cssi/SciSciGPT-SciSciNet huggingface dataset:
Observations of Solar Coronal Rain in Null Point Topologies

Coronal rain is the well-known phenomenon in which hot plasma high in the Sun's corona undergoes rapid cooling (from ~106 to <104 K), condenses, and falls to the surface. Coronal rain appears frequently in active region coronal loops and is very common in post-flare loops. This Letter presents discovery observations, which show that coronal rain is ubiquitous in the commonly occurring coronal magnetic topology of a large (~100 Mm scale) embedded bipole very near a coronal hole boundary. Our observed structures formed when the photospheric decay of active-region-leading-sunspots resulted in a large parasitic polarity embedded in a background unipolar region. We observe coronal rain to appear within the legs of closed loops well under the fan surface, as well as preferentially near separatrices of the resulting coronal topology: the spine lines, null point, and fan surface. We analyze three events using SDO Atmospheric Imaging Assembly observations in the 304, 171, and 211 A channels, as well as SDO Helioseismic and Magnetic Imager magnetograms. The frequency of rain formation and the ease with which it is observed strongly suggests that this phenomenon is generally present in null point topologies of this size scale. We argue that these rain events could be explained by the classic process of thermal nonequilibrium or via interchange reconnection at the null; it is also possible that both mechanisms are present. Further studies with higher spatial resolution data and MHD simulations will be required to determine the exact mechanism(s).
Listwise Learning to Rank by Exploring Unique Ratings

In this paper, we propose new listwise learning-to-rank models that mitigate the shortcomings of existing ones. Existing listwise learning-to-rank models are generally derived from the classical Plackett-Luce model, which has three major limitations. (1) Its permutation probabilities overlook ties, i.e., a situation when more than one document has the same rating with respect to a query. This can lead to imprecise permutation probabilities and inefficient training because of selecting documents one by one. (2) It does not favor documents having high relevance. (3) It has a loose assumption that sampling documents at different steps is independent. To overcome the first two limitations, we model ranking as selecting documents from a candidate set based on unique rating levels in decreasing order. The number of steps in training is determined by the number of unique rating levels. More specifically, in each step, we apply multiple multi-class classification tasks to a document candidate set and choose all documents that have the highest rating from the document set. This is in contrast to taking one document step by step in the classical Plackett-Luce model. Afterward, we remove all of the selected documents from the document set and repeat until the remaining documents all have the lowest rating. We propose a new loss function and associated four models for the entire sequence of weighted classification tasks by assigning high weights to the selected documents with high ratings for optimizing Normalized Discounted Cumulative Gain (NDCG). To overcome the final limitation, we further propose a novel and efficient way of refining prediction scores by combining an adapted Vanilla Recurrent Neural Network (RNN) model with pooling given selected documents at previous steps. We encode all of the documents already selected by an RNN model. In a single step, we rank all of the documents with the same ratings using the last cell of the RNN multiple times. We have implemented our models using three settings: neural networks, neural networks with gradient boosting, and regression trees with gradient boosting. We have conducted experiments on four public datasets. The experiments demonstrate that the models notably outperform state-of-the-art learning-to-rank models.
Oxidation of Graphene on Metals

We use low-energy electron microscopy to investigate how graphene is removed from Ru(0001) and Ir(111) by reaction with oxygen. We find two mechanisms on Ru(0001). At short times, oxygen reacts with carbon monomers on the surrounding Ru surface, decreasing their concentration below the equilibrium value. This undersaturation causes a flux of carbon from graphene to the monomer gas. In this initial mechanism, graphene is etched at a rate that is given precisely by the same nonlinear dependence on carbon monomer concentration that governs growth. Thus, during both growth and etching, carbon attaches and detaches to graphene as clusters of several carbon atoms. At later times, etching accelerates. We present evidence that this process involves intercalated oxygen, which destabilizes graphene. On Ir, this mechanism creates observable holes. It also occurs mostly quickly near wrinkles in the graphene islands, depends on the orientation of the graphene with respect to the Ir substrate, and, in contrast to the f...
Hydrodynamic modeling and the QGP shear viscosity

In this article, we will briefly review the recent progress on hydrodynamic modeling and the extraction of the quark-gluon plasma (QGP) specific shear viscosity with an emphasis on the results obtained from the hybrid model VISHNU that couples viscous hydrodynamics for the macroscopic expansion of the QGP to the hadron cascade model for the microscopic evolution of the late hadronic stage.
Bi-Lipschitz embedding of projective metrics

We give a sufficient condition for a projective metric on a subset of a Euclidean space to admit a bi-Lipschitz embedding into Euclidean space of the same dimension.
An Open Catalog for Supernova Data

We present the Open Supernova Catalog, an online collection of observations and metadata for presently 36,000+ supernovae and related candidates. The catalog is freely available on the web (https://sne.space), with its main interface having been designed to be a user-friendly, rapidly searchable table accessible on desktop and mobile devices. In addition to the primary catalog table containing supernova metadata, an individual page is generated for each supernova, which displays its available metadata, light curves, and spectra spanning X-ray to radio frequencies. The data presented in the catalog is automatically rebuilt on a daily basis and is constructed by parsing several dozen sources, including the data presented in the supernova literature and from secondary sources such as other web-based catalogs. Individual supernova data is stored in the hierarchical, human- and machine-readable JSON format, with the entirety of each supernova’s data being contained within a single JSON file bearing its name. The setup we present here, which is based on open-source software maintained via git repositories hosted on github, enables anyone to download the entirety of the supernova data set to their home computer in minutes, and to make contributions of their own data back to the catalog via git. As the supernova data set continues to grow, especially in the upcoming era of all-sky synoptic telescopes, which will increase the total number of events by orders of magnitude, we hope that the catalog we have designed will be a valuable tool for the community to analyze both historical and contemporary supernovae.
The Sherrington-Kirkpatrick Model: An Overview

The goal of this paper is to review some of the main ideas that emerged from the attempts to confirm mathematically the predictions of the celebrated Parisi ansatz in the Sherrington-Kirkpatrick model. We try to focus on the big picture while sketching the proofs of only a few selected results, but an interested reader can find most of the missing details in Panchenko (The Sherrington-Kirkpatrick Model, Manuscript, 2012) and Talagrand (Mean-Field Models for Spin Glasses, Springer, Berlin, 2011).
Aggression Is Induced by Resource Limitation in the Monarch Caterpillar

Summary Food represents a limiting resource for the growth and developmental progression of many animal species. As a consequence, competition over food, space, or other resources can trigger territoriality and aggressive behavior. In the monarch butterfly, Danaus plexippus, caterpillars feed predominantly on milkweed, raising the possibility that access to milkweed is critical for growth and survival. Here, we characterize the role of food availability on aggression in monarch caterpillars and find that monarch caterpillars display stereotyped aggressive lunges that increase during development, peaking during the fourth and fifth instar stages. The number of lunges toward a conspecific caterpillar was significantly increased under conditions of low food availability, suggesting resource defense may trigger aggression. These findings establish monarch caterpillars as a model for investigating interactions between resource availability and aggressive behavior under ecologically relevant conditions and set the stage for future investigations into the neuroethology of aggression in this system.
A MASS-DEPENDENT YIELD ORIGIN OF NEUTRON-CAPTURE ELEMENT ABUNDANCE DISTRIBUTIONS IN ULTRA-FAINT DWARFS

One way to constrain the nature of the high-redshift progenitors of the Milky Way (MW) is to look at the low-metallicity stellar populations of the different Galactic components today. For example, high-resolution spectroscopy of very metal poor (VMP) stars demonstrates remarkable agreement between the distribution of [Ti/Fe] in the stellar populations of the MW halo and ultra-faint dwarf (UFD) galaxies. In contrast, for the neutron-capture (nc) abundance ratio distributions [(Sr, Ba)/Fe], the peak of the small UFD sample (6 stars) exhibits a significant under-abundance relative to the VMP stars in the larger MW halo sample (~300 stars). We present a simple scenario that can simultaneously explain these similarities and differences by assuming: (1) that the MW VMP stars were predominately enriched by a prior generation of stars which possessed a higher total mass than the prior generation of stars that enriched the UFD VMP stars; and (2) a much stronger mass-dependent yield (MDY) for nc-elements than for the (known) MDY for Ti. Simple statistical tests demonstrate that conditions (1) and (2) are consistent with the observed abundance distributions, albeit without strong constraints on model parameters. A comparison of the broad constraints for these nc-MDY with those derived in the literature seems to rule out Ba production from low-mass supernovae (SNe) and affirms models that primarily generate yields from high-mass SNe. Our scenario can be confirmed by a relatively modest (factor of ~3-4) increase in the number of high-resolution spectra of VMP stars in UFDs.
Evaluating Quantum Approximate Optimization Algorithm: A Case Study

Quantum Approximate Optimization Algorithm (QAOA) is one of the most promising quantum algorithms for the Noisy Intermediate-Scale Quantum (NISQ) era. Quantifying the performance of QAOA in the near-term regime is of utmost importance. We perform a large-scale numerical study of the approximation ratios attainable by QAOA is the low-to medium-depth regime. To find good QAOA parameters we perform 990 million 10-qubit QAOA circuit evaluations. We find that the approximation ratio increases only marginally as the depth is increased, and the gains are offset by the increasing complexity of optimizing variational parameters. We observe a high variation in approximation ratios attained by QAOA, including high variations within the same class of problem instances. We observe that the difference in approximation ratios between problem instances increases as the similarity between instances decreases. We find that optimal QAOA parameters concentrate for instances in out benchmark, confirming the previous findings for a different class of problems.
Some finiteness results for groups of automorphisms of manifolds

We prove that in dimensions not equal to 4, 5, or 7, the homology and homotopy groups of the classifying space of the topological group of diffeomorphisms of a disk fixing the boundary are finitely generated in each degree. The proof uses homological stability, embedding calculus and the arithmeticity of mapping class groups. From this we deduce similar results for the homeomorphisms of $R^n$ and various types of automorphisms of 2-connected manifolds.
Synthetic Spectra of Pair-instability Supernovae in 3D

Pair-Instability Supernovae (PISNe) may signal the deaths of extremely massive stars in the local Universe or massive primordial stars after the end of the Cosmic Dark Ages. Hydrodynamic simulations of these explosions, performed in 1D, 2D, and 3D geometry, have revealed the strong dependence of mixing in the PISN ejecta on dimensionality. This chemical rearrangement is mainly driven by Rayleigh-Taylor instabilities that start to grow shortly after the collapse of the carbon-oxygen core. We investigate the effects of such mixing on the spectroscopic evolution of PISNe by post-processing explosion profiles with the radiation diffusion-equilibrium code SNEC and the implicit Monte Carlo-discrete diffusion Monte Carlo (IMC-DDMC) radiation transport code SuperNu. The first 3D radiation transport calculation of a PISN explosion is presented yielding viewing angle-dependent synthetic spectra and lightcurves. We find that while 2D and 3D mixing does not significantly affect the lightcurves of PISNe, their spectroscopic and color evolution is impacted. Strong features of intermediate mass elements dominated by silicon, magnesium and oxygen appear at different phases and reach different intensities depending on the extent of mixing in the silicon/oxygen interface of the PISN ejecta. On the other hand, we do not find a significant dependence of PISN lightcurves and spectra on viewing angle. Our results showcase the capabilities of SuperNu to handle 3D radiation transport and highlight the importance of modeling time-series of spectra in identifying PISNe with future missions.
Planar Para Algebras, Reflection Positivity

We define a planar para algebra, which arises naturally from combining planar algebras with the idea of \({\mathbb{Z}_{N}}\) para symmetry in physics. A subfactor planar para algebra is a Hilbert space representation of planar tangles with parafermionic defects that are invariant under para isotopy. For each \({\mathbb{Z}_{N}}\), we construct a family of subfactor planar para algebras that play the role of Temperley–Lieb–Jones planar algebras. The first example in this family is the parafermion planar para algebra (PAPPA). Based on this example, we introduce parafermion Pauli matrices, quaternion relations, and braided relations for parafermion algebras, which one can use in the study of quantum information. An important ingredient in planar para algebra theory is the string Fourier transform (SFT), which we use on the matrix algebra generated by the Pauli matrices. Two different reflections play an important role in the theory of planar para algebras. One is the adjoint operator; the other is the modular conjugation in Tomita–Takesaki theory. We use the latter one to define the double algebra and to introduce reflection positivity. We give a new and geometric proof of reflection positivity by relating the two reflections through the string Fourier transform.
Evolution of displacements and strains in sheared amorphous solids

The local deformation of two-dimensional Lennard-Jones glasses under imposed shear strain is studied via computer simulations. Both the mean squared displacement and mean squared strain rise linearly with the length of the strain interval Δγ over which they are measured. However, the increase in displacement does not represent single-particle diffusion. There are long-range spatial correlations in displacement associated with slip lines with an amplitude of order the particle size. Strong dependence on system size is also observed. The probability distributions of displacement and strain are very different. For small Δγ the distribution of displacement has a plateau followed by an exponential tail. The distribution becomes Gaussian as Δγ increases to about 0.03. The strain distributions consist of sharp central peaks associated with elastic regions, and long exponential tails associated with plastic regions. The latter persist to the largest Δγ studied.
Constraining the initial state granularity with bulk observables in Au+Au collisions at \sqrt{s_{\rm NN}}=200 GeV

In this paper we conduct a systematic study of the granularity of the initial state of hot and dense QCD matter produced in ultra-relativistic heavy-ion collisions and its influence on bulk observables like particle yields, mT spectra and elliptic flow. For our investigation we use a hybrid transport model, based on (3+1)D hydrodynamics and a microscopic Boltzmann transport approach. The initial conditions are generated by a non-equilibrium hadronic transport approach and the size of their fluctuations can be adjusted by defining a Gaussian smoothing parameter σ. The dependence of the hydrodynamic evolution on the choices of σ and tstart is explored by means of a Gaussian emulator. To generate particle yields and elliptic flow that are compatible with experimental data the initial state parameters are constrained to be σ = 1 fm and tstart = 0.5 fm. In addition, the influence of changes in the equation of state is studied and the results of our event-by-event calculations are compared to a calculation with averaged initial conditions. We conclude that even though the initial state parameters can be constrained by yields and elliptic flow, the granularity needs to be constrained by other correlation and fluctuation observables.
Determining the refractive index, absolute thickness and local slope of a thin transparent film using multi-wavelength and multi-incident-angle interference

We describe a high-speed interferometric method, using multiple angles of incidence and multiple wavelengths, to measure the absolute thickness, tilt, the local angle between the surfaces, and the refractive index of a fluctuating transparent wedge. The method is well suited for biological, fluid and industrial applications.
Effelsberg Observations of Excited-State (6.0 GHz) OH in Supernova Remnants and W3(OH)

Although masers in the 1720 MHz transition of OH are detected toward many supernova remnants (SNRs), no other OH transition is seen as a maser in SNRs. We present a search for masers at 6049 MHz, which has recently been predicted to produce masers by pure collisional excitation at conditions similar to that required for 1720 MHz masing. The Effelsberg 100 m telescope was used to observe the excited-state 6016, 6030, 6035, and 6049 MHz lines of OH toward selected SNRs, most of which have previously detected bright 1720 MHz masers. No excited-state masers are found toward SNRs, consistent with previous observations of the 6049 MHz and other excited-state transitions. We do not see clear evidence of absorption toward SNR target positions, although we do see evidence of absorption in the molecular cloud at +50 km s-1 near Sgr A East. Weak absorption is detected at 6016 MHz toward W3(OH), whereas stronger, narrower emission is seen at 6049 MHz, suggesting that the 6049 MHz emission is a low-gain maser. We conclude that the conditions in SNRs are not conducive to excited-state maser emission, especially in excited-state satellite lines.
Young Circumstellar Disks near Evolved Massive Stars and Supernovae

There is increasing evidence that low-mass stars with circumstellar disks can be born close to massive stars, in some cases within tenths of a parsec. If the disks have lifetimes greater than those of the more massive stars, they are exposed to radiation fields and gas flows from the late evolutionary phases and supernovae of the massive stars. The fast flows from supernovae are likely to give some stripping of mass from the disks but do not typically lead to complete disruption of the disks. In the slow wind from a red supergiant star, there is the possibility of gravitational accretion of wind matter onto the circumstellar disk. In the supernova explosion of a red supergiant, the radiative flux at the time of shock breakout can heat and ionize a nearby disk, leading to transient, narrow-line emission. There are consequences for the solar nebula if it was born ~0.2 pc from a massive star that became a red supergiant. Accretion from the wind could supply a substantial amount of 26Al to the disk. The high radiative luminosity of the eventual supernova could lead to the melting of dust grains and the formation of chondrules. The passage of the supernova ejecta could drive a shock wave in the disk, heating it.
Monte Carlo methods for the self-avoiding walk

This article is a pedagogical review of Monte Carlo methods for the self-avoiding walk, with emphasis on the extraordinarily efficient algorithms developed over the past decade. Many more details can be found in [1] .
On Memory System Design for Stochastic Computing

Growing uncertainty in design parameters (and therefore, in design functionality) renders stochastic computing particularly promising, which represents and processes data as quantized probabilities. However, due to the difference in data representation, integrating conventional memory (designed and optimized for non-stochastic computing) in stochastic computing systems inevitably incurs a significant data conversion overhead. Barely any stochastic computing proposal to-date covers the memory impact. In this paper, as the first study of its kind to the best of our knowledge, we rethink the memory system design for stochastic computing. The result is a seamless stochastic system, StochMem, which features analog memory to trade the energy and area overhead of data conversion for computation accuracy. In this manner StochMem can reduce the energy (area) overhead by up-to 52.8% (93.7%) at the cost of at most 0.7% loss in computation accuracy.
Growth and Evolution of Thermal Instabilities in Idealized Galaxy Cluster Cores

Heat input roughly balances radiative cooling in the gaseous cores of galaxy clusters even when the central cooling time is short, implying that cooling triggers a feedback loop that maintains thermal balance. Furthermore, cores with short cooling times tend to have multiphase structure, suggesting that the intracluster medium (ICM) becomes locally thermally unstable for cooling times Gyr. Both observations and theoretical models have linked the condensation of cold gas with heating by an active galactic nucleus (AGN) through a cycle in which cooling gas fuels the AGN and drives energetic outbursts that reheat the ICM and maintain a state of approximate thermal balance. In this work, we use 2D and 3D hydrodynamic simulations to study the onset of condensation in idealized galaxy-cluster cores. In particular, we look at how the condensation process depends on the ratio of cooling time to freefall time and on the geometry of the gravitational potential. We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation. We find that instability leads to convection and that perturbations continue to grow while the gas convects. Condensation occurs when the timescale ratio in the low-entropy tail of the perturbation distribution drops below , even if the volume-averaged timescale ratio is substantially greater. In our simulations, the geometry of the gravitational potential does not have a strong effect on thermal stability. Finally, we find that if condensation is powering feedback, a conversion efficiency of around for converting the condensed mass into thermal energy is sufficient to maintain thermal balance in the ICM.
Imaging coherent electron wave flow in a two-dimensional electron gas

We measure the energy distribution of electrons passing through a two-dimensional electron gas using a scanning probe microscope. We present direct spatial images of coherent electron wave flow from a quantum point contact formed in a GaAs/AlGaAs two-dimensional electron gas using a liquid He cooled SPM. A negative voltage is placed on the tip, which creates a small region of depleted electrons that backscatters electron waves. Oscillating the voltage on the tip and locking into this frequency gives the spatial derivative of electron flow perpendicular to the direction of current flow. We show images of electron flow using this method. By measuring the amount of electrons backscattered as a function of the voltage applied to the tip, the energy distribution of electrons is measured.
On the asymptotic dimension of the curve complex

We give a bound, linear in the complexity of the surface, on the asymptotic dimension of the curve complex as well as the capacity dimension of the ending lamination space.
JET QUENCHING PARAMETER VIA SOFT COLLINEAR EFFECTIVE THEORY (SCET)

We analyze the transverse momentum broadening in the absence of radiation of an energetic parton propagating through quark-gluon plasma via Soft Collinear Effective Theory (SCET). We show that the probability for picking up transverse momentum k? is given by the Fourier transform of the expectation value of two transversely separated light-like path-ordered Wilson lines. The subtleties about the ordering of operators do not change the ˆ q value for the strongly coupled plasma of N = 4 SYM theory.
Non-particle dark matter from Hubble parameter

The measurements of the Hubble parameter using the cosmic microwave background radiation appear to be inconsistent with the measurements of this parameter using Cepheid variable stars. This inconsistency may be a result of using the $$\Lambda $$CDM cosmology, which assumes pressureless dark matter, in extrapolating the data from the recombination time to the present time. We show that both measurements are consistent if dark matter satisfies an equation of state in which the pressure p and the energy density $$\epsilon $$ are related by $$p=w\epsilon $$ with a negative value of w. The data give $$w\approx -0.01$$. The negative value of w indicates that dark matter would not be formed by particles, which is consistent with the lack of experimental evidence for them.
Covariant Density Functional Theory in Nuclear Physics and Astrophysics

How does subatomic matter organize itself? Neutron stars are cosmic laboratories uniquely poised to answer this fundamental question that lies at the heart of nuclear science. Newly commissioned ra...
ASYMPTOTIC LINEAR PROGRAMMING LOWER BOUNDS FOR THE ENERGY OF MINIMIZING RIESZ AND GAUSS CONFIGURATIONS

Utilizing frameworks developed by Delsarte, Yudin and Levenshtein, we deduce linear programming lower bounds (as , we obtain lower bounds for the energy of infinite configurations having a prescribed density.
AN UNEXPECTED DISCOVERY IN THE RICH OPEN CLUSTER NGC 6819 USING XMM-NEWTON

We present the first study of the X-ray population of the intermediate-age rich open cluster NGC 6819 using the XMM-Newton Observatory. In the past decade, Chandra X-ray observations have shown a relationship between the X-ray population of globular clusters and their internal dynamics and encounter frequency. We investigate the role dynamics possibly play in the formation of X-ray sources in NGC 6819, and compare our results with known properties of field and globular cluster X-ray populations. We implement a multi-wavelength approach to studying the X-ray sources, utilizing X-ray and UV data from XMM observations along with the wealth of photometry and radial-velocity data from the WIYN Open Cluster Study and the CFHT Open Cluster Survey. Within the cluster half-light radius, we detect 12 X-ray sources down to a luminosity of 1030 erg s–1 for cluster members. The sources include a candidate quiescent low-mass X-ray binary (qLMXB), a candidate cataclysmic variable, and two active binary systems. The presence of a qLMXB in an open cluster is previously unexpected given the known relationships between luminous X-ray sources and encounter frequency in globular clusters, and most likely has a dynamical origin.
Inverse diffusion theory of photoacoustics

This paper analyzes the reconstruction of diffusion and absorption parameters in an elliptic equation from knowledge of internal data. In the application of photoacoustics, the internal data are the amount of thermal energy deposited by high frequency radiation propagating inside a domain of interest. These data are obtained by solving an inverse wave equation, which is well studied in the literature. We show that knowledge of two internal data based on well-chosen boundary conditions uniquely determines two constitutive parameters in diffusion and Schrodinger equations. Stability of the reconstruction is guaranteed under additional geometric constraints of strict convexity. No geometric constraints are necessary when 2n internal data for well-chosen boundary conditions are available, where n is spatial dimension. The set of well-chosen boundary conditions is characterized in terms of appropriate complex geometrical optics solutions.
EVIDENCE FOR HIGHLY RELATIVISTIC VELOCITIES IN THE KILOPARSEC-SCALE JET OF THE QUASAR 3C 345

In this paper we use radio polarimetric observations of the jet of the nearby bright quasar 3C 345 to estimate the fluid velocity on kiloparsec scales. The jet is highly polarized, and surprisingly, the electric vector position angles in the jet are 'twisted' with respect to the jet axis. Simple models of magnetized jets are investigated in order to study various possible origins of the electric vector distribution. In a cylindrically symmetric transparent jet a helical magnetic field will appear either transverse or longitudinal due to partial cancellations of Stokes parameters between the front and back of the jet. Synchrotron opacity can break the symmetry, but it leads to fractional polarization less than that observed and to strong frequency dependence that is not seen. Modeling shows that differential Doppler boosting in a diverging jet can break the symmetry, allowing a helical magnetic field to produce a twisted electric vector pattern. Constraints on the jet inclination, magnetic field properties, intrinsic opening angle, and fluid velocities are obtained and show that highly relativistic speeds ({beta} {approx}> 0.95) are required. This is consistent with the observed jet opening angle, with the absence of a counter-jet, with the polarization of the knots at themore » end of the jet, and with some inverse-Compton models for the X-ray emission from the 3C 345 jet. This model can also apply on parsec scales and may help explain those sources where the electric vector position angles in the jet are neither parallel nor transverse to the jet axis.« less
Numerical Simulations of the Onset and Stability of Dynamical Mass Transfer in Binaries

Hydrodynamical simulations of semidetached, polytropic binary stars are presented in an effort to study the onset and stability of dynamical mass transfer events. Initial, synchronously rotating equilibrium models are constructed using a self-consistent field technique and then evolved with an Eulerian hydrodynamics code in a fully self-consistent manner. We describe code improvements introduced over the past few years that permit us to follow dynamical mass transfer events through more than 30 orbits. Mass transfer evolutions are presented for two different initial configurations: a dynamically unstable binary with initial mass ratio (donor/accretor) q0 = 1.3 that leads to a complete merger in ~10 orbits, and a double-degenerate binary with initial mass ratio q0 = 0.5 that, after some initial unstable growth of mass transfer, tends to separate as the mass transfer rate levels off.
Classical gluon production amplitude for nucleus-nucleus collisions: First saturation correction in the projectile

We calculate the classical single-gluon production amplitude in nucleus-nucleus collisions including the first saturation correction in one of the nuclei (the projectile) while keeping multiple-rescattering (saturation) corrections to all orders in the other nucleus (the target). In our approximation only two nucleons interact in the projectile nucleus: the single-gluon production amplitude we calculate is order-g 3 and is leading-order in the atomic number of the projectile, while resumming all order-one saturation corrections in the target nucleus. Our result is the first step towards obtaining an analytic expression for the first projectile saturation correction to the gluon production cross section in nucleus-nucleus collisions.
Using an isomorphic problem pair to learn introductory physics: Transferring from a two-step problem to a three-step problem

In this study, we examine introductory physics students' ability to perform analogical reasoning between two isomorphic problems which employ the same underlying physics principles but have different surface features. 382 students from a calculus-based and an algebra-based introductory physics course were administered a quiz in the recitation in which they had to learn from a solved problem provided and take advantage of what they learned from it to solve another isomorphic problem (which we call the quiz problem). The solved problem provided has two subproblems while the quiz problem has three subproblems, which is known from previous research to be challenging for introductory students. In addition to the solved problem, students also received extra scaffolding supports that were intended to help them discern and exploit the underlying similarities of the isomorphic solved and quiz problems. The data analysis suggests that students had great difficulty in transferring what they learned from a two-step problem to a three-step problem. Although most students were able to learn from the solved problem to some extent with the scaffolding provided and invoke the relevant principles in the quiz problem, they were not necessarily able to apply the principles correctly. We also conducted think-aloud interviews with six introductory students in order to understand in depth the difficulties they had and explore strategies to provide better scaffolding. The interviews suggest that students often superficially mapped the principles employed in the solved problem to the quiz problem without necessarily understanding the governing conditions underlying each principle and examining the applicability of the principle in the new situation in an in-depth manner. Findings suggest that more scaffolding is needed to help students in transferring from a two-step problem to a three-step problem and applying the physics principles appropriately. We outline a few possible strategies for future investigation.
Duality between atomic configurations and Bloch states in twistronic materials

In this work, crystal momentum and atomic stacking configuration are introduced as dual variables in electronic moir\'e systems. Within the context of this duality, the authors explain the microscopic origins of several twistronic spectral features and provide multiple approaches for predicting them in new materials.
Spatially dependent modeling and simulation of runaway electron mitigation in DIII-D

New simulations with the Kinetic Orbit Runaway electron (RE) Code (KORC) show RE deconfinement losses to the wall during plasma scrape off are the primary current dissipation mechanism in DIII-D experiments with high-Z impurity injection, and not collisional slowing down. The majority of simulations also exhibit an increase in the RE beam energy due to acceleration by the induced toroidal electric field, even while the RE beam current is decreasing. In this study, KORC integrates RE orbits using the relativistic guiding center equations of motion and incorporates time-sequenced, experimental reconstructions of the magnetic and electric fields and line integrated electron density to construct spatiotemporal models of electron and partially ionized impurity transport in the companion plasma. Comparisons of experimental current evolution and KORC results demonstrate the importance of including Coulomb collisions with partially ionized impurity physics, initial RE energy, pitch angle, and spatial distributions, and spatiotemporal electron and partially ionized impurity transport. This research provides an initial quantification of the efficacy of RE mitigation via injected impurities and identification of the critical role played by loss of confinement due to plasma scrape off on the inner wall as compared to the relatively slow collisional damping.
Constraints on axion inflation from the weak gravity conjecture

We derive constraints facing models of axion inflation based on decay constant alignment from a string-theoretic and quantum gravitational perspective. In particular, we investigate the prospects for alignment and ‘anti-alignment’ of C{sub 4} axion decay constants in type IIB string theory, deriving a strict no-go result in the latter case. We discuss the relationship of axion decay constants to the weak gravity conjecture and demonstrate agreement between our string-theoretic constraints and those coming from the ‘generalized’ weak gravity conjecture. Finally, we consider a particular model of decay constant alignment in which the potential of C{sub 4} axions in type IIB compactifications on a Calabi-Yau three-fold is dominated by contributions from D7-branes, pointing out that this model evades some of the challenges derived earlier in our paper but is highly constrained by other geometric considerations.
Dynamic critical properties of non-equilibrium Potts models with absorbing states

We present extensive numerical simulations of a family of non-equilibrium Potts models with absorbing states that allows for a variety of scenarios, depending on the number of spin states and the range of the spin-spin interactions. These scenarios encompass a voter critical point, a discontinuous transition as well as the presence of both a symmetry-breaking phase transition and an absorbing phase transition. While we also investigate standard steady-state quantities, our emphasis is on time-dependent quantities that provide insights into the transient properties of the models.
Some graftings of complex projective structures with Schottky holonomy

Let $${\mathcal{G} ^{*}(S, \rho)}$$ be the graph whose vertices are marked complex projective structures with holonomy $${\rho}$$ and whose edges are graftings from one vertex to another. If $${\rho}$$ is quasi-Fuchsian, a theorem of Goldman implies that $${\mathcal{G} ^{*}(S, \rho)}$$ is connected. If $${\rho ( \pi _{1}(S))}$$ is a Schottky group Baba has shown that $${\mathcal{G}(S, \rho)}$$ (the corresponding graph for unmarked structures) is connected. For the case that $${\rho ( \pi _{1}(S))}$$ is a Schottky group, this paper provides formulae for the composition of graftings in a basic setting. Using these formulae, one can construct an infinite number of (standard) projective structures which can be grafted to a common structure. Furthermore, one can construct pairs of projective structures which can be connected by grafting in an infinite number of ways.
Connectivity Patterns in Loop Percolation I: the Rationality Phenomenon and Constant Term Identities

Loop percolation, also known as the dense O(1) loop model, is a variant of critical bond percolation in the square lattice $${\mathbb{Z}^2}$$ whose graph structure consists of a disjoint union of cycles. We study its connectivity pattern, which is a random noncrossing matching associated with a loop percolation configuration. These connectivity patterns exhibit a striking rationality property whereby probabilities of naturally-occurring events are dyadic rational numbers or rational functions of a size parameter n, but the reasons for this are not completely understood. We prove the rationality phenomenon in a few cases and prove an explicit formula expressing the probabilities in the “cylindrical geometry” as coefficients in certain multivariate polynomials. This reduces the rationality problem in the general case to that of proving a family of conjectural constant term identities generalizing an identity due to Di Francesco and Zinn-Justin. Our results make use of, and extend, algebraic techniques related to the quantum Knizhnik-Zamolodchikov equation.
The Berry connection of the Ginzburg-Landau vortices

We analyze 2-dimensional Ginzburg–Landau vortices at critical coupling, and establish asymptotic formulas for the tangent vectors of the vortex moduli space using theorems of Taubes and Bradlow. We then compute the corresponding Berry curvature and holonomy in the large area limit.
Evidence for prolonged main sequence stellar evolution of F stars in close binaries

Binary F stars exhibit large brightness anomaly, which is dened here as the dierence between the absolute magnitude from the uvby photometry and the actual absolute magnitude of the star. We have found that the anomaly inversely correlates with the binary components separation. There is evidence that the correlation reflects actual population dierences between close and wide binary pairs, in which case it indicates that the anomaly is somehow associated with the interaction of binary's components. The anomaly has also been found to correlate with both kinematics and metallicity. The sense of the correlations implies that the anomaly increases as the star evolves, suggesting a peculiar evolution of a primary F star in a tight binary pair. This conclusion has further been supported by the study of the age-velocity relation (AVR) of F stars that are cataloged in the HIPPARCOS as single. Among these stars, those with brightness anomaly were previously shown to be most likely unidentied close binaries. We have found that the AVR of these binary candidates is dierent from that of the \truly single" F stars. The discrepancy between the two AVRs indicates that the putative binaries are, on average, older than similar normal single F stars at the same eective temperature and luminosity, which is consistent with the inferred peculiar evolution in close binaries. It appears that this peculiarity is caused by the impact of the components interaction in a tight pair on stellar evolution, which results in the prolonged main sequence lifetime of the primary F star.
Bringing Closure to Microlensing Mass Measurement

Interferometers offer multiple methods for studying microlensing events and determining the properties of the lenses. We investigate the study of microlensing events with optical interferometers, focusing on narrow-angle astrometry, visibility, and closure phase. After introducing the basics of microlensing and interferometry, we derive expressions for the signals in each of these three channels. For various forecasts of the instrumental performance, we discuss which method provides the best means of measuring the lens angular Einstein radius θE, a prerequisite for determining the lens mass. If the upcoming generation of large-aperture, AO-corrected long-baseline interferometers (e.g., VLTI or Keck) perform as well as expected, θE could be determined with signal-to-noise ratios greater than 10 for all bright events. We estimate that ~5 events per year will be sufficiently bright and have long enough durations to allow the measurement of the lens mass and distance from the ground. We also consider the prospects for a VLTI survey of all bright lensing events using a Fisher matrix analysis, and find that even without individual masses, interesting constraints can be placed on the bulge mass function, although large numbers of events would be required.
Common Envelope Evolution Leading to Supernovae with Dense Interaction

A variety of supernova events, including Type IIn supernovae and ultraluminous supernovae, appear to have lost up to solar masses of their envelopes in tens to hundreds of years leading up to the explosion. In order to explain the close timing of the mass loss and supernova events, we explore the possibility that the mass loss is driven by common envelope evolution of a compact object (neutron star or black hole) in the envelope of a massive star and the supernova is triggered by the inspiral of the compact object to the central core of the companion star. The expected rate of such events is smaller than the observed rate of Type IIn supernovae but the rates may agree within the uncertainties. The mass loss velocity is related to the escape velocity from the common envelope system and is comparable to the observed velocity of hundreds of kilometers per second in Type IIn events. The mass loss is expected to be denser near the equatorial plane of the binary system and there is good evidence that the circumstellar media in Type IIn supernovae are asymmetric. Some of these supernova types show evidence for energies in excess of the canonical 1051 erg, which might be the result of explosions from rapid accretion onto a compact object through a disk.
Topologically Trivial Closed Walks in Directed Surface Graphs

Let G be a directed graph with n vertices and m edges, embedded on a surface S, possibly with boundary, with first Betti number $$\beta $$ . We consider the complexity of finding closed directed walks in G that are either contractible (trivial in homotopy) or bounding (trivial in integer homology) in S. Specifically, we describe algorithms to determine whether G contains a simple contractible cycle in $$O(n+m)$$ time, or a contractible closed walk in $$O(n+m)$$ time, or a bounding closed walk in $$O(\beta (n+m))$$ time. Our algorithms rely on subtle relationships between strong connectivity in G and in the dual graph G*; our contractible-closed-walk algorithm also relies on a seminal topological result of Hass and Scott. We also prove that detecting simple bounding cycles is NP-hard. We also describe three polynomial-time algorithms to compute shortest contractible closed walks, depending on whether the fundamental group of the surface is free, abelian, or hyperbolic. A key step in our algorithm for hyperbolic surfaces is the construction of a context-free grammar with $$O(g^2L^2)$$ non-terminals that generates all contractible closed walks of length at most L, and only contractible closed walks, in a system of quads of genus $$g\ge 2$$ . Finally, we show that computing shortest simple contractible cycles, shortest simple bounding cycles, and shortest bounding closed walks are all NP-hard. Finally, we consider the complexity of detecting negative closed walks with trivial topology, when some edges of the input graph have negative weights. We show that negative bounding walks can be detected in polynomial time, by reduction to maximum flows. We also describe polynomial-time algorithms to find negative contractible walks in graphs on the torus or any surface with boundary; the remaining case of hyperbolic surfaces remains open. The corresponding problems for simple cycles are all NP-hard.
A Recommender System for Inverse Design of Polycarbonates and Polyesters

The convergence of artificial intelligence and machine learning with material science holds significant promise in rapidly accelerating the development timelines of new high-performance polymeric m...