cssi/SciSciGPT-SciSciNet huggingface dataset:
Multilevel Text Alignment with Cross-Document Attention

Text alignment finds application in tasks such as citation recommendation and plagiarism detection. Existing alignment methods operate at a single, predefined level and cannot learn to align texts at, for example, sentence \emph{and} document levels. We propose a new learning approach that equips previously established hierarchical attention encoders for representing documents with a cross-document attention component, enabling structural comparisons across different levels (document-to-document and sentence-to-document). Our component is weakly supervised from document pairs and can align at multiple levels. Our evaluation on predicting document-to-document relationships and sentence-to-document relationships on the tasks of citation recommendation and plagiarism detection shows that our approach outperforms previously established hierarchical, attention encoders based on recurrent and transformer contextualization that are unaware of structural correspondence between documents.
3D Monte Carlo simulation of light distribution in mouse brain in quantitative photoacoustic computed tomography

Background Photoacoustic computed tomography (PACT) detects light-induced ultrasound (US) waves to reconstruct the optical absorption contrast of the biological tissues. Due to its relatively deep penetration (several centimeters in soft tissue), high spatial resolution, and inherent functional sensitivity, PACT has great potential for imaging mouse brains with endogenous and exogenous contrasts, which is of immense interest to the neuroscience community. However, conventional PACT either assumes homogenous optical fluence within the brain or uses a simplified attenuation model for optical fluence estimation. Both approaches underestimate the complexity of the fluence heterogeneity and can result in poor quantitative imaging accuracy. Methods To optimize the quantitative performance of PACT, we explore for the first time 3D Monte Carlo (MC) simulation to study the optical fluence distribution in a complete mouse brain model. We apply the MCX MC simulation package on a digital mouse (Digimouse) brain atlas that has complete anatomy information. To evaluate the impact of the brain vasculature on light delivery, we also incorporate the whole-brain vasculature in the Digimouse atlas. k-wave toolbox was used to investigate the effect of inhomogeneous illumination on the reconstructed images and chromophore concentration estimation. Results The simulation results clearly show that the optical fluence in the mouse brain is heterogeneous at the global level and can decrease by a factor of five with increasing depth. Moreover, the strong absorption and scattering of the brain vasculature also induce the fluence disturbance at the local level. Conclusions Both global and local fluence heterogeneity contributes to the reduced quantitative accuracy of the reconstructed PACT images of mouse brain. Correcting the optical fluence distribution can improve the quantitative accuracy of PACT.
Triangulations and soliton graphs for totally positive Grassmannian

Abstract The KP equation is a nonlinear dispersive wave equation which provides an excellent model for resonant interactions of shallow-water waves. It is well known that regular soliton solutions of the KP equation may be constructed from points in the totally nonnegative Grassmannian Gr ( N , M ) ≥ 0 . Kodama and Williams studied the asymptotic patterns (tropical limit) of KP solitons, called soliton graphs, and showed that they correspond to Postnikov's Le-diagrams. In this paper, we consider soliton graphs for the KP hierarchy, a family of commuting flows which are compatible with the KP equation. For the positive Grassmannian Gr ( 2 , M ) > 0 , Kodama and Williams showed that soliton graphs are in bijection with triangulations of the M-gon. We extend this result to Gr ( N , M ) > 0 when N = 3 and M = 6 , 7 and 8. In each case, we show that soliton graphs are in bijection with Postnikov's plabic graphs, which generalize Le-diagrams.
Improving Dependability of Neuromorphic Computing With Non-Volatile Memory

As process technology continues to scale aggressively, circuit aging in a neuromorphic hardware due to negative bias temperature instability (NBTI) and time-dependent dielectric breakdown (TDDB) is becoming a critical reliability issue and is expected to proliferate when using non-volatile memory (NVM) for synaptic storage. This is because NVM devices require high voltages and currents to access their synaptic weights, which further accelerate the circuit aging in neuromorphic hardware. Current methods for qualifying reliability are overly conservative, since they estimate circuit aging considering worst-case operating conditions and unnecessarily constrain performance. This paper proposes RENEU, a reliability-oriented approach to map machine learning applications to neuromorphic hardware, with the aim of improving system-wide reliability, without compromising key performance metrics such as execution time of these applications on the hardware. Fundamental to RENEU is a novel formulation of the aging of CMOS-based circuits in a neuromorphic hardware considering different failure mechanisms. Using this formulation, RENEU develops a system- wide reliability model which can be used inside a design-space exploration framework involving the mapping of neurons and synapses to the hardware. To this end, RENEU uses an instance of Particle Swarm Optimization (PSO) to generate mappings that are Pareto-optimal in terms of performance and reliability. We evaluate RENEU using different machine learning applications on a state-of-the-art neuromorphic hardware with NVM synapses. Our results demonstrate an average 38% reduction in circuit aging, leading to an average 18% improvement in the lifetime of the hardware compared to current practices. RENEU only introduces a marginal performance overhead of 5% compared to a performance-oriented state-of-the-art.
An Intergenerational Model of Domestic Violence

This paper proposes and analyzes an intergenerational model of domestic violence (IMDV) in which behavioral strategies or scripts are transmitted from parents to children. The model rests upon three key assumptions: The probability that a husband will be violent depends on whether he grew up in a violent home. The probability that a wife will remain with a violent husband depends on whether she grew up in a violent home. Individuals who grew up in violent homes tend to marry individuals who grew up in violent homes. The IMDV calls attention to three features neglected in the domestic violence literature. The first is the marriage market. If some men are more likely than others to be violent as husbands and if some women are more likely than others to remain in violent marriages, then the level of violence is sensitive to the probability that such individuals will marry each other. The second neglected feature is divorce: ongoing domestic violence requires the conjunction of a husband who is violent and a wife who stays in the marriage. Third, variables and policies that reduce the rate of domestic violence in the current generation are likely to reduce it even further in future generations.
Follow the leader: Documents on the leading edge of semantic change get more citations

Abstract Diachronic word embeddings—vector representations of words over time—offer remarkable insights into the evolution of language and provide a tool for quantifying sociocultural change from t...
Linear, nonlinear and transitional regimes of second-mode instability

The evolution of the potent second-mode instability in hypersonic boundary layers (HBLs) is examined holistically, by tracking its linear and nonlinear evolution, followed by its role in initiating transition and eventual breakdown of the HBL into a fully turbulent state. Linear stability theory is utilized to first identify the features of the second-mode wave after -synchronization. These are then employed in separate linearly and nonlinearly forced two-dimensional (2-D) and three-dimensional (3-D) direct numerical simulations (DNS). The nonlinear 2-D DNS shows saturation of the fundamental frequency, and the resulting superharmonics induce tightly braided ‘rope-like’ patterns near the generalized inflection point (GIP). The instability exhibits a second region of growth constituted by the fundamental frequency downstream of the primary envelope, which is absent in the linear scenario. Subsequent fully 3-D DNS identify this region as crucial in amplifying oblique instabilities riding on the 2-D second-mode ‘rollers’. This results in lambda vortices below the GIP, which are detached from the rollers in the inner boundary layer. Streamwise vortex-stretching results in a localized peak in length scales inside the HBL, eventually forming hairpin vortices. Spectral analyses track the transformation of harmonic peaks into a turbulent spectrum. The appearance of oblique modes at the fundamental frequency suggests that fundamental resonance is the most dominant mechanism of transition. The bispectrum reveals coupled nonlinear interactions between the fundamental and its superharmonics leading to spectral broadening, as well as traces of subharmonic resonance. The global forms of the fundamental and subharmonic modes show that the former disintegrate at the location of spanwise breakdown, beyond which the latter amplify. Statistical analyses of the near-wall flow field indicate an increase in large-scale ‘splatting’ motions immediately following transition, resulting in extreme skin-friction events, which equilibrate as turbulence sets in. Fundamental resonance results in complete breakdown of streamwise streaks in the lower log-layer, ultimately resulting in a fully turbulent HBL.
AN ALMA CONTINUUM SURVEY OF CIRCUMSTELLAR DISKS IN THE UPPER SCORPIUS OB ASSOCIATION

We present ALMA 880 μm continuum observations of 20 K- and M-type stars in the Upper Scorpius OB association (Upper Sco) that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low-mass stars (0.1-1.6 M☉) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 μm dust continuum at ≥ 3σ with inferred dust masses between 0.3 and 52 M⊕. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p ≈ 0.03. The evolution in the dust content in disks was assessed by comparing the Upper Sco observations with published continuum measurements of disks around ~1-2 Myr stars in the Class II stage in the Taurus molecular cloud. While the dust masses in the Upper Sco disks are on average lower than in Taurus, any difference in the dust mass distributions is significant at less than 3σ. For stellar masses between 0.49 M☉ and 1.6 M☉, the mean dust mass in disks is lower in Upper Sco relative to Taurus by Δlog M_(dust) = 0.44 ± 0.26.
Astronomical data formats: What we have and how we got here

Abstract Despite almost all being acquired as photons, astronomical data from different instruments and at different stages in its life may exist in different formats to serve different purposes. Beyond the data itself, descriptive information is associated with it as metadata, either included in the data format or in a larger multi-format data structure. Those formats may be used for the acquisition, processing, exchange, and archiving of data. It has been useful to use similar formats, or even a single standard to ease interaction with data in its various stages using familiar tools. Knowledge of the evolution and advantages of present standards is useful before we discuss the future of how astronomical data is formatted. The evolution of the use of world coordinates in FITS is presented as an example.
Modeling noise and error correction for Majorana-based quantum computing

Majorana-based quantum computing seeks to use the non-local nature of Majorana zero modes to store and manipulate quantum information in a topologically protected way. While noise is anticipated to be significantly suppressed in such systems, finite temperature and system size result in residual errors. In this work, we connect the underlying physical error processes in Majorana-based systems to the noise models used in a fault tolerance analysis. Standard qubit-based noise models built from Pauli operators do not capture leading order noise processes arising from quasiparticle poisoning events, thus it is not obvious {\it a priori} that such noise models can be usefully applied to a Majorana-based system. We develop stochastic Majorana noise models that are generalizations of the standard qubit-based models and connect the error probabilities defining these models to parameters of the physical system. Using these models, we compute pseudo-thresholds for the d=5 Bacon-Shor subsystem code. Our results emphasize the importance of correlated errors induced in multi-qubit measurements. Moreover, we find that for sufficiently fast quasiparticle relaxation the errors are well described by Pauli operators. This work bridges the divide between physical errors in Majorana-based quantum computing architectures and the significance of these errors in a quantum error correcting code.
Ample filters of invertible sheaves

Abstract Let X be a scheme, proper over a commutative Noetherian ring A . We introduce the concept of an ample filter of invertible sheaves on X and generalize the most important equivalent criteria for ampleness of an invertible sheaf. We also prove the Theorem of the Base for X and generalize Serre's Vanishing Theorem. We then generalize results for twisted homogeneous coordinate rings which were previously known only when X was projective over an algebraically closed field. Specifically, we show that the concepts of left and right σ -ampleness are equivalent and that the associated twisted homogeneous coordinate ring must be Noetherian.
QuSpin: a Python package for dynamics and exact diagonalisation of quantum many body systems. Part II: bosons, fermions and higher spins

We present a major update to QuSpin, SciPostPhys.2.1.003 -- an open-source Python package for exact diagonalization and quantum dynamics of arbitrary boson, fermion and spin many-body systems, supporting the use of various (user-defined) symmetries in one and higher dimension and (imaginary) time evolution following a user-specified driving protocol. We explain how to use the new features of QuSpin using seven detailed examples of various complexity: (i) the transverse-field Ising chain and the Jordan-Wigner transformation, (ii) free particle systems: the Su-Schrieffer-Heeger (SSH) model, (iii) the many-body localized 1D Fermi-Hubbard model, (iv) the Bose-Hubbard model in a ladder geometry, (v) nonlinear (imaginary) time evolution and the Gross-Pitaevskii equation on a 1D lattice, (vi) integrability breaking and thermalizing dynamics in the translationally-invariant 2D transverse-field Ising model, and (vii) out-of-equilibrium Bose-Fermi mixtures. This easily accessible and user-friendly package can serve various purposes, including educational and cutting-edge experimental and theoretical research. The complete package documentation is available under this http URL.
TWO POPULATIONS OF OLD STAR CLUSTERS IN THE SPIRAL GALAXY M101 BASED ON HST/ACS OBSERVATIONS

We present a new photometric catalog of 326 candidate globular clusters (GCs) in the nearby spiral galaxy M101, selected from B, V, and I Hubble Space Telescope Advanced Camera for Surveys images. The luminosity function (LF) of these clusters has an unusually large number of faint sources compared with GCLFs in many other spiral galaxies. Accordingly, we separate and compare the properties of “bright” () versus “faint” (; one magnitude fainter than the expected GC peak) clusters within our sample. The LF of the bright clusters is well fit by a peaked distribution similar to those observed in the Milky Way (MW) and other galaxies. These bright clusters also have similar size (reff) and spatial distributions as MW GCs. The LF of the faint clusters, on the other hand, is well described by a power law, with , similar to those observed for young and intermediate-age cluster systems in star forming galaxies. We find that the faint clusters have larger typical reff than the bright clusters, and have a flatter surface density profile, being more evenly distributed, as we would expect for clusters associated with the disk. We use the shape of the LF and predictions for mass-loss driven by two-body relaxation to constrain the ages of the faint clusters. Our results are consistent with two populations of old star clusters in M101: a bright population of halo clusters and a fainter, possibly younger, population of old disk clusters.
The Galactic Millisecond Pulsar Population

Among the current sample of over 2000 radio pulsars known primarily in the disk of our Galaxy, millisecond pulsars now number almost 200. Due to the phenomenal success of blind surveys of the Galactic field, and targeted searches of Fermi gamma-ray sources, for the first time in over a decade, Galactic millisecond pulsars now outnumber their counterparts in globular clusters! In this paper, I briefly review earlier results from studies of the Galactic millisecond pulsar population and present new constraints based on a sample of 60 millisecond pulsars discovered by 20 cm Parkes multibeam surveys. I present a simple model of the population containing $\sim 30,000$ potentially observable millisecond pulsars with a luminosity function, radial distribution and scale height that matches the observed sample of objects. This study represents only a first step towards a more complete understanding of the parent population of millisecond pulsars in the Galaxy and I conclude with some suggestions for further study in this area.
Fourier-transform-based attribution priors improve the interpretability and stability of deep learning models for genomics

Abstract Deep learning models can accurately map genomic DNA sequences to associated functional molecular readouts such as protein–DNA binding data. Base-resolution importance (i.e. “attribution”) scores inferred from these models can highlight predictive sequence motifs and syntax. Unfortunately, these models are prone to overfitting and are sensitive to random initializations, often resulting in noisy and irreproducible attributions that obfuscate underlying motifs. To address these shortcomings, we propose a novel attribution prior, where the Fourier transform of input-level attribution scores are computed at training-time, and high-frequency components of the Fourier spectrum are penalized. We evaluate different model architectures with and without attribution priors trained on genome-wide binary or continuous molecular profiles. We show that our attribution prior dramatically improves models’ stability, interpretability, and performance on held-out data, especially when training data is severely limited. Our attribution prior also allows models to identify biologically meaningful sequence motifs more sensitively and precisely within individual regulatory elements. The prior is agnostic to the model architecture or predicted experimental assay, yet provides similar gains across all experiments. This work represents an important advancement in improving the reliability of deep learning models for deciphering the regulatory code of the genome.
Assessing Expertise in Introductory Physics Using Categorization Task.

The ability to categorize problems based upon underlying principles, rather than surface features or contexts, is considered one of several proxy predictors of expertise in problem solving. With inspiration from the classic study by Chi, Feltovich, and Glaser, we assess the distribution of expertise among introductory physics students by asking three introductory physics classes, each with more than a hundred students, to categorize mechanics problems based upon similarity of solution. We compare their categorization with those of physics graduate students and faculty members. To evaluate the effect of problem context on students' ability to categorize, two sets of problems were developed for categorization. Some problems in one set included those available from the prior study by Chi et al. We find a large overlap between calculus-based introductory students and graduate students with regard to their categorizations that were assessed as ``good.'' Our findings, which contrast with those of Chi et al., suggest that there is a wide distribution of expertise in mechanics among introductory and graduate students. Although the categorization task is conceptual, introductory students in the calculus-based course performed better than those in the algebra-based course. Qualitative trends in categorization of problems are similar between the non-Chi problems and problems available from the Chi study used in our study although the Chi problems used are more difficult on average.
Spacecraft Attitude and Reaction Wheel Desaturation Combined Control Method

Two popular types of spacecraft actuators are reaction wheels and magnetic torque coils. Magnetic torque coils are particularly interesting because they can be used for both attitude control and reaction wheel momentum management (desaturation control). Although these two tasks are performed at the same time using the same set of actuators, most design methods deal with only one of the these tasks or consider these two tasks separately. In this paper, a design with these two tasks in mind is formulated as a single problem. A periodic time-varying linear quadratic regulator design method is then proposed to solve this problem. A simulation example is provided to describe the benefit of the new strategy.
Growth and electronic properties of nanolines on TiO2-terminated SrTiO3(001) surfaces

Surfaces of homoepitaxially grown TiO2-terminated SrTiO3(001) were studied in situ with scanning tunneling microscopy and spectroscopy. By controlling the Ti/Sr ratio, two-dimensional domains of highly ordered linear nanostructures, so-called “nanolines,” are found to form on the surface. To further study how the surface structure affects the band structure, spectroscopic studies of these surfaces were performed. Our results reveal significantly more band bending for surfaces with the nanolines, indicative of an acceptor state associated with these features. Additionally, an in-gap state is observed on nanoline surfaces grown under high oxygen deficient conditions. This state appears to be the same as that observed previously, arising from the (++/+) transition level of surface oxygen vacancies.
Inflation After False Vacuum Decay: New Evidence from BICEP2

Last year we argued that if slow-roll inflation followed the decay of a false vacuum in a large landscape, the steepening of the scalar potential between the inflationary plateau and the barrier generically leads to a potentially observable suppression of the scalar power spectrum at large distances. Here we revisit this analysis in light of the recent BICEP2 results. Assuming that both the BICEP2 B-mode signal and the Planck analysis of temperature fluctuations hold up, we find that the data now discriminate more sharply between our scenario and ΛCDM. Nonzero tensor modes exclude standard ΛCDM with notable but not yet conclusive confidence: at ∼3.8σ if r = 0.2, or at ∼ 3.5σ if r = 0.15. Of the two steepening models of our previous work, one is now ruled out by existing bounds on spatial curvature. The other entirely reconciles the tension between BICEP2 and Planck. Upcoming EE polarization measurements have the potential to rule out unmodified ΛCDM decisively. Next generation Large Scale Structure surveys can further increase the significance. More precise measurements of BB at low l will help distinguish our scenario from other explanations. If steepening is confirmed, the prospects for detecting open curvature increase but need notmore » be large.« less
Composite gravitons from metric-independent quantum field theories

We review some recent works by Carone, Erlich and Vaman on composite gravitons in metric-independent quantum field theories, with the aim of clarifying a number of basic issues. Focusing on a theor...
A New Amplification Regime for Traveling Wave Tubes With Third-Order Modal Degeneracy

Engineering of the eigenmode dispersion of slow wave structures (SWSs) to achieve desired modal characteristics is an effective approach to enhance the performance of high-power traveling wave tube (TWT) amplifiers or oscillators. We investigate here for the first time a new synchronization regime in TWTs based on SWSs operating near a third-order degeneracy condition in their dispersion. This special three-eigenmode synchronization is associated with a stationary inflection point (SIP) that is manifested by the coalescence of three Floquet-Bloch eigenmodes in the SWS. We demonstrate the special features of “cold” (without electron beam) periodic SWSs with SIP modeled as coupled transmission lines and investigate resonances of SWSs of finite length. We also show that by tuning parameters of a periodic SWS, one can achieve an SIP with nearly ideal flat dispersion relationship with zero group velocity or a slightly slanted one with a very small (positive or negative) group velocity leading to different operating schemes. The SIP structure when synchronized with an electron beam has potential benefits for amplification which include: 1) gain enhancement; 2) gain-bandwidth product improvement; and 3) higher power efficiency, when compared to conventional Pierce-like TWTs. The proposed theory paves the way for a new approach for potential improvements in gain, power efficiency, and gain-bandwidth product in high-power microwave amplifiers.
Techniques of Radio Astronomy

This chapter provides an overview of the techniques of radio astronomy. This study began in 1931 with Jansky’s discovery of emission from the cosmos, but the period of rapid progress began fteen years later. From then to the present, the wavelength range expanded from a few meters to the sub-millimeters, the angular resolution increased from degrees to ner than milli arc seconds and the receiver sensitivities have improved by large factors. Today, the technique of aperture synthesis produces images comparable to or exceeding those obtained with the best optical facilities. In addition to technical advances, the scientic discoveries made in the radio range have contributed much to opening new visions of our universe. There are numerous national radio facilities spread over the world. In the near future, a new era of truly global radio observatories will begin. This chapter contains a short history of the development of the eld, details of calibration procedures, coherent/heterodyne and incoherent/bolometer receiver systems, observing methods for single apertures and interferometers, and an overview of aperture synthesis.
INFLUENCE OF ELECTRON-IMPACT MULTIPLE IONIZATION ON EQUILIBRIUM AND DYNAMIC CHARGE STATE DISTRIBUTIONS: A CASE STUDY USING IRON

We describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. Previous ionization balance calculations have largely neglected EIMI. Here, EIMI cross-section data are incorporated into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect and can usually be ignored. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.
On Predicting Geolocation of Tweets Using Convolutional Neural Networks

In many Twitter studies, it is important to know where a tweet came from in order to use the tweet content to study regional user behavior. However, researchers using Twitter to understand user behavior often lack sufficient geo-tagged data. Given the huge volume of Twitter data there is a need for accurate automated geolocating solutions. Herein, we present a new method to predict a Twitter user’s location based on the information in a single tweet. We integrate text and user profile meta-data into a single model using a convolutional neural network. Our experiments demonstrate that our neural model substantially outperforms baseline methods, achieving 52.8% accuracy and 92.1% accuracy on city-level and country-level prediction respectively.
TWO NEW TESTS OF THE METALLICITY SENSITIVITY OF THE CEPHEID PERIOD-LUMINOSITY RELATION (THE LEAVITT LAW)

We undertake a new test of the metallicity sensitivity of the Leavitt Law for classical Cepheids. We derive an empirical calibration of the apparent luminosities of Cepheids as measured from the optical through the mid-infrared (0.45-8.0 μm) as a function of spectroscopic [Fe/H] abundances of individual Cepheids in the Large Magellanic Cloud (LMC) from Romaniello et al. The cumulative trend over the entire wavelength range shows a nearly monotonic behavior. The sense of the trend is consistent with differential line blanketing in the optical, leading to stars of high metallicity being fainter in the optical. This is followed by a reversal in the trend at longer wavelengths, with the crossover occurring near the K band at about 2.2 μm, consistent with a subsequent redistribution of energy resulting in a mild brightening of Cepheids (with increased metallicity) at mid-infrared wavelengths. This conclusion agrees with that of Romaniello et al. based on a differential comparison of the mean V- and K-band Leavitt Laws for the Galaxy, Small Magellanic Cloud, and LMC, but is opposite in sign to most other empirical tests of the sensitivity of Cepheid distances to mean [O/H] H II region abundances. We also search for a correlation of Cepheid host-galaxy metallicity with deviations of the galaxy's Cepheid distance from that predicted from a pure Hubble flow. Based on Cepheid distances to 26 nearby galaxies in the local flow, only a very weak signal is detected giving δμ o = –0.17(± 0.31)([O/H] – 8.80) – 0.21(± 0.10). This is in agreement with previous determinations, but statistically inconclusive.
Kronecker STAP and SAR GMTI

As a high resolution radar imaging modality, SAR detects and localizes non-moving targets accurately, giving it an advantage over lower resolution GMTI radars. Moving target detection is more challenging due to target smearing and masking by clutter. Space-time adaptive processing (STAP) is often used on multiantenna SAR to remove the stationary clutter and enhance the moving targets. In (Greenewald et al., 2016),1 it was shown that the performance of STAP can be improved by modeling the clutter covariance as a space vs. time Kronecker product with low rank factors, providing robustness and reducing the number of training samples required. In this work, we present a massively parallel algorithm for implementing Kronecker product STAP, enabling application to very large SAR datasets (such as the 2006 Gotcha data collection) using GPUs. Finally, we develop an extension of Kronecker STAP that uses information from multiple passes to improve moving target detection.
Diagnostics of Data-Driven Models: Uncertainty Quantification of PM7 Semi-Empirical Quantum Chemical Method.

We report an evaluation of a semi-empirical quantum chemical method PM7 from the perspective of uncertainty quantification. Specifically, we apply Bound-to-Bound Data Collaboration, an uncertainty quantification framework, to characterize (a) variability of PM7 model parameter values consistent with the uncertainty in the training data and (b) uncertainty propagation from the training data to the model predictions. Experimental heats of formation of a homologous series of linear alkanes are used as the property of interest. The training data are chemically accurate, i.e., they have very low uncertainty by the standards of computational chemistry. The analysis does not find evidence of PM7 consistency with the entire data set considered as no single set of parameter values is found that captures the experimental uncertainties of all training data. A set of parameter values for PM7 was able to capture the training data within ±1 kcal/mol, but not to the smaller level of uncertainty in the reported data. Nevertheless, PM7 was found to be consistent for subsets of the training data. In such cases, uncertainty propagation from the chemically accurate training data to the predicted values preserves error within bounds of chemical accuracy if predictions are made for the molecules of comparable size. Otherwise, the error grows linearly with the relative size of the molecules.
Recent advances in high-contrast metastructures, metasurfaces, and photonic crystals

In the past decade, the research field that uses arrays of high-index-contrast near-wavelength dielectric structures on flat surfaces, known as high-contrast metastructures (HCMs) or metasurfaces, has emerged and expanded rapidly. Although HCMs and metasurfaces share great similarities in physical structures with photonic crystals (PhCs), i.e., periodic nanostructures, many differences exist in their design, analysis, operation conditions, and applications. In this paper, we provide a generalized theoretical understanding of the two subjects and show their intrinsic connections. We further discuss the simulation and design approaches, categorized by their functionalities and applications. We summarize the similarities and differences among HCMs, metasurfaces, and PhCs. New findings are presented regarding the physical connection between PhC band structures and 1D and 2D HCM scattering spectra under transverse and longitudinal tilt incidence. Novel designs using HCMs as holograms, spatial light modulators, and surface plasmonic couplers are discussed. Recent advances in HCMs, metasurfaces, and PhCs are reviewed and compared for applications such as broadband mirrors, waveguides, couplers, resonators, and reconfigurable optics.
Tidal Novae in Compact Binary White Dwarfs

Compact binary white dwarfs (WDs) undergoing orbital decay due to gravitational radiation can experience significant tidal heating prior to merger. In these WDs, the dominant tidal effect involves the excitation of outgoing gravity waves in the inner stellar envelope and the dissipation of these waves in the outer envelope. As the binary orbit decays, the WDs are synchronized from outside in (with the envelope synchronized first, followed by the core). We examine the deposition of tidal heat in the envelope of a carbon-oxygen WD and study how such tidal heating affects the structure and evolution of the WD. We show that significant tidal heating can occur in the star's degenerate hydrogen layer. This layer heats up faster than it cools, triggering runaway nuclear fusion. Such 'tidal novae' may occur in all WD binaries containing a CO WD, at orbital periods between 5 minutes and 20 minutes, and precede the final merger by 10{sup 5}-10{sup 6} years.
PSR J0737-3039B: A PROBE OF RADIO PULSAR EMISSION HEIGHTS

In the double pulsar system PSR J0737–3039A/B, the strong wind produced by pulsar A distorts the magnetosphere of pulsar B. The influence of these distortions on the orbital-dependent emission properties of pulsar B can be used to determine the location of the coherent radio emission generation region in the pulsar magnetosphere. Using a model of the wind-distorted magnetosphere of pulsar B and the well-defined geometrical parameters of the system, we determine the minimum emission height to be ~20R NS in the two bright orbital longitude regions. We can determine the maximum emission height by accounting for the amount of deflection of the polar field line with respect to the magnetic axis using the analytical magnetic reconnection model of Dungey and the semi-empirical numerical model of Tsyganenko. Both of these models estimate the maximum emission height to be ~2500R NS. The minimum and maximum emission heights we calculate are consistent with those estimated for normal isolated pulsars.
Completely splittable representations of affine Hecke-Clifford algebras

We classify and construct irreducible completely splittable representations of affine and finite Hecke-Clifford algebras over an algebraically closed field of characteristic not equal to 2.
Equilibrium states beyond specification and the Bowen property

It is well-known that for expansive maps and continuous potential functions, the specification property (for the map) and the Bowen property (for the potential) together imply the existence of a unique equilibrium state. We consider symbolic spaces that may not have specification, and potentials that may not have the Bowen property, and give conditions under which uniqueness of the equilibrium state can still be deduced. Our approach is to ask that the collection of cylinders which are obstructions to the specification property or the Bowen property is small in an appropriate quantitative sense. This allows us to construct an ergodic equilibrium state with a weak Gibbs property, which we then use to prove uniqueness. We do not use inducing schemes or the Perron--Frobenius operator, and we strengthen some previous results obtained using these approaches. In particular, we consider $\beta$-shifts and show that the class of potential functions with unique equilibrium states strictly contains the set of potentials with the Bowen property. We give applications to piecewise monotonic interval maps, including the family of geometric potentials for examples which have both indifferent fixed points and a non-Markov structure.
THE STRUCTURE OF ADS BLACK HOLES AND CHERN–SIMONS THEORY IN 2 + 1 DIMENSIONS

We study anti-de Sitter black holes in 2 + 1 dimensions in terms of Chern–Simons gauge theory of the anti-de Sitter group coupled to a source. Taking the source to be an anti-de Sitter state specified by its Casimir invariants, we show how all the relevant features of the black hole are accounted for. The requirement that the source be a unitary representation leads to a discrete tower of excited states which provide a microscopic model for the black hole.
Flux Accretion and Coronal Mass Ejection Dynamics

Coronal mass ejections (CMEs) are the primary drivers of severe space weather disturbances in the heliosphere. Models of CME dynamics have been proposed that do not fully include the effects of magnetic reconnection on the forces driving the ejection. Both observations and numerical modeling, however, suggest that reconnection likely plays a major role in most, if not all, fast CMEs. Here, we theoretically investigate the accretion of magnetic flux onto a rising ejection by reconnection involving the ejection’s background field. This reconnection alters the magnetic structure of the ejection and its environment, thereby modifying the forces acting upon the ejection, generically increasing its upward acceleration. The modified forces, in turn, can more strongly drive the reconnection. This feedback process acts, effectively, as an instability, which we refer to as a reconnective instability. Our analysis implies that CME models that neglect the effects of reconnection cannot accurately describe observed CME dynamics. Our ultimate aim is to understand changes in CME acceleration in terms of observable properties of magnetic reconnection, such as the amount of reconnected flux. This flux can be estimated from observations of flare ribbons and photospheric magnetic fields.
Evidence against non-gravitational acceleration of 1I/2017 U1 ‘Oumuamua

Micheli et al. (Nature 559:223, 2018) reported that a seven-parameter fit to the orbit of 1I/2017 U1 ‘Oumuamua indicated a non-gravitational acceleration in the anti-Solar direction, and attributed it to recoil from comet-like outgassing. The implied gas to dust ratio is at least 100 times greater than that of known Solar System comets. The reported collapse of the scatter of nearly contemporaneous coordinate residuals upon inclusion of the non-gravitational term in the orbital fits is difficult to understand. There are grounds for skepticism.
Tangle solutions for a family of DNA-rearranging proteins

We study two systems of tangle equations that arise when modeling the action of the Integrase family of proteins on DNA. These two systems—direct and inverted repeats—correspond to two different possibilities for the initial DNA sequence. We present one new class of solutions to the tangle equations. In the case of inverted repeats we prove that any solution not in these, or 2 previously known classes, would have to belong to one specific class. In the case of direct repeats we prove that the three classes are the only solutions possible.
ON FERMION ZERO MODES IN INSTANTON V - A MODELS WITH SPONTANEOUS SYMMETRY BREAKING

The left- and right-handed fermion zero modes are examined. Their behavior under the variation of the size of the instanton, ρI, and the size of the Higgs core, ρH, for a range of Yukawa couplings corresponding to the fermion masses in the electroweak theory are studied. It is shown that the characteristic radii of the zero modes, in particular those of the left-handed fermions, are locked to the instanton size, and are not affected by the variation of ρH, except for fermion masses much larger than those in the standard electroweak theory.
Spontaneous Lorentz violation and baryogenesis

In the presence of background fields that spontaneously violate Lorentz invariance, a matter-antimatter asymmetry can be generated even in thermal equilibrium. In this paper we systematically investigate models of this type, showing that either high-energy or electroweak versions of baryogenesis are possible, depending on the dynamics of the Lorentz-violating fields. We identify two scenarios of interest: baryogenesis from a weak-scale pseudo-Nambu-Goldstone boson with intermediate-scale baryon-number violation, and sphaleron-induced baryogenesis driven by a constant-magnitude vector with a late-time phase transition.
HORIZON MASS THEOREM

A new theorem for black holes is found. It is called the horizon mass theorem. The horizon mass is the mass which cannot escape from the horizon of a black hole. For all black holes, neutral, charged or rotating, the horizon mass is always twice the irreducible mass observed at infinity. Previous theorems on black holes are: (i) the singularity theorem, (ii) the area theorem, (iii) the uniqueness theorem, (iv) the positive energy theorem. The horizon mass theorem is possibly the last general theorem for classical black holes. It is crucial for understanding Hawking radiation and for investigating processes occurring near the horizon.
Polyradical character and spin frustration in fullerene molecules: an ab initio non-collinear Hartree-Fock study.

Most ab initio calculations on fullerene molecules have been carried out on the basis of the paradigm of the Huckel model. This is consistent with the restricted nature of the independent-particle ...
Calculation of local formal Mellin transforms

Much recent work has been done on the local Fourier transforms for connections on the punctured formal disk. Specifically, the local Fourier transforms have been introduced, shown to induce certain equivalences of categories, and explicit formulas have been found to calculate them. In this paper, we prove analogous results in a similar situation, the local Mellin transforms for connections on the punctured formal disk. Specifically, we introduce the local Mellin transforms and show that they induce equivalences between certain categories of vector spaces with connection and vector spaces with invertible difference operators, as well as find formulas for explicit calculation in the same spirit as the calculations for the local Fourier transforms.
Spin critical opalescence in zero-temperature Bose-Einstein condensates

Cold-atom developments suggest the prospect of measuring scaling properties and long-range fluctuations of continuous phase transitions at zero temperature. We discuss the conditions for characterizing the phase separation of Bose-Einstein condensates of boson atoms in two distinct hyperfine spin states. The mean-field description breaks down as the system approaches the transition from the miscible side. An effective spin description clarifies the ferromagnetic nature of the transition. We show that a difference in the scattering lengths for the bosons in the same spin state leads to an effective internal magnetic field. The point at which the internal magnetic field vanishes (i.e., equal values of the like-boson scattering lengths) is a special point. We show that the long-range density fluctuations are suppressed near that point, while the effective spin exhibits the long-range fluctuations that characterize critical points. The zero-temperature system exhibits critical opalescence with respect to long-wavelength waves of impurity atoms that interact with the bosons in a spin-dependent manner.
A QM/MM approach for the study of monolayer-protected gold clusters

We report the development and implementation of hybrid methods that combine quantum mechanics (QM) with molecular mechanics (MM) to theoretically characterize thiolated gold clusters. We use, as training systems, structures such as Au25(SCH2–R)18 and Au38(SCH2–R)24, which can be readily compared with recent crystallographic data. We envision that such an approach will lead to an accurate description of key structural and electronic signatures at a fraction of the cost of a full quantum chemical treatment. As an example, we demonstrate that calculations of the 1H and 13C NMR shielding constants with our proposed QM/MM model maintain the qualitative features of a full DFT calculation, with an order-of-magnitude increase in computational efficiency.
Near-field edge fringes at sharp material boundaries

We have studied the formation of near-field fringes when sharp edges of materials are imaged using scattering-type scanning near-field optical microscope (s-SNOM). The materials we have investigated include dielectrics, metals, a near-perfect conductor, and those that possess anisotropic permittivity and hyperbolic dispersion. For our theoretical analysis, we use a technique that combines full-wave numerical simulations of tip-sample near-field interaction and signal demodulation at higher orders akin to what is done in typical s-SNOM experiments. Unlike previous tip-sample interaction near-field models, our advanced technique allows simulation of the realistic tip and sample structure. Our analysis clarifies edge imaging of recently emerged layered materials such as hexagonal boron nitride and transition metal dichalcogenides (in particular, molybdenum disulfide), as well as traditional plasmonic materials such as gold. Hexagonal boron nitride is studied at several wavelengths, including the wavelength where it possesses excitation of phonon-polaritons and hyperbolic dispersion. Based on our results of s-SNOM imaging in different demodulation orders, we specify resonant and non-resonant types of edges and describe the edge fringes for each case. We clarify near-field edge-fringe formation at material sharp boundaries, both outside bright fringes and the low-contrast region at the edge, and elaborate on the necessity of separating them from propagating waves on the surface of polaritonic materials.
LINE OVERLAP AND SELF-SHIELDING OF MOLECULAR HYDROGEN IN GALAXIES

The effect of line overlap in the Lyman and Werner bands, often ignored in galactic studies of the atomic-to-molecular transition, greatly enhances molecular hydrogen self-shielding in low metallicity environments and dominates over dust shielding for metallicities below about 10% solar. We implement that effect in cosmological hydrodynamics simulations with an empirical model, calibrated against the observational data, and provide fitting formulae for the molecular hydrogen fraction as a function of gas density on various spatial scales and in environments with varied dust abundance and interstellar radiation field. We find that line overlap, while important for detailed radiative transfer in the Lyman and Werner bands, has only a minor effect on star formation on galactic scales, which, to a much larger degree, is regulated by stellar feedback.