cssi/SciSciGPT-SciSciNet huggingface dataset:
Detectors and cooling technology for direct spectroscopic biosignature characterization

Direct spectroscopic biosignature characterization (hereafter “biosignature characterization”) will be a major focus for future space observatories equipped with coronagraphs or starshades. Our aim in this article is to provide an introduction to potential detector and cooling technologies for biosignature characterization. We begin by reviewing the needs. These include nearly noiseless photon detection at flux levels as low as <0.001 photons s−1 pixel−1 in the visible and near-infrared. We then discuss potential areas for further testing and/or development to meet these needs using noncryogenic detectors (electron multiplying charge coupled devices, HgCdTe array, HgCdTe APD array), and cryogenic single-photon detectors (microwave kinetic inductance device arrays and transition-edge sensor microcalorimeter arrays). Noncryogenic detectors are compatible with the passive cooling that is strongly preferred by coronagraphic missions but would add nonnegligible noise. Cryogenic detectors would require active cooling, but in return, deliver nearly quantum-limited performance. Based on the flight dynamics of past NASA missions, we discuss reasonable vibration expectations for a large UV-Optical-IR space telescope (LUVOIR) and preliminary cooling concepts that could potentially fit into a vibration budget without being the largest element. We believe that a cooler that meets the stringent vibration needs of a LUVOIR is also likely to meet those of a starshade-based Habitable Exoplanet Imaging Mission.
Probing transverse-momentum dependent evolution with groomed jets

We propose an observable which involves measuring the properties (transverse momentum ph⊥ and energy fraction zh) of an identified hadron inside a groomed jet. The jet is identified with an anti-kT/CA algorithm and is groomed by implementing the modified mass drop procedure with an energy cut-off parameter, zcut. The transverse momentum of the hadron inside the jet is measured with respect to the groomed jet axis. We obtain a factorization theorem in the framework of Soft Collinear Effective Theory (SCET), to define a Transverse Momentum Dependent Fragmenting Jet Function (TMDFJF). The TMDFJF is factorized into collinear and collinear soft modes by matching onto SCET+. We resum large logarithms in EJ /ph⊥, where EJ is the ungroomed jet energy, to NLL accuracy and apply this formalism for computing the shape of the ph⊥ distribution of a pion produced in an e+ + e− collision. We observe that the introduction of grooming makes this observable insensitive to non-global logarithms and particularly sensitive to non-perturbative physics of the transverse momentum dependent evolution at low values of ph⊥, which can be probed in the variation of the cut-off parameter, zcut, of the groomer. We discuss how this observable can be used to distinguish between non-perturbative models that describe universal TMD evolution and provide a window into the three dimensional structure of hadrons.
New potentials for conformal mechanics

We find under some mild assumptions that the most general potential of one-dimensional conformal systems with time-independent couplings is expressed as V = V0 + V1, where V0 is a homogeneous function with respect to a homothetic motion in configuration space and V1 is determined from an equation with source a homothetic potential. Such systems admit at most an conformal symmetry which, depending on the couplings, is embedded in in three different ways. In one case, is also embedded in Diff(S1). Examples of such models include those with potential V = αx2 + βx−2 for arbitrary couplings α and β, the Calogero models with harmonic oscillator couplings and nonlinear models with suitable metrics and potentials. In addition, we give the conditions on the couplings for a class of gauge theories to admit a conformal symmetry. We present examples of such systems with general gauge groups and global symmetries that include the isometries of AdS2 × S3 and AdS2 × S3 × S3 which arise as backgrounds in AdS2/CFT1.
Particle Model Predictive Control: Tractable Stochastic Nonlinear Output-Feedback MPC

Abstract We combine conditional state density construction with an extension of the Scenario Approach for stochastic Model Predictive Control to nonlinear systems to yield a novel particle-based formulation of stochastic nonlinear output-feedback Model Predictive Control. Conditional densities given noisy measurement data are propagated via the Particle Filter as an approximate implementation of the Bayesian Filter. This enables a particle-based representation of the conditional state density, or information state, which naturally merges with scenario generation from the current system state. This approach attempts to address the computational tractability questions of general nonlinear stochastic optimal control. The Particle Filter and the Scenario Approach are shown to be fully compatible and–based on the time- and measurement-update stages of the Particle Filter–incorporated into the optimization over future control sequences. A numerical example is presented and examined for the dependence of solution and computational burden on the sampling configurations of the densities, scenario generation and the optimization horizon.
TeV string theories, mini black holes and trans-GZK cosmic rays

We review the proposal that trans-GZK cosmic ray interactions are caused by neutrino primaries. The primaries cause excitations of strings and give rise to extensive air showers (EAS) resembling EAS induced by nuclei. We also show that in “low scale” ( M ∗ ≈ 70 TeV ) string models the excited string and the mini black hole pictures are equivalent.
Online Cyber-Attack Detection in Smart Grid: A Reinforcement Learning Approach

Early detection of cyber-attacks is crucial for a safe and reliable operation of the smart grid. In the literature, outlier detection schemes making sample-by-sample decisions and online detection schemes requiring perfect attack models have been proposed. In this paper, we formulate the online attack/anomaly detection problem as a partially observable Markov decision process (POMDP) problem and propose a universal robust online detection algorithm using the framework of model-free reinforcement learning (RL) for POMDPs. Numerical studies illustrate the effectiveness of the proposed RL-based algorithm in timely and accurate detection of cyber-attacks targeting the smart grid.
Millisecond Pulsars as Probes of Mass Segregation in the Galactic Center

We propose a simple test for the existence of a cluster of black hole remnants around Sgr A* that is based on a small sample of any type of Galactic center objects, provided they are substantially less massive than the black holes and constitute part of an old (1 Gyr) population. The test relies on the fact that, in the presence of such a cluster of heavy remnants and because of energy equipartition, lower mass objects would be expelled from the central regions and settle into a distribution very different from the cusp expected to be induced by the supermassive black hole alone. We show that with a sample of just 50 objects and using only their angular positions on the sky relative to Sgr A*, it is possible to clearly differentiate between a distribution consistent with the presence of the cluster of black holes and a power-law cusp distribution. We argue that millisecond pulsars might currently be the best candidate to perform this test, because of the large uncertainties involved in the age determination of less exotic objects. In addition, by measuring their first and second period derivatives, millisecond pulsars offer the rare opportunity to determine the complete phase-space information of the objects. We show that this extra information improves the detection of mass segregation by about 30%.
Sparse poisson intensity reconstruction algorithms

The observations in many applications consist of counts of discrete events, such as photons hitting a dector, which cannot be effectively modeled using an additive bounded or Gaussian noise model, and instead require a Poisson noise model. As a result, accurate reconstruction of a spatially or temporally distributed phenomenon (f) from Poisson data (y) cannot be accomplished by minimizing a conventional l 2 - l 1 objective function. The problem addressed in this paper is the estimation of f from y in an inverse problem setting, where (a) the number of unknowns may potentially be larger than the number of observations and (b) f admits a sparse approximation in some basis. The optimization formulation considered in this paper uses a negative Poisson log-likelihood objective function with nonnegativity constraints (since Poisson intensities are naturally nonnegative). This paper describes computational methods for solving the constrained sparse Poisson inverse problem. In particular, the proposed approach incorporates key ideas of using quadratic separable approximations to the objective function at each iteration and computationally efficient partition-based multiscale estimation methods.
The highly real quasinormal modes of Schwarzschild-Anti de Sitter black holes

A recent investigation has led to the possibility of the existence of an interesting region of the asymptotic quasinormal mode spectrum of Schwarzschild-anti de Sitter black holes. In this asymptotic region, the real part of quasinormal mode frequencies approaches infinity while the damping rate approaches a finite value. These quasinormal mode frequencies were calculated using an analytic technique based on the complex coordinate WKB method. In this paper, we use a different analytic technique to calculate such quasinormal mode frequencies. The results of this paper provide further support of the possibility of the existence of these modes.
A Framework for Robust Assessment of Power Grid Stability and Resiliency

Security assessment of large-scale, strongly nonlinear power grids containing thousands to millions of interacting components is a computationally expensive task. Targeting at reducing the computational cost, this paper introduces a framework for constructing a robust assessment toolbox that can provide mathematically rigorous certificates for the grids’ stability in the presence of variations in power injections, and for the grids’ ability to withstand a bunch sources of faults. By this toolbox we can “offline” screen a wide range of contingencies or power injection profiles, without reassessing the system stability on a regular basis. In particular, we formulate and solve two novel robust stability and resiliency assessment problems of power grids subject to the uncertainty in equilibrium points and uncertainty in fault-on dynamics. Furthermore, we bring in the quadratic Lyapunov functions approach to transient stability assessment, offering real-time construction of stability/resiliency certificates and real-time stability assessment. The effectiveness of the proposed techniques is numerically illustrated on a number of IEEE test cases.
Local unitary periods and relative discrete series

Let $F$ be a $p$-adic field ($p\neq 2$), let $E$ be a quadratic Galois extension of $F$, and let $n \geq 2$. We construct representations in the discrete spectrum of the $p$-adic symmetric space $H \backslash G$, where $G = \mathbf{GL}_{2n}(E)$ and $H = \mathbf{U}_{E/F}(F)$ is a quasi-split unitary group over $F$.
Aharonov–Bohm effect revisited

Aharonov–Bohm effect is a quantum mechanical phenomenon that attracted the attention of many physicists and mathematicians since the publication of the seminal paper of Aharonov and Bohm [1] in 1959. We consider different types of Aharonov–Bohm effects such as the magnetic AB effect, electric AB effect, combined electromagnetic AB effect, AB effect for the Schrodinger equations with Yang–Mills potentials, and the gravitational analog of AB effect. We shall describe different approaches to prove the AB effect based on the inverse scattering problems, the inverse boundary value problems in the presence of obstacles, spectral asymptotics, and the direct proofs of the AB effect.
Status of reaction theory for studying rare isotopes

Reactions are an important tool to study nuclear structure and for extracting reactions relevant for astrophysics. In this paper we focus on deuteron induced reactions which can provide information on neutron shell evolution as well as neutron capture cross sections. We review recent work on the systematic comparison of the continuum discretized coupled channel method, the adiabatic wave approximation and the Faddeev momentum-space approach. We also explore other aspects of the reaction mechanism and discuss in detail difficulties encountered in the calculations.
INDICATION OF INSENSITIVITY OF PLANETARY WEATHERING BEHAVIOR AND HABITABLE ZONE TO SURFACE LAND FRACTION

It is likely that unambiguous habitable zone terrestrial planets of unknown water content will soon be discovered. Water content helps determine surface land fraction, which influences planetary weathering behavior. This is important because the silicate-weathering feedback determines the width of the habitable zone in space and time. Here a low-order model of weathering and climate, useful for gaining qualitative understanding, is developed to examine climate evolution for planets of various land-ocean fractions. It is pointed out that, if seafloor weathering doesnotdependdirectlyonsurfacetemperature,therecanbenoweathering-climatefeedbackonawaterworld.This would dramatically narrow the habitable zone of a waterworld. Results from our model indicate that weathering behavior does not depend strongly on land fraction for partially ocean-covered planets. This is powerful because it suggests that previous habitable zone theory is robust to changes in land fraction, as long as there is some land. Finally, a mechanism is proposed for a waterworld to prevent complete water loss during a moist greenhouse through rapid weathering of exposed continents. This process is named a “waterworld self-arrest,” and it implies that waterworlds can go through a moist greenhouse stage and end up as planets like Earth with partial ocean coverage. This work stresses the importance of surface and geologic effects, in addition to the usual incident stellar flux, for habitability.
A Detailed Analysis of a Cygnus Loop Shock-Cloud Interaction

The XA region of the Cygnus Loop is a complex zone of radiative and nonradiatve shocks interacting with interstellar clouds. We combine five far ultraviolet spectral observations from the Hopkins Ultraviolet Telescope (HUT), a grid of 24 IUE spectra, and a high-resolution long-slit Hα spectrum to study the spatial emission line variations across the region. These spectral data are placed in context using ground-based optical emission-line images of the region and a far-UV image obtained by the Ultraviolet Imaging Telescope (UIT). The presence of high-ionization species (O VI, N V, and C IV) indicates a shock velocity near 170 km s-1 while other diagnostics indicate vsh ≈ 140 km s-1. It is likely that a large range of shock velocities may exist at a spatial scale smaller than we are able to resolve. By comparing C IV λ1550, C III λ977, and C III] λ1909, we explore resonance scattering across the region. We find that a significant column depth is present at all positions, including those not near bright optical or UV filaments. Analysis of the O VI doublet ratio suggests an average optical depth of about unity in that ion, while flux measurements of [Si VIII] λ1443 suggest a hot component in the region at just below 106 K. Given the brightness of the O VI emission and the age of the interaction, we rule out the mixing-layer interpretation of the UV emission. Furthermore, we formulate a picture of the XA region as that of an encounter of the blast wave with a finger of dense gas protruding inward from the pre-supernova cavity.
Wilson lines in the MHV action

The MHV action is the Yang-Mills action quantized on the light-front, where the two explicit physical gluonic degrees of freedom have been canonically transformed to a new set of fields. This transformation leads to the action with vertices being off-shell continuations of the MHV amplitudes. We show that the solution to the field transformation expressing one of the new fields in terms of the Yang-Mills field is a certain type of the Wilson line. More precisely, it is a straight infinite gauge link with a slope extending to the light-cone minus and the transverse direction. One of the consequences of that fact is that certain MHV vertices reduced partially on-shell are gauge invariant — a fact discovered before using conventional light-front perturbation theory. We also analyze the diagrammatic content of the field transformations leading to the MHV action. We found that the diagrams for the solution to the transformation (given by the Wilson line) and its inverse differ only by light-front energy denominators. Further, we investigate the coordinate space version of the inverse solution to the one given by the Wilson line. We find an explicit expression given by a power series in fields. We also give a geometric interpretation to it by means of a specially defined vector field. Finally, we discuss the fact that the Wilson line solution to the transformation is directly related to the all-like helicity gluon wave function, while the inverse functional is a generating functional for solutions of self-dual Yang-Mills equations.
A distributed control approach for heterogeneous linear multiagent systems

This paper considers an internal model-based distributed control approach to the cooperative output regulation problem of heterogeneous linear time-invariant multiagent systems over fixed directed ...
Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1−x films

Topology and strong electron correlations are crucial ingredients in emerging quantum materials, yet their intersection in experimental systems has been relatively limited to date. Strongly correlated Weyl semimetals, particularly when magnetism is incorporated, offer a unique and fertile platform to explore emergent phenomena in novel topological matter and topological spintronics. The antiferromagnetic Weyl semimetal Mn3Sn exhibits many exotic physical properties such as a large spontaneous Hall effect and has recently attracted intense interest. In this work, we report synthesis of epitaxial Mn3+x Sn1-x films with greatly extended compositional range in comparison with that of bulk samples. As Sn atoms are replaced by magnetic Mn atoms, the Kondo effect, which is a celebrated example of strong correlations, emerges, develops coherence, and induces a hybridization energy gap. The magnetic doping and gap opening lead to rich extraordinary properties, as exemplified by the prominent DC Hall effects and resonance-enhanced terahertz Faraday rotation.
On the Dynamics and Structure of Three-dimensional Trans-Alfvénic Jets

Three-dimensional magnetohydrodynamical simulations of strongly magnetized "light" conical jets have been performed. An investigation of the transition from sub-Alfvenic to super-Alfvenic flow has been made for nearly poloidal and for helical magnetic fields. The jets are stable to asymmetric modes of jet distortion provided they are sub-Alfvenic over most of their interior but destabilize rapidly when they become on average super-Alfvenic. The jets are precessed at the origin, and the resulting small-amplitude azimuthal motion is communicated down the jet to the Alfven point, where it couples to a slowly moving and rapidly growing helical twist. Significant jet rotation can contribute to destabilization via increase in the velocity shear between the jet and the external medium. Destabilization is accompanied by significant mass entrainment, and the jets slow down significantly as denser external material is entrained. Synchrotron intensity images satisfactorily reveal large-scale helical structures but have trouble distinguishing a large-amplitude elliptical jet distortion that appears as an apparent pinching in an intensity image. Smaller scale jet distortions are not clearly revealed in intensity images, largely as a result of the relatively small total pressure variations that accompany destabilization and growing distortions. Fractional polarization is high as a result of the strong ordered magnetic fields except where the intensity image suggests cancellation of polarization vectors by integration through twisted structures.
HEAVY AND LIGHT QUARKS WITH LATTICE CHIRAL FERMIONS

The feasibility of using lattice chiral fermions which are free of O(a) errors for both the heavy and light quarks is examined. The fact that the effective quark propagators in these fermions have the same form as that in the continuum with the quark mass being only an additive parameter to a chirally symmetric anti-Hermitian Dirac operator is highlighted. This implies that there is no distinction between the heavy and light quarks and no mass dependent tuning of the action or operators as long as the discretization error O(m2a2) is negligible. Using the overlap fermion, we find that the O(m2a2) (and O(ma2)) errors in the dispersion relations of the pseudoscalar and vector mesons and the renormalization of the axial-vector current and scalar density are small. This suggests that the applicable range of ma may be extended to ~0.56 with only 5% error, which is a factor of ~2.4 larger than the corresponding range of the improved Wilson action. We show that the generalized Gell–Mann–Oakes–Renner relation with unequal masses can be utilized to determine the finite ma corrections in the renormalization of the matrix elements for the heavy-light decay constants and semileptonic decay constants of the B/D meson.
Online Learning of Rested and Restless Bandits

In this paper, we study the online learning problem involving rested and restless bandits, in both a centralized and a decentralized setting. In a centralized setting, the system consists of a single player/user and a set of K finite-state discrete-time Markov chains (arms) with unknown state spaces (rewards) and statistics. The objective of the player is to decide in each step which M of the K arms to play over a sequence of trials so as to maximize its long-term reward. In a decentralized setting, multiple uncoordinated players each makes its own decision on which arm to play in a step, and if two or more players select the same arm simultaneously, a collision results and none of the players selecting that arm gets a reward. The objective of each player again is to maximize its long-term reward. We first show that logarithmic regret algorithms exist both for the centralized rested and restless bandit problems. For the decentralized setting, we propose an algorithm with logarithmic regret with respect to the optimal centralized arm allocation. Numerical results and extensive discussion are also provided to highlight insights obtained from this study.
Identification of Stellar Flares Using Differential Evolution Template Optimization

We explore methods for the identification of stellar flare events in irregularly sampled data of ground-based time domain surveys. In particular, we describe a new technique for identifying flaring stars, which we have implemented in a publicly available Python module called "PyVAN." The approach uses the Differential Evolution algorithm to optimize parameters of empirically derived light curve templates for different types of stars to fit a candidate light curve. The difference of the likelihoods that these best-fit templates produced the observed data is then used to delineate targets that are well-explained by a flare template but simultaneously poorly explained by templates of common contaminants. By testing on light curves of known identity and morphology, we show that our technique is capable of recovering flaring status in 69% of all light curves containing a flare event above thresholds drawn to include <1% of any contaminant population. By applying to Palomar Transient Factory data, we show consistency with prior samples of flaring stars, and identify a small selection of candidate flaring G-type stars for possible follow-up.
Model-dependence of minimal-twist OPEs in d > 2 holographic CFTs

Following recent work on heavy-light correlators in higher-dimensional conformal field theories (CFTs) with a large central charge CT, we clarify the properties of stress tensor composite primary operators of minimal twist, [Tm], using arguments in both CFT and gravity. We provide an efficient proof that the three-point coupling $$ \left\langle {\mathcal{O}}_L{\mathcal{O}}_L\left[{T}^m\right]\right\rangle $$ , where $$ {\mathcal{O}}_L $$ is any light primary operator, is independent of the purely gravitational action. Next, we consider corrections to this coupling due to additional interactions in AdS effective field theory and the corresponding dual CFT. When the CFT contains a non-zero three-point coupling $$ \left\langle TT{\mathcal{O}}_L\right\rangle $$ , the three-point coupling $$ \left\langle {\mathcal{O}}_L{\mathcal{O}}_L\left[{T}^2\right]\right\rangle $$ is modified at large CT if $$ \left\langle TT{\mathcal{O}}_L\right\rangle \sim \sqrt{C_T} $$ . This scaling is obeyed by the dilaton, by Kaluza-Klein modes of prototypical supergravity compactifications, and by scalars in stress tensor multiplets of supersymmetric CFTs. Quartic derivative interactions involving the graviton and the light probe field dual to $$ {\mathcal{O}}_L $$ can also modify the minimal-twist couplings; these local interactions may be generated by integrating out a spin-l ≥ 2 bulk field at tree level, or any spin l at loop level. These results show how the minimal-twist OPE coefficients can depend on the higher-spin gap scale, even perturbatively.
SilhoNet: An RGB Method for 6D Object Pose Estimation

Autonomous robot manipulation involves estimating the translation and orientation of the object to be manipulated as a 6-degree-of-freedom (6D) pose. Methods using RGB-D data have shown great success in solving this problem. However, there are situations where cost constraints or the working environment may limit the use of RGB-D sensors. When limited to monocular camera data only, the problem of object pose estimation is very challenging. In this letter, we introduce a novel method called SilhoNet that predicts 6D object pose from monocular images. We use a convolutional neural network pipeline that takes in region of interest proposals to simultaneously predict an intermediate silhouette representation for objects with an associated occlusion mask and a 3D translation vector. The 3D orientation is then regressed from the predicted silhouettes. We show that our method achieves better overall performance on the YCB-Video dataset than two networks for 6D pose estimation from monocular image input.
XMM-Newton and Chandra Spectroscopy of the Variable High-Energy Absorption of PG 1115+080: Refined Outflow Constraints

We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the mini-broad absorption line (BAL) quasar PG 1115+080. This is one of the few X-ray-detected mini-BAL quasars to date that is bright enough in the X-ray band, mostly due to large gravitational-lensing magnifications, to allow in-depth spectral analysis. The present XMM-Newton observations of PG 1115+080 have provided the highest signal-to-noise ratio X-ray spectra of a mini-BAL quasar obtained to date. By modeling the spectra of PG 1115+080 we have obtained constraints on the column density and ionization state of its outflowing absorbing gas. A comparison between these constraints over several epochs indicates significant variability in the properties of the outflowing absorbers in PG 1115+080. The depths of the high-energy broad absorption features in PG 1115+080 show a significant decrease between the first two observation epochs separated by a rest-frame timescale of ~1 yr. This variability supports the intrinsic nature of these absorbers. Assuming the interpretation that the high-energy absorption features arise from highly ionized Fe XXV, we constrain the fraction of the total bolometric energy released by quasars PG 1115+080 and APM 08279+5255 into the intergalactic medium in the form of kinetic energy to be k = 0.64 (68% confidence) and 0.09, respectively. According to recent theoretical studies this range of efficiencies is large enough to significantly influence the formation of the host galaxy and to regulate the growth of the central black hole.
DETERMINING THE GALACTIC HALO'S EMISSION MEASURE FROM UV AND X-RAY OBSERVATIONS

We analyze a pair of Suzaku shadowing observations in order to determine the X-ray spectrum of the Galaxy's gaseous halo. Our data consist of an observation toward an absorbing filament in the southern Galactic hemisphere and an observation toward an unobscured region adjacent to the filament. We simultaneously fit the spectra with models having halo, local, and extragalactic components. The intrinsic intensities of the halo O VII triplet and O VIII Ly {alpha} emission lines are 9.98{sup +1.10}{sub -1.99} LU (line unit; photons cm{sup -2} s{sup -1} sr{sup -1}) and 2.66{sup +0.37}{sub -0.30} LU, respectively. These results imply the existence of hot gas with a temperature of {approx}10{sup 6.0} K to {approx}10{sup 7.0} K in the Galactic halo. Meanwhile, FUSE O VI observations for the same directions and SPEAR C IV observations for a nearby direction indicate the existence of hot halo gas at temperatures of {approx}10{sup 5.0} K to {approx}10{sup 6.0} K. This collection of data implies that the hot gas in the Galactic halo is not isothermal, but its temperature spans a relatively wide range from {approx}10{sup 5.0} K to {approx}10{sup 7.0} K. We therefore construct a differential emission measure (DEM) model for the halo's hot gas, consistingmore » of two components. In each, dEM/dlog T is assumed to follow a power-law function of the temperature and the gas is assumed to be in collisional ionizational equilibrium. The low-temperature component (LTC) of the broken power-law DEM model covers the temperature range of 10{sup 4.80}-10{sup 6.02} K with a slope of 0.30 and the high-temperature component (HTC) covers the temperature range of 10{sup 6.02}-10{sup 7.02} K with a slope of -2.21. We compare our observations with predictions from models for hot gas in the halo. The observed spatial distribution of gas with temperatures in the range of our HTC is smoother than that of the LTC. We thus suggest that two types of sources contribute to our broken power-law model. We find that a simple model in which hot gas accretes onto the Galactic halo and cools radiatively cannot explain both the observed UV and X-ray portions of our broken power-law model. It can, however, explain the intensity in the Suzaku bandpass if the mass infall rate is 1.35 x 10{sup -3} M{sub sun} yr{sup -1} kpc{sup -2}. The UV and X-ray intensities and our broken power-law model can be well explained by hot gas produced by supernova explosions or by supernova remnants supplemented by a smooth source of X-rays.« less
On the problem of steady bifurcation of a falling sphere in a Navier–Stokes liquid

We study steady bifurcation for the coupled system body-liquid consisting of a sphere freely falling in a Navier–Stokes liquid under the action of gravity. In particular, we show that, under the assumption that for the bifurcating solution, the translational velocity of the sphere is parallel to the gravity, bifurcation takes place, provided that 1 is a simple eigenvalue of a suitable linear operator and the transversality property holds. Moreover, we also give sufficient conditions for symmetry breaking.
Adversarial Training for Code Retrieval with Question-Description Relevance Regularization.

Code retrieval is a key task aiming to match natural and programming languages. In this work, we propose adversarial learning for code retrieval, that is regularized by question-description relevance. First, we adapt a simple adversarial learning technique to generate difficult code snippets given the input question, which can help the learning of code retrieval that faces bi-modal and data-scarce challenges. Second, we propose to leverage question-description relevance to regularize adversarial learning, such that a generated code snippet should contribute more to the code retrieval training loss, only if its paired natural language description is predicted to be less relevant to the user given question. Experiments on large-scale code retrieval datasets of two programming languages show that our adversarial learning method is able to improve the performance of state-of-the-art models. Moreover, using an additional duplicated question detection model to regularize adversarial learning further improves the performance, and this is more effective than using the duplicated questions in strong multi-task learning baselines.
Generating buoyant magnetic flux ropes in solar-like convective dynamos

Our Sun exhibits strong convective dynamo action which results in magnetic flux bundles emerging through the stellar surface as magnetic spots. Global-scale dynamo action is believed to generate large-scale magnetic structures in the deep solar interior through the interplay of convection, rotation and shear. Portions of these large-scale magnetic structures are then believed to rise through the convective layer, forming magnetic loops which then pierce the photosphere as sunspot pairs. Previous global simulations of three-dimensional magnetohydrodynamic convection in rotating spherical shells have demonstrated mechanisms whereby large-scale magnetic wreaths can be generated in the bulk of the convection zone. Our recent simulations have achieved sufficiently high levels of turbulence to permit portions of these wreaths to become magnetically buoyant and rise through the simulated convective layer through a combination of magnetic buoyancy and advection by convective giant cells. These buoyant magnetic loops are created in the bulk of the convective layer as strong Lorentz force feedback in the cores of the magnetic wreaths dampen small-scale convective motions, permitting the amplification of local magnetic energies to over 100 times the local kinetic energy. While the magnetic wreaths are largely generated the shearing of axisymmetric poloidal magnetic fields by axisymmetric rotational shear (the Ω-effect), the loops are amplified to their peak field strengths before beginning to rise by non-axisymmetric processes. This further extends and enhances a new paradigm for the generation of emergent magnetic flux bundles, which we term turbulence-enabled magnetic buoyancy.
Vacuum stress and closed paths in rectangles, pistons and pistols

Rectangular cavities are solvable models that nevertheless touch on many of the controversial or mysterious aspects of the vacuum energy of quantum fields. This paper is a thorough study of the two-dimensional scalar field in a rectangle by the method of images, or closed classical (or optical) paths, which is exact in this case. For each point r and each specularly reflecting path beginning and ending at r, we provide formulae for all components of the stress tensor Tμν(r), for all values of the curvature coupling constant ξ and all values of an ultraviolet cutoff parameter. Arbitrary combinations of Dirichlet and Neumann conditions on the four sides can be treated. The total energy is also investigated, path by path. These results are used in an attempt to clarify the physical reality of the repulsive (outward) force on the sides of the box predicted by calculations that neglect both boundary divergences and the exterior of the box. Previous authors have studied 'piston' geometries that avoid these problems and have found the force to be attractive. We consider a 'pistol' geometry that comes closer to the original problem of a box with a movable lid. We find again an attractive force, although its origin and detailed behavior are somewhat different from the piston case. However, the pistol (and the piston) model can be criticized for extending idealized boundary conditions into short distances where they are physically implausible. Therefore, it is of interest to see whether leaving the ultraviolet cutoff finite yields results that are more plausible. We then find that the force depends strongly on a geometrical parameter; it can be made repulsive, but only by forcing that parameter into the regime where the model is least convincing physically.
Developing an improved crystal graph convolutional neural network framework for accelerated materials discovery

The recently proposed crystal graph convolutional neural network (CGCNN) offers a highly versatile and accurate machine learning (ML) framework by learning material properties directly from graphlike representations of crystal structures (``crystal graphs''). Here, we develop an improved variant of the CGCNN model (iCGCNN) that outperforms the original by incorporating information of the Voronoi tessellated crystal structure, explicit three-body correlations of neighboring constituent atoms, and an optimized chemical representation of interatomic bonds in the crystal graphs. We demonstrate the accuracy of the improved framework in two distinct illustrations: First, when trained/validated on 180 000/20 000 density functional theory (DFT) calculated thermodynamic stability entries taken from the Open Quantum Materials Database (OQMD) and evaluated on a separate test set of 230 000 entries, iCGCNN achieves a predictive accuracy that is significantly improved, i.e., 20% higher than that of the original CGCNN. Second, when used to assist a high-throughput search for materials in the $\mathrm{ThC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ structure-type, iCGCNN exhibited a success rate of $31%$ which is 155 times higher than an undirected high-throughput search and 2.4 times higher than that of the original CGCNN. Using both CGCNN and iCGCNN, we screened 132 600 compounds with elemental decorations of the $\mathrm{ThC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ prototype crystal structure and identified a total of 97 unique stable compounds by performing 757 DFT calculations, accelerating the computational time of the high-throughput search by a factor of 65. Our results suggest that the iCGCNN can be used to accelerate high-throughput discoveries of new materials by quickly and accurately identifying crystalline compounds with properties of interest.
On-chip silicon waveguide Bragg grating photonic temperature sensor

Resistance thermometry is a time-tested method for taking temperature measurements. In recent years, fundamental limits to resistance-based approaches have spurred considerable interest in developing photonic temperature sensors as a viable alternative. In this study, we demonstrate that our photonic thermometer, which consists of a silicon waveguide integrated with a Bragg grating, can be used to measure temperature changes over the range of 5°C-160°C, with a combined expanded uncertainty [k=2, 95% confidence level] of 1.25°C. Computational modeling of the sensor predicts the resonance wavelength and effective refractive index within 4% of the measured value.
Categories of Holomorphic Vector Bundles on Noncommutative Two-Tori

In this paper we study the category of standard holomorphic vector bundles on a noncommutative two-torus. We construct a functor from the derived category of such bundles to the derived category of coherent sheaves on an elliptic curve and prove that it induces an equivalence with the subcategory of stable objects. By the homological mirror symmetry for elliptic curves this implies an equivalence between the derived category of holomorphic bundles on a noncommutative two-torus and the Fukaya category of the corresponding symplectic (commutative) torus.
Thin Sequences and Their Role in Model Spaces and Douglas Algebras

We study thin interpolating sequences $$\{\lambda _n\}$$ and their relationship to interpolation in the Hardy space $$H^2$$ and the model spaces $$K_\Theta = H^2 \ominus \Theta H^2$$ , where $$\Theta $$ is an inner function. Our results, phrased in terms of the functions that do the interpolation as well as Carleson measures, show that under the assumption that $$\Theta (\lambda _n) \rightarrow 0$$ the interpolation properties in $$H^2$$ are essentially the same as those in $$K_\Theta $$ .
Recurrent proofs of the irrationality of certain trigonometric values

(2010). Recurrent Proofs of the Irrationality of Certain Trigonometric Values. The American Mathematical Monthly: Vol. 117, No. 4, pp. 360-362.
Friction Variability in Planar Pushing Data: Anisotropic Friction and Data-Collection Bias

Friction plays a key role in manipulating objects. Most of what we do with our hands, and the most of what robots do with their grippers, is based on the ability to control frictional forces. This letter aims to better understand the variability and predictability of planar friction. In particular, we focus on the analysis of a recent dataset on planar pushing by [K.-T. Yu, M. Bauza, N. Fazeli, and A. Rodriguez, More than a Million Ways to Be Pushed: A High-Fidelity Experimental Data Set of Planar Pushing, in Proceeding of the IEEE/RSJ Internatinonal Conference on Intelligent Robots and Systems, 2016, pp. 30-37.] devised to create a data-driven footprint of planar friction. We show in this letter how we can explain a significant fraction of the observed unconventional phenomena, e.g., stochasticity and multimodality, by combining the effects of material nonhomogeneity, anisotropy of friction and biases due to data collection dynamics, hinting that the variability is explainable but inevitable in practice. We introduce an anisotropic friction model and conduct simulation experiments comparing with more standard isotropic friction models. The anisotropic friction between the object and supporting surface results in convergence of initial condition during the automated data collection. Numerical results confirm that the anisotropic friction model explains the bias in the dataset and the apparent stochasticity in the outcome of a push. The fact that the data collection process itself can originate biases in the collected datasets, resulting in deterioration of trained models, calls attention to the data collection dynamics.
ZEROS OF SPARSE POLYNOMIALS OVER LOCAL FIELDS OF CHARACTERISTIC p

LetK be a field of characteristic p > 0 equipped with a valuation v : K∗ → G taking values in an ordered abelian group G. Let OK = {α ∈ K : v(α) ≥ 0} and mK = {α ∈ K : v(α) > 0} be the valuation ring and maximal ideal, respectively, and suppose that the residue field OK/mK is finite, with q elements. Theorem 1. If f(x) = a0x n0 + a1x n1 + · · · + akxk is a polynomial with k + 1 nonzero coefficients ai ∈ K∗, then f has at most q distinct zeros in K. This upper bound is sharp: if K is Fq((T )) with the usual discrete valuation v : K ∗ → Z, if V ⊂ K is an Fq-subspace of dimension k, and if c ∈ K is nonzero, then the polynomial f(x) := c ∏ α∈V (x− α) has the form a0x+ a1x + · · ·+ akx k for some a0, a1, . . . , ak ∈ K∗. Theorem 1 is the case d = 1 of the following generalization, which bounds the number of distinct zeros of bounded degree. Let μ(n) be the Mobius μ-function. Theorem 2. Fix d ≥ 1. If f(x) = a0x0 + a1x1 + · · · + akxk is a polynomial with k + 1 nonzero coefficients ai ∈ K∗, then the number of distinct zeros of f in K of degree at most d over K is at most ∑d j=1 ∑ i|j q μ(j/i). This upper bound is sharp as well, for every q, k, and d. Let K = Fq((T )) and v be as before. Let F be a finite field containing Fqi for i ≤ d. Let V ⊂ F((T )) be a k-dimensional F-vector space that is Gal(F/Fq)-stable (or equivalently, has an F-basis of elements of K). Then equality is attained in Theorem 2 for f(x) := c ∏ α∈V (x − α) for any c ∈ K∗. (The inner sum in Theorem 2 performs the inclusion-exclusion to count zeros of exact degree j.) We make no claim that these are the only polynomials that attain equality; in fact there are many others. For example, if K, V , and f are as in the previous paragraph, and if the F-basis of V consists of elements of K of distinct valuation, with all these valuations divisible by a single integer e ≥ 1, then f(x) also attains equality, as a short argument involving Hensel’s lemma shows. Other examples can be constructed using the observation that if f(x) ∈ K[x] has N zeros in a given field extension L of K, one of which is 0, then the same holds for xf(1/x) when m > deg f . Remark. H. W. Lenstra, Jr. [Le1] proves related facts for finite extensions L of Qp, using very different methods. One of his results is that for any such L and any positive integer k, there exists a positive integer B = B(k, L) with the following property: if f ∈ L[x] is a nonzero polynomial with at most k + 1 nonzero terms and f(0) 6= 0, then f has at most B zeros in L, counted with multiplicities. His bound B(k, L) is explicit, but almost certainly not sharp. Finding a sharp bound seems difficult in general, although Lenstra does this for the case k = 2 and L = Q2 (the bound then is 6). He also applies his local result to bound
On automorphism groups of Hardy algebras

Let E be a $$W^{*}$$ -correspondence and let $$H^{\infty }(E)$$ be the associated Hardy algebra. The unit disc of intertwiners $$\mathbb {D}((E^{\sigma })^{*})$$ plays a central role in the study of $$H^{\infty }(E)$$ . We show a number of results related to groups of automorphisms of both $$H^{\infty }(E)$$ and $$\mathbb {D}((E^{\sigma })^{*})$$ . We find a matrix representation for these groups and describe several features of their algebraic structure. Furthermore, we show an application of $$Aut(\mathbb {D}({(E^{\sigma }})^*))$$ to the study of Morita equivalence of $$W^{*}$$ -correspondences.
A rank inequality for the Tate Conjecture over global function fields

We present an observation of Ramakrishnan concerning the Tate Conjecture for varieties over a global function field (i.e., the function field of a smooth projecture curve over a finite field), which was pointed out during a lecture given at the AIM's workshop on the Tate Conjecture in July 2007. The result is perhaps “known to the experts,” but we record it here, as it does not appear to be in print elsewhere. We use the global Langlands correspondence for the groups GL_n over global function fields, proved by Lafforgue [Chtoucas de Drinfeld et correspondance de Langlands, Invent. Math. 147 (2002) 1–241], along with an analytic result of Jacquet and Shalika [On Euler products and the classification of automorphic forms. I and II, Amer. J. Math. 103 (1981) 499–558, 777–815] on automorphic L-functions for GL_n. Specifically, we use these to show (see Theorem 2.1 below) that, for a prime l ≠ char k, the dimension of the subspace spanned by the rational cycles of codimension m on our variety in its 2m-th l-adic cohomology group (the so-called algebraic rank) is bounded above by the order of the pole at s=m+1 of the associated L-function (the so-called analytic rank). The interest in this result lies in the fact that, with the exception of some special instances like certain Shimura varieties and abelian varieties which are potentially CM type, the analogous result for varieties over number fields is still unknown in general, even for the case of divisors (m=1).
Multi-Center Vector Field Methods for Wave Equations

We develop the method of vector-fields to further study Dispersive Wave Equations. Radial vector fields are used to get a-priori estimates such as the Morawetz estimate on solutions of Dispersive Wave Equations. A key to such estimates is the repulsiveness or nontrapping conditions on the flow corresponding to the wave equation. Thus this method is limited to potential perturbations which are repulsive, that is the radial derivative pointing away from the origin. In this work, we generalize this method to include potentials which are repulsive relative to a line in space (in three or higher dimensions), among other cases. This method is based on constructing multi-centered vector fields as multipliers, cancellation lemmas and energy localization.