cssi/SciSciGPT-SciSciNet huggingface dataset:
INVERSE-COMPTON CONTRIBUTION TO THE STAR-FORMING EXTRAGALACTIC GAMMA-RAY BACKGROUND

Fermi has resolved several star-forming galaxies, but the vast majority of the star-forming universe is unresolved, and thus contributes to the extragalactic gamma-ray background (EGB). Here, we calculate the contribution of star-forming galaxies to the EGB in the Fermi range from 100 MeV to 100 GeV due to inverse-Compton (IC) scattering of the interstellar photon field by cosmic-ray electrons. We first construct one-zone models for individual star-forming galaxies assuming that supernovae power the acceleration of cosmic rays. We develop templates for both normal and starburst galaxies, accounting for differences in the cosmic-ray electron propagation and in the interstellar radiation fields. For both types of star-forming galaxies, the same IC interactions leading to gamma rays also substantially contribute to the energy loss of the high-energy cosmic-ray electrons. Consequently, a galaxy's IC emission is determined by the relative importance of IC losses in the cosmic-ray electron energy budget ({sup p}artial calorimetry{sup )}. We calculate the cosmological contribution of star-forming galaxies to the EGB using our templates and the cosmic star formation rate distribution. For all of our models, we find that the IC EGB contribution is almost an order of magnitude less than the peak of the emission due to cosmic-ray ionmore » interactions (mostly pionic p{sub cr} p{sub ism} {yields} {pi}{sup 0} {yields} {gamma}{gamma}); even at the highest Fermi energies, IC is subdominant. The flatter IC spectrum increases the high-energy signal of the pionic+IC sum, bringing it closer to the EGB spectral index observed by Fermi. Partial calorimetry ensures that the overall IC signal is relatively well constrained, with only uncertainties in the amplitude and spectral shape for plausible model choices. We conclude with a brief discussion on how the pionic spectral feature and other methods can be used to measure the star-forming component of the EGB.« less
Full-featured peak reduction in right-angled Artin groups

We prove a new version of the classical peak reduction theorem for automorphisms of free groups in the setting of right-angled Artin groups. We use this peak reduction theorem to prove two important corollaries about the action of the automorphism group of a right-angled Artin group AA on the set of k ‐tuples of conjugacy classes from AA : orbit membership is decidable, and stabilizers are finitely presentable. Further, we explain procedures for checking orbit membership and building presentations of stabilizers. This improves on a previous result of the author. We overcome a technical difficulty from the previous work by considering infinite generating sets for the automorphism groups. The method also involves a variation on the Hermite normal form for matrices. 20F36; 20F28, 15A36
C, N, and O Isotopic Heterogeneities in Low-density Supernova Graphite Grains from Orgueil

We report on the results of NanoSIMS isotope imaging of low-density supernova graphite grains from the Orgueil meteorite. 70 nm thick microtomed sections of three supernova graphite grains were deposited on Si wafers and isotopically imaged in the NanoSIMS. These sections contain hotspots of excesses in {sup 18}O and {sup 15}N, which are spatially well correlated, and are likely carried by internal TiC subgrains. These hotspots are considerably more enriched in {sup 18}O and {sup 15}N than the host graphite grain. Correlations between {sup 18}O and {sup 15}N excesses indicate that the grains incorporated material from the He/C supernova zone. Isotope images of the surfaces of some grains show heterogeneities in their N and O isotope compositions, with extreme excesses in {sup 15}N and {sup 18}O. In the microtome sections, we also observe two types of heterogeneities in the grains' C isotopic compositions: smooth, radial gradients in {sup 12}C/{sup 13}C, with this ratio trending toward solar with increasing radius; and highly anomalous pockets up to 2 {mu}m in size with {sup 12}C/{sup 13}C >> solar that are located near the centers of the grain sections. Partial isotopic equilibration does not likely explain the C isotopic heterogeneities. These grains and theirmore » constituent parts probably formed in a stellar environment with changing isotopic composition.« less
Detecting Cross-Modal Inconsistency to Defend Against Neural Fake News

Large-scale dissemination of disinformation online intended to mislead or deceive the general population is a major societal problem. Rapid progression in image, video, and natural language generative models has only exacerbated this situation and intensified our need for an effective defense mechanism. While existing approaches have been proposed to defend against neural fake news, they are generally constrained to the very limited setting where articles only have text and metadata such as the title and authors. In this paper, we introduce the more realistic and challenging task of defending against machine-generated news that also includes images and captions. To identify the possible weaknesses that adversaries can exploit, we create a NeuralNews dataset which is comprised of 4 different types of generated articles as well as conduct a series of human user study experiments based on this dataset. Coupled with providing a relatively effective approach based on detecting visual-semantic inconsistencies, the valuable insights gleaned from our user study experiments and, consequently, this paper will serve as an effective first line of defense and a valuable reference for future work in defending against machine-generated disinformation.
Approaches to the Optimal Nonlinear Analysis of Microcalorimeter Pulses

We consider how to analyze microcalorimeter pulses for quantities that are nonlinear in the data, while preserving the signal-to-noise advantages of linear optimal filtering. We successfully apply our chosen approach to compute the electrothermal feedback energy deficit (the “Joule energy”) of a pulse, which has been proposed as a linear estimator of the deposited photon energy.
Using Surface Brightness Fluctuations to Study Nearby Satellite Galaxy Systems: Calibration and Methodology

We explore the use of ground-based surface brightness fluctuation (SBF) measurements to constrain distances to nearby dwarf galaxies. Using archival CFHT Megacam imaging data for a sample of 27 nearby dwarfs, we demonstrate that reliable SBF measurements and distances accurate to 15\% are possible even for very low surface brightness (LSB, $\mu_{i0}>24$ mag/arcsec$^2$) galaxies with modest, $\sim$hour-long exposures with CFHT. Combining our sample with a recent sample of 7 dwarfs with SBF measured with HST from the literature, we provide the most robust empirical SBF calibration to-date for the blue colors expected for these low mass systems. Our calibration is credible over the color range $0.3\lesssim g-i\lesssim0.8$ mag. It is also the first SBF calibration tied completely to TRGB distances as each galaxy in the sample has a literature TRGB distance. We find that even though the intrinsic scatter in SBF increases for blue galaxies, the rms scatter in the calibration is still $\lesssim0.3$ mag. We verify our measurements by comparing with HST SBF measurements and detailed image simulations. We argue that ground-based SBF is a very useful tool for characterizing dwarf satellite systems and field dwarfs in the nearby, D$\lesssim$20 Mpc universe.
A remark on strict independence relations

We prove that if T is a complete theory with weak elimination of imaginaries, then there is an explicit bijection between strict independence relations for T and strict independence relations for $${T^{\rm eq}}$$Teq. We use this observation to show that if T is the theory of the Fraisse limit of finite metric spaces with integer distances, then $${T^{\rm eq}}$$Teq has more than one strict independence relation. This answers a question of Adler (J Math Log 9(1):1---20, 2009, Question 1.7).
An in-depth analysis of stochastic Kronecker graphs

Graph analysis is playing an increasingly important role in science and industry. Due to numerous limitations in sharing real-world graphs, models for generating massive graphs are critical for developing better algorithms. In this article, we analyze the stochastic Kronecker graph model (SKG), which is the foundation of the Graph500 supercomputer benchmark due to its favorable properties and easy parallelization. Our goal is to provide a deeper understanding of the parameters and properties of this model so that its functionality as a benchmark is increased. We develop a rigorous mathematical analysis that shows this model cannot generate a power-law distribution or even a lognormal distribution. However, we formalize an enhanced version of the SKG model that uses random noise for smoothing. We prove both in theory and in practice that this enhancement leads to a lognormal distribution. Additionally, we provide a precise analysis of isolated vertices, showing that the graphs that are produced by SKG might be quite different than intended. For example, between 50p and 75p of the vertices in the Graph500 benchmarks will be isolated. Finally, we show that this model tends to produce extremely small core numbers (compared to most social networks and other real graphs) for common parameter choices.
Integrable Systems from the Classical Reflection Equation

We construct integrable Hamiltonian systems on $G/K$, where $G$ is a quasitriangular Poisson Lie group and $K$ is a Lie subgroup arising as the fixed point set of a group automorphism $\sigma$ of $G$ satisfying the classical reflection equation. In the case that $G$ is factorizable, we show that the time evolution of these systems is described by a Lax equation, and present its solution in terms of a factorization problem in $G$. Our construction is closely related to the semiclassical limit of Sklyanin's integrable quantum spin chains with reflecting boundaries.
Emergent Gravity from Vanishing Energy-Momentum Tensor

A constraint of vanishing energy-momentum tensor is motivated by a variety of perspectives on quantum gravity. We demonstrate in a concrete example how this constraint leads to a metric-independent theory in which quantum gravity emerges as a nonperturbative artifact of regularization-scale physics. We analyze a scalar theory similar to the Dirac-Born-Infeld (DBI) theory with vanishing gauge fields, with the DBI Lagrangian modulated by a scalar potential. In the limit of a large number of scalars, we explicitly demonstrate the existence of a composite massless spin-2 graviton in the spectrum that couples to matter as in Einstein gravity. We comment on the cosmological constant problem and the generalization to theories with fermions and gauge fields.
On the Analytic Estimation of Radioactive Contamination from Degraded Alphas

The high energy spectrum of alpha particles emitted from a single isotope uniformly contaminating a bulk solid has a flat energy spectrum with a high end cutoff energy equal to the maximal alpha kinetic energy (Tα) of the decay. In this flat region of the spectrum, we show the surface rate rb (Bq keV−1cm−2) arising from a bulk alpha contamination ρb (Bq cm−3) from a single isotope is given by rb =ρb Δ R/ 4 Δ E , where Δ E = E1−E2>0 is the energy interval considered (keV) in the flat region of the spectrum and Δ R = R2−R1, where R2 (R1) is the amount of the bulk material (cm) necessary to degrade the energy of the alpha from Tα to E2 (E1). We compare our calculation to a rate measurement of alphas from 147Sm, (15.32 ± 0.03% of Sm(nat) and half life of (1.06 ± 0.01)× 1011 yr [1]), and find good agreement, with the ratio between prediction to measurement of 100.2%± 1.6% (stat)± 2.1% (sys). We derive the condition for the flat spectrum, and also calculate the relationship between the decay rate measured at the surface for a [near] surface contamination with an exponential dependence on depth and a second case of an alpha source with a thin overcoat. While there is excellent agreement between our implementation of the sophisticated Monte Carlo program SRIM [2] and our intuitive model in all cases, both fail to describe the measured energy distribution of a 148Gd alpha source with a thin (~200μg cm−2) Au overcoat. We discuss possible origins of the disagreement and suggest avenues for future study.
A Family-based Method of Quantifying NEOWISE Diameter Errors

Quantifying the accuracy with which physical properties of asteroids can be determined from thermal modeling is critical to measuring the impact of infrared data on our understanding of asteroids. Previous work has used independently derived diameters (from asteroid radar, occultations, and spacecraft visits) to test the accuracy of the NEOWISE diameter determinations. Here, we present a new and different method for bounding the actual NEOWISE diameter errors in the Main Belt based on our knowledge of the albedos of asteroid families. We show the 1σ relative diameter error for the Main Belt population must be less than 17.5% for the vast majority of objects. For a typical uncertainty on H magnitude of 0.2 mag, the relative error on diameter for the population would be ~10%.
Long-time evolution of interfacial structure of partial wetting

When a plate is swiftly pulled out of a liquid bath, a thin liquid film is dragged out by the moving surface. High-speed imaging reveals surprising structure of such a seemingly mundane process. A new technique allows precise measurement of the structure, and a systematic comparison with the reverse process of plunging a plate is carried out
The multiplicativity of fixed point invariants

We prove two general factorization theorems for fixed-point invariants of fibrations: one for the Lefschetz number and one for the Reidemeister trace. These theorems imply the familiar multiplicativity results for the Lefschetz and Nielsen numbers of a fibration. Moreover, the proofs of these theorems are essentially formal, taking place in the abstract context of bicategorical traces. This makes generalizations to other contexts straightforward. 55M20; 18D05, 55R05
A COHOMOLOGICAL INTERPRETATION OF THE MIGDAL–MAKEENKO EQUATIONS

The equations of motion of quantum Yang–Mills theory (in the planar "large-N" limit), when formulated in loop-space are shown to have an anomalous term, which makes them analogous to the equations of motion of WZW models. The anomaly is the Jacobian of the change of variables from the usual ones, i.e. the connection one-form A, to the holonomy U. An infinite-dimensional Lie algebra related to this change of variables (the Lie algebra of loop substitutions) is developed, and the anomaly is interpreted as an element of the first cohomology of this Lie algebra. The Migdal–Makeenko equations are shown to be the condition for the invariance of the Yang–Mills generating functional Z under the action of the generators of this Lie algebra. Connections of this formalism to the collective field approach of Jevicki and Sakita are also discussed.
Imaging point sources in heterogeneous environments

Imaging point sources in heterogeneous environments from boundary or far-field measurements has been extensively studied in the past. In most existing results, the environment, represented by the refractive index function in the model equation, is assumed known in the imaging process. In this work, we investigate the impact of environment uncertainty on the reconstruction of point sources inside it. Following the techniques developed by El Badia and El Hajj (C. R. Acad. Sci. Paris, Ser. I, 350 (2012), 1031-1035), we derive stability of reconstructing point sources in heterogeneous media with respect to measurement error as well as smooth changes in the environment, that is, the refractive index. Numerical simulations with synthetic data are presented to further explore the derived stability properties.
The Quantum Double Model with Boundary: Condensations and Symmetries

Associated to every finite group, Kitaev has defined the quantum double model for every orientable surface without boundary. In this paper, we define boundaries for this model and characterize condensations; that is, we find all quasi-particle excitations (anyons) which disappear when they move to the boundary. We then consider two phases of the quantum double model corresponding to two groups with a domain wall between them, and study the tunneling of anyons from one phase to the other. Using this framework we discuss the necessary and sufficient conditions when two different groups give the same anyon types. As an application we show that in the quantum double model for S3 (the permutation group over three letters) there is a chargeon and a fluxion which are not distinguishable. This group is indeed a special case of groups of the form of the semidirect product of the additive and multiplicative groups of a finite field, for all of which we prove a similar symmetry.
The Role of Pragmatic and Discourse Context in Determining Argument Impact

Research in the social sciences and psychology has shown that the persuasiveness of an argument depends not only the language employed, but also on attributes of the source/communicator, the audience, and the appropriateness and strength of the argument’s claims given the pragmatic and discourse context of the argument. Among these characteristics of persuasive arguments, prior work in NLP does not explicitly investigate the effect of the pragmatic and discourse context when determining argument quality. This paper presents a new dataset to initiate the study of this aspect of argumentation: it consists of a diverse collection of arguments covering 741 controversial topics and comprising over 47,000 claims. We further propose predictive models that incorporate the pragmatic and discourse context of argumentative claims and show that they outperform models that rely only on claim-specific linguistic features for predicting the perceived impact of individual claims within a particular line of argument.
Statistics for fixed points of the self-power map

The map x ↦ x x modulo p is related to a variation of the ElGamal digital signature scheme in a similar way as the discrete exponentiation map, but it has received much less study. We explore the number of fixed points of this map by a statistical analysis of experimental data. In particular, the number of fixed points can in many cases be modeled by a binomial distribution. We discuss the many cases where this has been successful, and also the cases where a good model may not yet have been found.
Characterizations of the round two-dimensional sphere in terms of closed geodesics

The question of whether a closed Riemannian manifold has infinitely many geometrically distinct closed geodesics has a long history. Though unsolved in general, it is well understood in the case of surfaces. For surfaces of revolution diffeomorphic to the sphere, a refinement of this problem was introduced by Borzellino, Jordan-Squire, Petrics, and Sullivan. In this article, we quantify their result by counting distinct geodesics of bounded length. In addition, we reframe these results to obtain a couple of characterizations of the round two-sphere.
Ultrasensitive inverse weak-value tilt meter.

We present an interferometric technique for measuring ultrasmall tilts. The information of a tilt in one of the mirrors of a modified Sagnac interferometer is carried by the phase difference between the counter-propagating laser beams. Using a small misalignment of the interferometer, orthogonal to the plane of the tilt, a bimodal (or two-fringe) pattern is induced in the beam’s transverse power distribution. By tracking the mean of such a distribution, using a split detector, a sensitive measurement of the phase is performed. With 1.2 mW of continuous-wave laser power, the technique has a shot noise limited sensitivity of 56 frad/Hz and a measured noise floor of 200 frad/Hz for tilt frequencies above 2 Hz. A tilt of 200 frad corresponds to a differential displacement of 4.0 fm in our setup. The novelty of the protocol relies on signal amplification due to the misalignment and on good performance at low frequencies. A noise floor of about 70 prad/Hz is observed between 2 and 100 mHz.
Time reversal for radiative transport with applications to inverse and control problems

In this paper we develop a time reversal method for the radiative transport equation to solve two problems: an inverse problem for the recovery of an initial condition from boundary measurements, and the exact boundary controllability of the transport field with finite steering time. Absorbing and scattering effects, modeled by coefficients with low regularity, are incorporated in the formulation of these problems. This time reversal approach leads to a convergent iterative procedure to reconstruct the initial condition provided that the scattering coefficient is sufficiently small in the L∞ norm. Then, using duality arguments, we show that the solvability of the inverse problem leads to exact controllability of the transport field with minimum-norm control obtained constructively. The solution approach to both of these problems may have applications in areas such as optical imaging and optimization of radiation delivery.
STAR-FORMING GAS IN YOUNG CLUSTERS

Initial conditions for star formation in clusters are estimated for protostars whose masses follow the initial mass function from 0.05 to 10 solar masses. Star-forming infall is assumed equally likely to stop at any moment, due to gas dispersal dominated by stellar feedback. For spherical infall, the typical initial condensation must have a steep density gradient, as in low-mass cores, surrounded by a shallower gradient, as in the clumps around cores. These properties match observed column densities in cluster-forming regions when the mean infall stopping time is 0.05 Myr and the accretion efficiency is 0.5. The infall duration increases with final protostar mass, from 0.01 to 0.3 Myr, and the mass accretion rate increases from 3 to 300 × 10–6 solar masses yr–1. The typical spherical accretion luminosity is ~5 solar luminosities, reducing the "luminosity problem" to a factor of ~3. The initial condensation density gradient changes from steep to shallow at radius 0.04 pc, enclosing 0.9 solar masses, with mean column density 2 × 1022 cm–2 and with effective central temperature 16 K. These initial conditions are denser and warmer than those for isolated star formation.
Competition between slow and fast regimes for extreme first passage times of diffusion

Many physical, chemical, and biological systems depend on the first passage time (FPT) of a diffusive searcher to a target. Typically, this FPT is much slower than the characteristic diffusion timescale. For example, this is the case if the target is small (the narrow escape problem) or if the searcher must escape a potential well. However, many systems depend on the first time a searcher finds the target out of a large group of searchers, which is the so-called extreme FPT. Since this extreme FPT vanishes in the limit of many searchers, the prohibitively slow FPTs of diffusive search can be negated by deploying enough searchers. However, the notion of ``enough searchers'' is poorly understood. How can one determine if a system is in the slow regime (dominated by small targets or a deep potential, for example) or the fast regime (dominated by many searchers)? How can one estimate the extreme FPT in these different regimes? In this paper, we answer these questions by deriving conditions which ensure that a system is in either regime and finding approximations of the full distribution and all the moments of the extreme FPT in these regimes. Our analysis reveals the critical effect that initial searcher distribution and target reactivity can have on extreme FPTs.
Correcting Type Ia Supernova Distances for Selection Biases and Contamination in Photometrically Identified Samples

We present a new technique to create a bin-averaged Hubble Diagram (HD) from photometrically identified SN~Ia data. The resulting HD is corrected for selection biases and contamination from core collapse (CC) SNe, and can be used to infer cosmological parameters. This method, called "BBC" (BEAMS with Bias Corrections), includes two fitting stages. The first BBC fitting stage uses a posterior distribution that includes multiple SN likelihoods, a Monte Carlo simulation to bias-correct the fitted SALT-II parameters, and CC probabilities determined from a machine learning technique. The BBC fit determines 1) a bin-averaged HD (average distance vs. redshift), and 2) the nuisance parameters alpha and beta, which multiply the stretch and color (respectively) to standardize the SN brightness. In the second stage, the bin-averaged HD is fit to a cosmological model where priors can be imposed. We perform high precision tests of the BBC method by simulating large (150,000 event) data samples corresponding to the Dark Energy Survey Supernova Program. Our tests include three models of intrinsic scatter, each with two different CC rates. In the BBC fit, the SALT-II nuisance parameters alpha and beta are recovered to within 1% of their true values. In the cosmology fit, we determine the dark energy equation of state parameter w using a fixed value of Omega_matter as a prior: averaging over all six tests based on 6 x 150,000 = 900,000 SNe, there is a small w-bias of 0.006 +- 0.002. Finally, the BBC fitting code is publicly available in the SNANA package.
Small generators of cocompact arithmetic Fuchsian groups

In the study of Fuchsian groups, it is a nontrivial problem to determine a set of generators. Using a dynamical approach we construct for any cocompact arithmetic Fuchsian group a fundamental region in $\mathbf{SL}_2(\mathbb{R})$ from which we determine a set of small generators.
Handlebody phases and the polyhedrality of the holographic entropy cone

The notion of a holographic entropy cone has recently been introduced and it has been proven that this cone is polyhedral. However, the original definition was fully geometric and did not strictly require a holographic duality. We introduce a new definition of the cone, insisting that the geometries used for its construction should be dual to states of a CFT. As a result, the polyhedrality of this holographic cone does not immediately follow. A numerical evaluation of the Euclidean action for the geometries that realize extremal rays of the original cone indicates that these are subdominant bulk phases of natural path integrals. The result challenges the expectation that such geometries are in fact dual to CFT states.
Towards the higher point holographic momentum space amplitudes

In this paper, we calculate higher point tree level vector amplitudes propagating in AdS_4, or equivalently the dual boundary current correlators. We use bulk perturbation theory to compute tree level Witten diagrams. We show that when these amplitudes are written in momentum space, they reduce to relatively simple expressions. We explicitly compute four and five point correlators and also sketch a general strategy to compute the full six-point correlators.
Galaxy Cluster Contribution to the Diffuse Extragalactic Ultraviolet Background

The diffuse ultraviolet background radiation has been mapped over most of the sky with 2\arcmin \ resolution using data from the \textit{GALEX} survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the \textit{Planck} survey. We use only high Galactic latitude ($|b| > 60^{\circ} $) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range $0.02 \leq z \leq 0.72$, which we further subdivide into four redshift bins. In analysing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with $z<0.3$. We then stacked these $z<0.3$ clusters to find a statistically significant excess of $12 \pm 2.3$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ A$^{-1}$ \ over the median of $\sim 380$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ A$^{-1}$ \ measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of $\sim 1$ Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.
The Fu-Yau equation with negative slope parameter

The Fu–Yau equation is an equation introduced by Fu and Yau as a generalization to arbitrary dimensions of an ansatz for the Strominger system. As in the Strominger system, it depends on a slope parameter $$\alpha ^{\prime }$$ . The equation was solved in dimension 2 by Fu and Yau in two successive papers for $$\alpha ^{\prime }>0$$ , and for $$\alpha ^{\prime }<0$$ . In the present paper, we solve the Fu–Yau equation in arbitrary dimension for $$\alpha ^{\prime }<0$$ . To our knowledge, these are the first non-trivial solutions of the Fu–Yau equation in any dimension strictly greater than 2.
Uncovering the effects of interface-induced ordering of liquid on crystal growth using machine learning

The process of crystallization is often understood in terms of the fundamental microstructural elements of the crystallite being formed, such as surface orientation or the presence of defects. Considerably less is known about the role of the liquid structure on the kinetics of crystal growth. Here atomistic simulations and machine learning methods are employed together to demonstrate that the liquid adjacent to solid-liquid interfaces presents significant structural ordering, which effectively reduces the mobility of atoms and slows down the crystallization kinetics. Through detailed studies of silicon and copper we discover that the extent to which liquid mobility is affected by interface-induced ordering (IIO) varies greatly with the degree of ordering and nature of the adjacent interface. Physical mechanisms behind the IIO anisotropy are explained and it is demonstrated that incorporation of this effect on a physically-motivated crystal growth model enables the quantitative prediction of the growth rate temperature dependence. Crystallization is a challenging process to model quantitatively. Here the authors use machine learning and atomistic simulations together to uncover the role of the liquid structure on the process of crystallization and derive a predictive kinetic model of crystal growth.
Large N (=3) neutrinos and random matrix theory

The large N limit has been successfully applied to QCD, leading to qualitatively correct results even for N = 3. In this work, we propose to treat the number N = 3 of Standard Model generations as a large number. Specifically, we apply this idea to the neutrino anarchy scenario and study neutrino physics using Random Matrix Theory, finding new results in both areas. For neutrino physics, we obtain predictions for the masses and mixing angles as a function of the generation number N. The Seesaw mechanism produces a hierarchy of order 1/N 3 between the lightest and heaviest neutrino, and a θ 13 mixing angle of order 1/N, in parametric agreement with experimental data when N goes to 3. For Random Matrix Theory, this motivates the introduction of a new type of ensemble of random matrices, the “Seesaw ensemble.” Basic properties of such matrices are studied, including the eigenvalue density and the interpretation as a Coulomb gas system. Besides its mathematical interest, the Seesaw ensemble may be useful in random systems where two hierarchical scales exist.
Computational Topology Techniques for Characterizing Time-Series Data

Topological data analysis (TDA), while abstract, allows a characterization of time-series data obtained from nonlinear and complex dynamical systems. Though it is surprising that such an abstract measure of structure—counting pieces and holes—could be useful for real-world data, TDA lets us compare different systems, and even do membership testing or change-point detection. However, TDA is computationally expensive and involves a number of free parameters. This complexity can be obviated by coarse-graining, using a construct called the witness complex. The parametric dependence gives rise to the concept of persistent homology: how shape changes with scale. Its results allow us to distinguish time-series data from different systems—e.g., the same note played on different musical instruments.
A hierarchical exact accelerated stochastic simulation algorithm

A new algorithm, “HiER-leap” (hierarchical exact reaction-leaping), is derived which improves on the computational properties of the ER-leap algorithm for exact accelerated simulation of stochastic chemical kinetics. Unlike ER-leap, HiER-leap utilizes a hierarchical or divide-and-conquer organization of reaction channels into tightly coupled “blocks” and is thereby able to speed up systems with many reaction channels. Like ER-leap, HiER-leap is based on the use of upper and lower bounds on the reaction propensities to define a rejection sampling algorithm with inexpensive early rejection and acceptance steps. But in HiER-leap, large portions of intra-block sampling may be done in parallel. An accept/reject step is used to synchronize across blocks. This method scales well when many reaction channels are present and has desirable asymptotic properties. The algorithm is exact, parallelizable and achieves a significant speedup over the stochastic simulation algorithm and ER-leap on certain problems. This algorithm offers a potentially important step towards efficient in silico modeling of entire organisms.
Far-UV Emission Properties of FR1 Radio Galaxies

The power mechanism and accretion geometry for low-power FR1 radio galaxies is poorly understood in comparison to Seyfert galaxies and QSOs. In this paper we use the diagnostic power of the Lya recombination line observed using the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST) to investigate the accretion flows in three well-known, nearby FR1s: M87, NGC4696, and HydraA. The Ly$\alpha$ emission line's luminosity, velocity structure and the limited knowledge of its spatial extent provided by COS are used to assess conditions within a few parsecs of the super-massive black hole (SMBH) in these radio-mode AGN. We observe strong Ly$\alpha$ emission in all three objects with similar total luminosity to that seen in BL Lacertae objects. M87 shows a complicated emission line profile in Lya which varies spatially across the COS aperture and possibly temporally over several epochs of observation. In both NGC 4696 and M87, the Ly$\alpha$ luminosities $\sim 10^{40}$ ergs/s are closely consistent with the observed strength of the ionizing continuum in Case B recombination theory and with the assumption of near unity covering factor. It is possible that the Ly$\alpha$ emitting clouds are ionized largely by beamed radiation associated with the jets. Long-slit UV spectroscopy can be used to test this hypothesis. Hydra A and the several BL Lac objects studied in this and previous papers have Lya luminosities larger than M87 but their extrapolated, non-thermal continua are so luminous that they over-predict the observed strength of Ly$\alpha$, a clear indicator of relativistic beaming in our direction. Given their substantial space density ($\sim 4\times10^{-3} Mpc^{-3}$) the unbeamed Lyman continuum radiation of FR1s may make a substantial minority contribution (~10%) to the local UV background if all FR1s are similar to M87 in ionizing flux level.
Kinematics and Chemistry of Stars along the Sagittarius Trailing Tidal Tail and Constraints on the Milky Way Mass Distribution

We present three-dimensional (3D) kinematics of Sagittarius (Sgr) trailing tidal debris in six fields located 70°-130° along the stream from the Sgr dwarf galaxy core. The data are from our proper-motion (PM) survey of Kapteyn's Selected Areas, in which we have measured accurate PMs to faint magnitudes in ~40' × 40' fields evenly spaced across the sky. The radial velocity (RV) signature of Sgr has been identified among our follow-up spectroscopic data in four of the six fields and combined with mean PMs of spectroscopically confirmed members to derive space motions of Sgr debris based on ~15-64 confirmed stream members per field. These kinematics are compared to predictions of the Law & Majewski model of Sgr disruption; we find reasonable agreement with model predictions in RVs and PMs along Galactic latitude. However, an upward adjustment of the local standard of rest velocity (ΘLSR) from its standard 220 km s–1 to at least 232 ± 14 km s–1 (and possibly as high as 264 ± 23 km s–1) is necessary to bring 3D model debris kinematics and our measurements into agreement. Satisfactory model fits that simultaneously reproduce known position, distance, and RV trends of the Sgr tidal streams, while significantly increasing ΘLSR, could only be achieved by increasing the Galactic bulge and disk mass while leaving the dark matter halo fixed to the best-fit values from Law & Majewski. We derive low-resolution spectroscopic abundances along this stretch of the Sgr stream and find a constant [Fe/H] ~ –1.15 (with ~0.5 dex scatter in each field—typical for dwarf galaxy populations) among the four fields with reliable measurements. A constant metallicity suggests that debris along the ~60° span of this study was all stripped from Sgr on the same orbital passage.
Hopf–Galois structures arising from groups with unique subgroup of order p

For Γ a group of order mp, where p is a prime with gcd(p,m) = 1, we consider the regular subgroups N ≤ Perm(Γ) that are normalized by λ(Γ), the left regular representation of Γ. These subgroups are in one-to-one correspondence with the Hopf–Galois structures on separable field extensions L∕K with Γ = Gal(L∕K). Elsewhere we showed that if p > m then all such N lie within the normalizer of the Sylow p-subgroup of λ(Γ). Here we show that one only need assume that all groups of a given order mp have a unique Sylow p-subgroup, and that p not be a divisor of the order of the automorphism groups of any group of order m. We thus extend the applicability of the program for computing these regular subgroups N and concordantly the corresponding Hopf–Galois structures on separable extensions of degree mp.
PROTON STRUCTURE FUNCTIONS FROM CHIRAL DYNAMICS AND QCD CONSTRAINTS

The spin fractions and deep inelastic lepton structure functions of the proton are analyzed using chiral field theory involving Goldstone bosons. A detailed comparison with recent chiral models sheds light on their successful description of the spin fractions of the proton as being due to neglecting helicity nonflip chiral transitions. This approximation is valid for zero mass but not for constituent quarks. Since the chiral spin fraction models with the pure spin-flip approximation reproduce the measured spin fractions of the proton, axialvector constituent-quark-Goldstone boson couplings are found to be inconsistent with the proton spin data. Initial quark valence distributions are then constructed using quark counting constraints at Bjorken x→1 and Regge behavior at x→0. Sea quark distributions predicted by chiral field theory on this basis have the correct order of magnitude and shape. The spin fractions also agree with the data.
A Variational Theory for Point Defects in Patterns

We derive a rigorous scaling law for minimizers in a natural version of the regularized Cross-Newell model for pattern formation far from threshold. These energy-minimizing solutions support defects having the same character as what is seen in experimental studies of the corresponding physical systems and in numerical simulations of the microscopic equations that describe these systems.
RADIATION TRANSFER OF MODELS OF MASSIVE STAR FORMATION. II. EFFECTS OF THE OUTFLOW

We present radiation transfer simulations of a massive (8 M ☉) protostar forming from a massive (M c = 60 M ☉) protostellar core, extending the model developed by Zhang and Tan. The two principal improvements are (1) developing a model for the density and velocity structure of a disk wind that fills the bipolar outflow cavities, based in part on the disk-wind model of Blandford and Payne; and (2) solving for the radially varying accretion rate in the disk due to a supply of mass and angular momentum from the infall envelope and their loss to the disk wind. One consequence of the launching of the disk wind is a reduction in the amount of accretion power that is radiated by the disk. We also include a non-Keplerian potential appropriate for a growing, massive disk. For the transition from dusty to dust-free conditions where gas opacities dominate, we now implement a gradual change as a more realistic approximation of dust destruction. We study how the above effects, especially the outflow, influence the spectral energy distributions (SEDs) and the synthetic images of the protostar. Dust in the outflow cavity significantly affects the SEDs at most viewing angles. It further attenuates the short-wavelength flux from the protostar, controlling how the accretion disk may be viewed, and contributes a significant part of the near- and mid-IR fluxes. These fluxes warm the disk, boosting the mid- and far-IR emission. We find that for near face-on views, i.e., looking down the outflow cavity (although not too close to the axis), the SED from the near-IR to about 60 μm is very flat, which may be used to identify such systems. We show that the near-facing outflow cavity and its walls are still the most significant features in images up to 70 μm, dominating the mid-IR emission and determining its morphology. The thermal emission from the dusty outflow itself dominates the flux at ~20 μm. The detailed distribution of the dust in the outflow affects the morphology, so the model can be constrained by considering detailed intensity profiles along and perpendicular to the outflow axis. For example, even though the outflow cavity is wide, at 10-20 μm, the dust in the disk wind can make the outflow appear narrower than in the near-IR bands.
Entropy and set cardinality inequalities for partition-determined functions

A new notion of partition-determined functions is introduced, and several basic inequalities are developed for the entropies of such functions of independent random variables, as well as for cardinalities of compound sets obtained using these functions. Here a compound set means a set obtained by varying each argument of a function of several variables over a set associated with that argument, where all the sets are subsets of an appropriate algebraic structure so that the function is well defined. On the one hand, the entropy inequalities developed for partition-determined functions imply entropic analogues of general inequalities of Plunnecke-Ruzsa type. On the other hand, the cardinality inequalities developed for compound sets imply several inequalities for sumsets, including for instance a generalization of inequalities proved by Gyarmati, Matolcsi and Ruzsa (2010). We also provide partial progress towards a conjecture of Ruzsa (2007) for sumsets in nonabelian groups. All proofs are elementary and rely on properly developing certain information-theoretic inequalities. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 40, 399–424, 2012 © 2012 Wiley Periodicals, Inc.
An Algorithm for Real-Time Optimal Photocurrent Estimation Including Transient Detection for Resource-Constrained Imaging Applications

Mega-pixel charge-integrating detectors are common in near-IR imaging applications. Optimal signal-to-noise ratio estimates of the photocurrents, which are particularly important in the low-signal regime, are produced by fitting linear models to sequential reads of the charge on the detector. Algorithms that solve this problem have a long history, but can be computationally intensive. Furthermore, the cosmic ray background is appreciable for these detectors in Earth orbit, particularly above the Earth’s magnetic poles and the South Atlantic Anomaly, and on-board reduction routines must be capable of flagging affected pixels. In this paper, we present an algorithm that generates optimal photocurrent estimates and flags random transient charge generation from cosmic rays, and is specifically designed to fit on a computationally restricted platform. We take as a case study the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), a NASA Small Explorer astrophysics experiment concept, and show that the algorithm can easily fit in the resource-constrained environment of such a restricted platform. Detailed simulations of the input astrophysical signals and detector array performance are used to characterize the fitting routines in the presence of complex noise properties and charge transients. We use both Hubble Space Telescope Wide Field Camera-3 and Wide-field Infrared Survey Explorer to develop an empirical understanding of the susceptibility of near-IR detectors in low earth orbit and build a model for realistic cosmic ray energy spectra and rates. We show that our algorithm generates an unbiased estimate of the true photocurrent that is identical to that from a standard line fitting package, and characterize the rate, energy, and timing of both detected and undetected transient events. This algorithm has significant potential for imaging with charge-integrating detectors in astrophysics, earth science, and remote sensing applications.
Prebiotically-relevant low polyion multivalency can improve functionality of membraneless compartments.

Multivalent polyions can undergo complex coacervation, producing membraneless compartments that accumulate ribozymes and enhance catalysis, and offering a mechanism for functional prebiotic compartmentalization in the origins of life. Here, we evaluate the impact of lower, more prebiotically-relevant, polyion multivalency on the functional performance of coacervates as compartments. Positively and negatively charged homopeptides with 1–100 residues and adenosine mono-, di-, and triphosphate nucleotides are used as model polyions. Polycation/polyanion pairs are tested for coacervation, and resulting membraneless compartments are analyzed for salt resistance, ability to provide a distinct internal microenvironment (apparent local pH, RNA partitioning), and effect on RNA structure formation. We find that coacervates formed by phase separation of the shorter polyions more effectively generated distinct pH microenvironments, accumulated RNA, and preserved duplexes than those formed by longer polyions. Hence, coacervates formed by reduced multivalency polyions are not only viable as functional compartments for prebiotic chemistries, they can outperform higher molecular weight analogues. Short cationic peptides and nucleotides can form complex coacervates, but the influence of reduced multivalency on coacervate functionality was not investigated. Here, the authors report that coacervates formed from short polyions generate distinct pH microenvironments, accumulate RNA and preserve nucleic acid duplexes more efficiently than their longer counterparts.
Relativistic partial waves for celestial amplitudes

The formalism of relativistic partial wave expansion is developed for four-point celestial amplitudes of massless external particles. In particular, relativistic partial waves are found as eigenfunctions to the product representation of celestial Poincare Casimir operators with appropriate eigenvalues. The requirement of hermiticity of Casimir operators is used to fix the corresponding integral inner product, and orthogonality of the obtained relativistic partial waves is verified explicitly. The completeness relation, as well as the relativistic partial wave expansion follow. Example celestial amplitudes of scalars, gluons, gravitons and open superstring gluons are expanded on the basis of relativistic partial waves for demonstration. A connection with the formulation of relativistic partial waves in the bulk of Minkowski space is made in appendices.