cssi/SciSciGPT-SciSciNet huggingface dataset:
Globular clusters and dark satellite galaxies through the stream velocity

The formation of purely baryonic globular clusters with no gravitationally bound dark matter is still a theoretical challenge. We show that these objects might form naturally whenever there is a relative stream velocity between baryons and dark matter. The stream velocity causes a phase shift between linear modes of baryonic and dark matter perturbations, which translates to a spatial offset between the two components when they collapse. For a 2σ (3σ) density fluctuation, baryonic clumps with masses in the range 105-2.5 × 106 M⊙ (105-4 × 106 M⊙) collapse outside the virial radii of their counterpart dark matter halos. These objects could survive as long-lived, dark-matter-free objects and might conceivably become globular clusters. In addition, their dark matter counterparts, which were deprived of gas, might become dark satellite galaxies. © 2014. The American Astronomical Society. All rights reserved.
Exact Renormalization Groups As a Form of Entropic Dynamics.

The Renormalization Group (RG) is a set of methods that have been instrumental in tackling problems involving an infinite number of degrees of freedom, such as, for example, in quantum field theory and critical phenomena. What all these methods have in common—which is what explains their success—is that they allow a systematic search for those degrees of freedom that happen to be relevant to the phenomena in question. In the standard approaches the RG transformations are implemented by either coarse graining or through a change of variables. When these transformations are infinitesimal, the formalism can be described as a continuous dynamical flow in a fictitious time parameter. It is generally the case that these exact RG equations are functional diffusion equations. In this paper we show that the exact RG equations can be derived using entropic methods. The RG flow is then described as a form of entropic dynamics of field configurations. Although equivalent to other versions of the RG, in this approach the RG transformations receive a purely inferential interpretation that establishes a clear link to information theory.
Local rings of embedding codepth 3: A classification algorithm

Let I be an ideal of a regular local ring Q with residue field k. The length of the minimal free resolution of RD Q=I is called the codepth of R. If it is at most 3, then the resolution carries the structure of a differential graded algebra, and the induced algebra structure on Tor Q.R; k/ provides for a classification of such local rings. We describe the Macaulay2 package CodepthThree that implements an algo- rithm for classifying a local ring as above by computation of a few cohomologi- cal invariants.
On a two-phase Hele-Shaw problem with a time-dependent gap and distributions of sinks and sources

A two-phase Hele-Shaw problem with a time-dependent gap describes the evolution of the interface, which separates two fluids sandwiched between two plates. The fluids have different viscosities. In addition to the change in the gap width of the Hele-Shaw cell, the interface is driven by the presence of some special distributions of sinks and sources located in both the interior and exterior domains. The effect of surface tension is neglected. Using the Schwarz function approach, we give examples of exact solutions when the interface belongs to a certain family of algebraic curves and the curves do not form cusps. The family of curves are defined by the initial shape of the free boundary.
Ejection of Matter and Energy from NGC 4258

It has been claimed by Miyoshi and Greenhill that the megamaser observations of the nucleus of NGC 4258 show that a massive black hole is present in its center. We show that the evidence of ejection of gas, radio plasma, and X-ray-emitting QSOs from this nucleus proves that the ejection is coming from the center in a curving flow within a cone with angle ~40°, centered at P.A. 100°. This is close to the direction in which the velocities from the megamaser have been measured, so that the evidence taken as a whole suggests that the masering gas also is being ejected in the same direction at velocities ±900 km s-1 rather than rotating about a massive black hole. Thus the gas does not provide evidence for a black hole in the center.
Constraining Stellar Coronal Mass Ejections through Multi-wavelength Analysis of the Active M Dwarf EQ Peg

Stellar coronal mass ejections remain experimentally unconstrained, unlike their stellar flare counterparts, which are observed ubiquitously across the electromagnetic spectrum. Low-frequency radio bursts in the form of a type II burst offer the best means of identifying and constraining the rate and properties of stellar CMEs. CME properties can be further improved through the use of proposed solar-stellar scaling relations and multi-wavelength observations of CMEs through the use of type II bursts and the associated flares expected to occur alongside them. We report on 20 hr of observation of the nearby, magnetically active, and well-characterized M dwarf star EQ Peg. The observations are simultaneously observed with the Jansky Very Large Array at their P-band (230–470 MHz) and at the Apache Point observatory in the SDSS u' filter (λ = 3557 A). Dynamic spectra of the P-band data, constructed to search for signals in the frequency-time domains, did not reveal evidence of drifting radio bursts that could be ascribed to type II bursts. Given the sensitivity of our observations, we are able to place limits on the brightness temperature and source size of any bursts that may have occurred. Using solar scaling rations on four observed stellar flares, we predict CME parameters. Given the constraints on coronal density and photospheric field strength, our models suggest that the observed flares would have been insufficient to produce detectable type II bursts at our observed frequencies. We consider the implications of these results, and other recent findings, on stellar mass loss.
Proof of a stronger version of the AJ Conjecture for torus knots

For a knot K in S , the sl2 –colored Jones function JK .n/ is a sequence of Laurent polynomials in the variable t that is known to satisfy non-trivial linear recurrence relations. The operator corresponding to the minimal linear recurrence relation is called the recurrence polynomial of K . The AJ Conjecture (see Garoufalidis [4]) states that when reducing t D 1 , the recurrence polynomial is essentially equal to the A–polynomial of K . In this paper we consider a stronger version of the AJ Conjecture, proposed by Sikora [14], and confirm it for all torus knots.
The hidden geometry of particle collisions

We establish that many fundamental concepts and techniques in quantum field theory and collider physics can be naturally understood and unified through a simple new geometric language. The idea is to equip the space of collider events with a metric, from which other geometric objects can be rigorously defined. Our analysis is based on the energy mover’s distance, which quantifies the “work” required to rearrange one event into another. This metric, which operates purely at the level of observable energy flow information, allows for a clarified definition of infrared and collinear safety and related concepts. A number of well-known collider observables can be exactly cast as the minimum distance between an event and various manifolds in this space. Jet definitions, such as exclusive cone and sequential recombination algorithms, can be directly derived by finding the closest few-particle approximation to the event. Several area- and constituent-based pileup mitigation strategies are naturally expressed in this formalism as well. Finally, we lift our reasoning to develop a precise distance between theories, which are treated as collections of events weighted by cross sections. In all of these various cases, a better understanding of existing methods in our geometric language suggests interesting new ideas and generalizations.
Krall–Laguerre commutative algebras of ordinary differential operators

In 1999, Grunbaum, Haine and Horozov defined a large family of commutative algebras of ordinary differential operators, which have orthogonal polynomials as eigenfunctions. These polynomials are mutually orthogonal with respect to a Laguerre-type weight distribution, thus providing solutions to Krall’s problem. In the present paper, we give a new proof of their result, which establishes a conjecture, concerning the explicit characterization of the dual commutative algebra of eigenvalues. In particular, for the Koornwinder’s generalization of Laguerre polynomials, our approach yields an explicit set of generators for the whole algebra of differential operators. We also illustrate how more general Sobolev-type orthogonal polynomials fit within this theory.
X-Rays From Galaxies

This talk will discuss early Chandra results in the context of the present picture of the X-ray properties of galaxies. It will also address possibilities for future improvements in this field.
Green’s function-stochastic methods framework for probing nonlinear evolution problems: Burger’s equation, the nonlinear Schrödinger’s equation, and hydrodynamic organization of near-molecular-scale vorticity

Abstract A framework which combines Green’s function (GF) methods and techniques from the theory of stochastic processes is proposed for tackling nonlinear evolution problems. The framework, established by a series of easy-to-derive equivalences between Green’s function and stochastic representative solutions of linear drift–diffusion problems, provides a flexible structure within which nonlinear evolution problems can be analyzed and physically probed. As a preliminary test bed, two canonical, nonlinear evolution problems – Burgers’ equation and the nonlinear Schrodinger’s equation – are first treated. In the first case, the framework provides a rigorous, probabilistic derivation of the well known Cole–Hopf ansatz. Likewise, in the second, the machinery allows systematic recovery of a known soliton solution. The framework is then applied to a fairly extensive exploration of physical features underlying evolution of randomly stretched and advected Burger’s vortex sheets. Here, the governing vorticity equation corresponds to the Fokker–Planck equation of an Ornstein–Uhlenbeck process, a correspondence that motivates an investigation of sub-sheet vorticity evolution and organization. Under the assumption that weak hydrodynamic fluctuations organize disordered, near-molecular-scale, sub-sheet vorticity, it is shown that these modes consist of two weakly damped counter-propagating cross-sheet acoustic modes, a diffusive cross-sheet shear mode, and a diffusive cross-sheet entropy mode. Once a consistent picture of in-sheet vorticity evolution is established, a number of analytical results, describing the motion and spread of single, multiple, and continuous sets of Burger’s vortex sheets, evolving within deterministic and random strain rate fields, under both viscous and inviscid conditions, are obtained. In order to promote application to other nonlinear problems, a tutorial development of the framework is presented. Likewise, time-incremental solution approaches and construction of approximate, though otherwise difficult-to-obtain backward-time GF’s (useful in solution of forward-time evolution problems) are discussed.
Detection of the Red Supergiant Wind from the Progenitor of Cassiopeia A

Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While providing a rare opportunity to study in detail the remnant of a Type IIb supernova, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Halpha emission nebulosities concentrated 10-15 pc (10-15 arcminutes) to the north and east. First reported by Minkowski as a faint H II region, these nebulosities exhibit distinct morphological and spectroscopic properties relative to the surrounding diffuse emissions. Compared to neighboring H II regions, these nebulae show stronger [N II] 6548, 6583 A and [S II] 6716, 6731 A emissions relative to Halpha. We show that Cas A's highest-velocity ejecta knots are interacting with some of the closest projected emission nebulae, thus providing strong evidence that these nebulae lie at the same distance as the remnant. We interpret these surrounding nebulosities to be the remains of the progenitor's red supergiant wind which accumulated against the southern edge of a large extended H II region located north of Cas A. Our findings are consistent with the view that Cas A's progenitor underwent considerable mass-loss, first from a fast main-sequence wind, then from a slower, clumpy red supergiant wind, and finally from a brief high-velocity wind, like that from a yellow supergiant.
State power and elite autonomy in a networked civil society: The board interlocking of Chinese non-profits

Abstract In response to failures of central planning, the Chinese government has experimented not only with free-market trade zones, but with allowing non-profit foundations to operate in a decentralized fashion. A network study shows how these foundations have connected together by sharing board members, in a structural parallel to what is seen in corporations in the United States and Europe. This board interlocking leads to the emergence of an elite group with privileged network positions. While the presence of government officials on non-profit boards is widespread, government officials are much less common in a subgroup of foundations that control just over half of all revenue in the network. This subgroup, associated with business elites, not only enjoys higher levels of within-elite links, but even preferentially excludes government officials from the NGOs with higher degree. The emergence of this structurally autonomous sphere is associated with major political and social events in the state–society relationship. Cluster analysis reveals multiple internal components within this sphere that share similar levels of network influence. Rather than a core-periphery structure centered around government officials, the Chinese non-profit world appears to be a multipolar one of distinct elite groups, many of which achieve high levels of independence from direct government control.
Tile number and space-efficient knot mosaics

In this paper, we introduce the concept of a space-efficient knot mosaic. That is, we seek to determine how to create knot mosaics using the least number of non-blank tiles necessary to depict the ...
Optimization and validation of a deep learning CuZr atomistic potential: Robust applications for crystalline and amorphous phases with near-DFT accuracy

We show that a deep-learning neural network potential (DP) based on density functional theory (DFT) calculations can well describe Cu-Zr materials, an example of a binary alloy system, that can coexist in as ordered intermetallic and as an amorphous phase. The complex phase diagram for Cu-Zr makes it a challenging system for traditional atomistic force-fields that cannot accurately describe the different properties and phases. Instead, we show that a DP approach using a large database with ∼300k configurations can render results generally on par with DFT. The training set includes configurations of pristine and bulk elementary metals and intermetallic structures in the liquid and solid phases in addition to slab and amorphous configurations. The DP model was validated by comparing bulk properties such as lattice constants, elastic constants, bulk moduli, phonon spectra, and surface energies to DFT values for identical structures. Furthermore, we contrast the DP results with values obtained using well-established two embedded atom method potentials. Overall, our DP potential provides near DFT accuracy for the different Cu-Zr phases but with a fraction of its computational cost, thus enabling accurate computations of realistic atomistic models, especially for the amorphous phase.
Crawling beneath the free surface: Water snail locomotion

Land snails move via adhesive locomotion. Through muscular contraction and expansion of their foot, they transmit waves of shear stress through a thin layer of mucus onto a solid substrate. Since a free surface cannot support shear stress, adhesive locomotion is not a viable propulsion mechanism for water snails that travel inverted beneath the free surface. Nevertheless, the motion of the freshwater snail, Sorbeoconcha physidae, is reminiscent of that of its terrestrial counterparts, being generated by the undulation of the snail foot that is separated from the free surface by a thin layer of mucus. Here, a lubrication model is used to describe the mucus flow in the limit of small-amplitude interfacial deformations. By assuming the shape of the snail foot to be a traveling sine wave and the mucus to be Newtonian, an evolution equation for the interface shape is obtained and the resulting propulsive force on the snail is calculated. This propulsive force is found to be nonzero for moderate values of the c...
M0.20-0.033: An Expanding Molecular Shell in the Galactic Center Radio Arc

We present high-frequency Karl G. Jansky Very Large Array (VLA) continuum and spectral line (NH3, H64${\alpha}$, and H63${\alpha}$) observations of the Galactic Center Radio Arc region, covering the Sickle H II region, the Quintuplet cluster, and molecular clouds M0.20-0.033 and M0.10-0.08. These observations show that the two velocity components of M0.20-0.033 (~25 & 80 km/s), previously thought to be separate clouds along the same line-of-sight, are physically connected in position-velocity space via a third southern component around 50 km/s. Further position-velocity analysis of the surrounding region, using lower-resolution survey observations taken with the Mopra and ATCA telescopes, indicates that both molecular components in M0.20-0.033 are physically connected to the M0.10-0.08 molecular cloud, which is suggested to be located on stream 1 in the Kruijssen et al. (2015) orbital model. The morphology and kinematics of the molecular gas in M0.20-0.033 indicate that the two velocity components in M0.20-0.033 constitute an expanding shell. Our observations suggest that the M0.20-0.033 expanding shell has an expansion velocity of 40 km/s, with a systemic velocity of 53 km/s, comparable to velocities detected in M0.10-0.08. The origin of the expanding shell is located near the Quintuplet cluster, suggesting that the energy and momentum output from this massive stellar cluster may have contributed to the expansion.
Extreme gravity tests with gravitational waves from compact binary coalescences: (I) inspiral–merger

The observation of the inspiral and merger of compact binaries by the LIGO/Virgo collaboration ushered in a new era in the study of strong-field gravity. We review current and future tests of strong gravity and of the Kerr paradigm with gravitational-wave interferometers, both within a theory-agnostic framework (the parametrized post-Einsteinian formalism) and in the context of specific modified theories of gravity (scalar–tensor, Einstein–dilaton–Gauss–Bonnet, dynamical Chern–Simons, Lorentz-violating, and extra dimensional theories). In this contribution we focus on (i) the information carried by the inspiral radiation, and (ii) recent progress in numerical simulations of compact binary mergers in modified gravity.
A topological introduction to knot contact homology

Knot contact homology is a Floer-theoretic knot invariant derived from counting holomorphic curves in the cotangent bundle of \(\mathbb{R}^{3}\) with Lagrangian boundary condition on the conormal bundle to the knot. Among other things, this can be used to produce a three-variable polynomial that detects the unknot and conjecturally contains many known knot invariants; a different part of the package yields an effective invariant of transverse knots in \(\mathbb{R}^{3}\).
From Bocce to Positivity: some probabilistic linear algebra

SummaryA question in geometric probability about the location of the balls in a game of bocce leads to related questions about the probability that a system of linear equations has a positive solution and the probability that a random zero-sum game favors the row player. Under reasonable assumptions, we are able to find these probabilities.
[C ii] emission from galactic nuclei in the presence of X-rays

Context. The luminosity of [C ii] is used as a probe of the star formation rate in galaxies, but the correlation breaks down in some active galactic nuclei (AGNs). Models of the [C ii] emission from galactic nuclei do not include the influence of X-rays on the carbon ionization balance, which may be a factor in reducing the [C ii] luminosity. Aims. We aim to determine the properties of the ionized carbon and its distribution among highly ionized states in the interstellar gas in galactic nuclei under the influence of X-ray sources. We calculate the [C ii] luminosity in galactic nuclei under the influence of bright sources of soft X-rays. Methods. We solve the balance equation of the ionization states of carbon as a function of X-ray flux, electron, atomic hydrogen, and molecular hydrogen density. These are input to models of [C ii] emission from the interstellar medium (ISM) in galactic nuclei representing conditions in the Galactic central molecular zone and a higher density AGN model. The behavior of the [C ii] luminosity is calculated as a function of the X-ray luminosity. We also solve the distribution of the ionization states of oxygen and nitrogen in highly ionized regions. Results. We find that the dense warm ionized medium (WIM) and dense photon dominated regions (PDRs) dominate the [C ii] emission when no X-rays are present. The X-rays in galactic nuclei can affect strongly the C + abundance in the WIM, converting some fraction to C 2+ and higher ionization states and thus reducing its [C ii] luminosity. For an X-ray luminosity L(X-ray) 10 43 erg s −1 the [C ii] luminosity can be suppressed by a factor of a few, and for very strong sources, L(X-ray) >10 44 erg s −1 such as found for many AGNs, the [C ii] luminosity is significantly depressed. Comparison of the model with several extragalactic sources shows that the [C ii] to far-infrared ratio declines for L(X-ray) 10 43 erg s −1 , in reasonable agreement with our model. Conclusions. We conclude that X-rays can suppress the C + abundance and, therefore, the [C ii] luminosity of the ISM in active galactic nuclei with a large X-ray flux. The X-ray flux can arise from a central massive accreting black hole and/or from many smaller discrete sources distributed throughout the nuclei. We also find that the lower ionization states of nitrogen and oxygen are also suppressed at high X-ray fluxes in warm ionized gas.
Deep data mining in a real space: separation of intertwined electronic responses in a lightly doped BaFe2As2.

Electronic interactions present in material compositions close to the superconducting dome play a key role in the manifestation of high-T c superconductivity. In many correlated electron systems, however, the parent or underdoped states exhibit strongly inhomogeneous electronic landscape at the nanoscale that may be associated with competing, coexisting, or intertwined chemical disorder, strain, magnetic, and structural order parameters. Here we demonstrate an approach based on a combination of scanning tunneling microscopy/spectroscopy and advanced statistical learning for an automatic separation and extraction of statistically significant electronic behaviors in the spin density wave regime of a lightly (~1%) gold-doped BaFe2As2. Lastly, we show that the decomposed STS spectral features have a direct relevance to fundamental physical properties of the system, such as SDW-induced gap, pseudogap-like state, and impurity resonance states.
Moduli of elliptic curves via twisted stable maps

Abramovich, Corti and Vistoli have studied modular compactifications of stacks of curves equipped with abelian level structures arising as substacks of the stack of twisted stable maps into the classifying stack of a finite group, provided the order of the group is invertible on the base scheme. Recently Abramovich, Olsson and Vistoli extended the notion of twisted stable maps to allow arbitrary base schemes, where the target is a tame stack, not necessarily Deligne-Mumford. In this dissertation, we use this extended notion of twisted stable maps to extend the results of Abramovich, Corti and Vistoli to the case of elliptic curves with level structures over arbitrary base schemes. We prove that we recover the compactified Katz-Mazur regular models, with a natural moduli interpretation in terms of level structures on Picard schemes of twisted curves. Additionally, we study the interactions of the different such moduli stacks contained in a stack of twisted stable maps in characteristics dividing the level.
A viable QCD axion in the MeV mass range

The QCD axion is one of the most compelling solutions of the strong CP problem. There are major current efforts into searching for an ultralight, invisible axion, which is believed to be the only phenomenologically viable realization of the QCD axion. Visible axions with decay constants at or below the electroweak scale are believed to have been long excluded by laboratory searches. Considering the significance of the axion solution to the strong CP problem, we revisit experimental constraints on QCD axions in the $$ \mathcal{O} $$ (10 MeV) mass window. In particular, we find a variant axion model that remains compatible with existing constraints. This model predicts new states at the GeV scale coupled hadronically, and a variety of low-energy axion signatures, such as rare meson decays, nuclear de-excitations via axion emission, and production in e+e− annihilation and fixed target experiments. This reopens the possibility of solving the strong CP problem at the GeV scale.
Cooperative local repair in distributed storage

Erasure-correcting codes, which support local repair of codeword symbols, have attracted substantial attention recently for their application in distributed storage systems. This paper investigates a generalization of the usual locally repairable codes. In particular, this paper studies a class of codes with the following property: any small set of codeword symbols can be reconstructed (repaired) from a small number of other symbols. This is referred to as cooperative local repair. The main contribution of this paper is bounds on the trade-off of the minimum distance and the dimension of such codes, as well as explicit constructions of families of codes that enable cooperative local repair. Some other results regarding cooperative local repair are also presented, including an analysis for the well-known Hadamard/Simplex codes.
Slicing Bing doubles

Bing doubling is an operation which produces a 2‐component boundary link B.K/ from a knot K . If K is slice, then B.K/ is easily seen to be boundary slice. In this paper, we investigate whether the converse holds. Our main result is that if B.K/ is boundary slice, then K is algebraically slice. We also show that the Rasmussen invariant can tell that certain Bing doubles are not smoothly slice. 57M25; 57M27
Graded quivers, generalized dimer models and toric geometry

The open string sector of the topological B-model on CY (m + 2)-folds is de- scribed by m-graded quivers with superpotentials. This correspondence extends to general m the well known connection between CY (m + 2)-folds and gauge theories on the world- volume of D(5 − 2m)-branes for m = 0, …, 3. We introduce m-dimers, which fully encode the m-graded quivers and their superpotentials, in the case in which the CY (m + 2)-folds are toric. Generalizing the well known m = 1, 2 cases, m-dimers significantly simplify the connection between geometry and m-graded quivers. A key result of this paper is the generalization of the concept of perfect matching, which plays a central role in this map, to arbitrary m. We also introduce a simplified algorithm for the computation of perfect matchings, which generalizes the Kasteleyn matrix approach to any m. We illustrate these new tools with a few infinite families of CY singularities.
Homa: a receiver-driven low-latency transport protocol using network priorities

Homa is a new transport protocol for datacenter networks. It provides exceptionally low latency, especially for workloads with a high volume of very short messages, and it also supports large messages and high network utilization. Homa uses in-network priority queues to ensure low latency for short messages; priority allocation is managed dynamically by each receiver and integrated with a receiver-driven flow control mechanism. Homa also uses controlled overcommitment of receiver downlinks to ensure efficient bandwidth utilization at high load. Our implementation of Homa delivers 99th percentile round-trip times less than 15 μs for short messages on a 10 Gbps network running at 80% load. These latencies are almost 100x lower than the best published measurements of an implementation. In simulations, Homa's latency is roughly equal to pFabric and significantly better than pHost, PIAS, and NDP for almost all message sizes and workloads. Homa can also sustain higher network loads than pFabric, pHost, or PIAS.
Locally stationary spatio-temporal interpolation of Argo profiling float data.

Argo floats measure seawater temperature and salinity in the upper 2000m of the global ocean. Statistical analysis of the resulting spatio-temporal dataset is challenging owing to its non-stationar...
Photovoltaic effect in multi-domain ferroelectric perovskite oxides

We propose a device model that elucidates the role of domain walls in the photovoltaic effect in multi-domain ferroelectric perovskites. The model accounts for the intricate interplay between ferroelectric polarization, space charges, photo-generation, and electronic transport. When applied to bismuth ferrite, results show a significant electric potential step across both 71° and 109° domain walls, which in turn contributes to the photovoltaic (PV) effect. We also find a strong correlation between polarization and oxygen octahedra tilts, which indicates the nontrivial role of the latter in the PV effect. The domain wall-based PV effect is further shown to be additive in nature, allowing for the possibility of generating the above-bandgap voltage.
Plasma compression in magnetic reconnection regions in the solar corona

It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region similarly to the case of diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model we consider a set of magnetic field configurations where magnetic reconnection can occur including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of the solar corona. Numerical simulations show that strong plasma compressions ($\geq 4$) in the reconnection regions can form when the plasma heating due to reconnection is efficiently removed by fast thermal conduction or radiative cooling process. The radiative cooling process which is negligible in the typical 1 MK corona can play an important role in the low corona/transition region. It is found that plasma compression is expected to be strongest in low-beta plasma $\beta \sim 0.01-0.07$ at reconnection magnetic nulls.
Reactive Rayleigh-Taylor turbulence

The Rayleigh-Taylor (RT) instability develops and leads to turbulence when a heavy fluid falls under the action of gravity through a light one. We consider a model in which the RT instability is accompanied by a reactive transformation between the fluids. We study the model using direct numerical simulations (DNSs), focusing on the effect of the reaction (flame) on the turbulent mixing. We discuss 'slow' reactions in which the characteristic reaction time exceeds the temporal scale of the RT instability, τ » t inst · In the early turbulent stage, t inst ≤t ≤ τ, effects of the flame are distributed over a maturing mixing zone, whose development is weakly influenced by the reaction. At t >τ the fully mixed zone transforms into a conglomerate of pure-fluid patches of sizes proportional to the mixing zone width. In this 'stirred flame' regime, temperature fluctuations are consumed by reactions in the regions separating the pure-fluid patches. This DNS-based qualitative description is followed by a phenomenology suggesting that thin turbulent flame is of a single-fractal character, and thus distribution of the temperature field is strongly intermittent.
Learning Monocular Visual Odometry via Self-Supervised Long-Term Modeling

Monocular visual odometry (VO) suffers severely from error accumulation during frame-to-frame pose estimation. In this paper, we present a self-supervised learning method for VO with special consideration for consistency over longer sequences. To this end, we model the long-term dependency in pose prediction using a pose network that features a two-layer convolutional LSTM module. We train the networks with purely self-supervised losses, including a cycle consistency loss that mimics the loop closure module in geometric VO. Inspired by prior geometric systems, we allow the networks to see beyond a small temporal window during training, through a novel a loss that incorporates temporally distant (e.g., O(100)) frames. Given GPU memory constraints, we propose a stage-wise training mechanism, where the first stage operates in a local time window and the second stage refines the poses with a “global” loss given the first stage features. We demonstrate competitive results on several standard VO datasets, including KITTI and TUM RGB-D.
Chiral magnetic effect reveals the topology of gauge fields in heavy-ion collisions

The topological structure of vacuum is the cornerstone of non-Abelian gauge theories describing strong and electroweak interactions within the standard model of particle physics. However, transitions between different topological sectors of the vacuum (believed to be at the origin of the baryon asymmetry of the Universe) have never been observed directly. An experimental observation of such transitions in quantum chromodynamics (QCD) has become possible in heavy-ion collisions, where the chiral magnetic effect converts the chiral asymmetry (generated by topological transitions in hot QCD matter) into an electric current, under the presence of the magnetic field produced by the colliding ions. The Relativistic Heavy Ion Collider programme on heavy-ion collisions such as the zirconium–zirconium and ruthenium–ruthenium isobars thus has the potential to uncover the topological structure of vacuum in a laboratory experiment. This discovery would have far-reaching implications for the understanding of QCD, the origin of the baryon asymmetry in the present-day Universe, and other areas, including condensed matter physics. Transitions between the topologically distinct vacuum sectors induce a chiral asymmetry in hot quark–gluon matter via a process analogous to the baryogenesis in the early Universe. This may soon be detected in heavy-ion collisions through the chiral magnetic effect.
Current Account Determinants for Oil-Exporting Countries

The paper characterizes the main determinants of the medium-term current account balance for oil-exporting countries using dynamic panel estimation techniques. It includes a large number of oil-exporting countries and extends the specifications commonly used in the literature to include an oil wealth variable as well as a proxy for the degree of maturity in oil production. The results reveal that factors that matter in determining the equilibrium current account balance of oil-exporting counties are fiscal balance, oil balance, oil wealth, age dependency, economic growth, and degree of oil production-related imports.
Training Strategies to Handle Missing Modalities for Audio-Visual Expression Recognition

Automatic audio-visual expression recognition can play an important role in communication services such as tele-health, VOIP calls and human-machine interaction. Accuracy of audio-visual expression recognition could benefit from the interplay between the two modalities. However, most audio-visual expression recognition systems, trained in ideal conditions, fail to generalize in real world scenarios where either the audio or visual modality could be missing due to a number of reasons such as limited bandwidth, interactors' orientation, caller initiated muting. This paper studies the performance of a state-of-the art transformer when one of the modalities is missing. We conduct ablation studies to evaluate the model in the absence of either modality. Further, we propose a strategy to randomly ablate visual inputs during training at the clip or frame level to mimic real world scenarios. Results conducted on in-the-wild data, indicate significant generalization in proposed models trained on missing cues, with gains up to 17% for frame level ablations, showing that these training strategies cope better with the loss of input modalities.
Linear resolutions over Koszul complexes and Koszul homology algebras

Abstract Let R be a standard graded commutative algebra over a field k, let K be its Koszul complex viewed as a differential graded k-algebra, and let H be the homology algebra of K. This paper studies the interplay between homological properties of the three algebras R, K, and H. In particular, we introduce two definitions of Koszulness that extend the familiar property originally introduced by Priddy: one which applies to K (and, more generally, to any connected differential graded k-algebra) and the other, called strand-Koszulness, which applies to H. The main theoretical result is a complete description of how these Koszul properties of R, K, and H are related to each other. This result shows that strand-Koszulness of H is stronger than Koszulness of R, and we include examples of classes of algebras which have Koszul homology algebras that are strand-Koszul.
Interpretable Safety Validation for Autonomous Vehicles

An open problem for autonomous driving is how to validate the safety of an autonomous vehicle in simulation. Automated testing procedures can find failures of an autonomous system but these failures may be difficult to interpret due to their high dimensionality and may be so unlikely as to not be important. This work describes an approach for finding interpretable failures of an autonomous system. The failures are described by signal temporal logic expressions that can be understood by a human, and are optimized to produce failures that have high likelihood. Our methodology is demonstrated for the safety validation of an autonomous vehicle in the context of an unprotected left turn and a crosswalk with a pedestrian. Compared to a baseline importance sampling approach, our methodology finds more failures with higher likelihood while retaining interpretability.
From Domain Decomposition to Homogenization Theory

Elliptic boundary value problems with oscillatory coefficients play a key role in the mathematical modelling and simulation of complex multiscale problems, for instance transport processes in porous media or the mechanical analysis of composite and multifunctional materials.
The Impact of Message Passing in Agent-Based Submodular Maximization

Submodular maximization problems are a relevant model set for many real-world applications. Since these problems are generally NP-Hard, many methods have been developed to approximate the optimal solution in polynomial time. One such approach uses an agent-based greedy algorithm, where the goal is for each agent to choose an action from its action set such that the union of all actions chosen is as high-valued as possible. Recent work has shown how the performance of the greedy algorithm degrades as the amount of information shared among the agents decreases, whereas this work addresses the scenario where agents are capable of sharing more information than allowed in the greedy algorithm. Specifically, we show how performance guarantees increase as agents are capable of passing messages, which can augment the allowable decision set for each agent. Under these circumstances, we show a near-optimal method for message passing, and how much such an algorithm could increase performance for any given problem instance.
The Original Understanding of Constitutional Legitimacy

This Article argues that three influential schools of originalism, which we might label as libertarian, progressive, and conservative, adhere to particular understandings of constitutional legitimacy, which then inform their particular constitutional hermeneutics. The Article demonstrates that as originally understood by the Founders, however, constitutional legitimacy depended on all three conceptions advocated by these schools of thought — that is, the Constitution had to protect natural rights, it had to enable self-government, and it had to be ratified by popular sovereignty. Further, the Article gives considerable treatment — remarkably for the first time in the law review literature — to James Madison’s letter in response to Thomas Jefferson’s famous “dead hand of the past” argument, in which we might find an understudied ground for constitutional obedience: prudence. The discussion on the Founders’ original understanding of constitutional legitimacy provides two principal insights: First, it provides us with a more holistic case for constitutional obedience than several modern originalist theories whose narrower theories of legitimacy may be unpersuasive standing alone. Second, it demonstrates that broader hermeneutics are necessary as an originalist matter, or simply because we find the Founders’ understanding more persuasive. The Article will also suggest, in the conclusion, that the more holistic account of constitutional legitimacy might provide a new justification for originalism.
Indexing and Inflation

Abstract Much of the opposition to indexation as a means of adapting to ongoing inflation arises from the view that indexation is itself inflationary. This paper examines the basic for that view in a simple macroeconomic model in which budget deficits are in part financed through the printing of money. It is shown that all aspects of indexing — wage indexation, bond indexation, and tax indexation — tend to increase the impact on the price level of any inflationary shock. However, this association between indexation and inflation is in large part a consequence of the monetary and fiscal policies being followed by the government. Evidence from a cross-section of forty countries on the effects of indexation on the inflationary impact of the oil price shock of 1973–1974 suggests that indexation did not in general increase the inflationary impact of the oil shock. The evidence is, further, consistent with the view that the absence of an excess inflationary effect of indexation is a result of the countries with substantial indexation not having accommodated the oil price shock as much as other countries.
Tracking Terrorist Financing Through SWIFT: When U.S. Subpoenas and Foreign Privacy Law Collide

This Note examines the jurisprudence surrounding production orders that require the ordered party to violate foreign law, using the Terrorist Finance Tracking Program - better known as the SWIFT Program - as a case study. This Note recommends that courts excuse or punish noncompliance with such production orders based solely on the good or bad faith acts of the ordered party. Although this approach will clarify the law in this area, in certain circumstances it may make it more difficult for the United States to obtain information abroad. Consequently, this Note urges the United States to pursue formal and informal information-sharing agreements with its allies in the war on terror.
Manager-Specific Effects on Earnings Guidance: An Analysis of Top Executive Turnovers

We investigate how managers contribute to the provision of earnings guidance by examining the association between top executive turnovers and guidance. Although firm and industry characteristics are important determinants of guidance, we conclude that CEOs participate in firm-level policy decisions, whereas CFOs are involved in the formation or discussion of guidance. Among firms that historically issued frequent guidance, breaks in guidance following CEO turnovers are relatively permanent and are potentially attributable to firm-initiated changes in guidance policy. Breaks following CFO turnovers, however, likely reflect uncertainty on the part of the newly appointed executive—they are concentrated in the two quarters following the turnover, are associated with the background of the newly appointed CFO, and extend to the relative precision of the guidance. Among firms that did not issue guidance historically, we find some evidence that newly appointed externally hired CEOs increase the likelihood of providing guidance.
The topology of overlapping portfolio networks

This paper analyzes the topology of the network of common asset holdings, where nodes represent managed portfolios and edge weights capture the impact of liquidations. Asset holdings data is extracted from the 13F filings. We consider the degree centrality as the degree in the subnetwork of weak links, where weak links are those that lead to significant liquidations. We explore the applications of this network representation to clustering and forecasting. To validate the weight attribution and the threshold used to define the weak links, we show that the degree centrality is correlated with excess returns, and is significant after we control for the Carhart four factors. The network of weak links has a scale free structure, similar to financial networks of balance sheet exposures. Moreover, a small number of clusters, densely linked, concentrate a significant proportion of the portfolios.
Incorporating Literary Methods and Texts in the Teaching of Tort Law

This essay, presented in a Law and Humanities Section panel at the 2012 AALS Annual Meeting, discusses my use of literature to aid and amplify legal analysis in a first-year Torts class. Literary texts and methods helped my students investigate how the law conceives of, and expresses, duties and losses among parties. The course drew on several diverse strands of law-and-literature methodology and it incorporated literary texts and methods into discussions of case law and legal policy to produce analysis that is deeply interdisciplinary. Content and methodology, to the extent they can be satisfactorily decoupled, informed my teaching of Torts in separate ways. First, I incorporated a central literary text that accompanied more traditional legal materials. Second, I required students to engage in close reading and I helped them theorize the act of reading itself. By emphasizing the textually mediated nature of the cases — both as a function of common law’s system of authority through analogy, and as a function of the casebook editors’ choices — I hope to have made clear to students that this is a new type of reading they are doing in law school, and that they are learning to think in new ways. In growing acculturated to legal analysis, law students are learning not just a new language, but a new awareness of how and why they read the way they do.The paper includes an appendix listing some discussion questions for The Sweet Hereafter, by Russell Banks, one of the texts I used in the class.