cssi/SciSciGPT-SciSciNet huggingface dataset:
Contamination Mechanisms of Proton Exchange Membrane Fuel Cells - Mass Transfer Overpotential Origin

Several experimental methods were used to identify the cause of the concurrent increase in kinetic and mass transfer overpotentials during the contamination of proton exchange membrane fuel cells o...
Some subtleties in the relationships among heat kernel invariants, eigenvalue distributions, and quantum vacuum energy

A common tool in Casimir physics (and many other areas) is the asymptotic (high-frequency) expansion of eigenvalue densities, employed as either input or output of calculations of the asymptotic behavior of various Green functions. Here we clarify some fine points and potentially confusing aspects of the subject. In particular, we show how recent observations of Kolomeisky et al (2013 Phys. Rev. A 87 042519) fit into the established framework of the distributional asymptotics of spectral functions.
Universal bounds on charged states in 2d CFT and 3d gravity

We derive an explicit bound on the dimension of the lightest charged state in two dimensional conformal field theories with a global abelian symmetry. We find that the bound scales with c and provide examples that parametrically saturate this bound. We also prove that any such theory must contain a state with charge-to-mass ratio above a minimal lower bound. We comment on the implications for charged states in three dimensional theories of gravity.
Factorizations of relative extremal projectors

We survey earlier results on factorizations of extremal projectors and relative extremal projectors and present preliminary results on non-commutative factorizations of relative extremal projectors: we deduce the existence of such factorizations for sl4 and sl5.
Physical and Morphological Properties of [O II] Emitting Galaxies in the HETDEX Pilot Survey

The Hobby-Eberly Dark Energy Experiment pilot survey identified 284 [O II] λ3727 emitting galaxies in a 169 arcmin2 field of sky in the redshift range 0 < z < 0.57. This line flux limited sample provides a bridge between studies in the local universe and higher-redshift [O II] surveys. We present an analysis of the star formation rates (SFRs) of these galaxies as a function of stellar mass as determined via spectral energy distribution fitting. The [O II] emitters fall on the main sequence of star-forming galaxies with SFR decreasing at lower masses and redshifts. However, the slope of our relation is flatter than that found for most other samples, a result of the metallicity dependence of the [O II] star formation rate indicator. The mass-specific SFR is higher for lower mass objects, supporting the idea that massive galaxies formed more quickly and efficiently than their lower mass counterparts. This is confirmed by the fact that the equivalent widths of the [O II] emission lines trend smaller with larger stellar mass. Examination of the morphologies of the [O II] emitters reveals that their star formation is not a result of mergers, and the galaxies' half-light radii do not indicate evolution of physical sizes.
On Hermitian-holomorphic classes related to uniformization, the dilogarithm, and the Liouville action

Metrics of constant negative curvature on a compact Riemann surface are critical points of the Liouville action functional, which in recent constructions is rigorously defined as a class in a Cech-de Rham complex with respect to a suitable covering of the surface. We show that this class is the square of the metrized holomorphic tangent bundle in hermitian-holomorphic Deligne cohomology. We achieve this by introducing a different version of the hermitian-holomorphic Deligne complex which is nevertheless quasi-isomorphic to the one introduced by Brylinski in his construction of Quillen line bundles. We reprove the relation with the determinant of cohomology construction. Furthermore, if we specialize the covering to the one provided by a Kleinian uniformization (thereby allowing possibly disconnected surfaces) the same class can be reinterpreted as the transgression of the regulator class expressed by the Bloch-Wigner dilogarithm.
Repulsive forces and the weak gravity conjecture

The Weak Gravity Conjecture is a nontrivial conjecture about quantum gravity that makes sharp, falsifiable predictions which can be checked in a broad range of string theory examples. However, in the presence of massless scalar fields (moduli), there are (at least) two inequivalent forms of the conjecture, one based on charge-to-mass ratios and the other based on long-range forces. We discuss the precise formulations of these two conjectures and the evidence for them, as well as the implications for black holes and for “strong forms” of the conjectures. Based on the available evidence, it seems likely that both conjectures are true, suggesting that there is a stronger criterion which encompasses both. We discuss one possibility.
Naked singularity and Gauss-Bonnet term in brane world scenarios

Abstract We add a Gauss–Bonnet term to the Einstein–Hilbert action and study the recent proposal to solve the cosmological constant problem. We also consider the possibility of adding a dilaton potential to the action. In the absence of supersymmetry, we obtain first order Bogomol'nyi equation as a solution-generating method in our scenario. When the coefficient of the Gauss–Bonnet term is positive, the dilaton potential is bounded below. Assuming a simple double-well potential, we find the dilaton field to be a kink in the fifth dimension.
A general method for calculating lattice green functions on the branch cut

We present a method for calculating the complex Green function $G_{ij} (\omega)$ at any real frequency $\omega$ between any two sites $i$ and $j$ on a lattice. Starting from numbers of walks on square, cubic, honeycomb, triangular, bcc, fcc, and diamond lattices, we derive Chebyshev expansion coefficients for $G_{ij} (\omega)$. The convergence of the Chebyshev series can be accelerated by constructing functions $f(\omega)$ that mimic the van Hove singularities in $G_{ij} (\omega)$ and subtracting their Chebyshev coefficients from the original coefficients. We demonstrate this explicitly for the square lattice and bcc lattice. Our algorithm achieves typical accuracies of 6--9 significant figures using 1000 series terms.
Topological Fulde–Ferrell superfluids of a spin–orbit coupled Fermi gas

Topological Fermi superfluids have played the central role in various fields of physics. However, all previous studies focus on the cases where Cooper pairs have zero center-of-mass momenta (i.e., normal superfluids). The topology of Fulde–Ferrell (FF) superfluids with nonzero momentum pairings have never been explored until recent findings that FF superfluids in a spin–orbit (SO) coupled Fermi gas can accommodate Majorana fermions in real space in low dimensions and Weyl fermions in momentum space in three dimension. In this review, we first discuss the mechanism of pairings in SO coupled Fermi gases in optical lattices subject to Zeeman fields, showing that SO coupling as well as Zeeman fields enhance FF states while suppress Larkin–Ovchinnikov states. We then present the low temperature phase diagram including both FF superfluids and topological FF superfluids phases in both two dimension and three dimension. In one dimension, Majorana fermions as well as phase dependent order parameter are visualized. In three dimension, we show the properties of Weyl fermions in momentum space such as anisotropic linear dispersion, Fermi arch, and gaplessness away from k⊥ = 0. Finally, we discuss some possible methods to probe FF superfluids and topological FF superfluids in cold atom systems.
Feedback synthesis for controllable underactuated systems using sequential second order actions

This paper derives nonlinear feedback control synthesis for general control affine systems using second-order actions---the needle variations of optimal control---as the basis for choosing each control response to the current state. A second result of the paper is that the method provably exploits the nonlinear controllability of a system by virtue of an explicit dependence of the second-order needle variation on the Lie bracket between vector fields. As a result, each control decision necessarily decreases the objective when the system is nonlinearly controllable using first-order Lie brackets. Simulation results using a differential drive cart, an underactuated kinematic vehicle in three dimensions, and an underactuated dynamic model of an underwater vehicle demonstrate that the method finds control solutions when the first-order analysis is singular. Moreover, the simulated examples demonstrate superior convergence when compared to synthesis based on first-order needle variations. Lastly, the underactuated dynamic underwater vehicle model demonstrates the convergence even in the presence of a velocity field.
Novel small RNAs expressed by Bartonella bacilliformis under multiple conditions reveal potential mechanisms for persistence in the sand fly vector and human host.

Bartonella bacilliformis, the etiological agent of Carrion's disease, is a Gram-negative, facultative intracellular alphaproteobacterium. Carrion's disease is an emerging but neglected tropical illness endemic to Peru, Colombia, and Ecuador. B. bacilliformis is spread between humans through the bite of female phlebotomine sand flies. As a result, the pathogen encounters significant and repeated environmental shifts during its life cycle, including changes in pH and temperature. In most bacteria, small non-coding RNAs (sRNAs) serve as effectors that may post-transcriptionally regulate the stress response to such changes. However, sRNAs have not been characterized in B. bacilliformis, to date. We therefore performed total RNA-sequencing analyses on B. bacilliformis grown in vitro then shifted to one of ten distinct conditions that simulate various environments encountered by the pathogen during its life cycle. From this, we identified 160 sRNAs significantly expressed under at least one of the conditions tested. sRNAs included the highly-conserved tmRNA, 6S RNA, RNase P RNA component, SRP RNA component, ffH leader RNA, and the alphaproteobacterial sRNAs αr45 and speF leader RNA. In addition, 153 other potential sRNAs of unknown function were discovered. Northern blot analysis was used to confirm the expression of eight novel sRNAs. We also characterized a Bartonella bacilliformis group I intron (BbgpI) that disrupts an un-annotated tRNACCUArg gene and determined that the intron splices in vivo and self-splices in vitro. Furthermore, we demonstrated the molecular targeting of Bartonella bacilliformis small RNA 9 (BbsR9) to transcripts of the ftsH, nuoF, and gcvT genes, in vitro.
A new class of probability distributions for describing the spatial statistics of area‐averaged rainfall

[1] Rainfall exhibits extreme variability at many space and timescales and calls for a statistical description. Based on an analysis of radar measurements of precipitation over the tropical oceans, we introduce a new probability law for the area-averaged rain rate within the class of log-infinitely divisible distributions that accurately describes the frequency of the most intense rain events. The dependence of its parameters on the spatial averaging length L allows one to relate spatial statistics at different scales. In particular, it enables us to explain the observed power law scaling of the moments of the rain rate data and successfully predicts the continuous spectrum of scaling exponents expressing the multiscaling property of the rain intensity field.
Denoising signals in cognitive radio systems using an evolutionary algorithm based adaptive filter

Noise originating from several sources in a RF environment degrades the performance of communication systems. In wideband systems, such as cognitive radios, noise at the receiver can also originate from non-linearity present in the RF front end, time-varying thermal noise within the receiver radio system, and noise from adjacent network nodes. Several denoising techniques have been proposed for cognitive radios, some of which are applied during spectrum sensing and others to received noisy signals. Examples of these techniques include least mean square (LMS) and its variants. However, these algorithms have low performance with non-linear signals and cannot locate the global optimum solution for noise cancellation. Therefore, application of global search optimization techniques, such as evolutionary algorithms, is considered for noise cancellation. In this paper, particle swarm optimization (PSO) and LMS algorithms are implemented and their performances compared. Extensive simulations were performed where Gaussian and nonlinear random noise were added to the transmitted signals. The performance comparison was done using two metrics: bit error rate and mean square error. The results show that PSO outperforms LMS under both Gaussian and non-linear random noise.
Topological and Subsystem Codes on Low-Degree Graphs with Flag Qubits

A new proposed family of quantum error correcting codes and a scalable and efficient flag-based decoding scheme are suitable for implementation in superconducting qubit architectures and offer competitive performance to other error-correction schemes.
A Test of the High-eccentricity Migration Scenario for Close-in Planets

In the high-eccentricity migration (HEM) scenario, close-in planets reach the vicinity of the central star on high-eccentricity orbits that become circularized---with a concomitant decrease in the semimajor axis---through a tidal interaction with the star. Giant planets that arrive with periastron distances that are smaller than the Roche limit $a_\mathrm{R}$ lose their gaseous envelopes, resulting in an inner edge to the surviving planets' distribution. The observational evidence for this effect, while extensive, is nonetheless somewhat ambiguous because of the effect of tidal orbital decay. Here we consider another key prediction of the HEM scenario---the existence of a spatial eccentricity gradient near the location where the circularization time becomes comparable to the planet's age for typical parameters. Previous studies already found evidence for this gradient and demonstrated that its properties are consistent with the circularization process being dominated by tidal dissipation in the planet (encapsulated by the tidal quality factor $Q^\prime_\mathrm{p}$). Our work extends these treatments by constructing explicit model distributions for comparison with the data and by carrying out backward-in-time integrations using observed system parameters. We show that circularization generally occurs outside the distribution's inner edge (which defines the boundary of the so-called sub-Jovian desert) and that typically $Q^\prime_\mathrm{p}\approx10^6$ in the circularization zone (to within a factor of 3). We also find tentative evidence for an eccentricity gradient in lower-mass planets, indicating that formation through HEM may be relevant down to Neptune scales.
Asymptotics of the Euler number of bipartite graphs

We define the Euler number of a bipartite graph on n vertices to be the number of labelings of the vertices with 1,...,n such that the vertices alternate in being local maxima and local minima. We reformulate the problem of computing the Euler number of certain subgraphs of the Cartesian product of a graph G with the path P"m in terms of self-adjoint operators. The asymptotic expansion of the Euler number is given in terms of the eigenvalues of the associated operator. For two classes of graphs, the comb graphs and the Cartesian product P"[email protected]?P"m, we numerically solve the eigenvalue problem.
Exotic relation modules and homotopy types for certain 1–relator groups

Using stably free non-free relation modules we construct an infinite collection of 2–dimensional homotopy types, each of Euler-characteristic one and with trefoil fundamental group. This provides an affirmative answer to a question asked by Berridge and Dunwoody [1]. We also give new examples of exotic relation modules. We show that the relation module associated with the generating set fx;yg for the Baumslag–Solitar group hx;y j xyx 1 D yi is stably free non-free of rank one.
Gravitational Slingshot of Young Massive Stars in Orion

The Orion Nebula Cluster (ONC) is the nearest region of massive star formation and thus a crucial testing ground for theoretical models. Of particular interest among the ONC's ~1000 members are: θ1 Ori C, the most massive binary in the cluster with stars of masses 38 and 9 M ☉; the Becklin-Neugebauer (BN) object, a 30 km s–1 runaway star of ~8 M ☉; and the Kleinmann-Low (KL) nebula protostar, a highly obscured, ~15 M ☉ object still accreting gas while also driving a powerful, apparently explosive outflow. The unusual behavior of BN and KL is much debated: How did BN acquire its high velocity? How is this related to massive star formation in the KL nebula? Here, we report the results of a systematic survey using ~107 numerical experiments of gravitational interactions of the θ1C and BN stars. We show that dynamical ejection of BN from this triple system at its observed velocity leaves behind a binary with total energy and eccentricity matching those observed for θ1C. Five other observed properties of θ1C are also consistent with it having ejected BN and altogether we estimate that there is only a 10–5 probability that θ1C has these properties by chance. We conclude that BN was dynamically ejected from the θ1C system about 4500 years ago. BN then plowed through the KL massive star-forming core within the last 1000 years causing its recently enhanced accretion and outflow activity.
Extreme Variability in a Broad Absorption Line Quasar

CRTS J084133.15+200525.8 is an optically bright quasar at z = 2.345 that has shown extreme spectral variability over the past decade. Photometrically, the source had a visual magnitude of V ~ 17.3 between 2002 and 2008. Then, over the following five years, the source slowly brightened by approximately one magnitude, to V ~ 16.2. Only ~1 in 10,000 quasars show such extreme variability, as quantified by the extreme parameters derived for this quasar assuming a damped random walk model. A combination of archival and newly acquired spectra reveal the source to be an iron low-ionization broad absorption line quasar with extreme changes in its absorption spectrum. Some absorption features completely disappear over the 9 years of optical spectra, while other features remain essentially unchanged. We report the first definitive redshift for this source, based on the detection of broad Hα in a Keck/MOSFIRE spectrum. Absorption systems separated by several 1000 km s^(−1) in velocity show coordinated weakening in the depths of their troughs as the continuum flux increases. We interpret the broad absorption line variability to be due to changes in photoionization, rather than due to motion of material along our line of sight. This source highlights one sort of rare transition object that astronomy will now be finding through dedicated time-domain surveys.
Timelike BKL singularities and chaos in AdS/CFT

We study the nature of a family of curvature singularities which are precisely the timelike cousins of the spacelike singularities studied by Belinski, Khalatnikov, and Lifshitz (BKL). We show that the approach to the singularity can be modeled by a billiard ball problem on hyperbolic space, just as in the case of BKL. For pure gravity, generic chaotic behavior is retained in (3+1) dimensions, and we provide evidence that it disappears in higher dimensions. We speculate that such singularities, if occurring in AdS/CFT and of the chaotic variety, may be interpreted as (transient) chaotic renormalization group flows which exhibit features reminiscent of chaotic duality cascades.
JNET: Learning User Representations via Joint Network Embedding and Topic Embedding

User representation learning is vital to capture diverse user preferences, while it is also challenging as user intents are latent and scattered among complex and different modalities of user-generated data, thus, not directly measurable. Inspired by the concept of user schema in social psychology, we take a new perspective to perform user representation learning by constructing a shared latent space to capture the dependency among different modalities of user-generated data. Both users and topics are embedded to the same space to encode users' social connections and text content, to facilitate joint modeling of different modalities, via a probabilistic generative framework. We evaluated the proposed solution on large collections of Yelp reviews and StackOverflow discussion posts, with their associated network structures. The proposed model outperformed several state-of-the-art topic modeling based user models with better predictive power in unseen documents, and state-of-the-art network embedding based user models with improved link prediction quality in unseen nodes. The learnt user representations are also proved to be useful in content recommendation, e.g., expert finding in StackOverflow.
Global existence and uniqueness of the solution to a nonlinear parabolic equation

Consider the equation $$ u'(t)-\Delta u+|u|^\rho u=0, \quad u(0)=u_0(x), (1), $$ where $ u':=\frac {du}{dt}$, $ \rho=const >0, $ $x\in \mathbb{R}^3$, $t>0$. Assume that $u_0$ is a smooth and decaying function, $$\|u_0\|\:=\sup_{x\in \mathbb{R}^3, t\in \mathbb{R}_+} |u(x,t)|.$$ It is proved that problem (1) has a unique global solution and this solution satisfies the following estimate $$\|u(x,t)\| 0$ does not depend on $x,t$.
Tensor Contractions with Extended BLAS Kernels on CPU and GPU

Tensor contractions constitute a key computational ingredient of numerical multi-linear algebra. However, as the order and dimension of tensors grow, the time and space complexities of tensor-based computations grow quickly. In this paper, we propose and evaluate new BLAS-like primitives that are capable of performing a wide range of tensor contractions on CPU and GPU efficiently. We begin by focusing on singleindex contractions involving all the possible configurations of second-order and third-order tensors. Then, we discuss extensions to more general cases. Existing approaches for tensor contractions spend large amounts of time restructuring the data which typically involves explicit copy and transpose operations. In this work, we summarize existing approaches and present library-based approaches that avoid memory movement. Through systematic benchmarking, we demonstrate that our approach can achieve 10x speedup on a K40c GPU and 2x speedup on dual-socket Haswell-EP CPUs, using MKL and CUBLAS respectively, for small and moderate tensor sizes. This is relevant in many machine learning applications such as deep learning, where tensor sizes tend to be small, but require numerous tensor contraction operations to be performed successively. Concretely, we implement a Tucker decomposition and show that using our kernels yields atleast an order of magnitude speedup as compared to state-of-the-art libraries.
Light-like Wilson line in QCD without path ordering

Unlike the Wilson line in QED the Wilson line in QCD contains path ordering. In this paper we get rid of the path ordering in the light-like Wilson line in QCD by simplifying all the infinite number of noncommuting terms in the SU(3) pure gauge. We prove that the light-like Wilson line in QCD naturally emerges when path integral formulation of QCD is used to prove factorization of soft and collinear divergences at all order in coupling constant in QCD processes at high energy colliders.
A collaborative filtering recommender system for test case prioritization in web applications

The use of relevant metrics of software systems could improve various software engineering tasks, but identifying relationships among metrics is not simple and can be very time consuming. Recommender systems can help with this decision-making process; many applications have utilized these systems to improve the performance of their applications. To investigate the potential benefits of recommender systems in regression testing, we implemented an item-based collaborative filtering recommender system that uses user interaction data and application change history information to develop a test case prioritization technique. To evaluate our approach, we performed an empirical study using three web applications with multiple versions and compared four control techniques. Our results indicate that our recommender system can help improve the effectiveness of test prioritization.
Silicate Composition of the Interstellar Medium

The composition of silicate dust in the diffuse interstellar medium and in protoplanetary disks around young stars informs our understanding of the processing and evolution of the dust grains leading up to planet formation. Analysis of the well-known 9.7{\mu}m feature indicates that small amorphous silicate grains represent a significant fraction of interstellar dust and are also major components of protoplanetary disks. However, this feature is typically modelled assuming amorphous silicate dust of olivine and pyroxene stoichiometries. Here, we analyze interstellar dust with models of silicate dust that include non-stoichiometric amorphous silicate grains. Modelling the optical depth along lines of sight toward the extinguished objects Cyg OB2 No. 12 and {\zeta} Ophiuchi, we find evidence for interstellar amorphous silicate dust with stoichiometry intermediate between olivine and pyroxene, which we simply refer to as "polivene." Finally, we compare these results to models of silicate emission from the Trapezium and protoplanetary disks in Taurus.
Location-aware sign-on and key exchange using attribute-based encryption and Bluetooth beacons

This work presents a mobile sign-on scheme, which utilizes Bluetooth Low Energy beacons for location awareness and Attribute-Based Encryption for expressive, broadcast-style key exchange. Bluetooth Low Energy beacons broadcast encrypted messages with encoded access policies. Within range of the beacons, a user with appropriate attributes is able to decrypt the broadcast message and obtain parameters that allow the user to perform a short or simplified login. The effect is a “traveling” sign-on that accompanies the user throughout different locations.
Voltage-Driven Building Block for Hardware Belief Networks

Editor’s note: In this article, the authors present a hardware building block for probabilistic spin logic (PSL) consisting of a probabilistic bit (p-bit) made from an embedded low-barrier unstable magnetic tunnel junction (MTJ) and a capacitive voltage adder. It was demonstrated through simulation that these interconnected building blocks can be designed to solve a small instance of the NP-complete Subset Sum Problem. —An Chen, Semiconductor Research Corporation
Symplectic Structures for the Cubic Schrödinger Equation in the Periodic and Scattering Case

We develop a unified approach for construction of symplectic forms for 1D integrable equations with the periodic and rapidly decaying initial data. As an example we consider the cubic nonlinear Schrodinger equation.
Surface deposition and imaging of large Ag clusters formed in He droplets.

The utility of a continuous beam of He droplets for the assembly and surface deposition of Ag N clusters, (N) ∼ 300-6000, is studied with transmission electron microscopy. Images of the clusters on amorphous carbon substrates obtained at short deposition times have provided for a measure of the size distribution of the metal clusters. The average sizes of the deposited clusters are in good agreement with an energy balance based estimate of Ag N cluster growth in He droplets. Measurements of the deposition rate indicate that upon impact with the surface the He-embedded cluster is attached with high probability. The stability of the deposited clusters on the substrate is discussed.
WiSeDB: a learning-based workload management advisor for cloud databases

Workload management for cloud databases deals with the tasks of resource provisioning, query placement, and query scheduling in a manner that meets the application's performance goals while minimizing the cost of using cloud resources. Existing solutions have approached these three challenges in isolation while aiming to optimize a single performance metric. In this paper, we introduce WiSeDB, a learning-based framework for generating holistic workload management solutions customized to application-defined performance goals and workload characteristics. Our approach relies on supervised learning to train cost-effective decision tree models for guiding query placement, scheduling, and resource provisioning decisions. Applications can use these models for both batch and online scheduling of incoming workloads. A unique feature of our system is that it can adapt its offline model to stricter/looser performance goals with minimal re-training. This allows us to present to the application alternative workload management strategies that address the typical performance vs. cost trade-off of cloud services. Experimental results show that our approach has very low training overhead while offering low cost strategies for a variety of performance metrics and workload characteristics.
TYPE Ia SUPERNOVA LIGHT CURVE INFERENCE: HIERARCHICAL MODELS IN THE OPTICAL AND NEAR-INFRARED

We have constructed a comprehensive statistical model for Type Ia supernova (SN Ia) light curves spanning optical through near-infrared (NIR) data. A hierarchical framework coherently models multiple random and uncertain effects, including intrinsic supernova (SN) light curve covariances, dust extinction and reddening, and distances. An improved BAYESN Markov Chain Monte Carlo code computes probabilistic inferences for the hierarchical model by sampling the global probability density of parameters describing individual SNe and the population. We have applied this hierarchical model to optical and NIR data of 127 SNe Ia from PAIRITEL, CfA3, Carnegie Supernova Project, and the literature. We find an apparent population correlation between the host galaxy extinction AV and the ratio of total-to-selective dust absorption RV . For SNe with low dust extinction, AV 0.4, we find RV 2.5-2.9, while at high extinctions, AV 1, low values of RV < 2 are favored. The NIR luminosities are excellent standard candles and are less sensitive to dust extinction. They exhibit low correlation with optical peak luminosities, and thus provide independent information on distances. The combination of NIR and optical data constrains the dust extinction and improves the predictive precision of individual SN Ia distances by about 60%. Using cross-validation, we estimate an rms distance modulus prediction error of 0.11 mag for SNe with optical and NIR data versus 0.15 mag for SNe with optical data alone. Continued study of SNe Ia in the NIR is important for improving their utility as precise and accurate cosmological distance indicators.
Habitability in the Omega Centauri Cluster

The search for exoplanets has encompassed a broad range of stellar environments, from single stars in the solar neighborhood to multiple stars and various open clusters. The stellar environment has a profound effect on planet formation and stability evolution and is thus a key component of exoplanetary studies. Dense stellar environments, such as those found in globular clusters, provide particularly strong constraints on sustainability of habitable planetary conditions. Here, we use Hubble Space Telescope observations of the core of the Omega Centauri cluster to derive fundamental parameters for the core stars. These parameters are used to calculate the extent of the habitable zone (HZ) of the observed stars. We describe the distribution of HZs in the cluster and compare them with the stellar density and expected stellar encounter rate and cluster dynamics. We thus determine the effect of the stellar environment within the Omega Centauri core on the habitability of planets that reside within the cluster. Our results show that the distribution of HZ outer boundaries generally lie within 0.5 au of the host stars, but that this small cross-sectional area is counter-balanced by a relatively high rate of stellar close encounters that would disrupt planetary orbits within the HZ of typical Omega Centauri stars.
Acoustic integrated extinction

The integrated extinction (IE) is defined as the integral of the scattering cross section as a function of wavelength. Sohl et al. (2007 J. Acoust. Soc. Am.122, 3206-3210. (doi:10.1121/1.2801546)) derived an IE expression for acoustic scattering that is causal, i.e. the scattered wavefront in the forward direction arrives later than the incident plane wave in the background medium. The IE formula was based on electromagnetic results, for which scattering is causal by default. Here, we derive a formula for the acoustic IE that is valid for causal and non-causal scattering. The general result is expressed as an integral of the time-dependent forward scattering function. The IE reduces to a finite integral for scatterers with zero long-wavelength monopole and dipole amplitudes. Implications for acoustic cloaking are discussed and a new metric is proposed for broadband acoustic transparency.
The second moment of $$GL(3) \times GL(2) L$$ -functions at special points

For a fixed \(SL(3,\mathbb Z )\) Maass form \(\phi \), we consider the family of \(L\)-functions \(L(\phi \times u_j, s)\) where \(u_j\) runs over the family of Hecke-Maass cusp forms on \(SL(2,\mathbb Z )\). We obtain an estimate for the second moment of this family of \(L\)-functions at the special points \({\frac{1}{2}}+ it_j\) consistent with the Lindelof Hypothesis. We also obtain a similar upper bound on the sixth moment of the family of Hecke-Maass cusp forms at these special points; this is apparently the first occurrence of a Lindelof-consistent estimate for a sixth power moment of a family of \(GL(2) L\)-functions.
DECIPHERING THERMAL PHASE CURVES OF DRY, TIDALLY LOCKED TERRESTRIAL PLANETS

Next-generation space telescopes will allow us to characterize terrestrial exoplanets. To do so effectively it will be crucial to make use of all available data. We investigate which atmospheric properties can, and cannot, be inferred from the broadband thermal phase curve of a dry and tidally locked terrestrial planet. First, we use dimensional analysis to show that phase curves are controlled by six nondimensional parameters. Second, we use an idealized general circulation model to explore the relative sensitivity of phase curves to these parameters. We find that the feature of phase curves most sensitive to atmospheric parameters is the peak-to-trough amplitude. Moreover, except for hot and rapidly rotating planets, the phase amplitude is primarily sensitive to only two nondimensional parameters: (1) the ratio of dynamical to radiative timescales and (2) the longwave optical depth at the surface. As an application of this technique, we show how phase curve measurements can be combined with transit or emission spectroscopy to yield a new constraint for the surface pressure and atmospheric mass of terrestrial planets. We estimate that a single broadband phase curve, measured over half an orbit with the James Webb Space Telescope, could meaningfully constrain the atmospheric mass of a nearby super-Earth. Such constraints will be important for studying the atmospheric evolution of terrestrial exoplanets as well as characterizing the surface conditions on potentially habitable planets.
Characterizing dust attenuation in local star-forming galaxies: UV and optical reddening

The dust attenuation for a sample of ~10,000 local (z ≾ 0.1) star-forming galaxies is constrained as a function of their physical properties. We utilize aperture-matched multiwavelength data available from the Galaxy Evolution Explorer and the Sloan Digital Sky Survey to ensure that regions of comparable size in each galaxy are being analyzed. We follow the method of Calzetti et al. and characterize the dust attenuation through the UV power-law index, β, and the dust optical depth, which is quantified using the difference in Balmer emission line optical depth, τ^1_ β = τ_(Hβ) – τ_(Hα). The observed linear relationship between β and τ^1_ β is similar to the local starburst relation, but the large scatter (σ_(int) = 0.44) suggests that there is significant variation in the local universe. We derive a selective attenuation curve over the range 1250 A < λ < 8320 A and find that a single attenuation curve is effective for characterizing the majority of galaxies in our sample. This curve has a slightly lower selective attenuation in the UV compared to previously determined curves. We do not see evidence to suggest that a 2175 A feature is significant in the average attenuation curve. Significant positive correlations are seen between the amount of UV and optical reddening and galaxy metallicity, mass, star formation rate (SFR), and SFR surface density. This provides a potential tool for gauging attenuation where the stellar population is unresolved, such as at high z.
WHAT IS THE RELATIONSHIP BETWEEN PHOTOSPHERIC FLOW FIELDS AND SOLAR FLARES

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking and Differential Affine Velocity Estimator methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96 minute cadence and ~2'' pixels, from 46 active regions (ARs) from 1996 to 1998 over the time interval τ45 when each AR was within 45° of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, ; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, . Several quantities derived from were also computed, including: Φ, the total unsigned flux; R, a measure of the unsigned flux near strong-field polarity inversion lines; and . Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both τ45 and shorter time windows of 6 and 24 hr. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during τ45. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, SR , was most strongly associated with flare flux, at a level comparable to that of R. All intensive flow properties studied were more poorly associated with flare flux than these extensive properties. Past flare activity was also associated with future flare occurrence. The largest coefficients of determination from correlations with flare flux that we performed are ~0.25, implying no single variable that we considered can explain the majority of variability in average flare flux.
Covert Wireless Communication With Artificial Noise Generation

Covert communication conceals the transmission of the message from an attentive adversary. Recent work on the limits of covert communication in additive white Gaussian noise channels has demonstrated that a covert transmitter (Alice) can reliably transmit a maximum of $\mathcal {O}(\sqrt {n})$ bits to a covert receiver (Bob) without being detected by an adversary (Warden Willie) in $n$ channel uses. This paper focuses on the scenario where other “friendly” nodes distributed according to a two-dimensional Poisson point process with density $m$ are present. We propose a strategy where the friendly node closest to the adversary, without close coordination with Alice, produces artificial noise. We show that this method allows Alice to reliably and covertly send $\mathcal {O}(\min \{{n,m^{\gamma /2}\sqrt {n}}\})$ bits to Bob in $n$ channel uses, where $\gamma $ is the path-loss exponent. We also consider a setting where there are $N_{\mathrm {w}}$ collaborating adversaries uniformly and randomly located in the environment and show that in $n$ channel uses, Alice can reliably and covertly send $\mathcal {O}(\min \{n,({m^{\gamma /2} \sqrt {n}}/{N_{\mathrm {w}}^{\gamma }})\})$ bits to Bob when $\gamma >2$ , and $\mathcal {O}(\min \{n,({m \sqrt {n}}/{N_{\mathrm {w}}^{2}\log ^{2} {N_{\mathrm {w}}}})\})$ when $\gamma = 2$ . Conversely, we demonstrate that no higher covert throughput is possible for $\gamma >2$ .
Don’t Parse, Generate! A Sequence to Sequence Architecture for Task-Oriented Semantic Parsing

Virtual assistants such as Amazon Alexa, Apple Siri, and Google Assistant often rely on a semantic parsing component to understand which action(s) to execute for an utterance spoken by its users. Traditionally, rule-based or statistical slot-filling systems have been used to parse “simple” queries; that is, queries that contain a single action and can be decomposed into a set of non-overlapping entities. More recently, shift-reduce parsers have been proposed to process more complex utterances. These methods, while powerful, impose specific limitations on the type of queries that can be parsed; namely, they require a query to be representable as a parse tree. In this work, we propose a unified architecture based on Sequence to Sequence models and Pointer Generator Network to handle both simple and complex queries. Unlike other works, our approach does not impose any restriction on the semantic parse schema. Furthermore, experiments show that it achieves state of the art performance on three publicly available datasets (ATIS, SNIPS, Facebook TOP), relatively improving between 3.3% and 7.7% in exact match accuracy over previous systems. Finally, we show the effectiveness of our approach on two internal datasets.
A Correlation between the Ionization State of the Inner Accretion Disk and the Eddington Ratio of Active Galactic Nuclei

X-ray reflection features observed from the innermost regions of accretion disks in active galactic nuclei (AGNs) allow important tests of accretion theory. In recent years, it has been possible to use the Fe Kα line and reflection continuum to parameterize the ionization state of the irradiated inner accretion disk. Here, we collect 10 measurements of ξ, the disk ionization parameter, from eight AGNs with strong evidence for reflection from the inner accretion disk and good black hole mass estimates. We find strong statistical evidence (98.56% confidence) for a nearly linear correlation between ξ and the AGN Eddington ratio. Moreover, such a correlation is predicted by a simple application of α-disk accretion theory, albeit with a stronger dependence on the Eddington ratio. The theory shows that there will be intrinsic scatter to any correlation as a result of different black hole spins and radii of reflection. There are several possibilities to soften the predicted dependence on the Eddington ratio to allow a closer agreement with the observed correlation, but the current data do not allow for a unique explanation. The correlation can be used to estimate that MCG-6-30-15 should have a highly ionized inner accretion disk, which would imply a black hole spin of ~0.8. Additional measurements of ξ from a larger sample of AGNs are needed to confirm the existence of this correlation, and will allow investigation of the accretion disk/corona interaction in the inner regions of accretion disks.
Classifying Supernovae Using Only Galaxy Data

We present a new method for probabilistically classifying supernovae (SNe) without using SN spectral or photometric data. Unlike all previous studies to classify SNe without spectra, this technique does not use any SN photometry. Instead, the method relies on host-galaxy data. We build upon the well-known correlations between SN classes and host-galaxy properties, specifically that core-collapse SNe rarely occur in red, luminous, or early-type galaxies. Using the nearly spectroscopically complete Lick Observatory Supernova Search sample of SNe, we determine SN fractions as a function of host-galaxy properties. Using these data as inputs, we construct a Bayesian method for determining the probability that an SN is of a particular class. This method improves a common classification figure of merit by a factor of >2, comparable to the best light-curve classification techniques. Of the galaxy properties examined, morphology provides the most discriminating information. We further validate this method using SN samples from the Sloan Digital Sky Survey and the Palomar Transient Factory. We demonstrate that this method has wide-ranging applications, including separating different subclasses of SNe and determining the probability that an SN is of a particular class before photometry or even spectra can. Since this method uses completely independent data from light-curve techniques, there is potential to further improve the overall purity and completeness of SN samples and to test systematic biases of the light-curve techniques. Further enhancements to the host-galaxy method, including additional host-galaxy properties, combination with light-curve methods, and hybrid methods, should further improve the quality of SN samples from past, current, and future transient surveys.
LIGHT QUARK MASSES FROM QUENCHED LATTICE QCD SIMULATIONS WITH DOMAIN WALL QUARKS

Values for the strange quark mass and average up/down mass have been obtained from quenched lattice QCD simulations using the domain wall fermion action. This discretization preserves the properties of flavor and chiral symmetry at nonzero lattice spacing. Results are shown for two values of the lattice spacing. The mass renormalization constant is computed nonperturbatively.
Metallicity and kinematical clues to the formation of the Local Group

The kinematics and elemental abundances of resolved stars in the nearby Universe can be used to infer conditions at high redshift, trace how galaxies evolve and constrain the nature of dark matter. This approach is complementary to direct study of systems at high redshift, but I will show that analysis of individual stars allows one to break degeneracies, such as between star formation rate and stellar Initial Mass Function, that complicate the analysis of unresolved, distant galaxies (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
The Swarm Telescope Concept

As telescope facilities become increasingly more capable, they also become increasingly complex and require additional resources to operate. This is particularly true for the current and future generations of “software defined telescopes” that can support a variety of observing programs simultaneously, either through commensal observations or through support for multiple pointing centers as in the case of dipole arrays or dishes equipped with phased array feeds. At the same time, many current and future facilities are also distributed over large geographic areas, making monitoring and maintenance more difficult and costly. For these reasons, we have developed a new paradigm for telescope operations called the “swarm telescope” that breaks large, single facilities into smaller groups of independent systems that can collaboratively work together to function as a single facility but with much less operational overhead. In this paper, we outline the swarm telescope concept and an example of its implementation...