cssi/SciSciGPT-SciSciNet huggingface dataset:
Evidence for the Galactic X-Ray Bulge. II.

A mosaic of five ROSAT PSPC-pointed observations in the Galactic plane (l ~ 25°) reveals X-ray shadows in the 0.5-2.0 keV band cast by distant molecular clouds. The observed on-cloud and off-cloud X-ray fluxes indicate that ~15% and ~37% of the diffuse X-ray background in this direction in the 3/4 and 1.5 keV bands, respectively, originates behind the molecular gas that is located at ~3 kpc from the Sun. The implication of the derived background X-ray flux beyond the absorbing molecular cloud is consistent with, and lends further support to, recent observations of a Galactic X-ray bulge.
Multiple Gaps in the Disk of the Class I Protostar GY 91

We present the highest spatial resolution ALMA observations to date of the Class I protostar GY 91 in the $\rho$ Ophiuchus L1688 molecular cloud complex. Our 870 $\mu$m and 3 mm dust continuum maps show that the GY 91 disk has a radius of $\sim$80 AU, and an inclination of $\sim$40$^{\circ}$, but most interestingly that the disk has three dark lanes located at 10 AU, 40 AU, and 70 AU. We model these features assuming they are gaps in the disk surface density profile and find that their widths are 7 AU, 30 AU, and 10 AU. These gaps bear a striking resemblance to the gaps seen in the HL Tau disk, suggesting that there may be Saturn-mass planets hiding in the disk. To constrain the relative ages of GY 91 and HL Tau, we also model the disk and envelope of HL Tau and find that they are of similar ages, although GY 91 may be younger. Although snow lines and magnetic dead zones can also produce dark lanes, if planets are indeed carving these gaps then Saturn-mass planets must form within the first $\sim$0.5 Myr of the lifetime of protoplanetary disks.
Interference Avoidance Position Planning in Dual-Hop and Multi-Hop UAV Relay Networks

We consider unmanned aerial vehicle (UAV)-assisted wireless communication employing UAVs as relays to increase the throughput between a pair of transmitter and receiver. We focus on developing effective methods to position the UAV(s) in the presence of interference in the environment, the existence of which makes the problem non-trivial and our methodology different from the current art. We study the optimal position planning, which aims to maximize the (average) signal-to-interference-ratio (SIR) of the system, in the presence of: i) one major source of interference, ii) stochastic interference. For each scenario, we first consider utilizing a single UAV in the dual-hop relay mode and determine its optimal position. Afterward, multiple UAVs in the multi-hop relay mode are considered, for which we investigate two novel problems concerned with determining the optimal number of required UAVs and developing an optimal distributed position alignment method. Subsequently, we propose a cost-effective method that simultaneously minimizes the number of UAVs and determines their optimal positions to guarantee a certain (average) SIR of the system. Alternatively, for a given number of UAVs, we develop a fully distributed placement algorithm along with its performance guarantee. Numerical simulations are provided to evaluate the performance of our proposed methods.
Thermal Pressures in Neutral Clouds inside the Local Bubble, as Determined from C I Fine-Structure Excitations

High-resolution spectra covering the absorption features from interstellar C I were recorded for four early-type stars with spectrographs on the Hubble Space Telescope, in a program to measure the fine-structure excitation of this atom within neutral clouds inside or near the edge of the Local Bubble, a volume of hot (T ~ 106 K) gas that emits soft X-rays and extends out to about 100 pc away from the Sun. The excited levels of C I are populated by collisions, and the ratio of excited atoms to those in the ground level give a measure of the local thermal pressure. Absorptions from the two lowest levels of C I were detected toward α Del and δ Cyg, while only marginal indications of excited C I were obtained for γ Ori and λ Lup. Along with temperature limits derived by other means, the C I fine-structure populations indicate that for the clouds in front of γ Ori, δ Cyg, and α Del, 103 cm-3 K 104 cm-3 K for the Local Bubble, based on the strength of X-ray and EUV emission from the hot gas. This inequality of pressure for these neutral clouds and their surroundings duplicates a condition that exists for the local, partly ionized cloud that surrounds the Sun. An appendix in the paper describes a direct method for determining and eliminating small spectral artifacts arising from variations of detector sensitivity with position.
RECONSTRUCTING THE SOLAR WIND FROM ITS EARLY HISTORY TO CURRENT EPOCH

Stellar winds from active solar-type stars can play a crucial role in removal of stellar angular momentum and erosion of planetary atmospheres. However, major wind properties except for mass-loss rates cannot be directly derived from observations. We employed a three-dimensional magnetohydrodynamic Alfven wave driven solar wind model, ALF3D, to reconstruct the solar wind parameters including the mass-loss rate, terminal velocity, and wind temperature at 0.7, 2, and 4.65 Gyr. Our model treats the wind thermal electrons, protons, and pickup protons as separate fluids and incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating to properly describe proton and electron temperatures of the solar wind. To study the evolution of the solar wind, we specified three input model parameters, the plasma density, Alfven wave amplitude, and the strength of the dipole magnetic field at the wind base for each of three solar wind evolution models that are consistent with observational constrains. Our model results show that the velocity of the paleo solar wind was twice as fast, ~50 times denser and 2 times hotter at 1 AU in the Sun's early history at 0.7 Gyr. The theoretical calculations of mass-loss rate appear to be in agreement with the empirically derived values for stars of various ages. These results can provide realistic constraints for wind dynamic pressures on magnetospheres of (exo)planets around the young Sun and other active stars, which is crucial in realistic assessment of the Joule heating of their ionospheres and corresponding effects of atmospheric erosion.
Scalable Exact Parent Sets Identification in Bayesian Networks Learning with Apache Spark

In Machine Learning, the parent set identification problem is to find a set of random variables that best explain selected variable given the data and some predefined scoring function. This problem is a critical component to structure learning of Bayesian networks and Markov blankets discovery, and thus has many practical applications, ranging from fraud detection to clinical decision support. In this paper, we introduce a new distributed memory approach to the exact parent sets assignment problem. To achieve scalability, we derive theoretical bounds to constraint the search space when MDL scoring function is used, and we reorganize the underlying dynamic programming such that the computational density is increased and fine-grain synchronization is eliminated. We then design efficient realization of our approach in the Apache Spark platform. Through experimental results, we demonstrate that the method maintains strong scalability on a 500-core standalone Spark cluster, and it can be used to efficiently process data sets with 70 variables, far beyond the reach of the currently available solutions.
Scaling behavior of quantum nanosystems: emergence of quasi-particles, collective modes, and mixed exchange symmetry states.

Examples of quantum nanosystems are graphene nanoribbons, molecular wires, and superconducting nanoparticles. The objective of the multiscale theory presented here is to provide a new perspective on the coupling of processes across scales in space and time underlying the dynamics of these systems. The long range objective for this multiscale approach is to serve as an efficient computational algorithm. Long space-time dynamics is derived using a perturbation expansion in the ratio ɛ of the nearest-neighbor distance to a nanometer-scale characteristic length and a theorem on the equivalence of long time-averages and expectation values. This dynamics is shown to satisfy a coarse-grained wave equation (CGWE) which takes a Schrodinger-like form with modified masses and interactions. The scaling of space and time is determined by the orders of magnitude of various contributions to the N-body potential. If the spatial scale of the coarse-graining is too large, the CGWE would imply an unbounded growth of gradien...
Supersingular distribution on average for congruence classes of primes

We demonstrate the existence of a congruence class bias in the distribution of supersingular primes on average for elliptic curves over $\Q$. For example, we show that on average there are twice as many supersingular primes congruent to 2 mod 3 as there are congruent to 1 mod 3. Our result is obtained using the averaging approach of Fouvry-Murty along with ideas of David-Pappalardi.
Scaling behavior of columnar structure during physical vapor deposition

The statistical effects of different conditions in physical vapor deposition, such as sputter deposition, have on thin film morphology has long been the subject of interest. One notable effect is that of column development due to differential chamber pressure in the well-known empirical model called the Thornton's Structure Zone Model. The model is qualitative in nature and theoretical understanding with quantitative predictions of the morphology is still lacking due, in part, to the absence of a quantitative description of the incident flux distribution on the growth front. In this work, we propose an incident Gaussian flux model developed from a series of binary hard-sphere collisions and simulate its effects using Monte Carlo methods and a solid-on-solid growth scheme. We also propose an approximate cosine-power distribution for faster Monte Carlo sampling. With this model, it is observed that higher chamber pressures widen the average deposition angle, and similarly increase the growth of column diame...
Microelectromechanical deformable mirror development for high-contrast imaging, part 1: miniaturized, flight-capable control electronics

Deformable mirrors (DMs) are a critical technology to enable coronagraphic direct imaging of exoplanets with current and planned ground- and space-based telescopes as well as future mission concepts, such as the Habitable Exoplanet Observatory and the Large UV/Optical/IR Surveyor. The latter concepts aim to image exoplanet types ranging from gas giants to Earth analogs. This places several requirements on the DMs such as requires a large actuator count (≳3000), fine surface height resolution (≲10 pm), and radiation hardened driving electronics with low mass and volume. We present the design and testing of a flight-capable, miniaturized DM controller. Having achieved contrasts on the order of 5 × 10 − 9 on a coronagraph testbed in vacuum in the high contrast imaging testbed facility at NASA’s Jet Propulsion Laboratory (JPL), we demonstrate that the electronics are capable of meeting the requirements of future coronagraph-equipped space telescopes. We also report on functionality testing on-board the high-altitude balloon experiment “Planetary Imaging Concept Testbed Using a Recoverable Experiment – Coronagraph,” which aims to directly image debris disks and exozodiacal dust around nearby stars. The controller is designed for the Boston Micromachines Corporation Kilo-DM and is readily scalable to larger DM formats. The three main components of the system (the DM, driving electronics, and mechanical and heat management) are designed to be compact and have low-power consumption to enable its use not only on exoplanet missions, but also in a wide-range of applications that require precision optical systems, such as direct line-of-sight laser communications. The controller is capable of handling 1024 actuators with 220 V maximum dynamic range, 16-bit resolution, 14-bit accuracy, and 1 kHz operating frequency. The system fits in a 10 × 10 × 5 cm3 volume, weighs <0.5 kg, and consumes <8 W. We have developed a turnkey solution reducing the risk for future missions, lowering their cost by significantly reducing volume, weight, and power consumption of the wavefront control hardware.
QUANTUM FLUIDS IN NANOPORES

We describe calculations of the properties of quantum fluids inside nanotubes of various sizes. Very small radius (R) pores confine the gases to a line, so that a one-dimensional (1D) approximation is applicable; the low temperature behavior of 1D 4He is discussed. Somewhat larger pores permit the particles to move off axis, resulting eventually in a transition to a cylindrical shell phase—a thin film near the tube wall; we explored this behavior for H2. At even larger R ~ 1 nm, both the shell phase and an axial phase are present. Results showing strong binding of cylindrical liquids 4He and 3He are discussed.
Independence of satellites of torus knots in the smooth concordance group

The main goal of this article is to obtain a condition under which an infinite collection $\mathscr{F}$ of satellite knots (with companion a positive torus knot and pattern similar to the Whitehead link) freely generates a subgroup of infinite rank in the smooth concordance group. This goal is attained by examining both the instanton moduli space over a 4-manifold with tubular ends and the corresponding Chern-Simons invariant of the adequate 3-dimensional portion of the 4-manifold. More specifically, the result is derived from Furuta's criterion for the independence of Seifert fibred homology spheres in the homology cobordism group of oriented homology 3-spheres. Indeed, we first associate to $\mathscr{F}$ the corresponding collection of 2-fold covers of the 3-sphere branched over the elements of $\mathscr{F}$ and then introduce definite cobordisms from the aforementioned covers of the satellites to a number of Seifert fibered homology spheres. This allows us to apply Furuta's criterion and thus obtain a condition that guarantees the independence of the family $\mathscr{F}$ in the smooth concordance group.
Trapped, Two-Armed, Nearly Vertical Oscillations in Disks with Toroidal Magnetic Fields II: Effects of Finite Thickness

We examine the radial trapping of two-armed (m = 2) vertical p-mode oscillations in geometrically thin relativistic disks that are vertically isothermal, but terminated at a certain height by the presence of hot and low-density corona. The disks are assumed to be subject to toroidalmagneticfields. The oscillationsare classified by n, anumber related to the node number of oscillations in the vertical direction, and starting from n = 1. In modes with n = 1, the frequencies of trapped oscillations depend little on the height of termination, but in modes with n = 2, 3, ��� the frequencies decrease and the radial extentions of the trapped region become wide, as the termination height decreases. This study is a preparation to examine whether these oscillations can describe kilo-hertz quasi-periodic oscillations (kHz QPOs), horizontal branch oscillations (HBOs), and their correlations.
Bias in the Effective Field Theory of Large Scale Structures

We study how to describe collapsed objects, such as galaxies, in the context of the Effective Field Theory of Large Scale Structures. The overdensity of galaxies at a given location and time is determined by the initial tidal tensor, velocity gradients and spatial derivatives of the regions of dark matter that, during the evolution of the universe, ended up at that given location. Similarly to what was recently done for dark matter, we show how this Lagrangian space description can be recovered by upgrading simpler Eulerian calculations. We describe the Eulerian theory. We show that it is perturbatively local in space, but non-local in time, and we explain the observational consequences of this fact. We give an argument for why to a certain degree of accuracy the theory can be considered as quasi time-local and explain what the operator structure is in this case. We describe renormalization of the bias coefficients so that, after this and after upgrading the Eulerian calculation to a Lagrangian one, the perturbative series for galaxies correlation functions results in a manifestly convergent expansion in powers of k/kNL and k/kM, where k is the wavenumber of interest, kNL is the wavenumber associated to the non-linear scale, and kM is the comoving wavenumber enclosing the mass of a galaxy.
On the ambiguity in the notion of transverse traceless modes of gravitational waves

Somewhat surprisingly, in many of the widely used monographs and review articles the term Transverse-Traceless modes of linearized gravitational waves is used to denote two entirely different notions. These treatments generally begin with a decomposition of the metric perturbation that is local in the momentum space (and hence non-local in physical space), and denote the resulting transverse traceless modes by $$h_{ab}^{\mathrm{TT}}$$ . However, while discussing gravitational waves emitted by an isolated system—typically in a later section—the relevant modes are extracted using a ‘projection operator’ that is local in physical space. These modes are also called transverse-traceless and again labeled $$h_{ab}^{\mathrm{TT}}$$ , implying that this is just a reformulation of the previous notion. But the two notions are conceptually distinct and the difference persists even in the asymptotic region. We show that this confusion arises already in Maxwell theory that is often discussed as a prelude to the gravitational case. Finally, we discuss why the distinction has nonetheless remained largely unnoticed, and also point out that there are some important physical effects where only one of the notions gives the correct answer.
Precision annealing Monte Carlo methods for statistical data assimilation and machine learning

The authors develop a method for transferring information from noisy data to an underlying dynamical or machine learning model. The work uses Precision Annealing which adds tools to the well-established Monte Carlo methods. The proposed method allows the desired transfer of information to be achieved with high accuracy and high computational efficiency by identifying the dominant parts in the high-dimensional expected value integrals that emerge.
Hagedorn transition for strings on pp-waves and tori with chemical potentials

Abstract It has been conjectured that string theory in a pp-wave background is dual to a sector of N =4 supersymmetric Yang–Mills theory. We study the Hagedorn transition for free strings in this background. We find that the free energy at the transition point is finite suggesting a confinement/deconfinement transition in the gauge theory. In the limit of vanishing mass parameter the free energy matches that of free strings on an 8-torus with momentum/winding chemical potential. The entropy in the microcanonical ensemble with fixed energy and fixed momentum/winding is computed in each case.
Casimir effect due to a single boundary as a manifestation of the Weyl problem

The Casimir self-energy of a boundary is ultraviolet-divergent. In many cases, the divergences can be eliminated by methods such as zeta-function regularization or through physical arguments (ultraviolet transparency of the boundary would provide a cutoff). Using the example of a massless scalar field theory with a single Dirichlet boundary, we explore the relationship between such approaches, with the goal of better understanding of the origin of the divergences. We are guided by the insight due to Dowker and Kennedy (1978 J. Phys. A: Math. Gen. 11 895) and Deutsch and Candelas (1979 Phys. Rev. D 20 3063) that the divergences represent measurable effects that can be interpreted with the aid of the theory of the asymptotic distribution of eigenvalues of the Laplacian discussed by Weyl. In many cases, the Casimir self-energy is the sum of cutoff-dependent (Weyl) terms having a geometrical origin, and an 'intrinsic' term that is independent of the cutoff. The Weyl terms make a measurable contribution to the physical situation even when regularization methods succeed in isolating the intrinsic part. Regularization methods fail when the Weyl terms and intrinsic parts of the Casimir effect cannot be clearly separated. Specifically, we demonstrate that the Casimir self-energy of a smooth boundary in two dimensions is a sum of two Weyl terms (exhibiting quadratic and logarithmic cutoff dependence), a geometrical term that is independent of cutoff and a non-geometrical intrinsic term. As by-products, we resolve the puzzle of the divergent Casimir force on a ring and correct the sign of the coefficient of linear tension of the Dirichlet line predicted in earlier treatments.
Optimum topology of quasi-one-dimensional nonlinear optical quantum systems

In this paper, we determine the optimum topology of quasi-one-dimensional nonlinear optical structures using generalized quantum graph models. Quantum graphs are relational graphs endowed with a metric and a multiparticle Hamiltonian acting on the edges, and have a long application history in aromatic compounds, mesoscopic and artificial materials, and quantum chaos. Quantum graphs have recently emerged as models of quasi-one-dimensional electron motion for simulating quantum-confined nonlinear optical systems. This paper derives the nonlinear optical properties of quantum graphs containing the basic star vertex and compares their responses across topological and geometrical classes. We show that such graphs have exactly the right topological properties to generate energy spectra required to achieve large, intrinsic optical nonlinearities. The graphs have the exquisite geometrical sensitivity required to tune wave function overlap in a way that optimizes the transition moments. We show that this class of graphs consistently produces intrinsic optical nonlinearities near the fundamental limits. We discuss the application of the models to the prediction and development of new nonlinear optical structures.
Neural Cross-Lingual Relation Extraction Based on Bilingual Word Embedding Mapping

Relation extraction (RE) seeks to detect and classify semantic relationships between entities, which provides useful information for many NLP applications. Since the state-of-the-art RE models require large amounts of manually annotated data and language-specific resources to achieve high accuracy, it is very challenging to transfer an RE model of a resource-rich language to a resource-poor language. In this paper, we propose a new approach for cross-lingual RE model transfer based on bilingual word embedding mapping. It projects word embeddings from a target language to a source language, so that a well-trained source-language neural network RE model can be directly applied to the target language. Experiment results show that the proposed approach achieves very good performance for a number of target languages on both in-house and open datasets, using a small bilingual dictionary with only 1K word pairs.
MINLP in transmission expansion planning

Transmission expansion planning requires forecasts of demand for electric power and a model of the underlying physics, i.e., power flows. We present three approaches to deriving exact solutions to the transmission expansion planning problem in the alternating-current model, for a given load.
Testing EUV/X-Ray Atomic Data for the Solar Dynamics Observatory

The Atmospheric Imaging Assembly (AIA) and the Extreme-ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) include spectral windows in the X-ray/EUV band. Accuracy and completeness of the atomic data in this wavelength range is essential for interpretation of the spectrum and irradiance of the solar corona, and of SDO observations made with the AIA and EVE instruments. Here, we test the X-ray/EUV data in the CHIANTI database to assess their completeness and accuracy in the SDO bands, with particular focus on the 94 A and 131 A AIA passbands. Given the paucity of solar observations adequate for this purpose, we use high-resolution X-ray spectra of the low-activity solar-like corona of Procyon obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We find that while spectral models overall can reproduce quite well the observed spectra in the soft X-ray range {lambda} {approx} 130 A, they significantly underestimate the observed flux in the 50-130 A wavelength range. The model underestimates the observed flux by a variable factor ranging from Almost-Equal-To 1.5, at short wavelengths below {approx}50 A, up to Almost-Equal-To 5-7 in the {approx}70-125 A range. In the AIAmore » bands covered by LETGS, i.e., 94 A and 131 A, we find that the observed flux can be underestimated by large factors ({approx}3 and {approx}1.9, respectively, for the case of Procyon presented here). We discuss the consequences for analysis of AIA data and possible empirical corrections to the AIA responses to model more realistically the coronal emission in these passbands.« less
Kinetics of first passage in a cone

We study statistics of first passage inside a cone in an arbitrary spatial dimension. The probability that a diffusing particle avoids the cone boundary decays algebraically with time. The decay exponent depends on two variables: the opening angle of the cone and the spatial dimension. In four dimensions, we find an explicit expression for the exponent, and in general, we obtain it as a root of a transcendental equation involving associated Legendre functions. At large dimensions, the decay exponent depends on a single scaling variable, while roots of the parabolic cylinder function specify the scaling function. Consequently, the exponent is of order one only if the cone surface is very close to a plane. We also perform asymptotic analysis for extremely thin and extremely wide cones.
Sharp distortion growth for bilipschitz extension of planar maps

This note addresses the quantitative aspect of the bilipschitz extension problem. The main result states that any bilipschitz embedding of R into R2 can be extended to a bilipschitz self-map of R2 with a linear bound on the distortion.
FUSE Measurements of Far-Ultraviolet Extinction. III. The Dependence on R(V) and Discrete Feature Limits from 75 Galactic Sightlines

We present a sample of 75 extinction curves derived from Far Ultraviolet Spectroscopic Explorer (FUSE) far-ultraviolet spectra supplemented by existing International Ultraviolet Explorer (IUE) spectra. The extinction curves were created using the standard pair method based on a new set of dereddened FUSE+IUE comparison stars. Molecular hydrogen absorption features were removed using individualized H2 models for each sightline. The general shape of the FUSE extinction (8.4 μm–1 9.6 μm–1 on features with a resolution of 104 (~0.1 A width).
LOBE OVERFLOW AS THE LIKELY CAUSE OF PERICENTER OUTBURST IN AN SMBH ORBITER

A very large lobe overflow event is suggested to explain the 0. m 4 brightening observed in K band at pericenter passage of the star known as S2 that orbits the Galaxy’s supermassive black hole (SMBH). Known observed properties of S2 that contribute to lobe filling are 1) the enormous mass ratio, MSMBH/MS2, 2) S2’s fast rotation, and 3) S2’s large orbital eccentricity. Published estimates have given limiting lobe sizes of order 100 to 300 R⊙ but, with S2’s fast rotation taken into account, the computed lobe size is much smaller, being compatible with either a main sequence OB star or a stripped evolved star. An important evolutionary consideration that predicts very large pericenter overflows is envelope expansion following mass loss that is characteristic of highly evolved stars. Material removed by lobe overflow at pericenter is replenished by envelope expansion as an evolved star awaits its next pericenter passage. An observational signature of lobe overflow for upcoming pericenter passages would be appearance of emission lines as the ejected gas expands and becomes optically thin.
EQUIVARIANT K-THEORY OF GRASSMANNIANS II: THE KNUTSON-VAKIL CONJECTURE

In 2005, A. Knutson-R. Vakil conjectured a puzzle rule for equivariantK-theory of Grassmannians. We resolve this conjecture. After giving a correction, we establish a modified rule by combinatorially connecting it to the authors' recently proved tableau rule for the same Schubert calculus problem.
Secure communications using nonlinear silicon photonic keys.

We present a secure communication system constructed using pairs of nonlinear photonic physical unclonable functions (PUFs) that harness physical chaos in integrated silicon micro-cavities. Compared to a large, electronically stored one-time pad, our method provisions large amounts of information within the intrinsically complex nanostructure of the micro-cavities. By probing a micro-cavity with a rapid sequence of spectrally-encoded ultrafast optical pulses and measuring the lightwave responses, we experimentally demonstrate the ability to extract 2.4 Gb of key material from a single micro-cavity device. Subsequently, in a secure communication experiment with pairs of devices, we achieve bit error rates below 10−5 at code rates of up to 0.1. The PUFs’ responses are never transmitted over the channel or stored in digital memory, thus enhancing the security of the system. Additionally, the micro-cavity PUFs are extremely small, inexpensive, robust, and fully compatible with telecommunications infrastructure, components, and electronic fabrication. This approach can serve one-time pad or public key exchange applications where high security is required.
From Little String Free Energies Towards Modular Graph Functions

We study the structure of the non-perturbative free energy of a one-parameter class of little string theories (LSTs) of A-type in the so-called unrefined limit. These theories are engineered by $N$ M5-branes probing a transverse flat space. By analysing a number of examples, we observe a pattern which suggests to write the free energy in a fashion that resembles a decomposition into higher-point functions which can be presented in a graphical way reminiscent of sums of (effective) Feynman diagrams: to leading order in the instanton parameter of the LST, the $N$ external states are given either by the fundamental building blocks of the theory with $N=1$, or the function that governs the counting of BPS states of a single M5-brane coupling to one M2-brane on either side. These states are connected via an effective coupling function which encodes the details of the gauge algebra of the LST and which in its simplest (non-trivial) form is captured by the scalar Greens function on the torus. More complicated incarnations of this function show certain similarities with so-called modular graph functions, which have appeared in the study of Feynman amplitudes in string- and field theory. Finally, similar structures continue to exist at higher instanton orders, which, however, also contain contributions that can be understood as the action of (Hecke) operators on the leading instanton result.
Inclined Pulsar Magnetospheres in General Relativity: Polar Caps for the Dipole, Quadrudipole, and Beyond

NSF [1205550, 1506027]; NASA [NNX15AT50H]; Porter Ogden Jacobus Fellowship by the graduate school of Princeton University; NASA/Ames HEC [SMD-16-6663, SMD-16-7816]
Area law unification and the holographic event horizon

We prove a new, large family of area laws in general relativity, which apply to certain classes of untrapped surfaces that we dub generalized holographic screens. Our family of area laws contains, as special cases, the area laws for marginally-trapped surfaces (holographic screens) and the event horizon (Hawking’s area theorem). In addition to these results in general relativity, we show that in the context of holography the geometry of a generalized holographic screen is related to the outer entropy of the screen. Specifically, we show for spherically-symmetric spacetimes that the area of the largest HRT surface consistent with the outer wedge can be computed in terms of the geometry of the general (not necessarily marginally-trapped) codimension-two surface defining the wedge. This outer entropy satisfies a second law of thermodynamics, growing monotonically along the generalized holographic screen. In particular, this result provides the holographic dual for the geometry of the event horizon for spherically-symmetric spacetimes.
Causal Holography of Traversing Flows

We study smooth traversing vector fields v on compact manifolds X with boundary. A traversing v admits a Lyapunov function $$f: X \rightarrow \mathbb R$$ such that $$df(v) > 0$$ . We show that the trajectory spaces $${\mathcal {T}}(v)$$ of traversally generic v-flows are Whitney stratified spaces, and thus admit triangulations amenable to their natural stratifications. Despite being spaces with singularities, $${\mathcal {T}}(v)$$ retain some residual smooth structure of X. Let $${\mathcal {F}}(v)$$ denote the oriented 1-dimensional foliation on X, produced by a traversing v-flow. With the help of a boundary generic v, we divide the boundary $$\partial X$$ of X into two complementary compact manifolds, $$\partial ^+X(v)$$ and $$\partial ^-X(v)$$ . Then, for a traversing v, we introduce the causality map $$C_v: \partial ^+X(v) \rightarrow \partial ^-X(v)$$ . Our main result claims that, for boundary generic traversing vector fields v, the causality map $$C_v$$ allows for a reconstruction of the pair $$(X, {\mathcal {F}}(v))$$ , up to a homeomorphism $$\Phi : X \rightarrow X$$ such that $$\Phi |_{\partial X} = id_{\partial X}$$ . In other words, for a massive class of ODEs, we show that the topology of their solutions, satisfying a given boundary value problem, is rigid. We call these results “holographic” since the $$(n+1)$$ -dimensional X and the un-parameterized dynamics of the v-flow are captured by a single map $$C_v$$ between two n-dimensional screens, $$\partial ^+X(v)$$ and $$\partial ^-X(v)$$ . This holography of traversing flows has numerous applications to the dynamics of general flows. Some of them are described in the paper. Others, are just outlined.
Springer Representations on the Khovanov Springer Varieties

Springer varieties are studied because their cohomology carries a natural action of the symmetric group S n and their top-dimensional cohomology is irreducible. In his work on tangle invariants, Khovanov constructed a family of Springer varieties X n as subvarieties of the product of spheres ( S 2 ) n . We show that if X n is embedded antipodally in ( S 2 ) n then the natural S n -action on ( S 2 ) n induces an S n -representation on the image of H ∗( X n ). This representation is the Springer representation. Our construction admits an elementary (and geometrically natural) combinatorial description, which we use to prove that the Springer representation on H ∗( X n ) is irreducible in each degree. We explicitly identify the Kazhdan-Lusztig basis for the irreducible representation of S n corresponding to the partition ( n /2, n /2).
An adjoint-based approach for finding invariant solutions of Navier–Stokes equations

We consider the incompressible Navier–Stokes equations with periodic boundary conditions and time-independent forcing. For this type of flow, we derive adjoint equations whose trajectories converge asymptotically to the equilibrium and travelling-wave solutions of the Navier–Stokes equations. Using the adjoint equations, arbitrary initial conditions evolve to the vicinity of a (relative) equilibrium at which point a few Newton-type iterations yield the desired (relative) equilibrium solution. We apply this adjoint-based method to a chaotic two-dimensional Kolmogorov flow. A convergence rate of is observed, leading to the discovery of new steady-state and travelling-wave solutions at Reynolds number . Some of the new invariant solutions have spatially localized structures that were previously believed to exist only on domains with large aspect ratios. We show that one of the newly found steady-state solutions underpins the temporal intermittencies, i.e. high energy dissipation episodes of the flow. More precisely, it is shown that each intermittent episode of a generic turbulent trajectory corresponds to its close passage to this equilibrium solution.
Finite-rank perturbations of random band matrices via infinitesimal free probability

We prove a sharp $\sqrt{N}$ transition for the infinitesimal distribution of a periodically banded GUE matrix. For band widths $b_N = \Omega(\sqrt{N})$, we further prove that our model is infinitesimally free from the matrix units and the normalized all-ones matrix. Our results allow us to extend previous work of Shlyakhtenko on finite-rank perturbations of Wigner matrices in the infinitesimal framework. For finite-rank perturbations of our model, we find outliers at the classical positions from the deformed Wigner ensemble.
Approximate Cross-Validation for Structured Models

Many modern data analyses benefit from explicitly modeling dependence structure in data -- such as measurements across time or space, ordered words in a sentence, or genes in a genome. A gold standard evaluation technique is structured cross-validation (CV), which leaves out some data subset (such as data within a time interval or data in a geographic region) in each fold. But CV here can be prohibitively slow due to the need to re-run already-expensive learning algorithms many times. Previous work has shown approximate cross-validation (ACV) methods provide a fast and provably accurate alternative in the setting of empirical risk minimization. But this existing ACV work is restricted to simpler models by the assumptions that (i) data across CV folds are independent and (ii) an exact initial model fit is available. In structured data analyses, both these assumptions are often untrue. In the present work, we address (i) by extending ACV to CV schemes with dependence structure between the folds. To address (ii), we verify -- both theoretically and empirically -- that ACV quality deteriorates smoothly with noise in the initial fit. We demonstrate the accuracy and computational benefits of our proposed methods on a diverse set of real-world applications.
Forward-Mode Differentiation of Maxwell’s Equations

We discuss the application of the forward-mode differentiation method to Maxwell’s equations, which is useful for the sensitivity analysis of photonic devices. This approach yields exact gradients ...
Under the Firelight: Stellar Tracers of the Local Dark Matter Velocity Distribution in the Milky Way

Author(s): Necib, L; Lisanti, M; Garrison-Kimmel, S; Wetzel, A; Sanderson, R; Hopkins, PF; Faucher-Giguere, CA; Keres, D | Abstract: The Gaia era opens new possibilities for discovering the remnants of disrupted satellite galaxies in the solar neighborhood. If the population of local accreted stars is correlated with the dark matter sourced by the same mergers, one can then map the dark matter distribution directly. Using two cosmological zoom-in hydrodynamic simulations of Milky-Way-mass galaxies from the Latte suite of the Fire-2 simulations, we find a strong correlation between the velocity distribution of stars and dark matter at the solar circle that were accreted from luminous satellites. This correspondence holds for dark matter that is either relaxed or in a kinematic substructure called debris flow, and is consistent between two simulated hosts with different merger histories. The correspondence is more problematic for streams because of possible spatial offsets between the dark matter and stars. We demonstrate how to reconstruct the dark matter velocity distribution from the observed properties of the accreted stellar population by properly accounting for the ratio of stars to dark matter contributed by individual mergers. This procedure does not account for the dark matter that originates from nonluminous satellites, which may constitute a nontrivial fraction of the local contribution. After validating this method using the Fire-2 simulations, we apply it to the Milky Way and use it to recover the dark matter velocity distribution associated with the recently discovered stellar debris field in the solar neighborhood. Based on results from Gaia, we estimate that of the local dark matter that is accreted from luminous mergers is in debris flow.
Constraining the Frequency of Free-floating Planets from a Synthesis of Microlensing, Radial Velocity, and Direct Imaging Survey Results

A microlensing survey by Sumi et al. (2011) exhibits an overabundance of short-timescale events (STEs; t_E ~10 AU) and free-floating planets. Assuming these STEs are indeed due to planetary-mass objects, we aim to constrain the fraction of these events that can be explained by bound but wide-separation planets. We fit the observed timescale distribution with a lens mass function comprised of brown dwarfs, main-sequence stars, and stellar remnants, finding and thus corroborating the initial identification of an excess of STEs. We then include a population of bound planets that are expected not to show signatures of the primary lens (host) in their microlensing light curves and that are also consistent with results from representative microlensing, radial velocity, and direct imaging surveys. We find that bound planets alone cannot explain the entire STE excess without violating the constraints from the surveys we consider and thus some fraction of these events must be due to free-floating planets, if our model for bound planets holds. We estimate a median fraction of STEs due to free-floating planets to be f=0.67 (0.23-0.85 at 95% confidence) when assuming "hot-start" planet evolutionary models and f=0.58 (0.14-0.83 at 95% confidence) for "cold-start" models. Assuming a delta-function distribution of free-floating planets of mass m_p=2 M_Jup yields a number of free-floating planets per main-sequence star of N=1.4 (0.48-1.8 at 95% confidence) in the "hot-start" case and N=1.2 (0.29-1.8 at 95% confidence) in the "cold-start" case.
Growth of Ni and Ni-Cr alloy thin films on MgO(001): Effect of alloy composition on surface morphology

The effects of substrate treatment, growth temperature, and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy and atomic force microscopy. We demonstrate that a combination of acid-etched substrates and high temperature deposition (400 °C) will result in smooth films with well-defined terraces (up to 30 nm wide) that are suitable for the study of progression of chemical reactions on the surface. Two different treatments are used to prepare the MgO substrates for deposition and they introduce characteristic differences in film surface morphology. Thin films that are grown on the phosphoric acid-treated substrates present reduced nucleation density during the initial stages of film growth which results in long and wide terraces. Due to the ≈16% lattice mismatch in the Ni(001)/MgO(001) system, film growth at 400 °C yields discontinuous films and a two-step growth process is necessary to obtain a continuous layer. Ni films are deposited at...
Aharonov-Bohm phase for an electromagnetic wave background

The canonical Aharonov–Bohm effect is usually studied with time-independent potentials. In this work, we investigate the Aharonov–Bohm phase acquired by a charged particle moving in time-dependent potentials. In particular, we focus on the case of a charged particle moving in the time-varying field of a plane electromagnetic wave. We work out the Aharonov–Bohm phase using both the potential (i.e. $$\oint A_\mu \mathrm{d}x ^\mu $$ ) and the field (i.e. $$\frac{1}{2}\int F_{\mu \nu } \mathrm{d}\sigma ^{\mu \nu }$$ ) forms of the Aharonov–Bohm phase. We give conditions in terms of the parameters of the system (frequency of the electromagnetic wave, the size of the space–time loop, amplitude of the electromagnetic wave) under which the time-varying Aharonov–Bohm effect could be observed.
VARIABILITY OF THE PULSED RADIO EMISSION FROM THE LARGE MAGELLANIC CLOUD PULSAR PSR J0529−6652

We have studied the variability of PSR J0529?6652, a radio pulsar in the Large Magellanic Cloud (LMC), using observations conducted at 1390?MHz with the Parkes 64?m telescope. PSR J0529?6652 is detectable as a single pulse emitter, with amplitudes that classify the pulses as giant pulses. This makes PSR J0529?6652 the second known giant pulse emitter in the LMC, after PSR B0540?69. The fraction of the emitted pulses detectable from PSR J0529?6652 at this frequency is roughly two orders of magnitude greater than it is for either PSR B0540?69 or the Crab pulsar (if the latter were located in the LMC). We have measured a pulse nulling fraction of 83.3% ? 1.5% and an intrinsic modulation index of 4.07 ? 0.29 for PSR J0529?6652. The modulation index is significantly larger than values previously measured for typical radio pulsars but is comparable to values reported for members of several other neutron star classes. The large modulation index, giant pulses, and large nulling fraction suggest that this pulsar is phenomenologically more similar to these other, more variable sources, despite having spin and physical characteristics that are typical of the unrecycled radio pulsar population. The large modulation index also does not appear to be consistent with the small value predicted for this pulsar by a model of polar cap emission outlined by Gil & Sendyk. This conclusion depends to some extent on the assumption that PSR J0529?6652 is exhibiting core emission, as suggested by its simple profile morphology, narrow profile width, and previously measured profile polarization characteristics.
Quantum Systems based upon Galois Fields - from Sub-quantum to Super-quantum Correlations -

In this paper, we describe our recent work on discrete quantum theory based on Galois fields. In particular, we discuss how discrete quantum theory sheds new light on the foundations of quantum theory and we review an explicit model of super-quantum correlations we have constructed in this context. We also discuss the larger questions of the origins and foundations of quantum theory, as well as the relevance of super-quantum theory for the quantum theory of gravity.
Two-dimensional compressible viscous flow around a circular cylinder

Direct numerical simulation is performed to study compressible viscous flow around a circular cylinder. The present study considers two-dimensional shock-free continuum flow by varying the Reynolds number between 20 and 100 and the free-stream Mach number between 0 and 0.5. The results indicate that compressibility effects elongate the near wake for cases above and below the critical Reynolds number for two-dimensional flow under shedding. The wake elongation becomes more pronounced as the Reynolds number approaches this critical value. Moreover, we determine the growth rate and frequency of linear instability for cases above the critical Reynolds number. From the analysis, it is observed that the frequency of the Benard–von Karman vortex street in the time-periodic fully saturated flow increases from the dominant unstable frequency found from the linear stability analysis as the Reynolds number increases from its critical value, even for the low range of Reynolds numbers considered. We also find that the compressibility effects reduce the growth rate and dominant frequency in the linear growth stage. Semi-empirical functional relationships for the growth rate and the dominant frequency in linearized flow around the cylinder in terms of the Reynolds number and free-stream Mach number are presented.