cssi/SciSciGPT-SciSciNet huggingface dataset:
Cutoff phenomena for random walks on random regular graphs

The cutoff phenomenon describes a sharp transition in the convergence of a family of ergodic finite Markov chains to equilibrium. Many natural families of chains are believed to exhibit cutoff, and yet establishing this fact is often extremely challenging. An important such family of chains is the random walk on G(n,d), a random d-regular graph on n vertices. It is well known that almost every such graph for d≥3 is an expander, and even essentially Ramanujan, implying a mixing time of O(logn). According to a conjecture of Peres, the simple random walk on G(n,d) for such d should then exhibit cutoff with high probability (whp). As a special case of this, Durrett conjectured that the mixing time of the lazy random walk on a random 3-regular graph is whp (6+o(1))log2n. In this work we confirm the above conjectures and establish cutoff in total-variation, its location, and its optimal window, both for simple and for non-backtracking random walks on G(n,d). Namely, for any fixed d≥3, the simple random walk on G(n,d) whp has cutoff at (d/(d−2))logd−1n with window order logn. Surprisingly, the non-backtracking random walk on G(n,d) whp has cutoff already at logd−1n with constant window order. We further extend these results to G(n,d) for any d=no(1) that grows with n (beyond which the mixing time is O(1)), where we establish concentration of the mixing time on one of two consecutive integers
Compton Echoes from Gamma-Ray Bursts: Unveiling Misaligned Jets in Nearby Type Ib/c Supernovae

There is now compelling evidence of a link between long-duration gamma-ray bursts (GRBs) and Type Ib/c supernovae (SNe). These core-collapse explosions are conjectured to radiate an anisotropic, beamed component associated with a decelerating, relativistic outflow and an unbeamed, isotropic component associated with the slowly expanding stellar debris. The anisotropic emission remains at a very low level until the Doppler cone of the beam intersects the observer's line of sight, making off-axis GRB jets directly detectable only at long wavelengths and late times (1 yr). Circumstellar material, however, will Compton scatter the prompt gamma-ray and afterglow radiation flux and give rise to a reflection echo. We show that the Compton echo of a misaligned GRB carries an X-ray luminosity that may exceed by many orders of magnitude that produced by the underlying subrelativistic SN during the first few weeks. Bright scattering echoes may therefore provide a means for detecting a population of misaligned GRBs associated with nearby Type Ib/c SNe and yield crucial information on the environment surrounding a massive star at the time of its death. The question of whether or not the interpretation of GRB 980425 as an ordinary GRB observed off-axis is consistent with the lack of an X-ray echo is addressed, along with the constraints derived on the possible existence of misaligned GRB jets in SN 1993J, SN 1994I, SN 1999em, and SN 2002ap.
Causal inference in travel demand modeling (and the lack thereof)

Abstract This paper is about the general disconnect that we see, both in practice and in literature, between the disciplines of travel demand modeling and causal inference. In this paper, we assert that travel demand modeling should be one of the many fields that focuses on the production of valid causal inferences, and we hypothesize about reasons for the current disconnect between the two bodies of research. Furthermore, we explore the potential benefits of uniting these two disciplines. We consider what travel demand modeling can gain from greater incorporation of techniques and perspectives from the causal inference literatures, and we briefly discuss what the causal inference literature might gain from the work of travel demand modelers. In this paper, we do not attempt to “solve” issues related to the drawing of causal inferences from travel demand models. Instead, we hope to spark a larger discussion both within and between the travel demand modeling and causal inference literatures. In particular, we hope to incite discussion about the necessity of drawing causal inferences in travel demand applications and the methods by which one might credibly do so.
A novel vectorcardiogram system

This paper presents the proof-of-concept investigation for a miniaturized vectorcardiogram [VCG] system for ambulatory on-body applications that continuously monitors the electrical activity of the heart in three dimensions. We investigate the minimum distance between a pair of leads in the X, Y and Z axes such that the signals are distinguishable from the noise. The target dimensions for our VCG are 3×3×2 cm and, based on our preliminary results, it is possible to achieve these dimensions. The next step in our research is to build the miniaturized VCG system that includes processing, learning and communication capabilities.
The Warm Neptunes around HD 106315 Have Low Stellar Obliquities

We present the obliquity of the warm Neptune HD 106315c measured via a series of spectroscopic transit observations. HD 106315c is a 4.4 REarth warm Neptune orbiting a moderately rotating late F-star with a period of 21.05 days. HD 106315 also hosts a 2.5 REarth super-Earth on a 9.55 day orbit. Our Doppler tomographic analyses of four transits observed by the Magellan/MIKE, HARPS, and TRES facilities find HD 106315c to be in a low stellar obliquity orbit, consistent with being well aligned with the spin axis of the host star at lambda = -10 +3.6/-3.8 deg. We suggest, via dynamical N-body simulations, that the two planets in the system must be co-planar, and thus are both well aligned with the host star. HD 106315 is only the fourth warm Neptune system with obliquities measured. All warm Neptune systems have been found in well aligned geometries, consistent with the interpretation that these systems are formed in-situ in the inner protoplanetary disk, and also consistent with the majority of Kepler multi-planet systems that are in low obliquity orbits. With a transit depth of 1.02 mmag, HD 106315c is among the smallest planets to have been detected in transit spectroscopy, and we discuss its detection in the context of TESS and the next generations of spectrographs.
ZODIACAL EXOPLANETS IN TIME (ZEIT). IV. SEVEN TRANSITING PLANETS IN THE PRAESEPE CLUSTER

Open clusters and young stellar associations are attractive sites to search for planets and to test theories of planet formation, migration, and evolution. We present our search for, and characterization of, transiting planets in the ~800 Myr old Praesepe (Beehive, M44) Cluster from K2 light curves. We identify seven planet candidates, six of which we statistically validate to be real planets, the last of which requires more data. For each host star we obtain high-resolution NIR spectra to measure its projected rotational broadening and radial velocity, the latter of which we use to confirm cluster membership. We combine low-resolution spectra with the known cluster distance and metallicity to provide precise temperatures, masses, radii, and luminosities for the host stars. Combining our measurements of rotational broadening, rotation periods, and our derived stellar radii, we show that all planetary orbits are consistent with alignment to their host star's rotation. We fit the K2 light curves, including priors on stellar density to put constraints on the planetary eccentricities, all of which are consistent with zero. The difference between the number of planets found in Praesepe and Hyades (8 planets) and a similar dataset for Pleiades (0 planets, ~125 Myr) suggests a trend with age, but may be due to incompleteness of current search pipelines for younger, faster-rotating stars. We see increasing evidence that some planets continue to lose atmosphere past 800 Myr, as now two planets at this age have radii significantly larger than their older counterparts from Kepler.
Plasmon-assisted photoresponse in Ge-coated bowtie nanojunctions

We demonstrate plasmon-enhanced photoconduction in Au bowtie nanojunctions containing nanogaps overlaid with an amorphous Ge film. The role of plasmons in the production of nanogap photocurrent is verified by studying the unusual polarization dependence of the photoresponse. With increasing Ge thickness, the nanogap polarization of the photoresponse rotates 90°, indicating a change in the dominant relevant plasmon mode, from the resonant transverse plasmon at low thicknesses to the nonresonant “lightning rod” mode at higher thicknesses. To understand the plasmon response in the presence of the Ge overlayer and whether the Ge degrades the Au plasmonic properties, we investigate the photothermal response (from the temperature-dependent Au resistivity) in no-gap nanowire structures, as a function of Ge film thickness and nanowire geometry. The film thickness and geometry dependence are modeled using a cross-sectional, finite element simulation. The no-gap structures and the modeling confirm that the striking...
Localization of Unitary Braid Group Representations

Governed by locality, we explore a connection between unitary braid group representations associated to a unitary R-matrix and to a simple object in a unitary braided fusion category. Unitary R-matrices, namely unitary solutions to the Yang-Baxter equation, afford explicitly local unitary representations of braid groups. Inspired by topological quantum computation, we study whether or not it is possible to reassemble the irreducible summands appearing in the unitary braid group representations from a unitary braided fusion category with possibly different positive multiplicities to get representations that are uniformly equivalent to the ones from a unitary R-matrix. Such an equivalence will be called a localization of the unitary braid group representations. We show that the q = eπi/6 specialization of the unitary Jones representation of the braid groups can be localized by a unitary 9 × 9 R-matrix. Actually this Jones representation is the first one in a family of theories (SO(N), 2) for an odd prime N > 1, which are conjectured to be localizable. We formulate several general conjectures and discuss possible connections to physics and computer science.
DAMA and WIMP dark matter

We study whether spin-independent scattering of weakly-interacting massive particles (WIMPs) with nuclei can account for the annual modulation signal reported by DAMA. We consider both elastic and inelastic scattering processes. We find that there is a region of WIMP parameter space which can simultaneously accommodate DAMA and the null results of CDMS, CRESST, and XENON. This region corresponds to an ordinary, elastically-scattering WIMP with a standard Maxwell-Boltzmann distribution, a mass 3mDM8, and a spin-independent cross section with nucleons 3 × 10−412σpSI5 × 10−392. This new region of parameter space depends crucially on the effect of channeling on the energy threshold for WIMP detection in the DAMA experiment; without the inclusion of this effect, the DAMA allowed region is essentially closed by null experiments. Such low-mass WIMPs arise in many theories of Beyond the Standard Model physics, from minimal extensions of the MSSM to solutions of the baryon-dark matter coincidence problem. We find that inelastic scattering channels do not open up a significant parameter region consistent with all experimental results. Future experiments with low energy thresholds for detecting nuclear recoils, such as CDMSII-Si and those utilizing ultra-low energy germanium detectors, will be able to probe the DAMA region of parameter space.
HELIUM-ABUNDANCE AND OTHER COMPOSITION EFFECTS ON THE PROPERTIES OF STELLAR SURFACE CONVECTION IN SOLAR-LIKE MAIN-SEQUENCE STARS

We investigate the effect of helium abundance and α-element enhancement on the properties of convection in envelopes of solar-like main-sequence stars using a grid of three-dimensional radiation hydrodynamic simulations. Helium abundance increases the mean molecular weight of the gas and alters opacity by displacing hydrogen. Since the scale of the effect of helium may depend on the metallicity, the grid consists of simulations with three helium abundances (Y = 0.1, 0.2, 0.3), each with two metallicities (Z = 0.001, 0.020). We find that changing the helium mass fraction generally affects structure and convective dynamics in a way opposite to that of metallicity. Furthermore, the effect is considerably smaller than that of metallicity. The signature of helium differs from that of metallicity in the manner in which the photospheric velocity distribution is affected. We also find that helium abundance and surface gravity behave largely in similar ways, but differ in the way they affect the mean molecular weight. A simple model for spectral line formation suggests that the bisectors and absolute Doppler shifts of spectral lines depend on the helium abundance. We look at the effect of α-element enhancement and find that it has a considerably smaller effect on the convective dynamics in the superadiabatic layer compared to that of helium abundance.
Matter-wave propagation in optical lattices: geometrical and flat-band effects

Author(s): Metcalf, Mekena; Chern, Gia-Wei; Di Ventra, Massimiliano; Chien, Chih-Chun | Abstract: The geometry of optical lattices can be engineered allowing the study of atomic transport along paths arranged in patterns that are otherwise difficult to probe in the solid state. A question readily accessible to atomic systems is related to the speed of propagation of matter-waves as a function of the lattice geometry. To address this issue, we have investigated theoretically the quantum transport of non-interacting and weakly-interacting ultracold fermionic atoms in several 2D optical lattice geometries. We find that the triangular lattice has a higher propagation velocity compared to the square lattice, despite supporting longer paths. The body-centered square lattice has even longer paths, nonetheless the propagation velocity is yet faster. This apparent paradox arises from the mixing of the momentum states which leads to different group velocities in quantum systems. Standard band theory provides an explanation and allows for a systematic way to search and design systems with controllable matter-wave propagation. Moreover, the presence of a flat band such as in a two-leg ladder geometry leads to a dynamical density discontinuity, which contrasts the behavior of mobile and localized atoms in quantum transport. Our predictions are realizable with present experimental capability.
Dynamics of Bayesian updating with dependent data and misspecified models

Much is now known about the consistency of Bayesian updating on infinite-dimensional parameter spaces with independent or Markovian data. Necessary conditions for consistency include the prior putting enough weight on the correct neighborhoods of the data-generating distribution; various sufficient conditions further restrict the prior in ways analogous to capacity control in frequentist nonparametrics. The asymptotics of Bayesian updating with mis-specified models or priors, or non-Markovian data, are far less well explored. Here I establish sufficient conditions for posterior convergence when all hypotheses are wrong, and the data have complex dependencies. The main dynamical assumption is the asymptotic equipartition (Shannon-McMillan-Breiman) property of information theory. This, along with Egorov’s Theorem on uniform convergence, lets me build a sieve-like structure for the prior. The main statistical assumption, also a form of capacity control, concerns the compatibility of the prior and the data-generating process, controlling the fluctuations in the log-likelihood when averaged over the sieve-like sets. In addition to posterior convergence, I derive a kind of large deviations principle for the posterior measure, extending in some cases to rates of convergence, and discuss the advantages of predicting using a combination of models known to be wrong. An appendix sketches connections between these results and the replicator dynamics of evolutionary theory.
Hyperbolic geometry of Kuramoto oscillator networks

Kuramoto oscillator networks have the special property that their trajectories are constrained to lie on the (at most) 3D orbits of the Mobius group acting on the state space T N (the N-fold torus). This result has been used to explain the existence of the constants of motion discovered by Watanabe and Strogatz for Kuramoto oscillator networks. In this work we investigate geometric consequences of this Mobius group action. The dynamics of Kuramoto phase models can be further reduced to 2D reduced group orbits, which have a natural geometry equivalent to the unit disk with the hyperbolic metric. We show that in this metric the original Kuramoto phase model (with order parameter Z 1 equal to the centroid of the oscillator configuration of points on the unit circle) is a gradient flow and the model with order parameter iZ 1 (corresponding to cosine phase coupling) is a completely integrable Hamiltonian flow. We give necessary and sufficient conditions for general Kuramoto phase models to be gradient or Hamiltonian flows in this metric. This allows us to identify several new infinite families of hyperbolic gradient or Hamiltonian Kuramoto oscillator networks which therefore have simple dynamics with respect to this geometry. We prove that for the Z 1 model, a generic 2D reduced group orbit has a unique fixed point corresponding to the hyperbolic barycenter of the oscillator configuration, and therefore the dynamics are equivalent on different generic reduced group orbits. This is not always the case for more general hyperbolic gradient or Hamiltonian flows; the reduced group orbits may have multiple fixed points, which also may bifurcate as the reduced group orbits vary.
Correlation functions in a cascading N = 1 gauge theory from supergravity

We study fluctuations around the warped conifold supergravity solution of Klebanov and Tseytlin [1], known to be dual to a cascading = 1 gauge theory. Although this supergravity background is not asymptotically AdS, corresponding to a non-conformal field theory, it is possible to apply the usual methods of AdS/CFT duality to extract the high energy behavior of field theory correlators by solving linearized equations of motion for fluctuations around the background. We consider the Goldstone vector dual to the anomalous R-symmetry current and compute its mass, which exactly matches the general prediction of [14]. We find the high energy 2-point functions for the R-current and two other vectors. As expected, the R-current 2-point function has a longitudinal part because R-symmetry is broken. We also calculate the high energy 2-point function of the energy-momentum tensor from fluctuations of modes in the graviton sector. This 2-point function has a trace part corresponding to broken conformal symmetry.
Measurement of the Parallax of PSR B0950+08 Using the VLBA

A new technique has been developed to remove the ionosphere's distorting effects from low-frequency VLBI data. By fitting dispersive and nondispersive components to the phases of multifrequency data, the ionosphere can be effectively removed from the data without the use of a priori calibration information. This technique, along with the new gating capability of the VLBA correlator, was used to perform accurate astrometry on pulsar B0950+08, resulting in a much improved measurement of this pulsar's proper motion (μα = -1.6 ± 0.4 mas yr-1, μδ = 29.5 ± 0.5 mas yr-1) and parallax (π = 3.6 ± 0.3 mas). This puts the pulsar at a distance of 280 ± 25 pc, about twice as far as previous estimates, but in good agreement with models of the electron density in the Local Bubble.
Derivation and precision of mean field electrodynamics with mesoscale fluctuations

Mean field electrodynamics (MFE) facilitates practical modelling of secular, large scale properties of astrophysical or laboratory systems with fluctuations. Practitioners commonly assume wide scale separation between mean and fluctuating quantities, to justify equality of ensemble and spatial or temporal averages. Often however, real systems do not exhibit such scale separation. This raises two questions: (I) What are the appropriate generalized equations of MFE in the presence of mesoscale fluctuations? (II) How precise are theoretical predictions from MFE? We address both by first deriving the equations of MFE for different types of averaging, along with mesoscale correction terms that depend on the ratio of averaging scale to variation scale of the mean. We then show that even if these terms are small, predictions of MFE can still have a significant precision error. This error has an intrinsic contribution from the dynamo input parameters and a filtering contribution from differences in the way observations and theory are projected through the measurement kernel. Minimizing the sum of these contributions can produce an optimal scale of averaging that makes the theory maximally precise. The precision error is important to quantify when comparing to observations because it quantifies the resolution of predictive power. We exemplify these principles for galactic dynamos, comment on broader implications, and identify possibilities for further work.
THREE-DIMENSIONAL FIELD THEORIES FROM INFINITE-DIMENSIONAL LIE ALGEBRAS

A procedure for constructing topological actions from centrally extended Lie algebras is introduced. For a Kac–Moody algebra, this produces the three-dimensional Chern–Simons theory, while for the Virasoro algebra, the result is a new three-dimensional topological field theory whose physical states satisfy the Virasoro Ward identity. This topological field theory is shown to be a first order formulation of two-dimensional induced gravity in the chiral gauge. The extension to W3 gravity is discussed.
The Aemulus Project. III. Emulation of the Galaxy Correlation Function

U.S. Department of Energy [DE-AC02-76SF00515]; NSF [AST-1211889]; Samuel P. Langley PITT PACC Postdoctoral Fellowship; Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]
Numerical Studies of Various Néel-VBS Transitions in SU( N ) Anti-Ferromagnets

In this manuscript we review recent developments in the numerical simulations of bipartite SU(N) spin models by quantum Monte Carlo (QMC) methods. We provide an account of a large family of newly discovered sign-problem free spin models which can be simulated in their ground states on large lattices, containing O(105) spins, using the stochastic series expansion method with efficient loop algorithms. One of the most important applications so far of these Hamiltonians are to unbiased studies of quantum criticality between Neel and valence bond phases in two dimensions - a summary of this body of work is provided. The article concludes with an overview of the current status of and outlook for future studies of the "designer" Hamiltonians.
Discovery of an X-Ray Synchrotron Nebula Associated with the Radio Pulsar PSR B1853+01 in the Supernova Remnant W44

We report the detection, using data from the Advanced Satellite for Cosmology and Astrophysics (ASCA), of a hard X-ray source in the vicinity of the radio pulsar PSR B1853+01, which is located within the supernova remnant (SNR) W44. PSR B1853+01, a 267 ms pulsar, has to date been detected only in the radio band. Previous observations at soft X-ray energies (e.g., with ROSAT HRI) have failed to detect any significant X-ray emission (pulsed or unpulsed) from the pulsar. In addition, no high-energy emission (4 keV) has been detected previously from W44. Over the 0.5-4.0 keV band, the ASCA data show soft thermal emission from W44, with a morphology very similar to that observed earlier by Einstein and ROSAT. In the high-energy band (4.0-9.5 keV), the SNR is, for the most part, invisible, although a source coincident with the position of PSR B1853+01 is evident. The observed ASCA spectra are consistent with a power-law origin (photon index ~2.3) for the X-ray emission from this source at a flux level (flux density ~0.5 μJy at 1 keV) consistent with previous upper limits. The maximum allowed size for the source is determined directly from the ASCA data (<5'), while the minimum size is derived from the nondetection of a point source in the ROSAT HRI data (30''). Timing analysis of the hard X-ray source failed to detect pulsations at the pulsar's period. Based on these lines of evidence, we conclude that the new hard source in W44 represents an X-ray synchrotron nebula associated with PSR B1853+01, rather than the beamed output of the pulsar itself. This discovery adds W44 to the small group of previously known plerionic SNRs. This nebula lies at the low end of, but is consistent with, the correlation between X-ray luminosity and pulsar spin-down energy loss found for such objects, lending further support to our interpretation.
Entropies from Coarse-graining: Convex Polytopes vs. Ellipsoids

We examine the Boltzmann/Gibbs/Shannon SBGS and the non-additive Havrda-Charvat/Daroczy/Cressie-Read/Tsallis Sq and the Kaniadakis κ-entropy Sκ from the viewpoint of coarse-graining, symplectic capacities and convexity. We argue that the functional form of such entropies can be ascribed to a discordance in phase-space coarse-graining between two generally different approaches: the Euclidean/Riemannian metric one that reflects independence and picks cubes as the fundamental cells in coarse-graining and the symplectic/canonical one that picks spheres/ellipsoids for this role. Our discussion is motivated by and confined to the behaviour of Hamiltonian systems of many degrees of freedom. We see that Dvoretzky’s theorem provides asymptotic estimates for the minimal dimension beyond which these two approaches are close to each other. We state and speculate about the role that dualities may play in this viewpoint.
Necessary and Sufficient Conditions for the Validity of Luttinger's Theorem

Luttinger's theorem is a major result in many-body physics that states the volume of the Fermi surface is directly proportional to the particle density. In its "hard" form, Luttinger's theorem implies that the Fermi volume is invariant with respect to interactions (as opposed to a "soft" Luttinger's theorem, where this invariance is lost). Despite it's simplicity, the conditions on the fermionic self energy under which Luttinger's theorem is valid remains a matter of debate, with possible requirements for its validity ranging from particle-hole symmetry to analyticity about the Fermi surface. In this paper, we propose the minimal requirements for the application of a hard Luttinger's Theorem to a generic fermionic system of arbitrary interaction strength by invoking the Atiyah-Singer index theorem to quantify the topologically-robust behavior of a generalized Fermi surface. We show that the applicability of a hard Luttinger's theorem in a D-dimensional system is directly dependent on the existence of a (D-1)-dimensional manifold of gapless chiral excitations at the Fermi level, regardless of whether the system exhibits Luttinger or Fermi surfaces (i.e., manifolds of zeroes of the Green's function and inverse Green's function, respectively). The exact form of the self-energy which guarantees validity of a hard Luttinger's theorem is derived, and agreement with current experiments, numerics, and theories are discussed.
Parity Violation in Neutrino Transport and the Origin of Pulsar Kicks

In proto-neutron stars with strong magnetic fields, the neutrino-nucleon scattering/absorption cross sections depend on the direction of neutrino momentum with respect to the magnetic field axis, a manifestation of parity violation in weak interactions. We study the deleptonization and thermal cooling (via neutrino emission) of proto-neutron stars in the presence of such asymmetric neutrino opacities. Significant asymmetry in neutrino emission is obtained because of multiple neutrino-nucleon scatterings. For an ordered magnetic field threading the neutron star interior, the fractional asymmetry in neutrino emission is about 0.006(B/1014 G), corresponding to a pulsar kick velocity of about 200(B/1014 G) km s−1 for a total radiated neutrino energy of 3×1053 ergs.
An Analysis on the Learning Rules of the Skip-Gram Model

To improve the generalization of the representations for natural language processing tasks, words are commonly represented using vectors, where distances among the vectors are related to the similarity of the words. While word2vec, the state-of-the-art implementation of the skip-gram model, is widely used and improves the performance of many natural language processing tasks, its mechanism is not yet well understood.In this work, we derive the learning rules for the skip-gram model and establish their close relationship to competitive learning. In addition, we provide the global optimal solution constraints for the skip-gram model and validate them by experimental results.
Knot contact homology and representations of knot groups

We study certain linear representations of the knot group that induce augmentations of knot contact homology. This perspective on augmentations enhances our understanding of the relationship between the augmentation polynomial and the A-polynomial of the knot. For example, we show that for 2-bridge knots the polynomials agree and that this is never the case for (non-2-bridge) torus knots, nor for a family of 3-bridge pretzel knots. In addition, we obtain a lower bound on the meridional rank of the knot. As a consequence, our results give another proof that torus knots and a family of pretzel knots have meridional rank equal to their bridge number.
Two-Photon Pathway to Ultracold Ground State Molecules of $^{23}$Na$^{40}$K

We report on high-resolution spectroscopy of ultracold fermionic 23Na40K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B1Π ~ c3Σ+intermediate state. Photoassociation in a 23Na–40K atomic mixture and one-photon spectroscopy on 23Na40K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c3Σ+state. Two of these levels are found to be strongly perturbed by nearby B1Π levels via spin–orbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex , or of resonantly mixed character in . The dominantly singlet level is used to locate the absolute rovibrational singlet ground state via Autler–Townes spectroscopy. We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state. Its binding energy is measured to be 5212.0447(1) cm−1, a thousand-fold improvement in accuracy compared to previous determinations. In their absolute singlet ground state, 23Na40K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye. Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.
DANR: Discrepancy-aware Network Regularization.

Network regularization is an effective tool for incorporating structural prior knowledge to learn coherent models over networks, and has yielded provably accurate estimates in applications ranging from spatial economics to neuroimaging studies. Recently, there has been an increasing interest in extending network regularization to the spatio-temporal case to accommodate the evolution of networks. However, in both static and spatio-temporal cases, missing or corrupted edge weights can compromise the ability of network regularization to discover desired solutions. To address these gaps, we propose a novel approach---{\it discrepancy-aware network regularization} (DANR)---that is robust to inadequate regularizations and effectively captures model evolution and structural changes over spatio-temporal networks. We develop a distributed and scalable algorithm based on the alternating direction method of multipliers (ADMM) to solve the proposed problem with guaranteed convergence to global optimum solutions. Experimental results on both synthetic and real-world networks demonstrate that our approach achieves improved performance on various tasks, and enables interpretation of model changes in evolving networks.
Semi-relativistic effects in spin-1/2 quantum plasmas

Emerging possibilities for creating and studying novel plasma regimes, e. g. relativistic plasmas and dense systems, in a controlled laboratory environment also require new modeling tools for such ...
A Search for the Optical Counterpart of the Luminous X-Ray Source in NGC 6652

We examine images of the field of X1832-330, the luminous (LX ~ 1036 ergs s-1) X-ray burst source near the center of the globular cluster NGC 6652, in order to identify the optical counterpart for further study. U and B ground-based images allow us to set a limit M 3.5 for the counterpart at the time of those observations, provided that the color is (U - B)0 ~ -1, similar to the sources known in other clusters. Archival Hubble Space Telescope observations survey most, but not all, of the 1 σ X-ray error circle and allow us to set limits M > 5.9 and M > 5.2 in the Wide Field Planetary Camera 1 (WF/PC-1) and Wide Field Planetary Camera 2 (WFPC2) regions, respectively. In the WF/PC-1 images we do weakly detect a faint object with UV excess, but it is located 117 from the ROSAT X-ray position. This considerable (2.3 σ) discrepancy in position suggests that this candidate be treated with caution, but it remains the only reasonable one advanced thus far. We measure for this star m439 = 20.2 ± 0.2 and m336 - m439 = -0.5 ± 0.2 and estimate M = 5.5 and (U - B)0 = -0.9, similar to other known optical counterparts. If this candidate is not the identification, our limits imply that the true counterpart, not yet identified, is probably the optically faintest cluster source yet known or, alternatively, that it did not show significant UV excess at the time of these observations. Finally, we assess the outlook for the identification of the remaining luminous globular cluster X-ray sources.
Improved theory of neutrino oscillations in matter

This is revision of the S-Matrix theory of neutrino oscillations used for many years. We evaluate the transition probability of a μ to e neutrino without an approximation used for many theoretical studies, and find important differences which could improve the extraction of neutrino parameters from experimental data in the future.
Fast Algorithm for Fuel-Optimal Impulsive Control of Linear Systems With Time-Varying Cost

This article presents a new fast and robust algorithm that provides fuel-optimal impulsive control input sequences that drive a linear time-variant system to a desired state at a specified time. This algorithm is applicable to a broad class of problems where the cost is expressed as a time-varying norm-like function of the control input, enabling inclusion of complex operational constraints in the control planning problem. First, it is shown that the reachable sets for this problem have identical properties to those in prior works using constant cost functions, enabling use of existing algorithms in conjunction with newly derived contact and support functions. By reformulating the optimal control problem as a semi-infinite convex program, it is also demonstrated that the semi-infinite component of the commonly studied primer vector is an outward normal vector to the reachable set at the target state. Using this formulation, a fast and robust algorithm that provides globally optimal impulsive control input sequences is proposed. The algorithm iteratively refines estimates of an outward normal vector to the reachable set at the target state and a minimal set of control input times until the optimality criteria are satisfied to within a user-specified tolerance. Next, optimal control inputs are computed by solving a quadratic program. The algorithm is validated through simulations of challenging example problems based on the recently proposed miniaturized distributed occulter/telescope small satellite mission, which demonstrate that the proposed algorithm converges several times faster than comparable algorithms in the literature.
Matched Photometric Catalogs of GALEX UV Sources with Gaia DR2 and SDSS DR14 Databases (GUVmatch)

We have matched the ultraviolet (UV) sources in GUVcat_AIS (Bianchi et al.2017) with optical databases having similar depth and wide sky coverage. GUVcat_AIS has GALEX far-UV (FUV, lambda-eff ~1528A) and near-UV (NUV, lambda-eff ~2310A) photometry of approx 83~million sources, covering 24,788 square degrees of the sky, with typical depth of FUV=19.9, NUV=20.8~ABmag. Matches with Gaia and SDSS databases are presented here. Gaia data release 2 (DR2), covering the entire GUVcat footprint (Bianchi et al. 2019), detected about one third of the $GUVcat\_AIS$ sources. We found 31,925,294 Gaia~DR2 counterparts to 30,024,791 GUVcat_AIS unique sources, with photometry in $Gaia$~$G$ band, and often also in $Gaia$~$BP$ and $RP$ bands; 26,275,572 matches have a parallax measurement, 21,084,628/18,588,140/16,357,505 with parallax error less than 50%/30%/20%. The match with SDSS data release 14 (DR14) yields 23,310,532 counterparts to 22,207,563 unique GUVcat_AIS sources, 10,167,460 of which are point-like, over a total overlap area of $\approx$11,100~square~degrees (Bianchi et al. 2019)}. SDSS adds to the UV photometry five optical magnitudes: $u,g,r,i,z$, and optical spectra of 860,224 matched sources. We used a match radius of 3arcsec, consistent with previous works (e.g., Bianchi et al. 2011a), although the positions agree to $\lesssim$1.5arcsec for the majority of [point-like] matched-sources, in order to identify possible multiple matches whose UV flux could be unresolved in GALEX imaging. The catalogs can be trimmed to a tighter match radius using the provided separation. The multi-band photometry is used to identify classes of astrophysical objects that are prominent in UV, to characterise the content of the $GUVmatch$ catalogs, where stars in different evolutionary stages, QSOs, and galaxies can be separated.
Minimal surfaces and weak gravity

We show that the Weak Gravity Conjecture (WGC) implies a nontrivial upper bound on the volumes of the minimal-volume cycles in certain homology classes that admit no calibrated representatives. In compactification of type IIB string theory on an orientifold X of a Calabi-Yau threefold, we consider a homology class [Σ] ∈ H4(X, ℝ) represented by a union Σ∪ of holomorphic and antiholomorphic cycles. The instanton form of the WGC applied to the axion charge [Σ] implies an upper bound on the action of a non-BPS Euclidean D3-brane wrapping the minimal-volume representative Σmin of [Σ]. We give an explicit example of an orientifold X of a hypersurface in a toric variety, and a hyperplane H ⊂ H4(X, ℝ), such that for any [Σ] ∈ H that satisfies the WGC, the minimal volume obeys Vol (Σmin) ≪ Vol(Σ∪): the holomorphic and antiholomorphic components recombine to form a much smaller cycle. In particular, the sub-Lattice WGC applied to X implies large recombination, no matter how sparse the sublattice. Non-BPS instantons wrapping Σmin are then more important than would be predicted from a study of BPS instantons wrapping the separate components of Σ∪. Our analysis hinges on a novel computation of effective divisors in X that are not inherited from effective divisors of the toric variety.
Generalized Forchheimer flows in heterogeneous porous media

We study the generalized Forchheimer flows of slightly compressible fluids in heterogeneous porous media. The media's porosity and coefficients of the Forchheimer equation are functions of the spatial variables. The partial differential equation for the pressure is degenerate in its gradient and can be both singular and degenerate in the spatial variables. Suitable weighted Lebesgue norms for the pressure, its gradient and time derivative are estimated. The continuous dependence on the initial and boundary data is established for the pressure and its gradient with respect to those corresponding norms. Asymptotic estimates are derived even for unbounded boundary data as time tends to infinity.
Flat space, dark energy, and the cosmic microwave background

This paper reviews some of the results of the Planck collaboration and shows how to compute the distance from the surface of last scattering, the distance from the farthest object that will ever be observed, and the maximum radius of a density fluctuation in the plasma of the CMB. It then explains how these distances together with well-known astronomical facts imply that space is flat or nearly flat and that dark energy is 69% of the energy of the universe.
SimAug : Learning Robust Representations from Simulation for Trajectory Prediction

This paper studies the problem of predicting future trajectories of people in unseen cameras of novel scenarios and views. We approach this problem through the real-data-free setting in which the model is trained only on 3D simulation data and applied out-of-the-box to a wide variety of real cameras. We propose a novel approach to learn robust representation through augmenting the simulation training data such that the representation can better generalize to unseen real-world test data. The key idea is to mix the feature of the hardest camera view with the adversarial feature of the original view. We refer to our method as SimAug. We show that SimAug achieves promising results on three real-world benchmarks using zero real training data, and state-of-the-art performance in the Stanford Drone and the VIRAT/ActEV dataset when using in-domain training data. Code and models are released at https://next.cs.cmu.edu/simaug.
Engineering a Culturable Serratia symbiotica Strain for Aphid Paratransgenesis

Aphids are global agricultural pests and important models for bacterial symbiosis. To date, none of the native symbionts of aphids have been genetically manipulated, which limits our understanding of how they interact with their hosts. Serratia symbiotica CWBI-2.3T is a culturable, gut-associated bacterium isolated from the black bean aphid. Closely related Serratia symbiotica strains are facultative aphid endosymbionts that are vertically transmitted from mother to offspring during embryogenesis. We demonstrate that CWBI-2.3T can be genetically engineered using a variety of techniques, plasmids, and gene expression parts. Then, we use fluorescent protein expression to track the dynamics with which CWBI-2.3T colonizes the guts of multiple aphid species, and we measure how this bacterium affects aphid fitness. Finally, we show that we can induce heterologous gene expression from engineered CWBI-2.3T in living aphids. These results inform the development of CWBI-2.3T for aphid paratransgenesis, which could be used to study aphid biology and enable future agricultural technologies.IMPORTANCE Insects have remarkably diverse and integral roles in global ecosystems. Many harbor symbiotic bacteria, but very few of these bacteria have been genetically engineered. Aphids are major agricultural pests and an important model system for the study of symbiosis. This work describes methods for engineering a culturable aphid symbiont, Serratia symbiotica CWBI-2.3T These approaches and genetic tools could be used in the future to implement new paradigms for the biological study and control of aphids.
Three-dimensional and four-dimensional scalar, vector, tensor cosmological fluctuations and the cosmological decomposition theorem

In cosmological perturbation theory it is convenient to use the scalar, vector, tensor basis as defined according to how these components transform under three-dimensional rotations. In attempting to solve the fluctuation equations that are automatically written in terms of gauge-invariant combinations of these components, the equations are taken to break up into separate scalar, vector and tensor sectors, the decomposition theorem. Here, without needing to specify a gauge, we solve the fluctuation equations exactly for some standard cosmologies, to show that in general the various gauge-invariant combinations only separate at a higher-derivative level. To achieve separation at the level of the fluctuation equations themselves one has to assume boundary conditions for the higher-derivative equations. While spatially asymptotic boundary conditions suffice for fluctuations around a de Sitter background or a spatially flat Robertson–Walker background, for fluctuations around a spatially non-flat Robertson–Walker background one additionally has to require that the fluctuations be well-behaved at the origin. We show that in certain cases the gauge-invariant combinations themselves involve both scalars and vectors. For such cases there is no decomposition theorem for the individual scalar, vector and tensor components themselves as that would violate gauge invariance, but for the gauge-invariant combinations there still can be. Given the lack of manifest covariance (though not of covariance itself) in defining a basis with respect to three-dimensional rotations, we introduce an alternate scalar, vector, tensor basis whose components are defined according to how they transform under four-dimensional general coordinate transformations. With this basis the fluctuation equations greatly simplify, and while one can again break them up into separate gauge-invariant sectors at the higher-derivative level, in general we find that even with boundary conditions we do not obtain a decomposition theorem in which the fluctuations separate at the level of the fluctuation equations themselves.
Snow on Arctic Sea Ice in a Warming Climate as Simulated in CESM

Earth system models are valuable tools for understanding how the Arctic snow-ice system and the feedbacks therein may respond to a warming climate. In this analysis, we investigate snow on Arctic sea ice to better understand how snow conditions may change under different forcing scenarios. First, we use in situ, airborne, and satellite observations to assess the realism of the Community Earth System Model (CESM) in simulating snow on Arctic sea ice. CESM versions one and two are evaluated, with V1 being the Large Ensemble experiment (CESM1-LE) and V2 being configured with low- and high-top atmospheric components. The assessment shows CESM2 underestimates snow depth and produces overly uniform snow distributions, whereas CESM1-LE produces a highly variable, excessively-thick snow cover. Observations indicate that snow in CESM2 accumulates too slowly in autumn, too quickly in winter-spring, and melts too soon and rapidly in late spring. The 1950-2050 trends in annual mean snow depths are markedly smaller in CESM2 (-0.8 cm decade-1) than in CESM1-LE (-3.6 cm decade-1) due to CESM2 having less snow overall. A perennial, thick sea-ice cover, cool summers, and excessive summer snowfall facilitate a thicker, longer-lasting snow cover in CESM1-LE. Under the SSP5-8.5 forcing scenario, CESM2 shows that, compared to present-day, snow on Arctic sea ice will: (1) undergo enhanced, earlier spring melt, (2) accumulate less in summer-autumn, (3) sublimate more, and (4) facilitate marginally more snow-ice formation. CESM2 also reveals that summers with snow-free ice can occur ∼30-60 years before an ice-free central Arctic, which may promote faster sea-ice melt.