally explain many of the observed characteristics of SNe Ia. To date there have been relatively few self-consistent simulations of merging WD systems using mesh-based hydrodynamics. This is the first paper in a series describing simulations of these systems using a hydrodynamics code with adaptive mesh refinement. In this paper we describe our numerical methodology and discuss our implementation in the compressible hydrodynamics code CASTRO, which solves the Euler equations, and the Poisson equation for self-gravity, and couples the gravitational and rotation forces to the hydrodynamics. Standard techniques for coupling gravitation and rotation forces to the hydrodynamics do not adequately conserve the total energy of the system for our problem, but recent advances in the literature allow progress and we discuss our implementation here. We present a set of test problems demonstrating the extent to which our software sufficiently models a system where large amounts of mass are advected on the computational domain over long timescales. Future papers in this series will describe our treatment of the initial conditions of these systems and will examine the early phases of the merger to determine its viability for triggering a thermonuclear detonation.
Coupling of erbium dopants to yttrium orthosilicate photonic crystal cavities for on-chip optical quantum memories

Erbium dopants in crystals exhibit highly coherent optical transitions well suited for solid-state optical quantum memories operating in the telecom band. Here, we demonstrate coupling of erbium dopant ions in yttrium orthosilicate to a photonic crystal cavity fabricated directly in the host crystal using focused ion beam milling. The coupling leads to reduction of the photoluminescence lifetime and enhancement of the optical depth in microns-long devices, which will enable on-chip quantum memories.
Volatility occupation times

We propose nonparametric estimators of the occupation measure and the occupation density of the diffusion coefficient (stochastic volatility) of a discretely observed Ito semimartingale on a fixed interval when the mesh of the observation grid shrinks to zero asymptotically. In a first step we estimate the volatility locally over blocks of shrinking length, and then in a second step we use these estimates to construct a sample analogue of the volatility occupation time and a kernel-based estimator of its density. We prove the consistency of our estimators and further derive bounds for their rates of convergence. We use these results to estimate nonparametrically the quantiles associated with the volatility occupation measure.
DYNAMIC STABILITY OF THE SOLAR SYSTEM: STATISTICALLY INCONCLUSIVE RESULTS FROM ENSEMBLE INTEGRATIONS

Due to the chaotic nature of the solar system, the question of its long-term stability can only be answered in a statistical sense, for instance, based on numerical ensemble integrations of nearby orbits. Destabilization of the inner planets, leading to close encounters and/or collisions can be initiated through a large increase in Mercury's eccentricity, with a currently assumed likelihood of ~1%. However, little is known at present about the robustness of this number. Here I report ensemble integrations of the full equations of motion of the eight planets and Pluto over 5 Gyr, including contributions from general relativity. The results show that different numerical algorithms lead to statistically different results for the evolution of Mercury's eccentricity (). For instance, starting at present initial conditions (), Mercury's maximum eccentricity achieved over 5 Gyr is, on average, significantly higher in symplectic ensemble integrations using heliocentric rather than Jacobi coordinates and stricter error control. In contrast, starting at a possible future configuration (), Mercury's maximum eccentricity achieved over the subsequent 500 Myr is, on average, significantly lower using heliocentric rather than Jacobi coordinates. For example, the probability for to increase beyond 0.53 over 500 Myr is >90% (Jacobi) versus only 40%-55% (heliocentric). This poses a dilemma because the physical evolution of the real system—and its probabilistic behavior—cannot depend on the coordinate system or the numerical algorithm chosen to describe it. Some tests of the numerical algorithms suggest that symplectic integrators using heliocentric coordinates underestimate the odds for destabilization of Mercury's orbit at high initial .
Efficient anharmonic lattice dynamics calculations of thermal transport in crystalline and disordered solids

Understanding heat transport in semiconductors and insulators is of fundamental importance because of its technological impact in electronics and renewable energy harvesting and conversion. Anharmonic lattice dynamics provides a powerful framework for the description of heat transport at the nanoscale. One of the advantages of this method is that it naturally includes quantum effects due to atoms vibrations, which are needed to compute the thermal properties of semiconductors widely used in nanotechnology, like silicon and carbon, even at room temperature. While the heat transport picture substantially differs between amorphous and crystalline semiconductors from a microscopic standpoint, a unified approach to simulate both crystals and glasses has been devised. Here, we introduce a unified workflow, which implements both the Boltzmann Transport equation and the quasi-harmonic Green-Kubo methods. We discuss how the theory can be optimized to exploit modern parallel architectures, and how it is implemented in κALD o: a versatile and scalable open-source software to compute phonon transport in solids. This approach is applied to crystalline and partially disordered silicon-based systems, including bulk silicon and clathrates, and on silicon–germanium alloy clathrates with largely reduced thermal conductivity.
Axion Periodicity and Coupling Quantization in the Presence of Mixing

Mixing of axion fields is widely used to generate EFTs with phenomenologically advantageous features, such as hierarchies between axion couplings to different gauge fields and/or large effective field ranges. While these features are strongly constrained by periodicity for models with only a single axion, mixing has been used in the literature (sometimes incorrectly) to try to evade some of these constraints. In this paper, we ask whether it is possible to use axion mixing to generate an EFT of axions that evades these constraints by flowing to a theory of a non-compact scalar in the IR. We conclude that as long as the light axion is exactly massless, it will inherit the periodicity and associated constraints of the UV theory. However, by giving the light axion a mass, we can relax these constraints with effects proportional to the axion mass squared, including non-quantized couplings and the realignment of monodromy to a light axion with a larger field range. To show this, we consider various examples of axions mixing with other axions or with non-compact scalar fields, and work in a basis where coupling quantization is manifest. This basis makes it clear that in the case where an axion is eaten through the Higgs or Stuckelberg mechanism, the light axion does not have a large effective field range, in contrast to some recent claims in the literature. Additionally, we relate our results about axion EFTs to a well-known fact about gauge theory: that QFTs with compact gauge groups in the UV flow to QFTs with compact gauge groups in the IR, and make this correspondence precise in the 2+1 dimensional case.
Analysis of a Custom Support Vector Machine for Photometric Redshift Estimation and the Inclusion of Galaxy Shape Information

Aims. We present a custom support vector machine classification package for photometric redshift estimation, including comparisons with other methods. We also explore the efficacy of including galaxy shape information in redshift estimation. Support vector machines, a type of machine learning, utilize optimization theory and supervised learning algorithms to construct predictive models based on the information content of data in a way that can treat different input features symmetrically, which can be a useful estimator of the information contained in additional features beyond photometry, such as those describing the morphology of galaxies. Methods. The custom support vector machine package we have developed is designated SPIDERz and made available to the community. As test data for evaluating performance and comparison with other methods, we apply SPIDERz to four distinct data sets: 1) the publicly available portion of the PHAT-1 catalog based on the GOODS-N field with spectroscopic redshifts in the range z We find that SPIDERz achieves results competitive with other empirical packages on the PHAT-1 data, and performs quite well in estimating redshifts with the COSMOS and AEGIS data, including in the cases of a large redshift range (0 < 3.9). We also determine from analyses with both the COSMOS and AEGIS data that the inclusion of morphological information does not have a statistically significant benefit for photometric redshift estimation with the techniques employed here.
Cadre Modeling: Simultaneously Discovering Subpopulations and Predictive Models

We consider the problem in regression analysis of identifying subpopulations that exhibit different patterns of response, where each subpopulation requires a different underlying model. Unlike statistical cohorts, these subpopulations are not known a priori; thus, we refer to them as cadres. When the cadres and their associated models are interpretable, modeling leads to insights about the subpopulations and their associations with the regression target. We introduce a discriminative model that simultaneously learns cadre assignment and target-prediction rules. Sparsity-inducing priors are placed on the model parameters, under which independent feature selection is performed for both the cadre assignment and targetprediction processes. We learn models using adaptive step size stochastic gradient descent, and we assess cadre quality with bootstrapped sample analysis. We present simulated results showing that, when the true clustering rule does not depend on the entire set of features, our method significantly outperforms methods that learn subpopulation-discovery and targetprediction rules separately. In a materials-by-design case study, our model provides state-of-the-art prediction of polymer glass transition temperature. Importantly, the method identifies cadres of polymers that respond differently to structural perturbations, thus providing design insight for targeting or avoiding specific transition temperature ranges. It identifies chemically meaningful cadres, each with interpretable models. Further experimental results show that cadre methods have generalization that is competitive with linear and nonlinear regression models and can identify robust subpopulations.
Four papers on contemporary software design strategies for statistical methodologists

Software design impacts much of statistical analysis and, as technology changes, dramatically so in recent years, it is exciting to learn how statistical software is adapting and changing. This leads to the collection of papers published here, written by John Chambers, Duncan Temple Lang, Michael Lawrence, Martin Morgan, Yihui Xie, Heike Hofmann and Xiaoyue Cheng.
The Orbital Parameters of the Eclipsing High-mass X-Ray Binary Pulsar IGR J16493-4348 from Pulsar Timing

IGR J16493–4348 is an eclipsing supergiant high-mass X-ray binary (sgHMXB), where accretion onto the compact object occurs via the radially outflowing stellar wind of its early B-type companion. We present an analysis of the system's X-ray variability and periodic modulation using pointed observations (2.5–25 keV) and Galactic bulge scans (2–10 keV) from the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA), along with Swift Burst Alert Telescope (BAT) 70-month snapshot (14–195 keV) and transient monitor (15–50 keV) observations. The orbital eclipse profiles from the PCA scan and BAT light curves are modeled using asymmetric and symmetric step and ramp functions. We obtain an improved orbital period measurement of 6.7828 ± 0.0004 days from an observed minus calculated (O–C) analysis of mid-eclipse times derived from the BAT transient monitor and PCA scan data. No evidence is found for the presence of a strong photoionization or accretion wake. We refine the superorbital period to 20.067 ± 0.009 days from the discrete Fourier transform (DFT) of the BAT transient monitor light curve. A pulse period of 1093.1036 ± 0.0004 s is measured from a pulsar timing analysis using pointed PCA observations spanning ~1.4 binary orbits. We present pulse times of arrival (ToAs), circular and eccentric timing models, and calculations of the system's Keplerian binary orbital parameters. We derive an X-ray mass function of f_x(M) = 13.2_(-2.5)^(+2.4) M_⊙ and find a spectral type of B0.5 Ia for the supergiant companion through constraints on the mass and radius of the donor. Measurements of the eclipse half-angle and additional parameters describing the system geometry are provided.
Residence Times of Particles in Diffusive Protoplanetary Disk Environments. I. Vertical Motions

The chemical and physical evolution of primitive materials in protoplanetary disks are determined by the types of environments they are exposed to and their residence times within each environment. Here, a method for calculating representative paths of materials in diffusive protoplanetary disks is developed and applied to understanding how the vertical trajectories that particles take impact their overall evolution. The methods are general enough to be applied to disks with uniform diffusivity, the so-called constant-{alpha} cases, and disks with a spatially varying diffusivity, such as expected in 'layered-disks'. The average long-term dynamical evolution of small particles and gaseous molecules is independent of the specific form of the diffusivity in that they spend comparable fractions of their lifetimes at different heights in the disk. However, the paths that individual particles and molecules take depend strongly on the form of the diffusivity leading to a different range of behavior of particles in terms of deviations from the mean. As temperatures, gas densities, chemical abundances, and photon fluxes will vary with height in protoplanetary disks, the different paths taken by primitive materials will lead to differences in their chemical and physical evolution. Examples of differences in gas phase chemistry and photochemistry are exploredmore » here. The methods outlined here provide a powerful tool that can be integrated with chemical models to understand the formation and evolution of primitive materials in protoplanetary disks on timescales of 10{sup 5}-10{sup 6} years.« less
Upper Limits on Planet Occurrence around Ultracool Dwarfs with K2

The occurrence of planets orbiting ultracool dwarfs is poorly constrained. We present results from a Guest Observer program on NASA's K2 spacecraft to search for transiting planets orbiting a sample of 827 ultracool dwarfs. Having found no transiting planets in our sample, we determined an upper limit on the occurrence of planets. We simulated planets orbiting our sample for a range of orbital periods and sizes. For the simulated planets that transit their host, we injected the transit light curve into the real K2 light curves, then attempted to recover the injected planets. For a given occurrence rate, we calculated the probability of seeing no planets, and use the results to place an upper limit on planet occurrence as a function of planet radius and orbital period. We find that short period, mini-Neptune- and Jupiter-sized planets are rare around ultracool dwarfs, consistent with results for early- and mid-type M dwarf stars. We constrain the occurrence rate $\eta$ for planets between $0.5$ and $10$ R$_{\oplus}$ with orbital periods between 1 and 26.3 days.