cssi/SciSciGPT-SciSciNet huggingface dataset:
Unique representation bases for the integers

Arbitrarily sparse sets A of integers are constructed with the property that every integer can be represented uniquely in the form n = a + a', where a and a' belong to the set A and a < a' or a = a'. Some related open problems are stated.
Universality at an endpoint for orthogonal polynomials with Geronimus-type weights

We provide a new closed form expression for the Geronimus polynomials on the unit circle and use it to obtain new results and formulas. Among our results is a universality result at an endpoint of an arc for polynomials orthogonal with respect to a Geronimus type weight on an arc of the unit circle. The key tool is a formula of McLaughlin for powers of a two-by-two matrix, which we use to derive convenient formulas for Geronimus polynomials.
FRACTIONAL QUANTUM HALL EFFECT FROM ANOMALIES IN WZNW MODEL

An approach to understand fractional quantum Hall effect (FQHE) using anomalies is studied in this letter. More specifically, this is done by looking at the anomaly in the current conservation equation of a WZNW theory describing fields living at the edge of the two-dimensional Hall sample. This WZNW theory itself comes from the non-Abelian bosonization of fermions living at the edge. By identifying the anomaly at the edge with the Hall conductivity in the bulk, it is shown that this model can describe the integer or the FQHE depending on the charge matrix used as the generator of gauge transformations at the boundary.
Strong correlations in actinide redox reactions.

Reduction–oxidation (redox) reactions of the redox couples An(VI)/An(V), An(V)/An(IV), and An(IV)/An(III), where An is an element in the family of early actinides (U, Np, and Pu), as well as Am(VI)/Am(V) and Am(V)/Am(III), are modeled by combining density functional theory with a generalized Anderson impurity model that accounts for the strong correlations between the 5f electrons. Diagonalization of the Anderson impurity model yields improved estimates for the redox potentials and the propensity of the actinide complexes to disproportionate.
Selective nucleation in porous media

Geometrical arguments suggest that pore-mediated nucleation happens in general in a two-step fashion, the first step being nucleation within the pore, the second being nucleation from the filled pore into solution [Page and Sear, Phys. Rev. Lett., 2006, 97, 65701]. The free energy barriers controlling the two steps of this process show opposite dependencies on pore size, implying that for given thermodynamic conditions there exists a pore size for which nucleation happens fastest. Here we show, within the two- and three-dimensional Ising lattice gas, that this preferred pore size tracks the size of the bulk critical nucleus, up to a numerical prefactor. This observation suggests a simple prescription for directing nucleation to certain locations within heterogeneous porous media.
Hypergraph expanders of all uniformities from Cayley graphs

Hypergraph expanders are hypergraphs with surprising, non-intuitive expansion properties. In a recent paper, the first author gave a simple construction, which can be randomized, of 3-uniform hypergraph expanders with polylogarithmic degree. We generalize this construction, giving a simple construction of r-uniform hypergraph expanders for all r ≥ 3.
Stable commutator length in Baumslag–Solitar groups and quasimorphisms for tree actions

This paper has two parts, on Baumslag–Solitar groups and on general G–trees. In the first part we establish bounds for stable commutator length (scl) in Baumslag–Solitar groups. For a certain class of elements, we further show that scl is computable and takes rational values. We also determine exactly which of these elements admit extremal surfaces. In the second part we establish a universal lower bound of 1/12 for scl of suitable elements of any group acting on a tree. This is achieved by constructing efficient quasimorphisms. Calculations in the group BS(2, 3) show that this is the best possible universal bound, thus answering a question of Calegari and Fujiwara. We also establish scl bounds for acylindrical tree actions. Returning to Baumslag–Solitar groups, we show that their scl spectra have a uniform gap: no element has scl in the interval (0, 1/12).
A simple test for ideal memristors

An ideal memristor is defined as a resistor with memory that, when subjected to a time-dependent current, , its resistance R M (q) depends only on the charge q that has flowed through it, so that its voltage response is . It has been argued that a clear fingerprint of these ideal memristors is a pinched hysteresis loop in their I? curves. However, a pinched I? hysteresis loop is not a definitive test of whether a resistor with memory is truly an ideal memristor because such a property is shared also by other resistors whose memory depends on additional internal state variables, other than the charge. Here, we introduce a very simple and unambiguous test that can be utilized to check experimentally if a resistor with memory is indeed an ideal memristor. Our test is based on the duality property of a capacitor-memristor circuit whereby, for any initial resistance states of the memristor and any form of the applied voltage, the final state of an ideal memristor must be identical to its initial state, if the capacitor charge finally returns to its initial value. In actual experiments, a sufficiently wide range of voltage amplitudes and initial states are enough to perform the test. The proposed test can help resolve some long-standing controversies still existing in the literature about whether an ideal memristor does actually exist or it is a purely mathematical concept.
On Factorizing Correlation Functions in String Theory Using Loop Variables

Factorization of string amplitudes is one way of constructing string interaction vertices. We show that correlation functions in string theory can be conveniently factorized using loop variables representing delta functionals. We illustrate this construction with some examples where one particle is off-shell. These vertices are “correct” in the sense that they are guaranteed, by construction, to reproduce S-matrix elements when combined with propagators in a well-defined way.
Optical synoptic telescopes: new science frontiers

Over the past decade, sky surveys such as the Sloan Digital Sky Survey (SDSS) have proven the power of large data sets for answering fundamental astrophysical questions. This observational progress, based on a synergy of advances in telescope construction, detectors, and information technology, has had a dramatic impact on nearly all fields of astronomy, and areas of fundamental physics. The next-generation instruments, and the surveys that will be made with them, will maintain this revolutionary progress. The hardware and computational technical challenges and the exciting science opportunities are attracting scientists and engineers from astronomy, optics, low-light-level detectors, high-energy physics, statistics, and computer science. The history of astronomy has taught us repeatedly that there are surprises whenever we view the sky in a new way. This will be particularly true of discoveries emerging from a new generation of sky surveys. Imaging data from large ground-based active optics telescopes with sufficient etendue can address many scientific missions simultaneously. These new investigations will rely on the statistical precision obtainable with billions of objects. For the first time, the full sky will be surveyed deep and fast, opening a new window on a universe of faint moving and distant exploding objects as well as unraveling the mystery of dark energy.
Quark recombination and heavy quark diffusion in hot nuclear matter

We discuss resonance recombination for quarks and show that it is compatible with quark and hadron distributions in local thermal equilibrium. We then calculate realistic heavy quark phase space distributions in heavy ion collisions using Langevin simulations with non-perturbative T-matrix interactions in hydrodynamic backgrounds. We hadronize the heavy quarks on the critical hypersurface given by hydrodynamics after constructing a criterion for the relative recombination and fragmentation contributions. We discuss the influence of recombination and flow on the resulting heavy meson and single electron RAA and elliptic flow. We will also comment on the effect of diffusion of open heavy flavor mesons in the hadronic phase.
Spectral statistics of non-Hermitian random matrix ensembles

Recently Burkhardt et al. introduced the k-checkerboard random matrix ensembles, which have a split limiting behavior of the eigenvalues (in the limit all but k of the eigenvalues are on the order ...
Bio-inspired filter banks for SSVEP-based brain-computer interfaces

Brain-computer interfaces (BCI) have the potential to play a vital role in future healthcare technologies by providing an alternative way of communication and control. More specifically, steady-state visual evoked potential (SSVEP) based BCIs have the advantage of higher accuracy and higher information transfer rate (ITR). In order to fully exploit the capabilities of such devices, it is necessary to understand the features of SSVEP and design the system considering its biological characteristics. This paper introduces bio-inspired filter banks (BIFB) for a novel SSVEP frequency detection method. It is known that SSVEP response to a flickering visual stimulus is frequency selective and gets weaker as the frequency of the stimuli increases. In the proposed approach, the gain and bandwidth of the filters are designed and tuned based on these characteristics while also incorporating harmonic SSVEP responses. This method not only improves the accuracy but also increases the available number of commands by allowing use of stimuli frequencies elicit weak SSVEP responses. The BIFB method achieved reliable performance when tested on datasets available online and compared with two well-known SSVEP frequency detection methods, power spectral density analysis (PSDA) and canonical correlation analysis (CCA). The results show the potential of bio-inspired design which will be extended to include further SSVEP characteristics (e.g. time-domain waveform) for future SSVEP based BCIs.
A new complex reflection group in PU(9,1) and the Barnes–Wall lattice

We show that the projectivized complex reflection group $\Gamma$ of the unique $(1+i)$-modular Hermitian $\mathbb{Z}[i]$-module of signature $(9,1)$ is a new arithmetic reflection group in $PU(9,1)$. We find $32$ complex reflections of order four generating $\Gamma$. The mirrors of these $32$ reflections form the vertices of a sort of Coxeter-Dynkin diagram $D$ for $\Gamma$ that encode Coxeter-type generators and relations for $\Gamma$. The vertices of $D$ can be indexed by sixteen points and sixteen affine hyperplanes in $\mathbb{F}_2^4$. The edges of $D$ are determined by the finite geometry of these points and hyperplanes. The group of automorphisms of the diagram $D$ is $2^4 \colon (2^3 \colon L_3(2)) \colon 2$. This group transitively permutes the $32$ mirrors of generating reflections and fixes an unique point $\tau$ in $\mathbb{C} H^9$. These $32$ mirrors are precisely the mirrors closest to $\tau$. These results are strikingly similar to the results satisfied by the complex hyperbolic reflection group at the center of Allcock's monstrous proposal.
Charged particle dynamics near an X-point of a non-symmetric magnetic field with closed field lines

Understanding particle drifts in a non-symmetric magnetic field is of primary interest in designing optimized stellarators in order to minimize the neoclassical radial loss of particles. Quasisymmetry and omnigeneity, two distinct properties proposed to ensure radial localization of collisionless trapped particles in stellarators, have been explored almost exclusively for magnetic fields with nested flux surfaces. In this work, we examine radial particle confinement when all field lines are closed. We then study charged particle dynamics in the special case of a non-symmetric vacuum magnetic field with closed field lines obtained recently by Weitzner & Sengupta (Phys. Plasmas, vol. 27, 2020, 022509). These magnetic fields can be used to construct magnetohydrodynamic equilibria for low pressure. Expanding in the amplitude of the non-symmetric fields, we explicitly evaluate the omnigeneity and quasisymmetry constraints. We show that the magnetic field is omnigeneous in the sense that the drift surfaces coincide with the pressure surfaces. However, it is not quasisymmetric according to the standard definitions.
AZIMUTHAL DENSITY VARIATIONS AROUND THE RIM OF TYCHO's SUPERNOVA REMNANT

Spitzer images of Tycho's supernova remnant in the mid-infrared reveal limb-brightened emission from the entire periphery of the shell and faint filamentary structures in the interior. As with other young remnants, this emission is produced by dust grains, warmed to ~100 K in the post-shock environment by collisions with energetic electrons and ions. The ratio of the 70 to 24??m fluxes is a diagnostic of the dust temperature, which in turn is a sensitive function of the plasma density. We find significant variations in the 70/24 flux ratio around the periphery of Tycho's forward shock, implying order-of-magnitude variations in density. While some of these are likely localized interactions with dense clumps of the interstellar medium (ISM), we find an overall gradient in the ambient density surrounding Tycho, with densities 3-10?times higher in the northeast than in the southwest. This large density gradient is qualitatively consistent with the variations in the proper motion of the shock observed in radio and X-ray studies. Overall, the mean ISM density around Tycho is quite low (~0.1-0.2 cm?3), consistent with the lack of thermal X-ray emission observed at the forward shock. We perform two-dimensional hydrodynamic simulations of a Type?Ia supernova expanding into a density gradient in the ISM, and find that the overall round shape of the remnant is still easily achievable, even for explosions into significant gradients. However, this leads to an offset of the center of the explosion from the geometric center of the remnant of up to 20%, although lower values of 10% are preferred. The best match with hydrodynamical simulations is achieved if Tycho is located at a large (3-4 kpc) distance in a medium with a mean preshock density of ~0.2 cm?3. Such preshock densities are obtained for highly ( 50%) porous ISM grains.
Small-scale dynamics of settling, bidisperse particles in turbulence

Mixing and collisions of inertial particles at the small scales of turbulence can be investigated by considering how pairs of particles move relative to each other. In real problems the two particles will have different sizes, i.e. they are bidisperse, and the effect of gravity on their motion is often important. However, how turbulence and gravity compete to control the motion of bidisperse inertial particles is poorly understood. Motivated by this, we use direct numerical simulations (DNS) to investigate the dynamics of settling, bidisperse particles in isotropic turbulence. In agreement with previous studies, we find that without gravity (i.e. , where is the Froude number), bidispersity leads to an enhancement of the relative velocities, and a suppression of their spatial clustering. For , the relative velocities in the direction of gravity are enhanced by the differential settling velocities of the bidisperse particles, as expected. However, we also find that gravity can strongly enhance the relative velocities in the ‘horizontal’ directions (i.e. in the plane normal to gravity). This non-trivial behaviour occurs because fast settling particles experience rapid fluctuations in the fluid velocity field along their trajectory, leading to enhanced particle accelerations and relative velocities. Indeed, the results show that even when , turbulence can still play an important role, not only on the horizontal motion, but also on the vertical motion of the particles. This is related to the fact that only characterizes the importance of gravity compared with some typical acceleration of the fluid, yet accelerations in turbulence are highly intermittent. As a consequence, there is a significant probability for particles to be in regions of the flow where the Froude number based on the local, instantaneous fluid acceleration is , even though the typically defined Froude number is . This could imply, for example, that extreme events in the mixing of settling, bidisperse particles are only weakly affected by gravity even when . We also find that gravity drastically reduces the clustering of bidisperse particles. These results are strikingly different to the monodisperse case, for which recent results have shown that when , gravity strongly suppresses the relative velocities in all directions, and can enhance clustering. Finally, we consider the implications of these results for the collision rates of settling, bidisperse particles in turbulence. We find that for , the collision kernel is almost perfectly predicted by the collision kernel for bidisperse particles settling in quiescent flow, such that the effect of turbulence may be ignored. However, for , turbulence plays an important role, and the collisions are only dominated by gravitational settling when the difference in the particle Stokes numbers is .
Distribution of positron annihilation radiation

Abstract The SPI instrument on-board the ESA/INTEGRAL satellite is engaged in a mission-long study of positron annihilation radiation from the Galaxy. Early results suggest that the disk component is only weakly detected at 511 keV by SPI. We review CGRO/OSSE, TGRS and SMM studies of 511 keV line and positronium continuum emission from the Galaxy in light of the early INTEGRAL/SPI findings. We find that when similar spatial distributions are compared, combined fits to the OSSE/SMM/TGRS data-sets produce bulge and disk fluxes similar in total flux and in B/D ratio to the fits reported for SPI observations. We further find that the 511 keV line width reported by SPI is similar to the values reported by TGRS, particularly when spectral fits include both narrow-line and broad-line components. Collectively, the consistency between these four instruments suggests that all may be providing an accurate view of positron annihilation in the Galaxy.
Joint downscale fluxes of energy and potential enstrophy in rotating stratified Boussinesq flows

We employ a coarse-graining approach to analyze non-linear cascades in Boussinesq flows using high-resolution simulation data. We derive budgets which resolve the evolution of energy and potential enstrophy simultaneously in space and in scale. We then use numerical simulations of Boussinesq flows, with forcing in the large scales, and fixed rotation and stable stratification along the vertical axis, to study the inter-scale flux of energy and potential enstrophy in three different regimes of stratification and rotation: i) strong rotation and moderate stratification, ii) moderate rotation and strong stratification, and iii) equally strong stratification and rotation. In all three cases, we observe constant fluxes of both global invariants, the mean energy and mean potential enstrophy, from large to small scales. The existence of constant potential enstrophy flux ranges provides the first direct empirical evidence in support of the notion of a cascade of potential enstrophy. The persistent forward cascade of the two invariants reflects a marked departure of these flows from two-dimensional turbulence.
Excitation of Gravity Waves by Fingering Convection, and the Formation of Compositional Staircases in Stellar Interiors

Fingering convection (or thermohaline convection) is a weak yet important kind of mixing that occurs in stably stratified stellar radiation zones in the presence of an inverse mean molecular weight gradient. Brown et al. recently proposed a new model for mixing by fingering convection, which contains no free parameter and was found to fit the results of direct numerical simulations in almost all cases. Notably, however, they found that mixing was substantially enhanced above their predicted values in the few cases where large-scale gravity waves, followed by thermo-compositional layering, grew spontaneously from the fingering convection. This effect is well known in the oceanographic context and is attributed to the excitation of the so-called collective instability. In this work, we build on the results of Brown et al. and of Traxler et al. to determine the conditions under which the collective instability may be expected. We find that it is only relevant in stellar regions that have a relatively large Prandtl number (the ratio of the kinematic viscosity to the thermal diffusivity), or larger. This implies that the collective instability cannot occur in main-sequence stars, where the Prandtl number is always much smaller than this (except in the outer layers of surface convection zones, where fingering is irrelevant anyway). It could in principle be excited in regions of high electron degeneracy, during He core flash, or in the interiors of white dwarfs. We discuss the implications of our findings for these objects, from both a theoretical and an observational point of view.
Mirage mediation from the landscape

This paper examines how the string theory landscape affects the mirage mediated SUSY breaking framework which has a comparable gravity/moduli-mediated and anomaly mediated contributions to soft terms and that a preferred mirage unification scale can be predicted.
Photon bubbles and the vertical structure of accretion disks

We consider the effects of "photon bubble" shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously in radiation-dominated accretion disks where magnetic pressure exceeds gas pressure, even in the presence of magnetorotational instability (MRI). They increase the rate at which radiation escapes from the disk and may allow disks to exceed the Eddington limit by a substantial factor without blowing themselves apart. To refine our earlier analysis of photon bubble transport in accretion disks, we generalize the theory of photon bubbles to include the effects of finite optical depths and radiation damping. Modifications to the diffusion law at low τ tend to "fill in" the low-density regions of photon bubbles, while radiation damping inhibits the formation of photon bubbles at large radii, small accretion rates, and small heights above the equatorial plane. Accretion disks dominated by photon bubble transport may reach luminosities from 10 to >100 times the Eddington limit (LEdd), depending on the mass of the central object, while remaining geometrically thin. However, photon bubble-dominated disks with α-viscosity are subject to the same thermal and viscous instabilities that plague standard radiation pressure-dominated disks, suggesting that they may be intrinsically unsteady. Photon bubbles can lead to a "core-halo" vertical disk structure. In super-Eddington disks the halo forms the base of a wind, which carries away substantial energy and mass, but not enough to prevent the luminosity from exceeding LEdd. Photon bubble-dominated disks may have smaller color corrections than standard accretion disks of the same luminosity. They remain viable contenders for some ultraluminous X-ray sources and may play a role in the rapid growth of supermassive black holes at high redshift.
A Duality Web in 2+1 Dimensions and Condensed Matter Physics

Abstract Building on earlier work in the high energy and condensed matter communities, we present a web of dualities in 2 + 1 dimensions that generalize the known particle/vortex duality. Some of the dualities relate theories of fermions to theories of bosons. Others relate different theories of fermions. For example, the long distance behavior of the 2 + 1 -dimensional analog of QED with a single Dirac fermion (a theory known as U ( 1 ) 1 2 ) is identified with the O ( 2 ) Wilson–Fisher fixed point. The gauged version of that fixed point with a Chern–Simons coupling at level one is identified as a free Dirac fermion. The latter theory also has a dual version as a fermion interacting with some gauge fields. Assuming some of these dualities, other dualities can be derived. Our analysis resolves a number of confusing issues in the literature including how time reversal is realized in these theories. It also has many applications in condensed matter physics like the theory of topological insulators (and their gapped boundary states) and the problem of electrons in the lowest Landau level at half filling. (Our techniques also clarify some points in the fractional Hall effect and its description using flux attachment.) In addition to presenting several consistency checks, we also present plausible (but not rigorous) derivations of the dualities and relate them to 3 + 1 -dimensional S -duality.
Near-Infrared Adaptive Optics Imaging of the Embedded Cluster NGC 2024

We present the results of a high-resolution near-infrared adaptive optics survey of the young obscured star-forming region NGC 2024. Out of the total 73 stars detected in the adaptive optics survey of the cluster, we find three binaries and one triple. The resulting companion star fraction, 7% ± 3% in the separation range of 035-23 (145-950 AU), is consistent with that expected from the multiplicity of mature solar-type stars in the local neighborhood. Our survey was sensitive to faint secondaries, but no companions with ΔK' > 1.2 mag are detected within 2'' of any star. The cluster has a K' luminosity function that peaks at ~12, and although our completeness limit was 17.7 mag at K', the faintest star we detected had a K' magnitude of 16.62.
Electrohydrodynamic Quincke rotation of a prolate ellipsoid

We experimentally study the occurrence of spontaneous spinning (Quincke rotation) of an ellipsoid in a uniform DC electric field. For an ellipsoid suspended in an unbounded fluid, we find two stable states characterized by the orientation of the ellipsoid long axis relative to the applied electric field : spinless (parallel) and spinning (perpendicular). The phase diagram of ellipsoid behavior as a function of field strength and aspect ratio is in close agreement with the theory of Cebers et al. Phys. Rev .E 63:016301 (2000). We also investigated the dynamics of the ellipsoidal Quincke rotor resting on a planar surface with normal perpendicular to the field direction. We find novel behaviors, such as swinging (long axis oscillating around the applied field direction) and tumbling, due to the confinement.
Probing the enhancon via calculations in supersymmetric gauge theory

Abstract We consider the N =2 gauge theory on N D7-branes wrapping K 3, with D3-brane probes. In the large N limit, the D7-branes blow up to form an enhancon shell. We probe the region inside and outside the enhancon shell using the D3-branes, and compute the probe metric using the Seiberg–Witten formalism. Supergravity arguments suggest a flat interior up to 1/ N corrections, and indeed our results for the D3-brane probes are consistent with that. By including the dynamics of the branes, these results, together with those of hep-th/0204050 , demonstrate the robustness of the enhancon mechanism beyond patching together of supergravity solutions with D-brane source junction conditions.
X-Ray Emission from Strongly Asymmetric Circumstellar Material in the Remnant of Kepler's Supernova

Kepler's supernova remnant resulted from a thermonuclear explosion, but is interacting with circumstellar material (CSM) lost from the progenitor system. We describe a statistical technique for isolating X-ray emission due to CSM from that due to shocked ejecta. Shocked CSM coincides well in position with 24 μm emission seen by Spitzer. We find most CSM to be distributed along the bright north rim, but substantial concentrations are also found projected against the center of the remnant, roughly along a diameter with position angle ~100°. We interpret this as evidence for a disk distribution of CSM before the supernova, with the line of sight to the observer roughly in the disk plane. We present two-dimensional hydrodynamic simulations of this scenario in qualitative agreement with the observed CSM morphology. Our observations require Kepler to have originated in a close binary system with an asymptotic giant branch star companion.
Evidence for Rotation in the Galaxy at z = 3.15 Responsible for a Damped Lyman-Alpha Absorption System in the Spectrum of Q2233+1310

Proof of the existence of a significant population of normal disk galaxies at redshift z > 2 would have profound implications for theories of structure formation and evolution. We present evidence based on Keck HIRES spectra that the damped Lyα absorber at z = 3.15 toward the quasar Q2233+1310 may well be such an example. Djorgovski et al. have recently detected the Lyα emission from the absorber, which we assume is at the systemic redshift of the absorbing galaxy. By examining the profiles of the metal absorption lines arising from the absorbing galaxy in relation to its systemic redshift, we find strong kinematical evidence for rotation. Therefore the absorber is likely to be a disk galaxy. The inferred circular velocity for the galaxy is greater than or equal to 200 km s-1. With a separation of 17 kpc (q0 = 0.1, H0 = 75) between the galaxy and the quasar sight line, the implied dynamic mass for the galaxy is greater than or equal to 1.6 × 1011 M☉. The metallicity of the galaxy is found to be [Fe/H] = -1.4, typical of damped Lyα galaxies at such redshifts. However, in another damped Lyα absorber at z = 2.81 toward Q0528-2505, no kinematical evidence for galactic rotation is evident. In the latter case, the damped Lyα absorber occurs near the background quasar in redshift, so its properties may be influenced by the background quasar. These represent the only two cases at present for which the technique used here may be applied. Future applications of the same technique to a large sample of damped Lyα galaxies may allow us to determine if a significant population of disk galaxies already existed only a few billion years after the big bang.
Effects of Gravitational Lensing in the Double Pulsar System J0737?3039

We investigate the effects of gravitational lensing in the binary pulsar system J0737-3039. Current measurement of the orbital inclination allows the millisecond pulsar (A) to pass very close (at Rmin ≈ 4000 km) in projection to the companion pulsar (B), with Rmin comparable to the Einstein radius (≈2600 km). For this separation at the conjunction, lensing causes small (about 10%) magnification of the pulsar A signal on a timescale of several seconds and displaces the pulsar image on the sky plane by about 1200 km. More importantly, lensing introduces a correction (of several microseconds) to the conventional Shapiro delay formula used in pulsar timing analysis and gives rise to a geometric time delay together with the delays associated with the pulsar spin period. These lensing effects can influence the determination of the system parameters by both timing and scintillation studies. Given the current uncertainty in the orbital inclination, more extreme manifestations of lensing (e.g., magnification by a factor of several) are possible. We compare our predictions with the existing observations and discuss the possibility of detecting gravitational lensing signatures in the system. The anomalously high point in pulsar A's light curve close to superior conjunction might be caused by gravitational lensing.
THE ORIGIN AND DISTRIBUTION OF COLD GAS IN THE HALO OF A MILKY-WAY-MASS GALAXY

We analyze an adaptive mesh refinement hydrodynamic cosmological simulation of a Milky-Way-sized galaxy to study the cold gas in the halo. H I observations of the Milky Way and other nearby spirals have revealed the presence of such gas in the form of clouds and other extended structures, which indicates ongoing accretion. We use a high-resolution simulation (136-272 pc throughout) to study the distribution of cold gas in the halo, compare it with observations, and examine its origin. The amount ({approx}10{sup 8} M{sub Sun} in H I), covering fraction, and spatial distribution of the cold halo gas around the simulated galaxy at z = 0 are consistent with existing observations. At z = 0, the H I mass accretion rate onto the disk is 0.2 M{sub Sun} yr{sup -1}. We track the histories of the 20 satellites that are detected in H I in the redshift interval 0.5 > z > 0 and find that most of them are losing gas, with a median mass-loss rate per satellite of 3.1 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. This stripped gas is a significant component of the H I gas seen in the simulation. In addition, we see filamentary material comingmore » into the halo from the intergalactic medium at all redshifts. Most of this gas does not make it directly to the disk, but part of the gas in these structures is able to cool and form clouds. The metallicity of the gas allows us to distinguish between filamentary flows and satellite gas. We find that the former accounts for at least 25%-75% of the cold gas in the halo seen at any redshift analyzed here. Placing constraints on cloud formation mechanisms allows us to better understand how galaxies accrete gas and fuel star formation at z = 0.« less
Matrix factorizations via Koszul duality

In this paper we prove a version of curved Koszul duality for . Similar results are also obtained in the orbifold case and in the graded case.
Understanding BERT Rankers Under Distillation

Deep language models, such as BERT pre-trained on large corpora, have given a huge performance boost to state-of-the-art information retrieval ranking systems. Knowledge embedded in such models allows them to pick up complex matching signals between passages and queries. However, the high computation cost during inference limits their deployment in real-world search scenarios. In this paper, we study if and how the knowledge for search within BERT can be transferred to a smaller ranker through distillation. Our experiments demonstrate that it is crucial to use a proper distillation procedure, which produces up to nine times speedup while preserving the state-of-the-art performance.
Instance influence estimation for hyperspectral target signature characterization using extended functions of multiple instances

The Extended Functions of Multiple Instances (eFUMI) algorithm1 is a generalization of Multiple Instance Learning (MIL). In eFUMI, only bag level (i.e. set level) labels are needed to estimate target signatures from mixed data. The training bags in eFUMI are labeled positive if any data point in a bag contains or represents any proportion of the target signature and are labeled as a negative bag if all data points in the bag do not represent any target. From these imprecise labels, eFUMI has been shown to be eﬀective at estimating target signatures in hyperspectral subpixel target detection problems. One motivating scenario for the use of eFUMI is where an analyst circles objects/regions of interest in a hyperspectral scene such that the target signatures of these objects can be estimated and be used to determine whether other instances of the object appear elsewhere in the image collection. The regions highlighted by the analyst serve as the imprecise labels for eFUMI. Often, an analyst may want to iteratively reﬁne their imprecise labels. In this paper, we present an approach for estimating the inﬂuence on the estimated target signature if the label for a particular input data point is modiﬁed. This instance inﬂuence estimation guides an analyst to focus on (re-)labeling the data points that provide the largest change in the resulting estimated target signature and, thus, reduce the amount of time an analyst needs to spend reﬁning the labels for a hyperspectral scene. Results are shown on real hyperspectral sub-pixel target detection data sets.
Dissecting the X-Ray Emission in the Young Planetary Nebula NGC 7027

We present analysis of a second observation of the young planetary nebula (PN) NGC 7027 by the Chandra X-ray Observatory. This latest 59.2 ks exposure with ACIS-S was acquired approximately 14 years after the initial 18.2 ks ACIS-S observation, and the improved photon statistics allow us to perform a detailed spatial and spectral analysis of the X-ray emission. Comparison with multiwavelength imaging of NGC 7027 reveals a strong anti-correlation between extinction across the nebula and the soft band X-ray emission. Dissecting the X-ray emission into low- and high-extinction regions results in more robust characterization of the plasma spectral properties. We determine that the X-ray emitting plasma has a temperature of $\sim3.6$ MK, is deficient in Fe, and has an X-ray luminosity of $L_{\rm X}\sim7\times10^{31}{\rm ~erg~s}^{-1}$, all of which are generally consistent with the plasma properties found in PN hot bubbles. We find no evidence of evolution in the X-ray surface brightness over the 14 year baseline between Chandra observations. Our analysis underscores the importance of accounting for nebular absorption of the X-ray emission in accurately determining plasma properties for hot bubbles within PNe.
Composition Operators and Endomorphisms

If b is an inner function, then composition with b induces an endomorphism, β, of \({L^\infty({\mathbb{T}})}\) that leaves \({H^\infty({\mathbb{T}})}\) invariant. We investigate the structure of the endomorphisms of \({B(L^2({\mathbb{T}}))}\) and \({B(H^2({\mathbb{T}}))}\) that implement β through the representations of \({L^\infty({\mathbb{T}})}\) and \({H^\infty({\mathbb{T}})}\) in terms of multiplication operators on \({L^2({\mathbb{T}})}\) and \({H^2({\mathbb{T}})}\) . Our analysis, which is based on work of Rochberg and McDonald, will wind its way through the theory of composition operators on spaces of analytic functions to recent work on Cuntz families of isometries and Hilbert C*-modules.
Non-Gaussian statistics of multiple filamentation

We consider the statistics of light amplitude fluctuations for the propagation of a laser beam subjected to multiple filamentation in an amplified Kerr media, with both linear and nonlinear dissipation. Dissipation arrests the catastrophic collapse of filaments, causing their disintegration into almost linear waves. These waves form a nearly Gaussian random field that seeds new filaments. For small amplitudes the probability density function (PDF) of light amplitude is close to Gaussian, while for large amplitudes the PDF has a long powerlike tail that corresponds to strong non-Gaussian fluctuations, i.e., intermittency of strong optical turbulence. This tail is determined by the universal form of near singular filaments and the PDF for the maximum amplitudes of the filaments.
Quantum state tomography across the exceptional point in a single dissipative qubit

Open physical systems can be described by effective non-Hermitian Hamiltonians that characterize the gain or loss of energy or particle numbers from the system. Experimental realization of optical1–7 and mechanical8–13 non-Hermitian systems has been reported, demonstrating functionalities such as lasing14–16, topological features7,17–19, optimal energy transfer20,21 and enhanced sensing22,23. Such realizations have been limited to classical (wave) systems in which only the amplitude information, not the phase, is measured. Thus, the effects of a systems’s proximity to an exceptional point—a degeneracy of such non-Hermitian Hamiltonians where the eigenvalues and corresponding eigenmodes coalesce24–29—on its quantum evolution remain unexplored. Here, we use post-selection on a three-level superconducting transmon circuit to carry out quantum state tomography of a single dissipative qubit in the vicinity of its exceptional point. We observe the spacetime reflection symmetry-breaking transition30,31 at zero detuning, decoherence enhancement at finite detuning and a quantum signature of the exceptional point in the qubit relaxation state. Our experiments show phenomena associated with non-Hermitian physics such as non-orthogonality of eigenstates in a fully quantum regime, which could provide a route to the exploration and harnessing of exceptional point degeneracies for quantum information processing. The dynamics of a single dissipative qubit undergoing non-Hermitian quantum dynamics in the vicinity of an exceptional point is experimentally studied in a superconducting transmon circuit.
Diffusion as a first model of spread of viral infection

The appearance of the coronavirus (COVID-19) in late 2019 has dominated the news in the last few months as it developed into a pandemic. In many mathematics and physics classrooms, instructors are using the time series of the number of cases to show exponential growth of the infection. In this manuscript, we propose a simple diffusion process as the mode of spreading infections. This model is less sophisticated than other models in the literature, but it can capture the exponential growth and it can explain it in terms of mobility (diffusion constant), population density, and probability of transmission. Students can change the parameters and determine the growth rate and predict the total number of cases as a function of time. Students are also given the opportunity to add other factors that are not considered in the simple diffusion model.
Low Regularity Solutions for Gravity Water Waves

We prove local well-posedness for the gravity water waves equations without surface tension, with initial velocity field in $$H^s$$ , $$s > \frac{d}{2} + 1 - \mu $$ , where $$\mu = \frac{1}{10}$$ in the case $$d = 1$$ and $$\mu = \frac{1}{5}$$ in the case $$d \ge 2$$ , extending previous results of Alazard–Burq–Zuily. The improvement primarily arises in two areas. First, we perform an improved analysis of the regularity of the change of variables from Eulerian to Lagrangian coordinates. Second, we perform a time-interval length optimization of the localized Strichartz estimates.
Low-mass Star Formation: Observations

I briefly review recent observations of regions forming low mass stars. The discussion is cast in the form of seven questions that have been partially answered, or at least illuminated, by new data. These are the following: where do stars form in molecular clouds; what determines the IMF; how long do the steps of the process take; how efficient is star formation; do any theories explain the data; how are the star and disk built over time; and what chemical changes accompany star and planet formation. I close with a summary and list of open questions.
Heated disc stars in the stellar halo

ABSTRACT Minor accretion events with mass ratio M sat :M host ≃ 1:10 are common in thecontext of ΛCDM cosmology. We use high-resolution simulations of Galaxy-analoguesystems to show that these mergers can dynamically eject disc stars into a diﬀuselight component that resembles a stellar halo both spatially and kinematically. Fora variety of initial orbital conﬁgurations, we ﬁnd that ∼ 3 − 5 × 10 8 M ⊙ of primarystellar disc material is ejected to a distance larger than 5 kpc above the galactic plane.This ejected contribution is similar to the mass contributed by the tidal disruption ofthe satellite galaxy itself, though it is less extended. If we restrict our analysis to theapproximate solar neighborhood in the disc plane, we ﬁnd that ∼ 1% of the initial discstars in that region would be classiﬁed kinematically as halo stars. Our results suggestthat the inner parts of galactic stellar halos contain ancient disc stars and that thesestars may have been liberated in the very same events that delivered material to theouter stellar halo.Key words: Cosmology: theory — galaxies: formation — galaxies: evolution
Entropically patchy particles: engineering valence through shape entropy.

Patchy particles are a popular paradigm for the design and synthesis of nanoparticles and colloids for self-assembly. In “traditional” patchy particles, anisotropic interactions arising from patterned coatings, functionalized molecules, DNA, and other enthalpic means create the possibility for directional binding of particles into higher-ordered structures. Although the anisotropic geometry of nonspherical particles contributes to the interaction patchiness through van der Waals, electrostatic, and other interactions, how particle shape contributes entropically to self-assembly is only now beginning to be understood. The directional nature of entropic forces has recently been elucidated. A recently proposed theoretical framework that defines and quantifies directional entropic forces demonstrates the anisotropic—that is, patchy—nature of these emergent, attractive forces. Here we introduce the notion of entropically patchy particles as the entropic counterpart to enthalpically patchy particles. Using thre...
Magnetic field corrections to the repulsive Casimir effect at finite temperature

I investigate the finite temperature Casimir effect for a charged and massless scalar field satisfying mixed (Dirichlet–Neumann) boundary conditions on a pair of plane parallel plates of infinite size. The effect of a uniform magnetic field, perpendicular to the plates, on the Helmholtz free energy and Casimir pressure is studied. The ζ-function regularization technique is used to obtain finite results. Simple analytic expressions are obtained for the zeta function and the free energy, in the limits of small plate distance, high temperature and strong magnetic field. The Casimir pressure is obtained in each of the three limits and the situation of a magnetic field present between and outside the plates, as well as that of a magnetic field present only between the plates is examined. It is discovered that, in the small plate distance and high temperature limits, the repulsive pressure is less when the magnetic field is present between the plates but not outside, than it is when the magnetic field is present between and outside the plates.
A nonsupersymmetric matrix orbifold

We construct the matrix description for a twisted version of the IIA string theory on S1 with fermions antiperiodic around a spatial circle. The result is a 2+1-dimensional U(N) × U(N) nonsupersymmetric Yang-Mills theory with fermionic matter transforming in the (N,). The the two U(N)'s are exchanged if one goes around a twisted circle of the worldvolume. Relations with type-0 theories are explored and we find type-0 matrix string limits of our gauge theory. We argue however that most of these results are falsified by the absence of SUSY nonrenormalization theorems and that the models do not in fact have a sensible Lorentz invariant space time interpretation.
Possible explanations for the NuTeV Weinberg angle measurement

The NuTeV collaboration has made an independent determination of the Weinberg angle by measuring charged- and neutral-current cross sections from neutrino and antineutrino DIS on iron. Their value differs by 3 standard deviations from that obtained from measurements at the Z pole. We review this experiment and assess various possible explanations for this result, both within the Standard Model (“old physics”), and outside the Standard Model (“new physics”).
Nonsingular Schwarzschild-de Sitter black hole

We combine notions of a maximal curvature scale in nature with that of a minimal curvature scale to construct a non-singular Schwarzschild-de Sitter black hole. We present an exact solution within the context of two-dimensional dilaton gravity. For a range of parameters the solution approaches Schwarzschild-de Sitter at large values of the radial coordinate, asymptotically approaching a de Sitter metric with constant minimal curvature, while approaching a maximal constant curvature smooth spacetime as the radial coordinate approaches zero. The spacetime is geodesically complete and generically has both a black hole horizon and a cosmological horizon.