cssi/SciSciGPT-SciSciNet huggingface dataset:
Photometric Variability and Astrometric Stability of the Radio Continuum Nucleus in the Seyfert Galaxy NGC 5548

The NRAO Very Large Array (VLA) and Very Long Baseline Array (VLBA) were used from 1988 November to 1998 June to monitor the radio continuum counterpart to the optical broad-line region (BLR) in the Seyfert galaxy NGC 5548. Photometric and astrometric observations were obtained at 21 epochs. The radio nucleus appeared resolved, so comparisons were limited to observations spanning 10-60 days and 3-4 yr and acquired at matched resolutions of 1210 mas = 640 pc (nine VLA observations), 500 mas = 260 pc (nine VLA observations), or 2.3 mas = 1.2 pc (three VLBA observations). The nucleus is photometrically variable at 8.4 GHz by 33% ± 5% and 52% ± 5% between VLA observations separated by 41 days and 4.1 yr, respectively. The 41 day changes are milder (19% ± 5%) at 4.9 GHz and exhibit an inverted spectrum (α ~ 0.3 ± 0.1, S ∝ ν+α) from 4.9 to 8.4 GHz. The nucleus is astrometrically stable at 8.4 GHz, to an accuracy of 28 mas = 15 pc between VLA observations separated by 4.1 yr and to an accuracy of 1.8 mas = 0.95 pc between VLBA observations separated by 3.1 yr. Such photometric variability and astrometric stability is consistent with a black hole being the ultimate energy source for the BLR but is problematic for star cluster models that treat the BLR as a compact supernova remnant and, for NGC 5548, require a new supernova event every 1.7 yr within an effective radius re = 42 mas = 22 pc. A deep image at 8.4 GHz with resolution 660 mas = 350 pc was obtained by adding data from quiescent VLA observations. This image shows faint bipolar lobes straddling the radio nucleus and spanning 12'' = 6.4 kpc. These synchrotron-emitting lobes could be driven by twin jets or a bipolar wind from the Seyfert 1 nucleus.
Imaging $^{55}$Fe Electron Tracks in a GEM-based TPC Using a CCD Readout

Images of resolved 5.9 keV electron tracks produced from $^{55}$Fe X-ray interactions are presented for the first time using an optical readout time projection chamber (TPC). The corresponding energy spectra are also shown, with the FWHM energy resolution in the 30-40\% range depending on gas pressure and gain. These tracks were produced in low pressure carbon tetrafluoride (CF$_4$) gas, and imaged with a fast lens and low noise CCD camera system using the secondary scintillation produced in GEM/THGEM amplification devices. The GEM/THGEMs provided effective gas gains of $\gtrsim 2 \times 10^5$ in CF$_4$ at low pressures in the 25-100 Torr range. The ability to resolve such low energy particle tracks has important applications in dark matter and other rare event searches, as well as in X-ray polarimetry. A practical application of the optical signal from $^{55}$Fe is that it provides a tool for mapping the detector gain spatial uniformity.
PROBING THE PHYSICAL CONDITIONS OF ATOMIC GAS AT HIGH REDSHIFT

A new method is used to measure the physical conditions of the gas in damped Lyα systems (DLAs). Using high-resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio of the upper and lower fine-structure levels of the ground state of C+ and Si+. These ratios are determined solely by the physical conditions of the gas. We explore the allowed physical parameter space using a Monte Carlo Markov chain method to constrain simultaneously the temperature, neutral hydrogen density, and electron density of each DLA. The results indicate that at least 5% of all DLAs have the bulk of their gas in a dense, cold phase with typical densities of ~100 cm–3 and temperatures below 500 K. We further find that the typical pressure of DLAs in our sample is log (P/kB ) = 3.4 (K cm–3), which is comparable to the pressure of the local interstellar medium (ISM), and that the components containing the bulk of the neutral gas can be quite small with absorption sizes as small as a few parsecs. We show that the majority of the systems are consistent with having densities significantly higher than expected for a purely canonical warm neutral medium, indicating that significant quantities of dense gas (i.e., n H > 0.1 cm–3) are required to match observations. Finally, we identify eight systems with positive detections of Si II*. These systems have pressures (P/kB ) in excess of 20,000 K cm–3, which suggest that these systems tag a highly turbulent ISM in young, star-forming galaxies.
Wind-reprocessed Transients

We consider the situation where the luminosity from a transient event is reprocessed by an optically thick wind. Potential applications are the tidal disruption of stars by black holes (BHs), engine-powered supernovae, and unique fast transients found by current and future wide-field surveys. We derive relations between the injected and observed luminosity for steady and time-dependent winds, and discuss how the temperature is set for scattering-dominated radiative transport. We apply this framework to specific examples of tidal disruption events and the formation of a BH by a massive star, as well as discuss other applications such as deriving observables from detailed hydrodynamic simulations. We conclude by exploring what is inferred about the mass-loss rate and underlying engine powering AT 2018cow if it is explained as a wind-reprocessed transient, demonstrating that its optical emission is consistent with reprocessing of the observed soft X-rays.
The Origin of Major Solar Activity: Collisional Shearing between Nonconjugated Polarities of Multiple Bipoles Emerging within Active Regions

Active Regions (ARs) that exhibit compact Polarity Inversion Lines (PILs) are known to be very flare-productive. However, the physical mechanisms behind this statistical inference have not been demonstrated conclusively. We show that such PILs can occur due to the collision between two emerging flux tubes nested within the same AR. In such multipolar ARs, the flux tubes may emerge simultaneously or sequentially, each initially producing a bipolar magnetic region (BMR) at the surface. During each flux tube's emergence phase, the magnetic polarities can migrate such that opposite polarities belonging to different BMRs collide, resulting in shearing and cancellation of magnetic flux. We name this process 'collisional shearing' to emphasize that the shearing and flux cancellation develops due to the collision. Collisional shearing is a process different from the known concept of flux cancellation occurring between polarities of a single bipole, a process that has been commonly used in many numerical models. High spatial and temporal resolution observations from the Solar Dynamics Observatory for two emerging ARs, AR11158 and AR12017, show the continuous cancellation of up to 40% of the unsigned magnetic flux of the smallest BMR, which occurs at the collisional PIL for as long as the collision persists. The flux cancellation is accompanied by a succession of solar flares and CMEs, products of magnetic reconnection along the collisional PIL. Our results suggest that the quantification of magnetic cancellation driven by collisional shearing needs to be taken into consideration in order to improve the prediction of solar energetic events and space weather.
FUSE Measurements of Rydberg Bands of Interstellar CO between 925 and 1150 Å

We report the detection of 11 Rydberg bands of CO in FUSE spectra of the sight line toward HD 203374A. Eight of these electronic bands are seen in the interstellar medium for the first time. Our simultaneous fit of five non-Rydberg A-X bands together with the strongest Rydberg band of CO, C-X (0-0), yields a four-component cloud structure toward the stellar target. With this model we synthesize the other Rydberg bands in order to derive their oscillator strengths. We find that the strength of some bands was underestimated in previously published results from laboratory measurements. The implication is important for theoretical calculations of the abundance of interstellar CO, because its dissociation and self-shielding depend on oscillator strengths for these bands.
THE SIZE, STRUCTURE, AND IONIZATION OF THE BROAD-LINE REGION IN NGC 3227

Hubble Space Telescope spectroscopy of the Seyfert 1.5 galaxy, NGC 3227, confirms previous reports that the broad Hα emission line flux is time variable, decreasing by a modest ~11% between 1999 and 2000 in response to a corresponding ~37% decrease in the underlying continuum. Modeling the gas distribution responsible for the broad Hα, Hβ, and Hγ emission lines favors a spherically symmetric inflow as opposed to a thin disk. Adopting a central black hole mass of 7.6 × 106 M ☉, determined from prior reverberation mapping, leads to the following dimensions for the size of the region emitting the broad Hα line: an outer radius ~90 lt-days and an inner radius ~3 lt-days. Thus, the previously determined reverberation size for the broad-line region (BLR) consistently coincides with the inner radius of a much larger volume of ionized gas. However, the perceived size of the BLR is an illusion, a consequence of the fact that the emitting region is ionization bounded at the outer radius and diminished by Doppler broadening at the inner radius. The actual dimensions of the inflow remain to be determined. Nevertheless, the steady-state mass inflow rate is estimated to be ~10–2 M ☉ yr–1 which is sufficient to explain the X-ray luminosity of the active galactic nucleus (AGN) in terms of radiatively inefficient accretion. Collectively, the results challenge many preconceived notions concerning the nature of BLRs in AGNs.
Astrophysical tests of modified gravity: the morphology and kinematics of dwarf galaxies

This paper is the third in a series on tests of gravity using observations of stars and nearby dwarf galaxies. We carry out four distinct tests using published data on the kinematics and morphology of dwarf galaxies, motivated by the theoretical work of Hui et al. (2009) and Jain & Vanderplas (2011). In a wide class of gravity theories a scalar field couples to matter and provides an attractive fifth force. Due to their different self-gravity, stars and gas may respond differently to the scalar force leading to several observable deviations from standard gravity. HI gas, red giant stars and main sequence stars can be displaced relative to each other, and the stellar disk can display warps or asymmetric rotation curves aligned with external potential gradients. To distinguish the effects of modified gravity from standard astrophysical phenomena, we use a control sample of galaxies that are expected to be screened from the fifth force. In all cases we find no significant deviation from the null hypothesis of general relativity. The limits obtained from dwarf galaxies are not yet competitive with the limits from cepheids obtained in our first paper, but can be improved to probe regions of parameter space that are inaccessible using other tests. We discuss how our methodology can be applied to new radio and optical observations of nearby galaxies.
Gamma-ray burst afterglows and their implications

The discovery of X-ray, optical and radio afterglows of GRBs provides an important tool for understanding these sources. Most current models envisage GRB as arising in a cataclysmic stellar event leading to a relativistically expanding fireball, where particle acceleration at shocks lead to nonthermal radiation. The predictions of this scenario are in substantial agreement with the bulk of the observations. In addition, the data show a diversity of finer structure behavior, which is providing constraints for more detailed models. Current issues of interest are the implications of the beaming for the energetics, the afterglow time structure, dependence on progenitor system, and the role of the environment.
Density and distribution evaluation for convolution of independent gamma variables

Convolutions of independent gamma variables are encountered in many applications such as insurance, reliability, and network engineering. Accurate and fast evaluations of their density and distribution functions are critical for such applications, but no open source, user-friendly software implementation has been available. We review several numerical evaluations of the density and distribution of convolution of independent gamma variables and compare them with respect to their accuracy and speed. The methods that are based on the Kummer confluent hypergeometric function are computationally most efficient. The benefit of employing the confluent hypergeometric function is further demonstrated by a renewal process application, where the gamma variables in the convolution are Erlang variables. We derive a new computationally efficient formula for the probability mass function of the number of renewals by a given time. An R package coga provides efficient C++ based implementations of the discussed methods and are available in CRAN.
Multi-Layer Architecture for Efficient Steganalysis of UnderMp3Cover in Multi-Encoder Scenario

Mp3 is a very popular audio format and hence it can be a good host for carrying hidden messages. Therefore, different steganography methods have been proposed for mp3 hosts, but current literature has only focused on steganalysis of mp3stego. In this paper, we mention some of the limitations of mp3stego and argue that UnderMp3Cover (Ump3c) does not have those limitations. Ump3c makes subtle changes only to the global gain of bitstream and keeps the rest of bitstream intact. Therefore, its detection is much harder than mp3stego. To address this, joint distributions between global gain and other fields of mp3 bit stream are used. The changes are detected by measuring the mutual information from those joint distributions. Furthermore, we show that different mp3 encoders have dissimilar performances. Consequently, a novel multi-layer architecture for steganalysis of Ump3c is proposed. In this manner, the first layer detects the encoder and the second layer performs the steganalysis job. One of advantages of this architecture is that feature extraction and feature selection can be optimized for each encoder separately. We show this multi-layer architecture outperforms the conventional single-layer methods. Comparing results of the proposed method with other works shows an improvement of 20.4% in the accuracy of steganalysis.
Divisors of Shifted Primes

We bound from below the number of shifted primes p+s x that have a divisor in a given interval (y;z). Kevin Ford has obtained upper bounds of the expected order of magnitude on this quantity as well as lower bounds in a special case of the parameters y and z. We supply here the corresponding lower bounds in a broad range of the parameters y and z. As expected, these bounds depend heavily on our knowledge about primes in arithmetic progressions. As an application of these bounds, we determine the number of shifted primes that appear in a multiplication table up to multiplicative constants.
Comment: the Importance of Jeffreys's Legacy

Theory of Probability is distinguished by several high-level philosophical attitudes, some stressed by Jeffreys, some implicit. By reviewing these we may recognize the importance in this work in the historical development of statistics.
PROPAGATION EFFECTS IN MAGNETIZED TRANSRELATIVISTIC PLASMAS

The transfer of polarized radiation in magnetized and nonmagnetized relativistic plasmas is an area of research with numerous flaws and gaps. The present paper is aimed at filling some gaps and eliminating the flaws. Starting from a Trubnikov's linear response tensor for a vacuum wave with |k| = ω/c in thermal plasma, the analytic expression for the dielectric tensor is found in the limit of high frequencies. The Faraday rotation and Faraday conversion measures are computed in their first orders in the ratio of the cyclotron frequency Ω0 to the observed frequency ω. The computed temperature dependencies of propagation effects bridge the known nonrelativistic and ultrarelativistic limiting formulae. The fitting expressions are found for high temperatures, where the higher orders in Ω0/ω cannot be neglected. The plasma eigenmodes are found to become linearly polarized at much larger temperatures than thought before. The results are applied to the diagnostics of the hot interstellar medium, hot accretion flows, and jets.
On the Bartnik conjecture for the static vacuum Einstein equations

We prove that given any smooth metric and smooth positive function H on there is a constant depending on and an asymptotically flat solution of the static vacuum Einstein equations on such that the induced metric and mean curvature of at are given by This gives a partial resolution of the conjecture of Bartnik.
Conditional Cash Incentive and Use of Health Care Services: New Evidence from a Household Experiment

Studies have recently provided insights into the effects of incentive modalities in the health care sector. However, there is insufficient evidence on the underlying causes of the partial effectiveness of these strategies in the health systems of developing countries. This study presents results from a large-scale randomized experiment across 6848 households in Afghanistan that evaluates the impact of a conditional incentive pay scheme on health facilities. Supported by the target-income hypothesis framework and relaxing the compliance assumption in the empirical modeling, the estimated coefficients yield causal effects of the supply-side conditional incentive on the utilization for health care services. After 2 years, the conditional incentive increased the use of pre-targeted maternal and children health care services among the households at lower levels and at contracted-out health facilities. Additionally, the incentive scheme is associated with sizable efficiency gains at the facility level. These gains are realized at the expense of deterring service users’ satisfaction with physicians’ communication qualities. This study establishes that margins of improvement do exist in the supply-side performance conditioning on an organizational structure and the service contractual arrangements of health facilities. This work provides a framework for the plausible implementation of incentive policies in the health care sector.
On integer solutions of Parsell–Vinogradov systems

We prove a sharp upper bound on the number of integer solutions of the Parsell–Vinogradov system in every dimension $$d\ge 2$$ .
DWARF GALAXIES WITH IONIZING RADIATION FEEDBACK. II: SPATIALLY-RESOLVED STAR FORMATION RELATION

We investigate the spatially-resolved star formation rela tion using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radi ation stabilizes gas against Jeans fragmentation, reducing the star formation rate. Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially-resolved observatio ns of star formation tracers, such as Hα emission. We can also observe how stellar feedback manifests itself in th e correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3× 10 11 M⊙, we find that the correlation between star formation rate density (estimated from mock Hα emission) and H2 density shows large scatter, especially at high resolutions of . 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution, and because Hα traces hot gas around star-forming regions and is displaced from the H2 peaks themselves. By examining the evolving environment around star clusters, we speculate that the bre akdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces, and molecular clouds being dispersed via stellar feedback. Subject headings: galaxies: formation — galaxies: evolution — galaxies: star clusters — galaxies: structure — stars: formation — stars: evolution — ISM: structure — ISM: evolution
An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

We present a library of empirical stellar spectra created using spectra from the Sloan Digital Sky Survey's Baryon Oscillation Spectroscopic Survey. The templates cover spectral types O5 through L3, are binned by metallicity from −2.0 dex through +1.0 dex, and are separated into main-sequence (dwarf) stars and giant stars. With recently developed M dwarf metallicity indicators, we are able to extend the metallicity bins down through the spectral subtype M8, making this the first empirical library with this degree of temperature and metallicity coverage. The wavelength coverage for the templates is from 3650 to 10200 A at a resolution of better than R ~ 2000. Using the templates, we identify trends in color space with metallicity and surface gravity, which will be useful for analyzing large data sets from upcoming missions like the Large Synoptic Survey Telescope. Along with the templates, we are releasing a code for automatically (and/or visually) identifying the spectral type and metallicity of a star.
DYNAMIC CONIC FINANCE: PRICING AND HEDGING IN MARKET MODELS WITH TRANSACTION COSTS VIA DYNAMIC COHERENT ACCEPTABILITY INDICES

In this paper we present a theoretical framework for determining dynamic ask and bid prices of derivatives using the theory of dynamic coherent acceptability indices in discrete time. We prove a version of the First Fundamental Theorem of Asset Pricing using the dynamic coherent risk measures. We introduce the dynamic ask and bid prices of a derivative contract in markets with transaction costs. Based on these results, we derive a representation theorem for the dynamic bid and ask prices in terms of dynamically consistent sequence of sets of probability measures and risk-neutral measures. To illustrate our results, we compute the ask and bid prices of some path-dependent options using the dynamic Gain-Loss Ratio.
Tropicalizing the positive semidefinite cone

We study the tropicalization of the cone of positive semidefinite matrices over the ordered field of real Puiseux series. The tropical PSD matrices form the normal cone of the Newton polytope of the symmetric determinant at the vertex corresponding to the product of diagonal entries. We find generators and defining inequalities of the cone. The PSD tropical quadratic forms are those that induce the trivial subdivision on the standard simplex dilated by two. We also show that the tropical PSD cone is the tropical convex hull of the set of symmetric matrices of tropical rank one and that every tropical PSD matrix can be factored as a tropical product of a matrix and its transpose.
Experimental demonstration of multiple monoenergetic gamma radiography for effective atomic number identification in cargo inspection

The smuggling of special nuclear materials (SNMs) through international borders could enable nuclear terrorism and constitutes a significant threat to global security. This paper presents the experimental demonstration of a novel radiographic technique for quantitatively reconstructing the density and type of material present in commercial cargo containers, as a means of detecting such threats. Unlike traditional techniques which use sources of bremsstrahlung photons with a continuous distribution of energies, multiple monoenergetic gamma radiography utilizes monoenergetic photons from nuclear reactions, specifically the 4.4 and 15.1 MeV photons from the 11B(d,nγ)12C reaction. By exploiting the Z-dependence of the photon interaction cross sections at these two specific energies, it is possible to simultaneously determine the areal density and the effective atomic number as a function of location for a 2D projection of a scanned object. The additional information gleaned from using and detecting photons of specific energies for radiography substantially increases the resolving power between different materials. This paper presents results from the imaging of mock cargo materials ranging from Z≈5−92, demonstrating accurate reconstruction of the effective atomic number and areal density of the materials over the full range. In particular, the system is capable of distinguishing pure materials with Z≳70, such as lead and uranium—a critical requirement of a system designed to detect SNM. This methodology could be used to screen commercial cargoes with high material specificity, to distinguish most benign materials from SNM, such as uranium and plutonium.
Simulation of beam-induced plasma in gas-filled rf cavities

Processes occurring in a radio-frequency (rf) cavity, filled with high pressure gas and interacting with proton beams, have been studied via advanced numerical simulations. Simulations support the experimental program on the hydrogen gas-filled rf cavity in the Mucool Test Area (MTA) at Fermilab, and broader research on the design of muon cooling devices. space, a 3D electromagnetic particle-in-cell (EM-PIC) code with atomic physics support, was used in simulation studies. Plasma dynamics in the rf cavity, including the process of neutral gas ionization by proton beams, plasma loading of the rf cavity, and atomic processes in plasma such as electron-ion and ion-ion recombination and electron attachment to dopant molecules, have been studied. Through comparison with experiments in the MTA, simulations quantified several uncertain values of plasma properties such as effective recombination rates and the attachment time of electrons to dopant molecules. Simulations have achieved very good agreement with experiments on plasma loading and related processes. The experimentally validated code space is capable of predictive simulations of muon cooling devices.
Quantifying Hypothesis Space Misspecification in Learning From Human–Robot Demonstrations and Physical Corrections

The human input has enabled autonomous systems to improve their capabilities and achieve complex behaviors that are otherwise challenging to generate automatically. Recent work focuses on how robots can use such inputs—such as, demonstrations or corrections—to learn intended objectives. These techniques assume that the human‘s desired objective already exists within the robot's hypothesis space. In reality, this assumption is often inaccurate: there will always be situations where the person might care about aspects of the task that the robot does not know about. Without this knowledge, the robot cannot infer the correct objective. Hence, when the robot's hypothesis space is misspecified , even methods that keep track of uncertainty over the objective fail because they reason about which hypothesis might be correct, and not whether any of the hypotheses are correct. In this article, we posit that the robot should reason explicitly about how well it can explain human inputs given its hypothesis space and use that situational confidence to inform how it should incorporate the human input. We demonstrate our method on a 7 degrees-of-freedom robot manipulator in learning from two important types of human inputs: demonstrations of motion planning tasks and physical corrections during the robot's task execution.
HOW PENGUINS STARTED TO FLY

A mechanism explaining a strong enhancement of nonleptonic weak decays was suggested in 1975, later to be dubbed the penguin. This mechanism extends Wilson's ideas about the operator product expansion at short distances and reveals an intricate interplay of subtle features of the theory such as heavy quark masses in Glashow–Iliopoulos–Maini cancellation, light quarks shaping the chiral properties of QCD, etc. The penguins have subsequently evolved to play a role in a variety of fields in present-day particle phenomenology. I will describe the history of this idea and review its subsequent development. The recent measurement of direct CP violation in K decays gives a new confirmation of the penguin mechanism.
Comments on Microcausality, Chaos, and Gravitational Observables

© 2015 IOP Publishing Ltd Printed in the UK. Observables in gravitational systems must be non-local so as to be invariant under diffeomorphism gauge transformations. But at the classical level some such observables can nevertheless satisfy an exact form of microcausality. This property is conjectured to remain true at all orders in the semiclassical expansion, though with limitations at finite h or lPlanck. We also discuss related issues concerning observables in black hole spacetimes and comment on the senses in which they do and do not experience the form of chaos identified by Shenker and Stanford. In particular, in contrast to the situation in a reflecting cavity, this chaos does not afflict observables naturally associated with Hawking radiation for evaporating black holes.
Pseudoconvexity for the special Lagrangian potential equation

The Special Lagrangian Potential Equation for a function u on a domain $$\Omega \subset {{\mathbb {R}}}^n$$ is given by $${\mathrm{tr}}\{\arctan (D^2 \,u) \} = \theta $$ for a contant $$\theta \in (-n {\pi \over 2}, n {\pi \over 2})$$ . For $$C^2$$ solutions the graph of Du in $$\Omega \times {{\mathbb {R}}}^n$$ is a special Lagrangian submanfold. Much has been understood about the Dirichlet problem for this equation, but the existence result relies on explicitly computing the associated boundary conditions (or, otherwise said, computing the pseudo-convexity for the associated potential theory). This is done in this paper, and the answer is interesting. The result carries over to many related equations—for example, those obtained by taking $$\sum _k \arctan \, \lambda _k^{{\mathfrak {g}}}= \theta $$ where $${{\mathfrak {g}}}: {\mathrm{Sym}}^2({{\mathbb {R}}}^n)\rightarrow {{\mathbb {R}}}$$ is a Garding-Dirichlet polynomial which is hyperbolic with respect to the identity. A particular example of this is the deformed Hermitian–Yang–Mills equation which appears in mirror symmetry. Another example is $$\sum _j \arctan \kappa _j = \theta $$ where $$\kappa _1,\ldots , \kappa _n$$ are the principal curvatures of the graph of u in $$\Omega \times {{\mathbb {R}}}$$ . We also discuss the inhomogeneous Dirichlet Problem $$\begin{aligned} {\mathrm{tr}}\{\arctan (D^2_x \,u)\} = \psi (x) \end{aligned}$$ where $$\psi : {\overline{\Omega }}\rightarrow (-n {\pi \over 2}, n {\pi \over 2})$$ . This equation has the feature that the pull-back of $$\psi $$ to the Lagrangian submanifold $$L\equiv {\mathrm{graph}}(Du)$$ is the phase function $$\theta $$ of the tangent spaces of L. On L it satisfies the equation $$\nabla \psi = -JH$$ where H is the mean curvature vector field of L.
Does Bohm’s Quantum Force Have a Classical Origin?

In the de Broglie–Bohm formulation of quantum mechanics, the electron is stationary in the ground state of hydrogenic atoms, because the quantum force exactly cancels the Coulomb attraction of the electron to the nucleus. In this paper it is shown that classical electrodynamics similarly predicts the Coulomb force can be effectively canceled by part of the magnetic force that occurs between two similar particles each consisting of a point charge moving with circulatory motion at the speed of light. Supposition of such motion is the basis of the Zitterbewegung interpretation of quantum mechanics. The magnetic force between two luminally-circulating charges for separation large compared to their circulatory motions contains a radial inverse square law part with magnitude equal to the Coulomb force, sinusoidally modulated by the phase difference between the circulatory motions. When the particles have equal mass and their circulatory motions are aligned but out of phase, part of the magnetic force is equal but opposite the Coulomb force. This raises a possibility that the quantum force of Bohmian mechanics may be attributable to the magnetic force of classical electrodynamics. It is further shown that relative motion between the particles leads to modulation of the magnetic force with spatial period equal to the de Broglie wavelength.
Brownian-time processes: The PDE connection II and the corresponding Feynman-Kac formula

We delve deeper into our study of the connection of Brownian-time processes (BTPs) to fourth-order parabolic PDEs, which we introduced in a recent joint article with W. Zheng. Probabilistically, BTPs and their cousins BTPs with excursions form a unifying class of interesting stochastic processes that includes the celebrated IBM of Burdzy and other new intriguing processes and is also connected to the Markov snake of Le Gall. BTPs also offer a new connection of probability to PDEs that is fundamentally different from the Markovian one. They solve fourth-order PDEs in which the initial function plays an important role in the PDE itself, not only as initial data. We connect two such types of interesting and new PDEs to BTPs. The first is obtained by running the BTP and then integrating along its path, and the second type of PDEs is related to what we call the Feynman-Kac formula for BTPs. A special case of the second type is a step towards a probabilistic solution to linearized Cahn-Hilliard and Kuramoto-Sivashinsky type PDEs, which we tackle in an upcoming paper.
Compact representation of temporal processes in echosounder time series via matrix decomposition

The recent explosion in the availability of echosounder data from diverse ocean platforms has created unprecedented opportunities to observe the marine ecosystems at broad scales. However, the critical lack of methods capable of automatically discovering and summarizing prominent spatio-temporal echogram structures has limited the effective and wider use of these rich datasets. To address this challenge, a data-driven methodology is developed based on matrix decomposition that builds compact representation of long-term echosounder time series using intrinsic features in the data. In a two-stage approach, noisy outliers are first removed from the data by principal component pursuit, then a temporally smooth nonnegative matrix factorization is employed to automatically discover a small number of distinct daily echogram patterns, whose time-varying linear combination (activation) reconstructs the dominant echogram structures. This low-rank representation provides biological information that is more tractable and interpretable than the original data, and is suitable for visualization and systematic analysis with other ocean variables. Unlike existing methods that rely on fixed, handcrafted rules, this unsupervised machine learning approach is well-suited for extracting information from data collected from unfamiliar or rapidly changing ecosystems. This work forms the basis for constructing robust time series analytics for large-scale, acoustics-based biological observation in the ocean.
Conservation of angular momentum in second harmonic generation from under-dense plasmas

Spin and orbital angular momentum of an optical beam are two independent parameters that exhibit distinct effects on mechanical objects. However, when laser beams with angular momentum interact with plasmas, one can observe the interplay between the spin and the orbital angular momentum. Here, by measuring the helical phase of the second harmonic 2ω radiation generated in an underdense plasma using a known spin and orbital angular momentum pump beam, we verify that the total angular momentum of photons is conserved and observe the conversion of spin to orbital angular momentum. We further determine the source of the 2ω photons by analyzing near field intensity distributions of the 2ω light. The 2ω images are consistent with these photons being generated near the largest intensity gradients of the pump beam in the plasma as predicted by the combined effect of spin and orbital angular momentum when Laguerre-Gaussian beams are used. The interaction of light possessing spin or orbital angular momentum with neutral matter has attracted attention by allowing new degrees of control, but its interaction with plasma is less studied. Here, the conservation of total angular momentum is examined via nonlinear optical processes in an under-dense plasma.
A Molecular Calcium Integrator Reveals a Striatal Cell Type Driving Aversion

The ability to record transient cellular events in the DNA or RNA of cells would enable precise, large-scale analysis, selection, and reprogramming of heterogeneous cell populations. Here, we report a molecular technology for stable genetic tagging of cells that exhibit activity-related increases in intracellular calcium concentration (FLiCRE). We used FLiCRE to transcriptionally label activated neural ensembles in the nucleus accumbens of the mouse brain during brief stimulation of aversive inputs. Using single-cell RNA sequencing, we detected FLiCRE transcripts among the endogenous transcriptome, providing simultaneous readout of both cell-type and calcium activation history. We identified a cell type in the nucleus accumbens activated downstream of long-range excitatory projections. Taking advantage of FLiCRE's modular design, we expressed an optogenetic channel selectively in this cell type and showed that direct recruitment of this otherwise genetically inaccessible population elicits behavioral aversion. The specificity and minute resolution of FLiCRE enables molecularly informed characterization, manipulation, and reprogramming of activated cellular ensembles.
Stability-Certified Reinforcement Learning: A Control-Theoretic Perspective

We investigate the important problem of certifying stability of reinforcement learning policies when interconnected with nonlinear dynamical systems. We show that by regulating the partial gradients of policies, strong guarantees of robust stability can be obtained based on a proposed semidefinite programming feasibility problem. The method is able to certify a large set of stabilizing controllers by exploiting problem-specific structures; furthermore, we analyze and establish its (non)conservatism. Empirical evaluations on two decentralized control tasks, namely multi-flight formation and power system frequency regulation, demonstrate that the reinforcement learning agents can have high performance within the stability-certified parameter space and also exhibit stable learning behaviors in the long run.
Interpreting Galaxy Deblender GAN from the Discriminator's Perspective.

In large galaxy surveys it can be difficult to separate overlapping galaxies, a process called deblending. Generative adversarial networks (GANs) have shown great potential in addressing this fundamental problem. However, it remains a significant challenge to comprehend how the network works, which is particularly difficult for non-expert users. This research focuses on understanding the behaviors of one of the network’s major components, the Discriminator, which plays a vital role but is often overlooked. Specifically, we propose an enhanced Layer-wise Relevance Propagation (LRP) algorithm called Polarized-LRP. It generates a heatmap-based visualization highlighting the area in the input image that contributes to the network decision. It consists of two parts i.e. a positive contribution heatmap for the images classified as ground truth and a negative contribution heatmap for the ones classified as generated. As a use case, we have chosen the deblending of two overlapping galaxy images via a branched GAN model. Using the Galaxy Zoo dataset we demonstrate that our method clearly reveals the attention areas of the Discriminator to differentiate generated galaxy images from ground truth images, and outperforms the original LRP method. To connect the Discriminator’s impact on the Generator, we also visualize the attention shift of the Generator across the training process. An interesting result we have achieved is the detection of a problematic data augmentation procedure that would else have remained hidden. We find that our proposed method serves as a useful visual analytical tool for more effective training and a deeper understanding of GAN models.
Personalized Food Recommendation as Constrained Question Answering over a Large-scale Food Knowledge Graph

Food recommendation has become an important means to help guide users to adopt healthy dietary habits. Previous works on food recommendation either i) fail to consider users' explicit requirements, ii) ignore crucial health factors (e.g., allergies and nutrition needs), or iii) do not utilize the rich food knowledge for recommending healthy recipes. To address these limitations, we propose a novel problem formulation for food recommendation, modeling this task as constrained question answering over a large-scale food knowledge base/graph (KBQA). Besides the requirements from the user query, personalized requirements from the user's dietary preferences and health guidelines are handled in a unified way as additional constraints to the QA system. To validate this idea, we create a QA style dataset for personalized food recommendation based on a large-scale food knowledge graph and health guidelines. Furthermore, we propose a KBQA-based personalized food recommendation framework which is equipped with novel techniques for handling negations and numerical comparisons in the queries. Experimental results on the benchmark show that our approach significantly outperforms non-personalized counterparts (average 59.7% absolute improvement across various evaluation metrics), and is able to recommend more relevant and healthier recipes.
Information Storage in the Stochastic Ising Model

Most information storage devices write data by modifying the local state of matter, in the hope that sub-atomic local interactions stabilize the state for sufficiently long time, thereby allowing later recovery. Motivated to explore how temporal evolution of physical states in magnetic storage media affects their capacity, this work initiates the study of information retention in locally-interacting particle systems. The system dynamics follow the stochastic Ising model (SIM) over a 2-dimensional $\sqrt {{n}}\times \sqrt {{n}}$ grid. The initial spin configuration $ {X}_{0}$ serves as the user-controlled input. The output configuration ${X}_{{t}}$ is produced by running $t$ steps of Glauber dynamics. Our main goal is to evaluate the information capacity ${I}_{{n}}({t}):=\max _{{p}_{{X}_{0}}}{I}({X}_{0};{X}_{{t}})$ when time $t$ scales with the system’s size $n$ . While the positive (but low) temperature regime is our main interest, we start by exploring the simpler zero-temperature dynamics. We first show that at zero temperature, order of $\sqrt {{n}}$ bits can be stored in the system indefinitely by coding over stable, striped configurations. While $\sqrt {{n}}$ is order optimal for infinite time, backing off to ${t} , higher orders of ${I}_{{n}}({t})$ are achievable. First, via linear coding arguments imply we show that ${I}_{{n}}({t}) = \Theta ({n})$ for ${t}={O}({n})$ . To go beyond the linear scale, we develop a droplet-based achievability scheme that reliably stores $\Omega \left ({{n}/\log {n}}\right)$ for ${t}={O}({n}\log {n})$ time ( $\log {n}$ can be replaced with any ${o}({n})$ function). Moving to the positive but low temperature regime, two main results are provided. First, we show that an initial configuration drawn from the Gibbs measure cannot retain more than a single bit for ${t}\geq \exp ({C}\beta {n}^{1/4+\epsilon })$ time. On the other hand, when scaling time with the inverse temperature $\beta $ , the stripe-based coding scheme (that stores for infinite time at zero temperature) is shown to retain its bits for ${e}^{{c}\beta }$ .
Systematic Analysis of Distributed Optimization Algorithms over Jointly-Connected Networks

We consider the distributed optimization problem, where a group of agents work together to optimize a common objective by communicating with neighboring agents and performing local computations. For a given algorithm, we use tools from robust control to systematically analyze the performance in the case where the communication network is time-varying. In particular, we assume only that the network is jointly connected over a finite time horizon (commonly referred to as B-connectivity), which does not require connectivity at each time instant. When applied to the distributed algorithm DIGing, our bounds are orders of magnitude tighter than those available in the literature.
Fiscal Decentralization and Economic Growth

Abstract Fiscal decentralization may indeed have a direct impact on economic growth but the theoretical underpinnings for this relationship remain largely undeveloped. A fair summary of the empirical search for a direct relationship between fiscal decentralization and economic growth is that it remains an open question. Much less attention has been devoted in the literature to the indirect channels through which fiscal decentralization may affect economic growth. We argue that much work remains to be done before policy advisors and decision makers can formulate and implement decentralization programs on the basis of improving the rate of economic growth.
Dawn of the Discipline-Based Law Faculty

This Article reports on an empirical study of the prevalence of Ph.D.s on law faculties, the rate at which J.D.-Ph.D.s are being hired by those faculties, the impact of that hiring on faculties’ legal experience levels, and the likely resulting future composition of law faculties. Approximately 29% of the tenure-track faculties of the top twenty-six law schools currently hold Ph.D.s, and 67% of those schools’ entry level hires in 2014 and 2015 are J.D.-Ph.D.s. Recent hiring has separated into two tracks. On the growing J.D.-Ph.D. track, both legal experience and preparation time is declining. On the fading J.D.-only track, legal experience and preparation time are increasing. Preparation time for a law teaching job is now slightly lower on the J.D.-Ph.D. track. If current hiring trends continue, a majority of the members of top twenty-six law faculties will hold Ph.D.s by 2028, and a large majority of them will have no experience in law practice. Although Ph.D.-hiring is strongly correlated with school rank, this transformation to discipline-based law faculties will not be confined to the top schools. Already, 11% of tenure-track faculty hires in the bottom quartile of law schools have Ph.D.s. When this transformation is complete, the disciplines will effectively control the scholarly agendas of American law schools.
Stretching the Truth: Elastic Justification and Motivated Communication of Uncertain Information

Although both cognitive and motivational factors can influence the communication of uncertain information, most of the work investigating the communication of uncertainty has focused on cognitive factors. In this article, we demonstrate that motivational factors influence the communication of private, uncertain information and we describe the relationship between elasticity (i.e. uncertainty and vagueness) and motivated communication. We report results from four experiments that demonstrate that motivated communication is not purely opportunistic. The values people report are constrained by the elasticity of private information even when the costs and benefits of misrepresenting information are held constant. Perceptions of justifiability mediate the relationship between elasticity and motivated communication, and we explain our results in terms of the self-justification process.
Trade Protection and Capital Imports in the Mexican Manufacturing Sector

Summary Several studies have investigated the link between trade protection and productivity in developing economies. Others have looked into the relationship between technology imports and in-house technology production. This paper contributes to the literature by estimating the effect of trade protection on purchases of foreign capital goods for a panel of Mexican manufacturing plants. Product-market tariffs lower the probability that a plant will import capital goods, while both output and input tariffs are associated with smaller quantities of capital imports. Capital imports are also associated with higher productivity. Thus, trade barriers may indirectly lower productivity by inhibiting the importation of foreign technologies through capital goods.