cssi/SciSciGPT-SciSciNet huggingface dataset:
Immersed boundary-finite element model of fluid-structure interaction in the aortic root.

It has long been recognized that aortic root elasticity helps to ensure efficient aortic valve closure, but our understanding of the functional importance of the elasticity and geometry of the aortic root continues to evolve as increasingly detailed in vivo imaging data become available. Herein, we describe a fluid–structure interaction model of the aortic root, including the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the sinotubular junction, that employs a version of Peskin’s immersed boundary (IB) method with a finite element description of the structural elasticity. As in earlier work, we use a fiber-based model of the valve leaflets, but this study extends earlier IB models of the aortic root by employing an incompressible hyperelastic model of the mechanics of the sinuses and ascending aorta using a constitutive law fit to experimental data from human aortic root tissue. In vivo pressure loading is accounted for by a backward displacement method that determines the unloaded configuration of the root model. Our model yields realistic cardiac output at physiological pressures, with low transvalvular pressure differences during forward flow, minimal regurgitation during valve closure, and realistic pressure loads when the valve is closed during diastole. Further, results from high-resolution computations indicate that although the detailed leaflet and root kinematics show some grid sensitivity, our IB model of the aortic root nonetheless produces essentially grid-converged flow rates and pressures at practical grid spacings for the high Reynolds number flows of the aortic root. These results thereby clarify minimum grid resolutions required by such models when used as stand-alone models of the aortic valve as well as when used to provide models of the outflow valves in models of left-ventricular fluid dynamics.
The complexity of identifying Ryu-Takayanagi surfaces in AdS3/CFT2

We present a constructive algorithm for the determination of Ryu-Takayanagi surfaces in AdS_3/CFT_2 which exploits previously noted connections between holographic entanglement entropy and max-flow/min-cut. We then characterize its complexity as a polynomial time algorithm.
Search for axion-like dark matter with ferromagnets

Ultralight axion-like particles are well-motivated dark matter candidates, naturally emerging from theories of physics at ultrahigh energies. Here we report the results of a direct search for electromagnetic interactions of axion-like dark matter in the mass range that spans three decades from 12 peV to 12 neV. The detection scheme is based on a modification of Maxwell’s equations in the presence of axion-like dark matter that mixes with a static magnetic field to produce an oscillating magnetic field. The experiment makes use of toroidal magnets with ferromagnetic powder cores made of an iron–nickel alloy, which enhance the static magnetic field by a factor of 24. Using superconducting quantum interference devices, we achieve magnetic sensitivity of 150 $$\mathrm{aT}\, {\mathrm{Hz}}^{-1/2}$$ , which is at the level of the most sensitive magnetic field measurements demonstrated with any broadband sensor. We recorded 41 h of data and improved the best limits on the magnitude of electromagnetic coupling constant for axion-like dark matter over a part of our mass range, at 20 peV reaching 4.0 × 10−11 GeV−1 (95% confidence level). Our measurements begin to explore the coupling strengths and masses of axion-like particles, where their mixing with photons could explain the anomalous transparency of the Universe to TeV γ-rays. The presence of axion-like dark matter candidates is expected to induce an oscillating magnetic field, enhanced by a ferromagnet. Limits on the electromagnetic coupling strength of axion-like particles are reported over a mass range spanning three decades.
Quantum Entanglement of a Tunneling Spin with Mechanical Modes of a Torsional Resonator

We solve Schrodinger equation describing a tunneling macrospin coupled to a torsional oscillator. Energy spectrum is studied for various quantum regimes. Magnetic susceptibility and noise spectrum are computed. We show that entanglement of the spin with mechanical modes of a subnanometer oscillator results in the decoherence of spin tunneling. For larger oscillators the presence of a tunneling spin can be detected through splitting of the mechanical mode at the resonance. Our results apply to experiments with magnetic molecules coupled to nanoresonators.
On $${\pi}$$-Surfaces of Four-Dimensional Parallelohedra

We show that every four-dimensional parallelohedron P satisfies a recently found condition of Garber, Gavrilyuk & Magazinov sufficient for the Voronoi conjecture being true for P. Namely, we show that for every four-dimensional parallelohedron P the one-dimensional homology group of its $${\pi}$$ -surface is generated by half-belt cycles.
The Stochastic-Calculus Approach to Multi-Receiver Poisson Channels

We study two-receiver Poisson channels using tools derived from stochastic calculus. We obtain a general formula for the mutual information over the Poisson channel that allows for conditioning and the use of auxiliary random variables. We then use this formula to compute necessary and sufficient conditions under which one Poisson channel is less noisy and/or more capable than another, which turn out to be distinct from the conditions under which this ordering holds for the discretized versions of the channels. We also use a general formula to determine the capacity region of the more capable Poisson broadcast channel with independent message sets, the more capable Poisson wiretap channel, and the general two-decoder Poisson broadcast channel with degraded message sets.
Improving the background of gravitational-wave searches for core collapse supernovae: A machine learning approach

Based on the prior O1-O2 observing runs, about 30% of the data collected by Advanced LIGO and Virgo in the next observing runs are expected to be single-interferometer data, i.e., they will be collected at times when only one detector in the network is operating in observing mode. Searches for gravitational wave signals from supernova events do not rely on matched filtering techniques because of the stochastic nature of the signals. If a Galactic supernova occurs during single-interferometer times, separation of its unmodelled gravitational-wave signal from noise will be even more difficult due to lack of coherence between detectors. We present a novel machine learning method to perform single-interferometer supernova searches based on the standard LIGO-Virgo coherentWave-Burst pipeline. We show that the method may be used to discriminate Galactic gravitational-wave supernova signals from noise transients, decrease the false alarm rate of the search, and improve the supernova detection reach of the detectors.
Power allocation with stackelberg game in femtocell networks: A self-learning approach

This paper investigates the energy-efficient power allocation for a two-tier, underlaid femtocell network. The behaviors of the Macrocell Base Station (MBS) and the Femtocell Users (FUs) are modeled hierarchically as a Stackelberg game. The MBS guarantees its own QoS requirement by charging the FUs individually according to the cross-tier interference, and the FUs responds by controlling the local transmit power non-cooperatively. Due to the limit of information exchange in intra- and inter-tiers, a self-learning based strategy-updating mechanism is proposed for each user to learn the equilibrium strategies. In the same Stackelberg-game framework, two different scenarios based on the continuous and discrete power profiles for the FUs are studied, respectively. The self-learning schemes in the two scenarios are designed based on the local best response. By studying the properties of the proposed game in the two situations, the convergence property of the learning schemes is provided. The simulation results are provided to support the theoretical finding in different situations of the proposed game, and the efficiency of the learning schemes is validated.
Optimally fast incremental Manhattan plane embedding and planar tight span construction

We describe a data structure, a rectangular complex, that can be used represent hyperconvex metric spaces that have the same topology (although not necessarily the same distance function) as subsets of the plane. We show how to use this data structure to construct the tight span of a metric space given as an n × n distance matrix, when the tight span is homeomorphic to a subset of the plane, in time O ( n 2 ), and to add a single point to a planar tight span in time O ( n ). As an application of this construction, we show how to test whether a given ﬁnite metric space embeds isometrically into the Manhattan plane in time O( n 2 ), and add a single point to the space and re-test whether it has such an embedding in time O ( n ).
Cohomology rings of almost-direct products of free groups

An almost-direct product of free groups is an iterated semidirect prod- uct of finitely generated free groups in which the action of the constituent free groups on the homology of one another is trivial. We determine the structure of the coho- mology ring of such a group. This is used to analyze the topological complexity of the associated Eilenberg-MacLane space.
Particle-in-cell modeling of laser Thomson scattering in low-density plasmas at elevated laser intensities

Incoherent Thomson scattering is a non-intrusive technique commonly used for measuring local plasma density. Within low-density, low-temperature plasmas and for sufficient laser intensity, the laser may perturb the local electron density via the ponderomotive force, causing the diagnostic to become intrusive and leading to erroneous results. A theoretical model for this effect is validated numerically via kinetic simulations of a quasi-neutral plasma using the particle-in-cell technique.
Shift symmetries in (anti) de Sitter space

We construct a class of extended shift symmetries for fields of all integer spins in de Sitter (dS) and anti-de Sitter (AdS) space. These generalize the shift symmetry, galileon symmetry, and special galileon symmetry of massless scalars in flat space to all symmetric tensor fields in (A)dS space. These symmetries are parametrized by generalized Killing tensors and exist for fields with particular discrete masses corresponding to the longitudinal modes of massive fields in partially massless limits. We construct interactions for scalars that preserve these shift symmetries, including an extension of the special galileon to (A)dS space, and discuss possible generalizations to interacting massive higher-spin particles.
Reconstruction for Liquid Argon TPC Neutrino Detectors Using Parallel Architectures

Neutrinos are particles that interact rarely, so identifying them requires large detectors which produce lots of data. Processing this data with the computing power available is becoming more difficult as the detectors increase in size to reach their physics goals. In liquid argon time projection chambers (TPCs) the charged particles from neutrino interactions produce ionization electrons which drift in an electric field towards a series of collection wires, and the signal on the wires is used to reconstruct the interaction. The MicroBooNE detector currently collecting data at Fermilab has 8000 wires, and planned future experiments like DUNE will have 100 times more, which means that the time required to reconstruct an event will scale accordingly. Modernization of liquid argon TPC reconstruction code, including vectorization, parallelization and code portability to GPUs, will help to mitigate these challenges. The liquid argon TPC hit finding algorithm within the LArSoft framework used across multiple experiments has been vectorized and parallelized. This increases the speed of the algorithm on the order of ten times within a standalone version on Intel architectures. This new version has been incorporated back into LArSoft so that it can be generally used. These methods will also be applied to other low-level reconstruction algorithms of the wire signals such as the deconvolution. The applications and performance of this modernized liquid argon TPC wire reconstruction will be presented.
Anatomy of a Periodically Driven p-Wave Superconductor

The topological properties of periodically driven many-body systems often have no static analogs and defy a simple description based on the effective Hamiltonian. To explore the emergent edge modes in driven p-wave superconductors in two dimensions, we analyze a toy model of Kitaev chains (one-dimensional spinless p-wave superconductors with Majorana edge states) coupled by time-periodic hopping. We show that with proper driving, the coupled Kitaev chains can turn into a fully gapped superconductor which is analogous to the $p_x+ip_y$ state but has two, rather than one, chiral edge modes. A different driving protocol turns it into a gapless superconductor with isolated point nodes and completely flat edge states at quasienergy $\omega=0$ or $\pi/T$, with $T$ the driving period. The time evolution operator $U(k_x,k_y,t)$ of the toy model is computed exactly to yield the phase bands. And the "topological singularities" of the phase bands are exhausted and compared to those of a periodically driven Hofstadter model which features counter-propagating chiral edge modes. These examples demonstrate the unique edge states in driven superconducting systems and suggest driving as a potentially fruitful route to engineer new topological superconductors.
Correlators of mixed symmetry operators in defect CFTs

We use the embedding formalism technique to study correlation functions of a d-dimensional Euclidean CFT in the presence of a q co-dimensional defect. The defect breaks the global conformal group SO(d + 1, 1) into SO(d − q + 1, 1) × SO(q). We calculate all possible invariant structures that can appear in one-point, two-point and three-point correlation functions of bulk and defect operators in mixed symmetry representation. Their generalization to n-point correlation functions are also worked out. Correlation functions in the presence of a defect, in arbitrary representation of SO(q), are also calculated.
Turbulent Disks are Never Stable: Fragmentation and Turbulence-promoted Planet Formation

A fundamental assumption in our understanding of disks is that when the Toomre Q ≫ 1, the disk is stable against fragmentation into self-gravitating objects (and so cannot form planets via direct collapse). But if disks are turbulent, this neglects a spectrum of stochastic density fluctuations that can produce rare, high-density mass concentrations. Here, we use a recently developed analytic framework to predict the statistics of these fluctuations, i.e., the rate of fragmentation and mass spectrum of fragments formed in a turbulent Keplerian disk. Turbulent disks are never completely stable: we calculate the (always finite) probability of forming self-gravitating structures via stochastic turbulent density fluctuations in such disks. Modest sub-sonic turbulence above Mach number M ~ 0.1 can produce a few stochastic fragmentation or "direct collapse" events over ~Myr timescales, even if Q ≫ 1 and cooling is slow (t_cool ≫ t_orbit). In transsonic turbulence this extends to Q ~ 100. We derive the true Q-criterion needed to suppress such events, which scales exponentially with Mach number. We specify to turbulence driven by magneto-rotational instability, convection, or spiral waves and derive equivalent criteria in terms of Q and the cooling time. Cooling times ≳ 50 t_dyn may be required to completely suppress fragmentation. These gravo-turbulent events produce mass spectra peaked near ~(Q M_disk/M*)^(2) M_disk (rocky-to-giant planet masses, increasing with distance from the star). We apply this to protoplanetary disk models and show that even minimum-mass solar nebulae could experience stochastic collapse events, provided a source of turbulence.
The Coevolution of Massive Quiescent Galaxies and Their Dark Matter Halos over the Last 6 Billion Years

We investigate the growth of massive quiescent galaxies at $z<0.6$ based on the Sloan Digital Sky Survey and the Smithsonian Hectospec Lensing Survey---two magnitude limited spectroscopic surveys of high data quality and completeness. Our three parameter model links quiescent galaxies across cosmic time by self-consistently evolving stellar mass, stellar population age sensitive $D_n4000$ index, half-light radius and stellar velocity dispersion. Stellar velocity dispersion is a robust proxy of dark matter halo mass; we use it to connect galaxies and dark matter halos and thus empirically constrain their coevolution. The typical rate of stellar mass growth is $\sim \! 10 \,\, M_\odot \,\, \mathrm{yr}^{-1}$ and dark matter growth rates from our empirical model are remarkably consistent with N-body simulations. Massive quiescent galaxies grow by minor mergers with dark matter halos of mass $10^{10} \,\, M_\odot \lesssim M_{DM} \lesssim 10^{12} \,\, M_\odot$ and evolve parallel to the stellar mass-halo mass relation based on N-body simulations. Thus, the stellar mass-halo mass relation of massive galaxies apparently results primarily from dry minor merging.
On the Non-Kolmogorov Nature of Flare-productive Solar Active Regions

A magnetic power spectral analysis is performed on 53 solar active regions, observed from 2011 August to 2012 July. Magnetic field data obtained from the Helioseismic and Magnetic Imager, inverted as Active Region Patches, are used to study the evolution of the magnetic power index as each region rotates across the solar disk. Active regions are classified based on the numbers and sizes of solar flares they produce in order to study the relationship between flare productivity and the magnetic power index. The choice of window size and inertial range plays a key role in determining the correct magnetic power index. The overall distribution of magnetic power indices has a range of 1.0–2.5. Flare-quiet regions peak at a value of 1.6. However, flare-productive regions peak at a value of 2.2. Overall, the histogram of the distribution of power indices of flare-productive active regions is well separated from flare-quiet active regions. Only 12% of flare-quiet regions exhibit an index greater than 2, whereas 90% of flare-productive regions exhibit an index greater than 2. Flare-quiet regions exhibit a high temporal variance (i.e., the index fluctuates between high and low values), whereas flare-productive regions maintain an index greater than 2 for several days. This shows the importance of including the temporal evolution of active regions in flare prediction studies, and highlights the potential of a 2–3 day prediction window for space weather applications.
Unsteady fluid-structure interactions in a soft-walled microchannel: A one-dimensional lubrication model for finite Reynolds number

What happens when a fluid is pumped into a soft microchannel with height as small as the diameter of a human hair? The microchannel inflates under the flow pressure, while the flow within is affected by the resistance of the wall to deformation. We develop a mathematical model and simulate the ensuing fluid--structure interaction. Even after complex oscillations of the channel wall, we show that the final inflated state is stable. Our model highlights the parameter sets that determine the steady state wall deformation and hydrodynamic pressure distribution across a wide range of systems.
Time-sliced quantum circuit partitioning for modular architectures

Current quantum computer designs will not scale. To scale beyond small prototypes, quantum architectures will likely adopt a modular approach with clusters of tightly connected quantum bits and sparser connections between clusters. We exploit this clustering and the statically-known control flow of quantum programs to create tractable partitioning heuristics which map quantum circuits to modular physical machines one time slice at a time. Specifically, we create optimized mappings for each time slice, accounting for the cost to move data from the previous time slice and using a tunable lookahead scheme to reduce the cost to move to future time slices. We compare our approach to a traditional statically-mapped, owner-computes model. Our results show strict improvement over the static mapping baseline. We reduce the non-local communication overhead by 89.8% in the best case and by 60.9% on average. Our techniques, unlike many exact solver methods, are computationally tractable.
Deep Neural Network Compression for Aircraft Collision Avoidance Systems

One approach to designing decision-making logic for an aircraft collision avoidance system frames the problem as a Markov decision process and optimizes the system using dynamic programming. The re...
Scattering Study of Pulsars below 100 MHz Using LWA1

Interstellar scattering causes pulsar profiles to grow asymmetrically, thus affecting the pulsar timing residuals, and is strongest at lower frequencies. Different Interstellar medium models predict different frequency ($\nu$) and dispersion measure (DM) dependencies for the scattering time-scale $\tau_{sc}$. For Gaussian inhomogeneity the expected scaling relation is $\tau_{sc} \propto \nu^{-4}\ DM^{2}$, while for a Kolmogorov distribution of irregularities, the expected relation is $\tau_{sc} \propto \nu^{-4.4}\ DM^{2.2}$. Previous scattering studies show a wide range of scattering index across all ranges of DM. A scattering index below 4 is believed to be either due to limitations of the underlying assumptions of the thin screen model or an anisotropic scattering mechanism. We present a study of scattering for seven nearby pulsars (DM $< 50$ pc cm$^{-3}$) observed at low frequencies ($10-88$ MHz), using the first station of the Long Wavelength Array (LWA1). We examine the scattering spectral index and DM variation over a period of about three years. The results yield insights into the small-scale structure of ISM as well as the applicability of the thin screen model for low DM pulsars.
Maximization of Laplace−Beltrami eigenvalues on closed Riemannian surfaces

Let ( M,g ) be a connected, closed, orientable Riemannian surface and denote by λ k ( M,g ) the k th eigenvalue of the Laplace−Beltrami operator on ( M,g ). In this paper, we consider the mapping ( M,g ) → λ k ( M,g ). We propose a computational method for finding the conformal spectrum Λ c k ( M ,[ g 0]), which is defined by the eigenvalue optimization problem of maximizing λ k ( M,g ) for k fixed as g varies within a conformal class [ g 0 ] of fixed volume vol( M,g ) = 1. We also propose a computational method for the problem where M is additionally allowed to vary over surfaces with fixed genus, γ . This is known as the topological spectrum for genus γ and denoted by Λ t k (γ) . Our computations support a conjecture of [N. Nadirashvili, J. Differ. Geom. 61 (2002) 335–340.] that Λ t k (0) = 8π k , attained by a sequence of surfaces degenerating to a union of k identical round spheres. Furthermore, based on our computations, we conjecture that Λ t k (1) = 8π2/√3 + 8π( k − 1) , attained by a sequence of surfaces degenerating into a union of an equilateral flat torus and k − 1 identical round spheres. The values are compared to several surfaces where the Laplace−Beltrami eigenvalues are well-known, including spheres, flat tori, and embedded tori. In particular, we show that among flat tori of volume one, the k th Laplace−Beltrami eigenvalue has a local maximum with value λ k = 4π 2 ⌈ k /2⌉ 2 (⌈ k /2⌉ 2 − 1/4) -1/2 . Several properties are also studied computationally, including uniqueness, symmetry, and eigenvalue multiplicity.
Dirac's method for constraints: an application to quantum wires

We investigate the Hubbard model in the limit U = ∞, which is equivalent to the statistical condition of exclusion of double occupancy. We solve this problem using Dirac's method for constraints. The constraints are solved within the bosonization method. We find that the constraints modify the anomalous commutator. We apply this theory to quantum wires at finite temperatures where the Hubbard interaction is U = ∞. We find that the anomalous commutator induced by the constraints gives rise to the 0.7 anomalous conductance.
Exploring the constraints on cosmological models with CosmoEJS

We introduce new CosmoEJS modules to improve the investigation of the consequences of constraints on the parameter values of cosmological models. We use CosmoMC to fit dark energy models and modified gravity models to recent data from the cosmic microwave background measurements of the Planck satellite, baryon acoustic oscillations, supernovae type Ia, Hubble Parameter H(z) measurements, and redshift space distortions. While the results are in agreement with previous constraints for these models, here, we add an investigation into the statistical fits with CosmoEJS, an interactive Java package of simulations that allow the user to explore the ramifications of choosing various values for the cosmological parameters of a particular model. We visually inspect the plots of the simulated theoretical values for comparisons to the observational values, calculate derived cosmological values, and finally plot the expansion history of cosmological models. These new simulations now include modified gravity cosmological models as well as observations of the growth of structures of galaxies for a more accurate description of the universe's dynamics. The latest version of CosmoEJS is available from this http URL.
EVIDENCE FOR AN EDGE-ON DISK AROUND THE YOUNG STAR MWC 778 FROM INFRARED IMAGING AND POLARIMETRY

MWC 778 is an unusual and little-studied young stellar object located in the IC 2144 nebula. Recent spectroscopy by Herbig & Vacca suggested the presence of an edge-on circumstellar disk around it. We present near-infrared adaptive optics imaging polarimetry and mid-infrared imaging which directly confirm the suspected nearly edge-on disk around MWC 778 (i ~ 70°-80°) plus reveal a more extensive envelope pierced by bipolar outflow cavities. In addition, our mid-infrared images and near-infrared polarization maps detect a spiral-shaped structure surrounding MWC 778, with arms that extend beyond 6'' on either side of the star. Although MWC 778 has previously been classified as a Herbig Ae/Be star, the properties of its central source (including its spectral type) remain fairly uncertain. Herbig & Vacca suggested an F or G spectral type based on the presence of metallic absorption lines in the optical spectrum, which implies that MWC 778 may belong to the fairly rare class of intermediate-mass T Tauri Stars (IMTTSs) which are the evolutionary precursors to Herbig Ae/Be objects. Yet its integrated bolometric luminosity, 750 L ☉ (for an assumed distance of 1 kpc) is surprisingly high for an F or G spectral type, even for an IMTTS. We speculate on several possible explanations for this discrepancy, including its true distance being much closer than 1 kpc, the presence of a binary companion, and/or a nonstellar origin for the observed absorption lines.
Stability of a Light Sail Riding on a Laser Beam

The stability of a light sail riding on a laser beam is analyzed both analytically and numerically. Conical sails on Gaussian beams, which have been studied in the past, are shown to be unstable without active control or additional mechanical modifications. A new architecture for a passively stable sail-and-beam configuration is proposed. The novel spherical shell design for the sail is capable of "beam riding" without the need for active feedback control. Full three-dimensional ray-tracing simulations are performed to verify our analytical results.
Gauduchon metrics with prescribed volume form

We prove that on any compact complex manifold one can find Gauduchon metrics with prescribed volume form. This is equivalent to prescribing the Chern–Ricci curvature of the metrics, and thus solves a conjecture of Gauduchon from 1984.
Gravity localization on string-like defects in codimension two and the AdS/CFT correspondence

We study the localization of gravity on string-like defects in codimension two. We point out that the gravity-localizing `local cosmic string' spacetime has an orbifold singularity at the horizon. The supergravity embedding and the AdS/CFT correspondence suggest ways to resolve the singularity. We find two resolutions of the singularity that have a semiclassical gravity description and study their effect on the low-energy physics on the defect. The first resolution leads, at long distances, to a codimension one Randall-Sundrum scenario. In the second case, the infrared physics is like that of a conventional finite-size Kaluza-Klein compactification, with no power-law corrections to the gravitational potential. Similar resolutions apply also in higher codimension gravity-localizing backgrounds.
Effective Soft-Core Potentials and Mesoscopic Simulations of Binary Polymer Mixtures

Mesoscopic molecular dynamics simulations are used to determine the large-scale structure of several binary polymer mixtures of various chemical architecture, concentration, and thermodynamic condi...
A Bit of Information Theory, and the Data Augmentation Algorithm Converges

The data augmentation (DA) algorithm is a simple and powerful tool in statistical computing. In this note basic information theory is used to prove a nontrivial convergence theorem for the DA algorithm.
A Discrete Stochastic Formulation for Reversible Bimolecular Reactions via Diffusion Encounter

The classical models for irreversible diffusion-influenced reactions can be derived by introducing absorbing boundary conditions to over-damped continuous Brownian motion (BM) theory. As there is a clear corresponding stochastic process, the mathematical description takes both Kolmogorov forward equation for the evolution of the probability distribution function and the stochastic sample trajectories. This dual description is a fundamental characteristic of stochastic processes and allows simple particle based simulations to accurately match the expected statistical behavior. However, in the traditional theory using the back-reaction boundary condition to model reversible reactions with geminate recombinations, several subtleties arise: it is unclear what the underlying stochastic process is, which causes complications in producing accurate simulations; and it is non-trivial how to perform an appropriate discretization for numerical computations. In this work, we derive a discrete stochastic model that recovers the classical models and their boundary conditions in the continuous limit. In the case of reversible reactions, we recover the back-reaction boundary condition, unifying the back-reaction approach with those of current simulation packages. Furthermore, all the complications encountered in the continuous models become trivial in the discrete model. Our formulation brings to attention the question: With computations in mind, can we develop a discrete reaction kinetics model that is more fundamental than its continuous counterpart?
a Closed Bianchi i Universe in String Theory

A special Bianchi I universe is constructed in 4D string theory. Geometrically it represents a 3D anti-de-Sitter space crossed with a flat direction whereas in terms of an associated conformal field theory it is an extremal case of a gauged WZWN theory with target the coset SU(1,1)×R2/R. Some of its properties are discussed.
Plato's cave and differential forms

Author(s): Manin, Fedor | Abstract: In the 1970s and again in the 1990s, Gromov gave a number of theorems and conjectures motivated by the notion that the real homotopy theory of compact manifolds and simplicial complexes influences the geometry of maps between them. The main technical result of this paper supports this intuition: we show that maps of differential algebras are closely shadowed, in a technical sense, by maps between the corresponding spaces. As a concrete application, we prove the following conjecture of Gromov: if $X$ and $Y$ are finite complexes with $Y$ simply connected, then there are constants $C(X,Y)$ and $p(X,Y)$ such that any two homotopic $L$-Lipschitz maps have a $C(L+1)^p$-Lipschitz homotopy (and if one of the maps is a constant, $p$ can be taken to be $2$.) We hope that it will lead more generally to a better understanding of the space of maps from $X$ to $Y$ in this setting.
A Reconstruction Theorem for Almost-Commutative Spectral Triples

We propose an expansion of the definition of almost-commutative spectral triple that accommodates non-trivial fibrations and is stable under inner fluctuation of the metric, and then prove a reconstruction theorem for almost-commutative spectral triples under this definition as a simple consequence of Connes's reconstruction theorem for commutative spectral triples. Along the way, we weaken the orientability hypothesis in the reconstruction theorem for commutative spectral triples, and following Chakraborty and Mathai, prove a number of results concerning the stability of properties of spectral triples under suitable perturbation of the Dirac operator.
The Compressional Beta Effect: Analytical Solution, Numerical Benchmark, and Data Analysis

This study derives a complete set of equatorially confined wave solutions from an anelastic equation set with the complete Coriolis terms, which include both the vertical and meridional planetary vorticity. The propagation mechanism can change with the effective static stability. When the effective static stability reduces to neutral, buoyancy ceases, but the role of buoyancy as an eastward-propagation mechanism is replaced by the compressional beta effect, i.e., vertical density-weighted advection of the meridional planetary vorticity. For example, the Kelvin mode becomes a compressional Rossby mode. Compressional Rossby waves are meridional vorticity disturbances that propagate eastward owing to the compressional beta effect. The compressional Rossby wave solutions can serve as a benchmark to validate the implementation of the nontraditional Coriolis terms (NCTs) in numerical models; with an effectively neutral condition and initial large-scale disturbances given a half vertical wavelength spanning the troposphere on Earth, compressional Rossby waves are expected to propagate eastward at a phase speed of 0.24 m s${}^{-1}$. The phase speed increases with the planetary rotation rate and the vertical wavelength and also changes with the density scale height. Besides, the compressional beta effect and the meridional vorticity tendency are reconstructed using reanalysis data and regressed upon tropical precipitation filtered for the Madden$-$Julian oscillation (MJO). The results suggest that the compressional beta effect contributes 10.8% of the meridional vorticity tendency associated with the MJO in terms of the ratio of the minimum values.
Sensitivity of Redshift Distortion Measurements to Cosmological Parameters

The multipole moments of the power spectrum of large-scale structure, observed in redshift space, are calculated for a finite sample volume, incorporating the effects of both the linear velocity field and cosmological geometry. A variance calculation that includes the effects of shot noise is also performed. The sensitivity with which a survey with the depth and geometry of the Sloan Digital Sky Survey (SDSS) can measure cosmological parameters Ω0 and b0 (the bias) or λ0 (the cosmological constant) and b0 is derived by fitting power spectrum moments to the large-scale structure in the linear regime in a way that is independent of the evolution of the galaxy number density. A fiducial model is assumed, and the region of parameter space that can then be excluded to a given confidence limit is determined. In the absence of geometric and evolutionary effects, the ratios of multipole moments (in particular the zeroth and second) are degenerate for models of constant β ≈ Ω0.6/b0. However, this degeneracy is broken by light-cone effects, so that in principle Ω0 and b0 can be measured separately by a deep enough galaxy redshift survey. We find that for surveys of the approximate depth of the SDSS, all models with Ω0 ≤ 1 are acceptable at the 99% confidence limit when a fiducial, open, Ω0 = 0.3 model is assumed and bias is unconstrained. At the 95% limit, Ω0 > 0.85 is ruled out. Furthermore, for this fiducial model, both flat (cosmological constant) and open models are expected to reasonably fit the data. For flat, cosmological constant models with a fiducial Ω0 = 0.3, we find that models with Ω0 > 0.48 are ruled out at the 95% confidence limit regardless of the choice of the bias parameter, and open models cannot fit the data even at the 99% confidence limit. We also find significant deviations in β from the naive estimate for both fiducial models. Thus, we conclude in the case of the SDSS that linear evolution-free statistics alone can strongly distinguish between Ω0 = 1 and low matter density models only for the fiducial cosmological constant model. For the open model, Ω0 = 1 is at best only nominally excluded unless Ω0 < 0.3.
SEDfit: Software for Spectral Energy Distribution Fitting of Photometric Data

This article describes SEDfit, the earliest—but continually upgraded—software package for spectral energy distribution fitting (SED fitting) of high-redshift photometric data, and the only one to properly treat nondetections. The principles of maximum-likelihood SED fitting are described, including formulae used for fitting both detected and undetected (upper limits) photometric data. The internal mechanics of the SEDfit package are presented and several illustrative examples of its use are given. The article concludes with a discussion of several issues and caveats applicable to SED fitting in general.
On the image of the Galois representation associated to a non-CM Hida family

Fix a prime p > 2. Let ρ : Gal(ℚ ¯∕ℚ) → GL2(I) be the Galois representation coming from a non-CM irreducible component I of Hida’s p-ordinary Hecke algebra. Assume the residual representation ρ is absolutely irreducible. Under a minor technical condition we identify a subring I0 of I containing ℤp[[T]] such that the image of ρ is large with respect to I0. That is, Imρ contains ker(SL2(I0) → SL2(I0∕a)) for some nonzero I0-ideal a. This paper builds on recent work of Hida who showed that the image of such a Galois representation is large with respect to ℤp[[T]]. Our result is an I-adic analogue of the description of the image of the Galois representation attached to a non-CM classical modular form obtained by Ribet and Momose in the 1980s.
A Likely Redback Millisecond Pulsar Counterpart of 3FGL J0838.8-2829

We obtained new optical observations of the X-ray source XMMU J083850.38-282756.8, the previously proposed counterpart of the gamma-ray source 3FGL J0838.8-2829. Time-series photometry in the $r'$ band reveals periodic modulation of $\approx1$ magnitude that is characteristic of the heating of the photosphere of a low-mass companion star by a compact object. The measured orbital period is 5.14817$\pm$0.00012 hr. The shape of the light curve is variable, evidently due to the effects of flaring and asymmetric heating. Spectroscopy reveals a companion of type M1 or later, having a radial velocity amplitude of 315$\pm$17 km/s, with period and phasing consistent with the heating interpretation. The mass function of the compact object is 0.69$\pm$0.11 $M_{\odot}$, which allows a neutron star in a high-inclination orbit. Variable, broad H$\alpha$ emission is seen, which is probably associated with a wind from the companion. These properties, as well as the X-ray and gamma-ray luminosities at the inferred distance of <1.7 kpc, are consistent with a redback millisecond pulsar in its non-accreting state. A search for radio pulsations is needed to confirm this interpretation and derive complete system parameters for modeling, although absorption by the ionized wind could hinder such detection.
Learning to Ignore: Long Document Coreference with Bounded Memory Neural Networks

Long document coreference resolution remains a challenging task due to the large memory and runtime requirements of current models. Recent work doing incremental coreference resolution using just the global representation of entities shows practical benefits but requires keeping all entities in memory, which can be impractical for long documents. We argue that keeping all entities in memory is unnecessary, and we propose a memory-augmented neural network that tracks only a small bounded number of entities at a time, thus guaranteeing a linear runtime in length of document. We show that (a) the model remains competitive with models with high memory and computational requirements on OntoNotes and LitBank, and (b) the model learns an efficient memory management strategy easily outperforming a rule-based strategy
PRover: Proof Generation for Interpretable Reasoning over Rules

Recent work by Clark et al. (2020) shows that transformers can act as "soft theorem provers'' by answering questions over explicitly provided knowledge in natural language. In our work, we take a step closer to emulating formal theorem provers, by proposing PRover, an interpretable transformer-based model that jointly answers binary questions over rule-bases and generates the corresponding proofs. Our model learns to predict nodes and edges corresponding to proof graphs in an efficient constrained training paradigm. During inference, a valid proof, satisfying a set of global constraints is generated. We conduct experiments on synthetic, hand-authored, and human-paraphrased rule-bases to show promising results for QA and proof generation, with strong generalization performance. First, PRover generates proofs with an accuracy of 87%, while retaining or improving performance on the QA task, compared to RuleTakers (up to 6% improvement on zero-shot evaluation). Second, when trained on questions requiring lower depths of reasoning, it generalizes significantly better to higher depths (up to 15% improvement). Third, PRover obtains near perfect QA accuracy of 98% using only 40% of the training data. However, generating proofs for questions requiring higher depths of reasoning becomes challenging, and the accuracy drops to 65% for "depth 5", indicating significant scope for future work.
Observational signatures of massive black hole formation in the early Universe

Space telescope observations of massive black holes during their formation may be key to understanding the origin of supermassive black holes and high-redshift quasars. To create diagnostics for their detection and confirmation, we study a simulation of a nascent massive ‘direct-collapse’ black hole that induces a wave of nearby massive metal-free star formation, unique to this seeding scenario and to very high redshifts. Here we describe a series of distinct colours and emission line strengths, dependent on the relative strength of star formation and black hole accretion. We predict that the forthcoming James Webb Space Telescope might be able to detect and distinguish a young galaxy that hosts a direct-collapse black hole in this configuration at redshift 15 with as little as a 20,000-second total exposure time across four filters, critical for constraining the seeding mechanisms and early growth rates of supermassive black holes. We also find that a massive seed black hole produces strong, H2-dissociating Lyman–Werner radiation. The James Webb Space Telescope may detect and distinguish a young galaxy that hosts a direct-collapse black hole and nearby massive metal-free star formation at redshift 15 with as little as a 20,000-second total exposure time across four filters.
Phases of five-dimensional theories, monopole walls, and melting crystals

Moduli spaces of doubly periodic monopoles, also called monopole walls or monowalls, are hyperkahler; thus, when four-dimensional, they are self-dual gravitational instantons. We find all monowalls with lowest number of moduli. Their moduli spaces can be identified, on the one hand, with Coulomb branches of five-dimensional supersymmetric quantum field theories on $ \mathbb{R} $ 3 × T 2 and, on the other hand, with moduli spaces of local Calabi-Yau metrics on the canonical bundle of a del Pezzo surface. We explore the asymptotic metric of these moduli spaces and compare our results with Seiberg’s low energy description of the five-dimensional quantum theories. We also give a natural description of the phase structure of general monowall moduli spaces in terms of triangulations of Newton polygons, secondary polyhedra, and associahedral projections of secondary fans.
Constrained Transport Algorithms for Numerical Relativity. I. Development of a Finite-Difference Scheme

A scheme is presented for accurately propagating the gravitational field constraints in finite-difference implementations of numerical relativity. The method is based on similar techniques used in astrophysical magnetohydrodynamics and engineering electromagnetics and has properties of a finite differential calculus on a four-dimensional manifold. It is motivated by the arguments that (1) an evolutionary scheme that naturally satisfies the Bianchi identities will propagate the constraints and (2) methods in which temporal and spatial derivatives commute will satisfy the Bianchi identities implicitly. The proposed algorithm exactly propagates the constraints in a local Riemann normal coordinate system; i.e., all terms in the Bianchi identities (which all vary as ∂3g) cancel to machine roundoff accuracy at each time step. In a general coordinate basis, these terms and those that vary as ∂g∂2g also can be made to cancel, but differences of connection terms, proportional to (∂g)3, will remain, resulting in a net truncation error. Detailed and complex numerical experiments with four-dimensional staggered grids will be needed to completely examine the stability and convergence properties of this method. If such techniques are successful for finite-difference implementations of numerical relativity, other implementations, such as finite-element (and eventually pseudospectral) techniques, might benefit from schemes that use four-dimensional grids and that have temporal and spatial derivatives that commute.
On the $p$-typical de Rham–Witt complex over $W(k)$

Hesselholt and Madsen (2004) define and study the (absolute, p-typical) de Rham–Witt complex in mixed characteristic, where p is an odd prime. They give as an example an elementary algebraic description of the de Rham–Witt complex over ℤ(p), W⋅Ωℤ(p)∙. The main goal of this paper is to construct, for k a perfect ring of characteristic p>2, a Witt complex over A=W(k) with an algebraic description which is completely analogous to Hesselholt and Madsen’s description for ℤ(p). Our Witt complex is not isomorphic to the de Rham–Witt complex; instead we prove that, in each level, the de Rham–Witt complex over W(k) surjects onto our Witt complex, and that the kernel consists of all elements which are divisible by arbitrarily high powers of p. We deduce an explicit description of WnΩA∙ for each n≥1. We also deduce results concerning the de Rham–Witt complex over certain p-torsion-free perfectoid rings.
A Stackelberg game for multi-period demand response management in the smart grid

This paper studies a multi-period demand response management problem in the smart grid where multiple utility companies compete among themselves. The user-utility interactions are modeled by a noncooperative game of a Stackelberg type where the interactions among the utility companies are captured through a Nash equilibrium. It is shown that this game has a unique Stackelberg equilibrium at which the utility companies set prices to maximize their revenues (within a Nash game) while the users respond accordingly to maximize their utilities subject to their budget constraints. Closed-form expressions are provided for the corresponding strategies of the users and the utility companies. It is shown that the multi-period scheme, compared with the single-period case, provides more incentives for the users to participate in the game. A necessary and sufficient condition on the minimum budget needed for a user to participate is provided.