cssi/SciSciGPT-SciSciNet huggingface dataset:
Complete Dictionary Recovery Over the Sphere II: Recovery by Riemannian Trust-Region Method

We consider the problem of recovering a complete (i.e., square and invertible) matrix $ A_{0}$ , from $ Y \in \mathbb R ^{n \times p}$ with $Y = \boldsymbol A_{0} X_{0}$ , provided $ X_{0}$ is sufficiently sparse. This recovery problem is central to theoretical understanding of dictionary learning, which seeks a sparse representation for a collection of input signals and finds numerous applications in modern signal processing and machine learning. We give the first efficient algorithm that provably recovers $ A_{0}$ when $ X_{0}$ has $O \left ({ n }\right )$ nonzeros per column, under suitable probability model for $ X_{0}$ . Our algorithmic pipeline centers around solving a certain nonconvex optimization problem with a spherical constraint, and hence is naturally phrased in the language of manifold optimization. In a companion paper, we have showed that with high probability, our nonconvex formulation has no “spurious” local minimizers and around any saddle point, the objective function has a negative directional curvature. In this paper, we take advantage of the particular geometric structure and describe a Riemannian trust region algorithm that provably converges to a local minimizer with from arbitrary initializations. Such minimizers give excellent approximations to the rows of $ X_{0}$ . The rows are then recovered by a linear programming rounding and deflation.
Desorption Kinetics and Binding Energies of Small Hydrocarbons

Small hydrocarbons are an important organic reservoir in protostellar and protoplanetary environments. Constraints on desorption temperatures and binding energies of such hydrocarbons are needed for accurate predictions of where these molecules exist in the ice versus gas phase during the different stages of star and planet formation. Through a series of temperature programmed desorption experiments, we constrain the binding energies of 2- and 3-carbon hydrocarbons (C_2H_2—acetylene, C_2H_4—ethylene, C_2H_6—ethane, C_3H_4—propyne, C_3H_6—propene, and C_3H_8—propane) to 2200–4200 K in the case of pure amorphous ices, to 2400–4400 K on compact amorphous H_2O, and to 2800–4700 K on porous amorphous H_2O. The 3-carbon hydrocarbon binding energies are always larger than the 2-carbon hydrocarbon binding energies. Within the 2- and 3-carbon hydrocarbon families, the alkynes (i.e., least-saturated) hydrocarbons exhibit the largest binding energies, while the alkane and alkene binding energies are comparable. Binding energies are ~5%–20% higher on water ice substrates compared to pure ices, which is a small increase compared to what has been measured for other volatile molecules such as CO and N_2. Thus in the case of hydrocarbons, H_2O has a less pronounced effect on sublimation front locations (i.e., snowlines) in protoplanetary disks.
Recurrent Very Long Type I X-Ray Bursts in the Low-Mass X-Ray Binary 4U 1636–53

Two flares with a duration of several hours are reported for the low-mass X-ray binary 4U 1636-53. The characteristics of these flares (i.e., decay timescales, spectral softening, fluences) are very similar to those of the very long type I X-ray bursts recently found in several other low-mass X-ray binaries, suggesting that the flares in 4U 1636-53 are also very long type I X-ray bursts. This would make this source the fifth to exhibit this phenomenon and the first one for which multiple bursts have been found. Interestingly, all five sources accrete at approximately 10% of the Eddington mass accretion rate. Although a chance coincidence or a selection effect cannot be ruled out at present, this correlation is suggestive and might indicate that such very long type I X-ray bursts can occur only at a narrow range of mass accretion rates.
Early metabolic priming under differing carbon sufficiency conditions influences peach fruit quality development

Crop load management is an important preharvest factor to balance yield, quality, and maturation in peach. However, few studies have addressed how preharvest factors impact metabolism on fruit of equal maturity. An experiment was conducted to understand how carbon competition impacts fruit internal quality and metabolism in 'Cresthaven' peach trees by imposing distinct thinning severities. Fruit quality was evaluated at three developmental stages (S2, S3, S4), while controlling for equal maturity using non-destructive visual to near-infrared spectroscopy. Non-targeted metabolite profiling was used to characterize fruit at each developmental stage from trees that were unthinned (carbon starvation) or thinned (carbon sufficiency). Carbon sufficiency resulted in significantly higher fruit dry matter content and soluble solids concentration at harvest when compared to the carbon starved, underscoring the true impact of carbon manipulation on fruit quality. Significant differences in the fruit metabolome between treatments were observed at S2 when phenotypes were similar, while less differences were observed at S4 when the carbon sufficient fruit exhibited a superior phenotype. This suggests a potential metabolic priming effect on fruit quality when carbon is sufficiently supplied during early fruit growth and development. In particular, elevated levels of catechin may suggest a link between secondary/primary metabolism and fruit quality development.
On the distortion of knots on embedded surfaces

Our main result is a nontrivial lower bound for the distortion of some specic knots. In particular, we show that the distortion of the torus knot Tp;q satises (Tp;q) 1 160 min(p;q). This answers a 1983 question of Gromov.
Free-Breathing Cardiovascular MRI Using a Plug-and-Play Method with Learned Denoiser

Cardiac magnetic resonance imaging (CMR) is a noninvasive imaging modality that provides a comprehensive evaluation of the cardiovascular system. The clinical utility of CMR is hampered by long acquisition times, however. In this work, we propose and validate a plug-and-play (PnP) method for CMR reconstruction from undersampled multi- coil data. To fully exploit the rich image structure inherent in CMR, we pair the PnP framework with a deep learning (DL)-based denoiser that is trained using spatiotemporal patches from high-quality, breath-held cardiac cine images. The resulting “PnP-DL” method iterates over data consistency and denoising subroutines. We compare the reconstruction performance of PnP-DL to that of compressed sensing (CS) using eight breath-held and ten real-time (RT) free-breathing cardiac cine datasets. We find that, for breath-held datasets, PnP-DL offers more than one dB advantage over commonly used CS methods. For RT free-breathing datasets, where ground truth is not available, PnP-DL receives higher scores in qualitative evaluation. The results highlight the potential of PnP-DL to accelerate RT CMR.
Recurrent Weil–Petersson geodesic rays with non-uniquely ergodic ending laminations

The Weil–Petersson (WP) metric on Teichmuller space provides a negatively curved, Riemannian alternative to the more familiar Teichmuller metric, a Finsler metric whose global geometry is not negatively curved in any general sense. While negative curvature allows one to harness a broad range of techniques from hyperbolic geometry, difficulties in implementing these techniques arise from the fact that the WP metric is incomplete and that its sectional curvatures approach both 0 and 1 asymptotically near the completion. Nevertheless, it is useful to draw analogies between these metrics and instructive to determine which of these are robust or obtainable through methods in negative curvature.
A Pattern Language for High-Performance Computing Resilience

High-performance computing systems (HPC) provide powerful capabilities for modeling, simulation, and data analytics for a broad class of computational problems. They enable extreme performance of the order of quadrillion floating-point arithmetic calculations per second by aggregating the power of millions of compute, memory, networking and storage components. With the rapidly growing scale and complexity of HPC systems for achieving even greater performance, ensuring their reliable operation in the face of system degradations and failures is a critical challenge. System fault events often lead the scientific applications to produce incorrect results, or may even cause their untimely termination. The sheer number of components in modern extreme-scale HPC systems and the complex interactions and dependencies among the hardware and software components, the applications, and the physical environment makes the design of practical solutions that support fault resilience a complex undertaking. To manage this complexity, we developed a methodology for designing HPC resilience solutions using design patterns. We codified the well-known techniques for handling faults, errors and failures that have been devised, applied and improved upon over the past three decades in the form of design patterns. In this paper, we present a pattern language to enable a structured approach to the development of HPC resilience solutions. The pattern language reveals the relations among the resilience patterns and provides the means to explore alternative techniques for handling a specific fault model that may have different efficiency and complexity characteristics. Using the pattern language enables the design and implementation of comprehensive resilience solutions as a set of interconnected resilience patterns that can be instantiated across layers of the system stack.
``Tilting'' the universe with the landscape multiverse: the dark flow

We argue that the recent observations of large scale bulk flows by Kashlinsky et al. has a natural explanation in terms of superhorizon inhomogeneities induced by nonlocal entanglement of our Hubble volume with modes and domains beyond the horizon. This entanglement gives rise to corrections to the Newtonian potential on a characteristic scale L1 103H?1, and it induces a dipole and quadrupole contribution in the CMB. We also show that these induced multipoles are aligned with each other, with the alignment axis normal to their plane being oriented along the preferred frame determined by the dipole. We also give other potential tests of our hypothesis.
PATTERN COROTATION RADII FROM POTENTIAL-DENSITY PHASE-SHIFTS FOR 153 OSUBGS SAMPLE GALAXIES

The potential-density phase-shift method is an effective new tool for investigating the structure and evolution of galaxies. In this paper, we apply the method to 153 galaxies in the Ohio State University Bright Galaxy Survey (OSUBGS) to study the general relationship between pattern corotation radii and the morphology of spiral galaxies. The analysis is based on near-infrared H-band images that have been deprojected and decomposed assuming a spherical bulge. We find that multiple pattern speeds are common in disk galaxies. By selecting those corotation radii close to or slightly larger than the bar radius as being the bar corotation (CR) radius, we find that the average and standard deviation of the ratio R = r(CR)/r(bar), is 1.20 {+-} 0.52 for 101 galaxies having well-defined bars. There is an indication that this ratio depends weakly on galaxy type in the sense that the average ranges from 1.03 {+-} 0.37 for 65 galaxies of type Sbc and earlier, to 1.50 {+-} 0.63 for 36 galaxies of type Sc and later. Our bar corotation radii are on average smaller than those estimated from single-pattern-speed numerical simulations, most likely because these simulations tend to find the pattern speed which generates a density response inmore » the gas that best matches the morphology of the outer spiral structure. Although we find CR radii in most of the sample galaxies that satisfy conventional ideas about the extent of bars, we also consider the alternative interpretation that in many cases the bar CR is actually inside the bar and that the bar ends close to its outer Lindblad resonance instead of its CR. These 'superfast' bars are the most controversial finding from our study. We see evidence in the phase-shift distributions for ongoing decoupling of patterns, which hints at the formation pathways of nested patterns, and which in turn further hints at the longevity of the density wave patterns in galaxies. We also examine how uncertainties in the orientation parameters of galaxies and in the shapes of bulges affect our results.« less
Convergence between Categorical Representations of Reeb Space and Mapper

The Reeb space, which generalizes the notion of a Reeb graph, is one of the few tools in topological data analysis and visualization suitable for the study of multivariate scientific datasets. First introduced by Edelsbrunner et al., it compresses the components of the level sets of a multivariate mapping and obtains a summary representation of their relationships. A related construction called mapper, and a special case of the mapper construction called the Joint Contour Net have been shown to be effective in visual analytics. Mapper and JCN are intuitively regarded as discrete approximations of the Reeb space, however without formal proofs or approximation guarantees. An open question has been proposed by Dey et al. as to whether the mapper construction converges to the Reeb space in the limit. In this paper, we are interested in developing the theoretical understanding of the relationship between the Reeb space and its discrete approximations to support its use in practical data analysis. Using tools from category theory, we formally prove the convergence between the Reeb space and mapper in terms of an interleaving distance between their categorical representations. Given a sequence of refined discretizations, we prove that these approximations converge to the Reeb space in the interleaving distance; this also helps to quantify the approximation quality of the discretization at a fixed resolution.
Graph Transformer Networks with Syntactic and Semantic Structures for Event Argument Extraction

The goal of Event Argument Extraction (EAE) is to find the role of each entity mention for a given event trigger word. It has been shown in the previous works that the syntactic structures of the sentences are helpful for the deep learning models for EAE. However, a major problem in such prior works is that they fail to exploit the semantic structures of the sentences to induce effective representations for EAE. Consequently, in this work, we propose a novel model for EAE that exploits both syntactic and semantic structures of the sentences with the Graph Transformer Networks (GTNs) to learn more effective sentence structures for EAE. In addition, we introduce a novel inductive bias based on information bottleneck to improve generalization of the EAE models. Extensive experiments are performed to demonstrate the benefits of the proposed model, leading to state-of-the-art performance for EAE on standard datasets.
A FRAMEWORK FOR THE CALIBRATION OF SOCIAL SIMULATION MODELS

Simulation with agent-based models is increasingly used in the study of complex socio-technical systems and in social simulation in general. This paradigm offers a number of attractive features, namely the possibility of modeling emergent phenomena within large populations. As a consequence, often the quantity in need of calibration may be a distribution over the population whose relation with the parameters of the model is analytically intractable. Nevertheless, we can simulate. In this paper we present a simulation-based framework for the calibration of agent-based models with distributional output based on indirect inference. We illustrate our method step by step on a model of norm emergence in an online community of peer production, using data from three large Wikipedia communities. Model fit and diagnostics are discussed.
Salem number stretch factors and totally real fields arising from Thurston’s construction

In 1974, Thurston proved that, up to isotopy, every automorphism of closed orientable surface is either periodic, reducible, or pseudo-Anosov. The latter case has lead to a rich theory with applications ranging from dynamical systems to low dimensional topology. Associated with every pseudo-Anosov map is a real number $\lambda > 1$ known as the stretch factor. Thurston showed that every stretch factor is an algebraic unit but it is unknown exactly which units can appear as stretch factors. In this paper we show that every Salem number has a power that is the stretch factor of a pseudo-Anosov map arising from a construction due to Thurston. We also show that every totally real number field $K$ is of the form $K = \mathbb{Q}(\lambda + \lambda^{-1})$, where $\lambda$ is the stretch factor of a pseudo-Anosov map arising from Thurston's construction.
ON THE OUTER EDGES OF PROTOPLANETARY DUST DISKS

The expectation that aerodynamic drag will force the solids in a gas-rich protoplanetary disk to spiral in toward the host star on short timescales is one of the fundamental problems in planet formation theory. The nominal efficiency of this radial drift process is in conflict with observations, suggesting that an empirical calibration of solid transport mechanisms in a disk is highly desirable. However, the fact that both radial drift and grain growth produce a similar particle size segregation in a disk (such that larger particles are preferentially concentrated closer to the star) makes it difficult to disentangle a clear signature of drift alone. We highlight a new approach, by showing that radial drift leaves a distinctive fingerprint in the dust surface density profile that is directly accessible to current observational facilities. Using an analytical framework for dust evolution, we demonstrate that the combined effects of drift and (viscous) gas drag naturally produce a sharp outer edge in the dust distribution (or, equivalently, a sharp decrease in the dust-to-gas mass ratio). This edge feature forms during the earliest phase in the evolution of disk solids, before grain growth in the outer disk has made much progress, and is preserved over longer timescales when both growth and transport effects are more substantial. The key features of these analytical models are reproduced in detailed numerical simulations, and are qualitatively consistent with recent millimeter-wave observations that find gas/dust size discrepancies and steep declines in dust continuum emission in the outer regions of protoplanetary disks.
Glass formation in binary alloys with different atomic symmetries

Prediction of the glass-forming ability (GFA) of alloys remains a major challenge. We are not yet able to predict the composition dependence of the GFA of even binary alloys. To investigate the effect of each element's propensity to form particular crystal structures on glass formation, we focus on binary alloys composed of elements with the same size but different atomic symmetries using the patchy-particle model. For mixtures with atomic symmetries that promote different crystal structures, the minimum critical cooling rate ${R}_{c}$ is only a factor of 5 lower than that for the pure substances. For mixtures with different atomic symmetries that promote local crystalline and icosahedral order, the minimum ${R}_{c}$ is more than three orders of magnitude lower than that for pure substances. Results for ${R}_{c}$ for the patchy-particle model are consistent with those from embedded atom method simulations and sputtering experiments of NiCu, TiAl, and high entropy alloys.
Long-term voltage stability assessment of an integrated transmission distribution system

Long-term voltage stability assessment (VSA) of independent transmission (T-VSA) and distribution (D-VSA) systems have been studied since long to estimate load margins. However, their impacts on each other have been neglected due to simplified assumptions i.e. in transmission systems, loads are assumed to be aggregated, and in distribution systems, substation bus voltage is assumed to be constant. This work investigates the VSA of integrated transmission-distribution (TD-VSA) using PV curve superimposition approach and reveals the possibility that the overall system loadability may be limited by the distribution system rather than the transmission system. In this paper, we analyze why T-VSA and D-VSA are not reliable enough to estimate true load margin of the overall system. The analysis has been verified on an integrated test system in different scenarios with and without DER penetration. Overall, the paper points out the need for integrated analysis and further builds a case why it is essential to develop a realistic co-simulation framework for a reliable long-term VSA of large-scale coupled T-D systems.
Second Order QCD Corrections to the Nonleptonic Decay of the b Quark in the Slow Charm Limit

The perturbative QCD corrections to the nonleptonic decay rate of the b quark are discussed. By considering the limit where the final charmed quarks are slow, it is argued that the coefficients of the terms, corresponding to the next-to-next-to-leading order in the standard renormalization group expansion in ln(mW/mb), are naturally large. The large coefficients arise from the final state gluon exchange between quarks and are associated with the region of rather low momenta, which may further enhance the phenomenological significance of these terms.
Uniformity of cosmic microwave background as a non-inflationary geometrical effect

The conventional ΛCDM cosmological model supplemented by the inflation concept describes the Universe very well. However, there are still a few concerns: new Planck data impose constraints on the shape of the inflaton potential, which exclude a lot of inflationary models; dark matter is not detected directly, and dark energy is not understood theoretically on a satisfactory level. In this brief sketch, we investigate an alternative cosmological model with spherical spatial geometry and an additional perfect fluid with the constant parameter ω = −1/3 in the linear equation of state. It is demonstrated explicitly that in the framework of such a model it is possible to satisfy the supernovae data at the same level of accuracy as within the ΛCDM model and at the same time suppose that the observed cosmic microwave background (CMB) radiation originates from a very limited space region. This is ensured by introducing an additional condition of light propagation between the antipodal points during the age of the Universe. Consequently, the CMB uniformity can be explained without the inflation scenario. The corresponding drawbacks of the model with respect to its comparison with the CMB data are also discussed.
TRIGGERING COLLAPSE OF THE PRESOLAR DENSE CLOUD CORE AND INJECTING SHORT-LIVED RADIOISOTOPES WITH A SHOCK WAVE. II. VARIED SHOCK WAVE AND CLOUD CORE PARAMETERS

A variety of stellar sources have been proposed for the origin of the short-lived radioisotopes that existed at the time of the formation of the earliest solar system solids, including Type II supernovae (SNe), asymptotic giant branch (AGB) and super-AGB stars, and Wolf-Rayet star winds. Our previous adaptive mesh hydrodynamics models with the FLASH2.5 code have shown which combinations of shock wave parameters are able to simultaneously trigger the gravitational collapse of a target dense cloud core and inject significant amounts of shock wave gas and dust, showing that thin SN shocks may be uniquely suited for the task. However, recent meteoritical studies have weakened the case for a direct SN injection to the presolar cloud, motivating us to re-examine a wider range of shock wave and cloud core parameters, including rotation, in order to better estimate the injection efficiencies for a variety of stellar sources. We find that SN shocks remain as the most promising stellar source, though planetary nebulae resulting from AGB star evolution cannot be conclusively ruled out. Wolf-Rayet (WR) star winds, however, are likely to lead to cloud core shredding, rather than to collapse. Injection efficiencies can be increased when the cloud is rotating about an axis aligned with the direction of the shock wave, by as much as a factor of ~10. The amount of gas and dust accreted from the post-shock wind can exceed that injected from the shock wave, with implications for the isotopic abundances expected for a SN source.
Gap symmetry and stability analysis in the multi-orbital Fe-based superconductors

The iron-based superconductors allow for a zoo of possible order parameters due to their orbital degrees of freedom. These order parameters are often written in an orbital basis for a microscopic analysis and a comprehensive symmetry classification. Unlike in standard single-band superconductors, where electrons of the same band—and hence, energy—are paired, a general order parameter in such a multi-orbital system also contains pairing of electrons belonging to different bands. As this corresponds to pairing of electrons of different energy, such order parameters are energetically less stable. Here, we present a simple criterion for a stability analysis of the orbital part of the gap function based on the basic principle that electrons of equal energy are paired in the superconducting state. This not only allows us to find the most stable states, but also to identify the terms in a (tight-binding) Hamiltonian suppressing any given superconducting state. Our approach thus allows us to identify the minimal Hamiltonian necessary to compare competing instabilities.
Predictions of the Atmospheric Composition of GJ 1132b

GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly characterizable small exoplanets currently known. In this paper we study the interaction of a magma ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the amount of O2 that can build up in the atmosphere as a result of hydrogen dissociation and loss. We find that the magma ocean absorbs at most ~10% of the O2 produced, whereas more than 90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our simulations is a tenuous atmosphere dominated by O2, although for very large initial water abundances atmospheres with several thousands of bars of O2 are possible. A substantial steam envelope would indicate either the existence of an earlier H2 envelope or low XUV flux over the system's lifetime. A steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further modeling is needed to study the evolution of CO2 or N2-rich atmospheres on GJ 1132 b.
On the existence of a connected component of a graph

We study the reverse mathematics and computability of countable graph theory, obtaining the following results. The principle that every countable graph has a connected component is equivalent to ACA0 over RCA0. The problem of decomposing a countable graph into connected components is strongly Weihrauch equivalent to the problem of finding a single component, and each is equivalent to its infinite parallelization. For graphs with finitely many connected components, the existence of a connected component is either provable in RCA0 or is equivalent to induction for 0 2 formulas, depending on the formulation of the bound on the number of components.
Cosmic Reionization and the First Nonlinear Structures in the Universe

In this Introduction, we outline expectations for when and how the hydrogen and helium atoms in the universe turned from neutral to ionized, focusing on the earliest, least well understood stages, and emphasize the most important open questions. We include a historical summary, and highlight the role of reionization as one of the few milestones in the evolution of the universe since the Big Bang, and its status as a unique probe of the beginning stages of structure formation.
A Gaussian Mixture Model for Nulling Pulsars

The phenomenon of pulsar nulling—where pulsars occasionally turn off for one or more pulses—provides insight into pulsar-emission mechanisms and the processes by which pulsars turn off when they cross the "death line." However, while ever more pulsars are found that exhibit nulling behavior, the statistical techniques used to measure nulling are biased, with limited utility and precision. In this paper, we introduce an improved algorithm, based on Gaussian mixture models, for measuring pulsar nulling behavior. We demonstrate this algorithm on a number of pulsars observed as part of a larger sample of nulling pulsars, and show that it performs considerably better than existing techniques, yielding better precision and no bias. We further validate our algorithm on simulated data. Our algorithm is widely applicable to a large number of pulsars even if they do not show obvious nulls. Moreover, it can be used to derive nulling probabilities of nulling for individual pulses, which can be used for in-depth studies.
LASR-guided stellar photometric variability subtraction - The Linear Algorithm for Significance Reduction

We develop a technique for removing stellar variability in the light curves of δ -Scuti and similar stars. Our technique, which we name the Linear Algorithm for Significance Reduction (LASR), subtracts oscillations from a time series by minimizing their statistical significance in frequency space. We demonstrate that LASR can subtract variable signals of near-arbitrary complexity and can robustly handle close frequency pairs and overtone frequencies. We demonstrate that our algorithm performs an equivalent fit as prewhitening to the straightforward variable signal of KIC 9700322. We also show that LASR provides a better fit to seismic activity than prewhitening in the case of the complex δ -Scuti KOI-976.
Spatial Population Genetics: It's About Time

Many important questions about the history and dynamics of organisms have a geographical component: How many are there, and where do they live? How do they move and interbreed across the landscape?...
Anomalous X-ray pulsars and soft gamma-ray repeaters in supernova remnants

Important constraints on the properties of the anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) can be provided by their associations with supernova remnants (SNRs). We have made a radio search for SNRs toward the AXPs RX J170849-400910 and 4U 0142+61. We find that the former lies near a possible new SNR with which it is unlikely to be physically associated, but we see no SNR in the vicinity of the latter. We review all claimed pairings between AXPs and SNRs; the three convincing associations imply that AXPs are young (<10 000 yr) neutron stars with low projected space velocities (<500 km s-1). Contrary to previous claims, we find no evidence that the density of the ambient medium around AXPs is higher than that in the vicinity of radio pulsars. Furthermore, the nondetection of radio emission from AXPs does not imply that these sources are radio-silent. We also review claimed associations between SGRs and SNRs. We find none of these associations to be convincing, consistent with a scenario in which SGRs and AXPs are both populations of high-field neutron stars ("magnetars") but the SGRs are an older or longer-lived group of objects than are the AXPs. If the SGR-SNR associations are shown to be valid, then SGRs must be high-velocity objects and most likely represent a different class of source to the AXPs.
Toward Precision Measurement of Central Black Hole Masses

We review briefly direct and indirect methods of measuring the masses of black holes in galactic nuclei, and then focus attention on supermassive black holes in active nuclei, with special attention to results from reverberation mapping and their limitations. We find that the intrinsic scatter in the relationship between the AGN luminosity and the broad-line region size is very small, �0.11dex, comparable to the uncertainties in the better reverberation measurements. We also find that the relationship between reverberation-based black hole masses and host-galaxy bulge luminosities also seems to have surprisingly little intrinsic scatter, � 0.17dex. We note, however, that there are still potential systematics that could affect the overall mass calibration at the level of a factor of a few. With the advent of suitable technology for high angular resolution spectroscopy, from space with Hubble Space Telescope and from the ground with adaptive optics assistance, it has become possible to measure the masses of the central black holes in many nearby galaxies. Observations of nearby galaxies have led to the identification of scaling relation- ships that then allow us to estimate masses of black holes in distant galaxies and thus determine, at least in principle, the mass function for supermassive black holes, both locally and over cosmic time. Consequently, there have been tremendous advances in our understanding of the evolution of the supermassive black hole population and that of the galaxies that host them over the history of the universe. Despite this incredible progress, it is important to understand that supermassive black hole measurement is a field in its infancy: even the methods deemed most reliable have systematic uncertainties that have not been mitigated in a completely satisfactory way. Masses based on stellar dynamics and gas dynamics are highly model dependent and are only as reliable as the underly- ing assumptions. An obvious example is the recent work of Gebhardt & Thomas (2009) who found that the mass of the black hole in M87, widely regarded as one of the most secure measurements, changed by a factor of two with the introduction of a dark matter halo into the models. It is also worth noting that only two black hole measurements, the Milky Way (based on orbital motion of stars in the Galactic Center) and NGC 4258 (based on motions of megamasers), meet the formal criterion of measuring the mass on a sufficiently compact scale that the black-hole nature of the central source is proven. In all other present measurements, it remains an article of faith that the central source is a singularity, although it is hard to see practically how these masses could be anything else. We will therefore adhere to the convention of referring to these objects as black holes.
Effects of fluctuating energy input on the small scales in turbulence

In the standard cascade picture of three-dimensional turbulent fluid flows, energy is input at a constant rate at large scales. Energy is then transferred to smaller scales by an intermittent process that has been the focus of a vast literature. However, the energy input at large scales is not constant in most real turbulent flows. We explore the signatures of these fluctuations of large-scale energy input on small-scale turbulence statistics. Measurements were made in a flow between oscillating grids, with up to 262, in which temporal variations in the large-scale energy input can be introduced by modulating the oscillating grid frequency. We find that the Kolmogorov constant for second-order longitudinal structure functions depends on the magnitude of the fluctuations in the large-scale energy input. We can quantitatively predict the measured change with a model based on Kolmogorov’s refined similarity theory. The effects of fluctuations of the energy input can also be observed using structure functions conditioned on the instantaneous large-scale velocity. A linear parametrization using the curvature of the conditional structure functions provides a fairly good match with the measured changes in the Kolmogorov constant. Conditional structure functions are found to provide a more sensitive measure of the presence of fluctuations in the large-scale energy input than inertial range scaling coefficients.
The integral cohomology of the group of loops

Let Ln be a collection of n unknotted, unlinked circles in 3-space, and let PΣn be the group of motions of Ln where each circle ends up back at its original position. This group was introduced in the PhD thesis of David Dahm, a student of Ralph Fox, and was later studied by various authors, notably Deborah Goldsmith. Alan Brownstein and Ronnie Lee succeeded in computing H(PΣn,Z) in [6], and at the end of their paper conjecture a presentation for the algebra H(PΣn,Z). Further evidence for this conjecture came when the cohomological dimension was computed (cd(PΣn) = n−1) by Collins in [8], and when the Euler characteristic was computed (χ(PΣn) = (1−n)n−1) in [13] (see also [11]). Here we establish the Brownstein-Lee Conjecture. As our argument is a mixture of spectral sequences and combinatorial identities, it seems that Birman was quite prescient in her Mathematical Review of the Brownstein-Lee paper: “The combinatorics of the cohomology ring appears to be rich, and the attendant geometric interpretations are very pleasing.”
Quantizing time: Interacting clocks and systems

This article generalizes the conditional probability interpretation of time in which time evolution is realized through entanglement between a clock and a system of interest. This formalism is based upon conditioning a solution to the Wheeler-DeWitt equation on a subsystem of the Universe, serving as a clock, being in a state corresponding to a time $t$. Doing so assigns a conditional state to the rest of the Universe $|\psi_S(t)\rangle$, referred to as the system. We demonstrate that when the total Hamiltonian appearing in the Wheeler-DeWitt equation contains an interaction term coupling the clock and system, the conditional state $|\psi_S(t)\rangle$ satisfies a time-nonlocal Schrodinger equation in which the system Hamiltonian is replaced with a self-adjoint integral operator. This time-nonlocal Schrodinger equation is solved perturbatively and three examples of clock-system interactions are examined. One example considered supposes that the clock and system interact via Newtonian gravity, which leads to the system's Hamiltonian developing corrections on the order of $G/c^4$ and inversely proportional to the distance between the clock and system.
Superoperator nonequilibrium Green's function theory of many-body systems; applications to charge transfer and transport in open junctions

Abstract Nonequilibrium Green’s functions provide a powerful tool for computing the dynamical response and particle exchange statistics of coupled quantum systems. We formulate the theory in terms of the density matrix in Liouville space and introduce superoperator algebra that greatly simplifies the derivation and the physical interpretation of all quantities. Expressions for various observables are derived directly in real time in terms of superoperator nonequilibrium Green’s functions (SNGF), rather than the artificial time-loop required in Schwinger’s Hilbert-space formulation. Applications for computing interaction energies, charge densities, average currents, current induced fluorescence, electroluminescence and current fluctuation (electron counting) statistics are discussed.
Loo.py: transformation-based code generation for GPUs and CPUs

Today's highly heterogeneous computing landscape places a burden on programmers wanting to achieve high performance on a reasonably broad cross-section of machines. To do so, computations need to be expressed in many different but mathematically equivalent ways, with, in the worst case, one variant per target machine.Loo.py, a programming system embedded in Python, meets this challenge by defining a data model for array-style computations and a library of transformations that operate on this model. Offering transformations such as loop tiling, vectorization, storage management, unrolling, instruction-level parallelism, change of data layout, and many more, it provides a convenient way to capture, parametrize, and re-unify the growth among code variants. Optional, deep integration with numpy and PyOpenCL provides a convenient computing environment where the transition from prototype to high-performance implementation can occur in a gradual, machine-assisted form.
TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS

To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs and show that it extends from ≈0.005 to 0.02 AU for white dwarfs with masses from 0.4 to 0.9 M ☉, temperatures less than ≈104 K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be deeply eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favor detection of planets similar to Earth: similar size, temperature, and rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.
A brachistochrone approach to reconstruct the inflaton potential

We propose a new way to implement an inflationary prior to a cosmological dataset that incorporates the inflationary observables at arbitrary order. This approach employs an exponential form for the Hubble parameter H() without taking the slow-roll approximation. At lowest non-trivial order, this H() has the unique property that it is the solution to the brachistochrone problem for inflation.
Accuracy and Limitations of Fitting and Stereoscopic Methods to Determine the Direction of Coronal Mass Ejections from Heliospheric Imagers Observations

Using data from the Heliospheric Imagers (HIs) onboard STEREO, it is possible to derive the direction of propagation of coronal mass ejections (CMEs) in addition to their speed with a variety of methods. For CMEs observed by both STEREO spacecraft, it is possible to derive their direction using simultaneous observations from the twin spacecraft and also, using observations from only one spacecraft with fitting methods. This makes it possible to test and compare different analysis techniques. In this article, we propose a new fitting method based on observations from one spacecraft, which we compare to the commonly used fitting method of Sheeley et al. (J. Geophys. Res.104, 24739, 1999). We also compare the results from these two fitting methods with those from two stereoscopic methods, focusing on 12 CMEs observed simultaneously by the two STEREO spacecraft in 2008 and 2009. We find evidence that the fitting method of Sheeley et al. (J. Geophys. Res.104, 24739, 1999) may result in significant errors in the determination of the CME direction when the CME propagates outside of 60°±20° from the Sun – spacecraft line. We expect our new fitting method to be better adapted to the analysis of halo or limb CMEs with respect to the observing spacecraft. We also find some evidence that direct triangulation in the HI fields-of-view should only be applied to CMEs propagating approximatively toward Earth (± 20° from the Sun – Earth line). Last, we address one of the possible sources of errors of fitting methods: the assumption of radial propagation. Using stereoscopic methods, we find that at least seven of the 12 studied CMEs had a heliospheric deflection of less than 20° as they propagated in the HI fields-of-view, which, we believe, validates this approximation.
a Stochastic Derivation of the Geodesic Rule

We argue that the geodesic rule, for global defects, is a consequence of the randomness of the values of the Goldstone field ϕ in each causally connected volume. As these volumes collide and coalescence, ϕ evolves by performing a random walk on the vacuum manifold ${\mathcal M}$. We derive a Fokker–Planck equation that describes the continuum limit of this process. Its fundamental solution is the heat kernel on ${\mathcal M}$, whose leading asymptotic behavior establishes the geodesic rule.
Equation Planting: A Tool for Benchmarking Ising Machines

Recent years have witnessed the flourishing of experimental $I\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}g$ $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}s$, special-purpose computational devices that promise to solve the world's toughest optimization problems in record times. Evaluating an Ising machine's performance is problematic, though, as it poses two seemingly contradictory requirements: On the one hand, the generated problem instances should be hard to solve, yet on the other hand they should have verifiable solutions. This study provides a methodology for generating random optimization-problem sets from linear systems of equations that possess both desired properties, thereby allowing direct, unbiased benchmarking of these physical optimization devices.
MULTIPLE HARMONIC SUMS AND WOLSTENHOLME'S THEOREM

We give a family of congruences for the binomial coefficient , with k an integer and p a prime. Our congruences involve multiple harmonic sums, and hold modulo arbitrary large powers of p. The general congruence in our family, which depends on a parameter n, involves n "elementary symmetric" multiple harmonic sums, and holds modulo p2n+3. These congruences are actually part of a much larger collection of congruences for in terms of the elementary symmetric multiple harmonic sums. Congruences in our family have been optimized, in that they involve the fewest multiple harmonic sums among those congruences holding modulo the same power of p. The coefficients in our congruences are given by polynomials in k.
Faint Object Detection in Multi-Epoch Observations via Catalog Data Fusion

Astronomy in the time-domain era faces several new challenges. One of them is the efficient use of observations obtained at multiple epochs. The work presented here addresses faint object detection and describes an incremental strategy for separating real objects from artifacts in ongoing surveys. The idea is to produce low-threshold single-epoch catalogs and to accumulate information across epochs. This is in contrast to more conventional strategies based on co-added or stacked images. We adopt a Bayesian approach, addressing object detection by calculating the marginal likelihoods for hypotheses asserting that there is no object or one object in a small image patch containing at most one cataloged source at each epoch. The object-present hypothesis interprets the sources in a patch at different epochs as arising from a genuine object; the no-object hypothesis interprets candidate sources as spurious, arising from noise peaks. We study the detection probability for constant-flux objects in a Gaussian noise setting, comparing results based on single and stacked exposures to results based on a series of single-epoch catalog summaries. Our procedure amounts to generalized cross-matching: it is the product of a factor accounting for the matching of the estimated fluxes of the candidate sources and a factor accounting for the matching of their estimated directions. We find that probabilistic fusion of multi-epoch catalogs can detect sources with similar sensitivity and selectivity compared to stacking. The probabilistic cross-matching framework underlying our approach plays an important role in maintaining detection sensitivity and points toward generalizations that could accommodate variability and complex object structure.
Anomalies and chiral symmetry in QCD

I review some aspects of the interplay between anomalies and chiral symmetry. The quantum anomaly that breaks the U(1) axial symmetry of massless QCD leaves behind a flavor-singlet discrete chiral invariance. When the mass is turned on this residual symmetry has a close connection with the strong CP violating parameter theta. One result is that a first order transition is usually expected when the strong CP violating angle passes through pi. This symmetry can be understood either in terms of effective chiral Lagrangians or in terms of the underlying quark fields.