cssi/SciSciGPT-SciSciNet huggingface dataset:
Possible Bright Starspots on TRAPPIST-1

The M8V star TRAPPIST-1 hosts seven roughly Earth-sized planets and is a promising target for exoplanet characterization. Kepler/K2 Campaign 12 observations of TRAPPIST-1 in the optical show an apparent rotational modulation with a 3.3 day period, though that rotational signal is not readily detected in the Spitzer light curve at 4.5 $\mu$m. If the rotational modulation is due to starspots, persistent dark spots can be excluded from the lack of photometric variability in the Spitzer light curve. We construct a photometric model for rotational modulation due to photospheric bright spots on TRAPPIST-1 which is consistent with both the Kepler and Spitzer light curves. The maximum-likelihood model with three spots has typical spot sizes of $R_\mathrm{spot}/R_\star \approx 0.004$ at temperature $T_\mathrm{spot} \gtrsim 5300 \pm 200$ K. We also find that large flares are observed more often when the brightest spot is facing the observer, suggesting a correlation between the position of the bright spots and flare events. In addition, these flares may occur preferentially when the spots are increasing in brightness, which suggests that the 3.3 d periodicity may not be a rotational signal, but rather a characteristic timescale of active regions.
The Formation and Role of Vortices in Protoplanetary Disks

We carry out a two-dimensional, compressible simulation of a disk, including dust particles, to study the formation and potential role of vortices in protoplanetary disks. We find that anticyclonic vortices can form out of an initial random perturbation of the vorticity field. Vortices have a typical decay time of the order of 50 orbital periods (for a viscosity parameter α = 10-4 and a disk aspect ratio of H/r = 0.15). If vorticity is continuously generated at a constant rate in the flow (e.g., by convection), then a large vortex can form and be sustained (because of the merger of vortices). We find that dust concentrates in the cores of vortices within a few orbital periods, when the drag parameter is of the order of the orbital frequency. Also, the radial drift of the dust induces a significant increase in the surface density of dust particles in the inner region of the disk. Thus, vortices may represent the preferred location for planetesimal formation in protoplanetary disks. The relative difficulty in forming such vortices, however, suggests that a further examination of this phenomenon is required in order to determine the viability of vortices as planet formation sites. We show that it is very difficult for vortex mergers to sustain a relatively coherent outward flux of angular momentum.
The Relation Between Black Hole Mass and Velocity Dispersion at z ~ 0.37

The velocity dispersion of 7 Seyfert 1 galaxies at z {approx} 0.37 is measured using high signal-to-noise Keck spectra. Black hole (BH) mass estimates are obtained via an empirically calibrated photoionization method. We derive the BH mass velocity dispersion relationship at z {approx} 0.37. We find an offset with respect to the local relationship, in the sense of somewhat lower velocity dispersion at a fixed BH mass at z {approx} 0.37 than today, significant at the 97% level. The offset corresponds to {Delta}log {sigma} = -0.16 with rms scatter of 0.13 dex. If confirmed by larger samples and independent checks on systematic uncertainties and selection effects, this result would be consistent with spheroids evolving faster than BHs in the past 4 Gyrs and inconsistent with pure luminosity evolution.
Generators of some non-commutative stochastic processes

A fundamental result of Biane (Math Z 227:143–174, 1998) states that a process with freely independent increments has the Markov property, but that there are two kinds of free Levy processes: the first kind has stationary increments, while the second kind has stationary transition operators. We show that a process of the first kind (with mean zero and finite variance) has the same transition operators as the free Brownian motion with appropriate initial conditions, while a process of the second kind has the same transition operators as a monotone Levy process. We compute an explicit formula for the generators of these families of transition operators, in terms of singular integral operators, and prove that this formula holds on a fairly large domain. We also compute the generators for the \(q\)-Brownian motion, and for the two-state free Brownian motions.
METALLICITY IN THE GRB 100316D/SN 2010bh HOST COMPLEX*

The recent long-duration GRB 100316D, associated with supernova SN 2010bh and detected by Swift, is one of the nearest gamma-ray burst (GRB)-supernovae (SNe) ever observed (z = 0.059). This provides us with a unique opportunity to study the explosion environment on ~kpc scale in relation to the host galaxy complex. Here we present spatially resolved spectrophotometry of the host galaxy, focusing on both the explosion site and the brightest star-forming regions. Using these data, we extract the spatial profiles of the relevant emission features (Hα, Hβ, [O III]λ5007, and [N II]λ6584) and use these profiles to examine variations in metallicity and star formation rate (SFR) as a function of position in the host galaxy. We conclude that GRB 100316D/SN2010bh occurred in a low-metallicity host galaxy, and that the GRB-SN explosion site corresponds to the region with the lowest metallicity and highest SFR sampled by our observations.
Axiomatic Information Thermodynamics

We present an axiomatic framework for thermodynamics that incorporates information as a fundamental concept. The axioms describe both ordinary thermodynamic processes and those in which information is acquired, used and erased, as in the operation of Maxwell’s demon. This system, similar to previous axiomatic systems for thermodynamics, supports the construction of conserved quantities and an entropy function governing state changes. Here, however, the entropy exhibits both information and thermodynamic aspects. Although our axioms are not based upon probabilistic concepts, a natural and highly useful concept of probability emerges from the entropy function itself. Our abstract system has many models, including both classical and quantum examples.
Evidence for Gamma-Ray Jets in the Milky Way

Although accretion onto supermassive black holes in other galaxies is seen to produce powerful jets in X-ray and radio, no convincing detection has ever been made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10 kpc tall gamma-ray bubbles in our Galaxy may be signs of earlier jet activity from the central black hole. In this paper, we identify a gamma-ray cocoon feature in the southern bubble, a jet-like feature along the cocoon's axis of symmetry, and another directly opposite the Galactic center in the north. Both the cocoon and jet-like feature have a hard spectrum with spectral index ~ – 2 from 1 to 100 GeV, with a cocoon total luminosity of (5.5 ± 0.45) × 1035 and luminosity of the jet-like feature of (1.8 ± 0.35) × 1035 erg s–1 at 1-100 GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.
Some features of (0,2) moduli space

Abstract We discuss some aspects of perturbative (0, 2) Calabi-You moduli space. In particular, we show how models with different (0, 2) data can meet along various sub-loci in their moduli space. In the simplest examples, the models differ by the choice of desingularization of a holomorphic V -bundle over the same resolved Calabi-You base while in more complicated examples, even the smooth Calabi-You base manifolds can be topologically distinct. These latter examples extend and clarify a previous observation which was limited to singular Calabi-You spaces and seem to indicate a multicritical structure in moduli space. This should have a natural F-theory counterpart in terms of the moduli space of Calabi-You four-folds.
Entropic dynamics, time and quantum theory

Quantum mechanics is derived as an application of the method of maximum entropy. No appeal is made to any underlying classical action principle whether deterministic or stochastic. Instead, the basic assumption is that in addition to the particles of interest x there exist extra variables y whose entropy S(x) depends on x. The Schrodinger equation follows from their coupled dynamics: the entropy S(x) drives the dynamics of the particles x while they in their turn determine the evolution of S(x). In this 'entropic dynamics' time is introduced as a device to keep track of change. A welcome feature of such an entropic time is that it naturally incorporates an arrow of time. Both the magnitude and the phase of the wavefunction are given statistical interpretations: the magnitude gives the distribution of x in agreement with the usual Born rule and the phase carries information about the entropy S(x) of the extra variables. Extending the model to include external electromagnetic fields yields further insight into the nature of the quantum phase.
Compactly supported wavelets and representations of the Cuntz relations, II

We show that compactly supported wavelets in L2 (R) of scale N may be effectively parameterized with a finite set of spin vectors in CN, and conversely that every set of spin vectors corresponds to a wavelet. The characterization is given in terms of irreducible representation of orthogonality relations defined form multiresolution wavelet filters.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Convection-aided Explosions in One-dimensional Core-collapse Supernova Simulations. I. Technique and Validation

Most one-dimensional core-collapse simulations fail to explode, yet multi-dimensional simulations often explode. A dominant multi-dimensional effect aiding explosion is neutrino-driven convection. We incorporate a convection model in approximate one-dimensional core-collapse supernova (CCSN) simulations. This is the 1D+ method. This convection model lowers the neutrino luminosity required for explosion by 30%, similar to the reduction observed in multi-dimensional simulations. The model is based upon the global turbulence model of Mabanta & Murphy (2018) and models the mean-field turbulent flow of neutrino-driven convection. In this preliminary investigation, we use simple neutrino heating and cooling algorithms to compare the critical condition in the 1D+ simulations with the critical condition observed in two-dimensional simulations. Qualitatively, the critical conditions in the 1D+ and the two-dimensional simulations are similar. The assumptions in the convection model affect the radial profiles of density, entropy, and temperature, and comparisons with the profiles of three dimensional simulations will help to calibrate these assumptions. These 1D+ simulations are consistent with the profiles and explosion conditions of equivalent two-dimensional CCSN simulations but are ~100 times faster, and the 1D+ prescription has the potential to be ~100,000 faster than three-dimensional CCSN simulations. The 1D+ technique will be ideally suited to test the explodability of thousands of progenitor models.
Snapping of bistable, prestressed cylindrical shells

Bistable shells can reversibly change between two stable configurations with very little energetic input. Understanding what governs the shape and snap-through criteria of these structures is crucial for designing devices that utilize instability for functionality. Bistable cylindrical shells fabricated by stretching and bonding multiple layers of elastic plates will contain residual stress that will impact the shell's shape and the magnitude of stimulus necessary to induce snapping. Using the framework of non-Euclidean shell theory, we first predict the mean curvature of a nearly cylindrical shell formed by arbitrarily prestretching one layer of a bilayer plate with respect to another. Then, beginning with a residually stressed cylinder, we determine the amount of the stimuli needed to trigger the snapping between two configurations through a combination of numerical simulations and theory. We demonstrate the role of prestress on the snap-through criteria, and highlight the important role that the Gaussian curvature in the boundary layer of the shell plays in dictating shell stability.
Variational consistent histories as a hybrid algorithm for quantum foundations.

Although quantum computers are predicted to have many commercial applications, less attention has been given to their potential for resolving foundational issues in quantum mechanics. Here we focus on quantum computers’ utility for the Consistent Histories formalism, which has previously been employed to study quantum cosmology, quantum paradoxes, and the quantum-to-classical transition. We present a variational hybrid quantum-classical algorithm for finding consistent histories, which should revitalize interest in this formalism by allowing classically impossible calculations to be performed. In our algorithm, the quantum computer evaluates the decoherence functional (with exponential speedup in both the number of qubits and the number of times in the history) and a classical optimizer adjusts the history parameters to improve consistency. We implement our algorithm on a cloud quantum computer to find consistent histories for a spin in a magnetic field and on a simulator to observe the emergence of classicality for a chiral molecule. The Consistent Histories formalism can solve paradoxes in quantum mechanics, but finding such consistent sets of histories requires a computational overhead which is exponential in the problem’s size. Here, the authors report a variational hybrid algorithm solving this problem using polynomial resources.
CAT-Gen: Improving Robustness in NLP Models via Controlled Adversarial Text Generation

NLP models are shown to suffer from robustness issues, i.e., a model's prediction can be easily changed under small perturbations to the input. In this work, we present a Controlled Adversarial Text Generation (CAT-Gen) model that, given an input text, generates adversarial texts through controllable attributes that are known to be invariant to task labels. For example, in order to attack a model for sentiment classification over product reviews, we can use the product categories as the controllable attribute which would not change the sentiment of the reviews. Experiments on real-world NLP datasets demonstrate that our method can generate more diverse and fluent adversarial texts, compared to many existing adversarial text generation approaches. We further use our generated adversarial examples to improve models through adversarial training, and we demonstrate that our generated attacks are more robust against model re-training and different model architectures.
Minimally intersecting filling pairs on surfaces

Let Sg denote the closed orientable surface of genus g . We construct exponentially many mapping class group orbits of pairs of simple closed curves which fill Sg and intersect minimally, by showing that such orbits are in correspondence with the solutions of a certain permutation equation in the symmetric group. Next, we demonstrate that minimally intersecting filling pairs are combinatorially optimal, in the sense that there are many simple closed curves intersecting the pair exactly once. We conclude by initiating the study of a topological Morse function Fg over the moduli space of Riemann surfaces of genus g , which, given a hyperbolic metric , outputs the length of the shortest minimally intersecting filling pair for the metric . We completely characterize the global minima of Fg and, using the exponentially many mapping class group orbits of minimally intersecting filling pairs that we construct in the first portion of the paper, we show that the number of such minima grows at least exponentially in g . 57M20, 57M50
Magnetic Field Line Twisting by Photospheric Vortices: Energy Storage and Release

We investigate the dynamics of a closed corona cartesian reduced magnetohydrodynamic (MHD) model where photospheric vortices twist the coronal magnetic field lines. We consider two corotating or counter-rotating vortices localized at the center of the photospheric plate, and additionally more corotating vortices that fill the plate entirely. Our investigation is specifically devoted to study the fully nonlinear stage, after the linear stage during which the vortices create laminar and smoothly twisting flux tubes. Our main goal is to understand the dynamics of photospheric vortices twisting the field lines of a coronal magnetic field permeated by finite amplitude broadband fluctuations. We find that depending on the arrangement and handedness of the photospheric vortices an inverse cascade storing a significant amount of magnetic energy may occur or not. In the first case a reservoir of magnetic energy available to large events such as destabilization of a pre-CME configuration develops, while in the second case the outcome is a turbulent heated corona. Although our geometry is simplified our simulations are shown to have relevant implications for coronal dynamics and CME initiation.
Toward Incremental FIB Aggregation with Quick Selections (FAQS)

Several approaches to mitigating the Forwarding Information Base (FIB) overflow problem were developed and software solutions using FIB aggregation are of particular interest. One of the greatest concerns to deploy these algorithms to real networks is their high running time and heavy computational overhead to handle thousands of FIB updates every second. In this work, we manage to use a single tree traversal to implement faster aggregation and update handling algorithm with much lower memory footprint than other existing work. We utilize 6-year realistic IPv4 and IPv6 routing tables from 2011 to 2016 to evaluate the performance of our algorithm with various metrics. To the best of our knowledge, it is the first time that IPv6 FIB aggregation has been performed. Our new solution is 2.53 and 1.75 times as fast as the-state-of-the-art FIB aggregation algorithm for IPv4 and IPv6 FIBs, respectively, while achieving a near-optimal FIB aggregation ratio.
Experimental fast quantum random number generation using high-dimensional entanglement with entropy monitoring

A quantum random number generator (QRNG) generates genuine randomness from the intrinsic probabilistic nature of quantum mechanics. The central problems for most QRNGs are estimating the entropy of the genuine randomness and producing such randomness at high rates. Here we propose and demonstrate a proof-of-concept QRNG that operates at a high rate of 24 Mbits/s by means of a high-dimensional entanglement system, in which the user monitors the entropy in real time via the observation of nonlocal quantum interference, without a detailed characterization of the devices. Our work provides an important approach to a robust QRNG with trusted but error-prone devices.
Practical Limits in the Sensitivity-Linearity Trade-off for Radio Telescope Front Ends in the HF and VHF-low Bands

Radio telescope front ends must have simultaneously low noise and sufficiently-high linearity to accommodate interfering signals. Typically these are opposing design goals. For modern radio telescopes operating in the HF (3–30MHz) and VHF-low (30–88MHz) bands, the problem is more nuanced in that front end noise temperature may be a relatively small component of the system temperature, and increased linearity may be required due to the particular interference problems associated with this spectrum. In this paper, we present an analysis of the sensitivity-linearity trade-off at these frequencies, applicable to existing commercially-available monolithic microwave integrated circuit (MMIC) amplifiers in single-ended, differential, and parallelized configurations. This analysis and associated findings should be useful in the design and upgrade of front ends for low frequency radio telescopes. The analysis is demonstrated explicitly for one of the better-performing amplifiers encountered in this study, the Mini...
State of matter at high density and entropy bounds

Entropy of all systems that we understand well is proportional to their volumes except for black holes given by their horizon area. This makes the microstates of any quantum theory of gravity drastically different from the ordinary matter. Because of the assumption that black holes are the maximum entropy states, there have been many conjectures that put the area, defined one way or another, as a bound on the entropy in a given region of spacetime. Here, we construct a simple model with entropy proportional to volume which exceeds the entropy of a single black hole. We show that a homogeneous cosmology filled with this gas exceeds one of the tightest entropy bounds, the covariant entropy bound and discuss the implications.
Weak and strong solutions to the inverse-square brachistochrone problem on circular and annular domains

In this paper we study the brachistochrone problem in an inverse-square gravitational field on the unit disk. We show that the time optimal solutions consist of either smooth strong solutions to the Euler-Lagrange equation or weak solutions formed by appropriately patched together strong solutions. This combination of weak and strong solutions completely foliates the unit disk. We also consider the problem on annular domains and show that the time optimal paths foliate the annulus. These foliations on the annular domains converge to the foliation on the unit disk in the limit of vanishing inner radius.
Cutoff-free traveling wave NMR

Recently, the concept of traveling wave NMR/MRI was introduced by Brunner et al. (Nature 2009;457:994–992), who demonstrated MR images acquired using radio frequency (RF) waves propagating down the bore of a MR scanner which acts as a waveguide. One of the significant limitations of this approach is that each bore has a specific cutoff frequency, which can be higher than most Larmor frequencies at the magnetic field strengths commonly in use for MR imaging and spectroscopy today. One can overcome this limitation by using a central conductor in the waveguide and thereby converting it in to a transmission line which has no cutoff frequency. Broadband propagation of waves through the sample thus becomes possible. NMR spectra and images with such an arrangement are presented and traveling wave behavior is demonstrated. In addition to facilitating NMR spectroscopy and imaging in smaller bores via traveling waves, this approach also allows one to perform multinuclear traveling wave experiments (an example of which is shown), and to study otherwise difficult-to-access samples in unusual geometries. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38: 253–267, 2011.
Toric bases for 6D F-theory models

We find all smooth toric bases that support elliptically fibered Calabi-Yau threefolds, using the intersection structure of the irreducible effective divisors on the base. These bases can be used for F-theory constructions of six-dimensional quantum supergravity theories. There are 61,539 distinct possible toric bases. The associated 6D supergravity theories have a number of tensor multiplets ranging from 0 to 193. For each base an explicit Weierstrass parameterization can be determined in terms of the toric data. The toric counting of parameters matches with the gravitational anomaly constraint on massless fields. For bases associated with theories having a large number of tensor multiplets, there is a large non-Higgsable gauge group containing multiple irreducible gauge group factors, particularly those having algebras 𝔢8, 𝔣4, and 𝔤g2 ⊕ 𝔰𝔲(2) with minimal (non-Higgsable) matter.
Bootstrapping the O(N) Vector Models

We study the conformal bootstrap for 3D CFTs with O(N ) global symmetry. We obtain rigorous upper bounds on the scaling dimensions of the first O(N ) singlet and symmetric tensor operators appearing in the ϕ i × ϕ j OPE, where ϕ i is a fundamental of O(N ). Comparing these bounds to previous determinations of critical exponents in the O(N ) vector models, we find strong numerical evidence that the O(N ) vector models saturate the bootstrap constraints at all values of N . We also compute general lower bounds on the central charge, giving numerical predictions for the values realized in the O(N ) vector models. We compare our predictions to previous computations in the 1/N expansion, finding precise agreement at large values of N .
Closed timelike curves and ‘effective’ superluminal travel with naked line singularities

We examine closed timelike curves (CTCs) and 'effective' superluminal travel in a spacetime containing naked line singularities, which we call 'wires'. Each wire may be straight-line singularity or a ring singularity. The weak energy condition (WEC) is preserved in all well-defined regions of the spacetime. (The singularities themselves are not well-defined, so the WEC is undefined there, but it is never explicitly violated.) Parallel to the wire, 'effective' superluminal travel is possible, in that the wire may be used as a shortcut between distant regions of spacetime. Our purpose in presenting the superluminal aspects of the wire is to dispel the commonly held view that explicit WEC violation is necessary for effective superluminal travel, whereas in truth the strictures against superluminal travel are more complicated. We also demonstrate how the existence of such 'wires' could create CTCs. We present a model spacetime which contains two wires which are free to move relative to each other. This spacetime is asymptotically flat: it becomes a Minkowski spacetime a finite distance away from each of the wires. The CTCs under investigation do not need to enter the wires' singularities, and can be confined to regions that are weak-field: this means that if these wires were physically possible, they would present causality problems even in nonsingular, energetically realistic regions of the spacetime. We conclude that the weak energy condition alone is not sufficient to prevent superluminal travel in asymptotically flat spacetimes.
Star formation at the galactic center

ABSTRACT.Molecular clouds at the Galactic center (GC) have environments considerably different from their disk counterparts. The GC may therefore provide important clues about how the environment affects star formation. Interestingly, while the inner 50 pc of our Galaxy include a remarkable population of high-mass stars, the initial mass function (IMF) appears to be consistent with a Salpeter slope down to ∼1 M⊙∼1 M⊙. We show here that the loss of turbulent pressure due to ambipolar diffusion and the damping of Alfven and fast MHD waves can lead to the formation of dense condensations exceeding their Jeans limit. The fragmentation and subsequent collapse of these condensations is similar to the diffusion-driven protostellar collapse mechanism expected to occur within nearby “regular” molecular clouds. As such, a Salpeter IMF at the GC is not surprising, though the short dynamical timescales associated with the GC molecular clouds may help explain the lower star formation efficiency observed from this region.
INTERESTING FEATURES IN THE COMBINED GALEX AND SLOAN COLOR DIAGRAMS OF SOLAR-LIKE GALACTIC POPULATIONS

We report on intriguing photometric properties of Galactic stars observed in the Galaxy Evolution Explorer (GALEX) satellite's far-UV (FUV) and near-UV (NUV) bandpasses, as well as from the ground-based Sloan Digital Sky Survey (SDSS) and the Kepler Input Catalog. The first property is that the (FUV – NUV) color distribution of stars in the Kepler field consists of two well-separated peaks. A second and more perplexing property is that for stars with spectral types G or later the mean (FUV – NUV) color becomes much bluer, contrary to expectation. Investigating this tendency further, we found in two samples of mid-F through K type stars that 17%-22% of them exhibit FUV excesses relative to their NUV fluxes and spectral types. A correction for FUV incompleteness of the FUV magnitude-limited star sample brings this ratio to 14%-18%. Nearly the same fractions are also discovered among members of the Kepler Eclipsing Binary Catalog and in the published list of Kepler Objects of Interest. These UV-excess ("UVe") colors are confirmed by the negative UV continuum slopes in GALEX spectra of members of the population. The SDSS spectra of some UVe stars exhibit metallic line weakening, especially in the blue. This suggests an enhanced contribution of UV flux relative to photospheric flux of a solar-type single star. We consider the possibility that the UV excesses originate from various types of hot stars, including white dwarf DA and sdB stars, binaries, and strong chromosphere stars that are young or in active binaries. The space density of compact stars is too low to explain the observed frequency of the UVe stars. Our model atmosphere-derived simulations of colors for binaries with main-sequence pairs with a hot secondary demonstrate that the color loci conflict with the observed sequence. As a preferred alternative we are left with the active chromospheres explanation, whether in active close binaries or young single stars, despite the expected paucity of young, chromospherically active stars in the field. We also address a third perplexing color property, namely, the presence of a prominent island of "UV red" stars surrounded by "UV blue" stars in the diagnostic (NUV–g), (g – i) color diagram. We find that the subpopulation composing this island is mainly horizontal branch stars. These objects do not exhibit UV excesses and therefore have UV colors typical for their spectral types. This subpopulation appears "red" in the UV only because the stars' colors are not pulled to the blue by the inclusion of UVe stars.
Optimal Control of Two-Player Systems With Output Feedback

In this article, we consider a fundamental decentralized optimal control problem, which we call the two-player problem. Two subsystems are interconnected in a nested information pattern, and output feedback controllers must be designed for each subsystem. Several special cases of this architecture have previously been solved, such as the state-feedback case or the case where the dynamics of both systems are decoupled. In this paper, we present a detailed solution to the general case. The structure of the optimal decentralized controller is reminiscent of that of the optimal centralized controller; each player must estimate the state of the system given their available information and apply static control policies to these estimates to compute the optimal controller. The previously solved cases benefit from a separation between estimation and control that allows the associated gains to be computed separately. This feature is not present in general, and some of the gains must be solved for simultaneously. We show that computing the required coupled estimation and control gains amounts to solving a small system of linear equations.
Gauge invariant spectral Cauchy characteristic extraction

We present gauge invariant spectral Cauchy characteristic extraction. We compare gravitational waveforms extracted from a head-on black hole merger simulated in two different gauges by two different codes. We show rapid convergence, demonstrating both gauge invariance of the extraction algorithm and consistency between the legacy Pitt null code and the much faster Spectral Einstein Code (SpEC).
From Bare Metal to Virtual: Lessons Learned when a Supercomputing Institute Deploys its First Cloud

As primary provider for research computing services at the University of Minnesota, the Minnesota Supercomputing Institute (MSI) has long been responsible for serving the needs of a user-base numbering in the thousands.In recent years, MSI---like many other HPC centers---has observed a growing need for self-service, on-demand, data-intensive research, as well as the emergence of many new controlled-access datasets for research purposes. In light of this, MSI constructed a new on-premise cloud service, named Stratus, which is architected from the ground up to easily satisfy data-use agreements and fill four gaps left by traditional HPC. The resulting OpenStack cloud, constructed from HPC-specific compute nodes and backed by Ceph storage, is designed to fully comply with controls set forth by the NIH Genomic Data Sharing Policy.Herein, we present twelve lessons learned during the ambitious sprint to take Stratus from inception and into production in less than 18 months. Important, and often overlooked, components of this timeline included the development of new leadership roles, staff and user training, and user support documentation. Along the way, the lessons learned extended well beyond the technical challenges often associated with acquiring, configuring, and maintaining large-scale systems.
Parton Coalescence and Spacetime

The influence of spacetime dynamics in hadronization via parton coalescence at RHIC is investigated using covariant parton transport theory: Key observables, the quark number scaling of elliptic flow and the enhancement of the p/π ratio, show strong dynamical effects and differ from earlier results based on the simple coalescence formulas.
Frobenius objects in the category of relations

We give a characterization, in terms of simplicial sets, of Frobenius objects in the category of relations. This result generalizes a result of Heunen, Contreras, and Cattaneo showing that special dagger Frobenius objects in the category of relations are in correspondence with groupoids. As an additional example, we construct a Frobenius object in the category of relations whose elements are certain cohomology classes in a compact oriented Riemannian manifold.
Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using an alpha–gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478 keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024%. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058%. We discuss the principle of the alpha–gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.
Supersymmetry Then and Now

A brief description of some salient aspects of four-dimensional supersymmetry: early history, supermanifolds, the MSSM, cold dark matter, the cosmological constant and the string landscape.
Hybrid piezoelectric-magnetic neurons: a proposal for energy-efficient machine learning

This paper proposes a spintronic neuron structure composed of a heterostructure of magnets and a piezoelectric with a magnetic tunnel junction (MTJ). The operation of the device is simulated using SPICE models. Simulation results illustrate that the energy dissipation of the proposed neuron compared to that of other spintronic neurons exhibits 70% improvement. Compared to CMOS neurons, the proposed neuron occupies a smaller footprint area and operates using less energy. Owing to its versatility and low-energy operation, the proposed neuron is a promising candidate to be adopted in artificial neural network (ANN) systems.
External energy paradigm for black holes

A new paradigm for black holes is introduced. It is known as the External Energy Paradigm. The paradigm asserts that all energies of a black hole are external quantities; they are absent inside the...
A CHEMICAL ABUNDANCE STUDY OF 10 OPEN CLUSTERS BASED ON WIYN*-HYDRA SPECTROSCOPY

We present a detailed chemical abundance study of evolved stars in 10 open clusters based on Hydra multi-object echelle spectra obtained with the WIYN 3.5 m telescope. From an analysis of both equivalent widths and spectrum synthesis, abundances have been determined for the elements Fe, Na, O, Mg, Si, Ca, Ti, Ni, Zr, and for two of the 10 clusters, Al and Cr. To our knowledge, this is the first detailed abundance analysis for clusters NGC 1245, NGC 2194, NGC 2355, and NGC 2425. These 10 clusters were selected for analysis because they span a Galactocentric distance range R gc ~ 9-13 kpc, the approximate location of the transition between the inner and outer disks. Combined with cluster samples from our previous work and those of other studies in the literature, we explore abundance trends as a function of cluster R gc, age, and [Fe/H]. As found previously by us and other studies, the [Fe/H] distribution appears to decrease with increasing R gc to a distance of ~12 kpc and then flattens to a roughly constant value in the outer disk. Cluster average element [X/Fe] ratios appear to be independent of R gc, although the picture for [O/Fe] is more complicated with a clear trend of [O/Fe] with [Fe/H] and sample incompleteness. Other than oxygen, no other element [X/Fe] exhibits a clear trend with [Fe/H]; likewise, there does not appear to be any strong correlation between abundance and cluster age. We divided clusters into different age bins to explore temporal variations in the radial element distributions. The radial metallicity gradient appears to have flattened slightly as a function of time, as found by other studies. There is also some indication that the transition from the inner disk metallicity gradient to the ~constant [Fe/H] distribution of the outer disk occurs at different Galactocentric radii for different age bins. However, interpretation of the time evolution of radial abundance distributions is complicated by the unequal R gc and [Fe/H] ranges spanned by clusters in different age bins.
Lie algebroid modules and representations up to homotopy

Abstract We establish a relationship between two different generalizations of Lie algebroid representations: representation up to homotopy and Vaĭntrob’s Lie algebroid modules. Specifically, we show that there is a noncanonical way to obtain a representation up to homotopy from a given Lie algebroid module, and that any two representations up to homotopy obtained in this way are equivalent in a natural sense. We therefore obtain a one-to-one correspondence, up to equivalence.
OUTCOMES AND DURATION OF TIDAL EVOLUTION IN A STAR-PLANET-MOON SYSTEM

We formulated tidal decay lifetimes for hypothetical moons orbiting extrasolar planets with both lunar and stellar tides. Previous works neglected the effect of lunar tides on planet rotation, and are therefore applicable only to systems in which the moon's mass is much less than that of the planet. This work, in contrast, can be applied to the relatively large moons that might be detected around newly discovered Neptune-mass and super-Earth planets. We conclude that moons are more stable when the planet/moon systems are further from the parent star, the planets are heavier, or the parent stars are lighter. Inclusion of lunar tides allows for significantly longer lifetimes for a massive moon relative to prior formulations. We expect that the semimajor axis of the planet hosting the first detected exomoon around a G-type star is 0.4-0.6 AU and is 0.2-0.4 AU for an M-type star.
SUZAKU OBSERVATIONS OF THE GALACTIC CENTER MICROQUASAR 1E 1740.7–2942

We present two Suzaku observations of the Galactic center microquasar 1E 1740.7–2942 separated by approximately 700 days. The source was observed on both occasions after a transition to the spectrally hard state. Significant emission from 1E 1740.7–2942 is detected out to an energy of 300 keV, with no spectral break or turnover evident in the data. We tentatively measure a lower limit to the cutoff energy of ~380 keV. The spectra are found to be consistent with a Comptonized corona on both occasions, where the high energy emission is consistent with a hard power-law (Γ ~ 1.8) with a significant contribution from an accretion disk with a temperature of ~0.4 keV at soft X-ray energies. The measured value for the inner radius of the accretion disk is found to be inconsistent with the picture whereby the disk is truncated at large radii in the low-hard state and instead favors a radius close to the ISCO (R in ~ 10 – 20 Rg ).
Observations on the moduli space of two dimensional string theory

We explore the moduli space of the two dimensional fermionic string with linear dilaton. In addition to the known 0A and 0B theories, there are two theories with chiral GSO projections, which we call IIA and IIB. They are similar to the IIA and IIB theories of ten dimensions, but are constructed with a different GSO projection. Compactifying these theories on various twisted circles leads to eight lines of theories. Three of them, 0A on a circle, super-affine 0A and super-affine 0B are known. The other five lines of theories are new. At special points on two of them we find the noncritical superstring.
Confidence Sets for the Source of a Diffusion in Regular Trees

We study the problem of identifying the source of a diffusion spreading over a regular tree. When the degree of each node is at least three, we show that it is possible to construct confidence sets for the diffusion source with size independent of the number of infected nodes. Our estimators are motivated by analogous results in the literature concerning identification of the root node in preferential attachment and uniform attachment trees. At the core of our proofs is a probabilistic analysis of Polya urns corresponding to the number of uninfected neighbors in specific subtrees of the infection tree. We also provide an example illustrating the shortcomings of source estimation techniques in settings where the underlying graph is asymmetric.
Enabling Robust State Estimation Through Measurement Error Covariance Adaptation

Accurate platform localization is an integral component of most robotic systems. As these robotic systems become more ubiquitous, it is necessary to develop robust state-estimation algorithms that are able to withstand novel and noncooperative environments. When dealing with novel and noncooperative environments, little is known a priori about the measurement error uncertainty; thus, there is a requirement that the uncertainty models of the localization algorithm be adaptive. In this paper, we propose the batch covariance estimation technique, which enables robust state estimation through the iterative adaptation of the measurement uncertainty model. The adaptation of the measurement uncertainty model is granted through nonparametric clustering of the residuals, which enables the characterization of the measurement uncertainty via a Gaussian mixture model. The provided Gaussian mixture model can be utilized within any nonlinear least squares optimization algorithm by approximately characterizing each observation with the sufficient statistics of the assigned cluster (i.e., each observation's uncertainty model is updated based on the assignment provided by the nonparametric clustering algorithm). The proposed algorithm is verified on several Global Navigation Satellite System collected datasets, where it is shown that the proposed technique exhibits some advantages when compared to other robust estimation techniques when confronted with degraded data quality.
What Fraction of the Young Clusters in the Antennae Galaxies Are “Missing”?*

A reexamination of the correspondence between 6 cm radio continuum sources and young star clusters in the Antennae galaxies indicates that ~85% of the strong thermal sources have optical counterparts, once the optical image is shifted 12 to the southwest. A sample of 37 radio-optical matches are studied in detail, showing correlations between radio properties (i.e., total flux and spectral index) and a variety of optical characteristics (i.e., intrinsic cluster brightness, Hα flux and equivalent width, extinction, and cluster ages). There is a strong correlation between the radio flux and the intrinsic optical brightness. In particular, the brightest radio source is also the intrinsically brightest optical cluster (WS 80). It is also the most extincted cluster in the sample, the strongest CO source, and the strongest 15 micron source. Furthermore, the 10 brightest radio sources are all among the youngest clusters, with ages in the range 0–4 Myr and extinctions from AV = 0.5 to 7.6 mag (with a median value of 2.6 mag). A weak correlation between age and AV suggests that ~6 Myr are typically required to remove enough dust to reach AV = 1 mag. The radio-bright phase lasts only about 10 Myr in these clusters, consistent with the interpretation that most of the radio emission originates from hot gas. Many of the nondetections are probably individual supernova remnants since they have relatively steep radio indices typical of nonthermal sources. Only a few of the very red clusters originally discovered by Whitmore and Schweizer are radio sources, contrary to earlier suggestions. Finally, a new hybrid method of determining cluster ages has been developed using both UBVI colors and Hα equivalent widths to break the age-reddening degeneracy. We find that the Bruzual and Charlot models, which use the Padova spectral evolution tracks, fit the data reasonably well, while the Leitherer & Heckman models, using the Geneva tracks, have a large red loop for ages 8–13 Myr that does not agree with the data.
Bursts of Activity: Temporal Patterns of Help-Seeking and Support in Online Mental Health Forums

Recent years have seen a rise in social media platforms that provide peer-to-peer support to individuals suffering from mental distress. Studies on the impact of these platforms have focused on either short-term scales of single-post threads, or long-term changes over arbitrary period of time (months or years). While important, such periods of time do not necessarily follow users’ progressions through acute periods of distress. Using data from Talklife, a mental health platform, we find that user activity follows a distinct pattern of high activity periods with interleaving periods of no activity, and propose a method for identifying such bursts & breaks in activity. We then show how studying activity during bursts can provide a personalized, medium-term analysis for a key question in online mental health communities: What characteristics of user activity lead some users to find support and help, while others fall short? Using two independent outcome metrics, moments of cognitive change and self-reported changes in mood during a burst of activity, we identify two actionable features that can improve outcomes for users: persistence within bursts, and giving complex emotional support to others. Our results demonstrate the value of considering bursts as a natural unit of analysis for psychosocial change in online mental health communities.
MmWave MU-MIMO for Aerial Networks

Millimeter wave offers high bandwidth for air-to-air (A2A) communication. In this paper, we evaluate the rate performance of a multiuser MIMO (MU-MIMO) configuration where several aircraft communicate with a central hub. We consider a hybrid subarray architecture, single path channels, and realistic atmospheric attenuation effects. We propose a mathematical framework for the analysis of millimeter wave (mmWave) MU-MIMO networks. Via Monte Carlo simulation, we demonstrate that mmWave is a promising technology for delivering gigabit connectivity in next-generation aerial networks.