cssi/SciSciGPT-SciSciNet huggingface dataset:
MAGNETIC INTERACTIONS IN COALESCING NEUTRON STAR BINARIES

It is expected on both evolutionary and empirical grounds that many merging neutron star (NS) binaries are composed of a highly magnetized NS in orbit with a relatively low magnetic field NS. I study the magnetic interactions of these binaries using the framework of a unipolar inductor model. The electromotive force generated across the non-magnetic NS as it moves through the magnetosphere sets up a circuit connecting the two stars. The exact features of this circuit depend on the uncertain resistance in the space between the stars R_(space). Nevertheless, I show that there are interesting observational and/or dynamical effects irrespective of its exact value. When R_(space) is large, electric dissipation as great as ~10^(46) erg s^(–1) (for magnetar-strength fields) occurs in the magnetosphere, which would exhibit itself as a hard X-ray precursor in the seconds leading up to merger. With less certainty, there may also be an associated radio transient. When R_(space) is small, electric dissipation largely occurs in the surface layers of the magnetic NS. This can reach ~10^(49) erg s^(–1) during the final ~1 s before merger, similar to the energetics and timescales of short gamma-ray bursts. In addition, for dipole fields greater than ≈10^(12) G and a small R_(space), magnetic torques spin up the magnetized NS. This drains angular momentum from the binary and accelerates the inspiral. A faster coalescence results in less orbits occurring before merger, which would impact matched-filtering gravitational-wave searches by ground-based laser interferometers and could create difficulties for studying alternative theories of gravity with compact inspirals.
A UNIFIED MONTE CARLO TREATMENT OF GAS-GRAIN CHEMISTRY FOR LARGE REACTION NETWORKS. II. A MULTIPHASE GAS-SURFACE-LAYERED BULK MODEL

The observed gas-phase molecular inventory of hot cores is believed to be significantly impacted by the products of chemistry in interstellar ices. In this study, we report the construction of a full macroscopic Monte Carlo model of both the gas-phase chemistry and the chemistry occurring in the icy mantles of interstellar grains. Our model treats icy grain mantles in a layer-by-layer manner, which incorporates laboratory data on ice desorption correctly. The ice treatment includes a distinction between a reactive ice surface and an inert bulk. The treatment also distinguishes between zeroth- and first-order desorption, and includes the entrapment of volatile species in more refractory ice mantles. We apply the model to the investigation of the chemistry in hot cores, in which a thick ice mantle built up during the previous cold phase of protostellar evolution undergoes surface reactions and is eventually evaporated. For the first time, the impact of a detailed multilayer approach to grain mantle formation on the warm-up chemistry is explored. The use of a multilayer ice structure has a mixed impact on the abundances of organic species formed during the warm-up phase. For example, the abundance of gaseous HCOOCH3 is lower in the multilayer model than in previous grain models that do not distinguish between layers (so-called two phase models). Other gaseous organic species formed in the warm-up phase are affected slightly. Finally, we find that the entrapment of volatile species in water ice can explain the two-jump behavior of H2CO previously found in observations of protostars.
Relativistic Components of the Ultra-fast Outflow in the Quasar PDS 456 from Chandra/HETGS, NuSTAR, and XMM-Newton Observations

We present the spectral analysis of Chandra/HETGS and NuSTAR observations of the quasar PDS 456 from 2015, and XMM-Newton and NuSTAR archival data from 2013-2014, together with Chandra/HETGS data from 2003. We analyzed these three different epochs in a consistent way, looking for absorption features corresponding to highly ionized blueshifted absorption lines from H-like and He-like ions of iron (and nickel), as well as of other elements (O, Ne, Si, and S) in the soft band. We confirm the presence of a persistent ultra-fast outflow (UFO) with a velocity of v_out=-0.24 - -0.29c, previously detected. We also report the detection of an additional faster component of the UFO with a relativistic velocity of v_out=-0.48c. We implemented photoionization modeling, using XSTAR analytic model warmabs, to characterize the physical properties of the different kinematic components of the ultra-fast outflow and of the partial covering absorber detected in PDS 456. These two relativistic components of the ultra-fast outflow observed in the three epochs analyzed in this paper are powerful enough to impact the host galaxy of PDS 456 through AGN feedback.
TIDAL EVOLUTION OF CLOSE-IN EXTRASOLAR PLANETS: HIGH STELLAR Q FROM NEW THEORETICAL MODELS

In recent years it has been shown that the tidal coupling between extrasolar planets and their stars could be an important mechanism leading to orbital evolution. Both the tides the planet raises on the star and vice versa are important and dissipation efficiencies ranging over four orders of magnitude are being used. In addition, the discovery of extrasolar planets extremely close to their stars has made it clear that the estimates of the tidal quality factor, Q, of the stars based on Jupiter and its satellite system and on main-sequence binary star observations are too low, resulting in lifetimes for the closest planets orders of magnitude smaller than their age. We argue that those estimates of the tidal dissipation efficiency are not applicable for stars with spin periods much longer than the extrasolar planets' orbital period. We address the problem by applying our own values for the dissipation efficiency of tides, based on our numerical simulations of externally perturbed volumes of stellar-like convection. The range of dissipation we find for main-sequence stars corresponds to stellar Q{sub *} of 10{sup 8} to 3 x 10{sup 9}. The derived orbit lifetimes are comparable to or much longer than the ages of themore » observed extrasolar planetary systems. The predicted orbital decay transit timing variations due to the tidal coupling are below the rate of ms yr{sup -1} for currently known systems, but within reach of an extended Kepler mission provided such objects are found in its field.« less
Vector Bosons in the Randall-Sundrum 2 and Lykken-Randall models and unparticles

Unparticle behavior is shown to be realized in the Randall-Sundrum 2 (RS 2) and the Lykken-Randall (LR) brane scenarios when brane-localized Standard Model currents are coupled to a massive vector field living in the five-dimensional warped background of the RS 2 model. By the AdS/CFT dictionary these backgrounds exhibit certain properties of the unparticle CFT at large Nc and strong ’t Hooft coupling. Within the RS 2 model we also examine and contrast in detail the scalar and vector position-space correlators at intermediate and large distances. Unitarity of brane-to-brane scattering amplitudes is seen to imply a necessary and sufficient condition on the positivity of the bulk mass, which leads to the well-known unitarity bound on vector operators in a CFT.
The Universal Gas Mass Fraction in Clusters of Galaxies

We obtained a deep 150 ks Chandra observation of the optically selected cluster of galaxies, RCS 2318+0034, to investigate the gas mass fraction in this system. Combining our deep Chandra observation with an archival 50 ks observation, we derive gas mass fractions of f gas = 0.06 ± .02 and 0.10 ± .02 within r 2500 and r 500, respectively. The gas mass fraction in RCS 2318+0034 within r 500 is typical of X-ray-selected clusters. Further study shows that the large-scale properties of RCS 2318+0034, including the relations between gas mass, X-ray luminosity, and gas temperature, are also consistent with the observed correlations of X-ray-selected clusters. However, the gas mass fraction within r 2500 is less than most X-ray-selected clusters, as previously reported. The deep Chandra image of RCS 2318+0034 shows that this system is currently undergoing a major merger which may have an impact on the inferred gas mass fraction within r 2500.
Star Clusters in the Galactic Anticenter Stellar Structure and the Origin of Outer Old Open Clusters

The Galactic anticenter stellar structure (GASS) has been identified with excess surface densities of field stars in several large-area sky surveys and with an unusual, stringlike grouping of five globular clusters. At least two of these are diffuse, young "transitional" clusters between open and globular types. Here we call attention to the fact that four younger open or transitional clusters extend the previously identified, stringlike cluster grouping, with at least one having a radial velocity consistent with the previously found GASS velocity-longitude trend. All nine clusters lie close to a plane tipped 17° to the Galactic plane. This planar orientation is used to forage for additional potential cluster members in the inner Galaxy, and a number are found along the same plane and stringlike sequence, including almost all 15 known outer, old open clusters. Tidal accretion of a dwarf satellite galaxy on a low-inclination orbit—perhaps the GASS system—appears to be a plausible explanation for the origin of the outer, old open and transitional clusters of the Milky Way. We use these clusters to explore the age-metallicity relation of the putative accreted GASS progenitor. Finally, we provide the first radial velocity of a star in the cluster BH 176 and discuss its implications.
The delay time of gravitational wave – gamma-ray burst associations

The first gravitational wave (GW) — gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by ∼1.7 s with respect to the merger time of the GW signal. We generally discuss the astrophysical origin of the delay time, Δt, of GW-GRB associations within the context of compact binary coalescence (CBC) — short GRB (sGRB) associations and GW burst — long GRB (lGRB) associations. In general, the delay time should include three terms, the time to launch a clean (relativistic) jet, Δtjet; the time for the jet to break out from the surrounding medium, Δtbo; and the time for the jet to reach the energy dissipation and GRB emission site, ΔtGRB. For CBC-sGRB associations, Δtjet and Δtbo are correlated, and the final delay can be from 10 ms to a few seconds. For GWB-lGRB associations, Δtjet and Δtbo are independent. The latter is at least ∼10 s, so that Δt of these associations is at least this long. For certain jet launching mechanisms of lGRBs, Δt can be minutes or even hours long due to the extended engine waiting time to launch a jet. We discuss the cases of GW170817/GRB 170817A and GW150914/GW150914-GBM within this theoretical framework and suggest that the delay times of future GW/GRB associations will shed light into the jet launching mechanisms of GRBs.
Love is patient: People are more willing to wait for things they like

How does liking of a target affect patience? One possibility is that the more people like a target the less patient they are for it, because it is more difficult to resist the attractive smaller-sooner option to wait for the larger-later option. However, across six studies (N = 2,774), we found evidence for the opposite effect. Specifically, an increase in liking was correlated with an increase in patience (Study 1), and when people made decisions about a target they liked more, they were more willing to wait for a better quality version of it (Studies 2 and 3) and a larger amount of it (Study 4). This is because when people like a target more, they perceive a greater difference in subjective value between its smaller-sooner and larger-later versions. Thus, the perceived difference in subjective value mediated the effect of liking on patience (Study 5). Further, consistent with this proposed mechanism, we found that liking increased both willingness to wait for a better quality version of a target and willingness to pay to receive the target sooner (Study 6). These findings suggest that patience, in part, results from believing the larger-later reward is worth waiting for. These findings also offer practical recommendations for people struggling with impatience: Individuals may benefit from reminding themselves why they like what they are waiting for. (PsycInfo Database Record (c) 2020 APA, all rights reserved).
Temperature dependence of atomic ordering and composition modulation in InAsSbBi grown by molecular beam epitaxy on GaSb substrates

Abstract The structural and optical properties of two 210 nm thick InAsSbBi epilayers grown on (100) GaSb substrates by molecular beam epitaxy at 400 and 280 °C are investigated using X-ray diffraction, Rutherford backscattering spectroscopy, transmission electron microscopy, and photoluminescence spectroscopy. Both samples are free of observable defects. The higher temperature growth results in reduced Bi incorporation, good optical performance, smooth interfaces, and lateral composition modulation of the Bi mole fraction. The lower temperature growth results in near unity Bi incorporation, poor optical performance, interface roughness, and CuPtB -type atomic ordering on the {111}B planes.
Mode-coupling theory for the steady-state dynamics of active Brownian particles.

We present a theory for the steady-state dynamics of a two-dimensional system of spherically symmetric active Brownian particles. The derivation of the theory consists of two steps. First, we integrate out the self-propulsions and obtain a many-particle evolution equation for the probability distribution of the particles’ positions. Second, we use the projection operator technique and a mode-coupling-like factorization approximation to derive an equation of motion for the density correlation function. The nonequilibrium character of the active system manifests itself through the presence of a steady-state correlation function that quantifies spatial correlations of microscopic steady-state currents of the particles. This function determines the dependence of the short-time dynamics on the activity. It also enters into the expression for the memory matrix and thus influences the long-time glassy dynamics.We present a theory for the steady-state dynamics of a two-dimensional system of spherically symmetric active Brownian particles. The derivation of the theory consists of two steps. First, we integrate out the self-propulsions and obtain a many-particle evolution equation for the probability distribution of the particles’ positions. Second, we use the projection operator technique and a mode-coupling-like factorization approximation to derive an equation of motion for the density correlation function. The nonequilibrium character of the active system manifests itself through the presence of a steady-state correlation function that quantifies spatial correlations of microscopic steady-state currents of the particles. This function determines the dependence of the short-time dynamics on the activity. It also enters into the expression for the memory matrix and thus influences the long-time glassy dynamics.
Operation of the 56 MHz superconducting rf cavity in RHIC with higher order mode damper

A 56 MHz superconducting rf cavity was designed and installed in the Relativistic Heavy Ion Collider (RHIC). It is the first superconducting quarter wave resonator (QWR) operating in a high-energy storage ring. We discuss herein a design of the cavity and its key components and the cavity operation with $\mathrm{Au}+\mathrm{Au}$ collisions, and with asymmetrical $\mathrm{Au}+^{3}\mathrm{He}$ collisions. The cavity is a storage cavity, meaning that it becomes active only at the energy of the experiment, after the acceleration cycle is completed. Without beam, the cavity reached 1.93 MV and a ${Q}_{0}$ of $3.0\ifmmode\times\else\texttimes\fi{}{10}^{8}$ after helium conditioning. The cavity voltage was limited at 300 kV with beam operation due to heating in the Higher Order Mode (HOM) coupler. With the cavity operating at 300 kV, an improvement in luminosity was detected from direct measurements, and the bunch length has been reduced. The uniqueness of the QWR necessitated development of an innovative design of the higher order mode dampers with high-pass filters, and a distinctive fundamental mode damper that enables the cavity to be transparent to the beam during acceleration.
Models of random knots

The study of knots and links from a probabilistic viewpoint provides insight into the behavior of “typical” knots, and opens avenues for new constructions of knots and other topological objects with interesting properties. The knotting of random curves arises also in applications to the natural sciences, such as in the context of the structure of polymers. We present here several known and new randomized models of knots and links. We review the main known results on the knot distribution in each model. We discuss the nature of these models and the properties of the knots they produce. Of particular interest to us are finite type invariants of random knots, and the recently studied Petaluma model. We report on rigorous results and numerical experiments concerning the asymptotic distribution of such knot invariants. Our approach raises questions of universality and classification of the various random knot models.
Three Dimensional Simplicial Yang-Mills Theory:. AN Approach to the Mass Gap

There has been substantial progress in recent years in understanding non-abelian Yang-Mills theories. The case of 1 + 1 dimensional Yang-Mills theory is particularly simple and has been solved in the lattice ’, hamiltonian and path integral3 formalisms. We will study here the case of two space and one time dimension, where Karabali et. aL4 have made remarkable progress; for example, they have computed the string tension and given an argument that the ‘magnetic mass’ is non-zero. (The magnetic mass is a quantity that determines the decay of certain gluon correlation functions at spatial infinity). It is our aim here to compute another, more direct, notion of a mass gap: the difference between the lowest two eigenvalues of the hamiltonian. We will do so rigorously within an approximation where the magnetic energy is ignored. It has been argued heuristically5 that the mass gap computed within this approximation is in fact the exact answer for the complete theory. This reduced theory is invariant under conformal transformations of the spatial metric. Our regularization has a discrete version of this symmetry, which allows us to take the continuum limit.(A conformal symmetry also plays an important role in the work of Karabali et al.) Our calculation gives answers that seem to agree with numerical simulations6. The analogous problem in three space and one time dimension is of course more interesting, but substantially more involved, because the ultraviolet divergences are worse; indeed it remains as one of the great challenges
Engineering a Flux-Dependent Mobility Edge in Disordered Zigzag Chains

A tunable transition between metallic and insulating states can appear in a lower-dimensional disordered environment, demonstrating how localization of quantum particles can be controlled through band-structure engineering.
Quantum limits of interferometer topologies for gravitational radiation detection

In order to expand the astrophysical reach of gravitational wave (GW) detectors, several interferometer topologies have been proposed, in the past, to evade the thermodynamic and quantum mechanical limits in future detectors. In this work, we make a systematic comparison among these topologies by considering their sensitivities and complexities. We numerically optimize their sensitivities by introducing a cost function that tries to maximize the broadband improvement over the sensitivity of current detectors. We find that frequency-dependent squeezed-light injection with a 100 m scale filter cavity yields a good broadband sensitivity, with low complexity, and good robustness against optical loss. This study gives us a guideline for the near-term experimental research programs in enhancing the performance of future GW detectors.
DISCOVERY OF RESOLVED DEBRIS DISK AROUND HD 131835

We report the discovery of the resolved disk around HD 131835 and present the analysis and modeling of its thermal emission. HD 131835 is a ∼15 Myr A2 star in the Scorpius–Centaurus OB association at a distance of 122.7- + 12.8 pc . The extended disk has been detected to ~ 1. 5 (200 AU) at 11.7 and 18.3 μm with T-ReCS on Gemini South. The disk is inclined at an angle of ∼75° with the position angle of ∼61°. The flux of the HD 131835 system is 49.3± 7.6 and 84 ± 45 mJy at 11.7 and 18.3 μm, respectively. A model with three grain populations gives a satisfactory fit to both the spectral energy distribution and the images simultaneously. This best-fit model is composed of a hot continuous power-law disk and two rings. We characterized the grain temperature profile and found that the grains in all three populations are emitting at temperatures higher than blackbodies. In particular, the grains in the continuous disk are unusually warm,even when considering small graphite particles as the composition.
CHIP: A Hawkes Process Model for Continuous-time Networks with Scalable and Consistent Estimation

In many application settings involving networks, such as messages between users of an on-line social network or transactions between traders in financial markets, the observed data consist of timestamped relational events, which form a continuous-time network. We propose the Community Hawkes Independent Pairs (CHIP) generative model for such networks. We show that applying spectral clustering to an aggregated adjacency matrix constructed from the CHIP model provides consistent community detection for a growing number of nodes and time duration. We also develop consistent and computationally efficient estimators for the model parameters. We demonstrate that our proposed CHIP model and estimation procedure scales to large networks with tens of thousands of nodes and provides superior fits than existing continuous-time network models on several real networks.
Comparison of Low-Mass and High-Mass Star Formation

I review theoretical models of star formation and how they apply across the stellar mass spectrum. Several distinct theories are under active study for massive star formation, especially Turbulent Core Accretion, Competitive Accretion and Protostellar Mergers, leading to distinct observational predictions. These include the types of initial conditions, the structure of infall envelopes, disks and outflows, and the relation of massive star formation to star cluster formation. Even for Core Accretion models, there are several major uncertainties related to the timescale of collapse, the relative importance of different processes for preventing fragmentation in massive cores, and the nature of disks and outflows. I end by discussing some recent observational results that are helping to improve our understanding of these processes.
ConfuciuX: Autonomous Hardware Resource Assignment for DNN Accelerators using Reinforcement Learning

DNN accelerators provide efficiency by leveraging reuse of activations/weights/outputs during the DNN computations to reduce data movement from DRAM to the chip. The reuse is captured by the accelerator’s dataflow. While there has been significant prior work in exploring and comparing various dataflows, the strategy for assigning on-chip hardware resources (i.e., compute and memory) given a dataflow that can optimize for performance/energy while meeting platform constraints of area/power for DNN(s) of interest is still relatively unexplored. The design-space of choices for balancing compute and memory explodes combinatorially, as we show in this work (e.g., as large as O(1072) choices for running MobileNet-V2), making it infeasible to do manual-tuning via exhaustive searches. It is also difficult to come up with a specific heuristic given that different DNNs and layer types exhibit different amounts of reuse.In this paper, we propose an autonomous strategy called Con-fuciuX to find optimized HW resource assignments for a given model and dataflow style. ConfuciuX leverages a reinforcement learning method, REINFORCE, to guide the search process, leveraging a detailed HW performance cost model within the training loop to estimate rewards. We also augment the RL approach with a genetic algorithm for further fine-tuning. Con-fuciuX demonstrates the highest sample-efficiency for training compared to other techniques such as Bayesian optimization, genetic algorithm, simulated annealing, and other RL methods. It converges to the optimized hardware configuration 4.7 to 24 times faster than alternate techniques.
The Two Most Recent Thermonuclear Supernovae in the Local Group: Radio Constraints on their Progenitors and Evolution

Young supernova remnants (SNRs) provide a unique perspective on supernova (SN) progenitors and connect the late evolution of SNe with the onset of the SNR phase. Here we study SN 1885A and G1.9+0.3, the most recent thermonuclear SNe in the Local Group (with ages $\sim 100$ years) with radio data, which provides a sensitive probe of the SN environment and energetics. We reduce and co-add 4-8 GHz observations from Karl G. Jansky Very Large Array (VLA) to produce the deepest radio image of the M31 central region (RMS noise of 1.3 $\mu$Jy/beam at 6.2 GHz). We detect some diffuse emission near SN 1885A at 2.6 $\sigma$, but the association with SN 1885A is uncertain because diffuse radio emission pervades the M31 central region. The VLA upper limit and HST measurements yield an ambient density, $n_0 < 0.04$ cm$^{-3}$ ($\pm$ 0.03 cm$^{-3}$ due to systematics) for SN 1885A, and kinetic energies, $E_k \sim (1.3-1.7) \times 10^{51}$ ergs for ejecta masses of $1-1.4$ M$_{\odot}$. For the same ejecta mass range, VLA observations of G1.9+0.3 yield $n_0 = 0.18$ cm$^{-3}$, and $E_k = (1-1.3) \times 10^{51}$ ergs. We argue that a sub-Chandrasekhar explosion model may be likely for SN 1885A, in agreement with X-ray studies, but in tension with models for the HST absorption spectra. The analysis of G1.9+0.3 is consistent with both Chandrasekhar and sub-Chandrasekhar SN Ia models, but rules out Type Iax explosions.
Lattice polytopes in coding theory

In this paper we discuss combinatorial questions about lattice polytopes motivated by recent results on minimum distance estimation for toric codes. We also include a new inductive bound for the minimum distance of generalized toric codes. As an application, we give new formulas for the minimum distance of generalized toric codes for special lattice point configurations.
The temperature/entropy connection for horizons, massless particle scattering, and the origin of locality

I explain, in nontechnical terms, the basic ideas of holographic spacetime (HST) models of quantum gravity (QG). The key feature is that the degrees of freedom (DOF) of QG, localized in a finite causal diamond are restrictions of an algebra of asymptotic currents, describing flows of quantum numbers out to null infinity in Minkowski space, with zero energy density on the sphere at infinity. Finite energy density states are constrained states of these DOF and the resulting relation between asymptotic energy and the number of constraints, explains the relation between black hole entropy and energy, as well as the critical energy/impact parameter regime in which particle scattering leads to black hole formation. The results of a general class of models, implementing these principles, are described, and applied to understand the firewall paradox, and to construct a finite model of the early universe, which implements inflation with only the minimal fine-tuning needed to obtain a universe containing localized excitations more complex than large black holes.
Commensurated subgroups, semistability and simple connectivity at infinity

A subgroup Q of a group G is commensurated if the commensurator of Q in G is the entire group G . Our main result is that a finitely generated group G containing an infinite, finitely generated, commensurated subgroup H of infinite index in G is one-ended and semistable at1. Furthermore, if Q and G are finitely presented and either Q is one-ended or the pair .G;Q/ has one filtered end, then G is simply connected at1. A normal subgroup of a group is commensurated, so this result is a generalization of M Mihalik’s result [17] and of B Jackson’s result [11]. As a corollary, we give an alternate proof of V M Lew’s theorem that a finitely generated group G containing an infinite, finitely generated, subnormal subgroup of infinite index is semistable at1. So several previously known semistability and simple connectivity at1 results for group extensions follow from the results in this paper. If W H ! H is a monomorphism of a finitely generated group and . H/ has finite index in H , then H is commensurated in the corresponding ascending HNN extension, which in turn is semistable at1. 20F69; 20F65
LDPC code design for the BPSK-constrained Gaussian wiretap channel

A coding scheme based on irregular low-density parity-check (LDPC) codes is proposed to send secret messages from a source over the Gaussian wiretap channel to a destination in the presence of a wiretapper, with the restriction that the source can send only binary phase-shift-keyed (BPSK) symbols. The secrecy performance of the proposed coding scheme is measured by the secret message rate through the wiretap channel as well as the equivocation rate about the message at the wiretapper. A code search procedure is suggested to obtain irregular LDPC codes that achieve good secrecy performance in such context.
EXTERNAL MASS ACCUMULATION ONTO CORE POTENTIALS: IMPLICATIONS FOR STAR CLUSTERS, GALAXIES, AND GALAXY CLUSTERS

Accretion studies have been focused on the flow around bodies with point mass gravitational potentials, but few general results are available for non-point mass distributions. Here, we study the accretion flow onto non-divergent, core potentials moving through a background medium. We use Plummer and Hernquist potentials as examples to study gas accretion onto star clusters, dwarf and large galaxy halos, and galaxy clusters in a variety of astrophysical environments. The general conditions required for a core potential to collectively accrete large quantities of gas from the external medium are derived using both simulations and analytic results. The consequences of large mass accumulation in galaxy nuclei, dwarf galaxies, and star clusters are twofold. First, if the gas cools effectively star formation can be triggered, generating new stellar members in the system. Second, if the collective potential of the system is able to alter the ambient gas properties before the gas is accreted onto the individual core members, the augmented mass supply rates could significantly alter the state of the various accreting stellar populations and result in an enhanced central black hole accretion luminosity.
Gamma-Ray Emission from Rotation-powered Pulsars

Using a simplified model of cascade pair creation over pulsar polar caps, presented in two previous papers, we investigate the expected γ-ray output from pulsars' low-altitude particle acceleration and pair creation regions. We divide pulsars into several categories, based on which mechanism truncates the particle acceleration off the polar cap, and give estimates for the expected luminosity of each category. We find that inverse Compton scattering above the pulsar polar cap provides the primary γ-rays that initiate the pair cascades in most pulsars. This reduces the expected γ-ray luminosity below previous estimates, which assumed that curvature γ-ray emission was the dominant initiator of pair creation in all pulsars. Even for the brightest pulsars, where curvature radiation sets the height of the pair formation front, we find predicted luminosities too low to explain the EGRET pulsars, suggesting that the source of that emission is an outer magnetosphere accelerator. The predicted polar cap luminosities are high enough, however, to be observable by upcoming γ-ray instruments, providing a firm test for this theory.
Faster search by lackadaisical quantum walk

In the typical model, a discrete-time coined quantum walk searching the 2D grid for a marked vertex achieves a success probability of $$O(1/\log N)$$ in $$O(\sqrt{N \log N})$$ steps, which with amplitude amplification yields an overall runtime of $$O(\sqrt{N} \log N)$$ . We show that making the quantum walk lackadaisical or lazy by adding a self-loop of weight 4 / N to each vertex speeds up the search, causing the success probability to reach a constant near 1 in $$O(\sqrt{N \log N})$$ steps, thus yielding an $$O(\sqrt{\log N})$$ improvement over the typical, loopless algorithm. This improved runtime matches the best known quantum algorithms for this search problem. Our results are based on numerical simulations since the algorithm is not an instance of the abstract search algorithm.
Modeling Heterogeneous Peer Assortment Effects Using Finite Mixture Exponential Random Graph Models

This article develops a class of models called sender/receiver finite mixture exponential random graph models (SRFM-ERGMs). This class of models extends the existing exponential random graph modeling framework to allow analysts to model unobserved heterogeneity in the effects of nodal covariates and network features without a block structure. An empirical example regarding substance use among adolescents is presented. Simulations across a variety of conditions are used to evaluate the performance of this technique. We conclude that unobserved heterogeneity in effects of nodal covariates can be a major cause of misfit in network models, and the SRFM-ERGM approach can alleviate this misfit. Implications for the analysis of social networks in psychological science are discussed.
HRC-SoS: Human Robot Collaboration Experimentation Platform as System of Systems

This paper presents an experimentation platform for human robot collaboration as a system of systems as well as proposes a conceptual framework describing the aspects of Human Robot Collaboration. These aspects are Awareness, Intelligence and Compliance of the system. Based on this framework case studies describing experiment setups performed using this platform are discussed. Each experiment highlights the use of the subsystems such as the digital twin, motion capture system, human-physiological monitoring system, data collection system and robot control and interface systems. A highlight of this paper showcases a subsystem with the ability to monitor human physiological feedback during a human robot collaboration task.
Disentangling by Subspace Diffusion

We present a novel nonparametric algorithm for symmetry-based disentangling of data manifolds, the Geometric Manifold Component Estimator (GEOMANCER). GEOMANCER provides a partial answer to the question posed by Higgins et al. (2018): is it possible to learn how to factorize a Lie group solely from observations of the orbit of an object it acts on? We show that fully unsupervised factorization of a data manifold is possible if the true metric of the manifold is known and each factor manifold has nontrivial holonomy -- for example, rotation in 3D. Our algorithm works by estimating the subspaces that are invariant under random walk diffusion, giving an approximation to the de Rham decomposition from differential geometry. We demonstrate the efficacy of GEOMANCER on several complex synthetic manifolds. Our work reduces the question of whether unsupervised disentangling is possible to the question of whether unsupervised metric learning is possible, providing a unifying insight into the geometric nature of representation learning.
A Mid-infrared Search for Substellar Companions of Nearby Planet-host Stars

Determining the presence of widely separated substellar-mass companion is crucial to understand the dynamics of inner planets in extrasolar planetary systems (e.g., to explain their high mean eccentricity as inner planets are perturbed by the Kozai mechanism). We report the results of our Spitzer/Infrared Array Camera (IRAC) imaging search for widely separated (10''-25'') substellar-mass companions for 14 planet-host stars within 15 pc of the Sun. Using deep 3.6 and 4.5 μm observations in subarray mode, we found one object in the field of 47 UMa with [3.6]–[4.5] color similar to a T5 dwarf, which is, however, unlikely to share common proper motion with 47 UMa. We also found three objects with brown-dwarf-like [3.6]–[4.5] color limits in the fields of GJ 86, HD 160691, and GJ 581, as well as another in the field of HD 69830 for which we have excluded common proper motion. We provide model-based upper mass limits for unseen objects around all stars in our sample, with typical sensitivity to 10 M {sub J} objects from a projected separation of 50-300 AU from the parent star. We also discuss our data analysis methods for point-spread-function subtraction, image co-alignment, and artifact subtraction of IRAC subarray images.
Loss compensation in Metamaterials through embedding of active transistor based negative differential resistance circuits

Dielectric and ohmic losses in metamaterials are known to limit their practical use. In this paper, an all-electronic approach for loss compensation in metamaterials is presented. Each unit cell of the meta-material is embedded with a cross-coupled transistor pair based negative differential resistance circuit to cancel these losses. Design, simulation and experimental results for Split Ring Resonator (SRR) metamaterials with and without loss compensation are presented. Results indicate that the quality factor (Q) of the SRR improves by over 400% at 1.6GHz, showing the effectiveness of the approach. The proposed technique is scalable over a broad frequency range and is limited only by the maximum operating frequency of transistors, which is reaching terahertz in today’s semiconductor technologies.
Privacy-Utility Trade-off of Linear Regression under Random Projections and Additive Noise

Data privacy is an important concern in machine learning, and is fundamentally at odds with the task of training useful learning models, which typically require acquisition of large amounts of private user data. One possible way of fulfilling the machine learning task while preserving user privacy is to train the model on a transformed, noisy version of the data, which does not reveal the data itself directly to the training procedure. In this work, we analyze the privacy-utility tradeoff of two such schemes for the problem of linear regression: additive noise, and random projections. In contrast to previous work, we consider a recently proposed notion of differential privacy that is based on conditional mutual information (MI-DP), which is stronger than the conventional $(\varepsilon,\delta)$ -differential privacy, and use relative objective error as the utility metric. We find that projecting the data to a lower-dimensional subspace before adding noise attains a better trade-off in general. We also make a connection between privacy problem and (non-coherent) SIMO, which has been extensively studied in wireless communication, and use tools from there for the analysis. We present numerical results demonstrating the performance of the schemes.
Giant eruptions of very massive stars

Giant eruptions or supernova-impostor events are far more mysterious than true supernovae. An extreme example can release as much radiative energy as a SN, ejecting several Mʘ of material. These events involve continuous radiation-driven outflows rather than blast waves. They constitute one of the main unsolved problems in stellar astrophysics, but have received little theoretical attention. The most notorious giant-eruption survivor, ƞ Carinae, is amazingly close to us for such a rare event. It offers a wealth of observational clues, many of them quite unexpected in terms of simple theory.
Explaining the prevalence, scaling and variance of urban phenomena

The prevalence of many urban phenomena changes systematically with population size1. We propose a theory that unifies models of economic complexity2,3 and cultural evolution4 to derive urban scaling. The theory accounts for the difference in scaling exponents and average prevalence across phenomena, as well as the difference in the variance within phenomena across cities of similar size. The central ideas are that a number of necessary complementary factors must be simultaneously present for a phenomenon to occur, and that the diversity of factors is logarithmically related to population size. The model reveals that phenomena that require more factors will be less prevalent, scale more superlinearly and show larger variance across cities of similar size. The theory applies to data on education, employment, innovation, disease and crime, and it entails the ability to predict the prevalence of a phenomenon across cities, given information about the prevalence in a single city. Gomez-Lievano and colleagues develop a new theory of scaling in cities — how the prevalence of phenomena such as education and crime changes with population size — by unifying models of economic complexity and cultural evolution.
Robust Estimation of Hypernasality in Dysarthria With Acoustic Model Likelihood Features

Hypernasality is a common characteristic symptom across many motor-speech disorders. For voiced sounds, hypernasality introduces an additional resonance in the lower frequencies and, for unvoiced sounds, there is reduced articulatory precision due to air escaping through the nasal cavity. However, the acoustic manifestation of these symptoms is highly variable, making hypernasality estimation very challenging, both for human specialists and automated systems. Previous work in this area relies on either engineered features based on statistical signal processing or machine learning models trained on clinical ratings. Engineered features often fail to capture the complex acoustic patterns associated with hypernasality, whereas metrics based on machine learning are prone to overfitting to the small disease-specific speech datasets on which they are trained. Here we propose a new set of acoustic features that capture these complementary dimensions. The features are based on two acoustic models trained on a large corpus of healthy speech. The first acoustic model aims to measure nasal resonance from voiced sounds, whereas the second acoustic model aims to measure articulatory imprecision from unvoiced sounds. To demonstrate that the features derived from these acoustic models are specific to hypernasal speech, we evaluate them across different dysarthria corpora. Our results show that the features generalize even when training on hypernasal speech from one disease and evaluating on hypernasal speech from another disease (e.g., training on Parkinson's disease, evaluation on Huntington's disease), and when training on neurologically disordered speech but evaluating on cleft palate speech.
Quo Vadis, Fascinum?

The recent progress in our understanding of heavy‐flavour decays allows us to define more reliably which future measurements on charm decays are needed to further advance our understanding of QCD and to get our theoretical tools ready for treating beauty decays. After sketching the theoretical landscape I list those required measurements. I argue that some—in particular those concerning inclusive semileptonic charm decays and their lepton spectra—can presumably be performed only at a tau‐charm factory.
A new class of non-linear stability preserving operators

We extend Branden's recent proof of a conjecture of Fisk, Stanley, McNamara and Sagan to a new class of non-linear operators that preserve weak Hurwitz stability and the Laguerre–Polya class.
Tropical independence I: Shapes of divisors and a proof of the Gieseker–Petri theorem

We develop a framework to apply tropical and nonarchimedean analytic methods to multiplication maps for linear series on algebraic curves, studying degenerations of these multiplications maps when the special fiber is not of compact type. As an application, we give a new proof of the GiesekerPetri Theorem, including an explicit tropical criterion for a curve over a valued field to be Gieseker-Petri general.
The Stellar Membership of the Taurus Star-forming Region*

The high-precision astrometry from the second data release of the Gaia mission has made it possible to greatly improve the census of members of nearby clusters and associations. I have applied the Gaia data to the Taurus star-forming region, refining the sample of known members and identifying candidates for undiscovered members. The resulting samples of members and candidates provide the best constraints to date on the distribution of ages and the initial mass function (IMF) in Taurus. Several studies over the last 30 years have proposed the existence of a population of older stars (>=10 Myr) that is associated with the Taurus clouds. The data from Gaia demonstrate that such a population does not exist. Meanwhile, previous IMF estimates for small fields surrounding the Taurus aggregates have exhibited a surplus of K7-M0 stars (0.7-0.8 Msun) relative to star-forming clusters like IC 348 and the Orion Nebula Cluster. However, that difference disappears when the new census of the entire region is considered, which should be complete for spectral types earlier than M6-M7 at A_J<1. Thus, there is little variation in the stellar IMF across the 3-4 orders of magnitude in stellar density that are present in nearby star-forming regions. Finally, I note that the proper motions of two previously known members, KPNO 15 and 2MASS J04355209+2255039, indicate that they may have been ejected from the same location within the L1536 cloud ~7200 years ago.
Scaling limits for internal aggregation models with multiple sources

We study the scaling limits of three different aggregation models on ℤ d : internal DLA, in which particles perform random walks until reaching an unoccupied site; the rotor-router model, in which particles perform deterministic analogues of random walks; and the divisible sandpile, in which each site distributes its excess mass equally among its neighbors. As the lattice spacing tends to zero, all three models are found to have the same scaling limit, which we describe as the solution to a certain PDE free boundary problem in ℝ d . In particular, internal DLA has a deterministic scaling limit. We find that the scaling limits are quadrature domains, which have arisen independently in many fields such as potential theory and fluid dynamics. Our results apply both to the case of multiple point sources and to the Diaconis-Fulton smash sum of domains.
Pointed admissible G -covers and G -equivariant cohomological field theories

For any finite group G we define the moduli space of pointed admissible G-covers and the concept of a G-equivariant cohomological field theory (G-CohFT), which, when G is the trivial group, reduces to the moduli space of stable curves and a cohomological field theory (CohFT), respectively. We prove that taking the ‘quotient’ by G reduces a G-CohFT to a CohFT. We also prove that a G-CohFT contains a G-Frobenius algebra, a G-equivariant generalization of a Frobenius algebra, and that the ‘quotient’ by G agrees with the obvious Frobenius algebra structure on the space of G-invariants, after rescaling the metric. We then introduce the moduli space of G-stable maps into a smooth, projective variety X with G action. Gromov–Witten-like invariants of these spaces provide the primary source of examples of G-CohFTs. Finally, we explain how these constructions generalize (and unify) the Chen–Ruan orbifold Gromov–Witten invariants of of Fantechi and Gottsche.