cssi/SciSciGPT-SciSciNet huggingface dataset:
Transient X-Ray Binaries in Elliptical Galaxies

Chandra observations of elliptical galaxies have revealed large numbers of low-mass X-ray binaries (LMXBs) accreting at rates greater than 10-9 M☉ yr-1. One scenario that generates this from an old stellar population is nuclear-driven mass transfer onto a neutron star or black hole from a Roche lobe-filling red giant. However, in our Galaxy, most of these systems accrete sporadically as transients because of a thermal instability in the accretion disk. Using the common criterion for disk instability (including irradiation), we find that this mode of mass transfer leads to transient accretion for at least 75% of the binary's life. Repeated Chandra observations of elliptical galaxies should reveal this population. The recurrence times might be very long (~100-10,000 yr depending on the orbital period at the onset of mass transfer), and outbursts might last for 1-100 yr. Mass transferring binaries can also be formed in old populations via interactions in dense stellar environments, such as globular clusters. These tend to have shorter orbital periods and are more likely stable accretors, making them apparently a large fraction of an elliptical galaxy's LMXB population.
Logarithmic Regret Bound in Partially Observable Linear Dynamical Systems

We study the problem of adaptive control in partially observable linear dynamical systems. We propose a novel algorithm, adaptive control online learning algorithm (AdaptOn), which efficiently explores the environment, estimates the system dynamics episodically and exploits these estimates to design effective controllers to minimize the cumulative costs. Through interaction with the environment, AdaptOn deploys online convex optimization to optimize the controller while simultaneously learning the system dynamics to improve the accuracy of controller updates. We show that when the cost functions are strongly convex, after T times step of agent-environment interaction, AdaptOn achieves regret upper bound of polylog(T). To the best of our knowledge, AdaptOn is the first algorithm which achieves polylog(T) regret in adaptive control of unknown partially observable linear dynamical systems which includes linear quadratic Gaussian (LQG) control.
Stellar Metallicity Gradients in SDSS Galaxies

We infer stellar metallicity and abundance ratio gradients for a sample of red galaxies in the Sloan Digital Sky Survey (SDSS) Main galaxy sample. Because this sample does not have multiple spectra at various radii in a single galaxy, we measure these gradients statistically. We separate galaxies into stellar mass bins, stack their spectra in redshift bins, and calculate the measured absorption-line indices in projected annuli by differencing spectra in neighboring redshift bins. After determining the line indices, we use stellar population modeling from the EZ_Ages software to calculate ages, metallicities, and abundance ratios within each annulus. Our data cover the central regions of these galaxies, out to slightly higher than . We find detectable gradients in metallicity and relatively shallow gradients in abundance ratios, similar to results found for direct measurements of individual galaxies. The gradients are only weakly dependent on stellar mass, and this dependence is well correlated with the change of Re with mass. Based on these data, we report mean equivalent widths, metallicities, and abundance ratios as a function of mass and velocity dispersion for SDSS early-type galaxies, for fixed apertures of 2.5 kpc and of 0.5Re.
Hydra: An Ensemble of Convolutional Neural Networks for Geospatial Land Classification

In this paper, we describe Hydra, an ensemble of convolutional neural networks (CNNs) for geospatial land classification. The idea behind Hydra is to create an initial CNN that is coarsely optimized but provides a good starting pointing for further optimization, which will serve as the Hydra’s body. Then, the obtained weights are fine-tuned multiple times with different augmentation techniques, crop styles, and classes weights to form an ensemble of CNNs that represent the Hydra’s heads. By doing so, we prompt convergence to different endpoints, which is a desirable aspect for ensembles. With this framework, we were able to reduce the training time while maintaining the classification performance of the ensemble. We created ensembles for our experiments using two state-of-the-art CNN architectures, residual network (ResNet), and dense convolutional networks (DenseNet). We have demonstrated the application of our Hydra framework in two data sets, functional map of world (FMOW) and NWPU-RESISC45, achieving results comparable to the state-of-the-art for the former and the best-reported performance so far for the latter. Code and CNN models are available at https://github.com/maups/hydra-fmow .
Non‐integrality of some Steinberg modules

We prove that the Steinberg module of the special linear group of a quadratic imaginary number ring which is not Euclidean is not generated by integral apartments. Assuming the generalized Riemann hypothesis, this shows that the Steinberg module of a number ring is generated by integral apartments if and only if the ring is Euclidean. We also construct new cohomology classes in the top dimensional cohomology group of the special linear group of some quadratic imaginary number rings.
Stability Limits of Circumbinary Planets: Is There a Pile-up in the Kepler CBPs?

The stability limit for circumbinary planets (CBPs) is not well defined and can depend on initial parameters defining either the planetary orbit or the inner binary orbit. We expand on the work of Holman & Wiegert (1999, AJ 117, 621) to develop numerical tools for quick, easy, and accurate determination of the stability limit. The results of our simulations, as well as our numerical tools, are available to the community through $\texttt{Zenodo}$ and $\texttt{GitHub}$, respectively. We employ a grid interpolation method based on $\sim$150 million full N-body simulations of initially circular, coplanar systems and compare to the 9 known Kepler CBP systems. Using a formalism from planet packing studies, we find that 55% of the Kepler CBP systems allow for an additional equal-mass planet to potentially exist on an interior orbit relative to the observed planet. Therefore, we do $\textit{not}$ find strong evidence for a pile-up in the Kepler CBP systems and more detections are needed to adequately characterize the formation mechanisms for the CBP population. Observations from the Transiting Exoplanet Survey Satellite are expected to substantially increase the number of detections using the unique geometry of CBP systems, where multiple transits can occur during a single conjunction.
Bars and Dark Matter Halo Cores

Self-consistent bars that form in galaxies embedded within cuspy halos are unable to flatten the cusp. Short bars form in models with quasi-flat rotation curves. They lose angular momentum to the halo through dynamical friction, but the continuous concentration of mass within the disk as the bar grows actually compresses the halo further, overwhelming any density reduction due to the modest angular momentum transfer to the halo. Thus, the Weinberg-Katz proposed solution to the nonexistence of the predicted cuspy halos from cold dark matter simulations would seem to be unworkable. I also find that the concerns over the performance of N-body codes raised by these authors do not apply to the methods used here.
Two dimensional, electronic particle tracking in liquids with a graphene-based magnetic sensor array

The investigation and control of liquid flow at the nanometer scale is a key area of applied research with high relevance to physics, chemistry, and biology. We introduce a method and a device that allows the spatial resolution of liquid flow by integrating an array of graphene-based magnetic (Hall) sensors that is used for tracking the movement of magnetic nanoparticles immersed in a liquid under investigation. With a novel device concept based on standard integration processes and experimentally verified material parameters, we numerically simulate the performance of a single sensor pixel, as well as the whole sensor array, for tracking magnetic nanoparticles having typical properties. The results demonstrate that the device enables (a) the detection of individual nanoparticles in the liquid with high accuracy and (b) the reconstruction of a particle's flow-driven trajectory across the integrated sensor array with sub-pixel precision as a function of time, in what we call the “Magnetic nanoparticle velocimetry” technique. Since the method does not rely on optical detection, potential lab-on-chip applications include particle tracking and flow analysis in opaque media at the sub-micron scale.
TIDAL DISRUPTION EVENTS PREFER UNUSUAL HOST GALAXIES

Tidal Disruption Events (TDEs) are transient events observed when a star passes close enough to a supermassive black hole to be tidally destroyed. Many TDE candidates have been discovered in host galaxies whose spectra have weak or no line emission yet strong Balmer line absorption, indicating a period of intense star formation that has recently ended. As such, TDE host galaxies fall into the rare class of quiescent Balmer-strong galaxies. Here, we quantify the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) with spectral properties like those of TDE hosts, determining the extent to which TDEs are over-represented in such galaxies. Galaxies whose spectra have Balmer absorption H$\delta_{\rm A}$ $-$ $\sigma$(H$\delta_{\rm A}$) $>$ 4 A (where $\sigma$(H$\delta_{\rm A}$) is the error in the Lick H$\delta_{\rm A}$ index) and H$\alpha$ emission EW $ $ 1.31 A and H$\alpha$ EW $ 80\times$ enhancement in such hosts and providing an observational link between the $\gamma$/X-ray-bright and optical/UV-bright TDE classes.
The extra scalar degrees of freedom from the two-Higgs doublet model for dark energy

In principle, a minimal extension of the standard model of Particle Physics, the two-Higgs doublet model (2HDM), can be invoked to explain the scalar field responsible for dark energy. The two doublets are in general mixed. After diagonalization, the lightest CP-even Higgs and CP-odd Higgs are jointly taken to be the dark energy candidate. The dark energy obtained from the Higgs fields in this case is indistinguishable from the cosmological constant.
Alexander- and Markov-type theorems for virtual trivalent braids

We prove Alexander- and Markov-type theorems for virtual spatial trivalent graphs and virtual trivalent braids. We provide two versions for the Markov-type theorem: one uses an algebraic approach s...
Criteria on Contractions for Entropic Discontinuities of Systems of Conservation Laws

We study the contraction properties (up to shift) for admissible Rankine–Hugoniot discontinuities of $${n\times n}$$ systems of conservation laws endowed with a convex entropy. We first generalize the criterion developed in (Serre and Vasseur, J l’Ecole Polytech 1, 2014), using the spatially inhomogeneous pseudo-distance introduced in (Vasseur, Contemp Math AMS, 2013). Our generalized criterion guarantees the contraction property for extremal shocks of a large class of systems, including the Euler system. Moreover, we introduce necessary conditions for contraction, specifically targeted for intermediate shocks. As an application, we show that intermediate shocks of the two-dimensional isentropic magnetohydrodynamics do not verify any of our contraction properties. We also investigate the contraction properties, for contact discontinuities of the Euler system, for a certain range of contraction weights. None of the results involve any smallness condition on the initial perturbation or on the size of the shock.
Brauer groups and étale cohomology in derived algebraic geometry

In this paper, we study Azumaya algebras and Brauer groups in derived algebraic geometry. We establish various fundamental facts about Brauer groups in this setting, and we provide a computational tool, which we use to compute the Brauer group in several examples. In particular, we show that the Brauer group of the sphere spectrum vanishes, which solves a conjecture of Baker and Richter, and we use this to prove two uniqueness theorems for the stable homotopy category. Our key technical results include the local geometricity, in the sense of Artin n‐stacks, of the moduli space of perfect modules over a smooth and proper algebra, the etale local triviality of Azumaya algebras over connective derived schemes and a local to global principle for the algebraicity of stacks of stable categories. 14F22, 18G55; 14D20, 18E30
Mitigating Shear-dependent Object Detection Biases with Metacalibration

Metacalibration is a new technique for measuring weak gravitational lensing shear that is unbiased for isolated galaxy images. In this work we test metacalibration with overlapping, or ``blended'' galaxy images. Using standard metacalibration, we find a few percent shear measurement bias for galaxy densities relevant for current surveys, and that this bias increases with increasing galaxy number density. We show that this bias is not due to blending itself, but rather to shear-dependent object detection. If object detection is shear independent, no deblending of images is needed, in principle. We demonstrate that detection biases are accurately removed when including object detection in the metacalibration process, a technique we call metadetection. This process involves applying an artificial shear to images of small regions of sky and performing detection on the sheared images, as well as measurements that are used to calculate a shear response. We demonstrate that the method can accurately recover weak shear signals even in highly blended scenes. In the metacalibration process, the space between objects is sheared coherently, which does not perfectly match the real universe in which some, but not all, galaxy images are sheared coherently. We find that even for the worst case scenario, in which the space between objects is completely unsheared, the resulting shear bias is at most a few tenths of a percent for future surveys. We discuss additional technical challenges that must be met in order to implement metadetection for real surveys.
Topological Interpretations of Lattice Gauge Field Theory

We construct lattice gauge field theory based on a quantum group on a lattice of dimension one. Innovations include a coalgebra structure on the connections and an investigation of connections that are not distinguishable by observables. We prove that when the quantum group is a deformation of a connected algebraic group G (over the complex numbers), then the algebra of observables forms a deformation quantization of the ring of $G$-characters of the fundamental group of the lattice. Finally, we investigate lattice gauge field theory based on quantum SL 2ℂ, and conclude that the algebra of observables is the Kauffman bracket skein module of a cylinder over a surface associated to the lattice.
Projector equivalences in K theory and families of non-commutative solitons

Projector equivalences used in the definition of the K-theory of operator algebras are shown to lead to generalizations of the solution generating technique for solitons in NC field theories, which has recently been used in the construction of branes from other branes in B-field backgrounds and in the construction of fluxon solutions of gauge theories. The generalizations involve families of static solutions as well as solutions which depend on euclidean time and interpolate between different configurations. We investigate the physics of these generalizations in the brane-construction as well as the fluxon context. These results can be interpreted in the light of recent discussions on the topology of the configuration space of string fields.
Two-Photon Total Annihilation of Molecular Positronium

The rate for complete two-photon annihilation of molecular positronium Ps2 is reported. This decay channel involves a four-body collision among the fermions forming Ps2, and two photons of 1.022 MeV, each, as the final state. The quantum electrodynamics result for the rate of this process is found to be . This decay channel completes the most comprehensive decay chart for Ps2 up to date.
Thermometry of Silicon Nanoparticles

Current thermometry techniques lack the spatial resolution needed to map temperature inside modern transistors, leaving it difficult to understand and mitigate the performance-limiting effects of self-heating. As a step toward solving this problem, the authors determine the temperature dependence of the bulk plasmon energy in silicon nanoparticles. With this knowledge, individual silicon nanoparticles can now be used as miniature thermometers, and a silicon transistor can be seen as a collection of them. If they can be queried, we will be able to map temperature inside the transistor with nanoscale spatial resolution.
A Low frequency Survey of Giant Pulses from the Crab Pulsar

We present a large survey of giant pulses from the Crab Pulsar as observed with the first station of the Long Wavelength Array. Automated methods for detecting giant pulses at low frequencies where scattering becomes prevalent are also explored. More than 1400 pulses were detected across four frequency bands between 20 and 84 MHz over a seven-month period beginning in 2013, with additional followup observations in late 2014 and early 2015. A handful of these pulses were detected simultaneously across all four frequency bands. We examine pulse characteristics, including pulse broadening and power law indices for amplitude distributions. We find that the flux density increases toward shorter wavelengths, consistent with a spectral turnover at 100 MHz. Our observations uniquely span multiple scattering epochs, manifesting as a notable trend in the number of detections per observation. These results are characteristic of the variable interface between the synchrotron nebula and the surrounding interstellar medium.
Star Formation on Galactic Scales: Empirical Laws

Empirical star formation laws from the last 20 years are reviewed with a comparison to simulations. The current form in main galaxy disks has a linear relationship between the star formation rate per unit area and the molecular cloud mass per unit area with a timescale for molecular gas conversion of about 2 Gyr. The local ratio of molecular mass to atomic mass scales nearly linearly with pressure, as determined from the weight of the gas layer in the galaxy. In the outer parts of galaxies and in dwarf irregular galaxies, the disk can be dominated by atomic hydrogen and the star formation rate per unit area becomes directly proportional to the total gas mass per unit area, with a consumption time of about 100 Gyr. The importance of a threshold for gravitational instabilities is not clear. Observations suggest such a threshold is not always important, while simulations generally show that it is. The threshold is difficult to evaluate because it is sensitive to magnetic and viscous forces, the presence of spiral waves and other local effects, and the equation of state.
Bayesian Nonparametric Weighted Sampling Inference

Survey weighting adjusts for known or expected dierences between sample and population. Weights are constructed on design or benchmarking variables that are predictors of inclusion probability. In this paper, we assume that the only information we have about the weighting procedure is the values of the weights in the sample. We propose a hierarchical Bayesian approach in which we model the weights of the nonsampled units in the population and simultaneously include them as predictors in a nonparametric Gaussian process regression to yield valid inference for the underlying nite population and capture the uncertainty induced by sampling and the unobserved outcomes. We use simulation studies to evaluate the performance of our procedure and compare it to the classical design-based estimator. We apply our method to the Fragile Family Child Wellbeing Study. Our studies nd the Bayesian nonparametric nite population estimator to be more robust than the classical design-based estimator without loss in eciency.
THE ENERGY DEPENDENCE of GRB MINIMUM VARIABILITY TIMESCALES

We constrain the minimum variability timescales for 938 GRBs observed by the Fermi/GBM instrument prior to July 11, 2012. The tightest constraints on progenitor radii derived from these timescales are obtained from light curves in the hardest energy channel. In the softer bands -- or from measurements of the same GRBs in the hard X-rays from Swift -- we show that variability timescales tend to be a factor 2--3 longer. Applying a survival analysis to account for detections and upper limits, we find median minimum timescale in the rest frame for long-duration and short-duration GRBs of 45 ms and 10 ms, respectively. Fewer than 10% of GRBs show evidence for variability on timescales below 2 ms. These shortest timescales require Lorentz factors $\gtrsim 400$ and imply typical emission radii $R \approx 1 {\times} 10^{14}$ cm for long-duration GRBs and $R \approx 3 {\times} 10^{13}$ cm for short-duration GRBs. We discuss implications for the GRB fireball model and investigate whether GRB minimum timescales evolve with cosmic time.
Interferometric Imaging Directly with Closure Phases and Closure Amplitudes

Interferometric imaging now achieves angular resolutions as fine as 10 microarcsec, probing scales that are inaccessible to single telescopes. Traditional synthesis imaging methods require calibrated visibilities; however, interferometric calibration is challenging, especially at high frequencies. Nevertheless, most studies present only a single image of their data after a process of "self-calibration," an iterative procedure where the initial image and calibration assumptions can significantly influence the final image. We present a method for efficient interferometric imaging directly using only closure amplitudes and closure phases, which are immune to station-based calibration errors. Closure-only imaging provides results that are as non-committal as possible and allows for reconstructing an image independently from separate amplitude and phase self-calibration. While closure-only imaging eliminates some image information (e.g., the total image flux density and the image centroid), this information can be recovered through a small number of additional constraints. We demonstrate that closure-only imaging can produce high fidelity results, even for sparse arrays such as the Event Horizon Telescope, and that the resulting images are independent of the level of systematic amplitude error. We apply closure imaging to VLBA and ALMA data and show that it is capable of matching or exceeding the performance of traditional self-calibration and CLEAN for these data sets.
High Dynamic Range X-Ray Detector Pixel Architectures Utilizing Charge Removal

Several charge integrating CMOS pixel front ends utilizing charge removal techniques have been fabricated to extend dynamic range for X-ray diffraction applications at synchrotron sources and X-ray free electron lasers (XFELs). The pixels described herein build on the mixed mode pixel array detector (MM-PAD) framework, developed previously by our group to perform high dynamic range imaging. These new pixels boast several orders of magnitude improvement in maximum flux over the MM-PAD, which is capable of measuring a sustained flux in excess of $10{^{8}}$ X-rays/pixel/s while maintaining sensitivity to smaller signals, down to single X-rays. To extend dynamic range, charge is removed from the integration node of the front-end amplifier without interrupting integration. The number of times this process occurs is recorded by a digital counter in the pixel. The parameter limiting full well is, thereby, shifted from the size of an integration capacitor to the depth of a digital counter. The result is similar to that achieved by counting pixel array detectors, but the integrators presented here are designed to tolerate a sustained flux $>10{^{11}}$ X-rays/pixel/s. Pixel front-end linearity was evaluated by direct current injection and results are presented. A small-scale readout ASIC utilizing these pixel architectures has been fabricated and the use of these architectures to increase single X-ray pulse dynamic range at XFELs is discussed briefly.
Near IR Astrometry of Magnetars

We report on the progress of our five-year program for astrometric monitoring of magnetars using high-resolution NIR observations using the laser guide star adaptive optics (LGS-AO) supported NIRC2 camera on the 10-meter Keck telescope. We have measured the proper motion of two of the youngest magnetars, SGR 1806–20 and SGR 1900+14, which have counterparts with K ~21 mag, and have placed a preliminary upper limit on the motion of the young AXP 1E 1841–045. The precision of the proper motion measurement is at the milliarcsecond per year level. Our proper motion measurements now provide evidence to link SGR 1806–20 and SGR 1900+14 with neighboring young star clusters. At the distances of these magnetars, their proper motion corresponds to transverse space velocities of 350 ± 100 km s^(−1) and 130 ± 30 km s^(−1) respectively. The upper limit on the proper motion of AXP 1E 1841–045 is 160 km s^(−1). With the sample of proper motions available, we conclude that the kinematics of the magnetar family are not distinct from that of pulsars.
IS THE GALACTIC BULGE DEVOID OF PLANETS

Considering a sample of 31 exoplanetary systems detected by gravitational microlensing, we investigate whether or not the estimated distances to these systems conform to the Galactic distribution of planets expected from models. We derive the expected distribution of distances and relative proper motions from a simulated microlensing survey, correcting for the dominant selection effects that affect the planet detection sensitivity as a function of distance, and compare it to the observed distribution using Anderson-Darling (AD) hypothesis testing. Taking the relative abundance of planets in the bulge to that in the disk, $f_{\rm bulge}$, as a model parameter, we find that our model is only consistent with the observed distribution for $f_{\rm bulge}<0.54$ (for a $p$-value threshold of 0.01) implying that the bulge may be devoid of planets relative to the disk. Allowing for a dependence of planet abundance on metallicity and host mass, or an additional dependence of planet sensitivity on event timescale does not restore consistency for $f_{\rm bulge}=1$. We examine the distance estimates of some events in detail, and conclude that some parallax-based distance estimates could be significantly in error. Only by combining the removal of one problematic event from our sample and the inclusion of strong dependences of planet abundance or detection sensitivity on host mass, metallicity and event timescale are we able to find consistency with the hypothesis that the bulge and disk have equal planet abundance.
Time independent universal computing with spin chains: quantum plinko machine

We present a scheme for universal quantum computing using XY Heisenberg spin chains. Information is encoded into packets propagating down these chains, and they interact with each other to perform universal quantum computation. A circuit using g gate blocks on m qubits can be encoded into chains of length for all with vanishingly small error.
Random walk invariants of string links from R–matrices

We show that the exterior powers of the matrix valued random walk invariant of string links, introduced by Lin, Tian, and Wang, are isomorphic to the graded components of the tangle functor associated to the Alexander polynomial by Ohtsuki divided by the zero graded invariant of the functor. Several resulting properties of these representations of the string link monoids are discussed.
Glimpses of Space-Time Beyond the Singularities Using Supercomputers

A fundamental problem of Einsteins theory of classical general relativity is the existence of singularities such as the big bang. All known laws of physics end at these boundaries of classical space-time. Thanks to recent developments in quantum gravity, supercomputers are now playing an important role in understanding the resolution of big bang and black hole singularities. Using supercomputers, explorations of the very genesis of space and time from quantum geometry are revealing a novel picture of what lies beyond classical singularities and the new physics of the birth of our universe.
EFFECTIVE THEORIES AND ELECTROWEAK PRECISION CONSTRAINTS

This is a pedagogical and self-contained review on obtaining electroweak precision constraints on TeV scale new physics using the effective theory method. We identify a set of relevant effective operators in the Standard Model and calculate from them corrections to all major electroweak precision observables. The corrections are compared with data to put constraints on the effective operators. Various approaches and applications in the literature are reviewed.
Traversable wormholes via a double trace deformation

After turning on an interaction that couples the two boundaries of an eternal BTZ black hole, we find a quantum matter stress tensor with negative average null energy, whose gravitational backreaction renders the Einstein-Rosen bridge traversable. Such a traversable wormhole has an interesting interpretation in the context of ER=EPR, which we suggest might be related to quantum teleportation. However, it cannot be used to violate causality. We also discuss the implications for the energy and holographic entropy in the dual CFT description.
Some electromagnetic properties of the nucleon from Relativistic Chiral Effective Field Theory

Abstract Considering the magnetic moment and polarizabilities of the nucleon we emphasize the need for relativistic chiral EFT calculations. Our relativistic calculations are done via the forward-Compton-scattering sum rules, thus ensuring the correct analytic properties. The results obtained in this way are equivalent to the usual loop calculations, provided no heavy-baryon expansion or any other manipulations which lead to a different analytic structure (e.g., infrared regularization) are made. The Baldin sum rule can directly be applied to calculate the sum of nucleon polarizabilities. In contrast, the GDH sum rule is practically unsuitable for calculating the magnetic moments. The breakthrough is achieved by taking the derivatives of the sum rule with respect to the anomalous magnetic moment. As an example, we apply the derivative of the GDH sum rule to the calculation of the magnetic moment in QED and reproduce the famous Schwinger’s correction from a tree-level cross-section calculation. As far as the nucleon properties are concerned, we focus on two issues: (1) chiral behavior of the nucleon magnetic moment and (2) reconciliation of the chiral loop and Δ -resonance contributions to the nucleon magnetic polarizability.
Theoretical Insights Into Multiclass Classification: A High-dimensional Asymptotic View

Contemporary machine learning applications often involve classification tasks with many classes. Despite their extensive use, a precise understanding of the statistical properties and behavior of classification algorithms is still missing, especially in modern regimes where the number of classes is rather large. In this paper, we take a step in this direction by providing the first asymptotically precise analysis of linear multiclass classification. Our theoretical analysis allows us to precisely characterize how the test error varies over different training algorithms, data distributions, problem dimensions as well as number of classes, inter/intra class correlations and class priors. Specifically, our analysis reveals that the classification accuracy is highly distribution-dependent with different algorithms achieving optimal performance for different data distributions and/or training/features sizes. Unlike linear regression/binary classification, the test error in multiclass classification relies on intricate functions of the trained model (e.g., correlation between some of the trained weights) whose asymptotic behavior is difficult to characterize. This challenge is already present in simple classifiers, such as those minimizing a square loss. Our novel theoretical techniques allow us to overcome some of these challenges. The insights gained may pave the way for a precise understanding of other classification algorithms beyond those studied in this paper.
Monte-Carlo imaging for optical interferometry

ABSTRACT We present a exible code created for imaging from the bispectrum and V 2 . By using a simulated annealingmethod, we limit the probability of convergingto local chi-squared minima as can occur when traditional imagingmethods are used on data sets with limited phase information. We present the results of our code used on asimulated data set utilizing a number of regularization schemes including maximum entropy. Using the statisticalproperties from Monte-Carlo Markovchains of images, we show how this code can place statistical limits on imagefeatures such as unseen binary companions.Keywords: astronomical software,aperture synthesis imaging, optical interferometry, Bayesian statistics 1. INTRODUCTION It is well known that a large class of images can be consistent with a particular interferometric data set. Thisis more true for optical inferferometry than radio interferometry, due to the general unavailability of absolutevisibility phase. An imaging algorithm such as CLEAN or Maximum Entropy combined with self-calibrationattempts to nd the best possible image consistent wi th the interferometric data. Both nding this bestimage and interpretation of features within the image can be dicult, and in general requires some kind ofregularization. Regularization punishes images that look bad (such as having too much unresolved structure)to nd a compromise between lowering the
Entropy Rain: Dilution and Compression of Thermals in Stratified Domains

Large-scale convective flows called giant cells were once thought to transport the Sun's luminosity in the solar convection zone, but recent observations have called their existence into question. In place of large-scale flows, some authors have suggested the solar luminosity may instead be transported by small droplets of rapidly falling, low entropy fluid. This "entropy rain" could propagate as dense vortex rings, analogous to rising buoyant thermals in the Earth's atmosphere. In this work, we develop an analytical theory describing the evolution of dense, negatively buoyant thermals. We verify the theory with 2D cylindrical and 3D cartesian simulations of laminar, axisymmetric thermals in highly stratified atmospheres. Our results show that dense thermals fall in two categories: a stalling regime in which the droplets slow down and expand, and a falling regime in which the droplets accelerate and shrink as they propagate downwards. We estimate that solar downflows are in the falling regime and maintain their entropy perturbation against diffusion until they reach the base of the convection zone. This suggests that entropy rain may be an effective nonlocal mechanism for transporting the solar luminosity.
TESTING CONVERGENCE FOR GLOBAL ACCRETION DISKS

Global disk simulations provide a powerful tool for investigating accretion and the underlying magnetohydrodynamic turbulence driven by magneto-rotational instability (MRI). Using them to accurately predict quantities such as stress, accretion rate, and surface brightness profile requires that purely numerical effects, arising from both resolution and algorithm, be understood and controlled. We use the flux-conservative Athena code to conduct a series of experiments on disks having a variety of magnetic topologies to determine what constitutes adequate resolution. We develop and apply several resolution metrics: (Q{sub z} ) and (Q{sub {phi}}), the ratio of the grid zone size to the characteristic MRI wavelength, {alpha}{sub mag}, the ratio of the Maxwell stress to the magnetic pressure, and /, the ratio of radial to toroidal magnetic field energy. For the initial conditions considered here, adequate resolution is characterized by (Q{sub z} ) {>=} 15, (Q{sub {phi}}) {>=} 20, {alpha}{sub mag} Almost-Equal-To 0.45, and /{approx}0.2. These values are associated with {>=}35 zones per scaleheight H, a result consistent with shearing box simulations. Numerical algorithm is also important. Use of the Harten-Lax-van Leer-Einfeldt flux solver or second-order interpolation can significantly degrade the effective resolution compared to the Harten-Lax-van Leer discontinuities flux solver and third-order interpolation. Resolutionmore » at this standard can be achieved only with large numbers of grid zones, arranged in a fashion that matches the symmetries of the problem and the scientific goals of the simulation. Without it, however, quantitative measures important to predictions of observables are subject to large systematic errors.« less
On the Mertens Conjecture for Function Fields

We study the natural analogue of the Mertens conjecture in the setting of global function fields. Building on the work of Cha, we show that most hyperelliptic curves do not satisfy the Mertens conjecture, but that if we modify the Mertens conjecture to have a larger constant, then this modified conjecture is satisfied by a positive proportion of hyperelliptic curves.
SYMPATHETIC MAGNETIC BREAKOUT CORONAL MASS EJECTIONS FROM PSEUDOSTREAMERS

We present high-resolution 2.5D MHD simulation results of magnetic breakout-initiated coronal mass ejections (CMEs) originating from a coronal pseudostreamer configuration. The coronal null point in the magnetic topology of pseudostreamers means that the initiation of consecutive sympathetic eruptions is a natural consequence of the system's evolution. A generic source region energization process—ideal footpoint shearing parallel to the pseudostreamer arcade polarity inversion lines—is all that is necessary to store sufficient magnetic energy to power consecutive CME eruptions given that the pseudostreamer topology enables the breakout initiation mechanism. The second CME occurs because the eruptive flare reconnection of the first CME simultaneously acts as the overlying pre-eruption breakout reconnection for the sympathetic eruption. We examine the details of the magnetic and kinetic energy evolution and the signatures of the overlying null point distortion, current sheet formation, and magnetic breakout reconnection giving rise to the runaway expansion that drives the flare reconnection below the erupting sheared field core. The numerical simulation's spatial resolution and output cadence are sufficient to resolve the formation of magnetic islands during the reconnection process in both the breakout and eruptive flare current sheets. We quantify the flux transfer between the pseudostreamer arcades and show that the eruptive flare reconnection processes flux ~10 times faster than the pre-eruption breakout reconnection. We show that the breakout reconnection jets cause bursty, intermittent upflows along the pseudostreamer stalk, as well as downflows in the adjacent pseudostreamer arcade, both of which may be observable as pre-eruption signatures. Finally, we examine the flux rope CME trajectories and show that the breakout current sheet provides a path of least resistance as an imbalance in the surrounding magnetic energy density and results in a non-radial CME deflection early in the eruption.
The basis of the Second Law of thermodynamics in quantum field theory

The result that closed systems evolve toward equilibrium is derived entirely on the basis of quantum field theory for a model system, without invoking any of the common extra-mathematical notions of particle trajectories, collapse of the wave function, measurement, or intrinsically stochastic processes. The equivalent of the Stosszahlansatz of classical statistical mechanics is found, and has important differences from the classical version. A novel result of the calculation is that interacting many-body systems in the infinite volume limit evolve toward diagonal states (states with loss of all phase information) on the time scale of the interaction time. The connection with the onset of off-diagonal phase coherence in Bose condensates is discussed.
On the Interaction of Jupiter's Great Red Spot and Zonal Jet Streams

Abstract In this paper, Jupiter’s Great Red Spot (GRS) is used to determine properties of the Jovian atmosphere that cannot otherwise be found. These properties include the potential vorticity of the GRS and its neighboring jet streams, the shear imposed on the GRS by the jet streams, and the vertical entropy gradient (i.e., Rossby deformation radius). The cloud cover of the GRS, which is often used to define the GRS’s area and aspect ratio, is found to differ significantly from the region of the GRS’s potential vorticity anomaly. The westward-going jet stream to the north of the GRS and the eastward-going jet stream to its south are each found to have a large potential vorticity “jump.” The jumps have opposite signs, and as a consequence of their interaction with the GRS, the shear imposed on the GRS is reduced. The aspect ratio of the GRS’s potential vorticity anomaly depends on the ratio of the imposed shear to the strength of the anomaly. The east–west to north–south aspect ratio is found to be ∼2:1, ...
Unsupervised Parsing via Constituency Tests

We propose a method for unsupervised parsing based on the linguistic notion of a constituency test. One type of constituency test involves modifying the sentence via some transformation (e.g. replacing the span with a pronoun) and then judging the result (e.g. checking if it is grammatical). Motivated by this idea, we design an unsupervised parser by specifying a set of transformations and using an unsupervised neural acceptability model to make grammaticality decisions. To produce a tree given a sentence, we score each span by aggregating its constituency test judgments, and we choose the binary tree with the highest total score. While this approach already achieves performance in the range of current methods, we further improve accuracy by fine-tuning the grammaticality model through a refinement procedure, where we alternate between improving the estimated trees and improving the grammaticality model. The refined model achieves 62.8 F1 on the Penn Treebank test set, an absolute improvement of 7.6 points over the previously best published result.
Identifying Functional Thermodynamics in Autonomous Maxwellian Ratchets

Author(s): Boyd, AB; Mandal, D; Crutchfield, JP | Abstract: We introduce a family of Maxwellian Demons for which correlations among information bearing degrees of freedom can be calculated exactly and in compact analytical form. This allows one to precisely determine Demon functional thermodynamic operating regimes, when previous methods either misclassify or simply fail due to approximations they invoke. This reveals that these Demons are more functional than previous candidates. They too behave either as engines, lifting a mass against gravity by extracting energy from a single heat reservoir, or as Landauer erasers, consuming external work to remove information from a sequence of binary symbols by decreasing their individual uncertainty. Going beyond these, our Demon exhibits a new functionality that erases bits not by simply decreasing individual-symbol uncertainty, but by increasing inter-bit correlations (that is, by adding temporal order) while increasing single-symbol uncertainty. In all cases, but especially in the new erasure regime, exactly accounting for informational correlations leads to tight bounds on Demon performance, expressed as a refined Second Law of thermodynamics that relies on the Kolmogorov-Sinai entropy for dynamical processes and not on changes purely in system configurational entropy, as previously employed. We rigorously derive the refined Second Law under minimal assumptions and so it applies quite broadly - for Demons with and without memory and input sequences that are correlated or not. We note that general Maxwellian Demons readily violate previously proposed, alternative such bounds, while the current bound still holds. As such, it broadly describes the minimal energetic cost of any computation by a thermodynamic system.
Robo-AO Discovery and Basic Characterization of Wide Multiple Star Systems in the Pleiades, Praesepe, and NGC 2264 Clusters

We identify and roughly characterize 66 candidate binary star systems in the Pleiades, Praesepe, and NGC 2264 star clusters, based on robotic adaptive optics imaging data obtained using Robo-AO at the Palomar 60'' telescope. Only ~10% of our imaged pairs were previously known. We detect companions at red optical wavelengths, with physical separations ranging from a few tens to a few thousands of au. A three-sigma contrast curve generated for each final image provides upper limits to the brightness ratios for any undetected putative companions. The observations are sensitive to companions with a maximum contrast of ~6^m at larger separations. At smaller separations, the mean (best) raw contrast at 2'' is 3.^m8 (6^m), at 1'' is 3.^m0 (4.^m5), and at 0.”5 is 1.^m9 (3^m). Point-spread function subtraction can recover nearly the full contrast in the closer separations. For detected candidate binary pairs, we report separations, position angles, and relative magnitudes. Theoretical isochrones appropriate to the Pleiades and Praesepe clusters are then used to determine the corresponding binary mass ratios, which range from 0.2 to 0.9 in q = m_2/m_1. For our sample of roughly solar-mass (FGK type) stars in NGC 2264 and sub-solar-mass (K and early M-type) primaries in the Pleiades and Praesepe, the overall binary frequency is measured at ~15.5% ± 2%. However, this value should be considered a lower limit to the true binary fraction within the specified separation and mass ratio ranges in these clusters, given that complex and uncertain corrections for sensitivity and completeness have not been applied.
A minimal model for microbial biodiversity can reproduce experimentally observed ecological patterns

Surveys of microbial biodiversity such as the Earth Microbiome Project (EMP) and the Human Microbiome Project (HMP) have revealed robust ecological patterns across different environments. A major goal in ecology is to leverage these patterns to identify the ecological processes shaping microbial ecosystems. One promising approach is to use minimal models that can relate mechanistic assumptions at the microbe scale to community-level patterns. Here, we demonstrate the utility of this approach by showing that the Microbial Consumer Resource Model (MiCRM) - a minimal model for microbial communities with resource competition, metabolic crossfeeding and stochastic colonization - can qualitatively reproduce patterns found in survey data including compositional gradients, dissimilarity/overlap correlations, richness/harshness correlations, and nestedness of community composition. By using the MiCRM to generate synthetic data with different environmental and taxonomical structure, we show that large scale patterns in the EMP can be reproduced by considering the energetic cost of surviving in harsh environments and HMP patterns may reflect the importance of environmental filtering in shaping competition. We also show that recently discovered dissimilarity-overlap correlations in the HMP likely arise from communities that share similar environments rather than reflecting universal dynamics. We identify ecologically meaningful changes in parameters that alter or destroy each one of these patterns, suggesting new mechanistic hypotheses for further investigation. These findings highlight the promise of minimal models for microbial ecology.
3-MANIFOLDS, TANGLES AND PERSISTENT INVARIANTS

Given a compact, connected, oriented 3-manifold M with boundary, and epimorphism χ from H1M to a free abelian group �, two invariants β, τ ∈ Zare defined. If M embeds in another such 3- manifold N such that χN factors through χ, then the product βτ divides �0(H1 ˜ N). A theorem of D. Krebes concerning 4-tangles embedded in links arises as a special case. Algebraic and skein theoretic generalizations for 2n-tangles provide invariants that persist in the corresponding invariants of links in which they embed. An example is given of a virtual 4-tangle for which Krebes's theorem does not hold.