cssi/SciSciGPT-SciSciNet huggingface dataset:
Shaping the Brown Dwarf Desert: Predicting the Primordial Brown Dwarf Binary Distributions from Turbulent Fragmentation

The formation of brown dwarfs (BDs) poses a key challenge to star formation theory. The observed dearth of nearby (≤5 AU) BD companions to solar mass stars, known as the BD desert, as well as the tendency for low-mass binary systems to be more tightly bound than stellar binaries, has been cited as evidence for distinct formation mechanisms for BDs and stars. In this paper, we explore the implications of the minimal hypothesis that BDs in binary systems originate via the same fundamental fragmentation mechanism as stars, within isolated, turbulent giant molecular cloud cores. We demonstrate analytically that the scaling of specific angular momentum with turbulent core mass naturally gives rise to the BD desert, as well as wide BD binary systems. Further, we show that the turbulent core fragmentation model also naturally predicts that very low mass binary and BD/BD systems are more tightly bound than stellar systems. In addition, in order to capture the stochastic variation intrinsic to turbulence, we generate 104 model turbulent cores with synthetic turbulent velocity fields to show that the turbulent fragmentation model accommodates a small fraction of binary BDs with wide separations, similar to observations. Indeed, the picture which emerges from the turbulent fragmentation model is that a single fragmentation mechanism may largely shape both stellar and BD binary distributions during formation.
Virtualization map for the Littelmann path model

We show the natural embedding of weight lattices from a diagram folding is a virtualization map for the Littelmann path model, which recovers a result of Kashiwara. As an application, we give a type-independent proof that certain Kirillov-Reshetikhin crystals respect diagram foldings, which is a known result on a special case of a conjecture given by Okado, Schilling, and Shimozono.
Transverse Chiral Optical Forces by Chiral Surface Plasmon Polaritons

Recently, the concepts of transverse spin angular momentum and Belinfante spin momentum of evanescent waves have drawn considerable attention. Here, we investigate these novel physical properties of electromagnetic fields in the context of chiral surface plasmon polaritons. We demonstrate, both analytically and numerically, that chiral surface plasmon polaritons possess transverse spin angular momentum and Belinfante momentum with rich and nontrivial characteristics. We also show that the transverse spin angular momentum of chiral surface plasmon polaritons leads to the emergence of transverse optical forces in opposite directions for chiral objects of different handedness. The magnitude of this chiral transverse optical force on a chiral particle is comparable to the magnitude of the achiral optical forces on the particle, namely, the gradient force that arises from the intensity gradient and the scattering force that is the result of the linear momentum transfer of the photon to the particle. This findi...
Design Studies for a TPC Readout Plane Using Zigzag Patterns With Multistage GEM Detectors

New design studies have been carried out for a readout plane for gas electron multiplier detectors using zigzag patterns that can significantly reduce the readout channel count while preserving excellent spatial resolution for tracking detectors. While zigzag patterns have been used in a number of applications, these studies were designed to investigate the fundamental limits of charge sharing between the electrodes to optimize the spatial resolution and minimize the nonuniformities across the readout plane, while exploring the limits of manufacturing capabilities for producing the readout board. Simulation studies were carried out to optimize the readout electrode structure, and readout boards were produced with similar zigzag designs that were tested in the laboratory using a scanning X-ray source. These studies were aimed at developing a readout board for the new time projection chamber for the sPHENIX experiment at relativistic heavy ion collider, but can readily be used in other applications, including various micropattern gas detectors, such as Micromegas.
Exts and the AGT Relations

We prove the connection between the Nekrasov partition function of \({\mathcal{N}=2}\) super-symmetric U(2) gauge theory with adjoint matter and conformal blocks for the Virasoro algebra, as predicted by the Alday–Gaiotto–Tachikawa relations. Mathematically, this is achieved by relating the Carlsson–Okounkov Ext vector bundle on the moduli space of rank 2 sheaves with Liouville vertex operators. Our approach is geometric in nature, and uses a new method for intersection-theoretic computations of the Ext operator.
A HIGH-RESOLUTION ATLAS OF URANIUM-NEON IN THE H BAND

We present a high-resolution (R Almost-Equal-To 50,000) atlas of a uranium-neon (U/Ne) hollow-cathode spectrum in the H band (1454-1638 nm) for the calibration of near-infrared spectrographs. We obtained this U/Ne spectrum simultaneously with a laser-frequency comb spectrum, which we used to provide a first-order calibration to the U/Ne spectrum. We then calibrated the U/Ne spectrum using the recently published uranium line list of Redman et al., which is derived from high-resolution Fourier transform spectrometer measurements. These two independent calibrations allowed us to easily identify emission lines in the hollow-cathode lamp that do not correspond to known (classified) lines of either uranium or neon, and to compare the achievable precision of each source. Our frequency comb precision was limited by modal noise and detector effects, while the U/Ne precision was limited primarily by the signal-to-noise ratio (S/N) of the observed emission lines and our ability to model blended lines. The standard deviation in the dispersion solution residuals from the S/N-limited U/Ne hollow-cathode lamp was 50% larger than the standard deviation of the dispersion solution residuals from the modal-noise-limited laser-frequency comb. We advocate the use of U/Ne lamps for precision calibration of near-infrared spectrographs, and this H-band atlas makes these lamps significantlymore » easier to use for wavelength calibration.« less
A Self-consistent Framework for Multiline Modeling in Line Intensity Mapping Experiments

Line intensity mapping (LIM) is a promising approach to study star formation and the interstellar medium (ISM) in galaxies by measuring the aggregate line emission from the entire galaxy population. In this work, we develop a simple yet physically-motivated framework for modeling the line emission as would be observed in LIM experiments, which is done by building on analytic models of the Cosmic Infrared Background that connect total infrared luminosity of galaxies to their host dark matter halos. We present models of the HI 21cm, CO(1-0), [C II] 158$\mu$m, and [N II] 122 and 205$\mu$m lines consistent with current observational constraints. With four case studies of various combinations of these lines that probe different ISM phases, we demonstrate the potential for reliably extracting physical properties of the ISM, and the evolution of these properties with cosmic time, from auto and cross-correlation analysis of these lines as measured by future LIM experiments.
Evidence for Decay of Turbulence by MHD Shocks in the ISM via CO Emission

We utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2 open time program (“COPS”, PI: J. Green) to identify previously predicted turbulent dissipation by magnetohydrodynamic (MHD) shocks in molecular clouds. We find evidence of the shocks expected for dissipation of MHD turbulence in material not associated with any protostar. Two models fit about equally well: model 1 has a density of 103 cm−3, a shock velocity of 3 km s−1, and a magnetic field strength of 4 μG; model 2 has a density of 103.5 cm−3, a shock velocity of 2 km s−1, and a magnetic field strength of 8 μG. Timescales for decay of turbulence in this region are comparable to crossing times. Transitions of CO up to J of 8, observed close to active sites of star formation, but not within outflows, can trace turbulent dissipation of shocks stirred by formation processes. Although the transitions are difficult to detect at individual positions, our Herschel-SPIRE survey of protostars provides a grid of spatially distributed spectra within molecular clouds. We averaged all spatial positions away from known outflows near seven protostars. We find significant agreement with predictions of models of turbulent dissipation in slightly denser (103.5 cm−3) material with a stronger magnetic field (24 μG) than in the general molecular cloud.
Projective Modules Over Quantum Projective Line

Taking a groupoid C*-algebra approach to the study of the quantum complex projective spaces ℙn(&#x1d4af; ) constructed from the multipullback quantum spheres introduced by Hajac and collaborators, we analyze the structure of the C*-algebra C(ℙ1(&#x1d4af; )) realized as a concrete groupoid C*-algebra, and find its K-groups. Furthermore, after a complete classification of the unitary equivalence classes of projections or equivalently the isomorphism classes of finitely generated projective modules over the C*-algebra C(ℙ1(&#x1d4af; )), we identify those quantum principal U(1)-bundles introduced by Hajac and collaborators among the projections classified.
Host galaxy effects in the SUSY model for Supernovae Ia

For more than forty years virtually all work on the theory of type Ia Supernovae (SN Ia) has assumed that these explosions were due to the transfer of mass to a degenerate star from a partner in a binary system. In these binary models, when the mass of one partner closely approaches the Chandrasekhar maximum for a stable degenerate system, fusion can be initiated and the star explodes. However, there are now a number of indications that fusion could instead be triggered by a phase transition in a sub-Chandrasekhar white dwarf star. Although these indications provide no clue as to what specific phase transition initiates the explosion, it is possible that remarkable and well established host galaxy effects as considered in the present work could point to a specific source of the energy deposition. These host galaxy correlations are, at first glance, surprising since the typical distance scale of white dwarf stars is the earth radius while the typical distance between stars is at the light year scale. Performing a least $\chi^2$ fit to the delay time distribution to fix parameters, we give predictions from the susy phase transition model for the host galaxy effects. In addition we discuss a susy insight into the Phillips relation which is basic to the cosmological importance of the type Ia supernovae.
An efficient solver for large structured eigenvalue problems in relativistic quantum chemistry

ABSTRACTWe report an efficient program for computing the eigenvalues and symmetry-adapted eigenvectors of very large quaternionic (or Hermitian skew-Hamiltonian) matrices, using which structure-preserving diagonalisation of matrices of dimension N > 10, 000 is now routine on a single computer node. Such matrices appear frequently in relativistic quantum chemistry owing to the time-reversal symmetry. The implementation is based on a blocked version of the Paige–Van Loan algorithm, which allows us to use the Level 3 BLAS subroutines for most of the computations. Taking advantage of the symmetry, the program is faster by up to a factor of 2 than state-of-the-art implementations of complex Hermitian diagonalisation; diagonalising a 12, 800 × 12, 800 matrix took 42.8 (9.5) and 85.6 (12.6) minutes with 1 CPU core (16 CPU cores) using our symmetry-adapted solver and Intel Math Kernel Library's ZHEEV that is not structure-preserving, respectively. The source code is publicly available under the FreeBSD licence.
BlinkML: Efficient Maximum Likelihood Estimation with Probabilistic Guarantees

The rising volume of datasets has made training machine learning (ML) models a major computational cost in the enterprise. Given the iterative nature of model and parameter tuning, many analysts use a small sample of their entire data during their initial stage of analysis to make quick decisions (e.g., what features or hyperparameters to use) and use the entire dataset only in later stages (i.e., when they have converged to a specific model). This sampling, however, is performed in an ad-hoc fashion. Most practitioners cannot precisely capture the effect of sampling on the quality of their model, and eventually on their decision-making process during the tuning phase. Moreover, without systematic support for sampling operators, many optimizations and reuse opportunities are lost. In this paper, we introduce BlinkML, a system for fast, quality-guaranteed ML training. BlinkML allows users to make error-computation tradeoffs: instead of training a model on their full data (i.e., full model), BlinkML can quickly train an approximate model with quality guarantees using a sample. The quality guarantees ensure that, with high probability, the approximate model makes the same predictions as the full model. BlinkML currently supports any ML model that relies on maximum likelihood estimation (MLE), which includes Generalized Linear Models (e.g., linear regression, logistic regression, max entropy classifier, Poisson regression) as well as PPCA (Probabilistic Principal Component Analysis). Our experiments show that BlinkML can speed up the training of large-scale ML tasks by 6.26×?629× while guaranteeing the same predictions, with 95% probability, as the full model.
Unfriendly colorings of graphs with finite average degree

In an unfriendly coloring of a graph the color of every node mismatches that of the majority of its neighbors. We show that every probability measure preserving Borel graph with finite average degree admits a Borel unfriendly coloring almost everywhere. We also show that every bounded degree Borel graph of subexponential growth admits a Borel unfriendly coloring.
Vision to Reality: From Robert R. Wilson's Frontier to Leon M. Lederman's Fermilab

We examine the roles of vision and leadership in creating and directing Fermi National Accelerator Laboratory from the late 1960s through the 1980s. The story divides into two administrations having different problems and accomplishments, that of Robert R. Wilson from 1967-1978, which saw the transformation from cornfield to frontier physics facility, and that of Leon M. Lederman from 1979-1989, in which the laboratory evolved into one of the world's major high-energy facilities. Lederman's pragmatic vision of a user-based experimental community helped him to convert the pioneering facility that Wilson had built frugally into a laboratory with a stable scientific, cultural, and funding environment.
Multilingual Argument Mining: Datasets and Analysis

The growing interest in argument mining and computational argumentation brings with it a plethora of Natural Language Understanding (NLU) tasks and corresponding datasets. However, as with many other NLU tasks, the dominant language is English, with resources in other languages being few and far between. In this work, we explore the potential of transfer learning using the multilingual BERT model to address argument mining tasks in non-English languages, based on English datasets and the use of machine translation. We show that such methods are well suited for classifying the stance of arguments and detecting evidence, but less so for assessing the quality of arguments, presumably because quality is harder to preserve under translation. In addition, focusing on the translate-train approach, we show how the choice of languages for translation, and the relations among them, affect the accuracy of the resultant model. Finally, to facilitate evaluation of transfer learning on argument mining tasks, we provide a human-generated dataset with more than 10k arguments in multiple languages, as well as machine translation of the English datasets.
Mapping the Landscape of Domain-Wall Pinning in Ferromagnetic Films Using Differential Magneto-Optical Microscopy

Understanding the pinning of magnetic domain walls is critical to controlling their motion, for switching, logic, and memory applications. Here a ferromagnetic vortex core, monitored by magneto-optical microscopy, is used as an integrated scanning probe to map the pinning potential in a soft magnetic film, with nanoscale resolution, at room temperature. This provides an unprecedented view of the pinning landscape arising from material defects, and will enable the directed optimization of materials processing to achieve the desired domain-wall-pinning behavior.
Monopoles and the Emergence of Black Hole Entropy

One of the remarkable features of black holes is that they possess a thermodynamic description, even though they do not appear to be statistical systems. We use self-gravitating magnetic monopole solutions as tools for understanding the emergence of this description as one goes from an ordinary spacetime to one containing a black hole. We describe how causally distinct regions emerge as a monopole solution develops a horizon. We define an entropy that is naturally associated with these regions and that has a clear connection with the Hawking–Bekenstein entropy in the critical black hole limit.
Random ancestor trees

We investigate a network growth model in which the genealogy controls the evolution. In this model, a new node selects a random target node and links either to this target node, or to its parent, or to its grandparent, etc; all nodes from the target node to its most ancient ancestor are equiprobable destinations. The emerging random ancestor tree is very shallow: the fraction gn of nodes at distance n from the root decreases super-exponentially with n, gn = e − 1/(n − 1)!. We find that a macroscopic hub at the root coexists with highly connected nodes at higher generations. The maximal degree of a node at the nth generation grows algebraically as N1/βn, where N is the system size. We obtain the series of nontrivial exponents which are roots of transcendental equations: , , etc. As a consequence, the fraction pk of nodes with degree k has an algebraic tail, pk ~ k − γ, with γ = β1 + 1 = 2.351 746.
Ultraviolet Flux Decrease Under a Grand Minimum from IUE Short-wavelength Observation of Solar Analogs

We have identified a sample of 33 Sun-like stars observed by the International Ultraviolet Explorer (IUE) with the short-wavelength spectrographs that have ground-based detections of chromospheric Ca ii H+K activity. Our objective is to determine if these observations can provide an estimate of the decrease in ultraviolet (UV) surface flux associated with a transition from a normal stellar cycle to a grand-minimum state. The activity detections, corrected to solar metallicity, span the range , and eight stars have log . The IUE-observed flux spectra are integrated over the wavelength range 1250–1910 A, transformed to surface fluxes, and then normalized to solar B − V. These normalized surface fluxes show a strong linear relationship with activity (R 2 = 0.857 after three outliers are omitted). From this linear regression we estimate a range in UV flux of 9.3% over solar cycle 22 and a reduction of 6.9% below solar cycle minimum under a grand minimum. The 95% confidence interval in this grand-minimum estimate is 5.5%–8.4%. An alternative estimate is provided by the IUE observations of τ Cet (HD 10700), a star having strong evidence of being in a grand-minimum state, and this star's normalized surface flux is 23.0 ± 5.7% lower than solar cycle minimum.
Energy-Constrained Private and Quantum Capacities of Quantum Channels

This paper establishes a general theory of energy-constrained quantum and private capacities of quantum channels. We begin by defining various energy-constrained communication tasks, including quantum communication with a uniform energy constraint, entanglement transmission with an average energy constraint, private communication with a uniform energy constraint, and secret key transmission with an average energy constraint. We develop several code conversions, which allow us to conclude non-trivial relations between the capacities corresponding to the above tasks. We then show how the regularized, energy-constrained coherent information is equal to the capacity for the first two tasks and is an achievable rate for the latter two tasks, whenever the energy observable satisfies the Gibbs condition of having a well-defined thermal state for all temperatures and the channel satisfies a finite output-entropy condition. For degradable channels satisfying these conditions, we find that the single-letter energy-constrained coherent information is equal to all of the capacities. We finally apply our results to degradable quantum Gaussian channels and recover several results already established in the literature (in some cases, we prove new results in this domain). Contrary to what may appear from some statements made in the literature recently, proofs of these results do not require the solution of any kind of minimum output entropy conjecture or entropy photon-number inequality.
Comparison of Diversity of Type IIb Supernovae with Asymmetry in Cassiopeia A Using Light Echoes

We compare the diversity of spectral line velocities in a large sample of type IIb supernovae (SNe IIb) with the expected asphericity in the explosion, as measured from the light echoes of Cassiopeia A (Cas A), which was a historical galactic SN IIb. We revisit the results of Rest et al. (2011a), who used light echoes to observe Cas A from multiple lines of sight and hence determine its asphericity, as seen in the velocity of three spectral lines (He I $\lambda$5876, H$\alpha$ and the Ca II NIR triplet). We confirm and improve on this measurement by reproducing the effect of the light echoes in the spectra of several extragalactic SNe IIb found in the literature as well as mean SN IIb spectra recently created by Liu et al. (2016), and comparing these to the observed light echo spectra of Cas A, including their associated uncertainties. In order to quantify the accuracy of this comparison we smooth the light echo spectra of Cas A using Gaussian processes and use a Monte Carlo method to measure the absorption velocities of these three features in the spectra. We then test the hypothesis that the diversity of ejecta velocities seen in SNe IIb can be explained by asphericity. We do this by comparing the range of velocities seen in the different light echoes, and hence different lines of sight, of Cas A to that seen in the population of SNe IIb. We conclude that these two ranges are of the same order and thus asphericity could be enough to explain the diversity in the expansion velocity alone.
Network experiment demonstrates converse symmetry breaking

Symmetry breaking—the phenomenon in which the symmetry of a system is not inherited by its stable states—underlies pattern formation, superconductivity and numerous other effects. Recent theoretical work has established the possibility of converse symmetry breaking, a phenomenon in which the stable states are symmetric only when the system itself is not. This includes scenarios in which interacting entities are required to be non-identical in order to exhibit identical behaviour, such as in reaching consensus. Here we present an experimental demonstration of this phenomenon. Using a network of alternating-current electromechanical oscillators, we show that their ability to achieve identical frequency synchronization is enhanced when the oscillators are tuned to be suitably non-identical and that converse symmetry breaking persists for a range of noise levels. These results have implications for the optimization and control of network dynamics in a broad class of systems whose function benefits from harnessing uniform behaviour. An experiment with three alternating-current generators demonstrates converse symmetry breaking—a phenomenon whereby the system achieves frequency synchronization when its component systems are tuned asymmetrically.
Nanocluster ionization energies and work function of aluminum, and their temperature dependence

Ionization threshold energies of Al(n) (n = 32-95) nanoclusters are determined by laser ionization of free neutral metal clusters thermalized to several temperatures in the range from 65 K to 230 K. The photoion yield curves of cold clusters follow a quadratic energy dependence above threshold, in agreement with the Fowler law of surface photoemission. Accurate data collection and analysis procedures make it possible to resolve very small (few parts in a thousand) temperature-induced shifts in the ionization energies. Extrapolation of the data to the bulk limit enables a determination of the thermal shift of the polycrystalline metal work function, found to be in excellent agreement with theoretical prediction based on the influence of thermal expansion. Small clusters display somewhat larger thermal shifts, reflecting their greater susceptibility to thermal expansion. Ionization studies of free size-resolved nanoclusters facilitate understanding of the interplay of surface, electronic, and lattice properties under contamination-free conditions.
Family unification, exotic states and magnetic monopoles

Abstract The embedding in SU (4)× SU (3)× SU (3) of the well studied gauge groups SU (4)× SU (2)× SU (2) and SU (3)× SU (3)× SU (3) naturally leads to family unification as opposed to simple family replication. An inescapable consequence is the predicted existence of (exotic) color singlet states that carry fractional electric charge. The corresponding magnetic monopoles carry multiple Dirac magnetic charge, can be relatively light (∼10 7 –10 13 GeV), and may be present in the galaxy not far below the Parker bound.
Constraining Radiatively Inefficient Accretion Flows with Polarization

The low-luminosity black hole Sgr A* provides a test bed for models of radiatively inefficient accretion flows (RIAFs). Recent submillimeter linear polarization measurements of Sgr A* have provided evidence that the electrons in the accretion flow are relativistic over a large range of radii. Here we show that these high temperatures result in elliptical plasma normal modes. Thus, polarized millimeter and submillimeter radiation emitted within RIAFs will undergo generalized Faraday rotation, a cyclic conversion between linear and circular polarization. This effect will not depolarize the radiation even if the rotation measure is extremely high. Rather, the beam will take on the linear and circular polarization properties of the plasma normal modes. As a result, polarization measurements of Sgr A* in this frequency regime will constrain the temperature, density, and magnetic profiles of RIAF models.
Computational complexity of the landscape II—Cosmological considerations

Abstract We propose a new approach for multiverse analysis based on computational complexity, which leads to a new family of “computational” measure factors. By defining a cosmology as a space–time containing a vacuum with specified properties (for example small cosmological constant) together with rules for how time evolution will produce the vacuum, we can associate global time in a multiverse with clock time on a supercomputer which simulates it. We argue for a principle of “limited computational complexity” governing early universe dynamics as simulated by this supercomputer, which translates to a global measure for regulating the infinities of eternal inflation. The rules for time evolution can be thought of as a search algorithm, whose details should be constrained by a stronger principle of “minimal computational complexity”. Unlike previously studied global measures, ours avoids standard equilibrium considerations and the well-known problems of Boltzmann Brains and the youngness paradox. We also give various definitions of the computational complexity of a cosmology, and argue that there are only a few natural complexity classes.
Scanning the skeleton of the 4D F-theory landscape

Using a one-way Monte Carlo algorithm from several different starting points, we get an approximation to the distribution of toric threefold bases that can be used in four-dimensional F-theory compactification. We separate the threefold bases into “resolvable” ones where the Weierstrass polynomials (f, g) can vanish to order (4, 6) or higher on codimension-two loci and the “good” bases where these (4, 6) loci are not allowed. A simple estimate suggests that the number of distinct resolvable base geometries exceeds 103000, with over 10250 “good” bases, though the actual numbers are likely much larger. We find that the good bases are concentrated at specific “end points” with special isolated values of h1,1 that are bigger than 1,000. These end point bases give Calabi-Yau fourfolds with specific Hodge numbers mirror to elliptic fibrations over simple threefolds. The non-Higgsable gauge groups on the end point bases are almost entirely made of products of E8, F4, G2 and SU(2). Nonetheless, we find a large class of good bases with a single non-Higgsable SU(3). Moreover, by randomly contracting the end point bases, we find many resolvable bases with h1,1(B) ∼ 50-200 that cannot be contracted to another smooth threefold base.
PROTOSTELLAR DISK FORMATION ENABLED BY WEAK, MISALIGNED MAGNETIC FIELDS

The gas from which stars form is magnetized, and strong magnetic fields can efficiently transport angular momentum. Most theoretical models of this phenomenon find that it should prevent formation of large (>100 AU), rotationally supported disks around most protostars, even when non-ideal magnetohydrodynamic (MHD) effects that allow the field and gas to decouple are taken into account. Using recent observations of magnetic field strengths and orientations in protostellar cores, we show that this conclusion is incorrect. The distribution of magnetic field strengths is very broad, and alignments between fields and angular momentum vectors within protostellar cores are essentially random. By combining the field strength and misalignment data with MHD simulations showing that disk formation is expected for both weak and misaligned fields, we show that these observations imply that we should expect disk fractions of ~10%-50% even when protostars are still deeply embedded in their parent cores, and even if the gas is governed by ideal MHD.
Kinematic Discovery of a Stellar Stream Located in Pisces

We report the kinematic discovery of the Pisces Stellar Stream (PSS), at Galactic longitude l ≈ 135° and –39° < b < –36°. We originally identified this halo substructure from velocities of red giant branch stars in the Sloan Digital Sky Survey (SDSS) Data Release 8, and confirmed its presence in turnoff stars from SDSS photometric data. The PSS is a narrow, kinematically cold tidal stream, with σ_(v, 0) ≈ 8 km s^(–1). Its metallicity is [Fe/H] ≈ –2.2, with ~0.3 dex dispersion. The color-magnitude signature of the stream turnoff, combined with our measured metallicity, places the PSS at a distance of 35 ± 3 kpc. The PSS is the same as the previously announced "Triangulum stream" and part of the proposed "stream a." We rule out an association of the PSS with other previously known Milky Way substructures in the same region of the sky.
Abelian F-theory models with charge-3 and charge-4 matter

This paper analyzes U(1) F-theory models admitting matter with charges q = 3 and 4. First, we systematically derive a q = 3 construction that generalizes the previous q = 3 examples. We argue that U(1) symmetries can be tuned through a procedure reminiscent of the SU(N ) and Sp(N ) tuning process. For models with q = 3 matter, the components of the generating section vanish to orders higher than 1 at the charge-3 matter loci. As a result, the Weierstrass models can contain non-UFD structure and thereby deviate from the standard Morrison-Park form. Techniques used to tune SU(N ) models on singular divisors allow us to determine the non-UFD structures and derive the q = 3 tuning from scratch. We also obtain a class of a q=4 models by deforming a prior U(1) × U(1) construction. To the author’s knowledge, this is the first published F-theory example with charge-4 matter. Finally, we discuss some conjectures regarding models with charges larger than 4.
Observed Limits on Charge Exchange Contributions to the Diffuse X-Ray Background

We present a high-resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for an approximately 1 sr region of the sky centered at l = 90 degrees b = +60 degrees using a 36 pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum s observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568 (sup +2 (sub -3) eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV and for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex. The dominance of thermal emission is consistent with much of the high-latitude O VII emission originating in 2-3 x 10(exp 6) K gas in the Galactic halo. On the other hand, the observed ratio of C VI Lygamma to Lyalpha is 0.3 plus or minus 0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 10(sup 6) K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only greater than 32% thermal emission for O VII and greater than 20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.
Odd viscosity in two-dimensional incompressible fluids

In everyday fluids, viscosity is resistance to flow and is dissipative, but a quantum Hall (QH) fluid at zero temperature has nondissipative viscosity (``odd'' viscosity). Using exact results we theoretically study observable consequences of odd viscosity in incompressible fluids in two dimensions.
Pfister’s theorem fails in the Hermitian case

We show that the Hermitian analogue of a famous result of Pfister fails. To do so we provide a Hermitian symmetric polynomial $r$ of total degree 2d such that any non-zero multiple of it cannot be written as a Hermitian sum of squares with fewer than $d+1$ squares.
Deceptive Labeling: Hypergames on Graphs for Stealthy Deception

With the increasing sophistication of attacks on cyber-physical systems, deception has emerged as an effective tool to improve system security and safety by obfuscating the attacker’s perception. In this letter, we present a solution to the deceptive game in which a control agent is to satisfy a Boolean objective specified by a co-safe temporal logic formula in the presence of an adversary. The agent intentionally introduces asymmetric information to create payoff misperception, which manifests as the misperception of the labeling function in the game model. Thus, the adversary is unable to accurately determine which logical formula is satisfied by a given outcome of the game. We introduce a model called hypergame on graph to capture the asymmetrical information with one-sided payoff misperception. Based on this model, we present the solution of such a hypergame and use the solution to synthesize stealthy deceptive strategies. Specifically, deceptive sure winning and deceptive almost-sure winning strategies are developed by reducing the hypergame to a two-player game and one-player stochastic game with reachability objectives. A running example is introduced to demonstrate the game model and the solution concept used for strategy synthesis.
THE X-RAY THROUGH OPTICAL FLUXES AND LINE STRENGTHS OF TIDAL DISRUPTION EVENTS

Observations of luminous flares resulting from the possible tidal disruption of stars by supermassive black holes have raised a number of puzzles. Outstanding questions include the origin of the optical and ultraviolet (UV) flux, the weakness of hydrogen lines in the spectrum, and the occasional simultaneous observation of x-rays. Here we study the emission from tidal disruption events (TDEs) produced as radiation from black hole accretion propagates through an extended, optically thick envelope formed from stellar debris. We analytically describe key physics controlling spectrum formation, and present detailed radiative transfer calculations that model the spectral energy distribution (SED) and optical line strengths of TDEs near peak brightness. The steady-state transfer is coupled to a non local thermodynamic equilibrium treatment of the excitation and ionization states of hydrogen, helium and oxygen (as a representative metal). Our calculations show how an extended envelope can reprocess a fraction of soft x-rays and produce the observed optical fluxes of order 10^43 ergs per second. Variations in the mass or size of the envelope may help explain how the optical flux changes over time with roughly constant color. For high enough accretion luminosities, x-rays can highly ionize the reprocessing region and escape to be observed simultaneously with the optical flux, producing an SED not described by a single blackbody. Due to optical depth effects, hydrogen Balmer line emission is often strongly suppressed relative to helium line emission (with HeII-to-H line ratios of at least 5:1 in some cases) even in the disruption of a solar-composition star. We discuss the implications of our results to understanding the type of stars destroyed in TDEs and the physical processes responsible for producing the observed flares.
Equivariant coherent sheaves on the exotic nilpotent cone

Let $G=Sp_{2n}(\mathbb{C})$, and $\mathfrak{N}$ be Kato's exotic nilpotent cone. Following techniques used by Bezrukavnikov in [5] to establish a bijection between $\Lambda^+$, the dominant weights for a simple algebraic group $H$, and $\textbf{O}$, the set of pairs consisting of a nilpotent orbit and a finite-dimensional irreducible representation of the isotropy group of the orbit, we prove an analogous statement for the exotic nilpotent cone. First we prove that dominant line bundles on the exotic Springer resolution $\widetilde{\mathfrak{N}}$ have vanishing higher cohomology, and compute their global sections using techniques of Broer. This allows to show that the direct images of these dominant line bundles constitute a quasi-exceptional set generating the category $D^b(Coh^G(\mathfrak{N}))$, and deduce that the resulting $t$-structure on $D^b(Coh^G(\mathfrak{N}))$ coincides with the perverse coherent $t$-structure. The desired result now follows from the bijection between costandard objects and simple objects in the heart of this $t$-structure on $D^b(Coh^G(\mathfrak{N}))$.
Variation of quasiconformal mappings on lines

We obtain improved regularity of homeomorphic solutions of the reduced Beltrami equation, as compared to the standard Beltrami equation. Such an improvement is not possible in terms of Holder or Sobolev regularity; instead, our results concern the generalized variation of restrictions to lines. Specifically, we prove that the restriction to any line segment has finite p-variation for all p>1 but not necessarily for p=1.
Rutile GeO2: An ultrawide-band-gap semiconductor with ambipolar doping

Ultra-wide-band-gap (UWBG) semiconductors have tremendous potential to advance electronic devices as device performance improves superlinearly with the increasing gap. Ambipolar doping, however, has been a major challenge for UWBG materials as dopant ionization energy and charge compensation generally increase with the increasing bandgap and significantly limit the semiconductor devices that can currently be realized. Using hybrid density functional theory, we demonstrate rutile germanium oxide (r-GeO2) to be an alternative UWBG (4.68 eV) material that can be ambipolarly doped. We identify SbGe, AsGe, and FO as possible donors with low ionization energies and propose growth conditions to avoid charge compensation by deep acceptors such as VGe and NO. On the other hand, acceptors such as AlGe have relatively large ionization energies (0.45 eV) due to the formation of localized hole polarons and are likely to be passivated by VO, Gei, and self-interstitials. Yet, we find that the co-incorporation of AlGe with interstitial H can increase the solubility limit of Al and enable hole conduction in the impurity band. Our results show that r-GeO2 is a promising UWBG semiconductor that can overcome current doping challenges and enable the next generation of power electronics devices.
Atomistic studies of transformation pathways and energetics in plutonium

One of the most challenging problems in understanding the structural phase transformations in Pu is to determine the energetically favoured, continuous atomic pathways from one crystal symmetry to another. This problem involves enumerating candidate pathways and studying their energetics to garner insight into instabilities and energy barriers. The purpose of this work is to investigate the energetics of two transformation pathways for the δ → α′ transformation in Pu that were recently proposed on the basis of symmetry. These pathways require the presence of either an intermediate hexagonal closed-packed (hcp) structure or a simple hexagonal (sh) structure. A subgroup of the parent fcc and the intermediate hexagonal structure, which has trigonal symmetry, facilitates the transformation to the intermediate hcp or sh structure. Phonons then break the translational symmetry from the intermediate hcp or sh structure to the final monoclinic symmetry of the α′ structure. We perform simulations using the modifie...
METRIC THICKENINGS, BORSUK–ULAM THEOREMS, AND ORBITOPES

Thickenings of a metric space capture local geometric properties of the space. Here we exhibit applications of lower bounding the topology of thickenings of the circle and more generally the sphere. We explain interconnections with the geometry of circle actions on Euclidean space, the structure of zeros of trigonometric polynomials, and theorems of Borsuk-Ulam type. We use the combinatorial and geometric structure of the convex hull of orbits of circle actions on Euclidean space to give geometric proofs of the homotopy type of metric thickenings of the circle. Homotopical connectivity bounds of thickenings of the sphere allow us to prove that a weighted average of function values of odd maps $S^n \to \mathbb{R}^{n+2}$ on a small diameter set is zero. We prove an additional generalization of the Borsuk-Ulam theorem for odd maps $S^{2n-1} \to \mathbb{R}^{2kn+2n-1}$. We prove such results for odd maps from the circle to any Euclidean space with optimal quantitative bounds. This in turn implies that any raked homogeneous trigonometric polynomial has a zero on a subset of the circle of a specific diameter; these results are optimal.
Low-loss composite photonic platform based on 2D semiconductor monolayers

The optical properties of transition metal dichalcogenides (TMDs) are known to change dramatically with doping near their excitonic resonances. However, little is known about the effect of doping on the optical properties of TMDs at wavelengths far from these resonances, where the material is transparent and therefore could be leveraged in photonic circuits. We demonstrate the strong electrorefractive response of monolayer tungsten disulfide (WS2) at near-infrared wavelengths (deep in the transparency regime) by integrating it on silicon nitride photonic structures to enhance the light–matter interaction with the monolayer. We show that the doping-induced phase change relative to the change in absorption (|∆n/∆k|) is ~125, which is significantly higher than the |∆n/∆k| observed in materials commonly employed for silicon photonic modulators, including Si and III–V on Si, while accompanied by negligible insertion loss. Strong electrorefractive effects in semiconductor transition metal dichalcogenides (TMDs) at near-infrared wavelengths, where the TMDs are transparent, are observed and used to demonstrate photonic devices based on a composite SiN–TMD platform with large phase modulation, minimal induced loss and low electrical power consumption.
Solar Flare Prediction Using SDO/HMI Vector Magnetic Field Data with a Machine-learning Algorithm

We attempt to forecast M- and X-class solar flares using a machine-learning algorithm, called support vector machine (SVM), and four years of data from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager, the first instrument to continuously map the full-disk photospheric vector magnetic field from space. Most flare forecasting efforts described in the literature use either line-of-sight magnetograms or a relatively small number of ground-based vector magnetograms. This is the first time a large data set of vector magnetograms has been used to forecast solar flares. We build a catalog of flaring and non-flaring active regions sampled from a database of 2071 active regions, comprised of 1.5 million active region patches of vector magnetic field data, and characterize each active region by 25 parameters. We then train and test the machine-learning algorithm and we estimate its performances using forecast verification metrics with an emphasis on the true skill statistic (TSS). We obtain relatively high TSS scores and overall predictive abilities. We surmise that this is partly due to fine-tuning the SVM for this purpose and also to an advantageous set of features that can only be calculated from vector magnetic field data. We also apply a feature selection algorithm to determine which of our 25 features are useful for discriminating between flaring and non-flaring active regions and conclude that only a handful are needed for good predictive abilities.
Scheduling of dynamic electric loads using energy storage and short term power forecasting

In this paper we formulate an optimization approach to schedule electrical loads given a short term prediction of time-varying power production and the ability to store only a limited amount of electrical energy. The proposed approach is unique and versatile as it allows scheduling of electrical loads that each have their own dynamic power demand during on/off switching, while also allowing the specification of minimum on/off times for each loads separately. The optimization approach is formulated as a parallel enumeration of all possible on/off times of the electrical loads using a moving time approach in which only a short term power production forecast is needed, while at the same time taking into account constraints on electrical energy storage and power delivery of a battery system. It is shown that the complexity of the optimization (number of enumerations) is limited by the number of data points in the short term power production forecast and the minimum on/off time of the electrical loads. The limited complexity along with parallel enumeration allows real-time operational scheduling of a large number of loads. The simulation results shown in this paper illustrate that relatively short term power forecast profiles can be used to effectively schedule dynamic loads with various dynamic load profiles.